Dissertations / Theses on the topic 'Time-dependent rates'

Viele Problemstellungen der Naturwissenschaften führen zur Betrachtung von nichtlinearen Wellengleichungen. Dabei ist von großem Interesse, ob zu vorgegebenen kleinen Daten Lösungen eindeutig existieren und ob diese stetig von den Daten abhängen. Hilfsmittel für diese Probleme sind Aussagen über lineare Wellengleichungen. In der vorliegenden Arbeit werden lineare Klein-Gordon Gleichungen, also Wellengleichungen mit Potentialterm, mit zeitabhängiger Masse bzgl. des Verhaltens ihrer Lösungen untersucht. Von speziellem Interesse sind Resultate mit Bezug auf verallgemeinerte Energieerhaltung und sogenannte Lp – Lq decay-Abschätzungen. Aus der Arbeit geht hervor, dass man eine Klassifizierung für Gleichungen mit fallendem Masseterm finden kann. Für Gleichungen vom Wellentyp ist der Einfluss des Potentialterms gering und die Lösungen verhalten sich wie Lösungen der Wellengleichung. Dem gegenüber stehen Gleichungen vom Klein-Gordon-Typ mit erkennbarem Einfluss des Masseterms. Ausgangspunkt für die Klassifizierung ist das kritische Verhalten der Lösungen einer skaleninvarianten Gleichung mit speziellem Masseterm.

The most important market segmentation in sports and entertainment industry is the competition between customers that buy bundle and single tickets. A common selling practice is starting the selling season with bundle ticket sales and switching to selling single tickets later on. The aim of this practice is to increase the number of customers that buy bundles, to create a fund before the season starts and to increase the load factor of the games with low demand. In this thesis, we investigate the effect of time dependent demand on dynamic switching times and the potential revenue gain over the case where the demand rate is assumed to be constant with time.

The current study consists of three major parts. Statistical modeling, the connection between statistical modeling and cluster analysis, and proposing new methods to cluster time dependent information. First, we perform a statistical modeling of the Carbon Dioxide (CO2) emission in South Korea in order to identify the attributable variables including interaction effects. One of the hot issues in the earth in 21st century is Global warming which is caused by the marriage between atmospheric temperature and CO2 in the atmosphere. When we confront this global problem, we first need to verify what causes the problem then we can find out how to solve the problem. Thereby, we find and rank the attributable variables and their interactions based on their semipartial correlation and compare our findings with the results from the United States and European Union. This comparison shows that the number one contributing variable in South Korea and the United States is Liquid Fuels while it is the number 8 ranked in EU. This comparison provides the evidence to support regional policies and not global, to control CO2 in an optimal level in our atmosphere. Second, we study regional behavior of the atmospheric CO2 in the United States. Utilizing the longitudinal transitional modeling scheme, we calculate transitional probabilities based on effects from five end-use sectors that produce most of the CO2 in our atmosphere, that is, the commercial sector, electric power sector, industrial sector, residential sector, and the transportation sector. Then, using those transitional probabilities we perform a hierarchical clustering procedure to classify the regions with similar characteristics based on nine US climate regions. This study suggests that our elected officials can proceed to legislate regional policies by end-use sectors in order to maintain the optimal level of the atmospheric CO2 which is required by global consensus. Third, we propose new methods to cluster time dependent information. It is almost impossible to find data that are not time dependent among floods of information that we have nowadays, and it needs not to emphasize the importance of data mining of the time dependent information. The first method we propose is called “Lag Target Time Series Clustering (LTTC)” which identifies actual level of time dependencies among clustering objects. The second method we propose is the “Multi-Factor Time Series Clustering (MFTC)” which allows us to consider the distance in multi-dimensional space by including multiple information at a time. The last method we propose is the “Multi-Level Time Series Clustering (MLTC)” which is especially important when you have short term varying time series responses to cluster. That is, we extract only pure lag effect from LTTC. The new methods that we propose give excellent results when applied to time dependent clustering. Finally, we develop appropriate algorithm driven by the analytical structure of the proposed methods to cluster financial information of the ten business sectors of the N.Y. Stock Exchange. We used in our clustering scheme 497 stocks that constitute the S&P 500 stocks. We illustrated the usefulness of the subject study by structuring diversified financial portfolio.

