Vascular plants appeared similar to 410 million years ago, then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes. We report here the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first nonseed vascular plant genome reported. By comparing gene content in evolutionarily diverse taxa, we found that the transition from a gametophyte- to a sporophyte-dominated life cycle required far fewer new genes than the transition from a nonseed vascular to a flowering plant, whereas secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in posttranscriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the trans-acting small interfering RNA pathway, and extensive RNA editing of organellar genes.

The intermediate Palomar Transient Factory reports our discovery of a young supernova, iPTF13bvn, in the nearby galaxy, NGC 5806 (22.5 Mpc). Our spectral sequence in the optical and infrared suggests a Type Ib classification. We identify a blue progenitor candidate in deep pre-explosion imaging within a 2 sigma error circle of 80 mas (8.7 pc). The candidate has an M-B luminosity of -5.52 +/- 0.39 mag and a B-I color of 0.25 +/- 0.25 mag. If confirmed by future observations, this would be the first direct detection for a progenitor of a Type Ib. Fitting a power law to the early light curve, we find an extrapolated explosion date around 0.6 days before our first detection. We see no evidence of shock cooling. The pre-explosion detection limits constrain the radius of the progenitor to be smaller than a few solar radii. iPTF13bvn is also detected in centimeter and millimeter wavelengths. Fitting a synchrotron self-absorption model to our radio data, we find a mass-loading parameter of 1.3x10(12) g cm(-1). Assuming a wind velocity of 10(3) km s(-1), we derive a progenitor mass-loss rate of 3 x 10(-5) M-circle dot yr(-1). Our observations, taken as a whole, are consistent with a Wolf-Rayet progenitor of the supernova iPTF13bvn.

Recent theoretical studies indicate that applying high pressure (up to tens of gigapascals) to simple compounds with triple bonds can convert the triple bonds to conjugated double bonds, which results in these compounds becoming electrically conductive or even superconductive. This might indicate a new route for the synthesis of inorganic/organic conductors of various compositions and properties and could greatly expand the field of conductive polymers. Here, we present a study of the phase behavior and electrical properties of K3Fe(CN)(6) up to similar to 15 GPa using Raman spectroscopy, synchrotron X-ray diffraction, and impedance spectroscopy at room temperature. In this pressure range, two new crystalline phases were identified, and their unit cells and space groups were determined. The cyanide ions react to form conjugated C=N bonds in two steps, and the electronic conductivity is enhanced by 3 orders of magnitude, from 10(-7) to 10(-4) S.cm(-1). Because this material is also an ionic conductor, these studies might "shed light" on the development of new cathode materials for alkali metal batteries. Enhancing the electrical conductivity by applying high pressure to compounds containing triple bonds could provide a potential route for synthesizing multifunctional conductive materials.

The motif of distinct H2O molecules in H-bonded networks is believed to persist up to the densest molecular phase of ice. At even higher pressures, where the molecule dissociates, it is generally assumed that the proton remains localized within these same networks. We report neutron-diffraction measurements on D2O that reveal the location of the D atoms directly up to 52 GPa, a pressure regime not previously accessible to this technique. The data show the onset of a structural change at similar to 13 GPa and cannot be described by the conventional network structure of ice VII above similar to 26 GPa. Our measurements are consistent with substantial deuteron density in the octahedral, interstitial voids of the oxygen lattice. The observation of this "interstitial" ice VII form provides a framework for understanding the evolution of hydrogen bonding in ice that contrasts with the conventional picture. It may also be a precursor for the superionic phase reported at even higher pressure with important consequences for our understanding of dense matter and planetary interiors.

