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

Verification of State/Event Systems by Quotienting

A rather new approach towards compositional verification of concurrent systems is the quotient technique, where components are gradually removed from the concurrent system while transforming the specification accordingly. When the intermediate specifications can be kept small using heuristics for minimization, the state explosion problemis avoided and there are already promising experimental results for systems with an interleaving semantics, including real-time systems. This paper extends the quotienting approach to deal with a synchronous framework in the shape of state/event systems. A state/event system is a concurrent system with a set of interdependent components operating synchronously according to stimuli (input events) provided by an environment while producing output events in return for the environment. A compositional modal logic M suitable for expressing general safety and liveness properties subsystems is introduced. A quotient construction for building components from a state/event system into the specification is presented and heuristics for minimizing formulae are proposed. The techniques are demonstrated on an example. The correctness of the techniques are justified by proofs in an appendix

Games as a Platform for Student Participation in Authentic Scientific Research

This paper presents results from the design and testing of an educational version of Quantum Moves, a Scientific Discovery Game that allows players to help solve authentic scientific challenges in the effort to develop a quantum computer. The primary aim of developing a game-based platform for student-research collaboration is to investigate if and how this type of game concept can strengthen authentic experimental practice and the creation of new knowledge in science education. Researchers and game developers tested the game in three separate high school classes (Class 1, 2, and 3). The tests were documented using video observations of students playing the game, qualitative interviews, and qualitative and quantitative questionnaires. The focus of the tests has been to study players' motivation and their experience of learning through participation in authentic scientific inquiry. In questionnaires conducted in the two first test classes students found that the aspects of doing “real scientific research” and solving physics problems were the more interesting aspects of playing the game. However, designing a game that facilitates professional research collaboration while simultaneously introducing quantum physics to high school students proved to be a challenge. A collaborative learning design was implemented in Class 3, where students were given expert roles such as experimental and theoretical physicists. This significantly improved the students’ feeling of learning physics compared to Class 1 and 2. Overall the results presented in this paper indicate that the possibility of participating in authentic scientific experiments, which this class of games opens, is highly motivating for students. The findings also show that the learning design in the class setting must be considered in order to improve the students’ experience of learning and that various design challenges remain to be addressed even further

Characterizing Land Use Systems within Awoja Watershed

This manuscript analyses trends in land use changes in Awoja Watershed with the aim of exploring the underlying causes of degradation in this watershed within the context of frequent draughts and floods. Changing trends of land use characteristics were used as indicators of ineffectiveness of control of access to resource use in the watershed. The study was carried out in the districts of Katakwi, Amuria and Sorotiin Eastern Uganda where the watershed is experiencing increasing trends of degradation despite the presence of elaborate watershed management institutions. The study used Remote Sensing, and focus group discussions to acquire relevant data on land use changes and their perceived causes. Perceptions of respondents on the effectiveness of the local governance processes were generated. The findings show increase in built-up areas from 0.21% between 1986-1996; to 3.28 between 2006 and 2016 and a notable decrease in forest cover from 107.48 Km2 in 1,986 to 6.94 Km2 by 2016. The results also show a dramatic increase in small scale farming area from 629.44 Km2 to 2,376.64 Km2 from 1986-2016 while the area of wetland reduced from 2,810.47 Km2 to 1,355 Km2over the same period. Results from focus group discussions revealed that although climatic and demographic factors were responsible for land use changes in Awoja, control of access to natural resources was inadequate to stop degradation. Climatic factors mentioned included increased frequency of floods and draughts that were perceived to have been responsible for changes in vegetation cover, water levels and infrastructure. Socio economic factors driving the changes in land use included increased cultivation of wetlands and communal land, increased sale of fuel wood, charcoal and sand, increased migration of cattle herders into the watershed during draughts and out of it during floods and increased fishing. While climatic factors were important, socio political factors such as displacements of communities, resettlements in the fragile environment brought about by government efforts to demarcate wetlands and wild life conservation areas were cited as drivers of degradation. The study concludes that besides climatic factors, inadequate management of access to resources was contributing to degradation of the watershed

Expected Labor Market Affiliation:A New Method Illustrated by Estimating the Impact of Perceived Stress on Time in Work, Sickness Absence and Unemployment of 37,605 Danish Employees

As detailed data on labor market affiliation become more accessible, new approaches are needed to address the complex patterns of labor market affiliation. We introduce the expected labor market affiliation (ELMA) method by estimating the time-restricted impact of perceived stress on labor market affiliation in a large sample of Danish employees. Data from two national surveys were linked with a national register. A multi-state proportional hazards model was used to calculate ELMA estimates, i.e., the number of days in work, sickness absence, and unemployment during a 4-year follow-up period, stratified by gender and age. Among employees reporting frequent work-related stress, the expected number of working days decreased with age, ranging from 103 days lost among older women to 37 days lost among younger and middle-aged men. Young and middle-aged women reporting frequent work- and personal life-related stress lost 62 and 81 working days, respectively, and had more days of sickness absence (34 days and 42 days). In conclusion, we showed that perceived stress affects the labor market affiliation. The ELMA estimates provide a detailed understanding of the impact of perceived stress on labor market affiliation over time, and may inform policy and practice towards a more healthy and sustainable working life