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1.
J. M. Léger J. Haines C. Chateau G. Bocquillon M. W. Schmidt S. Hull F. Gorelli A. Lesauze R. Marchand 《Physics and Chemistry of Minerals》2001,28(6):388-398
The structure of the cristobalite-like polymorph of phosphorus oxynitride PON has been refined using neutron powder diffraction
data. It is tetragonal, space group I&4macr;2d, Z=4. The four P–(O,N) distances are equal but the tetrahedron is compressed along c. In AX2 or ABX4 compounds, the tetragonal I&4macr;2d or I&4macr; structure is obtained when the average ratio of the cation to anion radius is below 1.186, whereas the tetragonal P41212 or orthorhombic C2221 structure is obtained at low temperatures for larger ratios. The cell parameters of this PON polymorph have been determined
as a function of hydrostatic pressure by in situ angle dispersive X-ray powder diffraction in a diamond-anvil cell. Under
truly hydrostatic pressure, a strong anisotropic behavior is observed with the c parameter being nearly incompressible. Very slight anisotropic stress strongly modifies the high-pressure behavior. According
to the pressure-temperature conditions of treatment, three phases, cristobalite-, moganite-, and quartz-like, have been obtained
by quenching experiments, and the P–T phase diagram of PON was derived. The high-pressure behavior of the α-quartz, moganite, and cristobalite-like polymorphs
of PON and SiO2 is discussed.
Received: 7 August 2000 / Accepted: 21 January 2001 相似文献
2.
The RHESSI Spectrometer 总被引：2，自引：0，他引：2
Smith D.M. Lin R.P. Turin P. Curtis D.W. Primbsch J.H. Campbell R.D. Abiad R. Schroeder P. Cork C.P. Hull E.L. Landis D.A. Madden N.W. Malone D. Pehl R.H. Raudorf T. Sangsingkeow P. Boyle R. Banks I.S. Shirey K. Schwartz Richard 《Solar physics》2002,210(1-2):33-60
RHESSI observes solar photons over three orders of magnitude in energy (3 keV to 17 MeV) with a single instrument: a set of
nine cryogenically cooled coaxial germanium detectors. With their extremely high energy resolution, RHESSI can resolve the
line shape of every known solar gamma-ray line except the neutron capture line at 2.223 MeV. High resolution also allows clean
separation of thermal and non-thermal hard X-rays and the accurate measurement of even extremely steep power-law spectra.
Detector segmentation, fast signal processing, and two sets of movable attenuators allow RHESSI to make high-quality spectra
and images of flares across seven orders of magnitude in intensity. Here we describe the configuration and operation of the
RHESSI spectrometer, show early results on in-flight performance, and discuss the principles of spectroscopic data analysis
used by the RHESSI software. 相似文献
3.
J. H. Hull 《地学学报》1989,1(6):524-529
This paper reviews the role of environmental geology, and the practice of environmental geology mapping, in the context of the geological, geophysical and geochemical factors which are relevant to human activity and safety.
It is concluded that informed planning policies for the offshore areas are necessary. These would allow mutually acceptable and sensible exploitation of all natural resources, engineering and military developments and recreational uses, and would also take account of natural and man-made hazards to such activities. The policies would follow from multidisciplinary, systematic, environmental studies involving international cooperation.
The imperative for the earth-science practitioner to remain sensitive to the requirements of the users of such information is recognized, as is the need to communicate unambiguously. It is concluded that geologists should look increasingly from the past to the future. 相似文献
It is concluded that informed planning policies for the offshore areas are necessary. These would allow mutually acceptable and sensible exploitation of all natural resources, engineering and military developments and recreational uses, and would also take account of natural and man-made hazards to such activities. The policies would follow from multidisciplinary, systematic, environmental studies involving international cooperation.
The imperative for the earth-science practitioner to remain sensitive to the requirements of the users of such information is recognized, as is the need to communicate unambiguously. It is concluded that geologists should look increasingly from the past to the future. 相似文献
4.
