Sudden infant death syndrome and the central nervous system: a review of the triple-risk theory

Sudden infant death syndrome (SIDS) is the devastating condition in which an infant suddenly and unexplainably passes away over the course of sleeping. This is an unfortunate situation that many new parents dread every night as they lay their newborns to rest. SIDS is the leading cause of death in infants aged from one month to one year, and the medical world still does not fully understand what causes it. However, the triple-risk theory is a new model that sets out to explain the pathology of this syndrome through the combination of genetic vulnerabilities, a critical time period, and external stressors. This thesis summarizes the current research in the realm of the central nervous system (specifically the cerebellum and brainstem) as a means of evaluating the validity of this new model. The analyzed literature concentrated on a few important topics, such as proven risk factors, evidence of homeostatic abnormalities, and significant associations with the occurrence of SIDS. It was found that there was central nervous system dysfunction on most levels, including: damaged Purkinje cells in the cerebellum, malformations of the human choroid plexus, decreased neuropeptide signaling (both orexin and brain-derived neurotrophic factors), malformations of the amino acid neurotransmitters (both excitatory glutamate and inhibitory GABA), and finally significant reductions in the receptor density and activity of the serotonin system. These irregularities were associated, in most studies, with either the prone sleeping position or known maternal nicotine use during pregnancy. In conclusion, the triple-risk model is currently the most accurate description of SIDS, given its reasonable three criteria and present-day research. This is because the studies, and real-life victims, were all concentrated within the critical time period of transition from intra-uterine to extra-uterine life, satisfying the first element of timing. The list of central nervous system dysfunctions found in SIDS cases was compelling enough to fulfill the second factor of inherent vulnerability. Finally, the associations between low oxygen rebreathing and the prone sleep position, or over-heating and tight swaddling displayed a strong relationship with the occurrence of SIDS and satisfied the third and final event, which was the induction of an exogenous stressor. These three factors of the triple-risk model allow for the variations in victim pathology, but still offers a compelling and coherent understanding of the sudden infant death syndrome

A test facility for assessing the performance of IEC61850 substation automation designs

Substation Automation Systems have undergone dramatic changes since the introduction of powerful micro-processing and digital communications devices over Ethernet based networks within the substation. Smart, multifunctional relays, known as Intelligent Electronic Devices, or IEDs, have replaced the traditional panels which contained multiple protection relays, control equipment, metering and status indicators. ActewAGL Distribution, a power utility company servicing Canberra, Australia, has recently decided to undertake a review of its substation automation systems throughout its electrical network. As a result, ActewAGL Distribution has decided to investigate the IEC 61850 – Communication Networks and Systems in Substations standard, by constructing a test facility to assess its performance and capability with the view of implementing the standard into its 132/11kV zone substations network in the near future. This report details the literature review, design, construction, and performance evaluation that was undertaken on the IEC 61850 substation automation designs developed with the use of the test facility. The major achievement of this research project has been the successful development and evaluation of a substation automation system that utilised the IEC 61850 standard incorporated with multiple vendor devices

Process issues in redox biocatalysis: Cyclohexanone monooxygenase catalysed chiral lactone syntheses

This thesis investigates the Baeyer-Villiger oxidation of cyclic ketones to optically enriched lactones by the enzyme cyclohexanone monooxygenase (CHMO), cloned into Escherichia coli JM107 pQR210. Two model substrates were selected (2-hexyl cyclopentanone and 4-methyl cyclohexanone) to conduct investigations with. A major constraint found was that whole cell catalysis produced low reaction rates and poor enzyme stability. Isolated enzyme was stabilised effectively by using elevated levels of the cofactor NADPH. Recycle of the expensive NADPH was investigated by detailed studies of thermostable glucose and alcohol dehydrogenases. These were characterised by marked product inhibition. Alcohol dehydrogenase from Thermoanaerobacter brockii (TBADH) was chosen for the ease of removal of the acetone product from the system and the high affinity for NADPH. The interaction between CHMO and TBADH was modeled by simultaneous numerical integration of their rate equations leading to an understanding of the effect of different enzyme ratios on system performance. This model also predicts the conditions necessary to maximise cofactor stability and re-usability. Quantification of a range of processing strategies was performed, fed-batch operation was found to be 2.5 times more productive than batch. Multi-gram syntheses of lactones were performed at 2L scale with both free and immobilised enzymes. NADPH recycle was effective at producing over 700 reaction cycles. Immobilised CHMO was found to be significantly more stable than free enzyme under process conditions, a catalyst with retained activity of 12% and specific activity of 1.2Ug-1 was produced. TBADH produced 42% retained and 13.6Ug-1 specific activity. Co-immobilisation of both enzymes on the same support produced a catalyst with an activity of 0.6Ug-1

