The two-phase flow displacement of a viscous fluid by a less viscous one in a confined environment leads to a viscous fingering instability commonly encountered in natural systems, for example, in flows through porous media or pulmonary airways. The classical study of viscous fingering has been conducted in rectangular channels of high aspect ratio (large channel width/height), known as Hele-Shaw channels where a unique, steady symmetric, semi-infinite bubble (finger) emerges. In this Journal Format thesis, the propagation of semi-infinite (open) and finite (closed) air bubbles is considered in Hele-Shaw channels where thin, axially-uniform occlusions are introduced. This configuration is known to generate symmetric, asymmetric and oscillatory modes with complex interactions and rich behaviour. Numerical results of finger propagation using a depth-averaged model in these constricted channels are found to be in quantitative agreement with experimental results once the aspect ratio reaches a value of $\alpha\geq40$ and capillary numbers below $Ca\leq 0.012$. The same evolution of the bifurcation scenario between multiple modes is found, however, it occurs for decreasing values of occlusion height as the value of aspect ratio is increased that the system exhibits sensitivity to small but finite depth-variations. The numerical simulations reveal multiple-tipped unstable symmetric solutions which interact with the single symmetric mode at vanishing occlusion heights resulting in stabilisation of the asymmetric and oscillatory modes. Moreover, deviations from the single symmetric mode are predicted when depth-variations of order of the roughness of the channel walls ($\sim 1$ $\mu$m) are introduced for larger aspect ratios of $\alpha\geq 155$. The propagation of finite bubbles is studied in a channel with constant aspect ratio of $\alpha=30$ and where the height of the occlusion, termed rail, is $1/40$ of the channel height. For bubble diameters of the order of the rail width, a tongue-shaped stability boundary for symmetric (on-rail) propagation is encountered so that for flow rates marginally larger than a critical value, a narrow band of bubble sizes can propagate (stably) over the rail while bubbles of other sizes segregate to the side of the rail. The numerical depth-averaged model is adapted for bubble propagation and captures in qualitative agreement the experimental observations. Time-dependent calculations are additionally performed, showing that on-rail bubble propagation is the result of a non-trivial dynamical interaction between capillary and viscous forces.

The present study is an effort to examine and understand the relationship between modernization and political instability. The following chapters focus on the effects of modernization on political instability. Data on twenty-four African nations are analyzed to test empirically the validity of the hypothesis. Chapter IV concludes the thesis by offering a general summary and conclusions.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / This letter has the purpose to comment the article by Marwaha et al. regarding affective instability and mental disorders. We wish to highlight the importance to report the proper measures of association in case-control studies, and the impact of adjusting the results when finding associations with possible confounders in the bivariate analysis. / Revisión por pares / Revisión por pares

