Metallische Nanostäbe mit einer Länge im Mikrometer-Bereich wirken als Antennen für infrarotes Licht: Indem unter Lichteinfall eine kollektive Schwingung der Leitungselektronen angeregt wird (ein sogenanntes Plasmon), wird das elektrische Feld an den Stabenden stark konzentriert. Besonders starke Feldkonzentrationen treten auf, wenn zwei Antennenarme durch eine schmale Lücke getrennt sind (Dimerantenne). Somit können die Antennen Licht-Materie-Wechselwirkungen -- wie beispielsweise die Absorption infraroten Lichtes von Molekülen -- verstärken. Dieses als oberflächenverstärkte Infrarotabsorption (SEIRA) bezeichnete Phänomen ist sehr nützlich, um Signale in der Infrarotspektroskopie zu verstärken. Diese Arbeit widmet sich der effizienten Herstellung von metallischen Nanostäben für SEIRA. Im ersten Schwerpunktthema werden Dimerantennen, die per Elektronenstrahllithographie (EBL) hergestellt wurden und eine auflösungsbegrenzte Lücke aufweisen, durch eine photochemische Reduktion von Metallsalzkomplexen nachträglich vergrößert. Dadurch verringert sich die Lückengröße und erreicht Werte deutlich unter der Auflösungsgrenze der EBL. Es wird gezeigt, dass diese photochemische Abscheidung die IR-optischen Eigenschaften der Dimerantennen durch plasmonische Kopplung entscheidend verändert. Zudem steigt die Infrarotabsorption von in der Lücke befindlichen Molekülen mit sinkender Lückengröße. Im zweiten Schwerpunktthema liegt der Fokus auf der günstigen Fabrikation einer Vielzahl von IR-Antennen in einem parallelen Prozess. Dabei werden poröse Template aus anodisiertem Aluminiumoxid (AAO) als Negativ für die herzustellenden Metallstäbe benutzt. Es wird zuerst gezeigt, dass die Poren des Templates durch die photochemische Reduktion von Goldsalzkomplexen befüllt werden können. Für eine gezielte Einstellung der Stäbchenlänge und die Generierung einer nanoskaligen Lücke wird weiterhin die elektrochemische Befüllung der Template untersucht. Die hiermit hergestellten IR-Antennen werden vereinzelt, auf ein Substrat aufgetragen und hinsichtlich ihrer Struktur und ihrer IR-optischen Eigenschaften charakterisiert. Die Vor- und Nachteile der untersuchten Herstellungsmethoden und ihre Eignung für die Fabrikation von IR-Antennen für SEIRA werden diskutiert. / Metallic nanorods with lengths in the micrometer regime act as antennas for infrared light: As incident light excites a collective oscillation of the conduction electrons (a so-called plasmon), the electric field is concentrated at the rod ends. In case two antenna arms are separated by a small gap (dimer antenna), a particularly high field concentration occurs. Thereby the antennas are capable of enhancing light-matter-interaction -- for example the absorption of infrared light by molecules. This phenomenon, termed as surface enhanced infrared absorption (SEIRA), is very useful to enhance absorption signals in infrared spectroscopy. This thesis attends to the efficient fabrication of metallic nanorods for SEIRA. The first topic in focus is the manipulation of dimer antennas fabricated by electron beam lithography (EBL), featuring a gap of resolution-limited size. By applying a photochemical reduction of metal salt complexes in solution, the dimer arms are subsequently enlarged. Thereby the gap size is reduced and reaches values clearly below the resolution limit of EBL. It is shown that the IR optical properties of dimer antennas dramatically change during photochemical metal deposition. This is due to plasmonic coupling. Additionally, the absorption of infrared light by molecules located in the gap increases with decreasing gap size. The second topic in focus is the cheap fabrication of a large number of IR antennas in a parallel process. Here, porous templates of anodized aluminum oxide (AAO) are used as a negative for the metal rods to be fabricated. Firstly, it is shown that the pores of the template can be filled by photochemical reduction of gold salt complexes. For a targeted adjustment of the rod lengths and the generation of a nanoscale gap, secondly, the electrochemical filling of acsu AAO is investigated. The IR antennas prepared by this method are extracted from the template, transferred to a substrate, and individually characterized in terms of their structure and IR optical properties. Advantages and drawbacks of the fabrication methods investigated in this work as well as their applicability to the fabrication of IR antennas for SEIRA are being discussed.