81 research outputs found
Characteristics of the polymer transport in ratchet systems
Molecules with complex internal structure in time-dependent periodic
potentials are studied by using short Rubinstein-Duke model polymers as an
example. We extend our earlier work on transport in stochastically varying
potentials to cover also deterministic potential switching mechanisms,
energetic efficiency and non-uniform charge distributions. We also use currents
in the non-equilibrium steady state to identify the dominating mechanisms that
lead to polymer transportation and analyze the evolution of the macroscopic
state (e.g., total and head-to-head lengths) of the polymers. Several numerical
methods are used to solve the master equations and nonlinear optimization
problems. The dominating transport mechanisms are found via graph optimization
methods. The results show that small changes in the molecule structure and the
environment variables can lead to large increases of the drift. The drift and
the coherence can be amplified by using deterministic flashing potentials and
customized polymer charge distributions. Identifying the dominating transport
mechanism by graph analysis tools is found to give insight in how the molecule
is transported by the ratchet effect.Comment: 35 pages, 17 figures, to appear in Phys. Rev.
Single-layer metal-on-metal islands driven by strong time-dependent forces
Non-linear transport properties of single-layer metal-on-metal islands driven
with strong static and time-dependent forces are studied. We apply a
semi-empirical lattice model and use master equation and kinetic Monte Carlo
simulation methods to compute observables such as the velocity and the
diffusion coefficient. Two types of time-dependent driving are considered: a
pulsed rotated field and an alternating field with a zero net force
(electrophoretic ratchet). Small islands up to 12 atoms were studied in detail
with the master equation method and larger ones with simulations. Results are
presented mainly for a parametrization of Cu on Cu(001) surface, which has been
the main system of interest in several previous studies. The main results are
that the pulsed field can increase the current in both diagonal and axis
direction when compared to static field, and there exists a current inversion
in the electrophoretic ratchet. Both of these phenomena are a consequence of
the coupling of the internal dynamics of the island with its transport. In
addition to the previously discovered "magic size" effect for islands in
equilibrium, a strong odd-even effect was found for islands driven far out of
equilibrium. Master equation computations revealed non-monotonous behavior for
the leading relaxation constant and effective Arrhenius parameters. Using cycle
optimization methods, typical island transport mechanisms are identified for
small islands.Comment: 39 pages, 20 figures, to appear in Phys. Rev. E [corrected typo of
the x-axis label in Fig. 6
Vulnerable warriors: the atmospheric marketing of military and policing equipment before and after 9/11
In this article, we analyse changes in the circulation of advertisements of policing products at security expos between 1995 and 2013. While the initial aim of the research was to evidence shifts in terrorist frames in the marketing of policing equipment before and after 9/11, our findings instead suggested that what we are seeing is the rise of marketing to police as “vulnerable warriors”, law enforcement officers in need of military weapons both for their offensive capabilities and for the protection they can offer to a police force that is always under threat
Local structure of relaxor ferroelectric SrxBa1-xNb2O6 from a pair distribution function analysis
Pair distribution function analysis of neutron-scattering data and of ab initio molecular dynamics results have been employed to study short-range structural correlations and their temperature dependence in a heavily disordered dielectric material SrxBa1-xNb2O6 (x = 0.35, 0.5, and 0.61). Intrinsic disorder caused by a partial occupation of the cationic sites by differently sized Sr and Ba atoms and their vacancies introduces important local strains to the structure and directly influences the Nb-O-6 octahedra tilting. The resulting complex system of tilts is found to be both temperature and Sr-doping sensitive with the biggest tilt magnitudes reached at low temperatures and high strontium contents, where ferroelectric relaxor behavior appears. We find evidence for two Nb-O-6 subsystems with different variations of niobium-oxygen bond lengths, distinct dynamics, and disparate levels of deviation from macroscopic polarization direction. These findings establish a detailed picture of the local structure of SrxBa1-xNb2O6 and provide a deeper insight into the origins of the materials dielectric properties.This work was supported by the Czech Science Foundation (Project No. 16-09142S). The computational part of this research was undertaken on the NCI National Facility in Canberra, Australia, which is supported by the Australian Commonwealth Government.
Hybrid polymer electrolyte membrane fuel cell-lithium-ion battery powertrain testing platform - hybrid fuel cell electric vehicle emulator
Abstract not availableP. Bujlo, C. J. Xie, D. Shen, O. Ulleberg, S. Pasupathi, G. Pasciak and B. G. Polle
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