High-order harmonic generation from Rydberg states at fixed Keldysh parameter

Because the commonly adopted viewpoint that the Keldysh parameter $\gamma$ determines the dynamical regime in strong field physics has long been demonstrated to be misleading, one can ask what happens as relevant physical parameters, such as laser intensity and frequency, are varied while $\gamma$ is kept fixed. We present results from our one- and fully three-dimensional quantum simulations of high-order harmonic generation (HHG) from various bound states of hydrogen with $n$ up to 40, where the laser intensities and the frequencies are scaled from those for $n=1$ in order to maintain a fixed Keldysh parameter $\gamma$$< 1$ for all $n$. We find that as we increase $n$ while keeping $\gamma$ fixed, the position of the cut-off scales in well defined manner. Moreover, a secondary plateau forms with a new cut-off, splitting the HHG plateau into two regions. First of these sub-plateaus is composed of lower harmonics, and has a higher yield than the second one. The latter extends up to the semiclassical $I_p+3.17U_p$ cut-off. We find that this structure is universal, and the HHG spectra look the same for all $n\gtrsim 10$ when plotted as a function of the scaled harmonic order. We investigate the $n$-, $l$- and momentum distributions to elucidate the physical mechanism leading to this universal structure

Phase-dependent interference fringes in the wavelength scaling of harmonic efficiency

We describe phase-dependent wavelength scaling of high-order harmonic generation efficiency driven by ultra-short laser fields in the mid-infrared. We employ both numerical solution of the time-dependent Schr\"{o}dinger equation and the Strong Field Approximation to analyze the fine-scale oscillations in the harmonic yield in the context of channel-closing effects. We show, by varying the carrier-envelope phase, that the amplitude of these oscillations depend strongly on the number of returning electron trajectories. Furthermore, the peak positions of the oscillations vary significantly as a function of the carrier-envelope phase. Owing to its practical applications, we also study the wavelength dependence of harmonic yield in the "single-cycle" limit, and observe a smooth variation in the wavelength scaling originating from the vanishing fine-scale oscillations.Comment: 5 pages, 4 figure

Anorexia Nervosa Ett Durkheimianskt perspektiv

I denna uppsats konstrueras en teoretisk modell över fenomenet självsvält/anorexia nervosa sett mot bakgrund av den teoretiska referensramen i Émile Durkheims studie Självmordet. Den empiriska metoden baserar sig på litteraturstudier och befintlig aktuell forskning om de båda fenomenen självsvält/anorexia nervosa och självmord. Mitt syfte är att utröna huruvida de sociala orsaksfaktorer som förklarar variationen av självmordsfrekvensen i olika typer av samhällen är de samma som ligger bakom fenomenet asketiskt religiöst fastande under medel-tiden och nutida anorektiskt beteende i icke-västerländska och västerländska samhällen. Durkheim betonade att patologiska sociala fenomen kan orsakas både av en alltför långt dri-ven individualism och av dess motsats, en alltför stark reglering och integrering. Anorexia nervosa såsom sjukdomen yttrar sig i den sydasiatiska kulturen skulle kunna ses som symtom på ett sociokulturellt system som genom sin struktur kan framkalla fenomen av fatalis-tisk/altruistisk art. I sina bakomliggande orsaker yttrar sig anorexia nervosa i denna kulturella kontext som en antites till de faktorer som förklarar fenomenet i västvärlden där samhälls-strukturen framkallar fenomen av egoistisk/anomisk art. På var sin sida av den imaginära ska-la där styrkan i samhällets integrering och reglering framträder och färgade av olika sociokulturella faktorer blir ändå konsekvensen samma sjukdomstillstånd

Microbial Biodegradation of Lignocellulose for Ethanol Production

Bioethanol can be produced from a range of substrates and it is considered to be renewable. Lignocellulose is one of the substrates that can be used for bioethanol production. Genetic engineering of a microorganism that can completely convert all the sugars of cellulosic material into ethanol is one of the important steps for the production process. This study has two parts that aim to produce bioethanol by using genetically modified microorganisms. The first part of the study deals with bioethanol production from lignocellulosic material by microbial fermentation in two steps. The first step is the degradation of the lignocellulosic material by Bacilli to produce cellobiose, and the second step is to convert cellobiose into glucose by a B-glucosidase expressing recombinant yeast strain. As lignocellulosic material, wood powder from industrial waste was used and the degradation of the wood powder into glucose was confirmed by following the growth curve of the microorganisms and through appropriate enzymatic assays. The second part of the study utilizes two novel technologies, Yeast Artificial Chromosome (YAC) and Bridge-Induced Translocation (BIT) to introduce new, multi-factorial genetic traits into a yeast strain, a process that would otherwise take several time-consuming and labor-intensive rounds of genetic engineering. After cloning exogenous cellulases onto a YAC vector, this was transformed into a PEP4 mutant yeast upon which BIT technology was applied. This technology allowed the research to gain two advantages; one of them was to stabilize the YAC within the yeast genome and the other one was to have increased gene expression level consequent to the translocation event. In conclusion, this work defines a successful microbial system that is able to efficiently utilize lignocellulosic material as a carbon source and a translocant yeast strain that has high level of cellulase activity