5,872 research outputs found
A molecular dynamics computer simulation study of room-temperature ionic liquids. I. Equilibrium solvation structure and free energetics
Solvation in 1-ethyl-3-methylmidazolium chloride and in
1-ethyl-3-methylimidazolium hexafluorophosphate near equilibrium is
investigated via molecular dynamics computer simulations with diatomic and
benzenelike molecules employed as probe solutes. It is found that
electrostriction plays an important role in both solvation structure and free
energetics. The angular and radial distributions of cations and anions become
more structured and their densities near the solute become enhanced as the
solute charge separation grows. Due to the enhancement in structural rigidity
induced by electrostriction, the force constant associated with solvent
configuration fluctuations relevant to charge shift and transfer processes is
also found to increase. The effective polarity and reorganization free energies
of these ionic liquids are analyzed and compared with those of highly polar
acetonitrile. Their screening behavior of electric charges is also
investigated.Comment: 12 page
Kinematic variations due to changes in pace during men's and women's 5 km road running
The purpose of this study was to investigate variations in kinematic parameters in men's and women's 5 km road racing. Athletes often vary their pace and changes particularly tend to occur towards the end of a race due to fatigue and sprint finishes. Twenty competitive distance runners (10 male, 10 female) were videoed as they completed the English National 5 km championships. Three-dimensional kinematic data were analysed using motion analysis software (SIMI, Munich). Data were recorded at 950 m, 2,400 m and 3,850 m. Repeated measures ANOVA showed significant decreases in speed due to reduced step length and cadence in both men and women. These decreases predominantly occurred between the first two measurement points. The hip, knee, ankle and shoulder angles at both initial contact and toe-off did not change significantly, but there were significant reductions in the elbow angle for both men (at initial contact) and women (at toe-off)
Analytic study of the urn model for separation of sand
We present an analytic study of the urn model for separation of sand recently
introduced by Lipowski and Droz (Phys. Rev. E 65, 031307 (2002)). We solve
analytically the master equation and the first-passage problem. The analytic
results confirm the numerical results obtained by Lipowski and Droz. We find
that the stationary probability distribution and the shortest one among the
characteristic times are governed by the same free energy. We also analytically
derive the form of the critical probability distribution on the critical line,
which supports their results obtained by numerically calculating Binder
cumulants (cond-mat/0201472).Comment: 6 pages including 3 figures, RevTe
Analytic study of the three-urn model for separation of sand
We present an analytic study of the three-urn model for separation of sand.
We solve analytically the master equation and the first-passage problem. We
find that the stationary probability distribution obeys the detailed balance
and is governed by the {\it free energy}. We find that the characteristic
lifetime of a cluster diverges algebraically with exponent 1/3 at the limit of
stability.Comment: 5pages, 4 figures include
Anisotropic Dirac fermions in a Bi square net of SrMnBi2
We report the highly anisotropic Dirac fermions in a Bi square net of
SrMnBi2, based on a first principle calculation, angle resolved photoemission
spectroscopy, and quantum oscillations for high-quality single crystals. We
found that the Dirac dispersion is generally induced in the (SrBi)+ layer
containing a double-sized Bi square net. In contrast to the commonly observed
isotropic Dirac cone, the Dirac cone in SrMnBi2 is highly anisotropic with a
large momentum-dependent disparity of Fermi velocities of ~ 8. These findings
demonstrate that a Bi square net, a common building block of various layered
pnictides, provide a new platform that hosts highly anisotropic Dirac fermions.Comment: 5 pages, 4 figure
Fragility, Stokes-Einstein violation, and correlated local excitations in a coarse-grained model of an ionic liquid
Dynamics of a coarse-grained model for the room-temperature ionic liquid,
1-ethyl-3-methylimidazolium hexafluorophosphate, couched in the united-atom
site representation are studied via molecular dynamics simulations. The
dynamically heterogeneous behavior of the model resembles that of fragile
supercooled liquids. At or close to room temperature, the model ionic liquid
exhibits slow dynamics, characterized by nonexponential structural relaxation
and subdiffusive behavior. The structural relaxation time, closely related to
the viscosity, shows a super-Arrhenius behavior. Local excitations, defined as
displacement of an ion exceeding a threshold distance, are found to be mainly
responsible for structural relaxation in the alternating structure of cations
and anions. As the temperature is lowered, excitations become progressively
more correlated. This results in the decoupling of exchange and persistence
times, reflecting a violation of the Stokes-Einstein relation.Comment: Published on the Phys. Chem. Chem. Phys. websit
High Speed Forming Press Using Electromagnetic Pulse Force
In this paper, the finite element analysis for the design of a high speed forming press
using electromagnetic pulse force has been performed. The punch of the press has been
fixed on a aluminium plate, which is driven by the electromagnetic pulse force. The force
is the repulsive force between aluminium plate and the coil. The coil has been supplied
with a high voltage AC current impulse from the capacitors and then the magnetized
aluminium plate has been forced to move upward with high speed. For the analysis of the
pressing, the coupled analysis of electromagnetic field and rigid-body dynamic of the
aluminium plate has been performed with a commercial FE-software, ANSYS and the
rigid-body dynamics theory
PRE- AND POST-IMPACT BALL AND RACQUET CHARACTERISTICS DURING TENNIS SERVES PERFORMED BY ELITE MALE AND FEMALE PLAYERS
This study quantified the pre- and post-impad 3-D kinematics of a tennis ball and racquet. Data were collected during the tennis competition of the 1996 Atlanta Olympic Games using two high-speed cameras (200 Hz). Two first serves were analysed for each subject. A one-way ANOVA for the factor of sex (p < .05) was performed for each parameter. The results indicate that, regardless of sex, the ball travelled forward and to the lefl during the flight phase before impact and the ball was hit near the peak height of the racquet. The males had significantly higher height of ball impact, greater pre-impad racquet velocity and greater post-impact ball velocity than their female counterparts. It is not certain whether the techniques used by males and females contributed to the differences in racquet speed observed
Disturbance Observer
Disturbance observer is an inner-loop output-feedback controller whose role
is to reject external disturbances and to make the outer-loop baseline
controller robust against plant's uncertainties. Therefore, the closed-loop
system with the DOB approximates the nominal closed-loop by the baseline
controller and the nominal plant model with no disturbances. This article
presents how the disturbance observer works under what conditions, and how one
can design a disturbance observer to guarantee robust stability and to recover
the nominal performance not only in the steady-state but also for the transient
response under large uncertainty and disturbance
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