744 research outputs found

    Electronic theory for superconductivity in Sr2_2RuO4_4: triplet pairing due to spin-fluctuation exchange

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    Using a two-dimensional Hubbard Hamiltonian for the three electronic bands crossing the Fermi level in Sr2_2RuO4_4 we calculate the band structure and spin susceptibility χ(q,ω)\chi({\bf q}, \omega) in quantitative agreement with nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) experiments. The susceptibility has two peaks at {\bf Q}i=(2π/3,2π/3)_i = (2\pi/3, 2\pi/3) due to the nesting Fermi surface properties and at {\bf q}i=(0.6π,0)_i = (0.6\pi, 0) due to the tendency towards ferromagnetism. Applying spin-fluctuation exchange theory as in layered cuprates we determine from χ(q,ω)\chi({\bf q}, \omega), electronic dispersions, and Fermi surface topology that superconductivity in Sr2_2RuO4_4 consists of triplet pairing. Combining the Fermi surface topology and the results for χ(q,ω)\chi({\bf q}, \omega) we can exclude ss- and dd-wave symmetry for the superconducting order parameter. Furthermore, within our analysis and approximations we find that ff-wave symmetry is slightly favored over p-wave symmetry due to the nesting properties of the Fermi surface.Comment: 5 pages, 5 figures, misprints correcte

    Effect of magnetism and temperature on the stability of (Cr-x, V1-x)(2)AlC phases

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    The stability of (Crx,V1-x)2AlC MAX phases, materials of interest for a variety of magnetic as well as high temperature applications, has been studied using density-functional-theory first-principles calculations. The enthalpy of mixing predicts these alloys to be unstable towards unmixing at 0 K. The calculations also predict, however, that these phases would be thermally stabilised by configurational entropy at temperatures well below the values used for synthesis. The temperature Ts below which they become unstable is found to be quite sensitive to the presence of magnetic moments on Cr ions, as well as to the material’s magnetic order, in addition to chemical order and composition. Allowing for magnetism, the value of Ts for (Cr0.5,V0.5)2AlC with chemically disordered Cr and V atoms, is estimated to be between 516 K and 645 K depending on the level of theory, while if constrained to spin-paired, Ts drops to 142 K. Antiferromagnetic spin arrangements are found to be favored. The combination of antiferromagnetic frustration and configurational disorder should give rise to interesting spin textures at low temperatures

    The moral muteness of managers: an Anglo-American phenomenon? German and British managers and their moral reasoning about environmental sustainability in business

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    Several studies in the Anglo-American context have indicated that managers present themselves as morally neutral employees who act only in the best interest of the company by employing objective skills. The reluctance of managers to use moral arguments in business is further accentuated in the now common argument presented as a neutral fact that the company must always prioritise shareholder value. These and other commercial aims are seen as an objective reality in business, whilst questions about sustainability, environmental problems or fair trade are seen as emotional or moral ones; a phenomenon described as ‘moral muteness’. This research explores whether this ‘moral muteness’ is an Anglo-American phenomenon and/or whether managers in other countries - in this case Germany - might express themselves in a different way. The focus is on moral arguments around environmental sustainability and the implications of this study for cross-cultural management. This article is based on a qualitative, comparative cross-cultural study of British and German managers in the Food Retail and Energy Sectors. In line with the studies mentioned above, British managers placed a strong emphasis on their moral neutrality. In contrast, German managers tended to use moral arguments when discussing corporate greening, often giving such arguments more weight than financial arguments. Overall, the study suggests that the ‘moral muteness’ of managers is a British phenomenon and quite distinct from the German approach. The article ends in a short exploration of how this understanding can help managers better manage people, organisations and change across cultures

    Geometric characterization of nodal domains: the area-to-perimeter ratio

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    In an attempt to characterize the distribution of forms and shapes of nodal domains in wave functions, we define a geometric parameter - the ratio ρ\rho between the area of a domain and its perimeter, measured in units of the wavelength 1/E1/\sqrt{E}. We show that the distribution function P(ρ)P(\rho) can distinguish between domains in which the classical dynamics is regular or chaotic. For separable surfaces, we compute the limiting distribution, and show that it is supported by an interval, which is independent of the properties of the surface. In systems which are chaotic, or in random-waves, the area-to-perimeter distribution has substantially different features which we study numerically. We compare the features of the distribution for chaotic wave functions with the predictions of the percolation model to find agreement, but only for nodal domains which are big with respect to the wavelength scale. This work is also closely related to, and provides a new point of view on isoperimetric inequalities.Comment: 22 pages, 11 figure

    Reproductive period and preclinical cerebrospinal fluid markers for Alzheimer disease: a 25-year study

