The stride interval of typical human gait is correlated over thousands of strides. This statistical persistence diminishes with age, disease, and pace-constrained walking. Considering the widespread use of treadmills in rehabilitation and research, it is important to understand the effect of this speed-constrained locomotor modality on stride interval dynamics. To this end, and given that the dynamics of children have been largely unexplored, this study investigated the impact of treadmill walking, both with and without handrail use, on paediatric stride interval dynamics. An initial stationarity analysis of stride interval time series identified both non-stationary and stationary signals during all walking conditions. Subsequent scaling analysis revealed diminished stride interval persistence during unsupported treadmill walking compared to overground walking. Finally, while the correlation between stride interval dynamics and gross energy expenditure was investigated in an effort to elucidate the clinical meaning of persistence, no simple linear correlation was found.

Sensory motor deficits, although not part of the diagnostic criteria, are frequently reported in autism spectrum disorder (ASD). The ob jective of this project is to study the temporal and spatial dynamics of an approximately periodic motor activity (circle drawing) in children with ASD. The natural rhythm of periodic motor activities such as circle drawing are known to exhibit statistical persistence in typically developing individuals. A sample of 15 children aged 4 to 8 years, with a primary diagnosis of ASD were asked to draw circles using a computerized tablet and pen, which record spatio-temporal data. Results were compared with those of 19 typically developing children. While no differences were seen in statistical persistence, differences were observed in timing of discontinuous circle drawing and in kinetic process variable such as grip and axial forces. Understanding the specific nature of graphomotor deficits is the first step towards developing targeted treatment for these impairments.

Sensory motor deficits, although not part of the diagnostic criteria, are frequently reported in autism spectrum disorder (ASD). The ob jective of this project is to study the temporal and spatial dynamics of an approximately periodic motor activity (circle drawing) in children with ASD. The natural rhythm of periodic motor activities such as circle drawing are known to exhibit statistical persistence in typically developing individuals. A sample of 15 children aged 4 to 8 years, with a primary diagnosis of ASD were asked to draw circles using a computerized tablet and pen, which record spatio-temporal data. Results were compared with those of 19 typically developing children. While no differences were seen in statistical persistence, differences were observed in timing of discontinuous circle drawing and in kinetic process variable such as grip and axial forces. Understanding the specific nature of graphomotor deficits is the first step towards developing targeted treatment for these impairments.

The stride interval of typical human gait is correlated over thousands of strides. This statistical persistence diminishes with age, disease, and pace-constrained walking. Considering the widespread use of treadmills in rehabilitation and research, it is important to understand the effect of this speed-constrained locomotor modality on stride interval dynamics. To this end, and given that the dynamics of children have been largely unexplored, this study investigated the impact of treadmill walking, both with and without handrail use, on paediatric stride interval dynamics. An initial stationarity analysis of stride interval time series identified both non-stationary and stationary signals during all walking conditions. Subsequent scaling analysis revealed diminished stride interval persistence during unsupported treadmill walking compared to overground walking. Finally, while the correlation between stride interval dynamics and gross energy expenditure was investigated in an effort to elucidate the clinical meaning of persistence, no simple linear correlation was found.

I compared the utility of two continuous time-series data measures for applied conservation biology by investigating how well each could predict future local persistence of a diverse set of bird species. I used 37 years of data from the North American Breeding Bird Survey to calculate abundance from yearly point-counts and permanence (i.e., consistent occupancy over time) from yearly presence-absence data in the early portion of the study period, then used the later portion of data to empirically evaluate how well each measure predicted persistence two decades into the future. I found that permanence could only match the ability of abundance to accurately predict local species persistence if multiple within-year repeated observations contributed to its calculation. Neither measure was effective at predicting persistence for regionally rarer species. I suggest the yearly and within-year repeated collection of abundance estimating data for use in applied conservation biology to best ensure biodiversity persistence.

We study diffusion-reaction-advection models describing population dynamics of aquatic organisms subject to a constant drift, with reflecting upstream and outflow downstream boundary conditions. We consider three different models: single logistically growing species, two and three competing species. In the case of a single population, we determine conditions for existence, uniqueness and stability of non-trivial steady-state solutions. We analyze the dependence of such solutions on advection speed, growth rate and length of the habitat. Such analysis offers a possible explanation of the "drift paradox" in our context. We also introduce a spatially implicit ODE (nonspatial approximation) model which captures the essential behavior of the original PDE model. In the case of two competing species, we use a diffusion-advection version of the Lotka-Volterra competition model. Combining numerical and analytical techniques, in both the spatial and nonspatial approximation settings, we describe the effect of advection on competitive outcomes. Finally, in the case of three species, we use the nonspatial approximation approach to analyze and classify the possible scenarios as we change the flow speed in the habitat.

