2,357 research outputs found

    Theoretical models for MHD turbulence in the solar wind

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    The in situ measurements of velocity, magnetic field, density and temperature fluctuations performed in the solar wind have greatly improved our knowledge of MHD turbulence not only from the point of view of space physics but also from the more general point of view of plasma physics. These fluctuations which extend over a wide range of frequencies (about 5 decades), a fact which seems to be the signature of turbulent nonlinear energy cascade, display, mainly in the trailing edge of high-speed streams, a number of features characteristic of a self-organized situation: i) a high degree of correlation between magnetic and velocity field fluctuations, ii) a very low level of fluctuations in mass density and magnetic-field intensity, iii) a considerable anisotropy revealed by minimum variance analysis of the magnetic-field correlation tensor. Many fundamental processes in plasma physics, which were largely unknown or not understood before their observations in the solar wind, have been explained, by building up analytical models or performing numerical simulations. We discuss the most recent analytical theories and numerical simulations and outline the limits implicit in any analysis which consider the low-frequency solar-wind fluctuations as a superposition of linear modes. The characterization of low-frequency fluctuations during Alfv´enic periods, which results from the models discussed, is finally presented

    Nonlinear evolution of the parametric instability: numerical predictions versus observations in the heliosphere

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    International audienceLow-frequency turbulence in the solar wind is characterized by a high degree of Alfvénicity close to the Sun. Cross-helicity, which is a measure of Alfvénic correlation, tends to decrease with increasing distance from the Sun at high latitudes as well as in slow-speed streams at low latitudes. In the latter case, large scale inhomogeneities (velocity shears, the heliospheric current sheet) are present, which are sources of decorrelation; yet at high latitudes, the wind is much more homogeneous, and a possible evolution mechanism is represented by the parametric instability. The parametric decay of an circularly polarized broadband Alfvén wave is then investigated, as a source of decorrelation. The time evolution is followed by numerically integrating the full set of nonlinear MHD equations, up to instability saturation. We find that, for ~ 1, the final cross-helicity is ~ 0.5, corresponding to a partial depletion of the initial correlation. Compressive fluctuations at a moderate level are also present. Most of the spectrum is dominated by forward propagating Alfvénic fluctuations, while backscattered fluctuations dominate large scales. With increasing time, the spectra of Elsässer variables tend to approach each other. Some results concerning quantities measured in the high-latitude wind are reviewed, and a qualitative agreement with the results of the numerical model is found

    Dissipation of Alfven waves in compressible inhomogeneous media

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    In weakly dissipative media governed by the magnetohydrodynamics (MHD) equations, any efficient mechanism of energy dissipation requires the formation of small scales. Using numerical simulations, we study the properties of Alfv´en waves propagating in a compressible inhomegeneous medium, with an inhomogeneity transverse to the direction of wave propagation. Two dynamical effects, energy pinching and phase mixing, are responsible for the small-scales formation, similarly to the incompressible case. Moreover, compressive perturbations, slow waves and a static entropy wave are generated; the former are subject to steepening and form shock waves, which efficiently dissipate their energy, regardless of the Reynolds number. Rough estimates show that the dissipation times are consistent with those required to dissipate Alfv´en waves of photospheric origin inside the solar corona

    On the probability distribution function of small scale interplanetary magnetic field fluctuations

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    In spite of a large number of papers dedicated to study MHD turbulence in the solar wind there are still some simple questions which have never been sufficiently addressed like: a)do we really know how the magnetic field vector orientation fluctuates in space? b) what is the statistics followed by the orientation of the vector itself? c) does the statistics change as the wind expands into the interplanetary space? A better understanding of these points can help us to better characterize the nature of interplanetary fluctuations and can provide useful hints to investigators who try to numerically simulate MHD turbulence. This work follows a recent paper presented by the same authors. This work follows a recent paper presented by some of the authors which shows that these fluctuations might resemble a sort of random walk governed by a Truncated Leevy Flight statistics. However, the limited statistics used in that paper did not allow final conclusions but only speculative hypotheses. In this work we aim to address the same problem using a more robust statistics which on one hand forces us not to consider velocity fluctuations but, on the other hand allows us to establish the nature of the governing statistics of magnetic fluctuations with more confidence. In addition, we show how features similar to those found in the present statistical analysis for the fast speed streams of solar wind, are qualitatively recovered in numerical simulations of the parametric instability. This might offer an alternative viewpoint for interpreting the questions raised above.Comment: 25pag, 20 jpg small size figures. In press on "ANnales Geophysicae" (September 2004

