Space-charge dynamics in microdiodes

Space-charge limited emission in vacuum microdiodes can go through transverse modulation under certain conditions. The frequency of this modulated current is in the terahertz band and it can be tuned by changing either the the gap spacing or the gap voltage of the diode. Doing the latter is the preferred mode of operation during the simulations which we did. As the power of such diode radiators would be very small, we coupled arrays of such diodes and showed that such an array, which synchronizes itself, can give powerful enough radiation for practical usage. For the emission process, it was first assumed that electrons would be emitted with zero initial velocity, as such an assumption is readily used in most emission calculations in the room temperature range. To further the research, we assumed non-zero initial velocities for the photoemitted electrons and found that, although, not without effect, the non-zero initial velocity does not significantly reduce the power of the radiator. The spatial structure of the beams was examined as well. Finally, a code for simulation of the space-charge effects in solar cells was tested, and although at present no claims can be made about these effects, the code proved to be a very good tool which replicated results from experiments and theory alike. Further experimental research on the detection of space-charge limited currents and the associated Coulomb oscillations is needed.Losun rafeinda frá díóðu í lofttæmi getur orðið fyrir láréttri mótun undir vissumskilyrðum. Tíðnin á þessum mótaða straumi getur verið á terahertz tíðni sviðinuog hægt er að stilla hana með því að breyta fjarlægð díóðu frá skauti og spennuniþar á milli. Seinni kosturinn er ákjósanlegri og sá möguleiki rannsakaður hér meðtölvulíkani.Aflið frá einni díóðu er frekar lítið og því eru mörgum díóðum raðað upp. Díóð-unar samstilla sig og geta saman gefið frá sér nóg afl til að verahagnýtanlegar. Ílosunar ferli rafeindana var fyrst gert ráð fyrir að þær hefðu engan upphafshraða.Slík nálgun er oft gerð jafnavel við herbergishita. En til aðganga lengra gerðumvið ráð fyrir að upphafshraða fyrir rafeindirnar og fundum að hann minnkar ekkimikið aflið. Dreifing rafeinda geislans var líka skoðuð. Í lokinn var tölvulíkanifyrir sólarrafhlöður notaður til að skoða áhrif hleðslannaá starfrækslu rafhlöðunn-ar. Kóðinn reyndist vera ágæt tæki og gat hermt eftir niðurstöðum úr tilraunum ogsvipuðum líkönum. Frekari rannsóknar er þörf á mettunar strauminn og Coulombsveiflunum í slíkum kerfum.This PhD project was financially supported by the IcelandicResearch Fund grant number 120009021. Additional funding for solar cellsimulations was received from EEA Financial Mechanism 2009-2014 project8SEE/30.06.2014

Normal and inverted hysteresis in perovskite solar cells

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO$_2$/CH$_3$NH$_3$PbI$_{3-x}$Cl$_x$/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, the behavior strictly depending on the pre-poling bias. NH typically appears at pre-poling biases larger than the open circuit bias, while pronounced IH occurs for negative bias pre-poling. The transition from NH to IH is marked by a intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model (DEM). Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the non-linear polarization. Introducing a three step measurement protocol, which includes stabilization, pre-poling and measurement, we put forward the difficulties and possible solutions for a correct PCE evaluation.Comment: 11 pages, 10 figure

Type IA supernovae from very long delayed explosion of core - WD merger

We study the spinning down time scale of rapidly rotating white dwarfs (WDs) in the frame of the core-degenerate (CD) scenario for type Ia supernovae (SNe Ia). In the CD scenario the Chandrasekhar or super-Chandrasekhar mass WD is formed at the termination of the common envelope phase or during the planetary nebula phase, from a merger of a WD companion with the hot core of a massive asymptotic giant branch star. In the CD scenario the rapidly rotating WD is formed shortly after the stellar formation episode, and the delay from stellar formation to explosion is basically determined by the spin-down time of the rapidly rotating merger remnant. We find that gravitational radiation is inefficient in spinning down WDs, while the magneto-dipole radiation torque can lead to delay times that are required to explain SNe Ia.Comment: MNRAS, in pres

Coding and regulatory variants are associated with serum protein levels and disease.

Circulating proteins can be used to diagnose and predict disease-related outcomes. A deep serum proteome survey recently revealed close associations between serum protein networks and common disease. In the current study, 54,469 low-frequency and common exome-array variants were compared to 4782 protein measurements in the serum of 5343 individuals from the AGES Reykjavik cohort. This analysis identifies a large number of serum proteins with genetic signatures overlapping those of many diseases. More specifically, using a study-wide significance threshold, we find that 2021 independent exome array variants are associated with serum levels of 1942 proteins. These variants reside in genetic loci shared by hundreds of complex disease traits, highlighting serum proteins' emerging role as biomarkers and potential causative agents of a wide range of diseases

Coding and regulatory variants are associated with serum protein levels and disease.

Circulating proteins can be used to diagnose and predict disease-related outcomes. A deep serum proteome survey recently revealed close associations between serum protein networks and common disease. In the current study, 54,469 low-frequency and common exome-array variants were compared to 4782 protein measurements in the serum of 5343 individuals from the AGES Reykjavik cohort. This analysis identifies a large number of serum proteins with genetic signatures overlapping those of many diseases. More specifically, using a study-wide significance threshold, we find that 2021 independent exome array variants are associated with serum levels of 1942 proteins. These variants reside in genetic loci shared by hundreds of complex disease traits, highlighting serum proteins' emerging role as biomarkers and potential causative agents of a wide range of diseases

Multi-ancestry sleep-by-SNP interaction analysis in 126,926 individuals reveals lipid loci stratified by sleep duration.

Both short and long sleep are associated with an adverse lipid profile, likely through different biological pathways. To elucidate the biology of sleep-associated adverse lipid profile, we conduct multi-ancestry genome-wide sleep-SNP interaction analyses on three lipid traits (HDL-c, LDL-c and triglycerides). In the total study sample (discovery + replication) of 126,926 individuals from 5 different ancestry groups, when considering either long or short total sleep time interactions in joint analyses, we identify 49 previously unreported lipid loci, and 10 additional previously unreported lipid loci in a restricted sample of European-ancestry cohorts. In addition, we identify new gene-sleep interactions for known lipid loci such as LPL and PCSK9. The previously unreported lipid loci have a modest explained variance in lipid levels: most notable, gene-short-sleep interactions explain 4.25% of the variance in triglyceride level. Collectively, these findings contribute to our understanding of the biological mechanisms involved in sleep-associated adverse lipid profiles

Space-charge dynamics in microdiodes

Space-charge limited emission in vacuum microdiodes can go through transverse modulation under certain conditions. The frequency of this modulated current is in the terahertz band and it can be tuned by changing either the the gap spacing or the gap voltage of the diode. Doing the latter is the preferred mode of operation during the simulations which we did. As the power of such diode radiators would be very small, we coupled arrays of such diodes and showed that such an array, which synchronizes itself, can give powerful enough radiation for practical usage. For the emission process, it was first assumed that electrons would be emitted with zero initial velocity, as such an assumption is readily used in most emission calculations in the room temperature range. To further the research, we assumed non-zero initial velocities for the photoemitted electrons and found that, although, not without effect, the non-zero initial velocity does not significantly reduce the power of the radiator. The spatial structure of the beams was examined as well. Finally, a code for simulation of the space-charge effects in solar cells was tested, and although at present no claims can be made about these effects, the code proved to be a very good tool which replicated results from experiments and theory alike. Further experimental research on the detection of space-charge limited currents and the associated Coulomb oscillations is needed