<p>Recent years have seen a growth in research on system reliability and maintenance. Various studies in the scientific fields of reliability engineering, quality and productivity analyses, risk assessment, software reliability, and probabilistic machine learning are being undertaken in the present era. The dependency of human life on technology has made it more important to maintain such systems and maximize their potential. In this dissertation, some methodologies are presented that maximize certain measures of system reliability, explain the underlying stochastic behavior of certain systems, and prevent the risk of system failure.</p> <p><br></p> <p>An overview of the dissertation is provided in Chapter 1, where we briefly discuss some useful definitions and concepts in probability theory and stochastic processes and present some mathematical results required in later chapters. Thereafter, we present the motivation and outline of each subsequent chapter.</p> <p><br></p> <p>In Chapter 2, we compute the limiting average availability of a one-unit repairable system subject to repair facilities and spare units. Formulas for finding the limiting average availability of a repairable system exist only for some special cases: (1) either the lifetime or the repair-time is exponential; or (2) there is one spare unit and one repair facility. In contrast, we consider a more general setting involving several spare units and several repair facilities; and we allow arbitrary life- and repair-time distributions. Under periodic monitoring, which essentially discretizes the time variable, we compute the limiting average availability. The discretization approach closely approximates the existing results in the special cases; and demonstrates as anticipated that the limiting average availability increases with additional spare unit and/or repair facility.</p> <p><br></p> <p>In Chapter 3, the system experiences two types of sporadic impact: valid shocks that cause damage instantaneously and positive interventions that induce partial healing. Whereas each shock inflicts a fixed magnitude of damage, the accumulated effect of k positive interventions nullifies the damaging effect of one shock. The system is said to be in Stage 1, when it can possibly heal, until the net count of impacts (valid shocks registered minus valid shocks nullified) reaches a threshold $m_1$. The system then enters Stage 2, where no further healing is possible. The system fails when the net count of valid shocks reaches another threshold $m_2  (> m_1)$. The inter-arrival times between successive valid shocks and those between successive positive interventions are independent and follow arbitrary distributions. Thus, we remove the restrictive assumption of an exponential distribution, often found in the literature. We find the distributions of the sojourn time in Stage 1 and the failure time of the system. Finally, we find the optimal values of the choice variables that minimize the expected maintenance cost per unit time for three different maintenance policies.</p> <p><br></p> <p>In Chapter 4, the above defined Stage 1 is further subdivided into two parts: In the early part, called Stage 1A, healing happens faster than in the later stage, called Stage 1B. The system stays in Stage 1A until the net count of impacts reaches a predetermined threshold $m_A$; then the system enters Stage 1B and stays there until the net count reaches another predetermined threshold $m_1 (>m_A)$. Subsequently, the system enters Stage 2 where it can no longer heal. The system fails when the net count of valid shocks reaches another predetermined higher threshold $m_2 (> m_1)$. All other assumptions are the same as those in Chapter 3. We calculate the percentage improvement in the lifetime of the system due to the subdivision of Stage 1. Finally, we make optimal choices to minimize the expected maintenance cost per unit time for two maintenance policies.</p> <p><br></p> <p>Next, we eliminate the restrictive assumption that all valid shocks and all positive interventions have equal magnitude, and the boundary threshold is a preset constant value. In Chapter 5, we study a system that experiences damaging external shocks of random magnitude at stochastic intervals, continuous degradation, and self-healing. The system fails if cumulative damage exceeds a time-dependent threshold. We develop a preventive maintenance policy to replace the system such that its lifetime is utilized prudently. Further, we consider three variations on the healing pattern: (1) shocks heal for a fixed finite duration $\tau$; (2) a fixed proportion of shocks are non-healable (that is, $\tau=0$); (3) there are two types of shocks---self healable shocks heal for a finite duration, and non-healable shocks. We implement a proposed preventive maintenance policy and compare the optimal replacement times in these new cases with those in the original case, where all shocks heal indefinitely.</p> <p><br></p> <p>Finally, in Chapter 6, we present a summary of the dissertation with conclusions and future research potential.</p>

