307,993 research outputs found
Dynamical simulations of charged soliton transport in conjugated polymers with the inclusion of electron-electron interactions
We present numerical studies of the transport dynamics of a charged soliton
in conjugated polymers under the influence of an external time-dependent
electric field. All relevant electron-phonon and electron-electron interactions
are nearly fully taken into account by simulating the monomer displacements
with classical molecular dynamics (MD) and evolving the wavefunction for the
electrons by virtue of the adaptive time-dependent density matrix
renormalization group (TDDMRG) simultaneously and nonadiabatically. It is found
that after a smooth turn-on of the external electric field the charged soliton
is accelerated at first up to a stationary constant velocity as one entity
consisting of both the charge and the lattice deformation. An ohmic region (6
mV/ 12 mV/) where the stationary
velocity increases linearly with the electric field strength is observed. The
relationship between electron-electron interactions and charged soliton
transport is also investigated in detail. We find that the dependence of the
stationary velocity of a charged soliton on the on-site Coulomb interactions
and the nearest-neighbor interactions is due to the extent of
delocalization of the charged soliton defect.Comment: 25 pages, 15 figure
The Big Picture on Small Screens Delivering Acceptable Video Quality in Mobile TV
Mobile TV viewers can change the viewing distance and (on some devices) scale the picture to their preferred viewing ratio, trading off size for angular resolution. We investigated optimal trade-offs between size and resolution through a series of studies. Participants selected their preferred size and rated the acceptability of the visual experience on a 200ppi device at a 4: 3 aspect ratio. They preferred viewing ratios similar to living room TV setups regardless of the much lower resolution: at a minimum 14 pixels per degree. While traveling on trains people required videos with a height larger than 35mm
"Not the Usual Suspects": A Study of Factors Reducing the Effectiveness of CCTV
Previous research on the effectiveness of Closed Circuit Television (CCTV) has focused on critically assessing police and government claims that CCTV is effective in reducing crime. This paper presents a field study that investigates the relationship between CCTV system design and the performance of operator tasks. We carried out structured observations and interviews with 13 managers and 38 operators at 13 CCTV control rooms. A number of failures were identified, including the poor configuration of technology, poor quality video recordings, and a lack of system integration. Stakeholder communication was poor, and there were too many cameras and too few operators. These failures have been previously identified by researchers; however, no design improvements have been made to control rooms in the last decade. We identify a number of measures to improve operator performance, and contribute a set of recommendations for security managers and practitioners. Security Journal (2010) 23, 134-154. doi:10.1057/sj.2008.2; published online 6 October 200
Vacua and Exact Solutions in Lower- Limits of EGB
We consider the action principles that are the lower dimensional limits of
the Einstein-Gauss-Bonnet gravity {\it via} the Kaluza-Klein route. We study
the vacua and obtain some exact solutions. We find that the reality condition
of the theories may select one vacuum over the other from the two vacua that
typically arise in Einstein-Gauss-Bonnet gravity. We obtain exact black hole
and cosmological solutions carrying scalar hair, including scalar hairy BTZ
black holes with both mass and angular momentum turned on. We also discuss the
holographic central charges in the asymptotic AdS backgrounds.Comment: Latex, 19 page
Dynamics of ligand substitution in labile cobalt complexes resolved by ultrafast T-jump
Ligand exchange of hydrated metal complexes is common in chemical and biological systems. Using the ultrafast T-jump, we examined this process, specifically the transformation of aqua cobalt (II) complexes to their fully halogenated species. The results reveal a stepwise mechanism with time scales varying from hundreds of picoseconds to nanoseconds. The dynamics are significantly faster when the structure is retained but becomes rate-limited when the octahedral-to-tetrahedral structural change bottlenecks the transformation. Evidence is presented, from bimolecular kinetics and energetics (enthalpic and entropic), for a reaction in which the ligand assists the displacement of water molecules, with the retention of the entering ligand in the activated state. The reaction time scale deviates by one to two orders of magnitude from that of ionic diffusion, suggesting the involvement of a collisional barrier between the ion and the much larger complex
Column size effects of DER fluids
The static yield stress of dielectric electrorheological(DER) fluids of
infinite column state and chain state are calculated from the first principle
method. The results indicate that the column surface contributions to ER
effects is very small and both states will give correct results to the real DER
fluids.Comment: 7 pages, 3 figure
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