In this study, high pressure infrared (IR) absorption and Raman scattering studies for ammonium azide (NH4N3) were carried out at room temperature up to 20 GPa and 22 GPa, respectively. For comparison and further assignment, the vibrational spectra at ambient conditions were calculated using CASTEP code, particularly for the far-and mid-IR modes. The recorded vibrational data consistently indicated a pressure-induced phase transition at 2.9 GPa. All observed vibrational modes maintained their identities at the high pressure phase, indicating that NH4N3 was still presented in the form of ammonium cations and azide anions linked by the hydrogen bond (N-H center dot center dot center dot N). Above 2.9 GPa, the relative magnitude of the torsional mode weakened and the N-H symmetric stretch displayed a redshift, indicating strengthened hydrogen bonding energy. The opposite effects were observed above 12 GPa, where the relative magnitude of the torsional mode strengthened and the N-H symmetric stretch reverted to a blueshift, indicating weakened hydrogen bonding energy. It can be concluded that the hydrogen bonding energy exhibited a weakening (0-2.9 GPa), strengthening (2.9-12 GPa), and then again weakening (12-22 GPa) phenomena with the increasing of compression. The hydrogen bonding energy changing with the increase of pressure can be ascribed to a phase transition at 2.9 GPa and a rotational or bending behavior of azide ions at 12 GPa. (C) 2014 AIP Publishing LLC.

We report the high-pressure studies of RbN3 by Raman and IR spectral measurements at room temperature with the pressure up to 28.5 and 30.2 GPa, respectively. All the fundamental vibrational modes were resolved by combination of experiment and calculation. Detailed spectroscopic analyses reveal two phase transitions at similar to 6.5 and similar to 16.0 GPa, respectively. Upon compression, the shearing distortion of the unit cell induced the displacive structural transition of phase alpha -> gamma. Further analyses of the mid-IR spectra indicate the evolution of N-3(-) with the arrangement sequence of orthogonal -> parallel -> orthogonal during the phase transition of phase alpha -> gamma -> delta. Additionally, the pressure-induced nonlinear/asymmetric existence of N=N=N and the two crystallographically nonequivalent sites of N-3(-) were observed in phase delta.

The geometrically frustrated pyrochlore Eu2Sn2O7 is an insulator with slight trigonal lattice distortion at ambient condition. High pressure is applied to this system to investigate the responses of structural evolution, optical emission and electrical transport properties. In situ high pressure synchrotron X-ray diffraction, Raman spectroscopy, and photoluminescence studies are performed in Eu2Sn2O7 up to 31.2 and 34.1 GPa, respectively. The abrupt change of the oxygen atomic position without breaking the crystal symmetry is accompanied by disappearing of Raman mode involving SnO6 octahedron distortion around 17.8 GPa. It indicates a pressure induced second-order iso-structural transition, which suppresses the trigonal distortion in the SnO6 octahedron but enhances the local symmetry distortion of EuO8 hexahedron. Anomalous luminescence of the Eu3+ 4f-4f transition is observed, which confirms the enhancement of EuO8 hexahedral distortion at high pressure region. In situ high-pressure electrical transport property is measured by alternating current (AC) impedance spectroscopy up to 32.5 GPa. A rapid increase in resistance with gain of 4 orders of magnitude by applied pressure is observed until 16.6 GPa, and it is followed by a slight decreasing to the highest pressure measured here. All these observations indicate a pressure-enhanced trigonal lattice distortion before the transition pressure, and thus it will enlarge an opening gap at the Fermi energy, followed by releasing distortion at higher pressures.

La2Sn2O7 is a transparent conducting oxide (TCO) material and shows a strong near-infrared fluorescent at ambient pressure and room temperature. By in situ high-pressure research, pressure-induced visible photoluminescence (PL) above 2 GPa near 2 eV is observed. The emergence of unusual visible PL behavior is associated with the seriously trigonal lattice distortion of the SnO6 octehedra, under which the Sn-O1-Sn exchange angle is decreased below 22.1 GPa, thus enhancing the PL quantum yield leading to Sn P-3(1) S-1(0) photons transition. Besides, bandgap closing followed by bandgap opening and the visible PL appearing at the point of the gap reversal, which is consistent with high-pressure phase decomposition, are discovered. The high-pressure PL results demonstrate a well-defined pressure window (7-17 GPa) with flat maximum PL yielding and sharp edges at both ends, which may provide a great calibration tool for pressure sensors for operation in the deep sea or at extreme conditions.

Many bioinformatics methods have been proposed for reducing the complexity of large gene or protein networks into relevant subnetworks or modules. Yet, how such methods compare to each other in terms of their ability to identify disease-relevant modules in different types of network remains poorly understood. We launched the 'Disease Module Identification DREAM Challenge', an open competition to comprehensively assess module identification methods across diverse protein-protein interaction, signaling, gene co-expression, homology and cancer-gene networks. Predicted network modules were tested for association with complex traits and diseases using a unique collection of 180 genome-wide association studies. Our robust assessment of 75 module identification methods reveals top-performing algorithms, which recover complementary trait-associated modules. We find that most of these modules correspond to core disease-relevant pathways, which often comprise therapeutic targets. This community challenge establishes biologically interpretable benchmarks, tools and guidelines for molecular network analysis to study human disease biology.