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Military historians have been debating the U.S. Army's World War II replacement system for decades, but no one has completed a detailed study of the War Department's policies and practice. Authors have focused primarily on how combat units overcame the system's limitations, but they have not conducted an in-depth examination of its creation, structure, and function. Nor did they question why infantry divisions had to devise their own replacement policies in the first place. The extant literature is too celebratory of the army and utilizes ultimate victory as a measure of efficiency and effectiveness. Such a myopic view has prevented these earlier studies from evaluating how the replacement system affected the overall course of the European war. This dissertation breaks new ground by presenting a comprehensive overview of the replacement system--from the War Department down to the squad, and from the last days of World War I through the post-World War II years. It will elucidate a process of failed administration and implementation at the highest levels of the War Department and army, but it will also relate a "grassroots" story of success at the divisional level and below. The War Department's managerial approach to the utilization of military manpower was both inefficient and wasteful. The army largely overlooked the impact of individuality, morale, psyche, experience, and training on a soldier's performance. Its insistence on rushing men to the line once combat operations began meant that it often neglected to train, orient, and equip replacements in a manner conducive to their favorable and effective integration into combat units. The GIs at the front, both veterans and replacements alike, suffered for this oversight. / History

Bakgrund: Perifera venkatetrar utgör en av de vanligast förekommande medicintekniska produkterna inom vården. För att minimera komplikationer som flebit, ocklusion, infiltration och bakteriemi finns det ur ett patientsäkerhetsperspektiv två olika riktlinjer för när perifera venkatetrar ska bytas. Byten sker antingen på regelbundet med 72–96 timmars mellanrum, vilket är nu rådande riktlinjer i Sverige, eller så ska byten endast ske då tecken på begynnande komplikation uppstår, alltså på klinisk indikation. Syfte: Syftet är att kartlägga om komplikationer vid användning av perifera venkatetrar ökar vid övergång till byte på klinisk indikation. Metod: Litteraturöversikten är genomförd med en kvantitativ metod för att skapa en översiktsbild av dagens kunskapsläge på området. Resultat: Ingen signifikant ökning av flebit och ocklusion framkom i åtta av nio studier. Infiltration ökade signifikant i tre av sju studier. Endast en studie, vilket även var den med marginal största, visade en signifikant ökning av bakteriemi, dock med fortsatt låg förekomst. Slutsats: Övergång till byte av perifera venkatetrar på klinisk indikation kan vara motiverat med tanke på den låga ökningen av komplikationer. / Background: Peripheral venous catheters are among the most common medical devices used in medical care. To minimize complications such as phlebitis, occlusion, infiltration and bacteremia there are two different policies as to when peripheral venous catheters should be replaced. Replacements either occur at regular intervals every 72-96 hours, as is currently the case in Sweden, or when signs of developing complications first occur, that is by clinical indication. Aim: The aim is to survey whether complications increase after transitioning to replacing peripheral venous catheters based on clinical implication. Method: A quantitative literature review was performed to survey the current knowledge of the subject. Result: No significant increase of phlebitis or occlusion was seen in eight out of nine studies. A significant increase of infiltration was seen in three out of seven studies. One study, which was also the largest one, saw a significant increase of bacteremia, even though the overall prevalence remained low. Conclusion: A transition to a policy of replacing peripheral venous catheters only when clinically indicated might be justified by the slight increase in complications.