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2017-05-05T17:56:32Z No. of bitstreams: 1 texto completo.pdf: 366555 bytes, checksum: 610a12118ed558f9d7da51082c77a5ca (MD5) / Made available in DSpace on 2017-05-05T17:56:32Z (GMT). No. of bitstreams: 1 texto completo.pdf: 366555 bytes, checksum: 610a12118ed558f9d7da51082c77a5ca (MD5) Previous issue date: 2002-05-27 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O tempo decorrido da semeadura até o estabelecimento da plântula de aspargo é relativamente longo, podendo levar de quatro a seis semanas, dependendo da temperatura e umidade do solo, justificando o uso de técnicas que acelerem a germinação, como o condicionamento osmótico ("priming") das sementes. O presente trabalho foi desenvolvido no Laboratório de Pesquisa de Sementes, do Departamento de Fitotecnia, da Universidade Federal de Viçosa, no período de janeiro a dezembro de 2000, tendo como objetivos: determinar as curvas de embebição para sementes de aspargo em água destilada, PEG 6000 e água do mar; estudar as interações entre potencial osmótico, agente condicionador e período de condicionamento adequados ao condicionamento osmótico dessas sementes; e avaliar os efeitos do condicionamento osmótico em lotes de sementes com diferentes níveis de vigor. Foram utilizadas sementes de aspargo 'Mary Washington', provenientes de quatro lotes. Inicialmente, determinaram-se as curvas de embebição das sementes de cada lote, em água destilada, em PEG 6000 a –1,0 e –1,2 MPa e em água do mar a –3,3 MPa, todas em incubadora BOD a 250C. Para o condicionamento em PEG 6000 e em água do mar, utilizaram-se períodos de embebição de 2, 4, 6, 8, 10, 12, 24, 48, 72, 96, 120, 144, 168, 336, 504 e 672 horas. Períodos de embebição de 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 24, 48, 72, 96, 120, 144 e 168 horas foram utilizados para o condicionamento em água destilada. Após cada período, o grau de umidade atingido pelas sementes foi determinado em estufa a 1300C por uma hora. Foram, então, estabelecidos os seguintes tratamentos de condicionamento osmótico: PEG 6000 a –1,0 MPa por 7 e 14 dias, PEG 6000 a –1,2 MPa por 7 e 14 dias, água do mar a –3,3 MPa por 7 e 14 dias e água destilada por 3 dias. Sementes não condicionadas e embebidas em água destilada foram utilizadas como testemunhas. Imediatamente após o condicionamento, o efeito dos tratamentos na qualidade fisiológica das sementes foi avaliado pelos seguintes testes: germinação e 1a contagem da germinação, deterioração controlada, pesos da matéria verde e seca das plântulas, germinação sob estresse hídrico (PEG 6000 a –0,4 MPa), germinação a baixa temperatura (150C), germinação a alta temperatura (350C), comprimentos da radícula, do epicótilo e da plântula e velocidade de emergência das plântulas em areia. O experimento foi instalado no delineamento inteiramente casualizado, com quatro repetições e oito tratamentos para cada lote. Os dados foram submetidos à análise combinada de variância envolvendo todos os lotes, sendo as médias comparadas pelo teste Duncan, ao nível de 5% de probabilidade. Os resultados permitiram concluir que: as curvas de embebição obtidas em PEG 6000 a –1,2 MPa e em água do mar a –3,3 MPa indicaram que, até 672 horas (28 dias) de embebição, não houve protrusão da radícula. Já para as sementes condicionadas em PEG 6000 a –1,0 MPa, a protrusão da radícula ocorreu a partir das 504 horas (21 dias) de embebição. Houve protrusão da radícula a partir das 120 horas (5o dia) de