Measurement studies have linked paraspinal muscle reflexes to low back pain. However, the role of reflexes in stabilizing the spine is not clear. Previous studies enlisted biomechanical models to aid in understanding of how intrinsic stiffness stabilizes the spine. This work expands these previous studies by modeling the neuromuscular dynamic control of the spine. The presence of delay in the reflexive system limits the availability of traditional stability analyses. However it is possible to investigate how reflex delay affects stability of the spine model using methods in linear time delayed stability. Such analyses find the maximum reflex delay, i.e., the delay margin for which stability is possible. Therefore a biomechanical model of the spine was developed that used these methods for stability. The model was able to demonstrate how reflex gains and delays affect stability. It was shown that increased proportional reflex gain reduced the amount of co-contraction required for stability. However, increased reflex gain required a reduced delay margin of the system. Differential reflex gain had no effect on the amount of co-contraction required for stability. However, it was shown to increase the delay margin for small gains. As the differential reflex gain approached the magnitude of intrinsic muscle damping the trend was reversed, and increased gain caused the delay margin to approach zero. Increased intrinsic muscle damping did not affect the minimum co-contraction required for stability, but was shown to increase the delay margin in all cases. This study provided a theoretical explanation for the role of reflexes in stabilizing the spine. Results agree with the trends in the published literature regarding patients with low-back pain. Specifically, these patients demonstrate abnormally larger reflex delay. To maintain stability, atypically small reflex gain is necessary. Compensatory co-contraction is required to offset the small reflex gain. Co-contraction and instability is observed in low back pain patients. The results presented here agree with measurement studies, and should aid in the development of hypotheses for future measurement studies. / Master of Science

Thesis advisor: Joanna Venator / This thesis explores an aspect of the work-family conflict by researching the impact of overtime work on divorce rates for high-income occupations. The work-family conflict refers to the conflict that exists within a relationship when work impedes on key, familial responsibilities. Overtime work is an example of this phenomenon, as increased time at the office can act as a catalyst for tension at home. I define overtime work by studying the usual hours worked in a week for individuals, and I specifically study various high-earning occupations to see how additional overtime work affects divorce rates. By analyzing ACS data from 2012-2019, I find that increased overtime hours tend to negatively impact divorce rates. Further, I find that this impact exists primarily in positions that work numerous overtime hours per week, whereas the effect is marginal for those who work limited overtime hours. / Thesis (BA) — Boston College, 2024. / Submitted to: Boston College. Morrissey School of Arts and Sciences. / Discipline: Economics. / Discipline: Departmental Honors.

No / The thermodynamic status of -carbamazepine has been clarified using equilibrium solubility measurements, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), heated X-ray powder diffraction (XRPD), and temperature-controlled X-ray scattering techniques. -Carbamazepine is the least stable of the three well-characterized anhydrous polymorphs of carbamazepine at 25°C. In addition, it was confirmed that -carbamazepine undergoes an exothermic transition to -carbamazepine at 130°C. The novel technique of time-resolved simultaneous small- and wide-angle X-ray scattering has been successfully applied to monitor this transition in situ. It was concluded that -carbamazepine has a monotropic relationship with -carbamazepine.

In this work, we demonstrate the mechanism for etching exfoliated graphene on SiO2 and other technological important substrates (Si, SiC and ITO), using low-energy electron sources. Our mechanism is based on helium ion sputtering and vacancy formation. Helium ions instead of incident electrons cause the defects that oxygen reacts with and etches graphene. We found that etching does not occur on low-resistivity Si and ITO. Etching occurs on higher resistivity Si and SiC, although much less than on SiO2. In addition, we studied the degradation mechanism of MoS2 under ambient conditions using as-grown and preheated mono- and thicker-layered MoS2 films. Thicker-layered MoS2 do not exhibit the growth of dendrites that is characteristic of monolayer degradation. Dendrites are observed to stop at the monolayer-bilayer boundary. Raman and photoluminescence spectra of the aged bilayer and thicker-layered films are comparable to those of as-grown films. We found that greater stability of bilayers and thicker layers supports a previously reported mechanism for monolayer degradation involving Förster resonance energy transfer. As a result, straightforward and scalable 2D materials integration, or air stable heterostructure device fabrication may be easily achieved. Our proposed mechanisms for etching graphene and ambient degradation of MoS2 could catalyze research on realizing new devices that are more efficient, stable, and reliable for practical applications.

