This dissertation aimed to investigate the utility of the ex-Gaussian approach to estimating intraindividual variability (IIV) of response times (RT) in diagnosing attention deficit/hyperactivity disorder (ADHD) in children ages 6 to 13 years old. Higher IIV is consistently noted in children with ADHD, but also with other disorders commonly associated with impairments in attention. Firstly, the relationship between IIV and attention abilities was investigated both in relation to parent ratings and participants’ objective performance. Secondly, IIVs utility as an objective measure for supplementing behavioural ratings in the diagnosis of ADHD, a diagnosis which is currently primarily assigned based on informant interviews and ratings of attention, was assessed. Participants included 46 children with ADHD and 58 children without ADHD. Children completed computerized tasks to estimate IIV and assess inattention and hyperactivity/impulsivity. Parents completed questionnaires aimed at assessing attention and hyperactive/impulsive behaviours of participants. Analyses revealed that IIV was predictive of parent ratings of inattention and hyperactivity/impulsivity as well as the number of omission errors made by participants. Regarding diagnostic utility, IIV significantly predicted group membership (ADHD vs Control). However, IIV did not improve diagnostic accuracy when parent ratings were used, such that parent ratings were superior at determining diagnosis. Overall, current results support the use of IIV, based on the ex-Gaussian approach, as an objective measure of attention problems such that it appears to be superior to omission errors on sustained attention CPT-type tasks. Additionally, while parent ratings of attention impairment remain the best predictor of ADHD diagnostic status, IIV may be helpful in determining when further assessment is required in the absence of those ratings. / Graduate / 2021-06-17

La représentation des temps de parcours est un enjeu influençant la qualité de l’information transmise aux usagers des réseaux de transport. En particulier, la congestion constitue un inconvénient majeur dont la prise en compte n’est pas toujours maîtrisée au sein des calculateurs d’itinéraires. De même, les évènements comme les réductions de capacité, les perturbations climatiques, ou encore les pics de fréquentation incitent à dépasser la définition statique des temps de parcours. Des travaux antérieurs se sont focalisés sur des temps dynamiques, i.e. dépendants de la date de départ, de manière à affiner le détail de la représentation, et à prendre notamment en compte le caractère périodique des congestions. La considération d’informations en temps réel est aussi une amélioration indéniable, que ce soit lors de la préparation du trajet, ou lorsqu’il s’agit de s’adapter à des perturbations rencontrées en cours de route. Ceci dit, aussi fines qu’elles soient dans les calculateurs disponibles, ces modélisations présentent un inconvénient majeur : elles ne prennent pas en compte toutes les facettes de la variabilité des temps de parcours. Cette variabilité est très importante, en particulier si l’on considère le niveau d’aversion au risque des usagers. En outre, dans un réseau multimodal, les correspondances éventuelles rendent encore plus critique l’incertitude associée aux temps de parcours. En réponse à ces enjeux, les présents travaux de thèse ont ainsi été consacrés à l’étude de temps de parcours stochastiques, i.e. vus comme des variables aléatoires distribuées.Dans une première étape, nous nous intéressons à la modélisation statistique des temps de parcours et à la quantification de leur variabilité. Nous proposons l’utilisation d’un système de lois développé dans le domaine de l’hydrologie, la famille des lois de Halphen. Ces lois présentent les caractéristiques typiques des distributions de temps de parcours, elles vérifient par ailleurs la propriété de fermeture par l’addition sous certaines hypothèses afférentes à leurs paramètres. En exploitant les ratios de moments associés aux définitions de ces lois de probabilité, nous mettons également au point de nouveaux indicateurs de fiabilité, que nous confrontons avec la palette d’indicateurs classiquement utilisés. Cette approche holistique de la variabilité des temps de parcours nous semble ainsi ouvrir de nouvelles perspectives quant au niveau de détail de l’information, notamment à destination des gestionnaires de réseaux.Par la suite, nous étendons le cadre d’analyse aux réseaux, en utilisant les résultats obtenus à l’étape précédente. Différentes lois de probabilité sont ainsi testées dans le cadre de la recherche du plus court chemin stochastique. Cette première étude nous permet de dresser un panorama des chemins identifiés en fonction du choix de modélisation. S’il est montré que le choix du modèle est important, il s’agit surtout d’affirmer que le cadre stochastique est pertinent. Ensuite, nous soulevons la relative inefficacité des algorithmes de recherche du plus court chemin stochastique, ceux-ci nécessitant des temps de calcul incompatibles avec un passage à l’échelle industrielle. Pour pallier cette difficulté, un nouvel algorithme mettant en oeuvre une technique d’accélération tirée du cadre déterministe est développé dans la dernière partie de la thèse. Les résultats obtenus soulignent la pertinence de l’intégration de modèles stochastiques au sein des calculateurs d’itinéraires. / The travel time representation has a major impact on user-oriented routing information. In particular, congestion detection is not