Sea floor bedforms and their influence on slope accommodation (2019)

We sincerely thank Petroleum Geo-Services (PGS) Investigação Petrolífera Limitada, and specifically David Hajovsky and Scott Opdyke, that kindly provided the dataset and allowed us to show these results. We would also like to thank Schlumberger for providing academic licenses of their software (Petrel). We are grateful to Associate Editor Kei Ogata for his support, and we sincerely thank reviewers Daniele Casalbore and Kamaldeen Omosanya for their comments and suggestions that significantly improved the quality of the manuscript.Peer reviewedPostprin

Insights from exact social contagion dynamics on networks with higher-order structures

Recently there has been an increasing interest in studying dynamical processes on networks exhibiting higher-order structures, such as simplicial complexes, where the dynamics acts above and beyond dyadic interactions. Using simulations or heuristically derived epidemic spreading models it was shown that new phenomena can emerge, such as bi-stability/multistability. Here, we show that such new emerging phenomena do not require complex contact patterns, such as community structures, but naturally result from the higher-order contagion mechanisms. We show this by deriving an exact higher-order SIS model and its limiting mean-field equivalent for fully connected simplicial complexes. Going beyond previous results, we also give the global bifurcation picture for networks with 3- and 4-body interactions, with the latter allowing for two non-trivial stable endemic steady states. Differently from previous approaches, we are able to study systems featuring interactions of arbitrary order. In addition, we characterise the contributions from higher-order infections to the endemic equilibrium as perturbations of the pairwise baseline, finding that these diminish as the pairwise rate of infection increases. Our approach represents a first step towards a principled understanding of higher-order contagion processes beyond triads and opens up further directions for analytical investigations.Comment: 19 pages, 14 figure

The BMV experiment : a novel apparatus to study the propagation of light in a transverse magnetic field

In this paper, we describe in detail the BMV (Bir\'efringence Magn\'etique du Vide) experiment, a novel apparatus to study the propagation of light in a transverse magnetic field. It is based on a very high finesse Fabry-Perot cavity and on pulsed magnets specially designed for this purpose. We justify our technical choices and we present the current status and perspectives.Comment: To be published in the European Physical Journal

Characterisation of submarine depression trails driven by upslope migrating cyclic steps: Insights from the Ceará Basin (Brazil)

Circular to elliptical topographic depressions, isolated or organized in trails, have been observed on the modern seabed in different contexts and water depths. Such features have been alternatively interpreted as pockmarks generated by fluid flow, as sediment waves generated by turbidity currents, or as a combination of both processes. In the latter case, the dip of the slope has been hypothesized to control the formation of trails of downslope migrating pockmarks. In this study, we use high-quality 3D seismic data from the offshore Ceará Basin (Equatorial Brazil) to examine vertically stacked and upslope-migrating trails of depressions visible at the seabed and in the subsurface. Seismic reflection terminations and stratal architecture indicate that these features are formed by cyclic steps generated by turbidity currents, while internal amplitude anomalies point to the presence of fluid migration. Amplitude Versus Offset analysis (AVO) performed on partial stacks shows that the investigated anomalies do not represent hydrocarbon indicators. Previous studies have suggested that the accumulation of permeable and porous sediments in the troughs of vertically stacked cyclic steps may create vertical pathways for fluid migration, and we propose that this may have facilitated the upward migration of saline pore water due to fluid buoyancy. The results of this study highlight the importance of gravity-driven processes in shaping the morphology of the Ceará Basin slope and show how non-hydrocarbon fluids may interact with vertically stacked cyclic steps

Tectonic and stratigraphic evolution based on seismic sequence stratigraphy: Central rift section of the campos basin, offshore brazil

The rift section of the Brazilian basins represent the sedimentary record associated with the first stages of Gondwana break‐up in the Early Cretaceous phase (Berriasian to Aptian). The rift succession of the Campos Basin constitutes one of the main petroleum systems of Brazil’s marginal basins. This interval contains the main source rock and important reservoirs in the Lagoa Feia Group deposits. The Lagoa Feia Group is characterized by siliciclastic, carbonate and evaporite sediments deposited during the rift and post‐rift phases. Despite the economic relevance, little is known in stratigraphic terms regarding this rift interval. To date, most studies of the Lagoa Feia Group have adopted a lithostratigraphic approach, while this study proposes a tectonostrati-graphic framework for the deep‐rift succession of the Campos Basin (Lagoa Feia Group), using the fundamentals of seismic sequence stratigraphy. This work also aims to establish a methodological and practical procedure for the stratigraphic analysis of rift basins, using seismic data and seismofacies, and focusing on tectonicstratigraphic analysis. The dataset comprised 2D seismic lines, core and lithological logs from exploration wells. Three seismic facies were identified based on reflector patterns and lithologic data from well cores, providing an improved subdivision of the pre‐, syn‐ and post‐rift stages. The syn‐rift stage was further subdivided based on the geometric patterns of the reflectors. Tectonics was the main controlling factor in the sedimentary succession, and the pattern and geometry of the seismic reflectors of the syn‐rift interval in the Campos Basin allowed the identification of three tectonic systems tracts: (i) a Rift Initiation Systems Tract; (ii) a High Tectonic Activity Systems Tract and (iii) a Low Tectonic Activity Systems Tract

Light propagation in non-trivial QED vacua

Within the framework of effective action QED, we derive the light cone condition for homogeneous non-trivial QED vacua in the geometric optics approximation. Our result generalizes the ``unified formula'' suggested by Latorre, Pascual and Tarrach and allows for the calculation of velocity shifts and refractive indices for soft photons travelling through these vacua. Furthermore, we clarify the connection between the light velocity shift and the scale anomaly. This study motivates the introduction of a so-called effective action charge that characterizes the velocity modifying properties of the vacuum. Several applications are given concerning vacuum modifications caused by, e.g., strong fields, Casimir systems and high temperature.Comment: 13 pages, REVTeX, 3 figures, to appear in Phys. Rev.

