4,225 research outputs found
Energy transfer in two-dimensional magnetohydrodynamic turbulence: formalism and numerical results
The basic entity of nonlinear interaction in Navier-Stokes and the
Magnetohydrodynamic (MHD) equations is a wavenumber triad ({\bf k,p,q})
satisfying . The expression for the combined energy transfer
from two of these wavenumbers to the third wavenumber is known. In this paper
we introduce the idea of an effective energy transfer between a pair of modes
by the mediation of the third mode, and find an expression for it. Then we
apply this formalism to compute the energy transfer in the quasi-steady-state
of two-dimensional MHD turbulence with large-scale kinetic forcing. The
computation of energy fluxes and the energy transfer between different
wavenumber shells is done using the data generated by the pseudo-spectral
direct numerical simulation. The picture of energy flux that emerges is quite
complex---there is a forward cascade of magnetic energy, an inverse cascade of
kinetic energy, a flux of energy from the kinetic to the magnetic field, and a
reverse flux which transfers the energy back to the kinetic from the magnetic.
The energy transfer between different wavenumber shells is also complex---local
and nonlocal transfers often possess opposing features, i.e., energy transfer
between some wavenumber shells occurs from kinetic to magnetic, and between
other wavenumber shells this transfer is reversed. The net transfer of energy
is from kinetic to magnetic. The results obtained from the studies of flux and
shell-to-shell energy transfer are consistent with each other.Comment: 27 pages REVTEX; 14 ps figure
巨大衝突により生じた周惑星円盤からの天王星の衛星形成
京都大学新制・課程博士博士(理学)甲第23007号理博第4684号新制||理||1672(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 嶺重 慎, 准教授 前田 啓一, 教授 太田 耕司学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA
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Panel 3 Paper 3.2: Nature, agriculture and rural resilience: Interdependencies between natural protected areas and rural landscapes in Satoyama/Satoumi in Japan
The Capacity Building Workshops on Nature-Culture Linkages in Heritage Conservation (CBWNCL), held at the University of Tsukuba in Japan, gather Asia-Pacific heritage professionals with the aim of creating a platform of mutual-learning and exchange between the culture and nature sectors. In the first workshop on Agricultural Landscapes, from 14 case studies, 5 showed natural protected areas in tense relations with their rural landscape surroundings. However, these agricultural landscapes are essential for protecting natural values, as they form part of their larger ecosystems. In the second workshop on Sacred Landscapes, from 16 case studies, 5 case studies were also agricultural landscapes, and 8 case studies featured natural protected areas which embody spiritual values for their surrounding rural communities. In the third workshop on Disasters and Resilience, from 15 case studies, 7 presented the struggles faced by rural communities in the conservation of their natural environment and their cultural practices in a context of increasing disasters.
By looking at the Japanese experience, we learned from the concepts of Satoyama and Satoumi, that the protection of nature can be interlinked with the maintenance of agricultural landscapes, that the continuity of spiritual practices is essential for identity and community cohesion, and that the maintenance of cultural practices represent community’s strength for post-disaster recovery. These lessons demonstrated that resilience lies in people and their community networks -beyond human, and underpinned on their natural and cultural heritage (both tangible and intangible)-, and that the stronger these networks are, and the more autonomy and decision-making power is recognized at local level, the higher level of resilience a landscape would show. This finding, however, raises concern, as these landscapes are facing pressures not only from urban development, but mostly from depopulation due to migration and ageing communities, processes that are eroding these networks and consequently, rural landscape resilience
Calculation of renormalized viscosity and resistivity in magnetohydrodynamic turbulence
A self-consistent renormalization (RG) scheme has been applied to nonhelical
magnetohydrodynamic turbulence with normalized cross helicity and
. Kolmogorov's 5/3 powerlaw is assumed in order to compute the
renormalized parameters. It has been shown that the RG fixed point is stable
for . The renormalized viscosity and resistivity
have been calculated, and they are found to be positive for all
parameter regimes. For and large Alfv\'{e}n ratio (ratio of
kinetic and magnetic energies) , and . As
is decreased, increases and decreases, untill where both and are approximately zero. For large ,
both and vary as . The renormalized parameters for
the case are also reported.Comment: 19 pages REVTEX, 3 ps files (Phys. Plasmas, v8, 3945, 2001
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