[Truncated abstract] The present thesis is devoted to the development of new methods for transient stability-constrained optimal power flow, probabilistic transient stability assessment and security-constrained ancillary services allocation. The key objective of the thesis is to develop novel dispatch and assessment methods for power systems operation in the new environment of electricity markets to ensure power systems security, particularly transient stability. A new method for economic dispatch together with nodal price calculations which includes transient stability constraints and, at the same time, optimises the reference inputs to the Flexible AC Transmission System (FACTS) devices for maintaining power systems transient stability and reducing nodal prices is developed. The method draws on the sensitivity analysis of time-domain transient stability simulation results to derive a set of linearised stability constraints expressed in terms of generator active powers and FACTS devices input references. '...' The low computing time requirement of the two-point estimate method allows online applications, and the use of detailed power systems dynamic model for time-domain simulation which offers high accuracy. The two-point estimate method is integrated in a straightforward manner with the existing transient stability analysis tools. The integrated software facility has potential applications in control rooms to assist the system operator in decision making process based on instability risks. The software system when implemented on a cluster of processors also makes it feasible to re-assess online transient stability for any change in system configuration arising from switching control. The method proposed has been tested on a representative power system and validated using the Monte Carlo simulation. In conjunction with the energy market, by which forecasted load demand is met by generator dispatch, ancillary services are required in relation to control for secure system operation and power quality. The final part of the thesis has a focus on the key aspect of allocating these ancillary services, subject to an important constraint that the dispatch of the ancillary services will not impair the system security achieved in the load dispatch. With this focus and requirement, the thesis develops a new dispatch formulation in which the network security constraints are represented in the optimal determination of generator active power schedule and allocation of ancillary services. Contingencies considered include power demand variations at individual load nodes from the values specified for the current dispatch calculation. The required changes in generator active powers to meet the new load demands are represented by additional control variables in the new dispatch formulation which augment those variables in the traditional OPF dispatch calculation. Based on the Lagrange function which includes the extended set of security constraints, the formulation derives the optimality condition to be satisfied by the dispatch solution, together with the marginal prices for individual ancillary service providers and LMPs. The effects of the security constraints are investigated and discussed. Case studies for representative power systems are presented to verify the new dispatch calculation procedure.

Over the last forty or so years interest in the study of wing-tip vortices has increased, primarily due to the introduction of larger passenger aircraft and their subsequent interaction with smaller aircraft. The vortices generated by these larger aircraft present a problem in two main areas; the wake hazard problem, where other aircraft can be subjected to the large tangential velocities of the vortex, and the interaction with ground based features of vortices created during landing and take-off. The first of these is particularly dangerous close to the ground when aircraft are in a high lift configuration at take-off and landing. As the vortices effectively scale with aircraft wing span, significant encounters between large vortices and smaller aircraft have been documented over the years. An example of one such documented wake vortex interaction incident can be found in Ogawa. In this study, the system of vortices are described as classical Batchelor vortices (or linear superpositions thereof) which are then subjected to small perturbations. By discretising the domain and solving for the eigenvalues of the system it is possible to ascertain the stability characteristics of the flow as a function of the system parameters which include the axial wave-number, the spacing of the vortices, their cross-flow decay rate and their axial strength. We first consider the inviscid instability of multiple tip vortices, an approximation which is valid in the limit of large Reynolds numbers. In this limit the stability of the flow is dominated by the axial component of the basic vortex flow. The governing equations of continuity and momentum are reduced to a second order partial differential equation (PDE). This equation is solved numerically to determine which vortex configurations produce the greatest instability growth rate. These results are extended to consider the effect of compressibility on the inviscid instability. Finally we consider the effects of viscosity on the stability of the full Batchelor similarity solution which results in a second order PDE in four dependent variables. The stability equations are solved both globally (for the entire eigenspectra) and locally (for a single eigenvalue in a pre-determined region) using codes that run in both serial and parallel form. The numerical methods are based on pseudospectral discretisation (Chebyshev polynomials for Cartesian and radial directions and Fourier for azimuthal) in the global scheme, the eigenvalues being recovered either with a QZ algorithm or a shift-and-invert Arnoldi algorithm. For the local scheme, fourth order centred finite-diffences are used in conjunction with an iterative eigenvalue recovery method. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1383207 / Thesis (Ph.D.) - University of Adelaide, School of Mathematical Sciences, 2010