A spectrum scanning Stokes polarimeter 总被引：1，自引：0，他引：1
5.
A high pressure neutron powder diffraction study of portlandite [Ca(OH)2] has been performed at ISIS facility (U.K.); nine spectra have been collected increasing the pressure by steps, up to 10.9 GPa,
by means of a Paris-Edinburgh cell installed on the POLARIS diffractometer. The tensorial formalism of the lagrangian finite
strain theory and the Birch-Murnaghan equation of state have been used to determine, independently, two values of the bulk
modulus of portlandite, obtaining K
0=38.3(±1.1) GPa [linear incompressibilities: K
0a=188.4(±9.9), K
0c=64.5(±2.5) GPa] and K
0=34.2(±1.4) GPa, respectively. The present results comply with values from previous measurements by X-ray diffraction [K
0=37.8(±1.8) GPa] and Brillouin spectroscopy [K
0=31.7(±2.5) GPa]. Reasonably, Ca(OH)2 has revealed to be bulkly softer than Mg(OH)2 [K
0=41(±2), K
0a=313, K
0c=57 GPa]. The Ca(OH)2 linear incompressibility values reflect the nature of forces acting to stabilize the (001) layer structure and, further,
prove that the replacement Ca/Mg mainly affects the elastic properties in the (001) plane, rather than along the [001] direction.
Data from a full refinement of the structure at room pressure are reported.
Received January 12, 1996/Revised, accepted June 15, 1996 相似文献
6.
An instrument to observe low-degree solar oscillations 总被引：1，自引：0，他引：1
We have constructed an instrument optimized to observe solar oscillations of low degree. The primary goal of this instrument, which we call LOWL, is to measure the frequency splitting of the low-degree modes in order to determine the rotation rate of the solar core. The LOWL is a Doppler imager based on a magneto-optical filter. It employs a two-beam technique to simultaneously observe solar images in opposite wings of the absorption line of potassium at 769.9 nm. This instrument is very stable against drifts in the wavelength zero-point, is insensitive to noise sources due to intensity fluctuations and image motion, and has a Doppler analyzer with no moving parts. The LOWL has been deployed at HAO's observing station on Mauna Loa, Hawaii and will operate for a period of at least two years.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
7.
Sara R. Heap Qian Gong Tony Hull Jeffrey Kruk Lloyd Purves 《Astrophysics and Space Science》2014,354(1):211-214
One of the key goals of NASA’s astrophysics program is to answer the question: How did galaxies evolve into the spirals and elliptical galaxies that we see today? We describe a space mission concept called Galaxy Evolution Spectroscopic Explorer (GESE) to address this question by making a large spectroscopic survey of galaxies at a redshift, z～1 (look-back time of ～8 billion years). GESE is a 1.5-m space telescope with an ultraviolet (UV) multi-object slit spectrograph that can obtain spectra of hundreds of galaxies per exposure. The spectrograph covers the spectral range, 0.2–0.4 μm at a spectral resolving power, R～500. This observed spectral range corresponds to 0.1–0.2 μm as emitted by a galaxy at a redshift, z=1. The mission concept takes advantage of two new technological advances: (1) light-weighted, wide-field telescope mirrors, and (2) the Next-Generation MicroShutter Array (NG-MSA) to be used as a slit generator in the multi-object slit spectrograph. 相似文献
8.
