198 research outputs found
Dealing with uncertainty in agent-based models for short-term predictions
Agent-based models (ABMs) are gaining traction as one of the most powerful modelling tools within the social sciences. They are particularly suited to simulating complex systems. Despite many methodological advances within ABM, one of the major drawbacks is their inability to incorporate real-time data to make accurate short-term predictions. This paper presents an approach that allows ABMs to be dynamically optimized. Through a combination of parameter calibration and data assimilation (DA), the accuracy of model-based predictions using ABM in real time is increased. We use the exemplar of a bus route system to explore these methods. The bus route ABMs developed in this research are examples of ABMs that can be dynamically optimized by a combination of parameter calibration and DA. The proposed model and framework is a novel and transferable approach that can be used in any passenger information system, or in an intelligent transport systems to provide forecasts of bus locations and arrival times
The second law, Maxwell's daemon and work derivable from quantum heat engines
With a class of quantum heat engines which consists of two-energy-eigenstate
systems undergoing, respectively, quantum adiabatic processes and energy
exchanges with heat baths at different stages of a cycle, we are able to
clarify some important aspects of the second law of thermodynamics. The quantum
heat engines also offer a practical way, as an alternative to Szilard's engine,
to physically realise Maxwell's daemon. While respecting the second law on the
average, they are also capable of extracting more work from the heat baths than
is otherwise possible in thermal equilibrium
Sub-kHz lasing of a CaF_2 Whispering Gallery Mode Resonator Stabilized Fiber Ring Laser
We utilize a high quality calcium fluoride whispering-gallery-mode resonator
to stabilize a simple erbium doped fiber ring laser with an emission frequency
of 196 THz (wavelenght 1530 nm) to a linewidth below 650 Hz. This corresponds
to a relative stability of 3.3 x 10^(-12) over 16 \mus. In order to
characterize the linewidth we use two identical self-built lasers and a
commercial laser to determine the individual lasing linewidth via the
three-cornered hat method.Comment: 4 pages, 3 figure
Quantum hypercomputation based on the dynamical algebra su(1,1)
An adaptation of Kieu's hypercomputational quantum algorithm (KHQA) is
presented. The method that was used was to replace the Weyl-Heisenberg algebra
by other dynamical algebra of low dimension that admits infinite-dimensional
irreducible representations with naturally defined generalized coherent states.
We have selected the Lie algebra , due to that this algebra
posses the necessary characteristics for to realize the hypercomputation and
also due to that such algebra has been identified as the dynamical algebra
associated to many relatively simple quantum systems. In addition to an
algebraic adaptation of KHQA over the algebra , we
presented an adaptations of KHQA over some concrete physical referents: the
infinite square well, the infinite cylindrical well, the perturbed infinite
cylindrical well, the P{\"o}sch-Teller potentials, the Holstein-Primakoff
system, and the Laguerre oscillator. We conclude that it is possible to have
many physical systems within condensed matter and quantum optics on which it is
possible to consider an implementation of KHQA.Comment: 25 pages, 1 figure, conclusions rewritten, typing and language errors
corrected and latex format changed minor changes elsewhere and
Fluid Flows of Mixed Regimes in Porous Media
In porous media, there are three known regimes of fluid flows, namely,
pre-Darcy, Darcy and post-Darcy. Because of their different natures, these are
usually treated separately in literature. To study complex flows when all three
regimes may be present in different portions of a same domain, we use a single
equation of motion to unify them. Several scenarios and models are then
considered for slightly compressible fluids. A nonlinear parabolic equation for
the pressure is derived, which is degenerate when the pressure gradient is
either small or large. We estimate the pressure and its gradient for all time
in terms of initial and boundary data. We also obtain their particular bounds
for large time which depend on the asymptotic behavior of the boundary data but
not on the initial one. Moreover, the continuous dependence of the solutions on
initial and boundary data, and the structural stability for the equation are
established.Comment: 33 page
Large energy mode locking of an erbium-doped fiber laser with atomic layer graphene
We report on large energy pulse generation in an erbium-doped fiber laser
passively mode-locked with atomic layer graphene. Stable mode locked pulses
with single pulse energy up to 7.3 nJ and pulse width of 415 fs have been
directly generated from the laser. Our results show that atomic layer graphene
could be a promising saturable absorber for large energy mode locking.Comment: 14 pages 4 figure
Electric charge quantisation from gauge invariance of a Lagrangian: A catalogue of baryon number violating scalar interactions
In gauge theories like the standard model, the electric charges of the
fermions can be heavily constrained from the classical structure of the theory
and from the cancellation of anomalies. There is however mounting evidence
suggesting that these anomaly constraints are not as well motivated as the
classical constraints. In light of this we discuss possible modifications of
the minimal standard model which will give us complete electric charge
quantisation from classical constraints alone. Because these modifications to
the standard model involve the consideration of baryon number violating scalar
interactions, we present a complete catalogue of the simplest ways to modify
the standard model so as to introduce explicit baryon number violation. This
has implications for proton decay searches and baryogenesis.Comment: 15 pages, 7 Postscript figure
Perturbative analysis for Kaplan's lattice chiral fermions
Perturbation theory for lattice fermions with domain wall mass terms is
developed and is applied to investigate the chiral Schwinger model formulated
on the lattice by Kaplan's method. We calculate the effective action for gauge
fields to one loop, and find that it contains a longitudinal component even for
anomaly-free cases. From the effective action we obtain gauge anomalies and
Chern-Simons current without ambiguity. We also show that the current
corresponding to the fermion number has a non-zero divergence and it flows off
the wall into the extra dimension. Similar results are obtained for a proposal
by Shamir, who used a constant mass term with free boundaries instead of domain
walls.Comment: 25 page, 5 PostScript figures, [some changes in the conclusion
Solving the subset-sum problem with a light-based device
We propose a special computational device which uses light rays for solving
the subset-sum problem. The device has a graph-like representation and the
light is traversing it by following the routes given by the connections between
nodes. The nodes are connected by arcs in a special way which lets us to
generate all possible subsets of the given set. To each arc we assign either a
number from the given set or a predefined constant. When the light is passing
through an arc it is delayed by the amount of time indicated by the number
placed in that arc. At the destination node we will check if there is a ray
whose total delay is equal to the target value of the subset sum problem (plus
some constants).Comment: 14 pages, 6 figures, Natural Computing, 200
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