Browsing by Author "Soares, Filipa"
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- Automatic completion of data gaps applied to a system of water pumpsPublication . EnguiƧa, Ricardo; Soares, FilipaWe consider a time series with real data from a water lift station, equipped with three water pumps which are activated and deactivated depending on certain starting and halting thresholds. Given the water level and the number of active pumps, both read every 5 min, we aim to infer when each pump was activated or deactivated. To do so, we build an algorithm that sets a hierarchy of criteria based on the past and future of a given interval to identify which thresholds have been crossed during that interval. We then fill the gaps between the 5 min time steps, modeling the water level continuously with a piecewise linear function. This filling takes into account not only every water level reading and every previously identified change of status, but also the fact that activation and deactivation of a pump has no immediate effect on water level. This allows for the fulfillment of the ultimate objective of the problem in its real context, which is to provide the water management company an estimate of how long each pump has been working. Additionally, our estimates correct the errors contained in the time series regarding the number of active pumps.
- Howson's property for semidirect products of semilattices by groupsPublication . Silva, Pedro V.; Soares, FilipaAn inverse semigroup S is a Howson inverse semigroup if the intersection of finitely generated inverse subsemigroups of S is finitely generated. Given a locally finite action of a group G on a semilattice E, it is proved that E*G is a Howson inverse semigroup if and only if G is a Howson group. It is also shown that this equivalence fails for arbitrary actions.
- Local finiteness for Green's relations in semigroup varietiesPublication . Volkov, Mikhail; Silva, Pedro; Soares, FilipaA semigroup variety is said to be locally š¦-finite, where š¦ stands for any of Greenās relations ā, ā, ā, š, or š„, if every finitely generated semigroup in this variety has only finitely many š¦-classes. We characterize locally š¦-finite varieties of finite axiomatic rank in the language of āforbidden objectsā.
- The semigroup ring of a restriction semigroup with an inverse skeletonPublication . Gomes, Gracinda M. S.; Santa-Clara, Catarina; Soares, FilipaIn this paper we investigate some classes of semigroup rings with respect to (semi)primeness and (semi)primitivity. We do so by extending the techniques developed by Munn in (Proc R Soc Edinbur Sect A 107:175-196, 1987) and (Proc R Soc Edinbur Sect A 115:109-117, 1990) for the study of semigroup rings of inverse semigroups. Restriction, weakly ample and ample semigroups are considered.