Die relativ hohe seismische Aktivität der Tote-Meer-Störungszone (Dead Sea Fault Zone - DSFZ) ist mit einem hohen Gefahrenpotential verbunden, welches zu einem erheblichen Erdbebenrisiko für die Ballungszentren in den Ländern Syrien, Libanon, Palästina, Jordanien und Israel führt. Eine Vielzahl massiver, zerstörerischer Erdbeben hat sich in diesem Raum in den letzten zwei Jahrtausenden ereignet. Ihre Wiederholungsrate zeigt Anzeichen für eine zeitliche Abhängigkeit, insbesondere wenn lange Zeiträume in Betracht gezogen werden. Die Berücksichtigung der zeitlichen Abhängigkeit des Auftretens von Erdbeben ist für eine realistische seismische Gefährdungseinschätzung von großer Bedeutung. Ziel der vorliegenden Arbeit ist es, anhand des zeitabhängigen Auftretens von Erdbeben eine robuste wahrscheinlichkeitstheoretische seismische Gefährdungseinschätzung am Beispiel der DSFZ zu entwickeln. Mittels dieser Methode soll die zeitliche Abhängigkeit des Auftretens von großen Erdbeben (Mw ≥ 6) untersucht und somit eine Gefährdungseinschätzung für das Untersuchungsgebiet getroffen werden. Primär gilt es zu prüfen, ob das Auftreten von großen Erdbeben tatsächlich einer zeitlichen Abhängigkeit unterliegt und wenn ja, inwiefern diese bestimmt werden kann. Zu diesem Zweck werden insgesamt vier zeitabhängige statistische Verteilungen (Weibull, Gamma, Lognormal und Brownian Passage Time (BPT)) sowie die zeitunabhängige Exponentialverteilung (Poisson-Prozess) getestet. Zur Abschätzung der jeweiligen Modellparameter wird eine modifizierte Methode der gewichteten Maximum-Likelihood-Schätzung (MLE) verwendet. Um einzuschätzen, ob die Wiederholungsrate von Erdbeben einer unimodalen oder multimodalen Form folgt, wird ein nichtparametrischer Bootstrap-Test für Multimodalität durchgeführt. Im Falle einer multimodalen Form wird neben der MLE zusätzlich eine Erwartungsmaximierungsmethode (EM) herangezogen. Zur Auswahl des am besten geeigneten Modells wird zum einem das Bayesschen Informationskriterium (BIC) und zum anderen der modifizierte Kolmogorow-Smirnow-Goodness-of-Fit-Test angewendet. Abschließend werden mittels der Bootstrap-Methode die Konfidenzintervalle der geschätzten Parameter berechnet. Als Datengrundlage werden Erdbeben mit Mw ≥ 6 seit dem Jahre 300 n. Chr. herangezogen. Das Untersuchungsgebiet erstreckt sich von 29.5° N bis 37° N und umfasst ein ca. 40 km breites Gebiet entlang der DSFZ. Aufgrund der seismotektonischen Situation im Untersuchungsgebiet wird zwischen einer südlichen, zentralen und nördlichen Subzone unterschieden. Dabei kann die südliche Subzone aus Mangel an Daten nicht für die Analysen herangezogen werden. Die Ergebnisse für die zentrale Subzone zeigen keinen signifikanten multimodalen Verlauf der Wiederholungsrate von Erdbeben. Des Weiteren ist kein signifikanter Unterschied zwischen den zeitabhängigen und dem zeitunabhängigem Modell zu verzeichnen. Da das zeitunabhängige Modell vergleichsweise einfach interpretierbar ist, wird die Wiederholungsrate von Erdbeben in dieser Subzone unter Annahme der Exponentialverteilungs-Hypothese abgeschätzt. Sie wird demnach als zeitunabhängig betrachtet und beträgt 9.72 * 10-3 Erdbeben (mit Mw ≥ 6) pro Jahr. Einen besonderen Fall stellt die nördliche Subzone dar. In diesem Gebiet tritt im Durchschnitt alle 51 Jahre ein massives Erdbeben (Mw ≥ 6) auf. Das letzte Erdbeben dieser Größe ereignete sich 1872 und liegt somit bereits 137 Jahre zurück. Somit ist in diesem Gebiet ein Erdbeben dieser Stärke überfällig. Im statistischen Mittel liegt die Zeit zwischen zwei Erdbeben zu 96% unter 137 Jahren. Zudem wird eine deutliche zeitliche Abhängigkeit der Erdbeben-Wiederauftretensrate durch die Ergebnisse der in der Arbeit neu entwickelten statistischen Verfahren bestätigt. Dabei ist festzustellen, dass die Wiederholungsrate insbesondere kurz nach einem Erdbeben eine sehr hohe zeitliche Abhängigkeit aufweist. Am besten repräsentiert werden die seismischen Bedingungen in der genannten Subzone durch ein bi-modales Weibull-Weibull-Modell. Die Wiederholungsrate ist eine glatte Zeitfunktion, welche zwei Häufungen von Datenpunkten in der Zeit nach dem Erdbeben zeigt. Dabei umfasst die erste Häufung einen Zeitraum von 80 Jahren, ausgehend vom Zeitpunkt des jeweiligen Bebens. Innerhalb dieser Zeitspanne ist die Wiederholungsrate extrem zeitabhängig. Die Wiederholungsrate direkt nach einem Beben ist sehr niedrig und steigert sich in den folgenden 10 Jahren erheblich bis zu einem Maximum von 0.024 Erdbeben/Jahr. Anschließend sinkt die Rate und erreicht ihr Minimum nach weiteren 70 Jahren mit 0.0145 Erdbeben/Jahr. An dieses Minimum schließt sich die zweite Häufung von Daten an, dessen Dauer abhängig von der Erdbebenwiederholungszeit ist. Innerhalb dieses Zeitfensters nimmt die Erdbeben-Wiederauftretensrate annähernd konstant um 0.015 Erdbeben/Jahr zu. Diese Ergebnisse bilden die Grundlage für eine zeitabhängige probabilistische seismische Gefährdungseinschätzung (PSHA) für die seismische Quellregion, die den nördlichen Raum der DSFZ umfasst.