embebição em água destilada; o condicionamento em PEG a –1,0 MPa por 336 horas (14 dias), de modo geral, foi o tratamento mais adequado; sementes de aspargo condicionadas apresentaram maior porcentagem de germinação e maior vigor em relação às sementes não condicionadas; o condicionamento osmótico mostrou-se benéfico tanto para o lote de baixa quanto o de alta qualidade fisiológica, embora o efeito tenha sido mais expressivo para o lote de menor vigor; o condicionamento osmótico apresentou efeito benéfico no vigor das sementes, tanto no lote de baixa quanto no de alta qualidade fisiológica, sob condições de estresse térmico e hídrico. / The period of time between the sowing and the establishment of asparagus seedling is relatively long, being able to take four at six weeks, depending on temperature and soil moisture, justifying the use of techniques that speed up the germination, as the osmotic priming of the seeds. The study was carried out at the Seed Research Laboratory of the Universidade Federal de Viçosa, in january-december period of 2000, with the objectives: to determine the imbibition curves for asparagus seeds in distilled water, PEG 6000 and seawater; to study the interactions between osmotic potential, priming agent and period of time suitable for seed priming, and to evaluate the effect of the osmotic priming in seed lots with different vigor levels. Four seed lots of 'Mary Washington' asparagus were used. Initially imbibition curves were drawn for each seed lot imbibed in distilled water, PEG 6000 at -1,0 and -1,2 MPa and in seawater at -3,3 MPa at 250C. For the priming in PEG 6000 and seawater, imbibition periods of 2, 4, 6, 8, 10, 12, 24, 48, 72, 96, 120, 144, 168, 336, 504 and 672 hours had been used. For the priming in distilled water, imbibition periods of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 24, 48, 72, 96, 120, 144 and 168 hours had been used. After each period of priming was monitored the moisture degree reaching for the seeds in stove at 1300C for one hour. The following osmotic priming treatments were established: seeds imbibed in PEG 6000 at -1,0 MPa for 7 days and 14 days, in PEG 6000 at -1,2 MPa for 7 days and 14 days, in seawater at -3,3 MPa for 7 days and 14 days and distilled water for 3 days. Unprimed seeds and seeds imbibed in distilled water were used as controls. Immediately after the priming, the effect of the treatments in the physiological quality of the seeds was evaluated by the following tests: standard germination (first count and final count); controlled deterioration; dry and fresh matter weight of the seedlings; germination under water stress (PEG 6000 at - 0,4 MPa); cool germination (150C); germination at high temperature (350C); radicle, epicotyl and seedling lenght; and seedling emergence speed in sand. The experiment was arranged in a completely randomized design, with four replications and eight treatments for each lot. The data were submitted to the joint analysis of variance involving all the lots. The treatment means were compared using the Duncan test at 5% probability level. The results allowed the following conclusions: the imbibition curves in PEG 6000 at -1,2 MPa and in seawater at -3,3 MPa had indicated that there was no radicle protrusion until the 672 hours (28th day) of imbibition. For the seeds imbibed in PEG 6000 at -1,0 MPa, radicle protrusion occurred from the 504 hours (21th day) of imbibition. There was radicle protrusion from the 120 hours (fifth day) of imbibition in distilled water; the seed priming in PEG at -1,0 MPa for 336 hours (14 days), in general, was the most effective treatment; primed asparagus seeds presented greater germination and vigor in relation to the untreated seeds; the osmotic priming had beneficial effect on vigor and seedling growth; the osmotic priming showed benificial effect on vigor in the seed lots with high and low physiological quality, specially over stress conditions. / Não foi localizado o cpf do autor.

