In situ Raman and Brillouin light scattering techniques were used to study thermally induced high-density amorphous (HDA) to low-density amorphous (LDA) transition in silica glass densified in hot compression (up to 8 GPa at 1100 degrees C). Hot-compressed silica samples are shown to retain structural and mechanical stability through 600 degrees C or greater, with reduced sensitivity in elastic response to temperature as compared with pristine silica glass. Given sufficient thermal energy to overcome the energy barrier, the compacted structure of the HDA silica reverts back to the LDA state. The onset temperature for the HDA to LDA transition depends on the degree of densification during hot compression, commencing at lower temperatures for samples with higher density, but all finishing within a temperature range of 250-300 degrees C. Our studies show that the HDA to LDA transition at high temperatures in hot-compressed samples is different from the gradual changes starting from room temperature in cold-compressed silica glass, indicating greater structural homogeneity achieved by hot compression. Furthermore, the structure and properties of hot-compressed silica glass change continuously during the thermally induced HDA to LDA transition, in contrast to the abrupt and first-order-like polyamorphic transitions in amorphous ice. Different HDA to LDA transition mechanisms in amorphous silica and amorphous ice are explained by their different energy landscapes. Published by AIP Publishing.

Mineral-hosted melt inclusions have become an important source of information on magmatic processes. As the number of melt inclusion studies increases, so does the need to establish recommended practice guidelines for collecting and reporting melt inclusion data. These guidelines are intended to ensure certain quality criteria are met and to achieve consistency among published melt inclusion data in order to maximize their utility in the future. Indeed, with the improvement of analytical techniques, new processes affecting melt inclusions are identified. It is thus critical to be able to reprocess any previously published data, such that reporting the raw data is one of the first 'recommended practices' for authors and a publication-criteria that reviewers should be sensitive to. Our guidelines start with melt inclusion selection, which is a critical first step, and then continue on to melt inclusion preparation and analysis, covering the entire field of methods applicable to melt inclusions.

We present measurements of optical emission-line flux variations based on spectra of the Seyfert galaxy NGC 5548 obtained between 1988 December and 1989 October during the course of a large-scale international monitoring effort. The data presented here supplement previously published measurements of the UV lines and continuum, optical continuum, and broad Hbeta emission line. All of the measured optical emission lines, Halpha, Hbeta, Hgamma, He I lambda5876, and He II lambda4686, show the same qualitative behavior as the UV and optical continua, but with short time delays, or lags, which are different for the various lines. We apply cross-correlation analysis to measure the lags between the various lines and the continuum. We find similar lags with respect to the UV continuum for Halpha and Hbeta, 17 and 19 days, respectively. The lag for Hgamma is shorter (13 days), only somewhat larger than the lag measured for Lyalpha (about 10 days). The helium lines respond to continuum variations more rapidly than the hydrogen lines, with lags of about 7 days for He II lambda4686 and 11 days for He I lambda5876.

We present the data and initial results from a combined HST/IUE/ground-based spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once every 2 days for a period of 74 days beginning on 1993 March 14. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations(both CCD imaging and aperture photometry), are reported for the period 1992 October-1993 September, although many of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution we describe the acquisition and reduction of all of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies.

We present the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every similar to 70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy.

This paper combines data from the three preceding papers in order to analyze the multi-wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (similar to 1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA = 6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of similar to 100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Angstrom These data do not probe extreme ultraviolet (1200 Angstrom to 0.1 keV) or hard X-ray (2-50 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of less than or similar to 0.15 day between 1275 Angstrom and the other ultraviolet bands, less than or similar to 0,3 day between 1275 Angstrom and 1.5 keV, and less than or similar to 1 day between 1275 and 5125 Angstrom These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (a less than or equal to -2.5).

[1] We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties ( at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive ( isotope dilution) and comparative bulk ( e. g., INAA, ICPMS, SSMS) and microanalytical ( e. g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.

