46,812 research outputs found
On Multiobjective Evolution Model
Self-Organized Criticality (SOC) phenomena could have a significant effect on
the dynamics of ecosystems. The Bak-Sneppen (BS) model is a simple and robust
model of biological evolution that exhibits punctuated equilibrium behavior.
Here we will introduce random version of BS model. Also we generalize the
single objective BS model to a multiobjective one.Comment: 6 pages, 5 figure
A parallel algorithm for Hamiltonian matrix construction in electron-molecule collision calculations: MPI-SCATCI
Construction and diagonalization of the Hamiltonian matrix is the
rate-limiting step in most low-energy electron -- molecule collision
calculations. Tennyson (J Phys B, 29 (1996) 1817) implemented a novel algorithm
for Hamiltonian construction which took advantage of the structure of the
wavefunction in such calculations. This algorithm is re-engineered to make use
of modern computer architectures and the use of appropriate diagonalizers is
considered. Test calculations demonstrate that significant speed-ups can be
gained using multiple CPUs. This opens the way to calculations which consider
higher collision energies, larger molecules and / or more target states. The
methodology, which is implemented as part of the UK molecular R-matrix codes
(UKRMol and UKRMol+) can also be used for studies of bound molecular Rydberg
states, photoionisation and positron-molecule collisions.Comment: Write up of a computer program MPI-SCATCI Computer Physics
Communications, in pres
Sidelobe Control in Collaborative Beamforming via Node Selection
Collaborative beamforming (CB) is a power efficient method for data
communications in wireless sensor networks (WSNs) which aims at increasing the
transmission range in the network by radiating the power from a cluster of
sensor nodes in the directions of the intended base station(s) or access
point(s) (BSs/APs). The CB average beampattern expresses a deterministic
behavior and can be used for characterizing/controling the transmission at
intended direction(s), since the mainlobe of the CB beampattern is independent
on the particular random node locations. However, the CB for a cluster formed
by a limited number of collaborative nodes results in a sample beampattern with
sidelobes that severely depend on the particular node locations. High level
sidelobes can cause unacceptable interference when they occur at directions of
unintended BSs/APs. Therefore, sidelobe control in CB has a potential to
increase the network capacity and wireless channel availability by decreasing
the interference. Traditional sidelobe control techniques are proposed for
centralized antenna arrays and, therefore, are not suitable for WSNs. In this
paper, we show that distributed, scalable, and low-complexity sidelobe control
techniques suitable for CB in WSNs can be developed based on node selection
technique which make use of the randomness of the node locations. A node
selection algorithm with low-rate feedback is developed to search over
different node combinations. The performance of the proposed algorithm is
analyzed in terms of the average number of trials required to select the
collaborative nodes and the resulting interference. Our simulation results
approve the theoretical analysis and show that the interference is
significantly reduced when node selection is used with CB.Comment: 30 pages, 10 figures, submitted to the IEEE Trans. Signal Processin
Managing the Uncertainty Associated with Hydrogen Gas Hazards and Operability Issues in Nuclear Chemical Plants
The complex and diverse nature of reprocessing and decommissioning operations in existing nuclear chemical plants within the UK results in a variety of challenges. The
challenges relate to the quantified risk from hydrogen explosions and how best to manage the associated uncertainties.
Several knowledge gaps in terms of the Quantified Risk Assessment (QRA) of hydrogen hazards have been identified in this research work. These include radiolytic hydrogen explosions in sealed process pipes, the failure of ventilation systems used to dilute radiolytic hydrogen in process vessels, the decision uncertainty in installing additional hydrogen purge systems and the uncertainty associated with hold-up of hydrogen in radioactive sludges. The effect of a subsequent sudden release of the heldup hydrogen gas into a vessel ullage space presents a further knowledge gap. Nuclear decommissioning and reprocessing operations also result in operational risk knowledge gaps including the mixing behaviour of radioactive sludges, the performance of robotics for nuclear waste characterisation and control of nuclear fission products associated with solid wastes.
Bayesian Belief Networks (BBNs) and Monte Carlo Simulation (MC) techniques have been deployed in this research work to address the identified knowledge gaps. These techniques provide a powerful means of uncertainty analysis of complex systems involving multiple interdependent variables such as those affecting nuclear decommissioning and reprocessing.
Through the application of BBN and MC Simulation methodologies to a series of nuclear chemical plant case studies, new knowledge in decommissioning and reprocessing operations has been generated. This new knowledge relates to establishing a realistic quantified risk from hydrogen explosions and nuclear plant operability issues. New knowledge in terms of the key sensitivities affecting the quantified risk of hydrogen explosions and operability in nuclear environments as well as the optimum improvements necessary to mitigate such risks has also been gained
Low Momentum Classical Mechanics with Effective Quantum Potentials
A recently introduced effective quantum potential theory is studied in a low
momentum region of phase space. This low momentum approximation is used to show
that the new effective quantum potential induces a space-dependent mass and a
smoothed potential both of them constructed from the classical potential. The
exact solution of the approximated theory in one spatial dimension is found.
The concept of effective transmission and reflection coefficients for effective
quantum potentials is proposed and discussed in comparison with an analogous
quantum statistical mixture problem. The results are applied to the case of a
square barrier.Comment: 4 figure
Exceptional Point of Degeneracy in Linear-Beam Tubes for High Power Backward-Wave Oscillators
Abstract An exceptional point of degeneracy (EPD) is induced in a system made
of an electron beam interacting with an electromagnetic (EM) guided mode. This
enables a degenerate synchronous regime in backward wave oscillators (BWOs)
where the electron beams provides distributed gain to the EM mode with
distributed power extraction. Current particle-in-cell simulation results
demonstrate that BWOs operating at an EPD have a starting-oscillation current
that scales quadratically to a non-vanishing value for long interaction lengths
and therefore have higher power conversion efficiency at arbitrarily higher
level of power generation compared to standard BWOs
Is the Attainment Gap Fundamentally Flawed? Challenges and Opportunities
Inequality of outcome has become one of the most pressing issues in education. Nowhere is this more apparent than in the performance of disadvantaged students. However, despite increased support, no school in England or Wales has managed to consistently close the attainment gap between disadvantaged students and their peers. This raises many questions, none more important than: is there an error in how we measure the performance of disadvantaged students? Furthermore, what are the implications of such a potential error? This paper argues that the attainment gap as it is currently calculated is ineffective in identifying the locus of underperformance, the specific needs of disadvantaged students and the support needed to improve outcomes. Finally, this paper attempts to address this by discussing a pilot project focused on identifying and addressing disadvantaged students’ needs and the challenges and opportunities this raises
- …