A instabilidade do ombro é a incapacidade de manter a cabeça umeral centralizada na fossa glenóide. Os requisitos para o diagnóstico clínico incluem história clínica, exame físico geral e testes objetivos para avaliar a presença e o grau de instabilidade do ombro. O objetivo do presente trabalho é comparar os achados por imagem das alterações anatômicas da artrotomografia computadorizada multislice com a artrorressonância magnética na avaliação da instabilidade do ombro correlacionando com os achados artroscópicos assim como verificar a eficácia da artrotomografia computadorizada multislice na avaliação das alterações anatômicas relacionadas com a instabilidade do ombro. Trata-se de um estudo prospectivo onde, inicialmente, 30 pacientes com o diagnóstico clínico de instabilidade do ombro foram submetidos à artrotomografia computadorizada com cortes de espessura de 0,5 mm e reconstrução a cada 3 mm e à artrorressonância magnética nas seqüências convencionais ponderadas em T1 e T2 com e sem saturação de gordura. Comparado com a artroscopia, a artrorressonância magnética mostrou uma sensibilidade de 93,33% para lesão labral superior, 96,30% para lesão labral anterior e 83,3% para lesão labral ântero-superior e a artrotomografia computadorizada multislice mostrou uma sensibilidade de 90%, 88,89% e 77,78%, respectivamente. A sensibilidade da artrorressonância magnética para lesão de cartilagem articular foi de 16,67% comparado com uma sensibilidade 33,30% da artrotomografia computadorizada multislice. A artrorressonância magnética e artrotomografia computadorizada multislice mostraram a mesma sensibilidade para detecção da lesão de Hill-Sachs (100%), lesão labral ântero-inferior (100%), anormalidades capsulares (88,89%) e lesões de Bankart ósseo (80%). Com base nos resultados, concluímos que a artrorressonância magnética é um método de acurácia superior à artroTCMS na avaliação das lesões labrais ântero-superior, superior e anterior e que a artrotomografia computadorizada multislice mostrou-se eficaz nas estruturas relacionadas à instabilidade, com resultados semelhantes à Artro- RM para o diagnóstico de lesões labrais ântero-inferiores (ALPSA e Bankart), lesões de Hill-Sachs, redundância capsular e Bankart ósseo, sendo superior à artro-RM no diagnóstico de lesões de cartilagem articular / Shoulder instability is characterized by the incapacity to keep the humeral head centered within the glenoid fossa. Clinical diagnosis should include a history of prior events, a complete physical examination, and a set of objective tests to evaluate the presence and extent of shoulder instability. This study aims to compare the imaging of anatomical deformities seen in shoulder instability by employing both multislice computerized tomography (MSCT) arthrography and magnetic resonance arthrography (MRA). A correlation between those images and the arthroscopic findings was important to determining the efficacy of MSCT arthrography in the assessment of shoulder instability. The 30 patients in this prospective study, who had had a previous clinical diagnosis of shoulder instability, underwent CT arthrography using 0.5 mm-thick slices with reconstructions every 3 mm, and T1- and T2-weighted sequential MR imaging arthrography with and without fat saturation. MRA was shown to be 93.33 % sensitive in detecting superior labral lesion, 96.30% in anterior labral lesion, and 83.3% sensitive in anterosuperior labral lesion, whereas the respective results for MSCT arthrography were 90%, 88.89%, and 77.78%. MRA and MSCT arthrography afforded 16.67% and 33.30% sensitivity for joint cartilage injury, respectively. Both techniques were equally sensitive in detecting Hill-Sachs lesion (100%), anteroinferior labral lesion (100%), capsular abnormalities (88.89%), and bony Bankart lesions (80%). The results herein led us to conclude that MRA is more accurate than MSCT arthrography in assessing anterosuperior, superior (SLAP) and anterior labral lesions and the MSCT arthrography had good results in the evaluation of the structures related to shoulder instability. Both methods yielded equivalent results for Hill-Sachs, ALPSA and Bankart lesions. The MSCT arthrography furnished better results than MRA in the diagnosis of articular cartilage lesions

Ankle instability (AI) and fatigue impair neuromuscular control as well as dynamic joint stability of the lower extremity. No one has comprehensively examined the effects of AI and fatigue on neuromechanics of the lower extremity during a functional activity. Deficits associated with AI and fatigue could be additive in increasing the risk for injury in patients with AI. PURPOSE: To examine the interaction of AI and fatigue on lower extremity muscle activity, kinematic, and kinetic patterns during a forward-side jump. METHODS: 25 AI (23.3 ± 1.9 yrs, 176.5 ± 10.5 cm, 70.9 ± 11.4 kg), and 25 matched control subjects (23.7 ± 2.5 yrs, 175.0 ± 10.8 cm, 70.3 ± 12.8 kg) were categorized according to the Foot and Ankle Ability Measure (FAAM) (ADL: 84.3 ± 7.6%, Sport: 63.6 ± 8.6%) and the Modified Ankle Instability Instrument (MAII) (3.7 ± 1.2). Fifty-nine reflective markers were place over anatomical landmarks and eight electromyography (EMG) electrodes were placed on tibialis anterior (TA), peroneus longus (PL), medial gastrocmedius (MG), medial hamstring (MH), vastus lateralis (VL), adductor longus (AL), gluteus medius (GMed), and gluteus maximus (GMax) muscles in the involved leg. Subjects performed five forward-side jumps on a force plate before and after functional fatiguing exercises. To induce fatigue, subjects began 5-min incremental running on a treadmill between 5 and 6 mph. Next, subjects performed 20-second lateral counter movement jumps (CMJ), and 20 vertical CMJs. After each fatigue cycle, subjects performed one max vertical jump. Subjects repeated three exercises until Borg's rating of perceived exertion (RPE) reached 17 and the vertical jump height fell below 80% of their max jump height. Functional analysis of variance (FANOVA) (p < 0.05) was used to evaluate differences (a group by fatigue interaction) between two conditions (pre- vs post-fatigue) in each group (AI and control) for lower-extremity kinematic, kinetic and neuromuscular patterns. Pairwise comparison functions as well as 95% confidence interval (CI) bands were plotted to determine specific differences. If 95% CI bands did not cross the zero line, we considered the difference significant. RESULTS: Compared to the control group, the AI group demonstrated less range of dorsiflexion, knee and hip flexion motions during early phase of landing after fatigue. For sagittal-plane hip kinetics, subjects with AI decreased the hip extension moment while control subjects increased hip extension moments during landing following functional fatiguing exercise. The AI group showed less reduction of anterior-posterior ground reaction force (AP GRF) during transition phase of a forward-side jump after fatigue compared to control subjects. The AI group decreased EMG amplitude of PL, MH, and GMed while increased VL and GMax during landing after fatigue compared to control subjects. CONCLUSION: AI subjects demonstrated greater impairments in neuromechanical control patterns than a matched control group during a sport movement as fatigue progressed. Compared to AI group, control subjects showed a coordinated joint control strategy after fatigue, increasing joint angles from distal (ankle) to proximal (hip) joints by increasing hip extensor moments during landing from a forward-side jump in an attempt to reduce ground impact force. EMG alterations were consistent with patterns observed in injured patients, which may predispose patients to poor positions associated with lower extremity joint injury. These interactions between neuromuscular fatigue and AI may predispose individuals to lower extremity injuries.