    Hubungan Penggunaan Helm Dengan Derajat Cedera Kepala Akibat Kecelakaan Lalu Lintas Darat Di Rsup. Prof. Dr. R. D. Kandou Manado Dan RS. Bhayangkara Tk. III Manado

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    : Head injury is a traumatic disruption of brain function with or without bleeding in the brain substance interstiil without being followed by the dissolution of the continuity of the brain. Helmets worn to protect the head of motorcycle users in order to avoid a collision with the road in the fall or slip. Helmets are intended to reduce the risk of severe head and brain injuries by reducing the influence of the force of the collision the head. The purpose of research for the use of helmets relationship with the degree of head injuries caused by traffic accidents ashore in the department of Prof. Dr. R. D. Kandou RS Bhayangkara TK.III Manado Manado. The study design using analytic observational with cross sectional approach. The sampling technique is calculated by the formula Lemeshow for cross-sectional study using the proportion of head injuries in North Sulawasi of 10% was obtained 139 respondents. The research instrument used questionnaire. The data were analyzed using the Spearman test at 95% significance level (α <0.05). The results were obtained value of P = 0.017. Conclusion There Helmet Usage Relationships With Head Injuries Degrees Traffic Accident In the Army Hospital. Prof. Dr. R. D. Kandou Manado and RS. Bhayangkara TK.III Manado

    Hubungan Dukungan Emosional Keluarga Dengan Penerimaan Diri Pada Lansia Di Desa Watutumou III

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    : Family support is a form of servant behavior performed by the family both in the form of emotional support, awards, information and instrumental. Self-acceptance of the elderly is a high appreciation or not being cynical about self-relating to the elderly's willingness to open up or express thoughts, feelings, and reactions to others and able to accept his shortcomings as well as his ability to accept the advantages. The purpose of this study to analyze The relationship between the emotional support of the family and the self-acceptance of the elderly in Watutumou Village III. The research method is analytical descriptive with cross sectional design. The sampling technique in this study is purposive sampling with the sample number of 60 respondents.The data collection is done by using a questionnaire and interview sheet. Processing data using computer program with Pearson chi-square test with a significance level of 95% (α =, 005). The results of this study using pearson chi-square analysis showed that there was a relationship between the emotional support of the family and the self-acceptance of the elderly in Watutumou III Village (p = 0,000). Conclusion There is a relationship between the emotional support of the family with self-acceptance in the elderly in Watutumou Village III

    Faktor-faktor Yang Berhubungan Dengan Kekambuhan Penyakit Rematik Di Wilayah Puskesmas Beo Kabupaten Talaud

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    : Rheumatic is a chronic systemic inflammatory disease that attacks the joints, especially the synovialjoints. Factors that can cause the occurrence of rheumatic recurrence is the level of knowledge, work / activityand diet.The Purpose of this research was to knowing the factors related to the recurrence of rheumaticdiseases in Community Health Center Beo District Talaud. Design Research used cross sectional study whichthe data related to independent variable or risk and independent variable consequence collated in the sametime. Tehnique Sampling that is total sampling is 32 samples. Statistical Test Result Chi-Square test withconfidence level of 95% (a = 0,05) and obtained p value 0,002 < 0,05 and 0,004 < 0,05 and p value 0,017 <0,05. Conclussion there are correlation factors the level of knowledge, work / activity and eating patterns withthe recurrence of rheumatic diseases in Community Health Center Beo District Talaud
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