1,721,376 research outputs found
Some considerations on the nomenclatural and taxonomic status of the upper Miocene ocean sunfish Orthagoriscus (Mola) lathanicus Gagnaison & Bouilly, 2009
No full textThe family Molidae comprises one of the tetraodontiform lineages with the least known fossil record. Each new addition to the short list of extinct molid taxa significantly contributes to shed light on the patterns of diversity and distribution of ocean sunfishes through time. This is particularly true for the Miocene, which is regarded as an interval of increased abundance and diversity of ocean sunfishes worldwide. Here, we reconsider the nomenclatural status of the fossil ocean sunfish taxon Orthagoriscus (Mola) lathanicus Gagnaison & Bouilly, 2009 from the upper Miocene of central-western France and argue that it represents an unavailable species name in light of the ICZN Code's criteria. In addition, we briefly discuss the taxonomic significance of the specimens that have been assigned to Orthagoriscus (Mola) lathanicus in the broader framework of the upper Miocene fossil record of the family Molidae from the Northeastern Atlantic region. We conclude that these fossils are too fragmentary to comprise the hypodigm of a new species, and should rather be regarded as not diagnostic below the family-level
Nonconvex Distributed Optimization via Lasalle and Singular Perturbations
Full text linkIn this letter we address nonconvex distributed consensus optimization, a popular framework for distributed big-data analytics and learning. We consider the Gradient Tracking algorithm and, by resorting to an elegant system theoretical analysis, we show that agent estimates asymptotically reach consensus to a stationary point. We take advantage of suitable coordinates to write the Gradient Tracking as the interconnection of a fast dynamics and a slow one. To use a singular perturbation analysis, we separately study two auxiliary subsystems called boundary layer and reduced systems, respectively. We provide a Lyapunov function for the boundary layer system and use Lasalle-based arguments to show that trajectories of the reduced system converge to the set of stationary points. Finally, a customized version of a Lasalle's Invariance Principle for singularly perturbed systems is proved to show the convergence properties of the Gradient Tracking
Timescale Separation for Discrete-Time Nonlinear Stochastic Systems
No full textIn this letter, we present a timescale separation result for discrete-time stochastic systems. We consider the feedback interconnection of two stochastic subsystems, referred to as fast and slow dynamics, and analyze them by combining timescale separation theory and stochastic LaSalle and Lyapunov theorems. Specifically, we separately focus on two auxiliary dynamics, named the boundary layer system (related to the fast part) and the reduced system (related to the slow part). For each of these auxiliary schemes, we identify a stochastic LaSalle testing condition and guarantee that satisfying both conditions is sufficient to prove almost sure LaSalle-type convergence of the original stochastic interconnection. Finally, we focus on stochastic optimization and exploit this new tool to prove almost sure convergence of the popular Stochastic Averaged Gradient and SAGA algorithms in a general nonconvex framework
The early studies on the Eocene Bolca Fossil-Lagerstätte (Italy). An historical overview
No full textThe Eocene Bolca Fossil-Lagerstätte represents one of the best known and most important fossil sites of the Cenozoic Era. Vertebrate, invertebrate and plant fossil remains from Bolca, characterized by an extraordinary completeness, diversity and conservation, can in fact be considered as true icons of Italian paleontology, with specimens that, over the years, have embellished a number of European and North American collections. In addition to the great paleontological and scientific significance of the sites in general, representing a unique example of an ancient biodiversity hotspot approaching the origin of modern reefal ecosystems, fossils from Bolca have been described, figured and discussed for over four centuries, proving of great importance also for the history of paleontology and geology. In this paper we report a historical review of the first contributions by Italian scientists to the knowledge of the fossil sites of the Bolca area, in a period between the sixteenth and the end of the eighteenth century. This period was characterized by cogent debates in the emerging field of Earth Sciences, which find a clear reflection and influence also in the works dedicated to the fossils of Bolca. Although the hypotheses proposed by various scholars to explain the origin of the fossil fish deposits are often in contrast to each other, as in many other cases, several Italian authors that dealt with the Bolca Lagerstätte showed the ability to propose seminal concepts for the Earth Sciences, starting invariably from empiric data collected in the field
Cenozoic vertebrates from the central Mediterranean Basin: A tribute to the palaeontological legacy of Giovanni Capellini (1833-1922)
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Innovative Nanomaterials for Biomedical Applications
Full text linkResearch focusing on innovative nanomaterials for applications in biomedicine and bioengineering has steadily gained attention over the last 20 years [...]
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