This thesis examines to what extent the firm size influences on firm growth and their behaviour of Spanish manufactures and service industries between 1994 and 2002 from the stochastic growth theory. The study has not only responded to the need of considering firm size as a key variable for future firm growth, but it has also examined the impacts of different industries for the development of firms, the learning process and the impact of internal and external firm characteristics. The firm growth is the process affecting firms while they remain active in the market. While some theories justify the firm growth as an adjustment of size due to internal or external environment, others have justified the change of size as a response to luck factors.To analyse it we have based on Gibrat's Law or Law of Proportionate Effects. Gibrat's Law suggests that all firms have the same probability to grow independently of their size. Although the researcher's interest to analyse it there are some mix results in the literature and there are still some lacks in the literature. According to the empirical review of the Gibrat's Law, several are the results to be stood out. Firstly, the firm growth is a complex process affected by internal and external characteristics which may be due to deterministic or random factors. Secondly, there appear some outstanding lacks of empirical studies. On the one hand, there are few empirical studies analysing the service industries. On the other hand, there is a scarcity of researchers incorporating the spatial dimension in their analysis.Our results refuse Gibrat's Law both for manufactures and service industries and, more interestingly, those results do not vary when introducing the firm learning process in the market. In reference to the differences between each individual sector, there appear different growth behaviours depending on the industry. It is well known that the firm growth pattern depends on the characteristics of industry and our results show a different behaviour depending on the industry. Therefore, if we consider different sectors, the firm growth pattern presents a heterogeneous trend. Each industry has quite different technologies and perhaps different growth processes, which might explain the mixed nature of the results.The persistence of firm growth offers a dynamic approach to the growth pattern. The relationship between past and current growth rates have been another aspect related with Gibrat's Law. The persistence of firm growth is highly important for policy-makers and managers, who should consider the pattern driving firm growth in order to increase the profitability of their investments, the job creation and the economic growth. As it was expected, the effect of the persistence depends on the proximity of the growth. In other words, a positive growth will have more impact on the following period than two periods later. Related to the analysis of the presence of different equilibria of firm growth, our results show that there is a significant difference in growth between manufacturing and service sector firms which persist when controlling for other firm specific characteristics. Nevertheless, the introduction of the location variables generates that those different trends are not significant. In order to know how important the differentiation between manufactures and service industries is, we estimate Gibrat's Law for manufactures and service industries in separate equations. When we separate the estimation of both industries, our results accept that the equilibria are different including the locational variables.In reference to the determinants of firm growth, variables such as the territorial R&D and the growth of GDP have positive externalities to firm growth. On the other hand, the industrial diversity or specialisation present different results depending on the sector. Finally, barriers to entry such as capital intensity and minimum efficient size behave as barriers to grow. That means that sectors which are highly capital intensive, they will prevent firms from growing. Conversely, sectors with low barriers to entry have low barriers to grow. However, those barriers to grow may be surpassed with internal characteristics such as innovation, cooperation, increase of human capital, etc. / Aquesta tesis examina la influència de la dimensió de l'empresa en el creixement empresarial, així com el comportament de les manufactures i els serveis d'Espanya entre 1994 i 2002 des d'una perspectiva estocàstica. Aquesta tesis no només respon a la necessitat de considerar el tamany de l'empresa com una variable crucial per al futur de l'empresa sinó també les característiques sectorials, el procés d'aprenentatge i les característiques internes i externes. El creixement empresarial és el procés que afecta a les empreses mentre estan actives en el mercat. Mentre que algunes teories justifiquen el creixement de l'empresa com un procés d'ajust cap al tamany òptim, altres teories justifiquen el creixement a un conjunt de factors aleatoris. Per tal d'analitzar el creixement empresarial, ens basem en la Llei de Gibrat o Llei dels Efectes Proporcionals. Llei de Gibrat suggereix que totes les empreses tenen la mateixa probabilitat per créixer independentment del seu tamany. Tot i l'interès del tema, els resultats en la literatura empírica són contradictoris i existeixen encara alguns buits. D'acord amb la revisió empírica de la Llei de Gibrat, diferents resultants poden ser destacats. En primer lloc, el creixement empresarial és un procés complex que depén de característiques internes i externes que poden afecten de forma determinística o aleatòria. En segon lloc, hi ha varies buits en la literatura. Per una banda, pocs estudis empírica analitzen els serveis. Per altra banda, hi ha una escassetat d'investigadors que incorporen la dimensió locacional.Els nostres resultats refusen la Llei de Gibrat per les manufactures I els serveis i, a més a més, aquests resultats no varien quan introduïm el procés d'aprenentatge de l'empresa en el mercat. Quant a les diferències entre cada sector individual, apareixen comportaments de creixement diferents en funció de la indústria. És un fet conegut que el creixement de l'empresa depèn de les característiques de la indústria i els nostres resultats mostren un comportament diferent en funció del sector industrial. Per tant, cada indústria té diferents característiques tecnològiques i diferent processos de creixement, els quals poden explicar els resultats contradictoris de la literatura.La persistència del creixement empresarial ofereix una perspectiva dinàmica del creixement de l'empresa. La relació entre creixement passat i actual és un alter aspecte relacionat amb la Llei de Gibrat. La persistència del creixement empresarial és molt important per als agents públics i directors, els quals hauries de tenen compte el comportament que dirigeix el creixement empresarial per tal d'incrementar els beneficis de les seves inversions, la creació de l'ocupació i el creixement econòmic. Com era d'esperar, l'efecte de la persistència depèn de la proximitat temporal del creixement. En altres paraules, un creixement positiu tindrà més impacte en el període següent que dos períodes després. Quant a l'anàlisi de la presència de diferents equilibris de creixement empresarial, els nostres resultats mostren que hi ha una diferència significativa en el creixement entre els sectors manufacturers i els serveis la qual persisteix quan controlem per altres característiques específiques de l'empresa. No obstant, la introducció de les variables locacionals generata que aquesta tendència sigui no significativa. Per tal de saber com d'important és la diferenciació entre manufactures i serveis s'estima la Llei de Gibrat per a les indústries manufactureres i els serveis en equacions separades. En separar les estimacions d'ambdues indústries, els nostres resultats accepten l'existència de diferents equilibris quan s'inclouen les variables locacionals. Quant als determinants dels creixement empresarial, variables com la intensitat tecnològica territorial i el creixement del PIB presenten externalitats positives sobre el creixement empresarial. Per altra banda, la diversitat o especialització industrial tenen impactes diferents en funció del sector a analitzar. Finalment, barreres d'entrada com la intensitat del capital i el tamany mínim eficient es comporten com barreres al creixement. Això vol dir que sectors que són intensiu en capital dificultaran el creixement de les empreses. Pel contrari, sectors amb baixes barreres d'entrada tenen baixes barreres al creixement. No obstant, aquestes barreres al creixement poden ser superades amb característiques internes com la innovació, la cooperació, l'increment del capital humà, etc.

