8,525 research outputs found
Catching Cheats: Detecting Strategic Manipulation in Distributed Optimisation of Electric Vehicle Aggregators
Given the rapid rise of electric vehicles (EVs) worldwide, and the ambitious
targets set for the near future, the management of large EV fleets must be seen
as a priority. Specifically, we study a scenario where EV charging is managed
through self-interested EV aggregators who compete in the day-ahead market in
order to purchase the electricity needed to meet their clients' requirements.
With the aim of reducing electricity costs and lowering the impact on
electricity markets, a centralised bidding coordination framework has been
proposed in the literature employing a coordinator. In order to improve privacy
and limit the need for the coordinator, we propose a reformulation of the
coordination framework as a decentralised algorithm, employing the Alternating
Direction Method of Multipliers (ADMM). However, given the self-interested
nature of the aggregators, they can deviate from the algorithm in order to
reduce their energy costs. Hence, we study the strategic manipulation of the
ADMM algorithm and, in doing so, describe and analyse different possible attack
vectors and propose a mathematical framework to quantify and detect
manipulation. Importantly, this detection framework is not limited the
considered EV scenario and can be applied to general ADMM algorithms. Finally,
we test the proposed decentralised coordination and manipulation detection
algorithms in realistic scenarios using real market and driver data from Spain.
Our empirical results show that the decentralised algorithm's convergence to
the optimal solution can be effectively disrupted by manipulative attacks
achieving convergence to a different non-optimal solution which benefits the
attacker. With respect to the detection algorithm, results indicate that it
achieves very high accuracies and significantly outperforms a naive benchmark
Energy storage for a lunar base by the reversible chemical reaction: CaO+H2O reversible reaction Ca(OH)2
A thermochemical solar energy storage concept involving the reversible reaction CaO + H2O yields Ca(OH)2 is proposed as a power system element for a lunar base. The operation and components of such a system are described. The CaO/H2O system is capable of generating electric power during both the day and night. The specific energy (energy to mass ratio) of the system was estimated to be 155 W-hr/kg. Mass of the required amount of CaO is neglected since it is obtained from lunar soil. Potential technical problems, such as reactor design and lunar soil processing, are reviewed
Thermochemical energy storage for a lunar base
A thermochemical solar energy storage concept involving the reversible reaction CaO + H2O yields Ca(OH)2 is proposed as a power system element for a lunar base. The operation and components of such a system are described. The CaO/H2O system is capable of generating electric power during both the day and night. Mass of the required amount of CaO is neglected since it is obtained from lunar soil. Potential technical problems, such as reactor design and lunar soil processing, are reviewed
PEPS as unique ground states of local Hamiltonians
In this paper we consider projected entangled pair states (PEPS) on arbitrary
lattices. We construct local parent Hamiltonians for each PEPS and isolate a
condition under which the state is the unique ground state of the Hamiltonian.
This condition, verified by generic PEPS and examples like the AKLT model, is
an injective relation between the boundary and the bulk of any local region.
While it implies the existence of an energy gap in the 1D case we will show
that in certain cases (e.g., on a 2D hexagonal lattice) the parent Hamiltonian
can be gapless with a critical ground state. To show this we invoke a mapping
between classical and quantum models and prove that in these cases the
injectivity relation between boundary and bulk solely depends on the lattice
geometry.Comment: 8 page
Toward color image segmentation in analog VLSI: Algorithm and hardware
Standard techniques for segmenting color images are based on finding normalized RGB discontinuities, color histogramming, or clustering techniques in RGB or CIE color spaces. The use of the psychophysical variable hue in HSI space has not been popular due to its numerical instability at low saturations. In this article, we propose the use of a simplified hue description suitable for implementation in analog VLSI. We demonstrate that if theintegrated white condition holds, hue is invariant to certain types of highlights, shading, and shadows. This is due to theadditive/shift invariance property, a property that other color variables lack. The more restrictive uniformly varying lighting model associated with themultiplicative/scale invariance property shared by both hue and normalized RGB allows invariance to transparencies, and to simple models of shading and shadows. Using binary hue discontinuities in conjunction with first-order type of surface interpolation, we demonstrate these invariant properties and compare them against the performance of RGB, normalized RGB, and CIE color spaces. We argue that working in HSI space offers an effective method for segmenting scenes in the presence of confounding cues due to shading, transparency, highlights, and shadows. Based on this work, we designed and fabricated for the first time an analog CMOS VLSI circuit with on-board phototransistor input that computes normalized color and hue
A symmetry adapted approach to vibrational excitations in atomic clusters
An algebraic method especially suited to describe strongly anharmonic
vibrational spectra in molecules may be an appropriate framework to study
vibrational spectra of Na clusters, where nearly flat potential energy
surfaces and the appearance of close lying isomers have been reported. As an
illustration we describe the model and apply it to the Be, H, Be
and Na clusters.Comment: 8 pages with 2 tables, invited talk at `Atomic Nuclei & Metallic
Clusters: Finite Many-Fermion Systems', Prague, Czech Republic, September
1-5, 199
Comment on ``Boson-realization model for the vibrational spectra of tetrahedral molecules''
An algebraic model in terms of a local harmonic boson realization was
recently proposed to study molecular vibrational spectra [Zhong-Qi Ma et al.,
Phys. Rev. A 53, 2173 (1996)]. Because of the local nature of the bosons the
model has to deal with spurious degrees of freedom. An approach to eliminate
the latter from both the Hamiltonian and the basis was suggested. We show that
this procedure does not remove all spurious components from the Hamiltonian and
leads to a restricted set of interactions. We then propose a scheme in which
the physical Hamiltonian can be systematically constructed up to any order
without the need of imposing conditions on its matrix elements. In addition, we
show that this scheme corresponds to the harmonic limit of a symmetry adapted
algebraic approach based on U(2) algebras.Comment: 9 pages Revtex, submitted February 199
- …