671 research outputs found

    Groups with Decomposable Set of Quasinormal Subgroups

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    A subgroup H of a group G is said to be quasinormal if HX = XH for all subgroups X of G. In this article groups are characterized for which the partially ordered set of quasinormal subgroups is decomposable

    Ocular-based automatic summarization of documents: is re-reading informative about the importance of a sentence?

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    Automatic document summarization (ADS) has been introduced as a viable solution for reducing the time and the effort needed to read the ever-increasing textual content that is disseminated. However, a successful universal ADS algorithm has not yet been developed. Also, despite progress in the field, many ADS techniques do not take into account the needs of different readers, providing a summary without internal consistency and the consequent need to re-read the original document. The present study was aimed at investigating the usefulness of using eye tracking for increasing the quality of ADS. The general idea was of that of finding ocular behavioural indicators that could be easily implemented in ADS algorithms. For instance, the time spent in re-reading a sentence might reflect the relative importance of that sentence, thus providing a hint for the selection of text contributing to the summary. We have tested this hypothesis by comparing metrics based on the analysis of eye movements of 30 readers with the highlights they made afterward. Results showed that the time spent reading a sentence was not significantly related to its subjective value, thus frustrating our attempt. Results also showed that the length of a sentence is an unavoidable confounding because longer sentences have both the highest probability of containing units of text judged as important, and receive more fixations and re-fixations

    Groups with normality conditions for subgroups of infinite rank

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    A well-known theorem of B. H. Neumann states that a group has finite conjugacy classes of subgroups if and only if it is central-by-finite. It is proved here that if G is a generalized radical group of infinite rank in which the conjugacy classes of subgroups of infinite rank are finite, then every subgroup of G has finitely many conjugates, and so G=Z(G) is finite. Corresponding results are proved for groups in which every subgroup of infinite rank has fiznite index in its normal closure, and for those in which every subgroup of infinite rank is finite over its core

    Groups with many abelian subgroups

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    AbstractIt is known that a (generalized) soluble group whose proper subgroups are abelian is either abelian or finite, and finite minimal non-abelian groups are classified. Here we describe the structure of groups in which every subgroup of infinite index is abelian

    Sedimentation and time-of-transition techniques for measuring grain-size distributions in lagoonal flats: comparability of results

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    A comparative study was performed of three instruments used to measure the grain-size distribution of thirty sediment samples from shallow lagoonal flats: the hydrometer, the Sedigraph 5100 and the CIS-1. The hydrometer and Sedigraph are based on sedimentation whereas the CIS-1 uses the time of transition. The percentage of the samples accounted for by the <8 lm fraction was not affected by the technique used, but this was not the case with the clay fraction (<2 lm). Due to its relative independence from the analytical method applied, the <8 lm fraction can be used in ternary diagram classifications. This fraction also has an environmental significance in coastal lagoons in terms of hydrodynamics, organic enrichment and macrozoobenthos assemblages. The linear relationships obtained in this study may provide useful operational indications for similar studies

    Geomorphological Evolution of Volcanic Cliffs in Coastal Areas: The Case of Maronti Bay (Ischia Island)

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    The morphoevolution of coastal areas is due to the interactions of multiple continental and marine processes that define a highly dynamic environment. These processes can occur as rapid catastrophic events (e.g., landslides, storms, and coastal land use) or as slower continuous processes (i.e., wave, tidal, and current actions), creating a multi-hazard scenario. Maronti Bay (Ischia Island, Southern Italy) can be classified as a pocket beach that represents an important tourist and environmental area for the island, although it has been historically affected by slope instability, sea cliff recession, and coastal erosion. In this study, the historical morphoevolution of the shoreline was analysed by means of a dataset of aerial photographs and cartographic information available in the literature over a 25-year period. Furthermore, the role of cliff recession and its impact on the beach was also explored, as in recent years, the stability condition of the area was worsened by the occurrence of a remarkable landslide in 2019. The latter was reactivated following a cloudburst on the 26th of November 2022 that affected the whole Island and was analysed with the Dem of Difference technique. It provided an estimate of the mobilised volumes and showed how the erosion and deposition areas were distributed and modified by wave action. The insights from this research can be valuable in developing mitigation strategies and protective measures to safeguard the surrounding environment and ensure the safety of residents and tourists in this multi-hazard environment

    Groups with many self-normalizing subgroups

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    This paper investigates the structure of groups in which all members of a given relevant set of subgroups are selfnormalizing. In particular, soluble groups in which every nonabelian (or every infinite non-abelian) subgroup is self-normalizing are described

    Groups whose non-normal subgroups have small commutator subgroup

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    The structure of groups whose non-normal subgroups have a finite commutator subgroup is investigated. In particular, it is proved that if k is a positive integer and G is a locally graded group in which every non-normal subgroup has finite commutator subgroup of order at most k, then the commutator subgroup of G is finite. Moreover, groups with finitely many normalizers of subgroups with large commutator subgroup are studied

    Early cementation and accommodation space dictate the evolution of an overstepping barrier system during the Holocene

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    The morphology and stratigraphic features of a well-preserved drowned barrier system, located on the western coast of Sardinia (Mediterranean Sea), are presented here. The barriers were mapped using a multibeam echosounder. The Digital Terrain Model of the seabed revealed five sub-parallel barriers in a depth range of 18\u201337 m, with a distance of ~ 300 m between each single barrier. Direct inspection by scuba diving, revealed that the barriers consist of beachrocks, topped by seagrass meadows growing on a biogenic hardground. The inner-most barrier is limited landward by a steep cliff, 10 m high, bordering the back-barrier area. About 200 km of seismic lines were collected along the barrier system using a 0.4\u20131.0 kJ sparker source and a 3.5 kHz Chirp Subbottom profiler. The seismic data, calibrated with vibrocores, allowed us to recognize the subaerial topographic surface of the last glacial maximum as well as several seismic units interpreted as the Pliocene marine sediments, the pre-Holocene deposits and the Holocene barrier\u2013lagoon complex composed of shoreface, barrier, lagoonal/deltaic and beach deposits. Despite the relatively high seabed gradient (0.3\ub0\u20130.4\ub0) and the relatively low rate of sea-level rise (10\u201315 mm y 12 1), the barriers were well preserved due to the early diagenetic processes which led to a rapid cementation with the formation of beachrocks, and the subsequent overstepping with the rise of the sea level. The development of the overstepping barrier system is strictly related to the antecedent subaerial topography which is, in turn, related to the tectonic setting of the area. The Pliocene seismic unit was lowered by a direct fault at the entrance of the gulf forming a depression filled by sediments. The overstepping barrier system developed following the increase of the seabed gradient and was limited landward by the above-mentioned depression which increased the accommodation space. Following the sea-level rise and the barrier formation, this depression was filled by lagoonal sediments, washover fans and sediments coming from the rivers. The age model of barrier evolution, based on previous sea-level-rise curves during the Holocene, supported by radiocarbon data, highlighted that the whole system evolved over a time period of 1 ka; while the time elapsed from this formation to the drowning of single barriers was estimated to be in the order of magnitude of centuries. Scenarios of short-term evolution of modern barrier\u2013lagoon systems of the adjacent coastal sector, under conditions of accelerated sea-level rise, according to Church et al. (2013) (2013 IPCC report) and Rahmstorf (2007) projections, were elaborated. The study of this ancient analogue suggests that the processes of adaptation of coastal systems to the rising sea level would require times evaluable from centuries to millennia
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