In situ X-ray and acoustic observations of deep seismic faulting upon phase transitions in mantle olivine

Activity of deep earthquakes, which increases with depth from ~400 km to a peak at ~600 km and abruptly decreases to zero at 680 km, is enigmatic, because brittle failure is unlikely to occur under the corresponding pressures of 13−24 GPa. It has been suggested that pressure-induced phase transitions of olivine in subducted slabs are responsible for occurrence of the deep earthquakes, based on deformation experiments under pressure. However, most experiments were made using analogue materials of mantle olivine and at pressures below ~5 GPa, which are not applicable directly to the actual slabs. Here we report the results of deformation experiments combined with in situ X-ray observations and acoustic emission measurements on (Mg,Fe)2SiO4 olivine at 11−17 GPa and 860−1250 K, equivalent to the conditions of colder regions of the slabs subducted into the mantle transition region. We find that faulting occurs only at very limited temperatures of 1100−1160 K, accompanied by intense acoustic emissions from both inside and outside of the sample, immediately before the rupture. The formation of lenticular packets filled with nanocrystalline olivine and wadsleyite is confirmed in the recovered sample without faulting, indicating that the faulting is caused by adiabatic shear heating along the weak layer of the connected lenticular packets, where nanocrystalline olivine plays important roles. Our study suggests that the transformational faulting occurs on the isothermal surface of the metastable olivine wedge in subducted slabs, leading to deep earthquakes in limited regions and depth range.

Pressure-induced metallic phase transition in gallium arsenide up to 24.3 GPa under hydrostatic conditions

A series of experiments of structural, vibrational and electrical transport characterization of gallium arsenide (GaAs) have been performed up to 24.3 GPa under hydrostatic conditions in a diamond anvil cell (DAC) in conjunction with in situ Raman scattering spectroscopy, electrical conductivity measurements, high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Upon compression, a phase transition from the zinc-blende (zb) to the orthorhombic (Cmcm) structure of GaAs was observed at 12.2 GPa through the discontinuous variations of the Raman shifts, Raman full-width at half-maximum values and electrical conductivity. Furthermore, the results of variable temperature electrical conductivity experiments confirmed that the high-pressure phase (Cmcm) exhibited one obvious metallic behavior. Upon decompression, the Raman scattering results of the recovered sample under ambient conditions indicated that the phase transition was reversible under hydrostatic conditions. The reversibility of the phase transition was further verified by HRTEM and AFM images for the recovered sample.

Deep lower-mantle water reservoir implied by the stability of a mixed-valence hydrous iron-rich oxide

The lower mantle, containing both primordial and recycled water, is the most massive potential water reservoir in the Earth. Geophysical and geochemical evidence combined have suggested that the largest heterogeneities in the deep lower mantle may serve as primitive deep-mantle reservoirs hosting a variety of incompatible species including hydrogen. To understand water storage in the deep lower mantle, we conducted experiments in the Fe-O-H, Fe-Al-O-H and Fe-Al-Mg-Si-O-H systems under high pressure-temperature (P-T) conditions, and discovered a previously unknown hexagonal phase (referred to as “H1-phase”) in all the systems. The single-crystal structure of the H1-phase was determined at 79 GPa with a unit-cell of a=10.022(2 )Å and c=2.6121(9) Å and the space group of P63/m, and its composition was obtained as Fe12.76O18H3.7 combining the structure determination and chemical analysis on the recovered sample. More importantly, about 20 mol% of MgO, Al2O3 and SiO2 can be incorporated into the H1-phase in a realistic mantle system Fe-Al-Mg-Si-O-H and its stability field is extended to at least 2400 km along a normal geotherm, implying that the H1-phase can store primordial water in the deepest lower mantle. Therefore, plume-generation zones originated from the deepest lower mantle provide a potential source for higher water contents in basalts associated with mantle plume components.

A Wildlife Forensic Study for the Species Identification of Indian Blackbuck through Forensically Informative Nucleotide Sequencing (FINS)

Identification of exhibits obtained in wildlife cases usually presents challenging tasks for the forensic science investigators. This study describes a casework, where a degraded tissue sample was recovered from pathology department LUVAS University Hisar, Haryana to resolve the identity of the questioned sample. The mitochondrial DNA region of the questioned sample was amplified and sequenced using universal primers of cytochrome b gene to determine the forensically informative nucleotide sites to find the species identity. The obtained sequencing results were compared with the most homologous sequences extracting from NCBI-GenBank database and a phylogenetic tree was done with the aligned sequences to determine the species identity with strong bootstrap support. The informative sites generated revealed that the degree of sequence similarity showed maximum homology (100%) with the sequence obtained from the database. Based on the FINS analysis the recovered sample related to Antilope cervicapra (family Bovidae).