For decades, researchers have documented how stereotyping and unfair treatment affect the lives of people with stigmatized characteristics. Pedophilic sexual interests, however, have received remarkably little academic attention. This research gap should be closed for two important reasons. First of all, people with pedophilia have a particularly high risk of experiencing negative stigma-related consequences as, arguably, one of the most feared and despised groups in Germany and many other Western countries. Secondly, vulnerability factors that are hypothesized to contribute to a higher risk of sexually abusive behavior towards children (e.g., low self-esteem, emotion regulation problems, and reduced motivation to seek mental health services) are likely to be enhanced by stigma-related stress. That means that stigmatization of people with pedophilia might not only have a negative effect on members of this group but may also compromise child sexual abuse prevention. This thesis aims at laying the much-needed groundwork for the scientific study of stigma against people with pedophilia by (1) conducting a systematic and comprehensive review of the literature on stigma against people with pedophilia, (2) assessing the prevalence and strength of public stigma against people with pedophilia compared to other despised groups, (3) developing and testing a theoretical framework for the study of stigma-related stress and associated problems among people with pedophilia, and (4) creating and evaluating an anti-stigma intervention program. (1) Our literature review documented a lack of research on this issue as well as the need for theoretical concepts and methodological designs conceptualized specifically for this field of study. (2) A scale to assess public stigma against people with pedophilia was designed and used to survey a sample of German pedestrians and US American workers from the Internet marketplace MTurk. A parallel set of items was employed to measure public stigma against other groups (people who abuse alcohol, sexual sadists, and people with antisocial tendencies). Results of these surveys documented people with pedophilia to be massively disadvantaged by stereotyping beliefs, negative affective reactions, and social distance, even compared to the three other stigmatized groups. (3) To reach the third sub-goal, the author of this thesis formulated the “Framework for the Effects of Stigma-related Stress among People with Pedophilia”. It contains a set of assumptions highlighting the relationship between the stigma-related stress and the risk of child sex offending, which is assumed to be mediated by impairments in emotional and social areas of functioning, as well as cognitive distortions, and the person’s motivation to seek mental health services. The model was tested in an online sample of men with a sexual interest in children. Overall, results provided preliminary evidence for the hypotheses previously laid out. (4) Finally, these ideas were put to practical use in the development of an anti-stigma program for psychotherapists in training that was experimentally validated online. Findings indicated that a number of stigma-related beliefs, affects, and behavioral intentions can be changed at a cost-effective level. Motivation to treat help-seeking patients with pedophilia, however, could not be increased within the sample. In summary, this thesis shows that stigma against pedophilia is a serious and widespread problem, and offers concrete propositions to promote a more realistic and empathetic view of this group. By approaching the emotionally charged concept of pedophilia from a stigma perspective, the research presented in this thesis challenges the way in which not only people from the general public, but also scientists and health care professionals think about pedophilia, and corroborates the importance of stigma reduction within the wider context of child sexual abuse prevention.

Medication adherence is a formidable challenge for the elderly who may have several prescribed medications while dealing with limited incomes and declining health. The primary purpose of this study was to evaluate the Liberty 6000, an automated capsule and tablet dispenser that provides proper medication dosages and is intended to encourage and track medication adherence. Seven focus groups were assembled; these comprised 49 men and women ages 65 to 98 years of Black, Anglo, and Hispanic descent who met the following criteria: living independently or semi-independently, had suffered one or more impairments, and were taking at least three prescription medications. Each focus group session lasted 90 minutes and was tape-recorded and transcribed verbatim, resulting in about 2,600 lines of text. Each question was designed to be open-ended to avoid introducing any bias that might influence the response. The Health Belief Model conceptually guided the study that addressed perceptions of illness susceptibility and severity, barriers, benefits, and cues to action associated with medication adherence. Main benefits of taking medications included avoiding inherited illnesses (or tendencies for illnesses), and reducing illness symptoms. Barriers to taking medications included forgetting, dexterity problems, and high cost. Benefits of the proposed intervention included reminding, caregiver notification, and providing a printed log of medications taken and missed. Barriers associated with the Liberty 6000 included its relatively large size, the difficulties that confronted older adults when loading the device, and its perceived cost. Using an adoption prediction model proposed a way to overcome barriers and encourage acceptance as well as a strategy to maintain acceptance over time. The model also can be used to evaluate a wide variety of medical devices for elderly people. This study identified the advantages and disadvantages of the Liberty 6000. Findings also suggest areas for further investigation by the nursing community and healthcare policy makers in finding solutions to the myriad problems faced by older people in medication adherence.

