2,508 research outputs found
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
A scanning drift tube apparatus for spatio-temporal mapping of electron swarms
A "scanning" drift tube apparatus, capable of mapping of the spatio-temporal
evolution of electron swarms, developing between two plane electrodes under the
effect of a homogeneous electric field, is presented. The electron swarms are
initiated by photoelectron pulses and the temporal distributions of the
electron flux are recorded while the electrode gap length (at a fixed electric
field strength) is varied. Operation of the system is tested and verified with
argon gas, the measured data are used for the evaluation of the electron bulk
drift velocity. The experimental results for the space-time maps of the
electron swarms - presented here for the first time - also allow clear
observation of deviations from hydrodynamic transport. The swarm maps are also
reproduced by particle simulations
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.
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
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
Drying and cracking mechanisms in a starch slurry
Starch-water slurries are commonly used to study fracture dynamics. Drying
starch-cakes benefit from being simple, economical, and reproducible systems,
and have been used to model desiccation fracture in soils, thin film fracture
in paint, and columnar joints in lava. In this paper, the physical properties
of starch-water mixtures are studied, and used to interpret and develop a
multiphase transport model of drying. Starch-cakes are observed to have a
nonlinear elastic modulus, and a desiccation strain that is comparable to that
generated by their maximum achievable capillary pressure. It is shown that a
large material porosity is divided between pore spaces between starch grains,
and pores within starch grains. This division of pore space leads to two
distinct drying regimes, controlled by liquid and vapor transport of water,
respectively. The relatively unique ability for drying starch to generate
columnar fracture patterns is shown to be linked to the unusually strong
separation of these two transport mechanisms.Comment: 9 pages, 8 figures [revised in response to reviewer comments
Drying and cracking mechanisms in a starch slurry
Starch-water slurries are commonly used to study fracture dynamics. Drying
starch-cakes benefit from being simple, economical, and reproducible systems,
and have been used to model desiccation fracture in soils, thin film fracture
in paint, and columnar joints in lava. In this paper, the physical properties
of starch-water mixtures are studied, and used to interpret and develop a
multiphase transport model of drying. Starch-cakes are observed to have a
nonlinear elastic modulus, and a desiccation strain that is comparable to that
generated by their maximum achievable capillary pressure. It is shown that a
large material porosity is divided between pore spaces between starch grains,
and pores within starch grains. This division of pore space leads to two
distinct drying regimes, controlled by liquid and vapor transport of water,
respectively. The relatively unique ability for drying starch to generate
columnar fracture patterns is shown to be linked to the unusually strong
separation of these two transport mechanisms.Comment: 9 pages, 8 figures [revised in response to reviewer comments
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
Cosmic ray tests of a GEM-based TPC prototype operated in Ar-CF4-isobutane gas mixtures
Argon with an admixture of CF4 is expected to be a good candidate for the gas
mixture to be used for a time projection chamber (TPC) in the future linear
collider experiment because of its small transverse diffusion of drift
electrons especially under a strong magnetic field. In order to confirm the
superiority of this gas mixture over conventional TPC gases we carried out
cosmic ray tests using a GEM-based TPC operated mostly in Ar-CF4-isobutane
mixtures under 0 - 1 T axial magnetic fields. The measured gas properties such
as gas gain and transverse diffusion constant as well as the observed spatial
resolution are presented.Comment: 22 pages, 18 figures. Published in Nuclear Instruments and Methods in
Physics Research A. Fig. 3 in the introduction was corrected since it had not
been properly normalized. Minor corrections and no changes in the conclusio
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