A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Maselli, V., Oppo, D., Moore, A. L., Gusman, A. R., Mtelela, C., Iacopini, D., Taviani, M., Mjema, E., Mulaya, E., Che, M., Tomioka, A. L., Mshiu, E., & Ortiz, J. D. A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa. Geology, 48(8), (2020): 808-813, doi:10.1130/G47257.1.The December 2004 Sumatra-Andaman tsunami prompted an unprecedented research effort to find ancient precursors and quantify the recurrence time of such a deadly natural disaster. This effort, however, has focused primarily along the northern and eastern Indian Ocean coastlines, in proximal areas hardest hit by the tsunami. No studies have been made to quantify the recurrence of tsunamis along the coastlines of the western Indian Ocean, leading to an underestimation of the tsunami risk in East Africa. Here, we document a 1000-yr-old sand layer hosting archaeological remains of an ancient coastal Swahili settlement in Tanzania. The sedimentary facies, grain-size distribution, and faunal assemblages indicate a tsunami wave as the most likely cause for the deposition of this sand layer. The tsunami in Tanzania is coeval with analogous deposits discovered at eastern Indian Ocean coastal sites. Numerical simulations of tsunami wave propagation indicate a megathrust earthquake generated by a large rupture of the Sumatra-Andaman subduction zone as the likely tsunami source. Our findings provide evidence that teletsunamis represent a serious threat to coastal societies along the western Indian Ocean, with implications for future tsunami hazard and risk assessments in East Africa.This work was funded by the National Geographic Society (grant N. CP-R008–17). Maselli acknowledges support from the Canada First Research Excellence Fund through the Ocean Frontier Institute. We are extremely grateful to the editor, two anonymous reviewers, J. Bourgeois, G. Eberli, A. Prendergast, and C. Gouramanis for all the suggestions provided, which greatly improved the quality of the manuscript. We would like to thank the United Republic of Tanzania and the University of Dar es Salaam for allowing us to perform the field work activity. This is ISMAR Bologna scientific contribution number 2024

A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa: reply

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Maselli, V., Oppo, D., Moore, A. L., Gusman, A. R., Mtelela, C., Iacopini, D., Taviani, M., Mjema, E., Mulaya, E., Che, M., Tomioka, A. L., Mshiu, E., & Ortiz, J. D. A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa: reply. Geology, 49(1), (2021): E516-E516, https://doi.org/10.1130/G48585Y.1.We appreciate Somerville’s (2020) interest in our work, and the opportunity to further expand the discussion about the occurrence of a trans-oceanic tsunami in the Indian Ocean generated by a megathrust earthquake ~1000 years ago. Somerville suggests a connection between the inferred tsunami deposit presented by us (Maselli et al., 2020) and a tsunami event reported to have occurred in Nagapattinam (India) in the year 900 CE and described in Kalaki Krishnamurty’s book (Rastogi and Jaiswal, 2006)

Production and detection of relic gravitons in quintessential inflationary models

A large class of quintessential inflationary models, recently proposed by Peebles and Vilenkin, leads to post-inflationary phases whose effective equation of state is stiffer than radiation. The expected gravitational waves logarithmic energy spectra are tilted towards high frequencies and characterized by two parameters: the inflationary curvature scale at which the transition to the stiff phase occurs and the number of (non conformally coupled) scalar degrees of freedom whose decay into fermions triggers the onset of a gravitational reheating of the Universe. Depending upon the parameters of the model and upon the different inflationary dynamics (prior to the onset of the stiff evolution) the relic gravitons energy density can be much more sizeable than in standard inflationary models, for frequencies larger than 1 Hz. We estimate the required sensitivity for detection of the predicted spectral amplitude and show that the allowed region of our parameter space leads to a signal smaller (by one 1.5 orders of magnitude) than the advanced LIGO sensitivity at a frequency of 0.1 KHz. The maximal signal, in our context, is expected in the GHz region where the energy density of relic gravitons in critical units (i.e. $h_0^2 \Omega_{GW}$) is of the order of $10^{-6}$, roughly eight orders of magnitude larger than in ordinary inflationary models. Smaller detectors (not necessarily interferometers) can be relevant for detection purposes in the GHz frequency window. We suggest/speculate that future measurements through microwave cavities can offer interesting perspectives.Comment: 24 pages in Revtex style, 7 figure

The Casimir force and the quantum theory of lossy optical cavities

We present a new derivation of the Casimir force between two parallel plane mirrors at zero temperature. The two mirrors and the cavity they enclose are treated as quantum optical networks. They are in general lossy and characterized by frequency dependent reflection amplitudes. The additional fluctuations accompanying losses are deduced from expressions of the optical theorem. A general proof is given for the theorem relating the spectral density inside the cavity to the reflection amplitudes seen by the inner fields. This density determines the vacuum radiation pressure and, therefore, the Casimir force. The force is obtained as an integral over the real frequencies, including the contribution of evanescent waves besides that of ordinary waves, and, then, as an integral over imaginary frequencies. The demonstration relies only on general properties obeyed by real mirrors which also enforce general constraints for the variation of the Casimir force.Comment: 18 pages, 6 figures, minor amendment