Advanced paternal age effects in neurodevelopmental disorders?review of potential underlying mechanisms

Multiple epidemiological studies suggest a relationship between advanced paternal age (APA) at conception and adverse neurodevelopmental outcomes in offspring, particularly with regard to increased risk for autism and schizophrenia. Conclusive evidence about how age-related changes in paternal gametes, or age-independent behavioral traits affect neural development is still lacking. Recent evidence suggests that the origins of APA effects are likely to be multidimensional, involving both inherited predisposition and de novo events. Here we provide a review of the epidemiological and molecular findings to date. Focusing on the latter, we present the evidence for genetic and epigenetic mechanisms underpinning the association between late fatherhood and disorder in offspring. We also discuss the limitations of the APA literature. We propose that different hypotheses relating to the origins of the APA effects are not mutually exclusive. Instead, multiple mechanisms likely contribute, reflecting the etiological complexity of neurodevelopmental disorders

Crack growth in single crystal gas turbine blade alloys under service-like conditions

This work concerns the fatigue crack growth behaviour of nickel base single crystal superalloys. The main industrial application of this class of materials is in gas turbine blades, where the ability to withstand severe mechanical loading in combination with high temperatures is required. In order to ensure the structural integrity of gas turbine blades, knowledge of the fatigue crack growth behaviour under service-like conditions is of utmost importance. The aim of the present work is both to improve the understanding of the crack growth behaviour of single crystal superalloys and to improve the testing and evaluation methodology for crack propagation under thermomechanical fatigue loading conditions. Single crystal superalloys have anisotropic mechanical properties and are prone to localization of inelastic deformation along the close packed planes of the crystal lattice. Under some conditions, crystallographic crack growth occurs along these planes, and this is a complicating factor throughout the whole chain of crack propagation life simulation; from material data generation to component calculation. Crack growth testing has been performed, both using conventional isothermal testing methods and using thermomechanical fatigue crack growth testing. Experimental observations regarding crystallographic crack growth have been made and its dependence on crystal orientation and testing temperature has been investigated. Quantitative crack growth data are presented for the case of Mode I crack growth under isothermal as well as thermomechanical fatigue conditions. Microstructural investigations have been undertaken to investigate the deformation mechanisms governing the crack growth behaviour. A compliance-based method for the evaluation of crack opening force under thermomechanical fatigue conditions was developed, to enable a detailed analysis of the test data. The crack opening force evaluation proved to be of key importance for the understanding of the crack driving force under different testing conditions. The influence of hold time on crack growth behaviour was analysed, both in terms of creep crack growth and in terms of creep effects on the crack opening force. The transition between non-crystallographic and crystallographic crack growth was studied in detail and a criterion was developed to enable accurate predictions of this transition under a wide range of loading conditions representative for gas turbine blades.Detta arbete behandlar sprickpropageringsbeteendet hos monokristallina nickelbaserade superlegeringar. Den huvudsakliga industriella tillämpningen för denna materialgrupp är som skovelmaterial i gasturbiner, vilket kräver förmågan att motstå hög mekanisk belastning i kombination med höga temperaturer. För att säkerställa gasturbinskovlarnas hållfasthet är kunskap om sprickpropageringsbeteendet, under driftsliknande förhållanden, av yttersta vikt. Målet med detta arbete är både att förbättra förståelsen för monokristallina nickelbaslegeringars sprickpropageringsbeteende och att förbättra metodiken för sprickpropageringsprovning med termomekanisk utmattningsbelastning. Monokristallina superlegeringar har anisotropa mekaniska egenskaper och en benägenhet till lokalisering av inelastisk deformation längs kristallgittrets tätpackade plan. Under vissa förhållanden sker kristallografisk spricktillväxt längs dessa plan och detta är en komplicerande faktor genom hela kedjan av sprickpropageringssimulering; från materialdatagenerering till komponentberäkningar. Sprickpropageringsprovning har utförts både med konventionella isoterma provningsmetoder och med termomekanisk sprickpropageringsprovning. Kristallografisk sprickpropagering har studerats experimentellt för att klargöra dess beroende av kristallorientering och temperatur. Kvantitativa sprickpropageringsdata presenteras för sprickväxt i Modus I, under isoterm såväl som termomekanisk utmattningsbelastning. Mikrostrukturundersökningar har gjorts för att studera deformationsmekanismerna som styr sprickpropageringsbeteendet. En kompliansbaserad metod för att utvärdera spricköppningskraften vid termomekanisk utmattning har utvecklats, för att möjliggöra en djupgående analys av provdatat. Spricköppningsutvärderingen visade sig ha en nyckelroll för förståelsen av drivkraften för sprickpropagering vid olika provningsförhållanden. Inverkan av hålltid på sprickpropageringsbeteendet analyserades både med avseende på krypspricktillväxt och med avseende på inverkan av krypdeformation på spricköppningskraften. Omslaget från icke-kristallografisk till kristallografisk sprickpropagering studerades i detalj och ett kriterium utvecklades för att möjliggöra tillförlitliga prediktioner av detta omslag under ett brett spann av förhållanden, representativa för gasturbinskovlar.Funding agencies: The Swedish Energy Agency and Siemens Energy</p

