9,104 research outputs found
Bi-Criteria and Approximation Algorithms for Restricted Matchings
In this work we study approximation algorithms for the \textit{Bounded Color
Matching} problem (a.k.a. Restricted Matching problem) which is defined as
follows: given a graph in which each edge has a color and a profit
, we want to compute a maximum (cardinality or profit)
matching in which no more than edges of color are
present. This kind of problems, beside the theoretical interest on its own
right, emerges in multi-fiber optical networking systems, where we interpret
each unique wavelength that can travel through the fiber as a color class and
we would like to establish communication between pairs of systems. We study
approximation and bi-criteria algorithms for this problem which are based on
linear programming techniques and, in particular, on polyhedral
characterizations of the natural linear formulation of the problem. In our
setting, we allow violations of the bounds and we model our problem as a
bi-criteria problem: we have two objectives to optimize namely (a) to maximize
the profit (maximum matching) while (b) minimizing the violation of the color
bounds. We prove how we can "beat" the integrality gap of the natural linear
programming formulation of the problem by allowing only a slight violation of
the color bounds. In particular, our main result is \textit{constant}
approximation bounds for both criteria of the corresponding bi-criteria
optimization problem
Metrics on semistable and numerically effective Higgs bundles
We provide notions of numerical effectiveness and numerical flatness for
Higgs vector bundles on compact K\"ahler manifolds in terms of fibre metrics.
We prove several properties of bundles satisfying such conditions and in
particular we show that numerically flat Higgs bundles have vanishing Chern
classes, and that they admit filtrations whose quotients are stable flat Higgs
bundles. We compare these definitions with those previously given in the case
of projective varieties. Finally we study the relations between numerically
effectiveness and semistability, establishing semistability criteria for Higgs
bundles on projective manifolds of any dimension.Comment: 25 pages. Changes in the expositio
Boundary Exchange Algebras and Scattering on the Half Line
Some algebraic aspects of field quantization in space-time with boundaries
are discussed. We introduce an associative algebra, whose exchange properties
are inferred from the scattering processes in integrable models with reflecting
boundary conditions on the half line. The basic properties of this algebra are
established and the Fock representations associated with certain involutions
are derived. We apply these results for the construction of quantum fields and
for the study of scattering on the half line.Comment: Enlarged version, to appear in Comm. Math. Phys. Tex file, macros
included, no figures, 32 page
Testing complete positivity
We study the modified dynamical evolution of the neutral kaon system under
the condition of complete positivity. The accuracy of the data from planned
future experiments is expected to be sufficiently precise to test such a
hypothesis.Comment: 12 pages, latex, no figures, to appear in Mod. Phys. Lett.
Multistage Switching Architectures for Software Routers
Software routers based on personal computer (PC) architectures are becoming an important alternative to proprietary and expensive network devices. However, software routers suffer from many limitations of the PC architecture, including, among others, limited bus and central processing unit (CPU) bandwidth, high memory access latency, limited scalability in terms of number of network interface cards, and lack of resilience mechanisms. Multistage PC-based architectures can be an interesting alternative since they permit us to i) increase the performance of single software routers, ii) scale router size, iii) distribute packet manipulation and control functionality, iv) recover from single-component failures, and v) incrementally upgrade router performance. We propose a specific multistage architecture, exploiting PC-based routers as switching elements, to build a high-speed, largesize,scalable, and reliable software router. A small-scale prototype of the multistage router is currently up and running in our labs, and performance evaluation is under wa
Cellular Automaton for Realistic Modelling of Landslides
A numerical model is developed for the simulation of debris flow in
landslides over a complex three dimensional topography. The model is based on a
lattice, in which debris can be transferred among nearest neighbors according
to established empirical relationships for granular flows. The model is then
validated by comparing a simulation with reported field data. Our model is in
fact a realistic elaboration of simpler ``sandpile automata'', which have in
recent years been studied as supposedly paradigmatic of ``self-organized
criticality''.
Statistics and scaling properties of the simulation are examined, and show
that the model has an intermittent behavior.Comment: Revised version (gramatical and writing style cleanup mainly).
Accepted for publication by Nonlinear Processes in Geophysics. 16 pages, 98Kb
uuencoded compressed dvi file (that's the way life is easiest). Big (6Mb)
postscript figures available upon request from [email protected] /
[email protected]
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