Using constraints to address the instabilities of automated prestack velocity analysis

Generalized prestack velocity analysis methods that use an automated approach to resolve laterally variable interval velocity fields are beset by a series of problems. The problem of resolving lateral velocity variations has inherent complications that prevent automated methods from being robust enough to be applied routinely to data from a variety of geologic provinces. The use of automated prestack velocity analysis methods will not eliminate the step of carefully producing an initial velocity model derived from regional geologic information and an interpretation of a conventionally processed section. For the methods to regularly produce useful additional information, the unique characteristics of each application must be input into the prestack velocity analysis with the use of inversion constraints. These constraints serve either to adapt the generalized prestack velocity analysis to a focused objective in a particular area or to provide iterative, interpretational tools that help the user produce a velocity model

Creation of two-dimensional coulomb crystals of ions in oblate Paul traps for quantum simulations

We develop the theory to describe the equilibrium ion positions and phonon modes for a trapped ion quantum simulator in an oblate Paul trap that creates two-dimensional Coulomb crystals in a triangular lattice. By coupling the internal states of the ions to laser beams propagating along the symmetry axis, we study the effective Ising spin-spin interactions that are mediated via the axial phonons and are less sensitive to ion micromotion. We find that the axial mode frequencies permit the programming of Ising interactions with inverse power law spin-spin couplings that can be tuned from uniform to $r^{-3}$ with DC voltages. Such a trap could allow for interesting new geometrical configurations for quantum simulations on moderately sized systems including frustrated magnetism on triangular lattices or Aharonov-Bohm effects on ion tunneling. The trap also incorporates periodic boundary conditions around loops which could be employed to examine time crystals.Comment: 17 pages, 8 figures, submitted to the journal EPJ Quantum Technology for the thematic Series on Quantum Simulation

In search of Leonardo: Computer-based facial image analysis of Renaissance artworks for identifying Leonardo as subject

One of the enduring mysteries in the history of the Renaissance is the adult appearance of the archetypical "Renaissance Man," Leonardo da Vinci. His only acknowledged self-portrait is from an advanced age, and various candidate images of younger men are difficult to assess given the absence of documentary evidence. One clue about Leonardo's appearance comes from the remark of the contemporary historian, Vasari, that the sculpture of David by Leonardo's master, Andrea del Verrocchio, was based on the appearance of Leonardo when he was an apprentice. Taking a cue from this statement, we suggest that the more mature sculpture of St. Thomas, also by Verrocchio, might also have been a portrait of Leonardo. We tested the possibility Leonardo was the subject for Verrocchio's sculpture by a novel computational technique for the comparison of three-dimensional facial configurations. Based on quantitative measures of similarities, we also assess whether another pair of candidate two-dimensional images are plausibly attributable as being portraits of Leonardo as a young adult. Our results are consistent with the claim Leonardo is indeed the subject in these works, but we need comparisons with images in a larger corpora of candidate artworks before our results achieve statistical significance

Capabilities and limitations of a new thermal finite volume model for the evaluation of laser-induced thermo-mechanical retinal damage

Many experimental studies focus on the physical damage mechanisms of short-term exposure to laser radiation. In the nanosecond (ns) pulse range, damage in the Retinal Pigment Epithelium (RPE) will most likely occur at threshold levels due to bubble formation at the surface of the absorbing melanosome. The energy uptake of the melanosomes is one key aspect in modeling the bubble formation and damage thresholds. This work presents a thermal finite volume model for the investigation of rising temperatures and the temperature distribution of irradiated melanosomes. The model takes the different geometries and thermal properties of melanosomes into account, such as the heat capacity and thermal conductivity of the heterogeneous absorbing melanosomes and the surrounding tissue. This is the first time the size and shape variations on the melanosomes‘ thermal behavior are considered. The calculations illustrate the effect of the geometry on the maximum surface temperature of the irradiated melanosome and the impact on the bubble formation threshold. A comparison between the calculated bubble formation thresholds and the RPE cell damage thresholds within a pulse range of 3 to 5000 ns leads to a mean deviation of = 22 mJ ∕ cm2 with a standard deviation of = 21 mJ ∕ cm2. The best results are achieved between the simulation and RPE cell damage thresholds for pulse durations close to the thermal confinement time of individual melanosomes

Steering the Surprisingly Modular π-Acceptor Properties of N-Heterocyclic Carbenes: Implications for Gold Catalysis