The polymetallic carbonate-replacement prospect at Piavitsa is part of the ore-forming system of the Stratoni Fault Zone within the Kassandra mining district in northeast Greece. This district constitutes the southern segment of the Serbo-Macedonian belt, a promising region for the exploration of precious and critical metals in Greece. This master thesis is framed within the X-MINE project under the Horizon 2020 program. Three main objectives are defined: (1) to characterize the mineralization at Piavitsa utilizing reflected light microscopy, microprobe, and laser-ablation inductively coupled mass spectrometry (LA-ICP-MS), and (2) to evaluate the contributions of the scanning GeoCore X10 (XRF-XCT) technology to the understanding of the ore, and (3) to assess potential environmental impacts. At Piavitsa, an early base-metal assemblage, composed of brecciated sphalerite and As-rich pyrite, is infilled and overprinted by an assemblage of As-poor to moderately-rich pyrite, alabandite, and Mnrich sphalerite. The latter two are corroded and replaced by Mn-rich carbonate. Fractures and interstices are infilled by a late assemblage of Ca-Mn-Mg carbonate, galena, As-poor pyrite, tetrahedrite-tennantite, and in the periphery of the orebody, seligmannite-bournonite and kesterite.  Based on absolute elemental concentrations obtained by in situ LA-ICP-MS, the mineral hosts (primary; secondary) are defined as: pyrite (Fe, Co, Ni, and Au; As), sphalerite (Zn, Ga, Ge, Cd, Sn; Mn), galena and bournonite (Pb, Se, Te, Tl, and Bi; Ag, Sb), alabandite (Mn; Cd and Sb), and tetrahedrite (Cu, As, Ag, and Sb). In cocrystallized assemblages, some differences are observed. In pyritetetrahedrite asemblages, tetrahedrite mainly hosts As and Au, instead of pyrite, whereas in sphaleritealabandite assemblages, alabandite is the host of Mn, As, Ag and Sb and sphalerite, of Cd and Sn. Three concentrates are produced from the current mining operations of Hellas Gold in the Stratoni area, e.g, Mavres Petres Zn-Pb mine. From LA-ICP-MS, it is inferred that a sphalerite concentrate from the Piavitsa ore would contain Ga (peripheral ore: 150 ppm; main ore: 10-40 ppm), Sn (peripheral ore: 800-1500 ppm; main ore: 25-230 ppm), and Cd (1600-4000 ppm). The galena concentrate would contain concentrations of Ag (1300-1700 ppm), Se (50 ppm), Sb (1200-1600 ppm), and Te (85-210 ppm). The pyrite concentrate would contain Au (0.5-24.5 ppm) but would be devoid of other economical trace elements. The values given here consider 100% purity, instead of 80-90% reported in previous studies. The GeoCore X10 technology provides a good indication of measurable elements. (&gt;0.01 wt.%), including Mn, Fe, Cu, Zn, and Pb; As, Sb and Sn. Moreover, it helps to quickly identify the main ore and gangue minerals and their distribution in the deposit. The distinction between the ore and gangue minerals can be easily achieved based on the difference in their X-ray attenuation. It is worth highlighting that mineralogical info obtained by other analytical methods is still essential to validate the outputs of the instrument and to improve the interpretations drawn from them. Regarding the environmental impacts of mining the ore, the potential for acid generation and pollutant mobilization are low due to the carbonate-rich matrix. The mining poses low radioactivity risks due to the low concentration of radionuclides. Establishing a pollutants baseline and monitoring the surrounding water bodies and soils is highly recommended to reduce overlooked environmental impacts.