Mining the Kilo-Degree Survey for solar system objects

Context. The search for minor bodies in the solar system promises insights into its formation history. Wide imaging surveys offer the opportunity to serendipitously discover and identify these traces of planetary formation and evolution. Aim. We aim to present a method to acquire position, photometry, and proper motion measurements of solar system objects (SSOs) in surveys using dithered image sequences. The application of this method on the Kilo-Degree Survey (KiDS) is demonstrated. Methods. Optical images of 346 deg2 fields of the sky are searched in up to four filters using the AstrOmatic software suite to reduce the pixel to catalog data. The SSOs within the acquired sources are selected based on a set of criteria depending on their number of observation, motion, and size. The Virtual Observatory SkyBoT tool is used to identify known objects. Results. We observed 20 221 SSO candidates, with an estimated false-positive content of less than 0.05%. Of these SSO candidates, 53.4% are identified by SkyBoT. KiDS can detect previously unknown SSOs because of its depth and coverage at high ecliptic latitude, including parts of the Southern Hemisphere. Thus we expect the large fraction of the 46.6% of unidentified objects to be truly new SSOs. Conclusions. Our method is applicable to a variety of dithered surveys such as DES, LSST, and Euclid. It offers a quick and easy-to-implement search for SSOs. SkyBoT can then be used to estimate the completeness of the recovered sample.

Experiment Study on the Hot-Shock Consolidation of Tungsten Powder

Experiments have been conducted to consolidate tungsten powder using hot-shock consolidation technique combining with underwater shock wave. An exothermic mixture (TiO2-C-Al-Fe2O3) was ignited by an electric wire coil to release a large mount of heat via a self-propagating high-temperature synthesis reaction which was used to pre-heat the sample powder. As getting the needed isothermal temperature, the powder was subsequently consolidated by shock wave generated by explosion of nitro methane, with a detonation velocity of 6.3 km/s and a detonation pressure of 11.9 GPa. The density and Vickers micro-hardness of the consolidated sample were determined and its microstructure was analyzed by scanning electron microscope (SEM). High-density tungsten samples were obtained by optimizing the experimental conditions. In this paper, the relative density and hardness of the recovered sample are 96.5% and 670 HV, respectively.

SHOCK COMPACTION OF Gd-DOPED CERIA CERAMICS

Gd -doped ceria nano powder(~5 nm) was shock-loaded by a plate impact experiment using a single stage light gas gun. A computational model was used to simulate the shock state (pressure and density changes along time) of the sample in two dimensional Eulerian code. The predicted density of compacted sample from the simulation was about 90%. To reveal the effect of shock compaction on sintering behavior, the recovered sample was heat-treated and the microstructure was compared with that of a conventionally compacted and heat-treated sample.

Shock Compaction of WC-Co Powder in Metallic Tube

The tungsten carbide - cobalt, (WC-Co) powder is compacted and bonded to on a stainless steel (SUS304) rod by using explosives. In this research, the experiments are conducted using two methods. They are the method of making the pressure of the explosive act directly on the powder and the method of explosively driving a metal pipe with high speed to create high pressure acting on powder. Crack free bulk material was recovered. Heat-treatment was performed on the recovered sample. After heat treatment, the value of hardness was increased compared with commercial material.

Intrusive Traumatic Childhood Memories in Depression: A Comparison Between Depressed, Recovered and Never Depressed Women

The extent of intrusive traumatic memories of upsetting childhood experiences was investigated in independent samples of female subjects: out-patients with a primary diagnosis of unipolar major depression, women recovered from clinical depression, and healthy controls who had never experienced major depression. Subjects completed self-report questionnaires to measure levels of depression, and intrusive memories of traumatic childhood events. There were no differences between the groups in whether or not they experienced intrusive memories, but severity of intrusions varied significantly. The depressed sample reported significantly more intrusion and avoidance than the recovered or control groups, and the recovered sample reported normal levels of intrusion but higher levels of avoidance of traumatic memories than controls. Severely depressed subjects reported significantly higher levels of intrusion and avoidance than moderately depressed subjects. Implications for psychological models and for the treatment of depression are discussed.

Extraction of 14C from Pore Water in Unsaturated Rock Using Vacuum Distillation

We discuss a vacuum-distillation method for obtaining representative 14C samples from dissolved inorganic carbon in rock pore-waters. Distillation offers four advantages over current centrifugation and compression methods for obtaining pore-water carbon: 1) carbon recovery is possible from rocks that will not yield water by centrifugation or compression; 2) the mass required for 14C analysis can typically be obtained in a single extraction, eliminating the need for storing and combining multiple pore-water collections; 3) water and carbon are extracted and isolated simultaneously, reducing the number of required steps and the potential for contamination; and 4) distillation requires less equipment at lower cost than centrifugation or compression. In this study, isotopic fractionation resulting from incomplete recovery of carbon during distillation was too high for stable isotope applications, but was relatively minor for 14C applications. The lighter isotopes were favored in the recovered phase, resulting in samples depleted in 14C by a maximum of 4%. Mass balance calculations indicate that there may be a significant reservoir of carbon absorbed to mineral surfaces that is only partially removed by this method. Incorporation of adsorbed carbon into the recovered sample did not measurably alter the 14C activity.