The intermediate Palomar Transient Factory (iPTF) detection of the most recent outburst of the recurrent nova (RN) system RX J0045.4+4154 in the Andromeda galaxy has enabled the unprecedented study of a massive (M > 1.3 M (circle dot)) accreting white dwarf (WD). We detected this nova as part of the near-daily iPTF monitoring of M31 to a depth of R approximate to 21 mag and triggered optical photometry, spectroscopy and soft X-ray monitoring of the outburst. Peaking at an absolute magnitude of M-R = -6.6 mag, and with a decay time of 1 mag per day, it is a faint and very fast nova. It shows optical emission lines of He/N and expansion velocities of 1900-2600 km s(-1) 1-4 days after the optical peak. The Swift monitoring of the X-ray evolution revealed a supersoft source (SSS) with kT(eff) approximate to 90-110 eV that appeared within 5 days after the optical peak, and lasted only 12 days. Most remarkably, this is not the first event from this system, rather it is an RN with a time between outbursts of approximately 1 yr, the shortest known. Recurrent X-ray emission from this binary was detected by ROSAT in 1992 and 1993, and the source was well characterized as a M > 1.3 M (circle dot) WD SSS. Based on the observed recurrence time between different outbursts, the duration and effective temperature of the SS phase, MESA models of accreting WDs allow us to constrain the accretion rate to M > 1.7 Chi 10(-7) M-circle dot yr(-1) and WD mass > 1.30 M-circle dot. If the WD keeps 30% of the accreted material, it will take less than a Myr to reach core densities high enough for carbon ignition (if made of C/O) or electron capture (if made of O/Ne) to end the binary evolution.

The addition polymerization of charged monomers like C C2- and C N- is scarcely seen at ambient conditions but can progress under external pressure with their conductivity significantly enhanced, which expands the research field of polymer science to inorganic salts. The reaction pressures of transition metal cyanides like Prussian blue and K3Fe(CN)(6) are much lower than that of alkali cyanides. To figure out the effect of the transition metal on the reaction, the crystal structure and electronic structure of K3Fe(CN)(6) under external pressure are investigated by in situ neutron diffraction, in situ X-ray absorption fine structure (XAFS), and neutron pair distribution functions (PDF) up to similar to 15 GPa. The cyanide anions react following a sequence of approaching-bonding-stabilizing. The Fe(III) brings the cyanides closer which makes the bonding progress at a low pressure (2-4 GPa). At similar to 8 GPa, an electron transfers from the CN to Fe(III), reduces the charge density on cyanide ions, and stabilizes the reaction product of cyanide. From this study we can conclude that bringing the monomers closer and reducing their charge density are two effective routes to decrease the reaction pressure, which is important for designing novel pressure induced conductor and excellent electrode materials.

Pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal-carbon network composite, thus providing a new route to synthesize inorganic/organic conductors with tunable composition and properties. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li3Fe(CN)(6) at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutron diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. The conductivity of the polymer is above 10(-3) S.cm(-1), which reaches the range of conductive polymers. This investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.

Pressure-induced polymerization (PIP) of aromatic molecules can generate saturated carbon nanostructures. As a strongly interacted pi-pi stacking unit, the C6H6-C6F6 adduct is widely applied in supramolecular chemistry, and it provides a good preorganization for the PIP. Here we investigated the structural variation of C6H6-C6F6 cocrystal and the subsequent PIP process under high pressure. Four new molecular-complex phases V, VI, VII, and VIII have been identified and characterized by the in situ Raman, IR, synchrotron X-ray, and neutron diffraction. The phase V is different from the phases observed at low temperature, which has a tilted column structure. Phases VI and VII have a structure similar to phase V. Phase VIII polymerizes irreversibly upon compression above 25 GPa without any catalyst, producing sp(3)(CH/F)(n) materials. The pi-pi interaction is still dominant below 0.5 GPa but is most likely to be overstepped under further compression, which is important for discussing the supramolecular phase transition and the polymerization process.

Li2C2 has the highest theoretical capacity (1400 mAh.g(-1)) as the electrode material for Li-ion battery, but suffers from low conductivity. Here we found that under external pressure its conductivity was irreversibly enhanced by 10(9)-fold. To explain that, we performed X-ray diffraction, Raman, IR, gas chromatography-mass spectrometry, and theoretical investigations under external pressure. We found that the C-2(2-) anions approached to each other and polymerized upon compression, which is responsible for the irreversible enhancement of conductivity. The polymer has a ribbon structure and disproportionates into Li3C4 (Li2-0.5C2) ribbon structure, Li6C3 (Li propenide) and Li4C3 (Li allenide) upon decompression, implying that the carbon skeletal is highly electrochemically active. Our work reported polymerized Li2C2 for the first time, demonstrated that applying pressure is an effective method to prepare novel Li-C frameworks, and hence shed light on the search for novel carbon-based electrode materials.