perfect in current route planners. Moreover, the travel times cannot be considered as static because of events such as capacity drops, weather disturbances, or demand peaks. Former researches focused on dynamic travel times, i.e. that depend on departure times, in order to improve the representation details, for example concerning the periodicity of congestions. Real-time information is also a significant improvement for users aiming to prepare their travel or aiming to react to on-line events. However these kinds of model still have an important drawback : they do not take into account all the aspects of travel time variability. This dimension is of huge importance, in particular if the user risk aversion is considered. Additionally in a multimodal network, the eventual connections make the travel time uncertainty critical. In this way the current PhD thesis has been dedicated to the study of stochastic travel times, seen as distributed random variables.In a first step, we are interested in the travel time statistical modeling as well as in the travel time variability. In this goal, we propose to use the Halphen family, a probability law system previously developed in hydrology. The Halphen laws show the typical characteristics of travel time distributions, plus they are closed under addition under some parameter hypothesis. By using the distribution moment ratios, we design innovative reliability indexes, that we compare with classical metrics. This holistic approach appears to us as a promising way to produce travel time information, especially for infrastructure managers.Then we extend the analysis to transportation networks, by considering previous results. A set of probability laws is tested during the resolution of the stochastic shortest path problem. This research effort helps us to describe paths according to the different statistical models. We show that the model choice has an impact on the identified paths, and above all, that the stochastic framework is crucial. Furthermore we highlight the inefficiency of algorithms designed for the stochastic shortest path problem. They need long computation times and are consequently incompatible with industrial applications. An accelerated algorithm based on a deterministic state-of-the-art is provided to overcome this problem in the last part of this document. The obtained results let us think that route planners might include travel time stochastic models in a near future.

Recent advances in travel demand modeling have concentrated on adding behavioral realism by focusing on an individual’s activity participation. And, to account for trip-chaining, tour-based methods are largely replacing trip-based methods. Alongside these advances and innovations in dynamic traffic assignment (DTA) techniques, however, time-of-day (TOD) modeling remains an Achilles’ heel. As congestion worsens and operators turn to variable road pricing, sensors are added to networks, cell phones are GPS-enabled, and DTA techniques become practical, accurate time-of-day forecasts become critical. In addition, most models highlight tradeoffs between travel time and cost, while neglecting variations in travel time. Research into stated and revealed choices suggests that travel time variability can be highly consequential. This dissertation introduces a method for imputing travel time variability information as a continuous function of time-of-day, while utilizing an existing method for imputing average travel times (by TOD). The methods employ ordinary least squares (OLS) regression techniques, and rely on reported travel time information from survey data (typically available to researchers), as well as travel time and distance estimates by origin-destination (OD) pair for free-flow and peak-period conditions from network data. This dissertation also develops two models of activity timing that recognize the imputed average travel times and travel time variability. Both models are based in random utility theory and both recognize potential correlations across time-of-day alternatives. In addition, both models are estimated in a Bayesian framework using Gibbs sampling and Metropolis-Hastings (MH) algorithms, and model estimation relies on San Francisco Bay Area data collected in 2000. The first model is the continuous cross-nested logit (CCNL) and represents tour outbound departure time choice in a continuous context (rather than discretizing time) over an entire day. The model is formulated as a generalization of the discrete cross-nested logit (CNL) for continuous choice and represents the first random utility maximization model to incorporate the ability to capture correlations across alternatives in a continuous choice context. The model is then compared to the continuous logit, which represents a generalization of the multinomial logit (MNL) for continuous choice. Empirical results suggest that the CCNL out-performs the continuous logit in terms of predictive accuracy and reasonableness of predictions for three tolling policy simulations. Moreover, while this dissertation focuses on time-of-day modeling, the CCNL could be used in a number of other continuous choice contexts (e.g., location/destination, vehicle usage, trip durations, and profit-maximizing production). The second model is a bivariate multinomial probit (BVMNP) model. While the model relies on discretization of time (into 30-minute intervals), it captures both key dimensions of a tour’s timing (rather than just one, as in this dissertation’s application of the CCNL model), which is important for