Over the last forty or so years interest in the study of wing-tip vortices has increased, primarily due to the introduction of larger passenger aircraft and their subsequent interaction with smaller aircraft. The vortices generated by these larger aircraft present a problem in two main areas; the wake hazard problem, where other aircraft can be subjected to the large tangential velocities of the vortex, and the interaction with ground based features of vortices created during landing and take-off. The first of these is particularly dangerous close to the ground when aircraft are in a high lift configuration at take-off and landing. As the vortices effectively scale with aircraft wing span, significant encounters between large vortices and smaller aircraft have been documented over the years. An example of one such documented wake vortex interaction incident can be found in Ogawa. In this study, the system of vortices are described as classical Batchelor vortices (or linear superpositions thereof) which are then subjected to small perturbations. By discretising the domain and solving for the eigenvalues of the system it is possible to ascertain the stability characteristics of the flow as a function of the system parameters which include the axial wave-number, the spacing of the vortices, their cross-flow decay rate and their axial strength. We first consider the inviscid instability of multiple tip vortices, an approximation which is valid in the limit of large Reynolds numbers. In this limit the stability of the flow is dominated by the axial component of the basic vortex flow. The governing equations of continuity and momentum are reduced to a second order partial differential equation (PDE). This equation is solved numerically to determine which vortex configurations produce the greatest instability growth rate. These results are extended to consider the effect of compressibility on the inviscid instability. Finally we consider the effects of viscosity on the stability of the full Batchelor similarity solution which results in a second order PDE in four dependent variables. The stability equations are solved both globally (for the entire eigenspectra) and locally (for a single eigenvalue in a pre-determined region) using codes that run in both serial and parallel form. The numerical methods are based on pseudospectral discretisation (Chebyshev polynomials for Cartesian and radial directions and Fourier for azimuthal) in the global scheme, the eigenvalues being recovered either with a QZ algorithm or a shift-and-invert Arnoldi algorithm. For the local scheme, fourth order centred finite-diffences are used in conjunction with an iterative eigenvalue recovery method. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1383207 / Thesis (Ph.D.) - University of Adelaide, School of Mathematical Sciences, 2010

This thesis is focused on territorial system of ecological stability. In the two cadastral areas are described all the individual parts of the local USES including the characteristics of actual condition. New elements were built, to strengthen the old ones.

Shallow flows are those whose width is significantly larger than their depth. In these types of flows, two dimensional coherent structures can be generated and can influence the flow greatly by the lateral transfer of mass and momentum. The development of coherent structures as a result of flow instabilities has been a topic of interest for environmental fluid mechanics for decades. Studies on the use of linear modal stability analysis is commonly found in literature. However, the relatively recent development in the field of hydrodynamic stability suggests that the traditional linear modal stability analysis does not describe the behaviour of the perturbations in finite time. The discrepancy between asymptotic behaviour and finite time behaviour is particularly large in shear driven flows and it is most likely to be the case for shallow flows. This study aims to provide a better understanding of finite time growth of perturbation energy in shallow flows. The three cases of shallow flows evaluated are the mixing layer, jet and wake. The critical cases are obtained through the linear modal analysis and nonmodal analysis was conducted to show the transient behaviour in finite time for what is so-called marginally stable. Finally, the thesis concludes by generalizing the finite time energy growth in the S-k space.

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