Crack growth in single crystal nickel base superalloys under isothermal and thermomechanical fatigue

This work concerns the fatigue crack growth behaviour of nickel base single crystal superalloys. The main industrial application of this class of materials is in gas turbine blades, where the ability to withstand severe mechanical loading in combination with high temperatures is required. In order to ensure the structural integrity of gas turbine blades, knowledge of the fatigue crack growth behaviour under service-like conditions is of utmost importance. The aim of the present work is both to improve the understanding of the crack growth behaviour of single crystal superalloys and also to improve the testing and evaluation methodology for crack propagation under thermomechanical fatigue loading conditions. Single crystal superalloys have anisotropic mechanical properties and are prone to localization of inelastic deformation along the close-packed planes of the crystal lattice. Under some conditions, crystallographic crack growth occurs along these planes and this is a complicating factor throughout the whole chain of crack propagation life simulation; from material data generation to component calculation. Fatigue crack growth testing has been performed, both using conventional isothermal testing methods and also using thermomechanical fatigue crack growth testing. Experimental observations regarding crystallographic crack growth have been made and its dependence on crystal orientation and testing temperature has been investigated. Quantitative crack growth data are however only presented for the case of Mode I crack growth under isothermal as well as thermomechanical fatigue conditions. Microstructural investigations have been undertaken to investigate the deformation mechanisms governing the crack growth behaviour. A compliance based method for the evaluation of crack opening force under thermomechanical fatigue conditions was developed, in order to enable a detailed analysis of the test data. The crack opening force evaluation proved to be of key importance in the understanding of the crack driving force under different testing conditions.In the printed version of the thesis the series name Linköping Studies in Science and Technology Licentiate of engineering thesis is incorrect. The correct series name is Linköping Studies in Science and Technology Licentiate thesis.</p

Oxidation och degradering av nickel-baslegeringar vid höga temperaturer

This master’s thesis work is a study of oxidation and degradation of nickel-base alloys at high temperatures. The materials studied are designed for use in critical gas turbine components such as turbine blades and vanes. Some of the alloys are used today, whereas others have not yet entered commercial application. In order to maximize the efficiency of gas turbines, there is an ambition to maximize the operating temperatures. There is therefore a demand for materials which can withstand the damage mechanisms active at high temperatures. Among these damage mechanisms are oxidation and microstructural degradation. To investigate the oxidation resistance of 7 different monocrystalline and polycrystalline alloys, samples have been exposed isothermally in still air at temperatures between 850 and 1000°C, for exposure times of up to 20000h. Two of the alloys were also exposed cyclically at 950°C. Oxidation during the heat treatment resulted in significant weight changes, which were measured after each cycle for cyclically exposed samples and after completed heat treatment for isothermally exposed samples. The weight change data was used to evaluate the relative oxidation resistance of the alloys. The ranking of the alloys with respect to oxidation resistance was generally in agreement with the oxidation resistance predicted by a simple consideration of the Cr and Al contents of the alloys. However, the single-crystal alloy PWA1483 displayed better oxidation resistance than predicted from its chemical composition. Metallographic analysis of the samples indicated that the oxide scales formed consisted of several different types of oxides. The oxide scales were mainly composed of Cr2O3 and Al2O3. Fragments of the oxide scales spalled off, primarily during cooling but also in some cases during the long-term heat treatments. Spalling of the oxide scale accelerated the oxidation process, since the ability of the oxide scale to impede diffusion decreased with its decrease in thickness. Oxidation caused depletion of Al and thereby local dissolution of the aluminum-rich γ′ particles, which are of vital importance to the mechanical properties of the material. A γ′ depleted zone thereby formed underneath the oxide scale. In this zone nitrides and needle-like particles, believed to be topologically close packed μ phase, precipitated during heat treatment. Recrystallization in the depletion zone was observed in some of the monocrystalline materials. MC carbides (M=metal) present in the virgin material decomposed during heat treatment and M23C6 carbides were formed. The γ′ particles coarsened during heat treatment, which resulted in decreased hardness. The hardness decreased with exposure temperature up to 950°C, as expected due to the increased coarsening rate. At 1000°C an unexpected increase in hardness was observed for all sample materials except one. A possible explanation for this hardness increase is redistribution of γ′, by dissolution of γ′ during heat treatment and reprecipitation during cooling as much finer particles. A fine dispersion of γ′ is expected to contribute more to the hardness than a corresponding volume of γ′ in the form of larger particles. For some of the sample series, clear correlations between hardness and γ′ particle size or exposition time were found. These relationships could potentially be used to estimate the exposure temperature of service-exposed material. A numerical model was implemented in Matlab to describe the process of oxide growth and spalling, cycle by cycle. The model was successfully adapted to experimental data from the cyclic oxidation measurements. The general applicability of the model to cyclic oxidation data at different temperatures and cycle frequencies was not investigated. At long times of cyclic exposure, the net weight loss of the samples could be well approximated as a linear function of the number of cycles. However, during the last few cycles the amount of oxide spalled in each cycle suddenly decreased. This change in spallation behavior was mainly observed for the samples cooled in air between every cycle and to a much smaller extent for the samples cooled in water. The proposed explanation is that spalling occurred preferentially at a weak subscale interface and that the spalling propensity decreased with decreasing area of this weak interface. The deviating results of the last few cycles were not included in the modeling of the cyclic oxidation process