tour- and activity-based models of travel demand. The BVMNP’s ability to capture correlations across scheduling alternatives is something no existing two-dimensional choice models of tour timing can claim. Both models represent substantial contributions for continuous choice modeling in transportation, business, biology, and various other fields. In addition, the empirical results of the models evaluated here enhance our understanding of individuals’ time-of-day decisions. For instance, average travel time and its variance are estimated to have a negative effect on workers’ utilities, as expected, but are not found to be that practically relevant here, probably because most workers are rather constrained in their activity scheduling and/or work hours. However, correlations are found to be rather strong in both models, particularly for home-to-work journeys, suggesting that if models fail to accommodate such correlations, biased application results may emerge. / text

Made available in DSpace on 2015-05-14T12:36:51Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1355559 bytes, checksum: fe1c88470e43ce75f706ec9d15cc7bb1 (MD5) Previous issue date: 2014-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / With the advent of technological advances, increasingly demand solutions that use fewer resources, are faster and low cost. As a result, this paper proposed a hybrid approach using metaheuristics Greedy Randomized Adaptive Search Procedure (GRASP) and Iterated Local Search (ILS) applied to the Response Time Variability Problem (RTVP). Since this problem may involve allocation of scarce resources, such as industrial machinery or meeting rooms, going for scheduling of banking customers that require certain conditions, planning of TV ads or route taken by vehicles of logistic companies, etc. For application of the procedure, the movements of shifting symbols, swapping positions between symbols and one called double bridge, which is a mix of movements of shifting and swapping involving opposite symbols were used. The neighborhood structures were based on the movements described above, varying the number of symbols involved. Thus, the results obtained demonstrate that such procedures satisfied the problem and brought consistent results when compared with the literature. / Com o advento dos avanços tecnológicos, cada vez mais se procura soluções que utilizem menos recursos, sejam mais rápidos e de baixo custo. Em virtude disso, este trabalho propôs uma abordagem meta-heurística híbrida utilizando Greedy Randomized Adaptive Search Procedure (GRASP) e Iterated Local Search (ILS) aplicados ao Problema da Variabilidade do Tempo de Resposta. Este problema pode envolver desde alocação de recursos escassos, como por exemplo, máquinas industriais ou salas de reunião, passando pelo agendamento de clientes de um banco que requerem certas condições, o planejamento das propagandas de TV ou o percurso feito por caminhões de empresas transportadoras, dentre outros. Para a aplicação do procedimento, foram utilizados os movimentos de deslocamento do mesmo, permuta de posição entre símbolos e de um movimento chamado double brigde, que é uma mistura dos movimentos de deslocamento e permutação envolvendo símbolos opostos. As estruturas de vizinhança compostas basearam-se nos movimentos descritos anteriormente, variando a quantidade de símbolos envolvidos. Desta forma, os resultados obtidos demonstram que tais procedimentos trouxeram resultados satisfatórios ao problema e condizentes quando comparados com a literatura.

In the present fierce global competition, poor responsiveness, low flexibility to meet the uncertainty of demand, and the low efficiency of traditional assembly lines are adequate motives to persuade manufacturers to adopt highly flexible production tools such as cross-trained workers who move along the assembly line while carrying out their planned jobs at different stations [1]. Cross-trained workers can be applied in various models in assembly lines. A novel model which taken into consideration in many industries nowadays is called the linear walking worker assembly line and employs workers who travel along the line and fully assemble the product from beginning to end [2]. However, these flexible assembly lines consistently endure imbalance in their stations which causes a significant loss in the efficiency of the lines. The operational time variability is one of the main sources of this imbalance [3] and is the focus of this study which investigated the possibility of decreasing the mentioned loss by arranging workers with different variability in a special order in walking worker assembly lines. The problem motivation comes from the literature of unbalanced lines which is focused on bowl phenomenon. Hillier and Boling [4] indicated that unbalancing a line in a bowl shape could reach the optimal production rate and called it bowl phenomenon.  This study chose a conceptual design proposed by a local automotive company as a case study and a discrete event simulation study as the research method to inspect the questions and hypotheses of this research.  The results showed an improvement of about 2.4% in the throughput due to arranging workers in a specific order, which is significant compared to the fixed line one which had 1 to 2 percent improvement. In addition, analysis of the results concluded that having the most improvement requires grouping all low skill workers together. However, the pattern of imbalance is significantly effective in this improvement concerning validity and magnitude.