Thumbnail image of graphical abstract Accept it! Although the π-acceptor properties of N-heterocyclic carbenes (NHCs) are often considered negligible, they can be enhanced to the extent that they start to dominate the catalytic behavior of gold–NHC complexes (see scheme). As it seems to be easier to tune the π acidity of NHCs than to alter their σ-donor properties, the general perception of this important class of ancillary ligands needs to be revised

DAS field dataset to compare technologies and deployment scenarios

This report describes a Distributed Acoustic Sensor (DAS) dataset acquired by DigiMon partners at the Containment and Monitoring Institute’s (CaMI) Field Research Station (FRS), Canada, between 6th to 10th September 2021. The field dataset contributes to the Deliverable D1.1 of the DigiMon project (DAS field dataset to compare technologies and deployment scenarios), which supports tasks 1.2 and 1.3 of the project. The objective of the DigiMon project is to develop an early-warning system for Carbon Capture and Storage (CCS), which utilises a broad range of sensor technologies including DAS. While the system is primarily focused on CCS projects located in shallow offshore environment of the North Sea, it is also intended to be adaptable to onshore settings. Some of the key areas that the systems will monitor include the movement of the plume within the reservoir, well integrity, and CO2 leakage into the overburden. A combination of both active and passive seismic methods will be deployed to track the movement of CO2, for example seismic reflection to image seismic velocity changes and microseismics to capture fault activation. Acquiring seismic surveys using DAS is highly novel and offers cost-effective approach which can significantly increase the spatial resolution of the survey data; however, it has had limited use in the operational environment with several technical challenges still needing to be resolved, such as the transfer function of DAS. CaMi FRS was selected as a field test location as the site has been specifically established to advance the development of monitoring technologies and protocols for CCS operations. At CaMi FRS, several different monitoring arrays have been installed which are directly applicable to DigiMon. This includes a 5km loop of DAS optical fibre, located with a 1.1 km surface trench and two observation wells, an array of surface and borehole geophone nodes, and 6 broadband seismometers operating by the University of Bristol. This monitoring infrastructure has been primarily installed to monitor CO2 injections into the Basal Belly River sandstone formation at approximately 300m below ground level. Injection of CO2 began at FRS in 2019 and during this time microseismic events have been recorded, albeit at shallower levels than the injection point. The site therefore provides a potential DAS dataset which contains both active and passive measurements for the DigiMon project. The abundance of instrumentation including DAS, geophones, and broadband seismometers provides a unique chance to test the capacity of these instruments for C02 storage monitoring

Youth, faith, climate change and environmental consciousness : a case for sustainable development

Climate change and environmental destruction are amongst the most threatening challenges to humanity and sustainable development globally. Young people find themselves right in the centre of debates about ecological (in)justice, environmental awareness, and climate change discourses and practices. Youth movements worldwide, such as ‘Extinction Rebellion’ and ‘Fridays for Future,’ demonstrate that youths are concerned about environmental problems and ready to become active in climate movements. Their willingness to act on their own behalf makes them one of the most important and interesting groups to learn more about in relation to the challenge of building a deeper awareness of environmental issues. Exploring and learning how youths are engaged with these discourses, how they contribute to a wider social consciousness of environmental issues and how such awareness is affected by different factors, such as the role and the contribution of young people’s own religious beliefs, are, therefore, of paramount importance.Special Collection: Youth, Faith, Climate Change and Environmental Consciousness: A Case for Sustainable Development, sub-edited by Jacques Beukes (University of Pretoria), Juliane Stork (Humboldt University, Berlin) and Ignatius Swart (University of the Western Cape).http://www.hts.org.za/am2022Practical Theolog

Youth, faith, climate change and environmental consciousness: A case for sustainable development

Climate change and environmental destruction are amongst the most threatening challenges to humanity and sustainable development globally. Young people find themselves right in the centre of debates about ecological (in)justice, environmental awareness, and climate change discourses and practices. Youth movements worldwide, such as ‘Extinction Rebellion’ and ‘Fridays for Future,’ demonstrate that youths are concerned about environmental problems and ready to become active in climate movements. Their willingness to act on their own behalf makes them one of the most important and interesting groups to learn more about in relation to the challenge of building a deeper awareness of environmental issues. Exploring and learning how youths are engaged with these discourses, how they contribute to a wider social consciousness of environmental issues and how such awareness is affected by different factors, such as the role and the contribution of young people’s own religious beliefs, are, therefore, of paramount importance