Search for: All records

We report on a total of 310 samples from marine sediments drilled in the Indian Ocean that were analyzed for glass shard compositions. Samples are mainly from International Ocean Discovery Program Expeditions 353 and 362 but are complemented by samples from Expedition 354; Ocean Drilling Program Legs 183, 121, 120, 119, 116, and 115; and Deep Sea Drilling Project Leg 22. We performed 4327 successful single glass shard analyses with the electron microprobe for major element compositions and conducted 937 successful single analyses with laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for trace element compositions on individual glass shards previously measured with the electron microprobe. In total, we were able to measure glass compositions for 254 samples. Of all the samples, 235 can be classified as tephra layers containing pyroclasts as the predominant component in their clast inventory between the 63 and 125 µm grain size fraction, often exceeding 90 vol%. The compositions of the Indian Ocean marine tephras range from basalt to rhyolite and from basaltic trachyandesite to trachyte and fall into the calc-alkaline, K-rich calc-alkaline, and shoshonitic magmatic series.

Abstract Recent discoveries of water-rich Neptune-like exoplanets require a more detailed understanding of the phase diagram of H 2 O at pressure–temperature conditions relevant to their planetary interiors. The unusual non-dipolar magnetic fields of ice giant planets, produced by convecting liquid ionic water, are influenced by exotic high-pressure states of H 2 O—yet the structure of ice in this state is challenging to determine experimentally. Here we present X-ray diffraction evidence of a body-centered cubic (BCC) structured H 2 O ice at 200 GPa and ~ 5000 K, deemed ice XIX, using the X-ray Free Electron Laser of the Linac Coherent Light Source to probe the structure of the oxygen sub-lattice during dynamic compression. Although several cubic or orthorhombic structures have been predicted to be the stable structure at these conditions, we show this BCC ice phase is stable to multi-Mbar pressures and temperatures near the melt boundary. This suggests variable and increased electrical conductivity to greater depths in ice giant planets that may promote the generation of multipolar magnetic fields.

Silicon (Si) is one of the most abundant elements on Earth, and it is the most widely used semiconductor. Despite extensive study, some properties of Si, such as its behaviour under dynamic compression, remain elusive. A detailed understanding of Si deformation is crucial for various fields, ranging from planetary science to materials design. Simulations suggest that in Si the shear stress generated during shock compression is released via a high-pressure phase transition, challenging the classical picture of relaxation via defect-mediated plasticity. However, direct evidence supporting either deformation mechanism remains elusive. Here, we use sub-picosecond, highly-monochromatic x-ray diffraction to study (100)-oriented single-crystal Si under laser-driven shock compression. We provide the first unambiguous, time-resolved picture of Si deformation at ultra-high strain rates, demonstrating the predicted shear release via phase transition. Our results resolve the longstanding controversy on silicon deformation and provide direct proof of strain rate-dependent deformation mechanisms in a non-metallic system.

While there is movement to create more equitable and holistic admission review processes, faculty continue to place strong emphasis on a single piece of information when making admissions decisions: standardized test scores. This study used an experimental design to test whether instructions provided to faculty prior to assessing doctoral applicants could support holistic review by reducing the weight of the general record examination (GRE) in faculty appraisals of competence and merit for graduate study. Tenured and/or tenure-track faculty ( N =271) were randomly assigned to one of three instructional conditions: Control (no instruction), “Diamond in the Rough,” and “Weed Out.” In addition, faculty participants were randomly assigned to read one of two vignettes of a prospective first-generation student who either received high or average GRE scores. Faculty then rated the applicant’s competence using a three-item survey. As expected, faculty who read the vignette describing the candidate with the high GRE rated him as more competent than faculty who read the average GRE vignette. In addition, being instructed to seek out diamonds in the rough buffered the effect of the GRE score on competence. Faculty were also asked to indicate whether they would need additional information to make an admissions decision.more »They were more likely to ask about grades and research skills than about psychosocial factors that might contextualize the candidate’s performance and perceived competence. The results of this study have implications for creating more equitable doctoral admissions processes that center equity, diversity, and inclusion in decision making.« less