The seismicity of the Dead Sea fault zone (DSFZ) during the last two millennia is characterized by a number of damaging and partly devastating earthquakes. These events pose a considerable seismic hazard and seismic risk to Syria, Lebanon, Palestine, Jordan, and Israel. The occurrence rates for large earthquakes along the DSFZ show indications to temporal changes in the long-term view. The aim of this thesis is to find out, if the occurrence rates of large earthquakes (Mw ≥ 6) in different parts of the DSFZ are time-dependent and how. The results are applied to probabilistic seismic hazard assessments (PSHA) in the DSFZ and neighboring areas. Therefore, four time-dependent statistical models (distributions), including Weibull, Gamma, Lognormal and Brownian Passage Time (BPT), are applied beside the exponential distribution (Poisson process) as the classical time-independent model. In order to make sure, if the earthquake occurrence rate follows a unimodal or a multimodal form, a nonparametric bootstrap test of multimodality has been done. A modified method of weighted Maximum Likelihood Estimation (MLE) is applied to estimate the parameters of the models. For the multimodal cases, an Expectation Maximization (EM) method is used in addition to the MLE method. The selection of the best model is done by two methods; the Bayesian Information Criterion (BIC) as well as a modified Kolmogorov-Smirnov goodness-of-fit test. Finally, the confidence intervals of the estimated parameters corresponding to the candidate models are calculated, using the bootstrap confidence sets. In this thesis, earthquakes with Mw ≥ 6 along the DSFZ, with a width of about 20 km and inside 29.5° ≤ latitude ≤ 37° are considered as the dataset. The completeness of this dataset is calculated since 300 A.D. The DSFZ has been divided into three sub zones; the southern, the central and the northern sub zone respectively. The central and the northern sub zones have been investigated but not the southern sub zone, because of the lack of sufficient data. The results of the thesis for the central part of the DSFZ show that the earthquake occurrence rate does not significantly pursue a multimodal form. There is also no considerable difference between the time-dependent and time-independent models. Since the time-independent model is easier to interpret, the earthquake occurrence rate in this sub zone has been estimated under the exponential distribution assumption (Poisson process) and will be considered as time-independent with the amount of 9.72 * 10-3 events/year. The northern part of the DSFZ is a special case, where the last earthquake has occurred in 1872 (about 137 years ago). However, the mean recurrence time of Mw ≥ 6 events in this area is about 51 years. Moreover, about 96 percent of the observed earthquake inter-event times (the time between two successive earthquakes) in the dataset regarding to this sub zone are smaller than 137 years. Therefore, it is a zone with an overdue earthquake. The results for this sub zone verify that the earthquake occurrence rate is strongly time-dependent, especially shortly after an earthquake occurrence. A bimodal Weibull-Weibull model has been selected as the best fit for this sub zone. The earthquake occurrence rate, corresponding to the selected model, is a smooth function of time and reveals two clusters within the time after an earthquake occurrence. The first cluster begins right after an earthquake occurrence, lasts about 80 years, and is explicitly time-dependent. The occurrence rate, regarding to this cluster, is considerably lower right after an earthquake occurrence, increases strongly during the following ten years and reaches its maximum about 0.024 events/year, then decreases over the next 70 years to its minimum about 0.0145 events/year. The second cluster begins 80 years after an earthquake occurrence and lasts until the next earthquake occurs. The earthquake occurrence rate, corresponding to this cluster, increases extremely slowly, such as it can be considered as an almost constant rate about 0.015 events/year. The results are applied to calculate the time-dependent PSHA in the northern part of the DSFZ and neighbouring areas.

