Structural study of Cactus Crater

The detailed structure of Cactus Crater, a 105 m diameter nuclear explosion crater formed in water-saturated carbonate rock of Eniwetok Atoll, is delineated using the high to low Mg calcite diagenetic transition as a stratigraphic tracer. Outside Cactus, this transition is observed as a discontinuous horizon which appears to be depressed, possibly as a result of the cratering event, near the crater. Beneath the crater, this transition occurs gradually over a 4.5 ± 0.5 m interval, leading to the following conclusions: material inside Cactus Crater underwent primarily in situ brecciation and mixing, the maximum depth of the excavation cavity is 20 m below sea level, and a fallback breccia lens, if it exists, has a maximum thickness of l m. A central uplift of 4.5 ± 0.5 m is inferred from the observation that the transition interval occurs at a 4 to 5 m greater depth at 1/2 crater radius than in the center. The excavation process, deduced from the Mg calcite transition as well as gamma well log data, involves high velocity injection of strongly shocked material to form the excavation cavity lining. The in situ brecciation and mixing appears to be a turbulent process, probably facilitated by fluidization of the carbonate rock. Based on the Mg calcite transition patterns beneath the crater floor, dynamic rebound is inferred as the modification mechanism for Cactus Crater. Using the Melosh Bingham model for dynamic rebound, a maximum strength of ~1 bar is inferred for the cratered carbonate medium. This strength value is representative of clays, such as those in which Snowball, a chemical explosion crater having dimensions and features similar to Cactus', was formed. Comparisons between Cactus and meteorite impact craters are also presented

Shock compression of aragonite and implications for the equation of state of carbonates

Hugoniot equation of state and release adiabat results are presented for c cut crystals of aragonite, the high-pressure polymorph of calcite, shocked to pressures of up to 40 GPa. A Hugoniot elastic limit is observed at 2.5±0.8 GPa and is similar to that of calcite, which, depending on orientation, ranges from 1.5 to 2.5 GPa. A phase transition, possibly displacive, occurs between 5.5 and 7.6 GPa. Above shock pressures of ∼10 GPa, the aragonite and calcite Hugoniots are nearly coincident, suggesting transformation of both polymorphs to the same phase. Model calculations, attempting to characterize the high pressure CaCO_3 phase are presented. Aragonite release adiabats centered at pressures between 9 and 14 GPa indicate that states with apparent zero-pressure densities from 2.9 to 3.2 g/cm^3 are achieved upon decompression from progressively greater shock pressures. Observed unloading paths from shock pressures above 17 GPa are significantly and consistently shallower (in a density-pressure plane) than those from lower pressures, and zero-pressure densities up to 20% below that of the initial aragonite density are achieved upon unloading; these features suggest that vaporization is occurring upon unloading. According to theoretical shock temperature and entropy calculations, however, the minimum shock pressure for vaporization upon release for aragonite is 55 GPa (and 33 GPa for calcite), significantly higher than the observed value

Dynamic Properties of Carbonates and Applications to Cratering Processes

The response of carbonate minerals and rocks under shock compression is investigated using equation of state, shock metamorphism, and crater morphology studies. Coralline limestone samples from Cactus Crater, a nuclear explosion crater on Runit Island in Eniwetok Atoll, are used in the investigations of shock deformation as well as the crater structural study. Carbonate minerals and rocks shocked in the laboratory to known dynamic stress levels are used to calibrate shock pressures in the Cactus samples. Very low shock pressure deformation effects are detected in the explosively and laboratory shocked samples by two bulk sample techniques: electron spin resonance (ESR) and powder X-ray diffraction. According to ESR studies on calcite from Cactus Crater samples, peak shock pressures of 4.5±0.5 GPa were experienced by the material beneath the crater. Aragonite peak broadening analyses of powder X-ray diffraction spectra allows differentiation between two modes of material deformation, mosaicism (or reduction of crystallite size) and strain; both of these effects are detected in Cactus and in laboratory shocked samples. According to the X-ray analysis, peak pressures of 3±1.5 GPa were experienced by the Cactus samples. A phase transition model, based on the variation of mosaicism and strain effects with shock pressure, is proposed. According to this model, residual strain in aragonite increases (crystallite size remaining approximately the same) until a threshold pressure of 8 to 10 GPa, corresponding to a phase transition, is reached; release from shock states above this pressure results in a discontinuous decrease in crystallite size and strain. The diagenetic high to low magnesium calcite transition boundary occurring in the immediate subsurface of Runit Island is used as a stratigraphic tracer to determine structural features beneath Cactus Crater, including the amount of permanent downward displacement, the presence of a 10 m thick breccia lens which is disturbed and extensively mixed in-situ, and a possible central uplift feature. Applying the Bingham plastic model to Cactus Crater gives a yield strength of approximately 1 bar for the shock-wave engulfed limestone rock; this value is similar to the yield strength of many clays, and suggests a partially liquefied state for the water-saturated limestone immediately after passage of the shock wave. The first aragonite Hugoniot equation of state data are presented. A Hugoniot elastic limit at 2.5±0.8 GPa and a phase transition at 6.5±1.5 GPa are observed. Above 10 GPa, the aragonite and calcite Hugoniots are approximately coincident, suggesting the transformation of both CaCO3 polymorphs to the same high pressure phase. Release adiabats centered at shock pressures above 18 GPa yield pressure-density isentropes which suggest possible dissociation, i.e. CO2 release, during the decompression process. These experimental data disagree with theoretical calculations, which predict incipient vaporization upon release from shock pressures of 55 and 33 GPa on the aragonite and calcite Hugoniots, respectively. Results from release adiabat experiments on calcite agree with the aragonite data and suggest vaporization upon unloading from shock pressures of approximately 37 GPa; a mass balance calculation using the experimental calcite release paths indicates that 45% of the CaCO3 has dissociated upon release to 0.2 GPa pressures.</p

