Processing information in the nervous system is energetically expensive, constraining the ability of the system to survive disturbances caused by stress. While some organisms compensate for extreme changes in the abiotic features of their environment, the mechanisms underlying this are poorly understood. We used the locust Descending Contralateral Movement Detector (DCMD) neuron to study how the propagation characteristics of action potentials (APs) change following an acute energy stress in control and heat shock (HS) pre-treated animals. We also attempted to determine if Ca2+ is involved in the DCMD AP and the possible changes indicated above. Conduction velocity decreased over an hour of recording in all groups, except those with minimal dissections, and we observed an increase in AP half-width and a decrease in the slope of the rising phase of the AP over time. After HS pre-treatment the response to a standard looming stimulus was delayed, showed significantly fewer APs and a lower peak frequency compared to controls. Brief application of sodium azide (NaN3) as an acute metabolic inhibitor did not subsequently affect DCMD’s conduction velocity or ability to fire at high frequencies during the recording period. There were no significant differences from control animals with extracellular Ca2+ manipulations; however we cannot conclude that Ca2+ does not contribute to DCMD’s AP because Na+ could have flowed through Ca2+ channels in the absence of extracellular Ca2+. Furthermore, examination of possible performance impairments with decreased Ca2+ currents, to indicate if Ca2+ current manipulation may account for the performance impairment, could not be conducted because no differences in AP characteristics were observed with Ca2+ manipulations. We suggest that the slowing of propagation in all groups represents a response to energetic stress and that HS modifies neuronal properties in ways that can be interpreted as saving energy in case of future stressors. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2009-08-11 08:36:26.571

The standard Kaluza-Klein theory is reviewed and its basic equations are rewritten in an anholonomic basis. A five dimensional Yang-Mills type quadratic and cubic curvature gravity model is introduced. By employing the Palatini variational principle, the field equations and the stress-energy tensors of these models are presented. Unification of gravity with electromagnetism is achieved through the Kaluza-Klein reduction mechanism. Reduced curvature invariants,field equations and stress-energy tensors in four dimensional space-time are obtained. The structure of interactions among the gravitational, electromagnetic and massless scalar fields are demonstrated in detail. It is shown that in addition to a set of generalized Maxwell and Yang-Mills type gravity equations the Lorentz force also emerges from this theory. Solutions of the standard Kaluza-Klein theory are explicitly demonstrated to be intrinsically contained in the quadratic model.

The fractal-like finite element method (FFEM) is developed to compute stress intensity factors (SIFs) for isotropic homogeneous and bi-material V-notched plates. The method is semi-analytical, because analytical expressions of the displacement fields are used as global interpolation functions (GIFs) to carry out a transformation of the nodal displacements within a singular region to a small set of generalised coordinates. The concept of the GIFs in reducing the number of unknowns is similar to the concept of the local interpolation functions of a finite element. Therefore, the singularity at a notch-tip is modelled accurately in the FFEM using a few unknowns, leading to reduction of the computational cost.The analytical expressions of displacements and stresses around a notch tip are derived for different cases of notch problems: in-plane (modes I and II) conditions and out-of-plane (mode III) conditions for isotropic and bi-material notches. These expressions, which are eigenfunction series expansions, are then incorporated into the FFEM to carry out the transformation of the displacements of the singular nodes and to compute the notch SIFs directly without the need for post-processing. Different numerical examples of notch problems are presented and results are compared to available published results and solutions obtained by using other numerical methods.A strain energy approach (SEA) is also developed to extract the notch SIFs from finite element (FE) solutions. The approach is based on the strain energy of a control volume around the notch-tip. The strain energy may be computed using commercial FE packages, which are only capable of computing SIFs for crack problems and not for notch problems. Therefore, this approach is a strong tool for enabling analysts to compute notch SIFs using current commercial FE packages. This approach is developed for comparison of the FFEM results for notch problems where available published results are scarce especially for the bi-material notch cases.A very good agreement between the SEA results and the FFEM results is illustrated. In addition, the accuracy of the results of both procedures is shown to be very good compared to the available results in the literature. Therefore, the FFEM as a stand-alone procedure and the SEA as a post-processing technique, developed in this research, are proved to be very accurate and reliable numerical tools for computing the SIFs of a general notch in isotropic homogeneous and bi-material plates.

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