Thermomechanical fatigue crack growth in a single crystal nickel base superalloy

Thermomechanical fatigue crack growth in a single crystal nickel base superalloy was studied. Tests were performed on single edge notched specimens, using in phase and out of phase thermomechanical fatigue cycling with temperature ranges of 100-750°C and 100-850°C and hold times at maximum temperature ranging from 10s to 6h. Isothermal testing at 100°C, 750°C and 850°C was also performed using the same test setup. A compliance-based method is proposed to experimentally evaluate the crack opening stress and thereby estimate the effective stress intensity factor range ΔKeff for both isothermal and nonisothermal conditions. For in phase thermomechanical fatigue, the crack growth rate is increased if a hold time is applied at the maximum temperature. By using the compliance-based crack opening evaluation, this increase in crack growth rate was explained by an increase in the effective stress intensity factor range which accelerated the cycle dependent crack growth. No significant difference in crack growth rate vs ΔKeff was observed between in phase thermomechanical fatigue tests and isothermal tests at the maximum temperature. For out of phase thermomechanical fatigue, the crack growth rate was insensitive to the maximum temperature and also to the length of hold time at maximum temperature. The crack growth rate vs ΔKeff during out of phase thermomechanical fatigue was significantly higher than during isothermal fatigue at the minimum temperature, even though the advancement of the crack presumably occurs at the same temperature. Dissolution of γ′ precipitates and recrystallization at the crack tip during out of phase thermomechanical fatigue is suggested as a likely explanation for this difference in crack growth rate.Funding agencies: Siemens Industrial Turbomachinery AB in Finspang, Sweden; Swedish Energy Agency, via the Research Consortium of Materials Technology for Thermal Energy Processes [KME-702]</p

Formation principles of the mother`s characterin Latviana prose at the turn of the 19th and 20th century

