12,013 research outputs found
Structural Phases of Bounded Three-Dimensional Screened Coulomb Clusters (Finite Yukawa System)
The formation of three-dimensional (3D) dust clusters within a complex plasma
modeled as a spatially confined Yukawa system is simulated using the box_tree
code. Similar to unscreened Coulomb clusters, the occurrence of concentric
shells with characteristic occupation numbers was observed. Both the occupation
numbers and radii were found to depend on the Debye length. Ground and low
energy meta-stable states of the shielded 3D Coulomb clusters were determined
for 4<N<20. The structure and energy of the clusters in different states was
analyzed for various Debye lengths. Structural phase transitions, including
inter-shell structural phase transitions and intra-shell structural phase
transitions, were observed for varying Debye length and the critical value for
transitions calculated
Spatially Distributed Stochastic Systems: equation-free and equation-assisted preconditioned computation
Spatially distributed problems are often approximately modelled in terms of
partial differential equations (PDEs) for appropriate coarse-grained quantities
(e.g. concentrations). The derivation of accurate such PDEs starting from finer
scale, atomistic models, and using suitable averaging, is often a challenging
task; approximate PDEs are typically obtained through mathematical closure
procedures (e.g. mean-field approximations). In this paper, we show how such
approximate macroscopic PDEs can be exploited in constructing preconditioners
to accelerate stochastic simulations for spatially distributed particle-based
process models. We illustrate how such preconditioning can improve the
convergence of equation-free coarse-grained methods based on coarse
timesteppers. Our model problem is a stochastic reaction-diffusion model
capable of exhibiting Turing instabilities.Comment: 8 pages, 6 figures, submitted to Journal of Chemical Physic
Generation of high-energy monoenergetic heavy ion beams by radiation pressure acceleration of ultra-intense laser pulses
A novel radiation pressure acceleration (RPA) regime of heavy ion beams from
laser-irradiated ultrathin foils is proposed by self-consistently taking into
account the ionization dynamics. In this regime, the laser intensity is
required to match with the large ionization energy gap when the successive
ionization of high-Z atoms passing the noble gas configurations [such as
removing an electron from the helium-like charge state to
]. While the target ions in the laser wing region are ionized
to low charge states and undergo rapid dispersions due to instabilities, a
self-organized, stable RPA of highly-charged heavy ion beam near the laser axis
is achieved. It is also found that a large supplement of electrons produced
from ionization helps preserving stable acceleration. Two-dimensional
particle-in-cell simulations show that a monoenergetic beam
with peak energy and energy spread of is obtained by
lasers at intensity .Comment: 5 pages, 4 figure
Media Coverage, Public Awareness and State Intervention in Child Abuse in China – An Analysis of High-Profile Cases
Abstract Key Practitioner Messages •Child abuse is a complex social problem that is often deeply rooted in the cultural, economic and social practices of the country in which it exists. •Child abuse in China is understood as deliberate and harmful acts, while many Western societies also include acts of omission such as neglect. •There is a complex relationship between public awareness, media coverage and state intervention
Hybrid solar cells from water-soluble polymers
We report on the use of a water-soluble, light-absorbing polythiophene polymer to fabricate novel photovoltaic devices. The polymer is a water-soluble thiophene known as sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] or PTEBS. The intention is to take advantage of the properties of conjugated polymers (flexible, tunable, and easy to process) and incorporate the additional benefits of water solubility (easily controlled evaporation rates and environmentally friendly). The PTEBS polythiophene has shown significant photovoltaic response and has been found to be effective for making solar cells. To date, solar cells in three different configurations have been produced: titanium dioxide (TiO2) bilayer cells, TiO2 bulk heterojunction solar cells, and carbon nanotubes (CNTs) in bulk heterojunctions. The best performance thus far has been achieved with TiO2 bilayer devices. These devices have an open circuit voltage (Voc) of 0.84V, a short circuit current (Jsc) of 0.15 mA/cm2, a fill factor (ff) of 0.91, and an efficiency (η) of 0.15 %
Water-soluble polythiophene∕nanocrystalline TiO2 solar cells
We report the characteristics of polymer∕nanocrystalline solar cells fabricated using an environmentally friendly water-soluble polythiophene and TiO2 in a bilayer configuration. The cells were made by dropping the polymer onto a TiO2nanocrystallinefilm and then repeatedly sweeping a clean glass rod across the polymer as it dried. The devices showed an open circuit voltage of 0.81 V, a short circuit current density of 0.35mA/cm2, a fill factor of 0.4, and an energy conversion efficiency of 0.13%. The water-soluble polythiophene showed significant photovoltaic behavior and the potential for use in solar cells
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