197 research outputs found
A reformulation of the Ponzano-Regge quantum gravity model in terms of surfaces
We reformulate the Ponzano-Regge quantum gravity model in terms of surfaces
on a 3-dimensional simplex lattice. This formulation (1) has a clear relation
to the loop representation of the canonical quantum general relativity in
3-dimensions, (2) may have a 4-dimensional analogue, in contrast to the 6-j
symbolic formalism of the Ponzano-Regge model, and (3) is purely a theory of
surfaces, in the sense that it does not include any field variables; hence it
is coordinate-free on the surface and background-free in spacetime. We discuss
implications and applications of this formulation.Comment: latex 11 page
Inertia, diffusion and dynamics of a driven skyrmion
Skyrmions recently discovered in chiral magnets are a promising candidate for
magnetic storage devices because of their topological stability, small size
(nm), and ultra-low threshold current density (A/m) to drive their motion. However, the time-dependent dynamics has
hitherto been largely unexplored. Here we show, by combining the numerical
solution of the Landau-Lifshitz-Gilbert equation and the analysis of a
generalized Thiele's equation, that inertial effects are almost completely
absent in skyrmion dynamics driven by a time-dependent current. In contrast,
the response to time-dependent magnetic forces and thermal fluctuations depends
strongly on frequency and is described by a large effective mass and a (anti-)
damping depending on the acceleration of the skyrmion. Thermal diffusion is
strongly suppressed by the cyclotron motion and is proportional to the Gilbert
damping coefficient . This indicates that the skyrmion position is
stable, and its motion responds to the time-dependent current without delay or
retardation even if it is fast. These findings demonstrate the advantages of
skyrmions as information carriers.Comment: 9 pages, 10 figure
Key Interactions in Integrin Ectodomain Responsible for Global Conformational Change Detected by Elastic Network Normal-Mode Analysis
AbstractIntegrin, a membrane protein with a huge extracellular domain, participates in cell-cell and cell-extracellular-matrix interactions for metazoan. A group of integrins is known to perform a large-scale structural change when the protein is activated, but the activation mechanism and generality of the conformational change remain to be elucidated. We performed normal-mode analysis of the elastic network model on integrin αVβ3 ectodomain in the bent form and identified key residues that influenced molecular motions. Iterative normal-mode calculations demonstrated that the specific nonbonded interactions involving the key residues work as a snap to keep integrin in the bent form. The importance of the key residues for the conformational change was further verified by mutation experiments, in which integrin αIIbβ3 was used. The conservation pattern of amino acid residues among the integrin family showed that the characteristic pattern of residues seen around these key residues is found in the limited groups of integrin β-chains. This conservation pattern suggests that the molecular mechanism of the conformational change relying on the interactions found in integrin αVβ3 is unique to the limited types of integrins
磁性体中におけるトポロジカルテクスチャのダイナミクスの研究
学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 永長 直人, 東京大学教授 十倉 好紀, 東京大学教授 川﨑 雅司, 東京大学准教授 千葉 大地, 東京大学准教授 桂 法称University of Tokyo(東京大学
- …