3,434 research outputs found
Brownian molecular motors driven by rotation-translation coupling
We investigated three models of Brownian motors which convert rotational
diffusion into directed translational motion by switching on and off a
potential. In the first model a spatially asymmetric potential generates
directed translational motion by rectifying rotational diffusion. It behaves
much like a conventional flashing ratchet. The second model utilizes both
rotational diffusion and drift to generate translational motion without spatial
asymmetry in the potential. This second model can be driven by a combination of
a Brownian motor mechanism (diffusion driven) or by powerstroke (drift driven)
depending on the chosen parameters. In the third model, elements of both the
Brownian motor and powerstroke mechanisms are combined by switching between
three distinct states. Relevance of the model to biological motor proteins is
discussed.Comment: 11 pages, 8 figure
A Microscopic Mechanism for Muscle's Motion
The SIRM (Stochastic Inclined Rods Model) proposed by H. Matsuura and M.
Nakano can explain the muscle's motion perfectly, but the intermolecular
potential between myosin head and G-actin is too simple and only repulsive
potential is considered. In this paper we study the SIRM with different complex
potential and discuss the effect of the spring on the system. The calculation
results show that the spring, the effective radius of the G-actin and the
intermolecular potential play key roles in the motion. The sliding speed is
about calculated from the model which well agrees with
the experimental data.Comment: 9 pages, 6 figure
Pressure-temperature phase diagram of ferromagnetic superconductors
The symmetry approach to the description of the (P,T) phase diagram of
ferromagnet superconductors with triplet pairing is developed. Taking into
account the recent experimental observations made on UCoGe it is considered the
case of a crystal with orthorhombic structure and strong spin-orbital coupling.
It is shown that formation of ferromagnet superconducting state from a
superconducting state is inevitably accompanied by the first order type
transition.Comment: 4 pages, 1 figur
Force Dependence of the Michaelis Constant in a Two-State Ratchet Model for Molecular Motors
We present a quantitative analysis of recent data on the kinetics of ATP
hydrolysis, which has presented a puzzle regarding the load dependence of the
Michaelis constant. Within the framework of coarse grained two-state ratchet
models, our analysis not only explains the puzzling data, but provides a
modified Michaelis law, which could be useful as a guide for future
experiments.Comment: 4 pages, 3 eps figures, accepted for publication on Physical Review
Letter
Theoretical Study on Coexistence of Ferromagnetism and Superconductivity
On the basis of a two-dimensional t-t' Hubbard model in ferromagnetic and
paramagnetic states, the triplet superconducting mechanism is investigated by
the third-order perturbation theory with respect to the on-site Coulomb
interaction U. In general, the superconducting state is more stable in the
paramagnetic state than in the ferromagnetic state. As a special case, the
dominant ferromagnetic superconductivity is obtained by the electron-electron
correlation between the electronlike majority and holelike minority bands.
Furthermore, it is pointed out that in some cases the two bands play an
essential role for the coexistence of superconductivity and ferromagnetism.Comment: 5 pages, 10 figure
The Magnetic Phase Diagram and the Pressure and Field Dependence of the Fermi Surface in UGe
The ac susceptibility and de Haas-van Alphen (dHvA) effect in UGe are
measured at pressures {\it P} up to 17.7 kbar for the magnetic field {\it B}
parallel to the {\it a} axis, which is the easy axis of magnetization. Two
anomalies are observed at {\it B}({\it P}) and {\it B}({\it P}) ({\it
B} {\it B} at any {\it P}), and the {\it P}-{\it B} phase diagram
is presented. The Fermi surface and quasiparticle mass are found to vary
smoothly with pressure up to 17.7 kbar unless the phase boundary {\it
B}({\it P}) is crossed. The observed dHvA frequencies may be grouped into
three according to their pressure dependences, which are largely positive,
nearly constant or negative. It is suggested that the quasiparticle mass
moderately increases as the boundary {\it B}({\it P}) is approached. DHvA
effect measurements are also performed across the boundary at 16.8 kbar.Comment: to be published in Phys. Rev.
One dimensional chain of quantum molecule motors as a mathematical physics model for muscle fibre
A quantum chain model of many molecule motors is proposed as a mathematical
physics theory on the microscopic modeling of classical force-velocity relation
and tension transients of muscle fibre. We proposed quantum many-particle
Hamiltonian to predict the force-velocity relation for the slow release of
muscle fibre which has no empirical relation yet, it is much more complicate
than hyperbolic relation. Using the same Hamiltonian, we predicted the
mathematical force-velocity relation when the muscle is stimulated by
alternative electric current. The discrepancy between input electric frequency
and the muscle oscillation frequency has a physical understanding by Doppler
effect in this quantum chain model. Further more, we apply quantum physics
phenomena to explore the tension time course of cardiac muscle and insect
flight muscle. Most of the experimental tension transients curves found their
correspondence in the theoretical output of quantum two-level and three-level
model. Mathematically modeling electric stimulus as photons exciting a quantum
three-level particle reproduced most tension transient curves of water bug
Lethocerus Maximus.Comment: 16 pages, 12 figures, Arguments are adde
Equilibrium magnetisation structures in ferromagnetic nanorings
The ground state of the ring-shape magnetic nanoparticle is studied.
Depending on the geometrical and magnetic parameters of the nanoring, there
exist different magnetisation configurations (magnetic phases): two phases with
homogeneous magnetisation (easy-axis and easy-plane phases) and two
inhomogeneous (planar vortex phase and out-of-plane one). The existence of a
new intermediate out-of-plane vortex phase, where the inner magnetisation is
not strongly parallel to the easy axis, is predicted. Possible transitions
between different phases are analysed using the combination of analytical
calculations and micromagnetic simulations.Comment: LaTeX, 19 pages, 11 figure
Ferromagnetic Quantum Critical Fluctuations and Anomalous Coexistence of Ferromagnetism and Superconductivity in UCoGe Revealed by Co-NMR and NQR Studies
Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)
studies were performed in the recently discovered UCoGe, in which the
ferromagnetic and superconducting (SC) transitions were reported to occur at
K and K (N. T. Huy {\it et al.}, Phys.
Rev. Lett. {\bf 99} (2007) 067006), in order to investigate the coexistence of
ferromagnetism and superconductivity as well as the normal-state and SC
properties from a microscopic point of view. From the nuclear spin-lattice
relaxation rate and Knight-shift measurements, we confirmed that
ferromagnetic fluctuations which possess a quantum critical character are
present above and the occurrence of ferromagnetic transition at
2.5 K in our polycrystalline sample. The magnetic fluctuations in the normal
state show that UCoGe is an itinerant ferromagnet similar to ZrZn and
YCo. The onset SC transition was identified at K, below
which of 30 % of the volume fraction starts to decrease due to the
opening of the SC gap. This component of , which follows a
dependence in the temperature range of K, coexists with the
magnetic components of showing a dependence below .
From the NQR measurements in the SC state, we suggest that the self-induced
vortex state is realized in UCoGe.Comment: 5 pages, 7 figures. submitted to J. Phys. Soc. Jpn. To appear in J.
Phys. Soc. Jp
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