Invasive exotic plants can persist and successfully spread within ecosystems and negatively affect the recruitment of native species. The exotic invasive Ailanthus altissima and the native Robinia pseudoacacia are frequently found in disturbed sites and exhibit similar growth and reproductive characteristics, yet each has distinct functional roles such as allelopathy and nitrogen fixation, respectively. 1) A four-month full additive series in the greenhouse and 2) spatial point pattern analysis of trees in a silvicultural experiment were used to analyze the intraspecific and interspecific interference between these two species. In the greenhouse experiment, total biomass responses per plant for both species were significantly affected by interspecific but not by intraspecific interference (p <0.05). Competition indices such as Relative Yield Total and Relative Crowding Coefficient suggested that A. altissima was the better competitor in mixed plantings. Ailanthus altissima consistently produced a larger above ground and below ground relative yield while R. pseudoacacia generated a larger aboveground relative yield in high density mixed species pots. However, R. pseudoacacia exhibited more variation for multiple biomass traits, occasionally giving it an above ground advantage in some mixed species pots. Analysis of spatial point patterns in the field with Ripley's K indicated that the two species were positively associated with each other along highly disturbed skid trails in the majority of the field sites. Locally, increased disturbances could lead to more opportunities for A. altissima to invade, negatively interact with R. pseudoacacia (as was evident in the greenhouse study), and become established in place of native species. / Master of Science

The issue of lead exposure through drinking water was re-examined in light of modern public health goals, recent high-profile cases of elevated lead in water, and emerging concerns regarding the efficacy of legally mandated remedial strategies. A critical literature review revealed that serious lead-in-water hazards are present at many US schools and homes, and that the threat to individuals is not eliminated by existing regulations. Health studies have provided strong links between lead in water and lead in blood of exposed populations, even at relatively low levels of exposure compared to reported lead occurrence in US tap water samples. As efforts shift from addressing pervasive lead sources that once elevated the blood lead of large percentages of the population, to more isolated individual cases requiring exceptional attention, the importance of carefully considering lead in water as a potential source for elevated blood lead increases. Consistent with decades of prior research linking elevated water lead to elevated blood lead (EBL), lead-contaminated water in the high-profile case of Washington DC markedly increased the incidence of EBL for very young children. Specifically, incidence of EBL for children aged ≤ 1.3 years increased more than 4 times during 2001-2003 when lead in water was high, compared to 2000 when lead in water was low. The incidence of EBL for children aged ≤ 1.3 years was highly correlated (R² = 0.81) to 90th percentile lead-in-water levels from 2000-2007, and the risk of exposure to high water lead levels varied markedly in different neighborhoods of the city. Analysis conducted herein focused on identifying "worst-case" neighborhoods and populations. Specifically, this was the first study of the Washington DC case to focus on infants who are most vulnerable to harm from lead in water, and to perform smaller area analysis at the neighborhood (i.e., zip code) level in order to capture pockets of high risk among local communities. Prior biokinetic modeling efforts, examining the potential adverse impacts of lead-in-water exposure, were re-examined to explicitly consider new public health goals. This included impacts on the most sensitive population groups (e.g., young children and particularly formula-fed infants), the potential variability in blood lead levels (BLLs) amongst exposed individuals within those groups (e.g., most sensitive children at the upper tail of the BLL distribution), more conservative BLL thresholds reflecting low-level adverse effects (e.g., 5, 2 and 1 µg/dL versus 10 µg/dL), and the possibility of acute health impacts. This re-evaluation creates a paradigm shift, in that levels of lead in water that were previously considered inconsequential are demonstrated to be of concern in specific circumstances. The replacement of lead service lines in front of consumers' homes is a costly, federally mandated remedial action if a water utility exceeds the US EPA lead action level. Because utilities do not own the entire lead service line, they often only replace the portion of the service line up to the property line, typically with copper pipe. Experiences in Washington DC, as revealed by Freedom of Information Act requests, indicated that partial pipe replacements were not decreasing lead in water, and were actually associated with relatively high incidence of childhood lead poisoning. This prompted the first comprehensive investigation of potential long-term problems arising from galvanic corrosion between the remaining lead pipe and the newly installed copper pipe. Bench-scale experiments demonstrated that galvanic connections between lead pipe (new or aged) and copper pipe increased lead release into the water by 1.1-16 times, when compared to a full length of lead pipe alone. The small area of lead pipe adjacent to the copper joint (<0.5 ft) was gravely affected by galvanic corrosion, and accumulated a thick lead-rust layer (1 inch wide) that constituted a reservoir for semi-random particulate lead detachment into the water. The work on simulated partial pipe replacements revealed that under worst-case scenarios of highly contaminated water samples, most of the lead was not quantified if water samples were not mixed thoroughly after standard preservation (i.e., after addition of 0.15% v/v HNO₃), or if water samples were transferred from one bottle to another prior to preservation. While there is no reason to believe that sample handling and pre-treatment dramatically skew regulatory compliance with the US EPA lead action level, slight variations from one approved protocol to another may cause lead-in-water health risks to be dramatically underestimated. This is of special concern in unusual situations of "worst-case" individual exposures to highly contaminated water, associated with childhood lead poisoning. This work provides the water industry and health agencies with important new insights and perspectives on an old problem. Results can improve strategies to detect and mitigate lead-in-water hazards for individuals or populations, and inform future revisions to the US EPA Lead and Copper Rule. / Ph. D.

