We present a general formalism linking modified entropy functions directly to a modified spacetime metric and, subsequently, to an effective matter sector of entropic origin. In particular, within the framework of general relativity, starting from the first law of black-hole thermodynamics we establish an explicit correspondence between the entropy derivative and the metric function, which naturally leads to an emergent stress-energy tensor representing an anisotropic effective fluid. This backreaction effect of horizon entropy may resolve possible inconsistencies recently identified in black hole physics with modified entropies. As specific examples, we apply this procedure to a wide class of modified entropies, such as Barrow, Tsallis-Cirto, Renyi, Kaniadakis, logarithmic, power-law, loop-quantum-gravity, and exponential modifications, and we derive the associated effective matter sectors, analyzing their physical properties and energy conditions.
The high-frequency decay of the Fourier amplitude spectrum of acceleration is commonly characterized by the parameter κ (kappa). In this study, we estimate the total κ (κr) for nine stiff-soil and rock stations in northwestern Iran using the classical Acceleration Spectrum (AS) method. The dataset (631 three-component strong-motion recordings out to epicentral distances of 50 km) is richer in near-source data than any past study in the region. It thus allows for a more detailed analysis and for minimizing errors and uncertainties stemming from the path, a limitation implicit in most κ studies. Distance dependence due to frequency-dependent anelastic attenuation (Q) is not clearly observed on κr for most stations. The estimated site-specific κ0 values span a relatively wide range despite broadly similar site conditions, from 0.027 to 0.067 s for the horizontal component and from 0.024 to 0.063 s for the vertical component. κ0h exceeds κ0v, with κ0h/κ0v ratios ranging from 0.9–1.9 and an average of about 1.4. Κ0 also shows no clear correlation with Vs30. Differences between stations may partly reflect uneven azimuthal coverage and source–receiver geometry, influencing the scatter of κr values but without clear azimuthal dependence. The event magnitudes span a significant range, from M2.5 to M6.5, and no discernable dependence on magnitude is found, indicating the AS method is appropriately used even for the small events in the dataset. Comparison with published κ0–Vs30 datasets shows that the estimated values fall within the broad range reported for Iranian sites and are more consistent with studies adopting the AS method than with broadband approaches. Horizontal-to-vertical spectral ratios (HVSR) are used as qualitative indicators of frequency-dependent site amplification, and reveal significant deviations within the κ fitting band (8–35 Hz) at several stations. These observations suggest that the measured κ values likely represent a combined effect of site attenuation and amplification, highlighting the need for improved site characterization to better constrain κ0 for seismic hazard applications.
Barrow and Tsallis Holographic Dark Energy (HDE) are two recently proposed extensions of the standard HDE framework, incorporating generalized corrections to horizon entropy through the use of Barrow and Tsallis entropies. Tsallis entropy arises from non-extensive statistical phenomena which account for long-range correlations and deviations from additivity, while Barrow entropy emerges from quantum-gravitational effects on the horizon geometry, associated with fractal modifications and deformations. At the cosmological level, both scenarios lead to the same equations, nevertheless the involved parameters obey different theoretical bounds. In this work, we use observational data from Supernova Type Ia (SNIa), Cosmic Chronometers (CC) and Baryonic acoustic oscillations (BAO), including the recently released DESI DR2 dataset, to place constraints on both scenaria. We show that both can be in agreement with observations, although they cannot alleviate the H_0 tension. However, applying information criteria we deduce that both of them are not favoured comparing to ΛCDM concordance cosmological paradigm.
Airborne pollen and fungal spores (bioaerosols) are important for organisms’ reproduction and at the same time they are also bio-indicators of environmental change and they may have serious impacts on human health, as they can trigger respiratory symptoms. Monitoring bioaerosols in urban settings provides information on the quality of the atmospheric environment, which can be used by urban planners for adopting measures towards optimizing the ecosystem services of the urban greenery. As people reside, work and recreate both outdoors and indoors and at different heights above the ground, three-dimensional bioaerosol monitoring is necessary to capture this spatial variability. The aim of this research was to assess bioaerosol diversity and abundance in a typical urban setting, namely along the height gradient of a multi-storey building of workplaces, in Thessaloniki, Greece, both outdoors and indoors. Two portable Hirst-type volumetric samplers were used simultaneously at the two settings and at four sampling heights, from near ground level and up to 25 m, twice per week, during January-December 2020, collecting a total of 392 outdoor and 392 indoor samples. Both the diversity and abundance of pollen grains and fungal spores decreased with increasing height; this was more pronounced for herbaceous plants (e.g., Poaceae and Urticaceae, p < 0.001) and all fungi (p < 0.001), which implies sources of their particles mostly of local origin, whereas woody plants showed variable patterns suggesting medium or long-range transport. Pollen and fungal spore total abundance was lower indoors than outdoors for all sampling heights, while indoor-outdoor dissimilarity (β-diversity) increased with height for both bioaerosol types. Our findings highlight the complexity of bioaerosol diversity and abundance at different heights and the need for height-specific three-dimensional monitoring.
Red supergiants (RSGs) are cool, evolved massive stars in their final evolutionary stage before exploding as a supernova. However, the evolution and fate of the most luminous RSGs remain uncertain. Observational evidence for luminous warm, post-RSG objects and the apparent lack of luminous RSGs as supernova progenitors suggest a bluewards evolution. Since the 1980s, WOH G64 has been considered the most extreme RSG in the Large Magellanic Cloud, given its large obscuration, outstanding size, luminosity and mass-loss rate. Here we report a sudden, yet smooth change in its apparent nature. Time-series photometry and subsequent spectroscopy reveal an extreme transition in the optical spectral features. We conclude that WOH G64 is a rare, massive symbiotic binary system where the RSG component has transitioned to a yellow hypergiant. This drastic transformation can be explained either by the partial ejection of the pseudo-atmosphere during a common-envelope phase or the return to a quiescent state after an outstanding eruption exceeding 30 years in duration. WOH G64 offers an opportunity to witness stellar evolution in real time and assess the role of binarity on the final phases of massive stars and their resulting supernovae.
