348 research outputs found
Maximum weight cycle packing in directed graphs, with application to kidney exchange programs
Centralized matching programs have been established in several countries to organize kidney exchanges between incompatible patient-donor pairs. At the heart of these programs are algorithms to solve kidney exchange problems, which can be modelled as cycle packing problems in a directed graph, involving cycles of length 2, 3, or even longer. Usually, the goal is to maximize the number of transplants, but sometimes the total benefit is maximized by considering the differences between suitable kidneys. These problems correspond to computing cycle packings of maximum size or maximum weight in directed graphs. Here we prove the APX-completeness of the problem of finding a maximum size exchange involving only 2-cycles and 3-cycles. We also present an approximation algorithm and an exact algorithm for the problem of finding a maximum weight exchange involving cycles of bounded length. The exact algorithm has been used to provide optimal solutions to real kidney exchange problems arising from the National Matching Scheme for Paired Donation run by NHS Blood and Transplant, and we describe practical experience based on this collaboration
Geometric approach to chaos in the classical dynamics of abelian lattice gauge theory
A Riemannian geometrization of dynamics is used to study chaoticity in the
classical Hamiltonian dynamics of a U(1) lattice gauge theory. This approach
allows one to obtain analytical estimates of the largest Lyapunov exponent in
terms of time averages of geometric quantities. These estimates are compared
with the results of numerical simulations, and turn out to be very close to the
values extrapolated for very large lattice sizes even when the geometric
quantities are computed using small lattices. The scaling of the Lyapunov
exponent with the energy density is found to be well described by a quadratic
power law.Comment: REVTeX, 9 pages, 4 PostScript figures include
Strange hyperon and antihyperon production from quark and string-rope matter
Hyperon and antihyperon production is investigated using two microscopical
models: {\bf (1)} the fast hadronization of quark matter as given by the ALCOR
model; {\bf (2)} string formation and fragmentation as in the HIJING/B model.
We calculate the particle numbers and momentum distributions for Pb+Pb
collisions at CERN SPS energies in order to compare the two models with each
other and with the available experimental data. We show that these two
theoretical approaches give similar yields for the hyperons, but strongly
differ for antihyperons.Comment: 11 pages, Latex, 3 EPS figures, contribution to the Proceedings of
the 4th International Conference on Strangeness in Quark Matter (SQM'98),
Padova, Italy, 20-24 July 199
Relativistic hydrodynamics with strangeness production
The relativistic hydrodynamic approach is used to describe production of
strangeness and/or heavy quarks in ultrarelativistic heavy ion reactions.
Production processes are important ingredients of dissipative effects in the
hadronic liquid. Beyond viscosity also chemo- and thermo-diffusion processes
are considered. This also allows to specify chemical and thermal freeze-out
conditions.Comment: v.2 with minor editorial corrections, 7 pages, talk given on the
SQM2007 conference, Levoca, June 24-29, 2007. To appear in the proceceeding:
Journal of Physics
How much is your diet? (Estimation about prices of “traditional Hungarian”, diabetic, low energy diets, and related life-style expenses)
Nutrition and lifestyle-related diseases are some of the leading morbidities among the Hungarian population. People who want to lose weight often complain that healthy diet is expensive.
Our aim was to quantify the costs of three different types of diet for a three-day period. We compared “traditional Hungarian”, low energy, and diabetic diets, considering both energy content and expenses related to lifestyle.
According to our estimation: diabetic (including medication) and ”traditional” Hungarian diets were the most expensive. Low energy diet proved to be the most cost-effective despite the extra expenditures of higher physical activity
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Chemical sensing properties of single wire and mat form sensor structures
fabricated from the same carbon nanotube (CNT) materials have been compared.
Sensing properties of CNT sensors were evaluated upon electrical response in
the presence of five vapours as acetone, acetic acid, ethanol, toluene, and
water. Diverse behaviour of single wire CNT sensors was found, while the mat
structures showed similar response for all the applied vapours. This indicates
that the sensing mechanism of random CNT networks cannot be interpreted as a
simple summation of the constituting individual CNT effects, but is associated
to another robust phenomenon, localized presumably at CNT-CNT junctions, must
be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and
Processing 201
Canonical Ensemble of Initial States Leading to Chiral Fluctuations
In energetic heavy ion collisions, if quark-gluon plasma is formed, its
hadronization may lead to observable critical fluctuations, i.e., DCC
formation. The strength and observability of these fluctuations depend on the
initial state. Here we study the canonical ensemble of initial states of chiral
fluctuations in heavy ion collisions and the probability to obtain observable
domains of chiral condensates.Comment: 13 pages (figures included) Accepted for publication in Phys. Rev.
Quantum Chaos in Compact Lattice QED
Complete eigenvalue spectra of the staggered Dirac operator in quenched
compact QED are studied on and lattices. We
investigate the behavior of the nearest-neighbor spacing distribution as
a measure of the fluctuation properties of the eigenvalues in the strong
coupling and the Coulomb phase. In both phases we find agreement with the
Wigner surmise of the unitary ensemble of random-matrix theory indicating
quantum chaos. Combining this with previous results on QCD, we conjecture that
quite generally the non-linear couplings of quantum field theories lead to a
chaotic behavior of the eigenvalues of the Dirac operator.Comment: 11 pages, 4 figure
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