7,810 research outputs found
Susceptibility of irradiated steels to hydrogen embrittlement
Investigation determined whether irradiated pressure-vessel steels 4340 and 212-B are susceptible to hydrogen embrittlement and to catastrophic failure. Hydrogen-charging conditions which completely embrittled 4340 steel had negligible effect on 212-B steel in tensile and delayed-failure tests
2-stack pushall sortable permutations
In the 60's, Knuth introduced stack-sorting and serial compositions of
stacks. In particular, one significant question arise out of the work of Knuth:
how to decide efficiently if a given permutation is sortable with 2 stacks in
series? Whether this problem is polynomial or NP-complete is still unanswered
yet. In this article we introduce 2-stack pushall permutations which form a
subclass of 2-stack sortable permutations and show that these two classes are
closely related. Moreover, we give an optimal O(n^2) algorithm to decide if a
given permutation of size n is 2-stack pushall sortable and describe all its
sortings. This result is a step to the solve the general 2-stack sorting
problem in polynomial time.Comment: 41 page
Simple permutations poset
This article studies the poset of simple permutations with respect to the
pattern involvement. We specify results on critically indecomposable posets
obtained by Schmerl and Trotter to simple permutations and prove that if
are two simple permutations such that then there
exists a chain of simple permutations such that - or 2
when permutations are exceptional- and . This
characterization induces an algorithm polynomial in the size of the output to
compute the simple permutations in a wreath-closed permutation class.Comment: 15 page
Longest Common Separable Pattern between Permutations
In this article, we study the problem of finding the longest common separable
pattern between several permutations. We give a polynomial-time algorithm when
the number of input permutations is fixed and show that the problem is NP-hard
for an arbitrary number of input permutations even if these permutations are
separable. On the other hand, we show that the NP-hard problem of finding the
longest common pattern between two permutations cannot be approximated better
than within a ratio of (where is the size of an optimal
solution) when taking common patterns belonging to pattern-avoiding classes of
permutations.Comment: 15 page
Average-case analysis of perfect sorting by reversals (Journal Version)
Perfect sorting by reversals, a problem originating in computational
genomics, is the process of sorting a signed permutation to either the identity
or to the reversed identity permutation, by a sequence of reversals that do not
break any common interval. B\'erard et al. (2007) make use of strong interval
trees to describe an algorithm for sorting signed permutations by reversals.
Combinatorial properties of this family of trees are essential to the algorithm
analysis. Here, we use the expected value of certain tree parameters to prove
that the average run-time of the algorithm is at worst, polynomial, and
additionally, for sufficiently long permutations, the sorting algorithm runs in
polynomial time with probability one. Furthermore, our analysis of the subclass
of commuting scenarios yields precise results on the average length of a
reversal, and the average number of reversals.Comment: A preliminary version of this work appeared in the proceedings of
Combinatorial Pattern Matching (CPM) 2009. See arXiv:0901.2847; Discrete
Mathematics, Algorithms and Applications, vol. 3(3), 201
Deciding the finiteness of the number of simple permutations contained in a wreath-closed class is polynomial
We present an algorithm running in time O(n ln n) which decides if a
wreath-closed permutation class Av(B) given by its finite basis B contains a
finite number of simple permutations. The method we use is based on an article
of Brignall, Ruskuc and Vatter which presents a decision procedure (of high
complexity) for solving this question, without the assumption that Av(B) is
wreath-closed. Using combinatorial, algorithmic and language theoretic
arguments together with one of our previous results on pin-permutations, we are
able to transform the problem into a co-finiteness problem in a complete
deterministic automaton
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Assessing Rhode Islandâs Temporary Caregiver Insurance Act: Insights from a Survey of Employers
This report provides new evidence on Rhode Islandâs Temporary Caregiver Insurance (TCI) law, which took effect in January 2014, based on a survey of small and medium-sized businesses in the food services and manufacturing sectors in Rhode Island, Connecticut, and Massachusetts that we carried out in December 2013 (just before the law came into effect) and in January/February 2015 (one year after the law came into effect). We collected information about firm characteristics and productivity, employee life events and work flow, and employer-provided benefits. Comparing Rhode Island employers pre-and post-law to Massachusetts and Connecticut employers over the same time period, we found little evidence of significant impacts of the law on employers (although we note that the sample size for these estimates was small; 104 employers in Rhode Island, and 133 in the other two states combined). We also asked Rhode Island employers directly about their views towards TCI one year after it came into effect and found that a majority of the 213 Rhode Island employers interviewed in 2015 support the new law. Thus, our results suggest that laws like Rhode Islandâs TCI may not have significant impacts on small and medium-sized employers and could garner support by such employers once they have experienced them
Combinatorial specification of permutation classes
This article presents a methodology that automatically derives a
combinatorial specification for the permutation class C = Av(B), given its
basis B of excluded patterns and the set of simple permutations in C, when
these sets are both finite. This is achieved considering both pattern avoidance
and pattern containment constraints in permutations.The obtained specification
yields a system of equations satisfied by the generating function of C, this
system being always positiveand algebraic. It also yields a uniform random
sampler of permutations in C. The method presentedis fully algorithmic
The Effects of Californiaâs Paid Family Leave Program on Mothersâ Leave-Taking and Subsequent Labor Market Outcomes
This analysis uses March Current Population Survey data from 1999-2010 and a differences-in-differences approach to examine how Californiaâs first in the nation paid family leave (PFL) program affected leave-taking by mothers following childbirth, as well as subsequent labor market outcomes. We obtain robust evidence that the California program more than doubled the overall use of maternity leave, increasing it from around three to six or seven weeks for the typical new mother â with particularly large growth for less advantaged groups. We also provide suggestive evidence that PFL increased the usual weekly work hours of employed mothers of one-to-three year-old children by 6 to 9% and that their wage incomes may have risen by a similar amount.
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