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Abstract Ocean acidification refers to a decrease in the pH of the world’s oceans from the oceanic uptake of human-derived atmospheric CO₂. Low pH is known to decrease the calcification and survival of many calcifying invertebrates. Shallow, hard bottom communities along the Western Antarctic Peninsula often have incredibly large numbers of invertebrate mesograzers that shelter on and are mutualists with the dominant brown macroalgae. The common amphipod speciesDjerboa furcipes,Gondogeneia antarctica,andProstebbingia graciliswere collected from the immediate vicinity of Palmer Station, Antarctica (64°46′S, 64°03′W) in January–February 2023 and maintained under three different pH treatments simulating ambient conditions (approximately pH 8.0), near-future conditions for 2100 (pH 7.7), and distant future conditions (pH 7.3) for 8 weeks. Molt number and mortality were monitored throughout the course of the experiment. After the 8 week exposure, amphipods were analyzed for their biochemical compositions including the Mg/Ca ratio of their exoskeletons. There was no significant difference in biochemical composition or survival among the pH treatments for any of the amphipod species. All three species, however, had significantly fewer total numbers of molts in the pH 7.3 treatment than in the ambient treatment. These results suggest that amphipods may be able to maintain their survival in decreased pH by reallocating energy into compensatory behaviors, such as acid–base regulation, and away from energy expensive processes like molting. 

Northern northeastern Brazil (NEB) is a climate change hotspot due to its high biological and social vulnerability to ongoing and future hydroclimate changes. Precipitation in this region is influenced by the Intertropical Convergence Zone (ITCZ), which is largely controlled by the strength of the Atlantic Meridional Overturning Circulation (AMOC). Accordingly, the projected weakening of the AMOC due to anthropogenic global warming may substantially change NEB hydroclimate. Heinrich Stadials (HS), past millennial-scale events during which the AMOC was significantly weaker, provide important insights into the AMOC-ITCZ dynamics. This is especially true for those HS that occurred under similar to modern boundary conditions. HS10 (ca. 110 thousand years ago) was the first HS of Marine Isotope Stage 5, providing an ideal target for investigating AMOC-ITCZ dynamics under relatively warm climate conditions. Here we investigate the response of the surface and deep western equatorial Atlantic (WEA) circulation, as well as NEB precipitation to HS10. Therefore, we use foraminiferal carbon and oxygen stable isotopes and bulk sediment major elemental data from a marine sediment core retrieved from the WEA. Our results record a weakening of the AMOC during HS10 and show a concurrent increased WEA upper stratification and precipitation over NEB. We suggest that the mechanism controlling the WEA upper ocean stratification during HS depends on the background climate. Furthermore, we infer that the southward shift of the ITCZ during HS10 was more limited if compared to the shifts that occurred under colder climate background. Our findings provide useful insights into how a weakening of the AMOC under a relatively warm climate can impact the ITCZ and tropical South American precipitation. 

A boron-rich boron–carbide material (B4+δC) was synthesized by spark plasma sintering of a ball-milled mixture of high-purity boron powder and graphitic carbon at a pressure of 7 MPa and a temperature of 1930 °C. This high-pressure, high-temperature synthesized material was recovered and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Vickers hardness measurements, and thermal oxidation studies. The X-ray diffraction studies revealed a single-phase rhombohedral structure (space group R-3m) with lattice parameters in hexagonal representation as a = 5.609 ± 0.007 Å and c = 12.082 ± 0.02 Å. The experimental lattice parameters result in a value of δ = 0.55, or the composition of the synthesized compound as B4.55C. The high-resolution scans of boron binding energy reveal the existence of a B-C bond at 188.5 eV. Raman spectroscopy reveals the existence of a 386 cm−1 vibrational mode representative of C-B-B linear chain formation due to excess boron in the lattice. The measured Vickers microhardness at a load of 200 gf shows a high hardness value of 33.8 ± 2.3 GPa. Thermal gravimetric studies on B4.55C were conducted at a temperature of 1300 °C in a compressed dry air environment, and its behavior is compared to other high-temperature ceramic materials such as high-entropy transition metal boride. The high neutron absorption cross section, high melting point, high mechanical strength, and thermal oxidation resistance make this material ideal for applications in extreme environments. 