Von der Entscheidung für ein Spiel bis zur Wahl einer Taktik, um die Schlafenszeit hinauszuzögern - wiederholte Entscheidungen sind für Kinder allgegenwärtig. Zwei paradigmatische Entscheidungsphänomene sind probability matching (dt. Angleichen der Wahrscheinlichkeit) und Maximieren. Um Belohnungen zu maximieren, sollte eine Person ausschließlich die Option auswählen, welche die höchste Wahrscheinlichkeit hat. Maximieren wird allgemein al ökonomisch rationales Verhalten angesehen. Probability matching beschreibt, dass eine Person jede Option mit der Wahrscheinlichkeit auswählt, wie deren zugrunde liegende Wahrscheinlichkeit einer Belohnung ist. Ob es sich bei probability matching um einen Fehlschluss oder einen adaptiven Mechanismus handelt, ist umstritten. Frühere Forschung zu probabilistischem Lernen zeigte das paradoxe Ergebnis, dass jüngere Kinder eher maximieren als ältere Kinder. Von älteren Kindern nimmt man hingegen an, dass sie probability matchen. Dabei wurde jedoch kaum berücksichtigt, dass Kinder die Struktur der Umwelt zu ihrem Vorteil nutzen können. Diese Dissertation untersucht die inter- und intraindividuelle Entwicklung des probabilistischen Lernens in der Kindheit unter ökologischen und kognitiven Aspekten. Vier empirischen Kapitel zeigen, dass die Interaktion zwischen heranreifenden kognitiven Funktionen, sowie Merkmalen der Lern- und Entscheidungsumgebung die Entwicklung des adaptiven Entscheidungsverhaltens prägt. Die Entwicklung des probabilistischen Lernens durchläuft in der Kindheit mehrere Phasen: von hoher Persistenz, aber auch hoher interindividueller Variabilität bei jüngeren Kindern zu wachsender Anpassungsfähigkeit durch zunehmende Diversifizierung und Exploration bei älteren Kindern. Die Ergebnisse dieser Dissertation unterstreichen insbesondere den Nutzen einer ökologischen Rationalitätsperspektive bei der Erforschung der Entwicklung des Entscheidungsvermögens. / From choosing which game to play to deciding how to effectively delay bedtime—making repeated choices is a ubiquitous part of childhood. Two often contrasted paradigmatic choice behaviors are probability matching and maximizing. Maximizing, described as consistently choosing the option with the highest reward probability, has traditionally been considered economically rational. Probability matching, in contrast, described by proportionately matching choices to underlying reward probabilities, is debated whether it reflects a mistake or an adaptive mechanism. Previous research on the development of probability learning and repeated choice revealed considerable change across childhood and reported the paradoxical finding that younger children are more likely to maximize—outperforming older children who are thought to be more likely to probability match. However, this line of research largely disregarded the mind’s ability to capitalize on the structure of the environment. In this dissertation, I investigate the inter- and intra-individual development of probability learning and repeated choice behavior in childhood under consideration of ecological, cognitive, and methodological aspects. Four empirical chapters demonstrate that the interaction between the maturing mind and characteristics of the learning and choice environment shapes the development of adaptive choice behavior. The development of probability learning and repeated choice behavior in childhood progresses from high persistence but also high inter-individual variability to emerging adaptivity marked by increased diversification and exploration. The present research highlights the benefit of taking an ecological rationality view in research on the development of decision making abilities.

