10,476 research outputs found
Near Critical States of Random Dirac Fermions
Random Dirac fermions in a two-dimensional space are studied numerically. We
realize them on a square lattice using the -flux model with random
hopping. The system preserves two symmetries, the time-reversal symmetry and
the symmetry denoted by with a matrix in an effective field theory. Although it belongs to the orthogonal ensemble,
the zero-energy states do not localize and become critical. The density of
states vanishes at zero energy as and the exponent
changes with strength of the randomness, which implies the existence of the
critical line. Rapid growth of the localization length near zero energy is
suggested and the eigenstates near zero energy exhibit anomalous behaviour
which can be interpreted as a critical slowing down in the available
finite-size system. The level-spacing distributions close to zero energy
deviate from both the Wigner surmise and the Poissonian, and exhibit critical
behaviour which reflects the existence of critical states at zero energy.Comment: latex209, REVTEX, 6 figure
Optimum design of magnetic field environment for axonal growth control in nerve cell regeneration process using electromagnetic field analyses
In this study, an optimum magnetic field environment for the nerve axonal extension and control of axonal growth direction in the nerve cell generation process was searched by using electromagnetic finite element analyses. Recently, the developments of 3D-scaffold structures employing biodegradable polymers have been an attracting attention for the clinical treatments of damaged nerve tissues. The magnetic stimulation is introduced to accelerate the regeneration speed of nerve axon inside the 3D-scaffold. According to experimental observation of Blackman, C.F. and his research group (1993) [1], it was found that 50 Hz AC magnetic field has promoted the regeneration of axonal extension in the case of pheochromocytoma cells (PC12). They identified the optimum configuration of the coil and the threshold value of driving current for the initiation of PC12 axon growth. However, they did not evaluate analytically the magnetic flux density and the magnetic field in the cell culture liquid for the PC12 axon growth initiation. Therefore, at first we employed the electromagnetic finite element analyses (FEA) to evaluate the magnetic flux density in the case of Blackman’s experiment. Simultaneously, we identified the relative magnetic permeability of Dulbecco’s Modified Eagle Medium (DMEM) as 1.01 at 50 Hz. Finally, we obtained the value of magnetic flux density inside DMEM as 4.2 T. Next, we try to design the configuration of Helmholtz coil, which can generate an optimum magnetic field to stimulate most effectively for PC12 axon extension. It is confirmed that the magnetic field gradient affect the extensional speed of PC12 axon, which can be achieved by setup the one peripheral coil and two coils at the center. We found an optimum configuration of Helmholtz coil to generate the magnetic field environment and fabricate an experimental bioreactor for PC12 cell culture. We examined the effectiveness of magnetic stimulation for PC12 nerve axon’s extension quantitatively. Further, we try to find the relationship between the magnetic field gradient and the direction of nerve axon’s extension
Correlation effects on the Fermi surface of the two-dimensional Hubbard model
Effects of electron correlation on the Fermi surface is investigated for the
two-dimensional Hubbard model by the quantum Monte Carlo method. At first, an
infinitesimal doping from the half filling is focused on and the momentum
dependent charge susceptibility is calculated
at a finite temperature. At the temperature , it shows
peak structure at on the Fermi surface (line). It is
consistent with the mean-field prediction of the d-wave pairing state or the
staggerd flux state. This momentum dependent structure disappears at the high
temperature . After summarizing the results of the half filling
case, we also discuss the effects of the doping on the momentum dependent
charge susceptibility. The anisotropic structure at half filling fades out with
sufficient doping.Comment: 6 pages, 3 figures; proceedings of ISSP
Reconstruction of the spontaneously broken gauge theory in non-commutative geometry
The scheme previously proposed by the present authors is modified to
incorporate the strong interaction by affording the direct product internal
symmetry. We do not need to prepare the extra discrete space for the color
gauge group responsible for the strong interaction to reconstruct the standard
model and the left-right symmetric gauge model(LRSM). The approach based on
non-commutative geometry leads us to presents many attractive points such as
the unified picture of the gauge and Higgs field as the generalized connection
on the discrete space; Minkowski space multipied by N-points discrete space.
This approach leads us to unified picture of gauge and Higgs fields as the
generalized connection. The standard model needs N=2 discrete space for
reconstruction in this formalism. \lr is still alive as a model with the
intermediate symmetry of the spontaneously broken SO(10) grand unified
theory(GUT). N=3 discrete space is needed for the reconstruction of LRSM to
include two Higgs bosons and which are as usual transformed as
(2,2*,0)$ and (1,3,-2) under left-handed SU(2)x right-handed SU(2)x U(1),
respectively. xi is responsible to make the right handed-neutrino Majorana
fermion and so well explains the seesaw mechanism. Up and down quarks have the
different masses through the vacuum expectation value of phi.Comment: 21 page
BRST invariant formulation of spontaneously broken gauge theory in generalized differential geometry
Noncommutative geometry(NCG) on the discrete space successfully reproduces
the Higgs mechanism of the spontaneously broken gauge theory, in which the
Higgs boson field is regarded as a kind of gauge field on the discrete space.
We could construct the generalized differential geometry(GDG) on the discrete
space which is very close to NCG in case of .
GDG is a direct generalization of the differential geometry on the ordinary
manifold into the discrete one. In this paper, we attempt to construct the BRST
invariant formulation of spontaneously broken gauge theory based on GDG and
obtain the BRST invariant Lagrangian with the t'Hooft-Feynman gauge fixing
term.Comment: 15 page
Exact Results on Superconductivity due to Interband Coupling
We present a family of exactly solvable models at arbitrary filling in any
dimensions which exhibit novel superconductivity with interband pairing. By the
use of the hidden algebra the Hamiltonians were diagonalized
explicitly. The zero-temperature phase diagrams and the thermodynamic
properties are discussed. Several new properties are revealed which are
different from those of the BCS-type superconductor
Sum Rule of the Hall Conductance in Random Quantum Phase Transition
The Hall conductance of two-dimensional {\it lattice} electrons
with random potential is investigated. The change of due to
randomness is focused on. It is a quantum phase transition where the {\it sum
rule} of plays an important role. By the {\it string} (anyon)
gauge, numerical study becomes possible in sufficiently weak magnetic field
regime which is essential to discuss the floating scenario in the continuum
model. Topological objects in the Bloch wavefunctions, charged vortices, are
obtained explicitly. The anomalous plateau transitions () and the trajectory of delocalized states are discussed.Comment: 7 pages RevTeX, 4 postscript figures, to appear in Physical Review
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