Intriguing latest Eocene land-faunal dispersals between South America and the Greater Antilles (northern Caribbean) has inspired the hypothesis of the GAARlandia (Greater Antilles Aves Ridge) land ...bridge. This landbridge, however, should have crossed the Caribbean oceanic plate, and the geological evolution of its rise and demise, or its geodynamic forcing, remain unknown. Here we present the results of a land-sea survey from the northeast Caribbean plate, combined with chronostratigraphic data, revealing a regional episode of mid to late Eocene, trench-normal, E-W shortening and crustal thickening by ∼25%. This shortening led to a regional late Eocene-early Oligocene hiatus in the sedimentary record revealing the location of an emerged land (the Greater Antilles-Northern Lesser Antilles, or GrANoLA, landmass), consistent with the GAARlandia hypothesis. Subsequent submergence is explained by combined trench-parallel extension and thermal relaxation following a shift of arc magmatism, expressed by a regional early Miocene transgression. We tentatively link the NE Caribbean intra-plate shortening to a well-known absolute and relative North American and Caribbean plate motion change, which may provide focus for the search of the remaining connection between 'GrANoLA' land and South America, through the Aves Ridge or Lesser Antilles island arc. Our study highlights the how regional geodynamic evolution may have driven paleogeographic change that is still reflected in current biology.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A highly nonlinear increase in electrical conductivity and concomitant photoemission occurs not only during “flash sintering” but also in presintered, dense specimens. We report results from ...experiments with dense specimens that show a strong correspondence between the intensity of photoemission and electrical conductivity of specimens under a variety of conditions of the electrical parameters. It is proposed that both properties are related to the concentration of electron–hole pairs generated in such experiments.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Abstract
The original flash sintering experiment was carried out by applying an electric field, and switching to current control at the onset of the flash, signaled by a rise in conductivity. Here, ...we consider experiments where the experiment is controlled from the very start, by injecting current, which is increased at a constant rate. The current rates are varied from 50 mA/min to 5000 mA/min. The experiment is continued until, in all cases, the current density reaches 100 mA/mm
2
. The total duration of the experiment ranged from approximately 7 seconds to 700 seconds. The following comparisons to the earlier voltage‐to‐current experiments are noted: (a) in both instances, the onset of the flash is signaled by an unusual rise in conductivity; however, since the power supply remains in the current control mode, the increase in conductivity is manifested by a drop in the voltage generated across the specimen; (b) the blackbody radiation model is modified to include the energy absorbed in specific heat, in order to determine the time‐dependent change in temperature as the current is increased—this correction is particularly significant at the very high current rates; (c) sintering occurs continuously, reaching full density, in all instances, when the current density reaches ~100 mA/mm
2
; and (d) these early experiments suggest that the current‐rate experiments yield fine‐grained microstructure across the entire gauge section of the dog‐bone specimen, presumably because the highly transient conditions of voltage‐to‐current flash experiments are sidestepped. The experiments were carried out on 3 mol% yttria‐stabilized zirconia.
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Ultrafast high‐temperature sintering (UHS) and flash sintering are novel methods for rapid sintering of ceramics, often completed in just a few seconds. Here, we show that both also share two ...additional features: an abrupt rise in electrical conductivity, which is electronic, and electroluminescence. More fundamentally, both are related to phonon physics where MD calculations have shown that proliferation of phonons at the edge of the Brillouin zone can induce Frenkel pairs without the application of electrical fields. Here, we show that, indeed, heating without the application of electric field, can also induce flash: Rapid heating processes of thin films of an oxide‐salt deposited on silk fibers, with a propane torch, are shown to induce electronic conductivity, electroluminescence, and rapid sintering of the oxide. The discussion in this article harkens back to two inventions, more than a century ago, which can now be related to flash and UHS: (i) the Nernst glow lamp circa 1900, made from zirconia, and (ii) the Welsbach mantle, constituted from ceria doped thorium oxide, in the late nineteenth century. Thus, the confluence between high heating rate and electric field induced flash phenomena links the past to the new. The emerging question is how injection of phonons that has been shown to create Frenkels can further induce high electronic conductivity and electroluminescence in oxides. Both electronic conductivity and luminescence are likely related to the generation of electron–hole pairs.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
5.