Bostadshusen från miljonprogrammet är i behov av genomgripande renoveringar. Samtidigt riskerar detta att medföra omfattande hyreshöjningar för hyresgästerna som utgör en socioekonomiskt utsatt grupp i samhället. De hyreshöjningar som hyresgästerna står inför, och som har stöd i rådande lagstiftning, kan resultera i en renovräkning som innebär att ett flertal hyresgäster behöver lämna sina hem.  Syftet med detta arbete är att erhålla en djupare förståelse för hur hyressättningssystemet i samband med renovering fungerar för att undersöka dels rimligheten i de hyreshöjningar som sker, dels om rådande lagstiftning skyddar hyresgästen i samband med detta. Främst fokus har riktats mot hyreslägenheterna som tillhör miljonprogrammet. Tre centrala frågeställningar har väglett arbetet: Vilka lagar och regler styr hyreshöjningar vid renoveringar av lägenheter inom miljonprogrammet? Hur bedöms rimligheten i en hyreshöjning efter renoveringar ur ett juridiskt perspektiv? Skyddar dagens lagstiftning hyresgäster från markanta hyreshöjningar? För att besvara samtliga frågeställningar har en rättsdogmatisk ansats tillämpats, där utgångspunkten har tagits i lagstiftning, rättspraxis, lagförarbeten, viss rättshistoria och doktrin. Vidare har tillhörande litteratur samt rättsfall studerats för att undersöka hur hyressättningssystemet kring renoveringar ter sig i praktiken.  Arbetet konstaterar att hyreshöjningar följt av renoveringar kan få betydande konsekvenser för hyresgästerna, speciellt i områden som tillhör miljonprogrammet, som präglas av socioekonomisk utsatthet. Rådande regelsystem möjliggör betydande hyreshöjningar där hyresgäster har ett begränsat inflytande trots de skyddsregler som idag finns för att tillgodose ett skydd för dem. Dagens lagstiftning står därmed inför stora utmaningar, inte minst när det gäller att tillgodose behovet av en rimlig bostadsstandard samtidigt som hyresgästens ekonomiska situation ska beaktas. / The residential buildings from the Million program are in need of extensive renovation. This can lead to substantial rent increases for the tenants, who represent a socio-economically vulnerable group in society. The rent increases, which are supported by current legislation, may result in renovation eviction, where several tenants are forced to leave their homes due to rent increase. The aim of this study is to gain a deeper understanding of how the rent setting system during renovation works, in order to examine both the reasonableness of the rent increases and whether current legislation protects the tenant in such cases. The focus has been on rental apartments from the Million program. Three central questions have guided this work: What laws and regulations govern rent increases when renovating apartments from the Million program? How is the reasonableness of a rent increase after renovations assessed from a legal perspective? Does current legislation protect tenants from significant rent increases? To answer the questions presented, different methods, including a legal-dogmatic approach, have been applied, where the current legislation, case law, selective legislative history and doctrine have been studied. Other literature on the subject have also been studied, in order to obtain an insight of the rent setting system during renovation, both from a theoretical and practical perspective.  This work finds that rent increases followed by renovation can have significant consequences for tenants, especially in areas belonging to the Million program with high socio-economic vulnerability. The current legislation allows for extensive rent increases where tenants have limited influence despite the current influence that is supported by law to provide protection for them. Today's legislation thus faces major challenges, not least when it comes to meeting the need for a reasonable standard of housing while taking into account the tenant's financial situation.