Aluminum alloys are of great importance in the automotive and truck industries due to the weight savings that they can help to achieve. However, the use of such alloys in applications where they are subjected to alternating stresses requires knowledge about their fatigue behavior. Moreover, extrusion induces a strong texture and microstructural heterogeneity in the material and gives a surface with long grooves parallel to the extrusion direction (ED), so-called die lines. This anisotropy in surface conditions and microstructure may affect the fatigue properties. To investigate how die lines and microstructure affects fatigue in aluminum, the high cycle fatigue properties cycles of three peak-aged AlMgSi alloys were evaluated. Flat profiles of 6060-T6, 6063-T6 and 6082-T6 were tested in uniaxial stress (R = 0.1) in a servo-hydraulic fatigue testing machine with a constant stress amplitude. Two specimen types were tested for 6063 and 6082: one with the ED parallel to the loading direction (longitudinal), and one with the ED perpendicular to it (transverse). It was found that both 6063 and 6082 displayed anisotropy in fatigue lives, with the longitudinal orientation performing better. The anisotropy was far stronger in 6082 than in 6063. Furthermore, 6060 longitudinal displayed higher fatigue strength than 6063 longitudinal at higher stress amplitudes, but lower fatigue strength at lower amplitudes. Metallographic investigations with SEM indicated that grain boundaries of the surface-layer grains were involved in the initiation of the fatigue crack. Intergranular crack propagation and separation was observed on the fracture surfaces, especially in the surface layer. The extruded surfaces also showed evidence of intergranular crack propagation. The exact sites of crack initiation could not be found so it could not be proven conclusively that die lines were sites of crack initiation in transverse specimens, but there were some indications from metallographic and macrofractographic investigations that this was the case. / Aluminiumlegeringar används mycket i bilindustrin på grund av de viktbesparingar som kan åstadkommas. Användandet av sådana legeringar i tillämpningar där det utsätts för cykliska laster kräver dock kunskap om deras utmattningsbeteende. Dessutom skapar extrusionsprocessen en stark textur och heterogenitet i mikrostrukturen och resulterar i en yta med fina fåror parallella med pressriktningen, s.k. die lines. Anisotropin i ytbeskaffningen och mikrostrukturen kan påverka utmattningshållfastheten. För att undersöka hur die lines och mikrostruktur påverkar utmattningen i aluminium testades högcykelutmattningsegenskaperna hos tre toppåldrade AlMgSi legeringar. Platta profiler av 6060-T6, 6063-T6 och 6082-T6 testades i enaxlig dragspänning (R = 0.1) i en servohydraulisk utmattningsmaskin med konstant lastamplitud. Två sorters provstavar testade av 6082 och 6063: en med pressriktningen parallell med lastriktningen (längsriktning) och en med pressriktningen vinkelrät mot lastriktningen (tvärriktning). Både 6063 och 6082 uppvisade olika utmattningsliv beroende på pressriktningens orientering mot lastriktningen, där längsriktningen hade längre utmattningsliv för båda legeringarna. Anisotropin var mycket starkare in 6082 än 6063. Dessutom uppvisade 6060 i längsriktningen högre utmattningsstyrka än 6063 vid höga lastamplituder, men lägre utmattningsstyrka vid lägre lastamplituder. Metallografiska undersökningar med SEM indikerade att korngränser i ytlagret var involverade i sprickinitieringen. Spricktillväxt i och separation av korngränser observerades på brottytorna, speciellt i ytlagret. Den extruderade ytan visade också bevis för interkristallin spricktillväxt. De exakta platserna för sprickinitering kunde inte hittas så det kunde inte entydigt bevisas att sprickinitieringen skedde i die lines i provstavar med pressriktningen vinkelrät mot lastriktningen, men i metallografiska och fraktografiska undersökningar fanns vissa indikationer att så var fallet.

Die Dresdner Werkzeugmaschinen-Fachseminare sind ein Forum zu ausgewählten Spezialthemen der Entwicklung und Nutzung von Werkzeugmaschinen. Das 16. WZM-Fachseminar berichtetet inhaltlich detailliert von aktuellen Arbeiten im Rahmen des DFG-Sonderforschungsbereiches "Thermo-Energetische Gestaltung von Werkzeugmaschinen" (SFB/TR 96) an den Standorten Dresden, Aachen und Chemnitz. Die Fachbeiträge berichten über experimentelle und modellgestützte Analyse von Wärmequellen und -übertragung in spanenden Werkzeugmaschinen sowie zu Lösungsansätzen zur Korrektur und Kompensation der thermo-elastischen Verlagerungen.