På senaste tiden har leveransprecision blivit allt viktigare eftersom kunder idag kännetecknas av att vara mer tidskänsliga och ständigt söker efter produkter som är specifikt anpassade till kunden. Tid har därmed betraktats som ett kriterium för konkurrens och är betydande för företag att kunna konkurrera på marknaden. Osäkerheter i marknaden har en stor påverkan på leveransprecision och det är en stor utmaning för företag att planera produktion utifrån dessa osäkerheter. När produktion för en artikel planeras måste en planerare ta hänsyn till osäkerheter som exempelvis att en maskin kan sluta fungera, att en defekt produkt måste omarbetas eller att det tar längre tid än planerat för att utföra ett arbetsmoment som leder till att en ledtid blir längre. Syftet med studien var att identifiera orsaker till skillnaden mellan planerad och verklig produktionstid samt ge förbättringsförslag för att minska skillnaden. Syftet har uppfyllts med hjälp utav en fallstudie på AQ Group i Pålsboda och genom intervjuer där planerad och verklig produktionstid har undersökts. En litteraturstudie har utnyttjats och tre frågeställningar har formulerats till studien. Dessa frågeställningar lyder: Hur ser skillnaden ut mellan planerad och verklig produktionstid? Vad är orsakerna till dessa skillnader? Hur kan dessa orsaker elimineras? Under det teoretiska avsnittet har fokuset varit på cykeltider, ställtider, produktionstid, Lean och produktionsplanering. Resultatet visar en total skillnad på 24 % mellan den planerade och verkliga produktionstiden över en 5-dagarsperiod. Några orsaker som påträffats är att de standardiserade arbetssätten inte är uppdaterade, inte är tvingande för operatörer att utföra och att det inte existerar några illustrationer för standardiseringen. En annan orsak är onödiga arbetsmoment där verktyg ligger långt ifrån arbetsstationerna och ibland fattas som gör att produktionstiden blir längre än planerat. Avslutningsvis presenteras kritiska förbättringsförslag som specifikt påverkar skillnaden i produktionstiderna och allmänna förbättringsförslag som AQ Group i Pålsboda kan ta nytta av för att effektivisera verksamheten. / In recent times delivery precision has become more important to customers, which today are characterized by being more time sensitive and constantly looking for products that are specifically tailored to the customer. Time is being seen as a criterion for competitors and it is important for companies to be able to compete in the market. Uncertainties in the current market have an effect on delivery precision and it is a major challenge for companies to plan production based on these uncertainties. When production for an article is planned, it should be planned in consideration of uncertainties, for example, a machine may break down, a defective product may need a rework or that it takes longer than planned to carry out an operation leading to a longer lead time. The purpose of the study was to identify causes of difference between planned and actual production time and to provide improvement suggestions to reduce the difference. The purpose has been achieved through a case study in AQ Group in Pålsboda with help of interviews where planned and actual production time has been investigated. A literature study has been used as well as three questions. These questions are: What is the difference between planned and actual production time? What are the causes of these differences? How can these causes be eliminated? During the theoretical section, the focus has been on cycle times, setup times, production time, Lean and production planning. The results show a total difference of 24% between the planned and actual production time over a 5-day period. Causes that have been found are that the standardized working methods are not up to date, are not mandatory for operators to perform and that there exist no illustrations for the standardization. Another cause is unnecessary work steps where tools is far away from the workstations and sometimes missing which leads to the production time being longer than planned. Lastly the study provides critical improvement suggestions that specifically affect the differences between planned and actual production times and general improvement suggestions that AQ Group in Pålsboda can take part of to streamline operations.