The purpose of this thesis is to set out the results of an investigation into the commonly used methods of performing material update calculations within the framework of the Finite Element Method, as well as an investigation into possible new methods of performing the material update procedures within the context of a rate dependent plastic material obeying the Von Mises yield condition. Material update procedures which have been used and analysed frequently are the Generalised Midpoint Algorithm, including the Midpoint Method, the Trapezoidal Rule and the Backward Euler Method with Radial Return. Each method displays its own advantages when applied to different input parameters (being material properties, initial stresses and strains, and increments in time and strain).

A unique tool is developed that allows the user to model physical representations of complicated glovebox facilities in two dimensions and determine neutral-particle flux and ambient dose-equivalent fields throughout that geometry. The code Pandemonium, originally designed to determine flux and dose rates only, has been improved to include realistic glovebox geometries, time-dependent source and detector positions, time-dependent shielding thickness calculations, time-integrated doses, a representative criticality accident scenario based on time-dependent reactor kinetics, and more rigorous photon treatment. The photon model has been significantly enhanced by expanding the energy range to 10 MeV to include fission photons, and by including a set of new buildup factors, the result of an extensive study into the previously unknown "purely-angular effect" on photon buildup. Purely-angular photon buildup factors are determined using discrete ordinates and coupled electron-photon cross sections to account for coherent and incoherent scattering and secondary photon effects of bremsstrahlung and florescence. Improvements to Pandemonium result in significant modeling capabilities for processing facilities using intense neutron and photon sources, and the code obtains comparable results to Monte Carlo calculations but within a fraction of the time required to run such codes as MCNPX.

Many patients with end-stage renal disease come to rely on catheters as their only means of hemodialysis when other options are no longer viable. These patients have a very poor quality of life due to their chronic illness as well as many long-term complications related to the use of tunneled catheters. Many prior attempts have been made to understand these catheter-related problems. Yet, they continue to be a major cause of morbidity and mortality in chronic catheter-reliant patients. We hope to examine the rate as well as long term time course of these complications such that in future, we may decrease their occurrence. We predict that over time, chronic catheter use decreases the mean indwell time for each catheterization and increases the incidence of complications. To study this, we conducted a retrospective study looking at all patients who had three or more tunneled catheter exchanges between July 2003 and July 2008. We collected information from Yale IDX database on the patients age and gender, the type of catheter used, the indwell time of the catheter, the vessel used as access, the indication for catheter removal, whether the procedure was performed by a medical doctor (M.D.) or physicians assistant (P.A.) and whether it was a de novo insertion or over-the-wire exchange. We collected a total of 764 data points on 191 patients (89 males and 102 females). They ranged from 8 to 87 years old with a median age of 56 years. Infection was the number one indication for catheter removal at 37%. The rate of infection was 3.34 per 1,000 catheter days. There was no difference in the rate of complications by the side of vessel accessed nor by type of catheter. However, right-sided catheters had a longer indwell time of 117 + 159 days compared to left-sided catheters, 87 + 124 days (p =0.008). There was no significant difference in the indwell duration of first catheter in comparison to all subsequent placements. There was also no difference in complications whether the catheter was exchanged over the wire or placed de novo. Nor were complication rates different among M.D. versus P.A. conducted procedures. We conclude that our rates of infection are similar to other institutions and the vessels located on the right-side of the neck are preferable to left-sided vessels to increase catheter longevity. Future research is needed to better assess how rates and incidences of complications change with long standing catheter-reliance.

With the aim to achieve a better understanding of the time- and rate-dependent behaviour of unsaturated clays, particularly stiff natural clays, a critical review of the literature and a program of laboratory testing were carried out as part of this research. With emphasis on examining the effect of suction on viscous response, mainly primary and secondary consolidation (creep), stress-relaxation, and rate-dependency, a series of conventional multi-stage loading (MSL) oedometer tests, long-term single-stage loading (SSL) oedometer tests, and advanced constant-rate-of-strain (CRS) oedometer tests were carried out on natural and corresponding reconstituted specimens of a stiff clay namely, London Clay, retrieved from a site in the Isle of Sheppey, UK. The results obtained provide a significant contribution to the existing database and address important knowledge gaps highlighted from the literature review. The experimental studies performed included; a) An investigation of the effect of water reservoir surface roughness on the cavitation mechanism and performance of a newly designed high-capacity tensiometer (HCT), with regard maximum sustainable suction (smax) and maximum duration of measurements (tmax). b) An examination of the influence of soil suction on the primary and secondary consolidation of natural and reconstituted London Clay from a set of MSL and SSL oedometer tests. c) Characterisation of the stress-relaxation behaviour of the reconstituted London Clay subjected to suction and strain-rate variations from a set of CRS oedometer tests in an in-house designed suction-monitored cell. d) An examination of the coupled effects of suction and strain-rate on one-dimensional (1D) stress-strain response of reconstituted London Clay. Based on the experimental findings, the validity of the empirical relationships proposed in the literature for correlating time- and rate-dependency coefficients was examined and necessary modifications were proposed. The main experimental findings can be outlined as: - The mechanism of cavitation in tensiometers is indeed influenced by the surface roughness of the water reservoir. The new approach for expanding the range and duration of suction measurements for a newly designed HCT, based on hydrophilic coating of the reservoir walls, sounds promising. - The compression index (Cc) and creep index (Cαe) and the ratio α = Cαe/Cc for Sheppey London Clay are stress- and suction-dependent. The hypothesis of constant α for natural clays, as suggested by Mesri et al. (1994), is therefore rejected. - The volumetric creep deformations of unsaturated stiff clays appear to be relatively simply modelled by a creep law based on a power function. - A coupled effect of suction and strain-rate on 1D compression response was identified. At a constant suction, the higher the strain-rate, the higher the apparent preconsolidation pressure (σ'p). Similarly, at a constant strain-rate, the higher the suction, the higher the σ'p. - The values of relaxation coefficient (Rα) differ in saturated and unsaturated states. However, a clear relationship between Rα and suction was not found. The Rα = Cαe/Cc relationship, suggested by Yin et al. (2014) for saturated soft clays, appears, with an approximation, to be valid for the unsaturated stiff London Clay in the range of applied vertical stresses and soil suctions in this study. - The process of stress-relaxation in unsaturated clays is highly influenced by factors such as soil suction, pre-relaxation strain, stress, and strain-rate.