Abstract The standard Bayesian technique for searching pulsar timing data for gravitational-wave bursts with memory (BWMs) using Markov Chain Monte Carlo (MCMC) sampling is very computationally expensive to perform. In this paper, we explain the implementation of an efficient Bayesian technique for searching for BWMs. This technique makes use of the fact that the signal model for Earth-term BWMs (BWMs passing over the Earth) is fully factorizable. We estimate that this implementation reduces the computational complexity by a factor of 100. We also demonstrate that this technique gives upper limits consistent with published results using the standard Bayesian technique, and may be used to perform all of the same analyses of BWMs that standard MCMC techniques can perform. 

Abstract Based on the rate of change of its orbital period, PSR J2043+1711 has a substantial peculiar acceleration of 3.5 ± 0.8 mm s^–1yr^–1, which deviates from the acceleration predicted by equilibrium Milky Way (MW) models at a 4σlevel. The magnitude of the peculiar acceleration is too large to be explained by disequilibrium effects of the MW interacting with orbiting dwarf galaxies (∼1 mm s^–1yr^–1), and too small to be caused by period variations due to the pulsar being a redback. We identify and examine two plausible causes for the anomalous acceleration: a stellar flyby, and a long-period orbital companion. We identify a main-sequence star in Gaia DR3 and Pan-STARRS DR2 with the correct mass, distance, and on-sky position to potentially explain the observed peculiar acceleration. However, the star and the pulsar system have substantially different proper motions, indicating that they are not gravitationally bound. However, it is possible that this is an unrelated star that just happens to be located near J2043+1711 along our line of sight (chance probability of 1.6%). Therefore, we also constrain possible orbital parameters for a circumbinary companion in a hierarchical triple system with J2043+1711; the changes in the spindown rate of the pulsar are consistent with an outer object that has an orbital period of 60 kyr, a companion mass of 0.3M_⊙(indicative of a white dwarf or low-mass star), and a semimajor axis of 1900 au. Continued timing and/or future faint optical observations of J2043+1711 may eventually allow us to differentiate between these scenarios. 

Holocene climate in the high tropical Andes was characterized by both gradual and abrupt changes, which disrupted the hydrological cycle and impacted landscapes and societies. High-resolution paleoenvironmental records are essential to contextualize archaeological data and to evaluate the sociopolitical response of ancient societies to environmental variability. Middle-to-Late Holocene water levels in Lake Titicaca were reevaluated through a transfer function model based on measurements of organic carbon stable isotopes, combined with high-resolution profiles of other geochemical variables and paleoshoreline indicators. Our reconstruction indicates that following a prolonged low stand during the Middle Holocene (4000 to 2400 BCE), lake level rose rapidly ~15 m by 1800 BCE, and then increased another 3 to 6 m in a series of steps, attaining the highest values after ~1600 CE. The largest lake-level increases coincided with major sociopolitical changes reported by archaeologists. In particular, at the end of the Formative Period (500 CE), a major lake-level rise inundated large shoreline areas and forced populations to migrate to higher elevation, likely contributing to the emergence of the Tiwanaku culture. 

Boron nitride (BN) is primarily a synthetically produced advanced ceramic material. It is isoelectronic to carbon and, like carbon, can exist as several polymorphic modifications. Microwave plasma chemical vapor deposition (MPCVD) of metastable wurtzite boron nitride is reported for the first time and found to be facilitated by the application of direct current (DC) bias to the substrate. The applied negative DC bias was found to yield a higher content of sp3 bonded BN in both cubic and metastable wurtzite structural forms. This is confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Nano-indentation measurements reveal an average coating hardness of 25 GPa with some measurements as high as 31 GPa, consistent with a substantial fraction of sp3 bonding mixed with the hexagonal sp2 bonded BN phase.