5,314 research outputs found

    Investigation of phonon behavior in Pr2NiMnO6 by micro-Raman spectroscopy

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    The temperature dependence of phonon excitations and the presence of spin phonon coupling in polycrystalline Pr2NiMnO6 samples were studied using micro-Raman spectroscopy and magnetometry. Magnetic properties show a single ferromagnetic-to-paramagnetic transition at 228 K and a saturation magnetization close to 4.95 \muB/f.u.. Three distinct Raman modes at 657, 642, and 511 cm-1 are observed. The phonon excitations show a clear hardening due to anharmonicity from 300 K down to 10 K. Further, temperature dependence of the 657 cm-1 mode shows only a small softening. This reflects the presence of a relatively weak spin-phonon coupling in Pr2NiMnO6 contrary to other double perovskites previously studied.Comment: 10 pages, 4 fig

    Predators reduce extinction risk in noisy metapopulations

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    Background Spatial structure across fragmented landscapes can enhance regional population persistence by promoting local “rescue effects.” In small, vulnerable populations, where chance or random events between individuals may have disproportionately large effects on species interactions, such local processes are particularly important. However, existing theory often only describes the dynamics of metapopulations at regional scales, neglecting the role of multispecies population dynamics within habitat patches. Findings By coupling analysis across spatial scales we quantified the interaction between local scale population regulation, regional dispersal and noise processes in the dynamics of experimental host-parasitoid metapopulations. We find that increasing community complexity increases negative correlation between local population dynamics. A potential mechanism underpinning this finding was explored using a simple population dynamic model. Conclusions Our results suggest a paradox: parasitism, whilst clearly damaging to hosts at the individual level, reduces extinction risk at the population level

    Letter from Bear, et al to Representative Burdick Regarding Property Laws, Undated

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    This undated resolution signed by Joe B. Bear, Adlai Stevenson, Alfred S. Smith, Jackson Dancing Bull, and Francis Stevenson concerns property issues related to the Three Affiliated Tribes of the Fort Berthold Reservation. The resolution states that the members of the Fort Berthold Americans Inc. do not agree with a law which would regard native property as a collective movement that denies property ownership. See also: Letter from Adlai Stevenson to Representative Burdick Regarding Lemke Bill, April 3, 1944https://commons.und.edu/burdick-papers/1212/thumbnail.jp

    Influence of lattice distortion on the Curie temperature and spin-phonon coupling in LaMn0.5_{0.5}Co0.5_{0.5}O3_{3}

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    Two distinct ferromagnetic phases of LaMn0.5_{0.5}Co0.5_{0.5}O3_{3} having monoclinic structure with distinct physical properties have been studied. The ferromagnetic ordering temperature Tc\textit{T}_{c} is found to be different for both the phases. The origin of such contrasting characteristics is assigned to the changes in the distance(s) and angle(s) between Mn - O - Co resulting from distortions observed from neutron diffraction studies. Investigations on the temperature dependent Raman spectroscopy provide evidence for such structural characteristics, which affects the exchange interaction. The difference in B-site ordering which is evident from the neutron diffraction is also responsible for the difference in Tc\textit{T}_{c}. Raman scattering suggests the presence of spin-phonon coupling for both the phases around the Tc\textit{T}_{c}. Electrical transport properties of both the phases have been investigated based on the lattice distortion.Comment: 9 figure

    More than just tracking time: Complex measures of user engagement with an internet-based health promotion intervention

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    BACKGROUND: There has been a rise in internet-based health interventions without a concomitant focus on new methods to measure user engagement and its effect on outcomes. We describe current user tracking methods for internet-based health interventions and offer suggestions for improvement based on the design and pilot testing of healthMpowerment.org (HMP). METHODS: HMP is a multi-component online intervention for young Black men and transgender women who have sex with men (YBMSM/TW) to reduce risky sexual behaviors, promote healthy living and build social support. The intervention is non-directive, incorporates interactive features, and utilizes a point-based reward system. Fifteen YBMSM/TW (age 20-30) participated in a one-month pilot study to test the usability and efficacy of HMP. Engagement with the intervention was tracked using a customized data capture system and validated with Google Analytics. Usage was measured in time spent (total and across sections) and points earned. RESULTS: Average total time spent on HMP was five hours per person (range 0-13). Total time spent was correlated with total points earned and overall site satisfaction. CONCLUSION: Measuring engagement in internet-based interventions is crucial to determining efficacy. Multiple methods of tracking helped derive more comprehensive user profiles. Results highlighted the limitations of measures to capture user activity and the elusiveness of the concept of engagement

    Cosmological performance of SKA H i galaxy surveys

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    The Square Kilometre Array (SKA) will conduct the biggest spectroscopic galaxy survey ever, by detecting the 21 cm emission line of neutral hydrogen (
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