Agricultural soils hold potential for the expansion of carbon sequestration. With this in mind, we investigated changes in the soil organic carbon (SOC) on the basis of an analysis of data sets extracted from 146 publications and further projected the SOC sequestration potential in China's cropland. Our results suggest that a significant increase in the SOC occurred in east and north China, while a decrease appeared in northeast China. As a whole, the organic carbon density in the topsoil to 30 cm depth increased by 3.36 (2.54 to 4.26) Mg/ha between 1980 and 2000. Accordingly, the croplands in China that cover an area of over 130 Mha sequestered 437 (331 to 555) Tg C, with an average rate of 21.9 (16.6 to 27.8) Tg/yr, during this period. The potential of SOC sequestration in China was estimated to be 2-2.5 Pg C, which could be achieved by the 2050s if crop production and field management are improved.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft while in orbit about Mercury observed highly localized, similar to 3-s-long reductions in the dayside magnetospheric magnetic field, with amplitudes up to 90% of the ambient intensity. These magnetic field depressions are termed cusp filaments because they were observed from just poleward of the magnetospheric cusp to midlatitudes, i.e., similar to 55 degrees to 85 degrees N. We analyzed 345 high- and low-altitude cusp filaments identified from MESSENGER magnetic field data to determine their physical properties. Minimum variance analysis indicates that most filaments resemble cylindrical flux tubes within which the magnetic field intensity decreases toward its central axis. If the filaments move over the spacecraft at an estimated magnetospheric convection speed of similar to 35km/s, then they have a typical diameter of similar to 105km or similar to 7gyroradii for 1keVH(+) ions in a 300nT magnetic field. During these events, MESSENGER's Fast Imaging Plasma Spectrometer observed H+ ions with magnetosheath-like energies. MESSENGER observations during the spacecraft's final low-altitude campaign revealed that these cusp filaments likely extend down to Mercury's surface. We calculated an occurrence-rate-normalized integrated particle precipitation rate onto the surface from all filaments of (2.700.09)x10(25)s(-1). This precipitation rate is comparable to published estimates of the total precipitation rate in the larger-scale cusp. Overall, the MESSENGER observations analyzed here suggest that cusp filaments are the magnetospheric extensions of the flux transfer events that form at the magnetopause as a result of localized magnetic reconnection.

Premise of research. As extreme climate events, such as California's 2012-2016 drought, become more frequent with climate change, it is imperative to understand how different native plant communities respond to drought-induced dehydration stress. Chaparral and California sage scrub (CSS), two widespread plant communities in California, face threats from droughts of increased frequency and severity. Despite chaparral and CSS plants being adapted to seasonal drought conditions, it is not known how the strategies of recovery from extreme multiyear droughts associated with changing climate differ between them. Methodology. We measured chlorophyll fluorescence and water potentials for two evergreen chaparral shrubs (Heteromeles arbutifolia and Quercus berberidifolia) and two drought deciduous CSS shrubs (Salvia leucophylla and Salvia mellifera) in the Santa Monica Mountains both during and after the extreme drought in California (between 2015 and 2017). Pivotal results. We found that the maximum electron transport rate (J(max)) varied seasonally for all species, decreasing in the dry season and recovering in the wet season. However, J(max) and the seasonal change in J(max) (Delta J(max)) were larger for the CSS species than for the chaparral species, and recovery of J(max) began earlier in the year for CSS species than for chaparral species. Dark-adapted maximum photochemical efficiency of photosystem II (Fv/Fm) and both midday (psi(MD)) and predawn (psi(PD)) water potential for all species also followed similar seasonal patterns-higher in the wet season than in the dry season, with CSS species exhibiting the largest seasonal changes in psi. A strong linear relationship was found between J(max) and psi(MD) for all species except Q. berberidifolia. Conclusions. Our results show that recovery from drought-induced dehydration differs between representatives of two major plant communities in California and is linked to life-history strategy: the higher sensitivity to and quicker recovery from seasonal drought for the CSS species compared with the chaparral species could be attributed to the shallower rooting depths and dehydration tolerance of the CSS species. In addition, water relations and chlorophyll fluorescence can serve as useful metrics to compare species-specific dehydration stress tolerance or avoidance strategies in the field.