The purpose of this study was to demonstrate the social and psychological implications created by unstable placements and trauma experienced by former foster youth. The participants of the study were recruited from college campuses via Extended Opportunity Program and Services liaisons as well as the Guardian Scholar Program liaisons. The sample included individuals that identified as former foster youth and individuals that identified as never being in foster care. The findings indicated the social and psychological differences among former foster youth that resided in unstable living arrangements as compared to youth that were not in foster care.

Highway systems world wide continue to see an ever increased number of vehicles and subsequently a rise in congested traffic. This results in longer commute times, wasted energy as vehicles idle in stop and go traffic, and increases the risk of accidents. In short, increased congestion costs time and money. These issues have prompted much research into Automated Highway Systems (AHS). In AHS vehicles using computer algorithms can safely travel at much smaller inter-vehicle distances than human drivers are capable of. This increases the capacity of existing highway systems. Sensors aboard each vehicle make this possible by monitoring their surroundings. Vehicles equipped with Adaptive Cruise Control (ACC) are capable of this type of close proximity travel. ACC packages are becoming common as a standard package on many mid-priced vehicles. Another form of automation, Cooperative Adaptive Cruise Control (CACC), which utilizes wireless communication between vehicles, has been proposed and will likely become available within the next couple decades. CACC allows each vehicle to communicate their intended speed or position changes to surrounding vehicles, further decreasing the possibility of collisions. These automation methods are proposed to reduce driver stress, increase highway throughput, and decrease accident rates. However, the fact that vehicles are being automated creates new opportunities for malicious individuals to wreak havoc on society. This research investigates the possibility that some vehicles on the highway might be under the control of malicious individuals who have modified their automated control systems to negatively affect vehicles around them. These malicious actors might also exploit the wireless communication of CACC vehicles and hack their control algorithms, causing them to become unstable. These hacked vehicles could become passive participants in the attack unbeknownst to the driver of the vehicle. The result of such attacks could be congested traffic, rapid changes in acceleration causing drivers discomfort, or multi-vehicle collisions. Such attacks could effectively negate the benefits of implementing AHS. The goal of this work is to bring to light possible weaknesses in the proposed systems so they can be rectified before becoming an issue to the public at large.

Degradation of transistor parameter values due to Negative Bias Temperature Instability (NBTI) has emerged as a major reliability problem in current and future technology generations. NBTI Aging of a Static Random Access Memory (SRAM) cell leads to a lower noise margin, thereby increasing the failure rate. The register file, which consists of an array of SRAM cells, can suffer from data loss, leading to a system failure. In this work, we study the source of NBTI stress in an architecture and physical register file. Based on our study, we modified the register file structure to reduce the NBTI degradation and improve the overall system reliability. Having evaluated new register file structures, we find that our techniques substantially improve reliability of the register files. The new register files have small overhead, while in some cases they provide saving in area and power.