We investigate the applicability of the method of maximum entropy regularization (MER) including convergence and convergence rates of regularized solutions to the specific inverse problem (SIP) of calibrating a purely time-dependent volatility function. In this context, we extend the results of [16] and [17] in some details. Due to the explicit structure of the forward operator based on a generalized Black-Scholes formula the ill-posedness character of the nonlinear inverse problem (SIP) can be verified. Numerical case studies illustrate the chances and limitations of (MER) versus Tikhonov regularization (TR) for smooth solutions and solutions with a sharp peak.

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xvi, 147 p.; also includes graphics Includes bibliographical references (p. 143-147). Available online via OhioLINK's ETD Center

This paper outlines a newly-developed method to include the effects of time variability in the radiative transfer code CMFGEN. It is shown that the flow timescale is often large compared to the variability timescale of LBVs. Thus, time-dependent effects significantly change the velocity law and density structure of the wind, affecting the derivation of the mass-loss rate, volume filling factor, wind terminal velocity, and luminosity. The results of this work are directly applicable to all active LBVs in the Galaxy and in the LMC, such as AG Car, HR Car, S Dor and R 127, and could result in a revision of stellar and wind parameters. The massloss rate evolution of AG Car during the last 20 years is presented, highlighting the need for time-dependent models to correctly interpret the evolution of LBVs.

Bibliography: pages 93-101.
The main aim of this thesis is to analyse two types of general finite element approximations to the solution of a time-dependent variational inequality. The two types of approximations considered are the following: 1. Semi-discrete approximations, in which only the spatial domain is discretised by finite elements; 2. fully discrete approximations, in which the spatial domain is again discretised by finite elements and, in addition, the time domain is discretised and the time-derivatives appearing in the variational inequality are approximated by backward differences. Estimates of the error inherent in the above two types of approximations, in suitable Sobolev norms, are obtained; in particular, these estimates express the rate of convergence of successive finite element approximations to the solution of the variational inequality in terms of element size h and, where appropriate, in terms of the time step size k. In addition, the above analysis is preceded by related results concerning the existence and uniqueness of the solution to the variational inequality and is followed by an application in elastoplasticity theory.

Endogenous viral elements, or viral genomic fossils, have proven extremely valuable in the study of the macroevolution of viruses, providing important, and otherwise unobtainable, insights into the ancient origin of viruses, and how their ancestors might have co-evolved with their hosts in the distant past. This type of investigation falls within the realm of paleovirology—the study of ancient viruses. Investigations of extant viruses and paleovirological analyses, however, often give conflicting results, especially those concerning viral evolutionary rates and timescales. Reconciling these two types of analyses is a necessary step towards a better understanding of the overall long-term evolutionary dynamics of viruses. The main study system of this thesis is foamy viruses (FVs). FVs are characterised by their stable co-speciation history with their hosts, allowing their evolutionary dynamics to be modelled and investigated over various timescales. This unique evolutionary feature makes FVs one of the best subjects for connecting recent and ancient viral evolution. The work here reports the discovery of several endogenous mammalian FVs, and examines how mammalian FVs co-evolve with their hosts. Analyses reveal a co-diversifying history of the two that could be dated back to the basal radiation of eutherians more than 100 million years ago. However, a small number of ancient FV cross-species transmissions could still be found, mostly involving New World monkey FVs. Based on this extended FV-mammal co-speciation pattern, this thesis investigates the long-term evolutionary rate dynamics of FVs, and shows that the rate estimates of FV evolution appear to decrease continuously as the rate measurement timescale increases, following a power-law decay function. The work presented here also shows that this so-called 'time-dependent rate phenomenon' is in fact a pervasive evolutionary feature of all viruses, and surprisingly, the rate estimates of evolution of all viruses seem to decay at the same speed, decreasing by approximately half for every 3-fold increase in the measurement timescale. Based on this power-law rate-decay pattern, we could infer evolutionary timescales of modern-day lentiviruses that are consistent with paleovirological analyses for the first time. Finally, this thesis reports the discovery of basal FV-like endogenous retroviruses (FLERVs) in amphibian and fish genomes. Phylogenetic analyses reveal that the progenitors of ray-finned fish FLERVs co-diversify broadly with their fish hosts, but also suggest that there might have been several ancient viral cross-class transmissions, involving lobe-finned fish, shark, and frog FLERVs. Again, by using the power-law rate-decay model, analyses in this thesis suggest that this major retroviral clade has an ancient Ordovician marine origin, originating together with their jawed vertebrate hosts more than 450 million years ago. This finding implies that the origin of retroviruses as a whole must be in the early Paleozoic Era, if not earlier. The results presented here bridge ancient and recent viral evolution.

