Photon-pair generation by non-instantaneous spontaneous four-wave mixing

We present a general model, based on a Hamiltonian approach, for the joint quantum state of photon pairs generated through pulsed spontaneous four-wave mixing, including nonlinear phase-modulation and a finite material response time. For the case of a silica fiber, it is found that the pair-production rate depends weakly on the waveguide temperature, due to higher-order Raman scattering events, and more strongly on pump-pair frequency detuning. From the analytical model, a numerical scheme is derived, based on the well-known split-step method. This scheme allows computation of joint states where nontrivial effects are included, such as group-velocity dispersion and Raman scattering. In this work, the numerical model is used to study the impact of the non-instantaneous response on the pre-filtering purity of heralded single photons. We find that for pump pulses shorter than 1 ps, a significant detuning-dependent change in quantum-mechanical purity may be observed in silica

Phylogeny of Somniosus sleeper sharks: insights from newly sequenced mitochondrial genomes

Mitochondrial DNA (mtDNA) has been extensively used to explore phylogenetics since the its use became available. This science is considered useful in discerning relationships and evolutionary histories that are not possible with morphological studies alone. The sleeper sharks (genus: Somniosus) are a group of poorly understood, long-lived, iconic species whose taxonomic status within the genus have been argued about for many years. The aim of this study was to sequence and characterize mitogenomes of all Somniosus species to gain a better phylogenetic understanding of the genus and to discriminate the delimitations between species. Using next-generation sequencing, complete to nearly-complete mitogenomes were assembled of all species within Somniosus. Clear divergence was shown between the subgenera S. Somniosus and S. Rhinoscymnus, estimated at 7.8 million years ago, with no discernable differentiation between Somniosus pacificus and Somniosus antarcticus, nor between Somniosus rostratus and Somniosus longus. The results suggest a panmictic population of Somniosus pacificus and Somniosus antarcticus, as well as between Somniosus rostratus and Somniosus longus. Combined, the results of this study show that a thorough revision is needed of the Somniosus genus to improve taxonomic resolution and allow more informed conservation related decisions to be made

Risk, reproducibility, and reproduction : Essays on scholar’s analytic decisions and consumers' product purchases

This thesis investigates how evolutionary biology theories can be used to better understand consumer behavior. The first paper lays the groundwork for the methodologies used throughout the thesis. Here, the focus is on the (ab-)use of p-values and how easy it is to find a false-positive research result under different common circumstances. The second paper investigates what happens with the willingness to engage in risky choices when people have a low level of blood glucose. The third and fourth papers focus on conspicuous consumption and examine the circumstances that induce people to purchase prestigious products. The empirical studies have in common the idea that the respective choices involved in each paper are embedded in an evolutionary process. In the first paper, we find that obtaining a false positive result is easy, especially when there is no pre-registration of the hypothesis or no correction of p-values for multiple hypothesis testing. In some important cases, pre-registration alone is not sufficient to overcome the problem of inflated false positives. Applying these insights to an empirical case and using theoretical arguments from evolutionary biology, the second paper uses cross-validation and a meta-analysis to show that people with low levels of blood glucose show a higher willingness to pay for risky food items, whereas this is not the case for non-food products. The third paper shows through two studies that conspicuous consumption is particularly prevalent among single men. Building on these findings, the fourth paper shows, through a newly constructed uncertainty index, that increased uncertainty amplifies people’s propensity to engage in conspicuous consumption. Overall, this thesis adds to the literature on false-positive findings and illuminates how social scientists can reach a deeper understanding of human behavior by adopting an evolutionary lens

Space Plug-and-Play Architecture Networking: A Self-Configuring Heterogeneous Network Architecture

The Space Plug-and-Play Architecture (SPA) networking approach outlined in this dissertation is an improvement over the previous approach used by the Satellite Data Model(SDM). The first improvement is the introduction of a SPA network model based on the Open Systems Interconnection (OSI) model. Second, a new addressing and routing scheme is presented, which places the burden of routing on the network infrastructure instead of the network endpoints. These improvements have been implemented in a software infrastructure called the SPA Services Manager (SSM). The SSM was developed under an International Organization for Standardization (ISO) 9001 certified development process, the details of which are presented. A collection of network timing graphs that measure latency and jitter of the SPA network is contained in this dissertation, as well as a runtime memory footprint. The maturity of the development process and these initial performance measurements demonstrate that the SSM is qualified for spaceflight

Expert Interventions for Democracy: The Historical and Epistemological Foundations of International Democracy

The subject of this dissertation research is the field of professional organizations in North America that promote and assist democratization movements around the world. These organizations use a form of specialized expert knowledge to help activists, politicians and civil society organizations build democratic institutions. Specifically, this research investigates how historical academic debates shape the everyday practices of professionals in this field, and how these practices in turn shape contemporary debates. The study adopts a mixed methods approach by combining an intellectual history of democracy research and qualitative interview research with professionals working in the field. By examining the everyday practice of expertise, this dissertation contributes to emerging scholarly debates spanning the intersections of the sociology of knowledge, political sociology and international development studies by asking an ancient question. How can democracy be a collection of popular political ideals, yet also the object of specialized, technical or social scientific knowledge? According to the findings of this research, the contemporary practice of democracy assistance emerged out of debates about this paradox and, more importantly, organizations within this field rely on the insoluble nature of democratic theory and practice to justify expert interventions in countries struggling for democracy

Engineering spectrally unentangled photon pairs from nonlinear microring resonators through pump manipulation

The future of integrated quantum photonics relies heavily on the ability to engineer refined methods for preparing the quantum states needed to implement various quantum protocols. An important example of such states are quantum-correlated photon pairs, which can be efficiently generated using spontaneous nonlinear processes in integrated microring-resonator structures. In this work, we propose a method for generating spectrally unentangled photon pairs from a standard microring resonator. The method utilizes interference between a primary and a delayed secondary pump pulse to effectively increase the pump spectral width inside the cavity. This enables on-chip generation of heralded single photons with state purities in excess of 99 % without spectral filtering.Comment: 5 pages, 5 figure

Emerging media, political protests, and government repression in autocracies and democracies from 1995 to 2012

© The Author(s) 2019. This study empirically analyzed the relationships between emerging media as tools in fomenting anti-government protest as well as government repression of political opposition. Using a dataset of 162 democratic and autocratic countries over 18 years, potential differences between these phenomena were examined. The results of a series of analytic models suggest that higher levels of internet and mobile phones are positively associated with more instances of both political protests and political repression, which have increased dramatically in recent years. The differences between democratic and autocratic countries\u27 emerging media and sociopolitical instability trends are explored and discussed

Spectrally pure heralded single photons by spontaneous four-wave mixing in a fiber: reducing impact of dispersion fluctuations

We model the spectral quantum-mechanical purity of heralded single photons from a photon-pair source based on nondegenerate spontaneous four-wave mixing taking the impact of distributed dispersion fluctuations into account. The considered photon-pair-generation scheme utilizes pump-pulse walk-off to produce pure heralded photons and phase matching is achieved through the dispersion properties of distinct spatial modes in a few-mode silica step-index fiber. We show that fiber-core-radius fluctuations in general severely impact the single-photon purity. Furthermore, by optimizing the fiber design we show that generation of single photons with very high spectral purity is feasible even in the presence of large core-radius fluctuations. At the same time, contamination from spontaneous Raman scattering is greatly mitigated by separating the single-photon frequency by more than 32 THz from the pump frequency