484 research outputs found
Hamiltonian cycles in faulty random geometric networks
In this paper we analyze the Hamiltonian properties of
faulty random networks.
This consideration is of interest when considering wireless
broadcast networks.
A random geometric network is a graph whose vertices
correspond to points
uniformly and independently distributed in the unit square,
and whose edges
connect any pair of vertices if their distance is below some
specified bound.
A faulty random geometric network is a random geometric
network whose vertices
or edges fail at random. Algorithms to find Hamiltonian
cycles in faulty random
geometric networks are presented.Postprint (published version
Combining spectral sequencing and parallel simulated annealing for the MinLA problem
In this paper we present and analyze new sequential and parallel
heuristics to approximate the Minimum Linear Arrangement problem
(MinLA). The heuristics consist in obtaining a first global solution
using Spectral Sequencing and improving it locally through Simulated
Annealing. In order to accelerate the annealing process, we present a
special neighborhood distribution that tends to favor moves with high
probability to be accepted. We show how to make use of this
neighborhood to parallelize the Metropolis stage on distributed memory
machines by mapping partitions of the input graph to processors and
performing moves concurrently. The paper reports the results obtained
with this new heuristic when applied to a set of large graphs,
including graphs arising from finite elements methods and graphs
arising from VLSI applications. Compared to other heuristics, the
measurements obtained show that the new heuristic improves the
solution quality, decreases the running time and offers an excellent
speedup when ran on a commodity network made of nine personal
computers.Postprint (published version
Under-the-cell routing to improve manufacturability
The progressive miniaturization of technology and the unequal scalability of the BEOL and FEOL layers aggravate the routing congestion problem and have a negative impact on manufacturability. Standard cells are designed in a way that they can be treated as black boxes during physical design. However, this abstraction often prevents an efficient use of its internal free resources.
This paper proposes an effective approach for using internal routing resources without sacrificing modularity. By using cell generation tools for regular layouts, libraries are enriched with cell instances that have lateral pins and allow under-the-cell connections between adjacent cells, thus reducing pin count, via count and routing congestion.
An approach to generate cells with regular layouts and lateral pins is proposed. Additionally, algorithms to maximize the impact of under-the-cell routing are presented. The proposed techniques are integrated in an industrial design flow. Experimental results show a significant reduction of design rule check violations with negligible impact on timing.Peer ReviewedPostprint (author's final draft
Chiral bound states in the continuum
We present a distinct mechanism for the formation of bound states in the
continuum (BICs). In chiral quantum systems there appear zero-energy states in
which the wave function has finite amplitude only in one of the subsystems
defined by the chiral symmetry. When the system is coupled to leads with a
continuum energy band, part of these states remain bound. We derive some
algebraic rules for the number of these states depending on the dimensionality
and rank of the total Hamiltonian. We examine the transport properties of such
systems including the appearance of Fano resonances in some limiting cases.
Finally, we discuss experimental setups based on microwave dielectric
resonators and atoms in optical lattices where these predictions can be tested.Comment: 9 pages, 8 figures. v2: includes results specific to honeycomb
lattice; matches published versio
A Distributed algorithm to find Hamiltonian cycles in Gnp random graphs
In this paper, we present a distributed algorithm to find Hamiltonian cycles in random binomial graphs Gnp. The algorithm works on a synchronous distributed setting by first creating a small cycle, then covering almost all vertices in the graph with several disjoint paths, and finally patching these paths and the uncovered vertices to the cycle. Our analysis shows that, with high probability, our algorithm is able to find a Hamiltonian cycle in Gnp when p_n=omega(sqrt{log n}/n^{1/4}). Moreover, we conduct an average case complexity analysis that shows that our algorithm terminates in expected sub-linear time, namely in O(n^{3/4+epsilon}) pulses.Postprint (published version
Measuring molecular electric dipoles using trapped atomic ions and ultrafast laser pulses
We study a hybrid quantum system composed of an ion and an electric dipole.
We show how a trapped ion can be used to measure the small electric field
generated by a classical dipole. We discuss the application of this scheme to
measure the electric dipole moment of cold polar molecules, whose internal
state can be controlled with ultrafast laser pulses, by trapping them in the
vicinity of a trapped ion.Comment: 13 pages, 6 figures. Substantially modified version, with 4 new
appendices; matches published versio
Collective modes of a trapped ion-dipole system
We study a simple model consisting of an atomic ion and a polar molecule
trapped in a single setup, taking into consideration their electrostatic
interaction. We determine analytically their collective modes of excitation as
a function of their masses, trapping frequencies, distance, and the molecule's
electric dipole moment. We then discuss the application of these collective
excitations to cool molecules, to entangle molecules and ions, and to realize
two-qubit gates between them. We finally present a numerical analysis of the
possibility of applying these tools to study magnetically ordered phases of
two-dimensional arrays of polar molecules, a setup proposed to quantum-simulate
some strongly-correlated models of condensed matter.Comment: v2: 13 pages, 8 figures (from 10 figure files). Matches published
version in Appl. Phys. B, special issue "Wolfgang Paul 100
A hierarchical mathematical model for automatic pipelining and allocation using elastic systems
The advent of FPGA-based accelerators has encouraged the use of high-level synthesis (HLS) for rapid prototyping and design space exploration. In this context, design optimization at behavioral level becomes a critical task for the delivery of high-quality solutions. Time elasticity opens a new avenue of optimizations that can be applied after HLS and before logic synthesis, proposing new sequential transformations that expand beyond classical retiming and enlarge the register-transfer level (RTL) exploration space. This paper proposes a mathematical model for RTL transformations that exploit elasticity to select the best implementation for each functional unit and add pipeline registers to increase performance. Two simple examples are used to validate the effectiveness and potential benefits of the model.Peer ReviewedPostprint (author's final draft
Spin dynamics and structure formation in a spin-1 condensate in a magnetic field
7 págs.; 5 figs.; PACS number s : 03.75.Mn, 03.75.Kk, 71.15.MbWe study the dynamics of a trapped spin-1 condensate in a magnetic field. First, we analyze the homogeneous system, for which the dynamics can be understood in terms of orbits in phase space. We analytically solve for the dynamical evolution of the populations of the various Zeeman components of the homogeneous system. This result is then applied via a local-density approximation to trapped quasi-one-dimensional condensates. Our analysis of the trapped system in a magnetic field shows that both the mean-field and Zeeman regimes are simultaneously realized, and we argue that the border between these two regions is where spin domains and phase defects are generated. We propose a method to experimentally tune the position of this border. ©2009 The American Physical SocietyThis work was supported by the UK EPSRC Grant No. EP/E025935.Peer Reviewe
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