Posttraumatic stress disorder (PTSD) is an anxiety disorder that may result from an exposure to a severely traumatic life-event. It is characterised by a delayed onset of psychological and physical symptoms including re-experiencing the event, avoidance of reminders associated with the trauma, increased autonomic arousal and distinct memory deficits. This disorder is also characterised by a maladaptive hypothalamic-pituitary-adrenal (HPA)-axis response and altered monoamine concentrations in the hippocampus and pre-frontal cortex. The Time Dependent Sensitization (TDS) model is a putative animal model of PTSD that is based on the concept of repeated trauma, using three acute stressors (TS) of intense severity followed by a mild situational reminder (RS) on day 7 subsequent to the acute stressors. The aims of this study were to determine if the Triple Stressor (TS) induces stress and if the situational reminder (RS) is necessary for the maintenance of the stress response over time and whether these two stress responses are qualitatively and quantitively different. This was done to further validate the TDS model and to characterize the development and progression of the stress-related pathology of PTSD. Methods used were High Performance Liquid Chromatography (HPLC) with electrochemical detection (biochemical correlates) for quantifying the monoamines dopamine (DA), noradrenaline (NA) and serotonin (5-HT) concentrations in the hippocampus and pre-frontal cortex (PFC); radio immuno assay (RIA) for the determination of plasma corticosterone concentrations (neuroendocrine parameter) and the use of the Elevated Plus Maze (EPM) to detect anxiety-like behaviour (behavioural analyses). The study was subdivided into an Acute and Re-Stress study (n = 10). In the Acute Study rats were exposed to TS as the only stressor. Group 1 was sacrificed immediately after TS, Group 2 was sacrificed 3 days post TS and Group 3 on day 7 post TS. In the Re-Stress Study both TS and RS were used as stressors. Group 4 was sacrificed immediately after the situational reminder, Group 5 was sacrificed 3 days post RS and Group 6 on day 7 post RS. A group of unstressed rats were used as Control. The results of this study found corticosterone concentrations elevated immediately after the TS (p<0.05). Exposure to the RS resulted in a profound hypocortisolism (p<0.05). These results indicate a possible disturbance in the regulation of the HPA-axis, which manifests as an enhanced negative feed-back upon re-introduction of the stressful situation. Changes in MA concentrations were evident. Although no definite fixed trend is apparent in this study, it is evident that the TDS model does induce monoamine dysregulation. Hippocampal NA. DA and 5-HT concentrations were noted to be elevated on day 7 post TS (p<0.05). On day 7 post RS only hippocampal 5HT was decreased significantly (p<0.05). Behavioural analyses indicate that stress related anxiety was not sustained after the TS but 7 days after the exposure to the RS rats were most anxious (p<0.05). The results confirm that the TDS model does induce PTSD-like symptoms in rats and that the situational reminder (RS) is necessary for the maintenance of the stress response. This model may be useful in the investigation of future experimental pharmacological interventions in the management of PTSD.
Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2005.