Objective. To examine the natural course of social anxiety disorder (SAD) in the community and to explore predictors for adverse long-term outcomes. Method. A community sample of N=3,021 subjects aged 14-24 was followed-up over 10 years using the DSM-IV/M-CIDI. Persistence of SAD is based on a composite score reflecting the proportion of years affected since onset. Diagnostic stability is the proportion of SAD subjects still affected at follow-up. Results. SAD reveals considerable persistence with more than half of the years observed since onset spent with symptoms. 56.7% of SAD cases revealed stability with at least symptomatic expressions at follow-up; 15.5% met SAD threshold criteria again. 15.1% were completely remitted (no SAD symptoms and no other mental disorders during follow-up). Several clinical features (early onset, generalized subtype, more anxiety cognitions, severe avoidance and impairment, co-occurring panic) and vulnerability characteristics (parental SAD and depression, behavioural inhibition, harm avoidance) predicted higher SAD persistence and -less impressively- diagnostic stability. Conclusion. A persistent course with a considerable degree of fluctuations in symptom severity is characteristic for SAD. Both, consistently meeting full threshold diagnostic criteria and complete remissions are rare. Vulnerability and clinical severity indicators predict poor prognosis and might be helpful markers for intervention needs.

Certain contemporary philosophers (e.g. Dainton, 2008; Strawson, 1999; Foster, 2008) have thought that the first-person, qualitative aspect of conscious experience should be taken seriously when it comes to our thinking about personal identity through time. These philosophers have thus argued that experiential continuity is essential to a person’s ability to persist identically through time. This is what I will call ‘the phenomenological theory’. In this thesis I describe the phenomenological theory and then discuss three problems that have plagued the history of this theory: the bridge problem, the token problem, and the ontological problem. I will argue that a recent version of the phenomenological theory proposed by Barry Dainton and Timothy Bayne (2005) provides satisfactory answers to two of these problems, but not the third. I will conclude this thesis by proposing a superior version of the phenomenological theory—one that can handle all three problems.

