On: X-ray diffraction from the electron gas in monatomic metallic hydrogen.

Solid hydrogen is expected to become a monatomic metal under sufficiently high compression. With hydrogen having only a single valence electron and no ion core, the nature of x-ray diffraction patterns from the electron gas of monatomic metallic hydrogen is uncertain, and it is unclear whether they may yield enough information for a crystal structure determination. With emphasis on the Cs-IV-type (I41/amd) structure predicted for hydrogen at ∼500 GPa, the electron density distributions, zero-point and thermal atomic motion, and x-ray diffraction intensities are determined from first-principles calculations for several candidate phases of metallic hydrogen.

The high-pressure, high-temperature phase diagram of cerium.

We present an experimental study of the high-pressure, high-temperature behaviour of cerium up to ∼22 GPa and 820 K using angle-dispersive x-ray diffraction and external resistive heating. Studies above 820 K were prevented by chemical reactions between the samples and the diamond anvils of the pressure cells. We unambiguously measure the stability region of the orthorhombic4 phase and find it reaches its apex at 7.

Quantum and isotope effects in lithium metal.

The crystal structure of elements at zero pressure and temperature is the most fundamental information in condensed matter physics. For decades it has been believed that lithium, the simplest metallic element, has a complicated ground-state crystal structure. Using synchrotron x-ray diffraction in diamond anvil cells and multiscale simulations with density functional theory and molecular dynamics, we show that the previously accepted martensitic ground state is metastable.

Constituents of the Leaves of Pandanus utilis.

Nineteen compounds, including seven triterpenoids (1-7), five steroids (8-12), four cyclohexenone derivatives (13-16), two benzenoid glycosides (17 and 18) and one lignan (19), were isolated and separated from the leaves of Pandanus utilis through bioactivity-guided fractionation. Among them, one new lanosterol- type triterpenoid was found and named as (24R)-24-methyl-5a-4-demethyllanosta-9(11),25-dien-3β-ol (1). The structures of the isolates were determined by mass and spectroscopic analyses, and the compounds were subjected to anti-inflammatory, anti-oxidative and cytotoxic assays.