5,794 research outputs found
A Review on the Application of Natural Computing in Environmental Informatics
Natural computing offers new opportunities to understand, model and analyze
the complexity of the physical and human-created environment. This paper
examines the application of natural computing in environmental informatics, by
investigating related work in this research field. Various nature-inspired
techniques are presented, which have been employed to solve different relevant
problems. Advantages and disadvantages of these techniques are discussed,
together with analysis of how natural computing is generally used in
environmental research.Comment: Proc. of EnviroInfo 201
Generalized Gibbs state with modified Redfield solution: Exact agreement up to second order
A novel scheme for the steady state solution of the standard Redfield quantum
master equation is developed which yields agreement with the exact result for
the corresponding reduced density matrix up to second order in the system-bath
coupling strength. We achieve this objective by use of an analytic continuation
of the off-diagonal matrix elements of the Redfield solution towards its
diagonal limit. Notably, our scheme does not require the provision of yet
higher order relaxation tensors. Testing this modified method for a heat bath
consisting of a collection of harmonic oscillators we assess that the system
relaxes towards its correct coupling-dependent, generalized quantum Gibbs state
in second order. We numerically compare our formulation for a damped quantum
harmonic system with the nonequilibrium Green's function formalism: we find
good agreement at low temperatures for coupling strengths that are even larger
than expected from the very regime of validity of the second-order Redfield
quantum master equation. Yet another advantage of our method is that it
markedly reduces the numerical complexity of the problem; thus allowing to
study efficiently large-sized \emph{system} Hilbert spaces.Comment: 11 pages, 2 figures, minor changes, Accepted for publication in J.
Chem. Phys. (JCP
Lattice gauge theories simulations in the quantum information era
The many-body problem is ubiquitous in the theoretical description of
physical phenomena, ranging from the behavior of elementary particles to the
physics of electrons in solids. Most of our understanding of many-body systems
comes from analyzing the symmetry properties of Hamiltonian and states: the
most striking example are gauge theories such as quantum electrodynamics, where
a local symmetry strongly constrains the microscopic dynamics. The physics of
such gauge theories is relevant for the understanding of a diverse set of
systems, including frustrated quantum magnets and the collective dynamics of
elementary particles within the standard model. In the last few years, several
approaches have been put forward to tackle the complex dynamics of gauge
theories using quantum information concepts. In particular, quantum simulation
platforms have been put forward for the realization of synthetic gauge
theories, and novel classical simulation algorithms based on quantum
information concepts have been formulated. In this review we present an
introduction to these approaches, illustrating the basics concepts and
highlighting the connections between apparently very different fields, and
report the recent developments in this new thriving field of research.Comment: Pedagogical review article. Originally submitted to Contemporary
Physics, the final version will appear soon on the on-line version of the
journal. 34 page
Projective simulation for artificial intelligence
We propose a model of a learning agent whose interaction with the environment
is governed by a simulation-based projection, which allows the agent to project
itself into future situations before it takes real action. Projective
simulation is based on a random walk through a network of clips, which are
elementary patches of episodic memory. The network of clips changes
dynamically, both due to new perceptual input and due to certain compositional
principles of the simulation process. During simulation, the clips are screened
for specific features which trigger factual action of the agent. The scheme is
different from other, computational, notions of simulation, and it provides a
new element in an embodied cognitive science approach to intelligent action and
learning. Our model provides a natural route for generalization to
quantum-mechanical operation and connects the fields of reinforcement learning
and quantum computation.Comment: 22 pages, 18 figures. Close to published version, with footnotes
retaine
Black-hole binaries, gravitational waves, and numerical relativity
Understanding the predictions of general relativity for the dynamical
interactions of two black holes has been a long-standing unsolved problem in
theoretical physics. Black-hole mergers are monumental astrophysical events,
releasing tremendous amounts of energy in the form of gravitational radiation,
and are key sources for both ground- and space-based gravitational-wave
detectors. The black-hole merger dynamics and the resulting gravitational
waveforms can only be calculated through numerical simulations of Einstein's
equations of general relativity. For many years, numerical relativists
attempting to model these mergers encountered a host of problems, causing their
codes to crash after just a fraction of a binary orbit could be simulated.
Recently, however, a series of dramatic advances in numerical relativity has
allowed stable, robust black-hole merger simulations. This remarkable progress
in the rapidly maturing field of numerical relativity, and the new
understanding of black-hole binary dynamics that is emerging is chronicled.
Important applications of these fundamental physics results to astrophysics, to
gravitational-wave astronomy, and in other areas are also discussed.Comment: 54 pages, 42 figures. Some typos corrected & references updated.
Essentially final published versio
Spin quantum plasmas - new aspects of collective dynamics
Quantum plasmas is a rapidly expanding field of research, with applications
ranging from nanoelectronics, nanoscale devices and ultracold plasmas, to
inertial confinement fusion and astrophysics. Here we give a short systematic
overview of quantum plasmas. In particular, we analyze the collective effects
due to spin using fluid models. The introduction of an intrinsic magnetization
due to the plasma electron (or positron) spin properties in the
magnetohydrodynamic limit is discussed. Finally, a discussion of the theory and
examples of applications is given.Comment: 17 pages, short review concerning quantum plasmas, to appear in the
Proceedings of the 2007 ICTP Summer College on Plasma Physics, Trieste 30
July - 24 August, 200
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