Petroleum hydrocarbons (PHCs) such as gasoline are ubiquitous organic compounds present at contaminated sites throughout the world. Accidental spills and leakage from underground storage tanks results in the formation of PHC source zones that release hundreds of organic compounds, including the high impact, acutely toxic and highly persistent aromatics (e.g., benzene, toluene, ethylbenzene, xylenes, trimethylbenzenes and naphthalene) into groundwater. Contamination by these compounds continues to persist until the PHC source zone is treated in place or removed. In situ chemical oxidation (ISCO) employing persulfate was identified as a potentially viable technology for the treatment of PHC source zones. The effectiveness and efficiency and, therefore, the overall economic feasibility of a persulfate-based ISCO treatment system depend upon the reactivity of the target organic compounds and the interaction of persulfate with aquifer media. The objective of this research was to investigate the persistence of unactivated and activated persulfate in the presence of aquifer materials, and to examine persulfate oxidation of PHC compounds at both the bench- and pilot-scales. A series of bench-scale studies were performed to estimate persulfate degradation kinetic parameters in the presence of seven well-characterized, uncontaminated aquifer materials and to quantify the changes in specific properties of these materials. Batch experiments were conducted in an experimental system containing 100 g of solids and 100 mL of persulfate solution at 1 or 20 g/L. Column experiments were designed to mimic in situ conditions with respect to oxidant to solids mass ratio and were performed in a stop-flow mode using a 1 g/L persulfate solution. The degradation of persulfate followed a first-order rate law for all aquifer materials investigated. An order of magnitude decrease in reaction rate coefficients was observed for systems that used a persulfate concentration of 20 g/L as compared to those that used 1 g/L due to ionic strength effects. As expected, the column experiments yielded higher reaction rate coefficients than batch experiments for the same persulfate concentration due to the lower oxidant to solids mass ratio. Bench-scale data was used to develop a kinetic model to estimate the kinetic response of persulfate degradation during these tests. The push-pull tests involved the injection of persulfate (1 or 20 g/L) and a conservative tracer into a hydraulically isolated portion of the sandy aquifer at CFB Borden, Canada. The kinetic model developed from the bench-scale data was able to reproduce the observed persulfate temporal profiles from these push-pull tests. This implies that persulfate degradation kinetics is scalable from bench-scale to in situ scale, and bench tests can be employed to anticipate in situ degradation. The estimated reaction rate coefficients indicate that persulfate is a persistent oxidant for the range of aquifer materials explored with half lives ranging from 2 to 600 days, and therefore in situ longevity of persulfate will permit advective and diffusive transport in the subsurface. This is critical for successful delivery of oxidant to dispersed residuals in the subsurface. Activation of persulfate is generally recommended to enhance its oxidation potential and reactivity towards organic compounds. This approach may influence the stability of persulfate-activator system in the presence of aquifer materials. A series of batch tests were performed to investigate persistence of persulfate at two concentrations (1 or 20 g/L) using three contemporary activation strategies (citric acid chelated-ferrous, peroxide and high pH ) in the presence of 4 well-characterized, uncontaminated aquifer materials. Chelation by citric acid was ineffective in controlling the interaction between persulfate and Fe(II) and a rapid loss in persulfate concentration was observed. Higher Fe(II) concentration (600 mg/L) led to greater destabilization of persulfate than lower Fe(II) concentration (150 mg/L) and the persulfate loss was stoichiometrically equivalent to the Fe(II) concentration employed. Subsequent to this rapid loss of persulfate, first-order degradation rate coefficients (kobs) were estimated which were up to 4 times higher than the unactivated case due to the interaction with Fe(III) and CA. Total oxidation strength (TOS) was measured for peroxide activation experiments and was observed to decrease rapidly at early time due peroxide degradation. This was followed by slow degradation kinetics similar to that of unactivated persulfate implying that the initial TOS degradation was peroxide dominated and the long-term kinetics were dominated by persulfate degradation. The kobs used to capture TOS degradation for later time were shown to depend upon unactivated persulfate and peroxide degradation rate coefficients, and peroxide concentration. Either a slow peroxide degradation rate and/or higher peroxide concentration allow a longer time for peroxide and persulfate to interact which led to kobs ~1 to 100 times higher than kobs for unactivated persulfate. For alkaline activation, kobs were only 1 to 4 times higher than unactivated persulfate and therefore alkaline conditions demonstrated the least impact on persulfate degradation among the various activation strategies used. For all activation