Parametric amplification of optical phonons

Amplification of light through stimulated emission or nonlinear optical interactions has had a transformative impact on modern science and technology. The amplification of other bosonic excitations, like phonons in solids, is likely to open up new remarkable physical phenomena. Here, we report on an experimental demonstration of optical phonon amplification. A coherent mid-infrared optical field is used to drive large amplitude oscillations of the Si-C stretching mode in silicon carbide. Upon nonlinear phonon excitation, a second probe pulse experiences parametric optical gain at all wavelengths throughout the reststrahlen band, which reflects the amplification of optical-phonon fluctuations. Starting from first principle calculations, we show that the high-frequency dielectric permittivity and the phonon oscillator strength depend quadratically on the lattice coordinate. In the experimental conditions explored here, these oscillate then at twice the frequency of the optical field and provide a parametric drive for lattice fluctuations. Parametric gain in phononic four wave mixing is a generic mechanism that can be extended to all polar modes of solids, as a new means to control the kinetics of phase transitions, to amplify many body interactions or to control phonon-polariton waves

Parallelizing a SAT-Based Product Configurator

This paper presents how state-of-the-art parallel algorithms designed to solve the Satisfiability (SAT) problem can be applied in the domain of product configuration. During an interactive configuration process, a user selects features step-by-step to find a suitable configuration that fulfills his desires and the set of product constraints. A configuration system can be used to guide the user through the process by validating the selections and providing feedback. Each validation of a user selection is formulated as a SAT problem. Furthermore, an optimization problem is identified to find solutions with the minimum amount of changes compared to the previous configuration. Another additional constraint is deterministic computation, which is not trivial to achieve in well performing parallel SAT solvers. In the paper we propose five new deterministic parallel algorithms and experimentally compare them. Experiments show that reasonable speedups are achieved by using multiple threads over the sequential counterpart

Analysis of Onshore Synthetic Inertia and Primary Control Reserve Contributions of Alternating Current-Side Meshed Offshore Grids with Voltage-Source Converter and Diode Rectifier Unit High-Voltage Direct Current Connections

The increasing use of renewable energy sources in place of conventional generation units is leading to a reduction in onshore inertia and to the development of offshore wind park grids connected by multiple high-voltage direct current (HVDC) connections to the onshore alternating current (AC) grid. For AC-side meshed offshore grids with voltage-source converter (VSC) and diode rectifier unit (DRU) HVDC connections towards onshore grids, this study focuses on the energetic feasibility of synthetic inertia (SI) and primary control reserve (PCR) contributions triggered locally at the onshore converters of both connection types. To this end, the obstacles preventing contributions for VSC HVDC connections and the mechanisms allowing contributions for DRU HVDC connections are identified first. Based on these findings, the article proposes an enhancement of the offshore HVDC converter controls that is continuously active and allows locally triggered onshore contributions at all onshore HVDC converters of both connection types without using communication and requiring only minimal system knowledge. Additional simulations confirm that, although the enhancement is continuously active, the operational performance of the offshore HVDC converter controls for normal offshore grid operation and its robustness against offshore AC-side faults are not affected

Why Hybrid Meson Coupling to Two S-wave Mesons is Suppressed

We introduce strong interaction selection rules for the two-body decay and production of hybrid and conventional mesons coupling to two S-wave hybrid or conventional mesons. The rules arise from symmetrization in states in the limit of non-relativistically moving quarks. The conditions under which hybrid coupling to S-wave states is suppressed are determined by the rules, and the nature of their breaking is indicated.Comment: 9 pages, LaTeX, 1 eps figures, uses epsf. Minor modifications, Title chang

The differentiation of single and dual career athletes falls short: A person-oriented approach to characterize typical objective life situations of elite athletes