Three epochs of high-resolution spectra of the star BD +20 307 show that it is a short-period (similar to 3.4 day) spectroscopic binary of two nearly identical stars. Surprisingly, the two stars, although differing in effective temperature by only similar to 250 K and having a mass ratio of 0.91, show very different Li line equivalent widths. A Li 6707 angstrom line is detected from only the primary star, and it is weak. This star is therefore likely to be older than 1 Gyr. If so, the large amount of hot circumbinary dust must be from a very large and recent, but very late evolutionarily, collision of planetesimals.

We have carried out a multiwavelength observational campaign demonstrating some of the remarkable properties of the infrared-bright variable star BP Psc. Surrounded by a compact dusty, gaseous disk, this little-studied late G ( or early K) type star emits about 75% of its detected energy flux at infrared wavelengths. Evidence for accretion of gas in conjunction with narrow bipolar jets and Herbig-Haro objects is apparently consistent with classification of BP Psc as a pre-main-sequence star, as postulated in most previous studies. If young, then BP Psc would be one of the nearest and oldest known classical T Tauri stars. However, such an evolutionary classification encounters various problems that are absent or much less severe if BP Psc is instead a luminosity class III post-main-sequence star. In this case, it would be the first known example of a first-ascent giant surrounded by a massive molecular disk with accompanying rapid gas accretion and prominent jets and HH objects. In this model, the genesis of the massive dusty gaseous disk could be a consequence of the envelopment of a low-mass companion star. Properties in the disk may be conducive to the current formation of planets, a gigayear or more after the formation of BP Psc itself.

We report HST NICMOS coronagraphic images of the HD 15115 circumstellar disk at 1.1 mm. We find a similar morphology to that seen in the visible and at H band-an edge-on disk that is asymmetric in surface brightness. Several aspects of the 1.1 mu m data are different, highlighting the need for multiwavelength images of each circumstellar disk. We find a flattening to the western surface brightness profile at 1.1 mu m interior to 2 '' ( 90 AU) and a warp in the western half of the disk. We measure the surface brightness profiles of the two disk lobes and create a measure of the dust scattering efficiency between 0.55 and 1.65 mu m at 1 '', 2 '', and 3 ''. At 2 '' the western lobe has a neutral spectrum up to 1.1 mu m and a strong absorption or blue spectrum 11.1 mu m, while a blue trend is seen in the eastern lobe. At 1 '' the disk has a red color in both lobes.

We present the results of a search for a young stellar moving group associated with the star HD 141569 - a nearby, isolated Herbig AeBe primary member of a 5 +/- 3 Myr-old triple star system on the outskirts of the Sco-Cen complex. Our spectroscopic survey identified a population of 21 Li-rich, less than or similar to 30 Myr-old stars within 30 degrees of HD 141569 which possess similar proper motions with the star. The spatial distribution of these Li-rich stars, however, is not suggestive of a moving group associated with the HD 141569 triplet, but rather this sample appears cospatial with Upper Scorpius (US) and Upper Centaurus Lupus (UCL). We apply a modified moving cluster parallax method to compare the kinematics of these youthful stars with those of the US and UCL. Eight new potential members of US and five new potential members of UCL are identified. A substantial moving group with an identifiable nucleus within 15 degrees (similar to 30 pc) of HD 141569 is not found in this sample. Evidently, the HD 141569 system formed similar to 5 Myr ago in relative isolation, tens of parsecs away from the recent sites of star formation in the Ophiucus-Scorpius-Centaurus region.

We have obtained high spatial resolution imaging observations of the HR 4796A circumstellar debris dust ring using the broad optical response of the Hubble Space Telescope Imaging Spectrograph (STIS) in coronagraphic mode. We use our visual wavelength observations to improve upon the earlier measured geometrical parameters of the ring-like disk. Two significant flux density asymmetries are noted: (1) preferential forward scattering by the disk grains and (2) an azimuthal surface brightness anisotropy about the morphological minor axis of the disk with corresponding differential ansal brightness. We find the debris ring offset from the location of the star by similar to 1.4 AU, a shift insufficient to explain the differing brightnesses of the northeast and southwest ansae simply by the 1/r(2) dimmunition of starlight. The STIS data also better quantify the radial confinement of the starlight-scattering circumstellar debris, to a characteristic region less than 14 AU in photometric half-width, with a significantly steeper inner truncation than outward falloff in radial surface brightness. The inferred spatial distribution of the disk grains is consistent with the possibility of one or more unseen co-orbital planetary-mass perturbers, and the colors of the disk grains are consistent with a collisionally evolved population of debris, possibly including ices reddened by radiation exposure to the central star.