Ryan M. Phelps Charles Kerans Robert G. Loucks Rui O.B.P. Da Gama Jason Jeremiah David Hull 《Sedimentology》2014,61(2):461-496
An integrated sequence stratigraphic study based on outcrop, core and wireline log data documents the combined impact of Cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern Gulf of Mexico. The diverse facies and abundant data of the Comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting Cretaceous platform development. Regional cross‐sections across the shoreline to shelf‐margin profile provide a detailed record of mixed carbonate–siliciclastic strata for the Hauterivian to lower Campanian stages (ca 136 to 80 Ma). The study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes. Three second‐order supersequences comprised of eight composite sequences are recognized in the Valanginian–Barremian, the Aptian–Albian and the Cenomanian–Campanian. The Valanginian–Barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting, as well as variable rates of mid‐ocean ridge volcanism. The Aptian–Albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b. The Cenomanian–Campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d, after which the platform evolved to a deep‐subtidal system consisting of anoxic/dysoxic shale and chalk in the time surrounding oceanic anoxic event 2. Each period of oceanic anoxia is associated with composite sequence maximum flooding, termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles. Composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain‐dominated facies and shallow‐subtidal to intertidal environments. Because they are products of eustacy and global oceanographic processes, the three supersequences and most composite sequences defined in the south Texas passive margin are recognizable in other carbonate platforms and published eustatic sea‐level curves. 相似文献
9.
Infaunal bivalve molluscs on the flood tidal delta of Tauranga Harbour, north‐eastern New Zealand, were surveyed twice over a 6‐month period, with the aim of assessing shellfish resources, assessing the magnitudes of temporal and spatial variability in abundances, and identifying potentially important processes. The surveys identified a total of 31 bivalve taxa from 27 sites. Species richness per site ranged between 0 and 9, and varied greatly in space and time, as did two other measures of diversity. Extremely high densities of bivalves (>20 000 m‐2) were encountered at several sites. Densities of several abundant species varied greatly in time, as a result of recruitment pulses. The abundances of the three species that dominated the fauna (Paphies australis, Tawera spissa, and Ruditapes largillierti) had characteristic spatial scales on the order of 200 m. Comparisons of size frequency distributions for individual sites suggested that mortality or emigration in the first year of benthic life was high. Substantial populations of bivalves occur on Centre Bank, and the most abundant of these are greatly influenced by events early in their lives. 相似文献
10.
Martin A. Briggs Andrea K. Tokranov Robert B. Hull Denis R. LeBlanc Adam B. Haynes John W. Lane 《水文研究》2020,34(10):2281-2291
Emerging groundwater contaminants such as per- and polyfluoroalkyl substances (PFAS) may impact surface-water quality and groundwater-dependent ecosystems of gaining streams. Although complex near-surface hydrogeology of stream corridors challenges sampling efforts, recent advances in heat tracing of discharge zones enable efficient and informed data collection. For this study, we used a combination of streambed temperature push-probe and thermal infrared methods to guide a discharge-zone-oriented sample collection along approximately 6 km of a coastal trout stream on Cape Cod, MA. Eight surface-water locations and discharging groundwater from 24 streambed and bank seepages were analysed for dissolved oxygen (DO), specific conductance, stable water isotopes, and a range of PFAS compounds, which are contaminants of emerging concern in aquatic environments. The results indicate a complex system of groundwater discharge source flowpaths, where the sum of concentrations of six PFAS compounds (corresponding to the U.S. Environmental Protection Agency third Unregulated Contaminant Monitoring Rule “UCMR 3”) showed a median concentration of 52 ± 331 (SD) ng/L with two higher outliers and three discharges with PFAS concentrations below the quantification limit. Higher PFAS concentration was related (− 0.66 Spearman rank, p < .001) to discharging groundwater that showed an evaporative signature (deuterium excess), indicating flow through at least one upgradient kettle lake. Therefore, more regional groundwater flowpaths originating from outside the local river corridor tended to show higher PFAS concentrations as evaluated at their respective discharge zones. Conversely, PFAS concentrations were typically low at discharges that did not indicate evaporation and were adjacent to steep hillslopes and, therefore, were classified as locally recharged groundwater. Previous research at this stream found that the native brook trout spawn at discharge points of groundwater recharged on local hillslopes, likely in response to generally higher levels of DO. Our study shows that by targeting high oxygen discharges the trout may thereby be avoiding emerging contaminants such as PFAS in groundwater recharged farther from the stream. 相似文献