Eine Erklärung, warum manche Wahrheiten notwendigerweise wahr sind, sollte verständlich machen, warum es für diese eine Wahrheitsgarantie gibt. Einen interessanten Ansatz für eine solche Erklärung liefert Kants Definition analytischer Wahrheiten als solche, die bereits in einem Begriff enthalten sind. Die notwendige Wahrheit analytischer Sätze kann hier über das Verhältnis ihrer Bestandteile erklärt werden. Diese Erklärung kann jedoch nur der Anfang einer generellen Erklärung von Notwendigkeit sein, denn einerseits sind nicht nur analytische Urteile notwendig, sondern auch andere, andererseits basiert die Erklärung auf einer umstrittenen Theorie von Begriffen. Die Dissertation untersucht nun, ob und wie die Strategie, Notwendigkeit über das Verhältnis zwischen den Bestandteilen von Repräsentationen zu erklären dennoch ausgeweitet und verteidigt werden kann, um zum Beispiel auch a posteriori Notwendigkeiten und essentialistische Urteile zu erfassen. Indem auf die die Referenz-Relation konstituierenden Fakten Bezug genommen wird, wird gezeigt, dass eine solche Erklärung tatsächlich möglich ist. Notwendige Wahrheit ist demnach eine Eigenschaft von wahrheitsfähigen Repräsentationen, die diese aufgrund des Verhältnisses zwischen den für die Wahrheit der Repräsentation nötigen Fakten und den Fakten, die die Referenz der Bestandteile der Repräsentation bestimmen, hat. Stehen diese in einem bestimmten Verhältnis, wird die Wahrheit der Repräsentation garantiert. Nachdem dieser Ansatz auf eine Reihe von Beispielen angewendet wird, zeigen sich interessante Parallelen zu essentialistischen Theorien von Notwendigkeit und es lässt sich zeigen, dass der Ansatz das Verhältnis zwischen Essenzen und Notwendigkeit richtig darstellt und es sogar erlaubt, ein besseres Verständnis davon zu entwickeln, was Essenzen sind. / An explanation of why some truths are necessarily true needs to make intelligible how it is that a truth is guaranteed to be true. The thesis argues that a promising starting point for an explanation of necessity can be found in Kant’s containment-account of analyticity, for it explains how the truth of a judgment is guaranteed by its structure and the relationship between its constituents. This, however, can merely be a starting point for a general explanation of necessary truth, for it is both too narrow, and presupposes a contentious view of concepts. The thesis thus explores how the general strategy, explaining necessary truth by certain relationships between the constituents of representations, can be expanded to cover further necessary truths, for example a posteriori necessities and essentialist claims. It is argued that the explanation can be generalized by focussing on what it is that constitutes reference between representations and the objects they represent as well as how these representations come together to form truth-evaluable representations. Necessary truth, on this account, is a property of truth-evaluable representations which a representation has in virtue of the appropriate relationship between what is required for its truth, and the way in which the reference of its constituents is determined. The appropriate relationship guarantees the truth of the representation. After applying the theory to a range of examples, interesting parallels to essentialist accounts of necessity emerge and it is argued that the proposed explanation gets the relationship between essence and necessity right and may even be used to elucidate what essences are.

Der erste Teil dieser Arbeit ist dem Kondogittermodell gewidmet. Für ein Elektron, das in einen ferromagnetisch gesättigten Hintergrund aus lokalen Spinmomenten eingebracht wird (ferromagnetisches Polaron), wird die stationäre Schrödingergleichung gelöst und das vollständige Eigenwertspektrum im endlichen und unendlichen Gitter abgeleitet. Danach wird die zeitabhängige Schrödingergleichung für beliebige Anfangsbedingungen gelöst und eine detaillierte Analyse des Down-Elektron-Zerfalls vorgenommen. Für endliche Bandfüllungen wird im Anschluss das magnetische Grundzustandsphasendiagramm mit Hilfe einer Molekularfeldtheorie bestimmt. Der Einfluss von Verdünnung/Unordnung im lokalen Momentensystem auf die auftretenden Phasen wird analysiert. Im zweiten Teil der Arbeit wird das Hubbardmodell untersucht. Für dieses wird mit Hilfe einer modifizierten Störungstheorie (englisch: modified perturbation theory, MPT) eine wellenzahlabhängige (nicht-lokale) Selbstenergie abgeleitet, die sowohl für schwache als auch für starke Coulombwechselwirkungen gute Ergebnisse liefert. Mit dieser werden dann Spektraldichten und Quasiteilchenzustandsdichten berechnet, wobei insbesondere die nicht-lokalen Korrelationseffekte im Fokus stehen. Daneben werden Ergebnisse für die optische Leitfähigkeit, die in einer renormierten diagrammatischen Ein-Schleifen-Näherung berechnet wurden, besprochen. Es wird dann gezeigt, dass nur unter Beachtung der nicht-lokalen Korrelationseffekte ein ferromagnetisches Phasendiagramm konstruiert werden kann, das in Einklang mit dem Mermin-Wagner-Theorem steht. / The first part of this work deals with the Kondo-lattice model. The stationary Schrödinger equation is solved for the case of one electron in a ferromagnetically saturated local moment system (the magnetic polaron). The complete eigensystem is derived for the finite and infinite lattice. The time-dependent Schrödinger equation is then solved for arbitrary initial conditions and a detailed analysis of the down-electron decay dynamics is given. For finite band occupations the magnetic ground-state phase diagram is constructed within a mean-field theory. The effect of disorder/dilution in the local moment system on the phase diagram is discussed. The second part concentrates on the investigation of the Hubbard model. A nonlocal self-energy is derived within a modified perturbation theory that interpolates between weak and strong Coulomb repulsion. Results for the spectral density and quasiparticle density of states are shown with special attention to the effects of nonlocal correlations. Results for the optical conductivity within a renormalized one-loop approximation are also discussed. The main result of this section is the importance of nonlocal correlations for the fulfillment of the Mermin-Wagner theorem. A phase diagram that shows regions of ferromagnetic order is calculated for the simple cubic lattice.

