Thermoelasticity of Fe2+-bearing bridgmanite

We present LDA+U calculations of high temperature elastic properties of bridgmanite with composition (Mg$_{(1-x)}$Fe$_{x}^{2+}$)SiO$_3$ for $0\le{x}\le0.125$. Results of elastic moduli and acoustic velocities for the Mg-end member (x=0) agree very well with the latest high pressure and high temperature experimental measurements. In the iron-bearing system, we focus particularly on the change in thermoelastic parameters across the state change that occurs in ferrous iron above $\sim$30 GPa, often attributed to a high-spin (HS) to intermediate spin (IS) crossover but explained by first principles calculations as a lateral displacement of substitutional iron in the perovskite cage. We show that the measured effect of this change on the equation of state of this system can be explained by the lateral displacement of substitutional iron, not by the HS to IS crossover. The calculated elastic properties of (Mg$_{0.875}$Fe$_{0.125}^{2+}$)SiO$_3$ along an adiabatic mantle geotherm, somewhat overestimate longitudinal velocities but produce densities and shear velocities quite consistent with Preliminary Reference Earth Model data throughout most of the lower mantle.Comment: Accepted for Geophysical Research Letters (DOI: 10.1002/2014GL062888

Anomalous thermal properties and spin crossover of ferromagnesite (Mg,Fe)CO3

Ferromagnesite (Mg,Fe)CO3, also referred to as magnesiosiderite at high iron concentration, is a solid solution of magnesite (MgCO3) and siderite (FeCO3). Ferromagnesite is believed to enter the Earth's lower mantle via subduction and is considered a major carbon carrier in the Earth's lower mantle, playing a key role in the Earth's deep carbon cycle. Experiments have shown that ferromagnesite undergoes a pressure-induced spin crossover, accompanied by volume and elastic anomalies, in the lower-mantle pressure range. In this work, we investigate thermal properties of (Mg,Fe)CO3 using first-principles calculations. We show that nearly all thermal properties of ferromagnesite are drastically altered by iron spin crossover, including anomalous reduction of volume, anomalous softening of bulk modulus, and anomalous increases of thermal expansion, heat capacity, and Guneisen parameter. Remarkably, the anomaly of heat capacity remains prominent (up to 40%) at high temperature without smearing out, which suggests that iron spin crossover may significantly affect the thermal properties of subducting slabs and the Earth's deep carbon cycle.Comment: Main text: 24 pages and 8 figures; Supplemental Material: 8 pages, 3 tables, and 1 figur

Huge enhancement of electronmechanical responses in compositionally modulated PZT

Monte Carlo simulations based on a first-principles-derived Hamiltonian are conducted to study the properties of PZT alloys compositionally modulated along the [100] pseudocubic direction near the morphotropic phase boundary (MPB). It is shown that compositional modulation causes the polarization to continuously rotate away from the modulation direction, resulting in the unusual triclinic and C-type monoclinic ground states and huge enhancement of electromechanical responses (the peak of piezoelectric coefficient is as high as 30000 pC/N). The orientation dependence of dipole-dipole interaction in modulated structure is revealed as the microscopic mechanism to be responsible for these anomalies.Comment: 5 pages, 4 figure

Constituency Parsing using LLMs

Constituency parsing is a fundamental yet unsolved natural language processing task. In this paper, we explore the potential of recent large language models (LLMs) that have exhibited remarkable performance across various domains and tasks to tackle this task. We employ three linearization strategies to transform output trees into symbol sequences, such that LLMs can solve constituency parsing by generating linearized trees. We conduct experiments using a diverse range of LLMs, including ChatGPT, GPT-4, OPT, LLaMA, and Alpaca, comparing their performance against the state-of-the-art constituency parsers. Our experiments encompass zero-shot, few-shot, and full-training learning settings, and we evaluate the models on one in-domain and five out-of-domain test datasets. Our findings reveal insights into LLMs' performance, generalization abilities, and challenges in constituency parsing

Elastic anisotropy of lizardite at subduction zone conditions

Subduction zones transport water into Earth's deep interior through slab subduction. Serpentine minerals, the primary hydration product of ultramafic peridotite, are abundant in most subduction zones. Characterization of their high-temperature elasticity, particularly their anisotropy, will help us better estimate the extent of mantle serpentinization and the Earth's deep water cycle. Lizardite, the low-temperature polymorph of serpentine, is stable under the P-T conditions of cold subduction slabs (< 260{\deg}C at 2 GPa), and its high-temperature elasticity remains unknown. Here we report ab initio elasticity and acoustic wave velocities of lizardite at P-T conditions of subduction zones. Our static results agree with previous studies. Its high-temperature velocities are much higher than previous experimental-based lizardite estimates with chrysotile but closer to antigorite velocities. The elastic anisotropy of lizardite is much larger than that of antigorite and could better account for the observed large shear-wave splitting in some cold slabs such as Tonga

The effect of acupuncture at the Taiyang acupoint on visual function and EEG microstates in myopia

ObjectiveAcupuncture has certain effects to improve myopia visual function, but its neural mechanism is unclear. In this study, we acupunctured at the right Taiyang acupoint of myopic patients to analyze the effects of acupuncture on visual function and electroencephalographic activity and to investigate the correlation between improvements in visual function and changes in the brain.MethodsIn this study, a total of 18 myopic patients were recruited. The contrast sensitivity (CS) of the subjects was examined before and after acupuncture, and electroencephalography (EEG) data of the entire acupuncture process were recorded.ResultsThe study found that compared with before acupuncture, the CS of both eyes in myopic patients at each spatial frequency was increased after acupuncture; compared with the resting state, the contribution of microstate C was decreased during the post-acupuncture state, and the transition probability between microstate A and microstate C was reduced; in addition, the contribution of microstate C was negatively correlated with CS at both 12 and 18 cpd.ConclusionThe contrast sensitivity of myopic patients was improved after acupuncture at the Taiyang acupoint (20 min), which may be related to microstate C