Northeast- or southwest-dipping subduction in the Cretaceous Caribbean gateway?

Most of the Caribbean plate, which currently lies between the American continents, represents a mantle plume-derived 8–20 km thick Cretaceous oceanic plateau that was formed in the Pacific region and moved eastwards. The northern islands of the Caribbean are largely made up of a dismembered island arc that was located along the western entrance to the inter-American region (termed the Great Arc of the Caribbean) in the mid-late Cretaceous. Importantly, the timing of Caribbean lithospheric movement into the inter-American region is controversial, with one hypothesis advocating that it happened in the Hauterivian-Albian (132.9–100.5 Ma), and a second hypothesis proposing the Turonian-Campanian (93.9–72.1 Ma). In order to investigate this problem, island arc rocks are studied on St. John, U.S. Virgin Islands, which are Barremian (127 Ma) to Santonian (83.6 Ma) in age. Immobile trace element and Ndsingle bondHf radiogenic isotope ratios demonstrate that the arc rocks are derived from the partial melting of an Atlantic MORB-like mantle source region that has been variably contaminated with slab-derived fluids composed of continental detritus and slow sediment clay components. We argue that the lack of a mantle plume geochemical signature in the rocks supports the idea that the movement of Caribbean lithosphere into the inter-American region occurred in the late Cretaceous (post-Santonian) due to a subduction polarity reversal caused by collision of the Caribbean oceanic plateau with the Great Arc of the Caribbean

A genetic algorithm optimization framework for the characterization of hyper-viscoelastic materials:application to human articular cartilage

This study aims to develop an automated framework for the characterization of materials which are both hyper-elastic and viscoelastic. This has been evaluated using human articular cartilage (AC). AC (26 tissue samples from 5 femoral heads) underwent dynamic mechanical analysis with a frequency sweep from 1 to 90 Hz. The conversion from a frequency- to time-domain hyper-viscoelastic material model was approximated using a modular framework design where finite element analysis was automated, and a genetic algorithm and interior point technique were employed to solve and optimize the material approximations. Three orders of approximation for the Prony series were evaluated at N = 1, 3 and 5 for 20 and 50 iterations of a genetic cycle. This was repeated for 30 simulations of six combinations of the above all with randomly generated initialization points. There was a difference between N = 1 and N = 3/5 of approximately ~5% in terms of the error estimated. During unloading the opposite was seen with a 10% error difference between N = 5 and 1. A reduction of ~1% parameter error was found when the number of generations increased from 20 to 50. In conclusion, the framework has proved effective in characterizing human AC

Fulminant immune-mediated necrotising myopathy (IMNM) mimicking myocardial infarction with non-obstructive coronary arteries (MINOCA)

A 74-year-old man, with inflammatory arthritis, recently commenced on adalimumab, presented with a 4-week history of left-sided chest pain, malaise and shortness of breath. Admission ECG showed age-indeterminate left bundle branch block. Troponin T was 4444 ng/L (normal range <15 ng/L) and acute coronary syndrome treatment was commenced. Catheter angiogram revealed mild-burden non-obstructive coronary disease. Cardiac magnetic resonance (CMR) was performed to refine the differential diagnosis and demonstrated no myocardial oedema or late gadolinium enhancement. Extracardiac review highlighted oedema and enhancement of the left shoulder girdle muscles consistent with acute myositis. Creatine kinase was subsequently measured and significantly elevated at 7386 IU/L (normal range 30–200 IU/L in men). Electrophoresis clarified that this was of predominantly skeletal muscle origin. Myositis protocol MRI revealed florid skeletal muscle oedema. The MR findings, together with positive anti-Scl-70 antibodies, suggested fulminant immune-mediated necrotising myopathy presenting as a rare mimic of myocardial infarction with non-obstructive coronary arteries, diagnosed by careful extracardiac CMR review

Biocompatibility and Surface Integrity of Zirconia Ceramics Treated by Laser-plasma Driven Shock-waves