Preparation and humidity sensitive impedance of spinel ceramic nickel germanate

This thesis concerns the formation, sintering and humidity dependent electrical behaviour of the spinel ceramic material nickel germanate, Ni(_2)Ge0(_4).Ni(_2)Ge0(_4) has been prepared via the solid state reaction between NiO and GeO(_2) over a range of temperatures, and characterised using a number of techniques. The sintering behaviour of pressed pellets of Ni(_2)Ge0(_4) has also been investigated, together with a characterisation of the microstructure of the sintered bodies. Substitutional doping of Ni(_2)GeO(_4) with Li as a replacement for Ni is found to promote a high degree of shrinkage in the sintering process, probably due to the formation of a liquid phase. XRD revealed that even when 10 % of the Ni atoms were replaced with Li, no change in the crystal structure could be detected. A C. impedance spectroscopy of Ni(_2)Ge0(_4) samples was used to investigate the humidity sensitivity of this material. Equivalent circuit analysis, based on a network of resistors and constant phase elements, shows that the humidity sensitivity is due to conduction in a surface layer of water, in agreement with the models currently popular in the Uterature. Measurement of the water adsorption isotherm of Ni(_2)Ge0(_4) in pellet form indicates that a single monolayer of water is formed at around 20 %R(_H), with an approximately linear increase in water layer thickness up to around 80 %R(_H), after which capillary condensation causes a large increase in the volume of adsorbed water. The information gained on the thickness of this layer of water has been correlated with the resistance of the layer measured by impedance spectroscopy, and subsequently used to provide evidence for a model of the humidity sensitive conduction. The conduction in the surface layer is thought to be due to dissociation of the water, where the amount of dissociation is exponentially dependent on the humidity

Two types of nineteenth century plays

Thesis (M.A.)--Boston University, 1929. This item was digitized by the Internet Archive

A Heart Artificial: Building the Foundation for the Development and Maintenance of In Vitro Tissue Mimetic Cardiovascular Models

Given the prevalence of cardiovascular disorders and the distinct lack of significant repair mechanisms within cardiovascular systems, effective therapy for long-term treatment of cardiovascular degeneration remains a significant challenge. Further, the fundamental importance of such systems to all mammalian life begs the development of realistic component structures for in vitro assessment. Significant effort was expended to create in vitro models which mimicked a subset of structure and function of coordinate native components within cardiovascular systems. Towards this end, we developed a 3D-Artificial Heart Muscle (AHM) model utilizing fibrin gel and neonatal cardiac myocytes. We extracted functional metrics in order to probe the optimal protocol for generation of the tissue model. Building on the outcome of this experiment, we applied the optimal 3D-AHM model to a decellularized adult rat heart in order to re-append function to a complex acellular scaffold. The resultant bioartifical heart (BAH) model was assessed to identify the efficacy of 3D-AHM as a functional delivery mechanism and to lay a framework for heart model development. An alternative strategy for the generation of 3D heart muscle was explored through magnetic levitation of cardiovascular cells. Magnetic sensitivity was appended to cells through incubation with ferromagnetic nanoparticles. The cells were then levitated and cultured within a magnetic field to form 3D multicellular aggregates. (MCAs) We utilized a magnetized fibrin gel scaffold in order to apply non-contact, magnetic stretch conditioning to our AHM model through a novel bioreactor system. We were able to develop a highly functional 3D-AHM and extracted 4M cells as the optimal concentration for the generation of our artificial heart muscle. Application of a layer of 3D-AHM to an acellular rat heart proved the 3D-AHM an effective mechanism for delivery of a subset of function to a structure. Magnetic levitation generated hundreds of cell-dense, functional and phenotypically relevant heart muscle analogs. We have developed a completely novel system for the application of mechanical stretch conditioning to artificial heart muscle models and are working to implement more complex conditioning systems. The work presented herein surveys the generation of 3 unique cardiovascular model systems and a novel method for model conditioning.Biomedical Engineering, Department o

Ventilatory Phenotypes among Four Strains of Adult Rats.

Our purpose in this study was to identify different ventilatory phenotypes among four different strains of rats. We examined 114 rats from three in-house, inbred strains and one outbred strain: Brown Norway (BN;n = 26), Dahl salt-sensitive (n = 24), Fawn-hooded Hypertensive (FHH: n = 27), and outbred Sprague-Dawley rats (SD; n = 37). We measured eupneic (room air) breathing and the ventilatory responses to hypoxia (12% O2-88% N2), hypercapnia (7% CO2), and two levels of submaximal exercise. Primary strain differences were between BN and the other strains. BN rats had a relatively attenuated ventilatory response to CO2 (P \u3c 0.001), an accentuated ventilatory response to exercise (P \u3c 0.05), and an accentuated ventilatory roll-off during hypoxia (P \u3c 0.05). Ventilation during hypoxia was lower than other strains, but hyperventilation during hypoxia was equal to the other strains (P \u3e 0.05), indicating that the metabolic rate during hypoxia decreased more in BN rats than in other strains. Another strain difference was in the frequency and timing components of augmented breaths, where FHH rats frequently differed from the other strains, and the BN rats had the longest expiratory time of the augmented breaths (probably secondary to the blunted CO2 sensitivity). These strain differences not only provide insight into physiological mechanisms but also indicate traits (such as CO2 sensitivity) that are genetically regulated. Finally, the data establish a foundation for physiological genomic studies aimed at elucidating the genetics of these ventilatory control mechanisms

Leaves_Compute

Control of gas exchange between a leafs interior and the surrounding air is accomplished by variations in the turgor pressures in the small epidermal and guard cells that cover the leafs surface. These pressures respond to changes in light intensity and color, temperature, CO2 concentration, and air humidity. The dynamical equations that describe these processes are formally identical to those that define computation in a two layer, adaptive, cellular nonlinear network. This identification suggests that leaf gas exchange processes can be understood as a kind of analog computation