807 research outputs found

    Nonlocal incoherent solitons

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    We investigate the propagation of partially coherent beams in spatially nonlocal nonlinear media with a logarithmic type of nonlinearity. We derive analytical formulas for the evolution of the beam parameters and conditions for the formation of nonlocal incoherent solitons.Comment: 5 pages, 3 figure

    Generic features of modulational instability in nonlocal Kerr media

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    The modulational instability (MI) of plane waves in nonlocal Kerr media is studied for a general, localized, response function. It is shown that there always exists a finite number of well-separated MI gain bands, with each of them characterised by a unique maximal growth rate. This is a general property and is demonstrated here for the Gaussian, exponential, and rectangular response functions. In case of a focusing nonlinearity it is shown that although the nonlocality tends to suppress MI, it can never remove it completely, irrespectively of the particular shape of the response function. For a defocusing nonlinearity the stability properties depend sensitively on the profile of the response function. It is shown that plane waves are always stable for response functions with a positive-definite spectrum, such as Gaussians and exponentials. On the other hand, response functions whose spectra change sign (e.g., rectangular) will lead to MI in the high wavenumber regime, provided the typical length scale of the response function exceeds a certain threshold. Finally, we address the case of generalized multi-component response functions consisting of a weighted sum of N response functions with known properties.Comment: 9 pages, 5 figure

    Decolonial Counter-conducts? Traces of Decentering Migrant Ecclesiologies

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    Decolonialisation concerns theology. As long as theology is preoccupied with engaging or explaining the other, it is not a decolonial project. As such this article makes a connection to Walter Mignolo’s claim that the researcher as much as the subject needs to be interrogated as part of the research in order to disrupt the subject/ object binary of colonial knowledge traditions. The main part of the article presents three narratives from the life of Nisha, a refugee woman from the DRC living in a South African township. The narratives also involve a researcher – I, the professor – and the pastor and gatekeeper that introduced Nisha to me. In all of the narratives, the two traditional subjects (professor and pastor) are decentered. Nisha makes money trading from a small kiosk, and she invites the two men to a meal at her township house. She walks the pastor and the professor through the neighborhood where she lives. Building on Michel Foucault`s theories of counter-conducts, the article argues that the three decentering narratives present Nisha’s everyday practices as counter-conducts and the two men as the decentered others. The article argues that such a decentering performs traces of a decolonialising theology. God is the one that lets hierarchy decenter in order to open spaces of others

    Structural and spectral studies of sunspots

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    Observations of umbral cores, both by multicolor photometry and by narrow band photometry in the vicinity of the sodium D lines, are described, and evidence is given which supports the validity of many umbral models, each of which describes different aspects of the observed umbral cores. Theoretical studies carried on at the observatory include the following: (1) Zeeman profiles of the sodium D sub 2 line and other lines; (2) turbulent heat conduction, sound waves, and the missing flux in sunspots; (3) chromospheric heating above spots by Alfven waves; (4) magnetic convection in the sun and solar neutrinos; (5) models of starspots on flare stars; (5) starspots on the primaries of contact binary systems; and (6) implications of starspots on red dwarfs

    No differences in cardiovascular autonomic responses to mental stress in chronic fatigue syndrome adolescents as compared to healthy controls

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    Chronic fatigue syndrome (CFS) is a disabling disease with unknown etiology. There is accumulating evidence of altered cardiovascular autonomic responses to different somatic stressors, in particular orthostatic stress, whereas autonomic responses to mental stress remain to be investigated. In this study, we explored cardiovascular autonomic responses to a simple mental stress test in CFS patients and healthy controls

    Structural and Spectral Studies of Sunspots

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    Instrumentation and solar observations at Bartol Observator

    Reduced Sympathetic Response to Head-Up Tilt in Subjects with Mild Cognitive Impairment or Mild Alzheimer's Dementia

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    Background: Hemodynamic control was compared in patients with mild cognitive impairment (MCI) or mild Alzheimer's dementia (AD) as well as in healthy elderly subjects. Methods: Noninvasive, continuous hemodynamic recordings were obtained from 14 patients and 48 controls during supine rest (tilt of 30 and 70°). Cardiac output, end-diastolic volume, total peripheral resistance, heart rate variability (HRV), systolic blood pressure variability (SBPV), and baroreceptor sensitivity were calculated. Results: At 70° tilt, the HRV indices differed significantly, with higher high-frequency (HF) variability as well as lower low-frequency (LF) variability and LF/HF ratios in the patients. The patients had significantly lower SBPV in the LF range at 30° tilt. Conclusions: The results indicate a poorer sympathetic response to orthostatic stress in MCI and mild AD

    Structural and spectral studies of sunspots Annual report, 1 Sep. 1969 - 31 Aug. 1970

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    Structural and spectral studies of sunspot
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