31 research outputs found

    Mode conversion and anomalous transport in Kelvin-Helmholtz vortices and kinetic Alfvén waves at the Earth's magnetopause

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    Observations at the Earth’s magnetopause identify mode conversion from surface to kinetic Alfvén waves at the Alfvén resonance. Kinetic Alfvén waves radiate into the magnetosphere from the resonance with parallel scales up to the order of the geomagnetic field-line length and spectral energy densities obeying a k⊥-2.4 power law. Amplitudes at the Alfvén resonance are sufficient to both demagnetize ions across the magnetopause and provide field-aligned electron bursts. These waves provide diffusive transport across the magnetopause sufficient for boundary layer formation

    A diagnosis of the plasma waves responsible for the explosive energy release of substorm onset

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    During geomagnetic substorms, stored magnetic and plasma thermal energies are explosively converted into plasma kinetic energy. This rapid reconfiguration of Earth’s nightside magnetosphere is manifest in the ionosphere as an auroral display that fills the sky. Progress in understanding of how substorms are initiated is hindered by a lack of quantitative analysis of the single consistent feature of onset; the rapid brightening and structuring of the most equatorward arc in the ionosphere. Here, we exploit state-of-the-art auroral measurements to construct an observational dispersion relation of waves during substorm onset. Further, we use kinetic theory of high-beta plasma to demonstrate that the shear Alfven wave dispersion relation bears remarkable similarity to the auroral dispersion relation. In contrast to prevailing theories of substorm initiation, we demonstrate that auroral beads seen during the majority of substorm onsets are likely the signature of kinetic Alfven waves driven unstable in the high-beta magnetotail

    Ion-scale Electromagnetic Waves in the Inner Heliosphere

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    International audienceUnderstanding the physical processes in the solar wind and corona that actively contribute to heating, acceleration, and dissipation is a primary objective of NASA's Parker Solar Probe (PSP) mission. Observations of circularly polarized electromagnetic waves at ion scales suggest that cyclotron resonance and wave-particle interactions are dynamically relevant in the inner heliosphere. A wavelet-based statistical study of circularly polarized events in the first perihelion encounter of PSP demonstrates that transverse electromagnetic waves at ion resonant scales are observed in 30-50% of radial field intervals. Average wave amplitudes of approximately 4 nT are measured, while the mean duration of wave events is on the order of 20 s; however, long-duration wave events can exist without interruption on hour-long timescales. Determination of wave vectors suggests propagation parallel/antiparallel to the mean magnetic field. Though ion-scale waves are preferentially observed during intervals with a radial mean magnetic field, we show that measurement constraints, associated with single spacecraft sampling of quasi-parallel waves superposed with anisotropic turbulence, render the measured coherent ion-wave spectrum unobservable when the mean magnetic field is oblique to the solar wind flow; these results imply that the occurrence of coherent ion-scale waves is not limited to a radial field configuration. The lack of radial scaling of characteristic wave amplitudes and duration suggests that the waves are generated in situ through plasma instabilities. Additionally, observations of proton distribution functions indicate that temperature anisotropy may drive the observed ion-scale

    Effects of lifestyle intervention in persons at risk for type 2 diabetes mellitus - results from a randomised, controlled trial