Neurone sind anregbare Zellen, die mit Hilfe von elektrischen Signalen miteinander kommunizieren. Im allgemeinen werden eingehende Signale von den Nervenzellen in einer nichtlinearen Art und Weise verarbeitet. Wie diese Verarbeitung in einer umfassenden und exakten Art und Weise mathematisch beschrieben werden kann, ist bis heute nicht geklärt und ist Gegenstand aktueller Forschung. In dieser Arbeit untersuchen wir die nichtlineare Übertragung und Verarbeitung von Signalen durch stochastische Nervenzellen und wenden dabei zwei unterschiedliche Herangehensweisen an. Im ersten Teil der Arbeit befassen wir uns mit der Frage, auf welche Art und Weise ein Signal mit einer bekannten Zeitabhängigkeit die Rate der neuronalen Aktivität beeinflusst. Im zweiten Teil der Arbeit widmen wir uns der Rekonstruktion eingehender Signale aus der durch sie hervorgerufenen neuronalen Aktivität und beschäftigen uns mit der Abschätzung der übertragenen Informationsmenge. Die Ergebnisse dieser Arbeit demonstrieren, wie die etablierten linearen Theorien, die die Modellierung der neuronalen Aktivitätsrate bzw. die Rekonstruktion von Signalen beschreiben, um Beiträge höherer Ordnung erweitert werden können. Einen wichtigen Beitrag dieser Arbeit stellt allerdings auch die Darstellung der Signifikanz der nichtlinearen Theorien dar. Die nichtlinearen Beiträge erweisen sich nicht nur als schwache Korrekturen zu den etablierten linearen Theorien, sondern beschreiben neuartige Effekte, die durch die linearen Theorien nicht erfasst werden können. Zu diesen Effekten gehört zum Beispiel die Anregung von harmonischen Oszillationen der neuronalen Aktivitätsrate und die Kodierung von Signalen in der signalabhängigen Varianz einer Antwortvariablen.
Neurons are excitable cells which communicate with each other via electrical signals. In general, these signals are processed by the Neurons in a nonlinear fashion, the exact mathematical description of which is still an open problem in neuroscience. In this thesis, the broad topic of nonlinear signal processing is approached from two directions. The first part of the thesis is devoted to the question how input signals modulate the neural response. The second part of the thesis is concerned with the nonlinear reconstruction of input signals from the neural output and with the estimation of the amount of the transmitted information. The results of this thesis demonstrate how existing linear theories can be extended to capture nonlinear contributions of the signal to the neural response or to incorporate nonlinear correlations into the estimation of the transmitted information. More importantly, however, our analysis demonstrates that these extensions do not merely provide small corrections to the existing linear theories but can account for qualitatively novel effects which are completely missed by the linear theories. These effects include, for example, the excitation of harmonic oscillations in the neural firing rate or the estimation of information for systems with a signal-dependent output variance.

This work aims to explore the use of genetic sequences sampled serially through time (heterochronous data), to infer the timescale of past evolutionary events. Such data can be generated from preserved sub-fossil or fossil organismal remains (like mummified tissues, fossilized bones or coprolites), and then used to observe genetic modifications in real-time. Most importantly, the dates of the samples provide firm temporal tie points for their genetic sequences, and can be used to calibrate phylogenetic reconstructions. This thesis presents several case studies where ancient DNA was used to re-calibrate evolutionary timescales. In every situation, the use of heterochronous data led to elevated molecular rate estimates, resulting in the reconstruction of younger timescales, as compared to estimates based on fossil calibrations. These observations are in agreement with the recent demonstration that molecular rates vary according to the time period over which they are calculated. This work shows that, ancient DNA offers crucial temporal information to reliably estimate the timescale of recent population evolution, and is generally the only source of direct calibration available for this specific timeframe. Along with the results specific to each organism studied (hyena, bison and human), an emphasis was placed on the methodological aspects of the use of ancient DNA to generate timed phylogenetic inferences. Additionally, simulated data and mathematical modelling were used to extend the understanding of specific aspects of the temporal dependence of molecular rates. The results discussed in the present study help to further elucidate the evolutionary mechanisms behind the molecular clock concept, and have implications for the development and application of statistical models to obtain accurate time estimates from genetic data.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2012

博士
國立清華大學
資訊工程學系
96
Real-time scheduling for task sets has been studied, and the corresponding schedulability analysis has been developed. Real-time systems using rate monotonic (RM) fixed priority scheduling can be checked for schedulability either by sufficient but pessimistic schedulability conditions or by exact test. In this thesis, a series of period-dependent schedulability test methods for real-time tasks scheduled by the RM policy on uniprocessor systems are proposed. In the first portion, we find the efficient schedulability test methods for periodic tasks. Both exact schedulability test methods and sufficient but pessimistic schedulability test methods are investigated. Exact testing provides a more precise result but may not be performed in polynomial time. Audsley et al. proposed one of the earliest methods by iteratively deriving the response times of jobs. Other researchers have improved the exact test method by using different initial values for testing. In this thesis, we first improve the iterative formula used to calculate the response times of jobs. Then, we propose a new initial value for Audsley’s test method to improve the efficiency. We show that the new initial values can significantly improve the efficiency of exact testing. In addition, a better RM schedulability bound for performing the sufficient but pessimistic schedulability is also proposed. The period ratios are considered in the schedulability bound. When more period ratios are considered, the schedulability bound can be higher. In the second portion, we find the efficient schedulability test methods for multiframe tasks. We explore both exact schedulability test methods and sufficient but pessimistic schedulability test methods. For the exact schedulability test, the period-dependent initial value is used for the test and effectively reduce the number of iterations for testing. For the sufficient but pessimistic schedulability test, we use the information of the relative period ratios between tasks in a system to derive a new schedulability condition. By considering the smallest and the largest period values in a system, we can show that the RM schedulability bound can be improved significantly. This method also can be applied to other test methods studied earlier to improve the schedulability of real-time multiframe systems.

