High-pressure behavior of dense hydrogen up to 3.5 TPa from density functional theory calculations

Structural behavior and equation of state of atomic and molecular crystal phases of dense hydrogen at pressures up to 3.5 TPa are systematically investigated with density functional theory. The results indicate that the Vinet EOS model that fitted to low-pressure experimental data overestimates the compressibility of dense hydrogen drastically when beyond 500 GPa. Metastable multi-atomic molecular phases with weak covalent bonds are observed. When compressed beyond about 2.8 TPa, these exotic low-coordinated phases become competitive with the groundstate and other high-symmetry atomic phases. Using nudged elastic band method, the transition path and the associated energy barrier between these high-pressure phases are evaluated. In particular for the case of dissociation of diatomic molecular phase into the atomic metallic Cs-IV phase, the existent barrier might raise the transition pressure about 200 GPa at low temperatures. Plenty of flat and broad basins on the energy surface of dense hydrogen have been discovered, which should take a major responsibility for the highly anharmonic zero point vibrations of the lattice, as well as the quantum structure fluctuations in some extreme cases. At zero pressure, our analysis demonstrates that all of these atomic phases of dense hydrogen known so far are unquenchable. NOTE: In the previous version of this paper (1010.3392v1) we made a mistake when evaluating the enthalpy of Cs-IV phase, which misled us to a conclusion that taking the multi-atomic molecular phases as the ground-state. After corrected this error, however, the atomic phase of Cs-IV becomes the static structure with the lowest enthalpy. Current version not only includes a substantial improvement of the previous one, but also contains many NEW interesting topics that were not touched before.Comment: 33 pages, 15 figures, published at J. Appl. Phys. 111, 063510 (2012

Anomalies in non-stoichiometric uranium dioxide induced by pseudo-phase transition of point defects

A uniform distribution of point defects in an otherwise perfect crystallographic structure usually describes a unique pseudo phase of that state of a non-stoichiometric material. With off-stoichiometric uranium dioxide as a prototype, we show that analogous to a conventional phase transition, these pseudo phases also will transform from one state into another via changing the predominant defect species when external conditions of pressure, temperature, or chemical composition are varied. This exotic transition is numerically observed along shock Hugoniots and isothermal compression curves in UO2 with first-principles calculations. At low temperatures, it leads to anomalies (or quasi-discontinuities) in thermodynamic properties and electronic structures. In particular, the anomaly is pronounced in both shock temperature and the specific heat at constant pressure. With increasing of the temperature, however, it transforms gradually to a smooth cross-over, and becomes less discernible. The underlying physical mechanism and characteristics of this type of transition are encoded in the Gibbs free energy, and are elucidated clearly by analyzing the correlation with the variation of defect populations as a function of pressure and temperature. The opportunities and challenges for a possible experimental observation of this phase change are also discussed.Comment: 11 pages, 5 figure

Enhancement of steady-state bosonic squeezing and entanglement in a dissipative optomechanical system

We systematically study the influence of amplitude modulation on the steady-state bosonic squeezing and entanglement in a dissipative three-mode optomechanical system, where a vibrational mode of the membrane is coupled to the left and right cavity modes via the radiation pressure. Numerical simulation results show that the steady-state bosonic squeezing and entanglement can be significantly enhanced by periodically modulated external laser driving either or both ends of the cavity. Remarkably, the fact that as long as one periodically modulated external laser driving either end of the cavities is sufficient to enhance the squeezing and entanglement is convenient for actual experiment, whose cost is that required modulation period number for achieving system stability is more. In addition, we numerically confirm the analytical prediction for optimal modulation frequency and discuss the corresponding physical mechanism.Comment: 25 pages, 8 figures, accepted for publication in Optics Expres

On the Nature of Fairness in Bargaining - Experimental Evidence from Germany and PR China

This paper presents a new perspective on the nature of fairness in bargaining by using verbal data from spontaneous team discussions and written statements on decision motives. Systematic content analysis proves a valuable source for providing new insights. The nature of fairness can be viewed as consisting of different facets or components. The ones we study are allocation aspects, power asymmetry, cultural background, the interplay between fairness and mentalizing, frequency of interactions and procedure of assigning positions. In one-shot UG experiments with randomly assigned positions, subjects who make fairness an issue- i.e. about 50% - view the Equal Split as the predominant fairness norm in both subject pools in the symmetric and in the asymmetric settings. Equal-Split related fairness discussions increase pro-posers' offers. Fairness concerns per se do not have such an effect. The Equal Split predominance vanishes in asymmetric bargaining situations where subjects interact repeatedly and work for their position. Here, the equitable but unequal allocations Split the Difference and Proportional Split are considered fair as well by more and less powerful players. The transcripts show that subjects mentalize when discussing fairness. They reason up to the second level in both the mechanisms we discovered in the verbal protocols. We found cultural differences in fairness perceptions in that fairness is not irrelevant for the Chinese but seems more important for the German participants. The lesson we draw from our findings is that power asymmetry, cultural back-ground and situational properties matter for fairness perceptions and should be accounted for when applying social preference models