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    Background: Lifestyle change is probably the most important single action to prevent type 2 diabetes mellitus. The purpose of this study was to assess the effects of a low-intensity individual lifestyle intervention by a physician and compare this to the same physician intervention combined with an interdisciplinary, group-based approach in a real-life setting. Methods: The “Finnish Diabetes Risk score” (FINDRISC) was used by GPs to identify individuals at high risk. A randomised, controlled design and an 18 month follow-up was used to assess the effect of individual lifestyle counselling by a physician (individual physician group, (IG)) every six months, with emphasis on diet and exercise, and compare this to the same individual lifestyle counselling combined with a group-based interdisciplinary program (individual and interdisciplinary group, (IIG)) provided over 16 weeks. Primary outcomes were changes in lifestyle indicated by weight reduction ≥ 5%, improvement in exercise capacity as assessed by VO2 max and diet improvements according to the Smart Diet Score (SDS). Results: 213 participants (104 in the IG and 109 in the IIG group, 50% women), with a mean age of 46 and mean body mass index 37, were included (inclusion rate > 91%) of whom 182 returned at follow-up (drop-out rate 15%). There were no significant differences in changes in lifestyle behaviours between the two groups. At baseline 57% (IG) and 53% (IIG) of participants had poor aerobic capacity and after intervention 35% and 33%, respectively, improved their aerobic capacity at least one metabolic equivalent. Unhealthy diets according to SDS were common in both groups at baseline, 61% (IG) and 60% (IIG), but uncommon at follow-up, 17% and 10%, respectively. At least 5% weight loss was achieved by 35% (IG) and 28% (IIG). In the combined IG and IIG group, at least one primary outcome was achieved by 93% while all primary outcomes were achieved by 6%. Most successful was the 78% reduction in the proportion of participants with unhealthy diet (almost 50% absolute reduction). Conclusion: It is possible to achieve important lifestyle changes in persons at risk for type 2 diabetes with modest clinical efforts. Group intervention yields no additional effects. The design of the study, with high inclusion and low dropout rates, should make the results applicable to ordinary clinical settings

    Highly structured slow solar wind emerging from an equatorial coronal hole

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    International audienceDuring the solar minimum, when the Sun is at its least active, the solar wind(1,2) is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvenic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind(3) of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain(4); theories and observations suggest that they may originate at the tips of helmet streamers(5,6), from interchange reconnection near coronal hole boundaries(7,8), or within coronal holes with highly diverging magnetic fields(9,10). The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfven-wave turbulence(11,12), heating by reconnection in nanoflares(13), ion cyclotron wave heating(14) and acceleration by thermal gradients1. At a distance of one astronomical unit, the wind is mixed and evolved, and therefore much of the diagnostic structure of these sources and processes has been lost. Here we present observations from the Parker Solar Probe(15) at 36 to 54 solar radii that show evidence of slow Alfvenic solar wind emerging from a small equatorial coronal hole. The measured magnetic field exhibits patches of large, intermittent reversals that are associated with jets of plasma and enhanced Poynting flux and that are interspersed in a smoother and less turbulent flow with a near-radial magnetic field. Furthermore, plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities(10,16) that are associated with plasma heating and thermalization processes. Our measurements suggest that there is an impulsive mechanism associated with solar-wind energization and that micro-instabilities play a part in heating, and we provide evidence that low-latitude coronal holes are a key source of the slow solar wind

    Satellite Observations of Separator Line Geometry of Three-Dimensional Magnetic Reconnection

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    Detection of a separator line that connects magnetic nulls and the determination of the dynamics and plasma environment of such a structure can improve our understanding of the three-dimensional (3D) magnetic reconnection process. However, this type of field and particle configuration has not been directly observed in space plasmas. Here we report the identification of a pair of nulls, the null-null line that connects them, and associated fans and spines in the magnetotail of Earth using data from the four Cluster spacecraft. With di and de designating the ion and electron inertial lengths, respectively, the separation between the nulls is found to be ~0.7di and an associated oscillation is identified as a lower hybrid wave with wavelength ~ de. This in situ evidence of the full 3D reconnection geometry and associated dynamics provides an important step toward to establishing an observational framework of 3D reconnection.Comment: 10 pages, 3 figures and 1 tabl

    International entrepreneurship in SMEs: a study of influencing factors in the textile industry

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    The final publication is available at Springer via http://dx.doi.org/10.1007/s11365-012-0242-3International entrepreneurship is an incipient research area with a rapidly increasing body of knowledge and contributions. An important part of this literature has focused on the analysis of the contributing factors to IE development. From these studies, this work attempts to analyse and validate through an integrative model the effect on this construct in SME of some of the main factors proposed by the literature such as Skills and Competences, Attitude and Proactiveness, Creativity and Innovation, Networking, Employees and Activity. To proceed with this aim, we conducted an empirical research focused on 174 textile SME in Spain. The results obtained confirm a positive relationship between the studied factors and the IE development. 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