4,580 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)
Theory of spin, electronic and transport properties of the lateral triple quantum dot molecule in a magnetic field
We present a theory of spin, electronic and transport properties of a
few-electron lateral triangular triple quantum dot molecule in a magnetic
field. Our theory is based on a generalization of a Hubbard model and the
Linear Combination of Harmonic Orbitals combined with Configuration Interaction
method (LCHO-CI) for arbitrary magnetic fields. The few-particle spectra
obtained as a function of the magnetic field exhibit Aharonov-Bohm
oscillations. As a result, by changing the magnetic field it is possible to
engineer the degeneracies of single-particle levels, and thus control the total
spin of the many-electron system. For the triple dot with two and four
electrons we find oscillations of total spin due to the singlet-triplet
transitions occurring periodically in the magnetic field. In the three-electron
system we find a transition from a magnetically frustrated to the
spin-polarized state. We discuss the impact of these phase transitions on the
addition spectrum and the spin blockade of the lateral triple quantum dot
molecule.Comment: 30 pages (one column), 9 figure
Chaotic exploration and learning of locomotion behaviours
We present a general and fully dynamic neural system, which exploits intrinsic chaotic dynamics, for the real-time goal-directed exploration and learning of the possible locomotion patterns of an articulated robot of an arbitrary morphology in an unknown environment. The controller is modeled as a network of neural oscillators that are initially coupled only through physical embodiment, and goal-directed exploration of coordinated motor patterns is achieved by chaotic search using adaptive bifurcation. The phase space of the indirectly coupled neural-body-environment system contains multiple transient or permanent self-organized dynamics, each of which is a candidate for a locomotion behavior. The adaptive bifurcation enables the system orbit to wander through various phase-coordinated states, using its intrinsic chaotic dynamics as a driving force, and stabilizes on to one of the states matching the given goal criteria. In order to improve the sustainability of useful transient patterns, sensory homeostasis has been introduced, which results in an increased diversity of motor outputs, thus achieving multiscale exploration. A rhythmic pattern discovered by this process is memorized and sustained by changing the wiring between initially disconnected oscillators using an adaptive synchronization method. Our results show that the novel neurorobotic system is able to create and learn multiple locomotion behaviors for a wide range of body configurations and physical environments and can readapt in realtime after sustaining damage
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
Factorization in graviton interactions
The study of factorization in the linearized gravity is extended to the
graviton scattering processes with a massive scalar particle, with a massless
vector boson and also with a graviton. Every transition amplitude is shown to
be completely factorized and the physical implications of their common factors
are discussed.Comment: 5 pages, Revtex 3.0, SNUTP 93-7
Spin selective Aharonov-Bohm oscillations in a lateral triple quantum dot
We present a theory for spin selective Aharonov-Bohm oscillations in a
lateral triple quantum dot. We show that to understand the Aharonov-Bohm (AB)
effect in an interacting electron system within a triple quantum dot molecule
(TQD) where the dots lie in a ring configuration requires one to not only
consider electron charge but also spin. Using a Hubbard model supported by
microscopic calculations we show that, by localizing a single electron spin in
one of the dots, the current through the TQD molecule depends not only on the
flux but also on the relative orientation of the spin of the incoming and
localized electrons. AB oscillations are predicted only for the spin singlet
electron complex resulting in a magnetic field tunable "spin valve".Comment: 4 pages, 4 figure
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