trials, lower stability of persulfate was observed at 1 g/L as compared to 20 g/L due to insufficient persulfate and/or ionic strength effects. A series of batch reactor trials were designed to observe the behavior of the nine high impact gasoline compounds and the bulk PHC fraction measures subjected to various persulfate activation strategies over a 28-day period. This bench-scale treatability used unactivated persulfate (1 or 20 g/L) and activated persulfate (20 g/L). Activation employed chelated-Fe(II), peroxide, high pH or two aquifer materials as activators. No significant oxidation of the monitored compounds was observed for unactivated persulfate at 1 g/L, but 20 g/L persulfate concentration resulted in their near-complete oxidation. Oxidation rates were enhanced by 2 to 18 times by activation with peroxide or chelated-Fe(II). For alkaline activation, pH 11 trials demonstrated ~2 times higher oxidation rates than the unactivated results. For pH 13 activation the oxidation rates of benzene, toluene and ethylbenzene were reduced by 50% while for the remaining monitored compounds they were enhanced by 5 to 100%. Natural activation by both aquifer materials produced oxidation rates similar to the unactivated results, implying that either activation by minerals associated with aquifer material was not significant or that any potential activation was offset by radical scavenging from aquifer material constituents. Acid-catalyzation at pH <3 may enhance oxidation rates in weakly buffered systems. Oxidation of the monitored compounds followed first-order reaction kinetics and rate coefficients were estimated for all the trials. Overall, activated and unactivated persulfate appear to be suitable for in situ treatment of gasoline. Persulfate under unactivated or naturally activated conditions demonstrated significant destruction of gasoline compounds and showed higher persulfate persistence when in contact with aquifer solids as compared to chelated-Fe(II) or peroxide-activated persulfate systems. This observation was used as the basis for selecting unactivated sodium persulfate for a pilot-scale treatment of gasoline-contaminated source zone at CFB Borden, Canada where a ~2000 L solution of persulfate (20 g/L) was injected into a PHC source zone. Concentration of organics and inorganics were frequently monitored over a 4 month period across a 90 point monitoring fence line installed down-gradient. Treatment performance was measured by estimating organic and inorganic mass loading across the monitoring fence. Increased mass loading for sodium was observed over time as the treatment volume moved across the fence-line indicating transport of the inorganic slug created upon oxidant injection. The mass loading also increased for sulfate which is a by-product generated either due to persulfate degradation during oxidation of organic compounds or during its interaction with aquifer materials. Oxidation of organic compounds was evident from the enhanced mass loading of dissolved carbon dioxide. More importantly, a significant (45 to 86%) decrease in mass loading of monitored compounds was observed due to oxidation by injected persulfate. The cumulative mass crossing the monitoring fence-line was 20 to 50% lower than that expected without persulfate treatment. As the inorganic slug was flushed through the source zone and beyond the monitoring fence, the mass loading rate of sodium, sulfate and carbon dioxide decreased and approached background condition. Mass loading of the monitored compounds increased to within 40 to 80% of the pre-treatment conditions, suggesting partial rebound. These investigations assessed the impact of activation on persulfate persistence and treatability of gasoline and served to establish guidelines for anticipating field-scale persulfate behavior under similar conditions. In summary, unactivated persulfate is a stable oxidant in the presence of aquifer materials and its persistence depends upon TOC and Fe(Am) content of the materials, ionic strength, and aquifer to solids mass ratio. Persulfate exhibits significant destruction of gasoline compounds and can be employed for the remediation of gasoline-contaminated sites. Peroxide and chelated-Fe(II) enhance oxidation rates of these compounds, but reduce stability of the persulfate-activator system. Persulfate activation using high pH conditions does not significantly impact persulfate persistence but reduces the overall destruction of gasoline compounds. Therefore, activation imposes a trade-off between enhanced oxidation rates and reduced persulfate persistence. Kinetic model is representative of persulfate degradation at bench- and pilot-scales and can be used for estimation of in situ degradation. The quantification of oxidation rates for gasoline compounds under activated and unactivated persulfate conditions will assist decision-making for identification of appropriate remediation options when targeting contamination by gasoline or by specific high impact gasoline compounds. While persulfate oxidation resulted in partial treatment of a small gasoline source zone, aggressive persulfate load will be required during injection for a complete clean-up. Overall, persulfate-based in situ chemical oxidation was demonstrated to be an effective and a viable technology for the remediation of contaminated soil and groundwater.