4,533 research outputs found
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
Color Behavior Of BL Lacertae Object OJ 287 During Optical Outburst
This paper aims to study the color behavior of the BL Lac object OJ 287
during optical outburst. According to the revisit of the data from the OJ-94
monitoring project and the analysis the data obtained with the 60/90 cm Schmidt
Telescope of NAOC, we found a bluer-when-brighter chromatism in this object.
The amplitude of variation tends to decrease with the decrease of frequency.
These results are consistent with the shock-in-jet model. We made some
simulations and confirmed that both amplitude difference and time delay between
variations at different wavelengths can result in the phenomenon of
bluer-when-brighter. Our observations confirmed that OJ 287 underwent a
double-peaked outburst after about 12 years from 1996, which provides further
evidence for the binary black hole model in this object.Comment: 25 pages, 13 figure
N′-(2-Hydroxy-4-methoxybenzylidene)-4-methylbenzohydrazide
The asymmetric unit of the title compound, C16H16N2O3, contains four independent molecules with different conformations; the dihedral angles between the two benzene rings in the molecules are 39.7 (3), 45.4 (3), 50.6 (3) and 51.6 (3)°. Intramolecular O—H⋯N hydrogen bonds are observed in the molecule. In the crystal, N—H⋯O hydrogen bonds link the molecules into two crystallographically independent chains propagating in [010], and each chain is formed by two alternating independent molecules. Weak C—H⋯O interactions also occur
- …