Joint Position Sense (JPS) of the shoulder as determined by repeated repositioning tasks has been performed under different constrained testing conditions. The variability in the testing protocols for JPS testing of the gleno-humeral joint may incorporate different movement patterns, numbers of trials used to derived a specific JPS variable and range of motion. All of these aspects may play an important role in the assessment of G-H JPS testing. When using a new instrument for assessing JPS all of these issues need to be examined to document the optimal testing protocols for subsequent clinical assessments. By undertaking these studies future clinical trials may be more optimally assessed to determine if there are differences between dominant and non-dominant arms as well as the presence of JPS changes in performance associated with pathology and rehabilitation. This study used a 3-dimensional tracking system to examined gleno-humeral JPS using 2 open kinetic chain movement patterns. The 'conventional' 90 degree abducted, externally rotated movement was compared to the hypothetically more functional D2 movement pattern used in proprioceptive neuromuscular facilitatory techniques. These two patterns were tested at different ranges (low and high). Two cohorts (n=12, n=16) of normal healthy athletic males aged 17-35 years, performed matching tasks of both left and right arms. The second cohort (n=16) were assessed with and without strapping the gleno-humeral joint with sports tape. Accuracy (overall bias) and precision (variability) scores were determined for progressively greater numbers of trials. The findings of the study show that estimates of JPS accuracy and precision become more stable from data derived from 5 to 6 matching trials. There were no statistical differences between sides [95%CI ± 1.5cm]. The accuracy but not precision improved as subjects approximated the 'high' end of range in the 'conventional' or D2 pattern. Furthermore, no systematic differences were detected at different ranges of movement or movement patterns with or without the application of sports tape. These findings provide a guide to the number of trials that optimise the testing of the gleno-humeral joint and also suggest that in normal controls the magnitude of differences between sides and movement patterns is similar. These findings also iii indicate that sports tape applied to the shoulder may not significantly change the JPS performance in healthy, athletic males.

Doctor of Philosophy / We investigate the linear growth and vertical structure of the magnetorotational instability (MRI) in weakly ionised, stratified accretion discs. The magnetic field is initially vertical and perturbations have vertical wavevectors only. Solutions are obtained at representative radial locations from the central protostar for different choices of the initial magnetic field strength, sources of ionisation, disc structure and configuration of the conductivity tensor. The MRI is active over a wide range of magnetic field strengths and fluid conditions in low conductivity discs. For the minimum-mass solar nebula model, incorporating cosmic ray and x-ray ionisation and assuming that charges are carried by ions and electrons only, perturbations grow at 1 AU for B < 8G. For a significant subset of these strengths (200mG < B < 5 G), the growth rate is of order the ideal MHD rate (0.75 Omega). Hall conductivity modifies the structure and growth rate of global unstable modes at 1 AU for all magnetic field strengths that support MRI. As a result, at this radius, modes obtained with a full conductivity tensor grow faster and are active over a more extended cross-section of the disc, than perturbations in the ambipolar diffusion limit. For relatively strong fields (e.g. B > 200 mG), ambipolar diffusion alters the envelope shapes of the unstable modes, which peak at an intermediate height, instead of being mostly flat as modes in the Hall limit are in this region of parameter space. Similarly, when cosmic rays are assumed to be excluded from the disc by the winds emitted by the magnetically active protostar, unstable modes grow at this radius for B < 2 G. For strong fields, perturbations exhibit a kink at the height where x-ray ionisation becomes active. Finally, for R = 5 AU (10 AU), unstable modes exist for B < 800 mG (B < 250 mG) and the maximum growth rate is close to the ideal-MHD rate for 20 mG < B < 500 mG (2 mG < B < 50 mG). Similarly, perturbations incorporating Hall conductivity have a higher wavenumber and grow faster than solutions in the ambipolar diffusion limit for B < 100 mG (B < 10 mG). Unstable modes grow even at the midplane for B > 100 mG (B ~ 1 mG), but for weaker fields, a small dead region exists. When a population of 0.1 um grains is assumed to be present, perturbations grow at 10 AU for B < 10 mG. We estimate that the figure for R = 1 AU would be of order 400 mG. We conclude that, despite the low magnetic coupling, the magnetic field is dynamically important for a large range of fluid conditions and field strengths in protostellar discs. An example of such magnetic activity is the generation of MRI unstable modes, which are supported at 1 AU for field strengths up to a few gauss. Hall diffusion largely determines the structure and growth rate of these perturbations for all studied radii. At radii of order 1 AU, in particular, it is crucial to incorporate the full conductivity tensor in the analysis of this instability, and more generally, in studies of the dynamics of astrophysical discs.