3,450 research outputs found
A 7/9 - Approximation Algorithm for the Maximum Traveling Salesman Problem
We give a 7/9 - Approximation Algorithm for the Maximum Traveling Salesman
Problem.Comment: 6 figure
Gauge fields, ripples and wrinkles in graphene layers
We analyze elastic deformations of graphene sheets which lead to effective
gauge fields acting on the charge carriers. Corrugations in the substrate
induce stresses, which, in turn, can give rise to mechanical instabilities and
the formation of wrinkles. Similar effects may take place in suspended graphene
samples under tension.Comment: contribution to the special issue of Solid State Communications on
graphen
Development of Smart Grid Standards in View of Energy System Functionalities
A range of technologies must be developed and deployed for achieving a decarbonised energy system. A smart grid aims to integrate these different technologies into a single, over-arching system that is at the same time both complex and interoperable, which cannot be achieved without standardisation. Moreover, standardisation is a method of transferring research into successful processes and products. Without this, existing conventional energy systems will not change much longer, as it is more difficult to achieve significant market penetration of new technologies and deployment of new functions and applications. It seems that standardisation issues are not sufficiently addressed in scientific publications and are treated as a very specific topic by community of researchers despite the fact that standards may serve as a knowledge base for further research and improvement of emerging technologies and approaches. This paper presents a bird's-eye smart grid standardisation review based on a unique functionality - technology approach developed within Horizon 2020 project PANTERA.acceptedVersio
Effect of the Output of the System in Signal Detection
We analyze the consequences that the choice of the output of the system has
in the efficiency of signal detection. It is shown that the signal and the
signal-to-noise ratio (SNR), used to characterize the phenomenon of stochastic
resonance, strongly depend on the form of the output. In particular, the SNR
may be enhanced for an adequate output.Comment: 4 pages, RevTex, 6 PostScript figure
Hitting all Maximal Independent Sets of a Bipartite Graph
We prove that given a bipartite graph G with vertex set V and an integer k,
deciding whether there exists a subset of V of size k hitting all maximal
independent sets of G is complete for the class Sigma_2^P.Comment: v3: minor chang
Development of Energy Communities in Europe
This paper presents a review study of energy communities (ECs) in Europe, and discusses the future development of such communities in Europe – both related to energy technologies, energy carriers, regional conditions (North, Central and South of Europe), emerging regulatory development etc. From the analysis, it emerged that the future ECs in Europe will focus on utilizing local renewable energy sources (sun, wind, run of river, biogas, biomass), for covering all or part of the energy consumption for end-use customers. The ECs can be a sustainable alternative to large power plants based on fossil fuels. This is also linked to the emerging regulatory developments started when European Commission introduced such concepts in the “Clean Energy for all Europeans” package. The main goal of eNeuron H2020 project is to develop innovative tools for the optimal design and operation of ECs, integrating distributed energy resources and multiple energy carriers at different scales.Development of Energy Communities in EuropeacceptedVersio
Inapproximability of maximal strip recovery
In comparative genomic, the first step of sequence analysis is usually to
decompose two or more genomes into syntenic blocks that are segments of
homologous chromosomes. For the reliable recovery of syntenic blocks, noise and
ambiguities in the genomic maps need to be removed first. Maximal Strip
Recovery (MSR) is an optimization problem proposed by Zheng, Zhu, and Sankoff
for reliably recovering syntenic blocks from genomic maps in the midst of noise
and ambiguities. Given genomic maps as sequences of gene markers, the
objective of \msr{d} is to find subsequences, one subsequence of each
genomic map, such that the total length of syntenic blocks in these
subsequences is maximized. For any constant , a polynomial-time
2d-approximation for \msr{d} was previously known. In this paper, we show that
for any , \msr{d} is APX-hard, even for the most basic version of the
problem in which all gene markers are distinct and appear in positive
orientation in each genomic map. Moreover, we provide the first explicit lower
bounds on approximating \msr{d} for all . In particular, we show that
\msr{d} is NP-hard to approximate within . From the other
direction, we show that the previous 2d-approximation for \msr{d} can be
optimized into a polynomial-time algorithm even if is not a constant but is
part of the input. We then extend our inapproximability results to several
related problems including \cmsr{d}, \gapmsr{\delta}{d}, and
\gapcmsr{\delta}{d}.Comment: A preliminary version of this paper appeared in two parts in the
Proceedings of the 20th International Symposium on Algorithms and Computation
(ISAAC 2009) and the Proceedings of the 4th International Frontiers of
Algorithmics Workshop (FAW 2010
From Fake Supergravity to Superstars
The fake supergravity method is applied to 5-dimensional asymptotically AdS
spacetimes containing gravity coupled to a real scalar and an abelian gauge
field. The motivation is to obtain bulk solutions with R x S^3 symmetry in
order to explore the AdS/CFT correspondence when the boundary gauge theory is
on R x S^3. A fake supergravity action, invariant under local supersymmetry
through linear order in fermion fields, is obtained. The gauge field makes
things more restrictive than in previous applications of fake supergravity
which allowed quite general scalar potentials. Here the superpotential must
take the form W(\phi) ~ exp(-k\phi) + c exp(2\phi/(3k)), and the only freedom
is the choice of the constant k. The fermion transformation rules of fake
supergravity lead to fake Killing spinor equations. From their integrability
conditions, we obtain first order differential equations which we solve
analytically to find singular electrically charged solutions of the Lagrangian
field equations. A Schwarzschild mass term can be added to produce a horizon
which shields the singularity. The solutions, which include "superstars", turn
out to be known in the literature. We compute their holographic parameters.Comment: 42 pages, 3 figure
An Improvement of the Piggyback Algorithm for Parallel Model Checking
This paper extends the piggyback algorithm to enlarge the set of liveness properties it can verify. Its extension is motivated by an attempt to express in logic the counterexamples it can detect and relate them to bounded liveness. The original algorithm is based on parallel breadth-first search and piggybacking of accepting states that are deleted after counting a fixed number of transitions. The main improvement is obtained by renewing the counter of transitions when the same accepting states are visited in the negated property automaton. In addition, we describe piggybacking of multiple states in either sets (exact) or Bloom filters (lossy but conservative), and use of local searches that attempt to connect cycles fragmented among processing cores. Finally it is proved that accepting cycle detection is in NC in the size of the product automaton's entire state space, including unreachable states
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