Research concerning athletic career development in high-performance sport typically uses demographic data, sport characteristics or pursuing a dual career (i.e. having an educational or vocational career simultaneous to the athletic career) to identify developmental processes. In defiance of these attempts, considerable heterogeneity remains within these subgroups of the elite athlete population. In line with the person-oriented approach, the objective of this study was to develop a comprehensive typology of athletes with similar objective life situations by considering both sport-related as well as non-sport related aspects. To this end, data were collected about athletic performance level, weekly amount of working time (i.e. sport-related activities, education, and vocation), and financial information (i.e. gross annual income and income generated from sport). Based on a sample of 733 elite athletes, a cluster analysis was performed to divide the sample into groups of similar patterns on the aforementioned factors. Five different athlete patterns were found: (1) working dual career athletes, (2) high-income professional athletes, (3) medium-income professional athletes, (4) family-supported athletes, and (5) student dual career athletes. These findings support the dual career literature of separating dual career (Cluster 1 and Cluster 5) from single career athletes, which, in turn, should also not be regarded as a single population, but further divided (Cluster 2, Cluster 3, and Cluster 4). This typology may aid federations and practitioners within athletic career development in providing individual assistance for elite athletes

Linking sports-related and socio-economic resources of retiring Olympic athletes to their subsequent vocational career

The aim of this study was to examine patterns of sports-related and socio-economic resources at the time of athletic retirement and their relation to the subsequent vocational career. We surveyed 341 former Olympic athletes representing Switzerland about their athletic, educational, and vocational careers. In order to adequately depict the heterogeneous situations of athletes during and after their athletic career, we applied a person-oriented approach. This involves adopting a holistic perspective and using nonlinear methods of analysis to allow for interactions between different aspects of an athlete’s career. Using cluster analytic techniques, we found different patterns of sports-related and socio-economic resources at the time of athletic retirement which were related with specific vocational career paths. In particular, clusters disposing of manifold resources had various opportunities in working life, whereas clusters with few resources fared less well. However, a lack of educational certificates could be compensated for by success in sports and popularity, provided that the vocational activity was pursued in sport. These findings may help career counsellors to better understand athletes’ career development options and provide services of ever-improving quality

Beyond PEMDAS: Teaching Students to Perceive Algebraic Structure

Evidence shows that transforming expressions is a major stumbling block for many algebra students. Using Sfard's (1991) theory of reification, I highlight the important roles that the process of parsing and the notions of subexpression and structural template play in competent expression transformation. Based on these observations, I argue that one reason students struggle with expression transformation is the inattentiveness of traditional curricula to parsing, subexpressions, and structural templates. However, simply refocusing attention on these ignored aspects of algebra will not alone ensure that students avoid common pitfalls. After examining evidence that students are very prone to overgeneralize, I argue for a connectionist view of how people's minds work when they are learning algebra. Utilizing these additional insights, the instructional strategies I ultimately recommend are strategies that focus on structure, but in ways that will make structure a winning competitor for student attention

Water Ice and Dust in the Innermost Coma of Comet 103P/Hartley 2

On November 4th, 2010, the Deep Impact eXtended Investigation (DIXI) successfully encountered comet 103P/Hartley 2, when it was at a heliocentric distance of 1.06 AU. Spatially resolved near-IR spectra of comet Hartley 2 were acquired in the 1.05-4.83 micron wavelength range using the HRI-IR spectrometer. We present spectral maps of the inner ~10 kilometers of the coma collected 7 minutes and 23 minutes after closest approach. The extracted reflectance spectra include well-defined absorption bands near 1.5, 2.0, and 3.0 micron consistent in position, bandwidth, and shape with the presence of water ice grains. Using Hapke's radiative transfer model, we characterize the type of mixing (areal vs. intimate), relative abundance, grain size, and spatial distribution of water ice and refractories. Our modeling suggests that the dust, which dominates the innermost coma of Hartley 2 and is at a temperature of 300K, is thermally and physically decoupled from the fine-grained water ice particles, which are on the order of 1 micron in size. The strong correlation between the water ice, dust, and CO2 spatial distribution supports the concept that CO2 gas drags the water ice and dust grains from the nucleus. Once in the coma, the water ice begins subliming while the dust is in a constant outflow. The derived water ice scale-length is compatible with the lifetimes expected for 1-micron pure water ice grains at 1 AU, if velocities are near 0.5 m/s. Such velocities, about three order of magnitudes lower than the expansion velocities expected for isolated 1-micron water ice particles [Hanner, 1981; Whipple, 1951], suggest that the observed water ice grains are likely aggregates.Comment: 51 pages, 12 figures, accepted for publication in Icaru