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Age-related differences in left ventricular structure and function between healthy men and women

Full Article Figures & data References Supplemental Citations Metrics Reprints & Permissions Get access Abstract Objectives: Cardiovascular function generally decreases with age, but whether this decrease differs between men and women is unclear. Our aims were twofold: (1) to investigate age-related sex differences in left ventricular (LV) structure, function and mechanics, and (2) to compare these measures between pre- and postmenopausal women in the middle-aged group. Methods: Resting echocardiography was performed in a cross-sectional sample of 82 healthy adults (14 young men, 19 middle-aged men, 15 young women, 34 middle-aged women: 15 premenopausal and 19 postmenopausal). Two-way ANOVAs were used to examine sex × age interactions, and t-tests to compare pre- and postmenopausal women (α < 0.1). Results: Normalized LV mass, stroke volume and end-diastolic volume were significantly lower in middle-aged than young men, but this difference was smaller between middle-aged and young women. Peak systolic apical mechanics were significantly greater in middle-aged men than in middle-aged women, but not between young men and women. Postmenopausal women had significantly lower LV relaxation and mechanics (torsion, twisting velocity and apical circumferential strain rates) compared with middle-aged premenopausal women. Conclusion: Our cross-sectional findings suggest that the hearts of men and women may age differently, with men displaying greater differences in LV volumes accompanied by differences in apical mechanics

Kelio sąnario navigacinio endoprotezavimo operacijų patirtis Lietuvoje

We conducted this multicentrical retrospective study in three Lithuanian hospitals to investigate the importance of using computer-assisted navigation systems during total knee arthroplasty. In this study we analyzed 143 patient navigation system registry data records from three Lithuanian hospitals who underwent a primary total knee arthroplasty operation. The multicentrical retrospective analysis period is from 2006 to 2012. The main evaluation criteria for the operation of computerassisted navigation system record data were the preoperative and postoperative mechanical axis of the limb and the knee joint function before and after surgery.Šio tyrimo tikslas – atlikti daugiacentrę retrospektyviąją analizę, įvertinti Lietuvoje atliktas kelio sąnario endoprotezavimo operacijas, kuriose buvo naudojamos navigacinės sistemos, bei išanalizuoti operacijų registro protokolų duomenis. Daugiacentrės retrospektyviosios analizės laikotarpis 2006–2012 metai. Tyrimo metu išanalizuoti trijų Lietuvos ligoninių 143 pacientai, kuriems buvo atlikta pirminė pilnutinė kelio sąnario endoprotezavimo operacija, ir navigacinių sistemų operacijų registro protokolai. Pagrindiniai vertinimo kriterijai navigacinių sistemų operacijos registrų protokole buvo priešoperacinė ir pooperacinė galūnės mechaninė ašis, kelio sąnario funkcija prieš operaciją ir po jos

GO-GN Research Review 2022

This report summarises some state-of-the-art research relevant to open educational resources (OER) and open educational practices (OEP) that was published recently. The reviews of these articles were written by doctoral and post-doctoral researchers who work in relevant fields and are members of the Global OER Graduate Network (GO-GN)

The Go-GN Open Research Handbook

This Handbook draws together work done between 2020 and 2023 by members of the Global OER Graduate Network (GO-GN). GO-GN is a network of PhD candidates around the world whose research projects include a focus on open education. GO-GN is currently funded through the OER programme of The William and Flora Hewlett Foundation and administered by the Open Education Research Hub from the Institute of Educational Technology at The Open University, UK. In our current phase of activity, we began these collaborative writing efforts with a Research Methods Handbook which was created during the depths of the Covid-19 pandemic. Working together at distance provided an important way to strengthen community links when meeting in person was not possible. The Research Methods Handbook was well received by a much larger audience than we anticipated, and went on to win an Open Research Award. We followed this up with a sister publication, our Conceptual Frameworks Guide. This explores a less well traversed (but nonetheless important) area of scholarly focus. Together, these two explore open approaches to the theory and practice of research in open education. One distinctive feature of our presentation is to foreground the authentic experiences of doctoral researchers who have used specific approaches in researching open education. While it is not possible to cover all approaches in this detail, we hope that important insights are presented in this form of open practice. Throughout 2020-2022 we also regularly engaged our membership through collective reviews of recently published papers and articles. The Research Reviews serve as an overview of recent research but also as a snapshot of the critical responses recorded by doctoral and post-doctoral researchers working in relevant areas. No one volume can claim to comprehensively contain the diversity and variety of open approaches, and this is no exception. But one virtue of openness is that we can draw on the openly licensed works of others to increase our coverage of relevant areas. The Additional Resources at the end of this volume bring together a range of openly licensed texts on open education research and suggests places for further reading and research. Consequently, the information contained here represents a wide range of contributors and collaborators. The original and intended audience for this volume is the doctoral student working on an open education research project - in short, the typical student member of GO-GN and the profile the network exists to support. However, we’ve learned through feedback and analytics that the potential audience for works like this is much larger. Many people who wouldn’t describe themselves as researchers still do research and evaluation. Presenting accessible insights into research foundations and practices helps with this and can be understood as a form of open practice