Individuelle Unterschiede in der kognitiven Entwicklung von Kindern korrelieren mit ihrem sozioökonomischen Status (engl. socioeconomic status, SES). Allerdings hat die bisherige Forschung längsschnittliche Dynamiken meist ignoriert. Des Weiteren sind die Mechanismen, die zu SES–bedingten Diskrepanzen in der kognitiven Entwicklung führen, weitgehend unbekannt. Gemäß einer Hypothese ist es die Dysregulation der Sekretion des Stresshormons Cortisol die SES Unterschiede vermittelt, da niedriger SES robust mit höherem chronischen Stress assoziiert. Die vorliegende Dissertation weist im Längsschnitt nach, dass Veränderungen im Familieneinkommen die kognitive Entwicklung von armen Kindern im späteren Kindesalter vorhersagen (Studie I). Bemerkenswerterweise wirkt kindliche Kognition auch auf Veränderungen im elterlichen Einkommen, was auf bisher vernachlässigte bidirektionale Familiendynamiken hinweist. Zudem liefert die Dissertation querschnittliche empirische Evidenz für die Hypothese, dass ein stressbezogener Mechanismus in SES–bedingten Unterschieden kognitiver Entwicklung involviert ist. Höherer Stress und ein geringeres Einkommen waren beide mit Anzeichen des Hypocortisolismus in Kindern charakterisiert (Studie II und III). Außerdem gab es Hinweise, dass kognitive Kontrolle vor den Effekten von Stress schützen könnte (Studie II). Schließlich zeigt die Dissertation erstmalig, dass hyporeaktive Cortisolprofile in Reaktion auf akuten Stress in ärmeren Kindern mit deren niedrigerer Gedächtnisleistung assoziiert ist (Studie III). Beachtenswert ist, dass Ergebnisse dieser Dissertation nicht auf Umwelt oder genetisch vermittelte Kausalität schließen lassen. In zukünftigen Interventionsstudien sollte weiter untersucht werden, ob Interventionen die Einkommensgewinne stärken, Stress reduzieren oder die Reaktion von Kindern auf akuten Stress verbessern, kognitive Unterschiede im Zusammenhang mit SES verringern. / Individual differences in cognitive development in childhood vary along gradients of socioeconomic status (SES). Yet, research has largely ignored longitudinal dynamics, despite evidence that SES, especially income, also changes over time. Furthermore, fairly little is known about the mechanisms by which SES explains cognitive disparities. Lower SES environments are marked by high chronic stress exposure, which has led to the hypothesis that dysregulation of the stress response system resulting in altered cortisol secretion mediates disparities in cognition. This dissertation provides longitudinal evidence for the notion that family income gains and losses predict poor children’s cognitive development throughout later childhood (Paper I). Remarkably, children’s cognition also predicts their parents’ earning ability, indicating previously neglected bidirectional family dynamics. Moreover, this dissertation provides cross–sectional evidence for a stress mechanism involved in SES disparities of cognitive functioning. Both higher stress and lower income are associated with patterns of hypocortisolism in middle childhood (Paper II & III). Further, cognitive control skills may buffer against the embedding of stress exposure in diurnal cortisol secretion (Paper II). Lastly, cortisol hyporeactivity to stress found in low–income children is uniquely associated with their lower memory performance. Notably, this dissertation does not warrant environmentally– or genetically–mediated assumptions of causality. Future intervention studies should continue to explore whether facilitating family income gains, reducing stress exposure, normalizing cortisol secretion, or improving children’s stress coping by training cognitive control alleviates SES–related disparities in cognition.