Latviešu literatūrā autori mātes tēlu savā daiļradē aktualizējuši visai bieži, tālab ikviens lasītājs, kurš kaut nedaudz ir zinošs par tautas prozas klasiku, varētu nosaukt kaut vienu mātes tēlu, kura būtu izteiksmīga – vai raksturā, vai vismaz personvārdā. 19.gadsimta nogalē latviešu literatūrā sevi pieteica spēcīgi, radoši prozas pārstāvji, kuri pēc Apsīšu Jēkaba parauga par sev tuvāko izvēlējās tieši reālisma virzienu. Šo izcilo meistaru vidū jāmin tādi vārdi kā Rūdolfs Blaumanis, Andrievs Niedra, Jānis Purapuķe un Augusts Saulietis. Katrs ar savu individuālo pieeju, tomēr visi vienlīdz veiksmīgi pratuši attēlot gadsimta aktuālāko situāciju – pāreju un savienošanos esošajai patriarhālajai un topošajai modernajai dzīves uztverei. Bakalaura darbā „Mātes tēla izveides principi 19.-20.gadsimta mijas latviešu prozā” aplūkota reālisma autoru prozas specifika – principi, pēc kādiem autors veido tēlus un to raksturus. Rakstīšanas īpatnības salīdzinātas ar psihologa Karla Gustava Junga izveidoto tēlu arhetipu rašanās teoriju un rakstītajā folklorā fiksēto mātes tēla atveidi. Atslēgas vārdi: mātes tēls, 19.-20.gs. mija, reālisms, folklora, arhetipsIn Latvian literature mother is very common character, for that reason anyone who is competent in the classics of folk prose, could name at least one expressive mother’s character. During the late 19th century, those authors who have proved themselves as creative prose writers, took inspiration from Apsīšu Jēkabs and chose the direction in realism. These experts were – Rūdolfs Blaumanis, Andrievs Niedra, Jānis Purapuķe and Augusts Saulietis. Each one has it’s own individual approach but still, they all have managed to describe century’s most significant situation – connection with patriarchal and emerging modern perception of life. Aim of the Bachelor paper „Formation principles of mother's character in Latvian prose at the turn of the 19th and 20th century” is to examine the specific features of prose written by realism authors and also how they make their characters. Peculiarities of writing are compared with character made by pschycologist Carl Gustav Jung archetype theory and reproduction of mother’s character stated in folklore. Key words: mother’s character, the turn of the 19th and 20th century, realism, folklore, archetyp

Effect of SO2 and water vapour on the low-cycle fatigue properties of nickel-base superalloys at elevated temperature

In this study the effect of SO2+water vapour on strain controlled low cycle fatigue resistance of three different nickel based superalloys has been studied at 450 °C and 550 °C. A negative effect was found on both the crack initiation and crack propagation process. The effect increases with increasing temperature and is likely to be influenced by both the chemical composition and the grain size of the material. In general the negative effect decreases with decreasing strain range even if this means that the total exposure time increases. This is explained by the importance of the protective oxide scale on the specimen surface, which is more likely to crack when the strain range increases. When the oxide scale cracks, preferably at the grain boundaries, oxidation can proceed into the material, causing preferable crack initiation sites and reduced fatigue resistance

Modelling of the transition from mode I to crystallographic crack growth in a single crystal gas turbine blade alloy under service-like loading conditions

In fatigue life prediction of single crystal gas turbine blades, the risk of rapid crystallographic crack growth along the close-packed planes poses a large uncertainty. A criterion is proposed to predict the transition from mode I to crystallographic crack growth, which is necessary for reliable prediction of the number of cycles from crack initiation to the onset of crystallographic crack growth. The proposed criterion is calibrated against tests performed under a wide range of conditions representative for a gas turbine blade, including isothermal fatigue crack growth tests and thermomechanical fatigue crack growth tests, some including hold times and pre-test aging.Funding agencies: The work has been supported financially by Siemens Energy AB in Finspång, Sweden and the Swedish Energy Agency, via the Research Consortium of Materials Technology for Thermal Energy Processes, Grant No. KME-702.</p

Crystallographic crack propagation rate in single-crystal nickelbase superalloys

Single-crystal nickel-base superalloys are often used in the hot sections of gas turbines due to their good mechanical properties at high temperatures such as enhanced creep resistance. However, the anisotropic material properties of these materials bring many difficulties in terms of modelling and crack growth prediction. Cracks tend to switch cracking mode from Mode I cracking to crystallographic cracking. Crystallographic crack growth is often associated with a decrease in crack propagation life compared to Mode I cracking and this must be taken into account for reliable component lifing. In this paper a method to evaluate the crystallographic crack propagation rate related to a crystallographic crack driving force parameter is presented. The crystallographic crack growth rate is determined by an evaluation of heat tints on the fracture surface of a specimen subjected to fatigue loading. The complicated crack geometry including two crystallographic crack fronts is modelled in a three dimensional finite element context. The crack driving force parameter is determined by calculating anisotropic stress intensity factors along the two crystallographic crack fronts by finite-element simulations and post-processing the data in a fracture mechanics tool that resolves the stress intensity factors on the crystallographic slip planes in the slip directions. The evaluated crack propagation rate shows a good correlation for both considered crystallographic cracks fronts