1,041 research outputs found
Polynomial combinatorial algorithms for skew-bisubmodular function minimization
Huber et al. (SIAM J Comput 43:1064–1084, 2014) introduced a concept of skew bisubmodularity, as a generalization of bisubmodularity, in their complexity dichotomy theorem for valued constraint satisfaction problems over the three-value domain, and Huber and Krokhin (SIAM J Discrete Math 28:1828–1837, 2014) showed the oracle tractability of minimization of skew-bisubmodular functions. Fujishige et al. (Discrete Optim 12:1–9, 2014) also showed a min–max theorem that characterizes the skew-bisubmodular function minimization, but devising a combinatorial polynomial algorithm for skew-bisubmodular function minimization was left open. In the present paper we give first combinatorial (weakly and strongly) polynomial algorithms for skew-bisubmodular function minimization
An improved bound for the rigidity of linearly constrained frameworks
We consider the problem of characterising the generic rigidity of bar-joint
frameworks in Rd in which each vertex is constrained to lie in a given a ne subspace.
The special case when d = 2 was previously solved by I. Streinu and L. Theran in 2010
and the case when each vertex is constrained to lie in an a ne subspace of dimension t,
and d t(t 1) was solved by Cruickshank, Guler and the rst two authors in 2019. We
extend the latter result by showing that the given characterisation holds whenever d 2t
A structural characterization for certifying Robinsonian matrices
A symmetric matrix is Robinsonian if its rows and columns can be simultaneously reordered in such a way that entries are monotone nondecreasing in rows and columns when moving toward the diagonal. The adjacency matrix of a graph is Robinsonian precisely when the graph is a unit interval graph, so that Robinsonian matrices form a matrix analogue of the class of unit interval graphs. Here we provide a structural characterization for Robinsonian matrices in terms of forbidden substructures, extending the notion of asteroidal triples to weighted graphs. This implies the known characterization of unit interval graphs and leads to an efficient algorithm for certifying that a matrix is not Robinsonian
Possibility of \Lambda\Lambda pairing and its dependence on background density in relativistic Hartree-Bogoliubov model
We calculate a \Lambda\Lambda pairing gap in binary mixed matter of nucleons
and \Lambda hyperons within the relativistic Hartree-Bogoliubov model. Lambda
hyperons to be paired up are immersed in background nucleons in a normal state.
The gap is calculated with a one-boson-exchange interaction obtained from a
relativistic Lagrangian. It is found that at background density
\rho_{N}=2.5\rho_{0} the \Lambda\Lambda pairing gap is very small, and that
denser background makes it rapidly suppressed. This result suggests a
mechanism, specific to mixed matter dealt with relativistic models, of its
dependence on the nucleon density. An effect of weaker \Lambda\Lambda
attraction on the gap is also examined in connection with revised information
of the \Lambda\Lambda interaction.Comment: 8 pages, 6 figures, REVTeX 4; substantially rewritten, emphasis is
put on the LL pairing in pure neutron matte
Effect of self-ion irradiation on hardening and microstructure of tungsten
AbstractThe irradiation hardening and microstructures of pure W and W–3%Re for up to 5.0 dpa by self-ion irradiation were investigated in this work. The ion irradiation was conducted using 18 MeV W6+ at 500 and 800°C. A focused ion beam followed by electro-polishing was used to make thin foil specimens for transmission electron microscope observations. Dislocation loops were observed in all the irradiated samples. Voids were observed in all of the specimens except the W–3%Re irradiated to 0.2 dpa. The hardness was measured by using nanoindentation. The irradiation hardening was saturated at 1.0 dpa for pure W. In the case of W–3%Re, the irradiation hardening showed a peak at 1.0 dpa. The correlation between the microstructure and hardening was investigated
Migration then assembly: Formation of Neptune mass planets inside 1 AU
We demonstrate that the observed distribution of `Hot Neptune'/`Super-Earth'
systems is well reproduced by a model in which planet assembly occurs in situ,
with no significant migration post-assembly. This is achieved only if the
amount of mass in rocky material is -- interior to 1
AU. Such a reservoir of material implies that significant radial migration of
solid material takes place, and that it occur before the stage of final planet
assembly.
The model not only reproduces the general distribution of mass versus period,
but also the detailed statistics of multiple planet systems in the sample.
We furthermore demonstrate that cores of this size are also likely to meet
the criterion to gravitationally capture gas from the nebula, although
accretion is rapidly limited by the opening of gaps in the gas disk. If the
mass growth is limited by this tidal truncation, then the scenario sketched
here naturally produces Neptune-mass objects with substantial components of
both rock and gas, as is observed.
The quantitative expectations of this scenario are that most planets in the
`Hot Neptune/Super-Earth' class inhabit multiple-planet systems, with
characteristic orbital spacings. The model also provides a natural division
into gas-rich (Hot Neptune) and gas-poor (Super-Earth) classes at fixed period.
The dividing mass ranges from at 10 day orbital periods to
at 100 day orbital periods. For orbital periods
days, the division is less clear because a gas atmosphere may be significantly
eroded by stellar radiation.Comment: 41 pages in preprint style, 15 figures, final version accepted to Ap
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