Continuous flash sintering Sortino, Emanuele; Lebrun, Jean‐Marie; Sansone, Andrea ...
Journal of the American Ceramic Society,
April 2018, 2018-04-00, 20180401, Volume:
101, Issue:
4
Journal Article
Peer reviewed
We develop an algorithm that relates the incubation time for flash initiation to the workpiece velocity as it is pulled through stationary electrodes in a continuous flash sintering experiment. ...Experiments with a whiteware green body that is sintered in this way are compared with the model. A processing map when the workpiece is drawn at a constant velocity is developed. The parameter space for the map is given by the speed and the current flowing through the workpiece. It distinguishes between the regimes for uniform and inhomogeneous sintering. All experiments were carried out at a furnace temperature of 900°C. The study shows the viability of continuous flash sintering of ceramics at speeds of up to 3 mm s−1 with electrodes that form a line contact with the workpiece. Remarkably, higher velocities and higher currents yield better sintering.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Conventional sintering of undoped Y2O3 requires temperatures above 1400°C for a few hours. We show that it can be sintered nearly instantaneously to nearly full density at furnace temperature of ...1133°C under a DC applied field of 500V/cm. At 1000V/cm sintering occurs at 985°C. The FLASH event, when sintering occurs abruptly, is preceded by gradually accelerated field-assisted sintering (FAST). This hybrid behaviour differs from earlier work on yttria-stabilized zirconia where all shrinkage occurred in the flash mode. The microstructure of flash-sintered specimens indicated that densification was accompanied by rapid grain growth. The single-phase nature of flash-sintered Y2O3 was confirmed by high-resolution transmission electron microscopy. The non-linear rise in conductivity accompanying the flash led to Joule heating. It is postulated that densification and grain growth were enhanced by accelerated solid-state diffusion, resulting from both Joule heating and the generation of defects under the applied field.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The flash phenomenon occurs when oxide ceramics are heated above a threshold temperature under an applied electric field. It is defined as an abrupt increase in the conductivity of the specimen. The ...specimen then can be held in this state of high conductivity by switching the power supply from voltage to current control. Here, we report on the emergence of new X‐ray diffraction peaks in 3 mol% yttria‐stabilized zirconia (3YSZ) when the specimen is held in this current controlled state. These peaks are indexed as a pseudocubic phase of zirconia. The peaks extinguish and reappear when the field is turned off and on. The specimen temperature in the flash state is measured from the thermal expansion of platinum, which is placed as a thin film on a small portion of the specimen surface. Experiments without the electric field, at even higher temperatures than those measured with the platinum standard, do not show any change of phase, thus ruling out Joule heating as the cause of this phenomenon. The time dependency of the growth and dissolution of the pseudo cubic phase is reported. These in situ experiments were carried out at the Advanced Photon Source Synchrotron at the Argonne National Laboratory.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Abstract
Triple negative breast cancer (TNBC) patients exhibit poor survival outcomes and lack effective targeted therapies. Using unbiased in vivo genome-wide CRISPR screening, we interrogated ...cancer vulnerabilities in TNBC and identified an interplay between oncogenic and tumor suppressor pathways. This study reveals tumor regulatory functions for essential components of the mTOR and Hippo pathways in TNBC. Using in vitro drug matrix synergy models and in vivo patient-derived xenografts, we further establish the therapeutic relevance of our findings and show that pharmacological inhibition of mTORC1/2 and oncoprotein YAP efficiently reduces tumorigenesis in TNBC. At the molecular level, we find that while verteporfin-induced YAP inhibition leads to apoptosis, torin1-mediated mTORC1/2 inhibition promotes macropinocytosis. Torin1-induced macropinocytosis further facilitates verteporfin uptake, thereby greatly enhancing its pro-apoptotic effects in cancer cells. Overall, our study underscores the power and robustness of in vivo CRISPR genome-wide screens in identifying clinically relevant and innovative therapeutic modalities in cancer.