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    OBJECTIVE: The aim of the study was to examine the association between reproductive period, as an indicator of endogenous estrogen, and levels of cerebrospinal fluid (CSF) biomarkers for Alzheimer disease (AD). METHODS: A population-based sample of women from Gothenburg, Sweden was followed from 1968 to 1994 (N = 75). All women had natural menopause and were free from dementia. Information on reproductive period (age at menarche to age at menopause) was obtained from interviews from 1968 to 1980. Lumbar puncture was performed from 1992 to 1994 and CSF levels of Aβ42, Aβ40, P-tau, and T-tau were measured with immunochemical methods. Linear regression models adjusted for potential confounders were used to analyze the relationship between reproductive period and CSF biomarkers for AD. RESULTS: Longer reproductive period was associated with lower levels of Aβ42 (β = -19.2, P  = 0.01), higher levels of P-tau (β = 0.03, P  = 0.01), and lower ratio of Aβ42/Aβ40 (β = -0.02, P  = 0.01), while no association was observed for T-tau (β = 0.01, P  = 0.46). In separate analyses, examining the different components of reproductive period, earlier age at menarche was associated higher levels of P-tau (β = -0.07, P  = 0.031) and lower ratio of Aβ42/Aβ40 (β = 0.05, P  = 0.021), whereas no association was observed with Aβ42 (β = 31.1, P  = 0.11) and T-tau (β = -0.001, P  = 0.98). Furthermore, no association was observed between age at menopause and CSF biomarkers for AD. CONCLUSIONS: Our findings suggest that longer exposure to endogenous estrogen may be associated with increased levels of AD biomarkers in the preclinical phase of AD. These findings, however, need to be confirmed in larger samples. / Video Summary: http://links.lww.com/MENO/A804

    Expanding the reflexive space: resilient young adults, institutional cultures, and cognitive schemas

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    For many U.S. young adults, being resilient to stressful events hinges on making meaning of such events and thereby minimizing their negative emotional impact. Yet why are some better able to do this than others? In this study, which uses an innovative outlier sampling strategy and linked survey and interview data, we argue that one important factor is connection to institutional cultures associated with higher education, religion/spirituality, and the military. Such cultures provide material for the development of cognitive schemas that can be adopted and applied to their stressful experiences, which include narratives of social progress, divine providence, and self‐discipline. Using a metaphor adapted from the pragmatist philosopher Charles Sanders Peirce, we argue the resulting schemas have the effect of “expanding the space” of reflexive thought, providing new cognitive material for interpreting stress and supporting resilience. Finally, we argue this framing improves in several ways on the concept of meaning making often used in stress process research.Accepted manuscrip

    Paradox as invitation to act in problematic change situations

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    It has been argued that organizational life typically contains paradoxical situations such as efforts to manage change which nonetheless seem to reinforce inertia. Four logical options for coping with paradox have been explicated, three of which seek resolution and one of which ‘keeps the paradox open’. The purpose of this article is to explore the potential for managerial action where the paradox is held open through the use of theory on ‘serious playfulness’. Our argument is that paradoxes, as intrinsic features in organizational life, cannot always be resolved through cognitive processes. What may be possible, however, is that such paradoxes are transformed, or ‘moved on’ through action and as a result the overall change effort need not be stalled by the existence of embedded paradoxes

    Polygenic risk scores for Alzheimer's disease are related to dementia risk in APOE ɛ4 negatives

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    Introduction: Studies examining the effect of polygenic risk scores (PRS) for Alzheimer's disease (AD) and apolipoprotein E (APOE) genotype on incident dementia in very old individuals are lacking. / Methods: A population‐based sample of 2052 individuals ages 70 to 111, from Sweden, was followed in relation to dementia. AD‐PRSs including 39, 57, 1333, and 13,942 single nucleotide polymorphisms (SNPs) were used. / Results: AD‐PRSs (including 39 or 57 SNPs) were associated with dementia (57‐SNPs AD‐PRS: hazard ratio 1.09, confidence interval 1.01–1.19, P = .03), particularly in APOE ɛ4 non‐carriers (57‐SNPs AD‐PRS: 1.15, 1.05–1.27, P = 4 × 10–3, 39‐SNPs AD‐PRS: 1.22, 1.10–1.35, P = 2 × 10–4). No association was found with the other AD‐PRSs. Further, APOE ɛ4 was associated with increased risk of dementia (1.60, 1.35–1.92, P = 1 × 10–7). In those aged ≥95 years, the results were similar for the AD‐PRSs, while APOE ɛ4 only predicted dementia in the low‐risk tertile of AD‐PRSs. / Discussion: These results provide information to identify individuals at increased risk of dementia
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