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Center for Research and Development in Mathematics and Applications
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On the invariance of certain vanishing subspaces of Morrey spaces with respect to some classical operators
Publication . Alabalik, Aysegul C.; Almeida, Alexandre; Samko, Stefan
We consider subspaces of Morrey spaces defined in terms of various vanishing properties of functions. Such subspaces were recently used to describe the closure of C-0(infinity) (R-n) in Morrey norm. We show that these subspaces are invariant with respect to some classical operators of harmonic analysis, such as the Hardy-Littlewood maximal operator, singular type operators and Hardy operators. We also show that the vanishing properties defining those subspaces are preserved under the action of Riesz potential operators and fractional maximal operators.
Preservation of certain vanishing properties of generalized Morrey spaces by some classical operators
Publication . Alabalik, Aysegul C.; Almeida, Alexandre; Samko, Stefan
We show that certain vanishing properties defining closed subspaces of generalized Morrey spaces are preserved under the action of various classical operators of harmonic analysis, such as maximal operators, singular-type operators, Hardy operators, and fractional integral operators. Those vanishing subspaces were recently used to deal with the delicate problem on the description of the closure of nice functions in Morrey norm.
Bounding anisotropic Lorentz invariance violation from measurements of the effective energy scale of quantum gravity
Publication . Guerrero, Merce; Campoy-Ordaz, Anna; Potting, Robertus; Gaug, Markus
Observations of energy-dependent photon time delays from distant flaring sources provide significant constraints on Lorentz invariance violation (LIV). Such effects originate from modified vacuum dispersion relations causing differences in propagation times for photons emitted simultaneously from gamma-ray bursts, active galactic nuclei, or pulsars. These modifications are often parametrized within a general framework by an effective quantum gravity energy scale EQG;n. While such general constraints are well established in the LIV literature, their translation into specific coefficients of alternative theoretical frameworks, such as the Standard-Model extension (SME), is rarely carried out. In particular, existing bounds on the quadratic case (n ¼ 2) of EQG;n can be systematically converted into constraints on the nonbirefringent, CPT-conserving SME coefficients c ð6Þ ðIÞjm. This work provides a concise overview of the relevant SME formalism and introduces a transparent conversion method from EQG;2 to SME parameters. We review the most stringent time-of-flight-based bounds on EQG;n and standardize them by accounting for systematics, applying missing prefactors, and transforming results into two-sided Gaussian uncertainties where needed. We then use these standardized constraints, along with additional bounds from the literature, to improve bounds on the individual SME coefficients of the photon sector by about an order of magnitude. A consistent methodology is developed to perform this conversion from the general LIV framework to the SME formalism.
Spatiotemporal patterns and environmental drivers of Physalia physalis strandings along mainland Portugal (northeastern Atlantic)
Publication . Carvalho, Patrícia; Henrique Cordeiro, Clara Maria; Pereira, Soraia; Santos, Antonina dos
Physalia physalis is a cosmopolitan colonial organism frequently observed in Portuguese waters. The species has long tentacles, provided with cnidocytes, which release a strong poison when in contact with other organisms, and cause skin reactions and severe pain in humans. Events of rapid reproduction, common in these species, may have important economic and social consequences. This study explores for the first time, the relationships between long-term assessment of P. physalis strandings, using data from the GelAvista citizen science project, and environmental variables - Sea Surface Temperature (SST), wind direction and intensity, the North Atlantic Oscillation (NAO), and upwelling indices - along the Portuguese coast, using a Generalized Linear Mixed-Effects Model. Strandings of P. physalis were concentrated along the western coast and were rare in the south. More than 54 % of the records corresponded to a single individual. Sightings peaked from November through May (winter and spring), mirroring the negative correlation with SST. Wind patterns strongly influenced stranding events: winds likely pushed colonies toward the shore, while calm conditions facilitated their arrival on beaches. In March 2018, an upwelling event in the south coast combined with a series of storms likely underlay the high stranding numbers observed in the southern area, with more than 50 individuals of P. physalis per record. A positive trend in sightings over the study period suggests that P. physalis occurrences may be rising, even after accounting for wind and SST, which might be linked to climate change. Our findings underscore the value of ongoing jellyfish monitoring via citizen science platforms like GelAvista and highlight the need for expanded high-resolution environmental datasets. Moreover, this work establishes a foundation for experimental studies to elucidate the mechanisms behind P. physalis strandings. For future research, time series techniques for imputing missing values may be utilized to enhance the completeness of environmental datasets and strengthen analytical robustness in subsequent studies focused on time series analysis.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UID/MAT/04106/2019