Our study aims to reconstruct the palaeogeography of the northern part of the Lesser Antilles in order to analyse whether emerged areas might have existed during the Cenozoic, favouring terrestrial ...faunal dispersals between South America and the Greater Antilles along the present-day Lesser Antilles arc. The stratigraphy and depositional environments of the islands of Anguilla, St Martin, Tintamarre, St Barthélemy, Barbuda and Antigua are reviewed in association with multichannel reflection seismic data acquired offshore since the 80's in the Saba, Anguilla and Antigua Banks and in the Kalinago Basin, including the most recent academic and industrial surveys. Seven seismic megasequences and seven regional unconformities are defined, and calibrated from deep wells on the Saba Bank and various dredges performed during marine cruises since the 70's in the vicinity of the islands. Onshore and offshore correlations allow us to depict an updated and detailed sedimentary organisation of the northern part of the Lesser Antilles from the late Eocene to the late Pleistocene. Paleogeographic reconstructions reveal sequences of uplift and emergence across hundredswide areas during the late Eocene, the late Oligocene, the early middle-Miocene and the latest Miocene-earliest Pliocene, interspersed by drowning episodes. The ~200 km-long and ~20 km-wide Kalinago Basin opened as an intra-arc basin during the late Eocene - early Oligocene. These periods of emergence may have favoured the existence of episodic mega-islands and transient terrestrial connections between the Greater Antilles, the Lesser Antilles and the northern part of the Aves Ridge (Saba Bank). During the Pleistocene, archipelagos and mega-islands formed repeatedly during glacial maximum episodes.
•The stratigraphy and depositional setting of the Cenozoic deposits of the northern Lesser Antilles are revisited•Offshore-onshore correlations allow establishing new paleogeographic maps•Paleogeographic maps are discussed in the frame of geodynamics and terrestrial fauna dispersal
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study presents an extensive geochemical data set of 23 samples from St. Barthélemy Island, which belongs to the extinct branch of the Lesser Antilles arc and is currently exposed in the northern ...part of the subduction forearc. Samples were selected to represent all lithologies and main periods of magmatism, that is, Middle‐Late Eocene, Early Oligocene and Late Oligocene. They show enrichment in light rare earth element/medium rare earth element, large ion lithophile elements (Rb and Ba) and isotopic characteristics, suggesting mixing between the mantle and a subduction component (oceanic crust + sediments). Trace element ratios suggest that primary magmas were generated in a normal mid‐oceanic ridge basalt‐type mantle‐wedge that underwent 8%–18% partial melting in the spinel‐stability field. The sediment contribution was low (0.1%–1%) irrespective of the age of the samples. This is similar to what is observed for the northern Lesser Antilles active branch. St. Barthélemy Island shares strong similarities with St. Martin Island, located on the same extinct arc branch, which suggests a similar geodynamic evolution. Oligocene samples displayed an increase in incompatible elements in the magma source, suggesting an increase in sediment melts, which could be correlated with a drastic change in the tectonic regime at that time, characterized by stretching perpendicular to the trench and subsequent basin opening. On Δ7/4Pb versus 206Pb/204Pb, the samples showed a similar trend for both active and extinct islands of the northern Lesser Antilles, suggesting negligible changes in the nature of the magma sources.
Plain Language Summary
Subduction zones, and subduction‐related processes, are responsible for the recycling of oceanic crust and sediments deep down into the mantle, the formation of continental crust and ultimately have a profound influence on both climate and tectonics. Present‐day arcs formed above subduction zones are exceptional natural laboratories for studying arc‐related processes and testing models depicting the Earth's evolution through times. To understand subduction‐related processes, we collected 23 volcanic samples from St. Barthélemy Island (Lesser Antilles Arc, West French Indies) spanning from Eocene to late Oligocene. Geochemical analyzes (major and trace elements and Pb, Sr, Nd, Hf isotopes) can be used to constrain magma genesis at depth, the interactions between the various components involved and their variability over time. Analyzes show that the magmas were formed by 8%–18% partial melting of the mantle wedge with 0.1%–1% of sediment contribution. However, the Oligocene samples are characterized by increased sediment melting in the magma source, which we relate to a change in the tectonic regime and stretching perpendicular to the arc trench. A comparison with lavas from the Greater Antilles arc (Cuba) indicates sources and processes close to those active in the Lesser Antilles.
Key Points
Saint Barthélemy volcanics were formed by 8%–18% partial melting of an N‐MORB type mantle mixed with less than 1% of sediment melts
Geochemical variation during the Early Oligocene is related to a sediment melt increase linked to a drastic change in the tectonic regime
The extinct and active branches of the northern segment of the Lesser Antilles Arc display similar geochemical characteristics
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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