This is a multi-disciplinary paper focused on the preliminary results of deploying laser shock treatment (LST) to ZrO2 ceramics. This work has significance in several industrial sectors for components that will benefit from strengthening. These components are, namely: dental implants; cutting and drawing tools; valves, bearings, pressure vessels, heat exchangers and high-performance scissors and knives, where modification of hard, brittle materials properties such as that of a ZrO2, can yield a performance boost. To elucidate the influence of LST on ZrO2 ceramics, an Nd: YAG laser was used, exhibiting (operating at discrete) laser energies of 17 mJ, 85 mJ and 170 mJ, a 2 mm spot size, a pulse repetition rate of 5 Hz and pulse duration of 10 ns was deployed at 532 nm wavelength. Investigation of ZrO2 ceramic surface integrity revealed a transition from a crack-free topology to a surface dominated by fractures, as the laser energy increased from 85 mJ to 170 mJ. Residual stresses obtained by incremental hole drilling (IHD) were measured to be tensile in the upper layer and the sub-surface layer. However, compression of -595 MPa was found in the sub-surface of the ZrO2 ceramic to a depth of 350 µm after LST, particularly in the transverse direction. Biological analysis metabolic activity measurements, indicated a rise in activity for all samples as the contact time increased (24 h, 3 d and 7 d). The as-received surface revealed a more limited change in metabolism, retaining similar biochemical levels during the first 3 days followed by a slight increase after a week of cultivation, bringing about significant increase in activity in all LST surfaces, relative to the as-received condition. This suggested that a ZrO2 LST exhibited enhanced cell response, particularly, after 7 days of contact-time. The overall outcome of this introductory paper, not only showed that ZrO2 ceramics, can be laser shock treated/peened, to induce some possible beneficial mechanical and physical effects, microstructural and surface topography changes, but also showed that LST can facilitate improvement in cell response to the ZrO2 ceramic. This opens-up, new prospects for treatment of ZrO2 based ceramics for biological applications such as tooth implant screws, where avoiding fractures from mechanical loading, strength enhancement, as well as biocompatibility are all important

Job security and the promotion of workers’ wellbeing in the midst of the COVID-19 pandemic: A study with Canadian workers one to two weeks after the initiation of social distancing measures

Background: Due to the current coronavirus (COVID-19) crisis, workplaces have had to make significant alterations in the way they conduct business. This, in addition to the current financial instability, may put workers at risk of experiencing job insecurity and, in turn, lower wellbeing. Job insecurity is a key determinant of wellbeing, but little is known on how it is impacted by public health crises, and more specifically how it relates to workers’ positive and negative wellbeing in the midst of a pandemic. Research is lacking on resilience levers that workplace interventions should target to support wellbeing in times of insecurity. Objective: Framed from a multidisciplinary perspective (public health, positive and organizational psychology), the study explores (1) workers’ job (in)security during the COVID-19 pandemic one to two weeks after social distancing measures were implemented by Canadian governments, (2) how job (in)security relates to wellbeing during the pandemic, and (3) the potential positive effects of workplace-related resilience levers. Method: 1,073 Canadian workers working full-/part-time or who were temporarily laid off completed an online survey, including measures of wellbeing at work or in general, job security and potential resilience levers (workplace disaster preparedness, policy, social capital). Results: Multiple regression findings highlight that marginalized workers (e.g., women, migrants, people facing financial hardships) reported lower job security, and having temporarily lost one’s job was negatively associated with job security. Low job security was related to lower scores across measures of wellbeing. Distress was high in the sample. Workplace disaster preparedness, policy and social capital were associated with higher wellbeing. The effects of these resilience levers tended to be stronger at higher job security levels. Discussion: Recommendations include a systemic, collaborative approach that includes policies fostering job security as well as resilience-promoting interventions in the workplace to protect/increase the wellbeing of workers during COVID-19