The proportional hazard (PH) cure rate model and the marginal structural Cox model (MSCM) are two broad areas used in analysing survival models with longitudinal data. Cure rate models were introduced to deal with survival models in the presence of a cure fraction and marginal structural models were introduced to adjust for time- ependent confounders through time-dependent weighting in longitudinal studies. However, few studies have tried to combine these two areas in building cure rate models in the presence of time-dependent covariates and time-dependent confounders. This thesis proposes an extension of the maximum likelihood estimation procedure for the PH cure rate model by incorporating (i) case weights, (ii) time-dependent covariates, and (iii) time-dependent weights in the presence of time-dependent covariates and time-dependent confounders into the model. Further, this thesis compares the performance of the PH cure rate model with case weights to the standard unweighted PH cure rate model through simulation studies. Results of these studies suggest that adding case weights in the PH cure rate model improves the estimation of the latency parameter when the sample size is relatively small.

碩士
淡江大學
管理科學學系
90
Most inventory models assume that the inventory can be stored indefinitely. However, in fact, if some inventories were stored for a long time, they will deteriorate, volatilize, or decay, so their value and quantity will also decrease. This type of inventory is therefore called “ Deteriorating Inventory “. If we did not consider deterioration, then we would have an incorrect cost-construction in the inventory model and a substantial lost would follow a wrong decision based on the model. Besides, most traditional inventory models considered the case where the demand rate is constant, but this assumption is not real. However, in the real situation, the demand rate is not only dependent of the product price but also inventory level. Furthermore, if backlogging time is too long, some customers will purchase with other companies. For the original company, it will result in opportunity cost due to lost sales. Therefore , the opportunity cost due to shortage, should be considered in our inventory model. On the other hand, during the past years, however, monetary situation of most countries has changed; this result in a sharp decline in the purchasing power of money. Therefore, the consideration on the effect of time-value of money is critical. Based on the above issues, we develop three inventory models in this thesis. In Chapter 2, we explore the inventory replenishment policy for deteriorating items with price-dependent demand over a fixed planning horizon, in which the backlogging quantity in the last period is made at time H. In Chapter 3, we also explore the inventory replenishment policy for deteriorating items with price-dependent demand over a fixed planning horizon, in which the shortages cannot occur in the last period. Final, in the Chapter 4, we present the inventory replenishment policy for deteriorating items with stock-dependent demand over a fixed planning horizon, in which the backlogging quantity in the last period is made at time H. The objective of these models in this thesis is to derive the optimal replenishment policy, in which the price, replenishment number and service level are common decision variables. For all models proposed in this thesis, we utilize the numerical examples to illustrate the effects of inventory systems associate with changing the values of parameters.

碩士
淡江大學
管理科學學系
87
In the classical inventory models, it is generally assumed that the demand rate is constant. However, it has been observed that in some situations the demand may be influenced by the on-hand inventory; i.e. the demand rate may go up or down if the on-hand inventory level increases or decrease. In the real market, occurrence of shortages in inventory system is a natural phenomenon. Under certain situations, the amount of demand backlogged is variable and may depend on the amount of demand already backlogged; i.e. the customers will not wait for goods if already many customers are waiting. With today's high rate of inflation and a consequent sharp decline in the purchasing power of money, it is no longer wise to ignore the effects of inflation and the time-value of money in inventory system. In this paper, we establish three various inventory replenishment policies with shortages, where the demand rate is assumed to be linearly dependent on the instantaneous stock level. The effects of stock-dependent demand rate, deterioration, inflation and the time-value of money are used in conjunction with the economic order quantity model are the focus of discussion. We shall be concern with finding the optimal replenishment and shortage points and hence to determine the optimal service rate and number of replenishments. Numerical examples and sensitivity analysis are presented to illustrate the proposed models. Furthermore, we identify the best alternative among various models on minimizing total relevant costs over a finite time-horizon.

Infectious disease models with switching are constructed and investigated in detail. Modelling infectious diseases as switched systems, which are systems that combine continuous dynamics with discrete logic, allows for the use of methods from switched systems theory. These methods are used to analyze the stability and long-term behaviour of the proposed switched epidemiological models. Switching is first incorporated into epidemiological models by assuming the contact rate to be time-dependent and better approximated by a piecewise constant. Epidemiological models with switched incidence rates are also investigated. Threshold criteria are established that are sufficient for the eradication of the disease, and, hence, the stability of the disease-free solution. In the case of an endemic disease, some criteria are developed that establish the persistence of the disease. Lyapunov function techniques, as well as techniques for stability of impulsive or non-impulsive switched systems with both stable and unstable modes are used. These methods are first applied to switched epidemiological models which are intrinsically one-dimensional. Multi-dimensional disease models with switching are then investigated in detail. An important part of studying epidemiology is to construct control strategies in order to eradicate a disease, which would otherwise be persistent. Hence, the application of controls schemes to switched epidemiological models are investigated. Finally, epidemiological models with switched general nonlinear incidence rates are considered. Simulations are given throughout to illustrate our results, as well as to make some conjectures. Some conclusions are made and future directions are given.