Hybrid Functional Study Rationalizes the Simple Cubic Phase of Calcium at High Pressures

Simple cubic (SC) phase has been long experimentally determined as the high-pressure phase III of elemental calcium (Ca) since 1984. However, recent density functional calculations within semi-local approximation showed that this SC phase is structurally unstable by exhibiting severely imaginary phonons, and is energetically unstable with respect to a theoretical body-centered tetragonal I41/amd structure over the pressure range of phase III. These calculations generated extensive debates on the validity of SC phase. Here we have re-examined the SC structure by performing more precise density functional calculations within hybrid functionals of Heyd-Scuseria-Erhzerhof (HSE) and PBE0. Our calculations were able to rationalize fundamentally the phase stability of SC structure over all other known phases by evidence of its actual energetic stability above 33 GPa and its intrinsically dynamical stability without showing any imaginary phonons in the entire pressure range studied. We further established that the long-thought theoretical I41/amd structure remains stable in a narrow pressure range before entering SC phase and is actually the structure of experimental Ca-III' synthesized recently at low temperature 14 K as supported by the excellent agreement between our simulated X-ray diffraction patterns and the experimental data. Our results shed strong light on the crucial role played by the precise electron exchange energy in a proper description of the potential energy of Ca.Comment: submitted to Physical Review

Implicit Biases and Byrne’s Epistemic Rule for Self-knowledge of Beliefs

Alex Byrne makes a normative claim in his book Transparency And Self-Knowledge, that the epistemic rule for self-knowledge of belief BEL (if P, believe that you believe that P), is a good rule. In this thesis, by utilizing both philosophical writings and empirical studies in psychology I reject Byrne’s claim that BEL is a good rule. More specifically, I argue that many cases of implicit biases are essentially beliefs, because they share many characteristics that are paradigmatic to beliefs. Then I argue that applying BEL, as a method of obtaining self-knowledge of beliefs, not only fails to discover many of our implicit biases, but also gives wrong verdict for many of our implicit biases. Finally, I conclude that BEL is not a good rule, and any good method for obtaining self-knowledge of belief should not ignore the importance of observing one’s own behaviors

Anomalous melting behavior of solid hydrogen at high pressures

Hydrogen is the most abundant element in the universe, and its properties under conditions of high temperature and pressure are crucial to understand the interior of of large gaseous planets and other astrophysical bodies. At ultra high pressures solid hydrogen has been predicted to transform into a quantum fluid, because of its high zero point motion. Here we report first principles two phase coexistence and Z method determinations of the melting line of solid hydrogen in a pressure range spanning from 30 to 600 GPa. Our results suggest that the melting line of solid hydrogen, as derived from classical molecular dynamics simulations, reaches a minimum of 367 K at about 430 GPa, at higher pressures the melting line of the atomics Cs IV phase regain a positive slope. In view of the possible importance of quantum effects in hydrogen at such low temperatures, we also determined the melting temperature of the atomic CsIV phase at pressures of 400, 500, 600 GPa, employing Feynman path integral simulations. These result in a downward shift of the classical melting line by about 100 K, and hint at a possible secondary maximum in the melting line in the region between 500 and 600 GPa, testifying to the importance of quantum effects in this system. Combined, our results imply that the stability field of the zero temperature quantum liquid phase, if it exists at all, would only occur at higher pressures than previously thought.Comment: Submitted to JC

Design of Environment Monitoring System in Hatcheries Based on WSN

The level of the environment monitoring system in hatcheries is low, and monitoring methods is not up to data, we propose a new environment monitoring method based on wireless sensor networks in hatcheries. The sensor nodes which distribute every room in hatcheries form a wireless surveillance sensor networks by Zigbee technology so as to provide information timely. When designing of the sensor nodes, we choose CC2430 from WXL Company, which integrate the CPU, RF transceiver, net protocol and the RAM together, as the core chip and combine the microcontroller technology. The design of coordinator node uses CC2420 and MSP430. Besides, the data collected by the nodes will be sent to monitoring platform of Visual Basic editor via the Zigbee network. The system automates the operation from the monitor to control, which can save the cost of labor and environmental monitoring