Akustiska kanaler för undervattenskommunikation är flervägskanaler där ljudet reflekteras från havets yta och botten och bryts vid ljudhastighetsförändringar. I grunt vatten är impulssvaret långt jämfört med symbolernas tidslängd i ett utskickat meddelande. Detta orsakar intersymbolinterferens, vilket gör det svårt att återskapa meddelandet. Denna avhandling behandlar fysikalisk modellering av kommunikationskanalen. Sådan modellering kan öka insikten om de svårigheter som finns vid design av kommunikationssystem och kan vara till hjälp vid utveckling av lämpliga modulationstekniker och avkodningsalgoritmer. Ljudutbredningen simuleras med en strålgångsmetod med reflektionskoefficienter beräknade för plana vågor. I artikel 4 och 5 utvidgas modellen till en algoritm för gaussisk strålsummation. De viktigaste vetenskapliga bidragen är följande. Artikel 1: Aktuell kunskap om impulssvaret hos kommunikationskanalen gör det betydligt lättare att tolka det mottagna meddelandet. I denna artikel studeras tidsvariabiliteten hos impulssvaret i termer av bitfelssannolikhet när ett gammalt impulssvar används för kanalutjämning. Tidsvariabiliteten visar sig variera avsevärt med mottagarpositionen, inte bara när det gäller avståndet till sändaren, utan även när det gäller placeringen i djupled. Artikel 2: En hybridmetod presenteras, där strålgång i ett avståndsberoende medium kombineras med lokal fullfältsmodellering av interaktionen med havsbottnen. Metoden används för simuleringar av akustisk kommunikation i grunt vatten. Artikel 3: För att kunna göra tillförlitliga simuleringar av ljudutbredning behöver man god kunskap om mediets ljudhastighetsprofil --- information som inte alltid är tillgänglig. I denna artikel används den hybrida strålgångsmetoden från artikel 2 för att skatta ljudhastighetsprofilen från kommunikationsdata. Miljöparametrarna som beräknats genom inversionen minskar avvikelsen mellan simulerade och observerade skattningar av impulssvaret jämfört med avvikelsen då en uppmätt, två dagar gammal ljudhastighetsprofil används vid simuleringen. Miljömodellen används också för en genomgång av alternativa käll- och mottagarpositioner. Artikel 4: Gaussisk strålsummation är en vågutbredningsmodell som liknar strålgång men kan ge korrekta resultat i strålgångens singulära områden, som skuggzoner och kaustikor. I denna artikel diskuteras hur några olika val av den komplexa strålparametern $\epsilon$ fungerar i grunda vågledare. Bäst resultat erhålls om man väljer $\epsilon$ så att strålen blir smal i punkten närmast mottagaren och får en plan vågfront där. Artikel 5: En adaptiv metod för gaussisk strålsummation i grunda vågledare presenteras. Algoritmen ger en noggrannhet som är bättre än eller minst lika bra som strålgångens, även i grunda vågledare med en starkt djupberoende ljudhastighet. / Acoustic underwater communication channels are multipath channels where sound is reflected from the surface and the bottom of the sea and refracted by sound speed variations. In shallow water, the impulse response is typically long compared to the time length of the symbols in a transmitted message. This causes inter-symbol interference, which makes the message difficult to decode. This thesis deals with physical modelling of the communication channel. Such modelling can provide insight into the difficulties of communication system design and may serve as an aid in the development of appropriate modulation techniques and decoding algorithms. The sound propagation is simulated by a ray tracing method with plane-wave reflection coefficients, in papers 4 and 5 expanded to a Gaussian beam summation algorithm. The main scientific contributions are the following. Paper 1: Up-to-date knowledge of the impulse response of the communication channel considerably simplifies the extraction of information from a detected signal. In this paper the time variability of the impulse response is studied in terms of the bit-error rate, when an old impulse response is used for channel equalisation. The time variability is found to vary significantly with the receiver position, not only in range, but also in depth. Paper 2: A hybrid raytrace method is presented, combining ray tracing in a range-dependent water column with local full-field modelling of the seabed interaction. The method is applied to simulations of acoustic communication in shallow water. Paper 3: To be able to make reliable simulations of sound propagation, one needs to know, quite accurately, the sound speed profile of the medium --- information which is not always available. In this paper the hybrid raytrace method from paper 2 is used to estimate the sound speed profile from communication data. The environmental model obtained by the inversion reduces the mismatch between the modelled and the observed impulse response estimates, compared to the mismatch with a two-days-old sound speed profile. The model is also used to investigate alternative source-receiver configurations. Paper 4: Gaussian beam summation is a wave propagation model similar to ray tracing, which can yield correct results in singular regions like shadow zones and caustic points. In this paper some different choices of the complex beam parameter $\epsilon$ are discussed for shallow waveguides. Best results are observed when $\epsilon$ is chosen so that each beam is narrow at the point where it is closest to the receiver and has a plane wavefront there. Paper 5: An adaptive method for Gaussian beam summation in shallow waveguides is presented. The algorithm yields better or at least as good accuracy as ray tracing, even in shallow waveguides with a strongly depth-dependent sound speed profile. / QC 20100819