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111.
The crystal structure of the rare secondary mineral cualstibite-1M (formerly cyanophyllite), originally reported to have the chemical formula 10CuO·2Al2O3·3Sb2O3·25H2O and orthorhombic symmetry, was solved from single-crystal intensity data (Mo-Kα X-radiation, CCD area detector, 293 K, 2θmax?=?80) collected on a twinned crystal containing very minor Mg. The mineral is monoclinic, P21/c (no. 14), with a?=?9.938(1), b?=?8.890(1), c?=?5.493(1) Å, β?=?102.90(1)°, V?=?473.05(11) Å3; R1(F)?=?0.0326. All crystals investigated turned out to be non-merohedric twins. The atomic arrangement has a distinctly layered character. Brucite-like sheets composed of two [4?+?2]-coordinated (Cu,Al,Mg) sites are linked by weak hydrogen-bonding (O···O?~?2.80 Å) to isolated regular Sb(OH)6 octahedra (<Sb-O>?=?1.975 Å). The layered, pseudotrigonal character explains the perfect cleavage and the proneness to twinning. The Sb site is fully occupied and the two (Cu,Al,Mg) sites have occupancies of Cu0.79Al0.17Mg0.04 and Cu0.72Al0.23Mg0.05. The Cu-richer site shows a slightly stronger Jahn-Teller-distortion. The resulting empirical formula, which necessitates a H2O-for-OH substitution to obtain charge balance, is (Cu2.23Al0.63Mg0.14)(OH)5.63(H2O)0.37[Sb5+(OH)6]. The ideal chemical formula is (Cu,Al)3(OH)6[Sb5+(OH)6], with Cu:Al = 2:1. The structure is closely related to those of trigonal cualstibite-1T [Cu2AlSb(OH)12, P-3, with ordered Cu-Al distribution in the brucite sheets], and its Zn analogue zincalstibite-1T [Zn2AlSb(OH)12]. Cualstibite-1M and cualstibite-1T are polytypes and, together with zincalstibite-1T, zincalstibite-9R and omsite, belong to the cualstibite group within the hydrotalcite supergroup, which comprises all natural members of the large family of layered double hydroxides (LDH). 相似文献
112.
Silicon-32 as a tool for dating the recent past 总被引:2,自引:2,他引:0
Silicon-32, with a half-life of approximately 140 years, has the potential to fill the dating gap that lies between those chronologies based on the shorter-lived isotopes of 3H and 210Pb, and those based on the longer-lived 14C. Silicon-32 is produced in the atmosphere by cosmic ray bombardment of argon, and falls out on the Earth's surface in precipitation. Silicon-32 methods may be used to date siliceous sediments and sponges, groundwater and glacier ice. Measurement of 32Si concentrations in these archives is, however, not straightforward. Two methods are available: radioactive-decay counting of the activity of the daughter nucleus, 32P, and accelerator mass spectrometry, but in both cases the detection of 32Si pushes the boundaries of the technique. Even the half-life of 32Si is not known to a precision of better than ±10%. In this paper, we review efforts to determine the isotope's half-life, survey the detection methods and discuss the applications of 32Si chronology. We show that at least some of the chronometric potential of this radioisotope is close to being realised as a result of recent improvements in methods of measurement. 相似文献
113.
The arguments presented by Lowe et al. [Lowe, D.J., Wilson, C.J.N., Newham, R.M., Hogg, A.G., 2010. Dating the Kawakawa/Oruanui eruption: comment on “optical luminescence dating of a loess section containing a critical tephra marker horizon, SW North Island of New Zealand” by R. Grapes et al. Quaternary Geochronology 5(4), 493–496] against our IRSL results, which suggested that the widespread Kawakawa tephra (KkT) could be considerably younger than the generally accepted 27.1 ka cal BP age, are unsustainable. We discuss the points raised by Lowe et al., in terms of: 1) Presentation and analysis of luminescence ages (comparison between reporting and error margins of luminescence and 14C ages, statistical treatment of age data); 2) Possible sources of error (“upbuilding pedogenesis” and its affect on U and Th distribution in loess, effect of biotubation, variation of K in loess, single grain luminescence dating of quartz, probability of luminescence age underestimation in dating tephra); 3) Stratigraphic and paleoenvironmental considerations (ages of tephras overlying KkT, timing of the end of Ohakea loess deposition and its distribution; 4) Radiocarbon-based ages of KkT (problems with the currently accepted 14C 27.1 ka cal BP age of KkT). We stress that our study was not to establish a new benchmark age for the KkT, but to open debate about the currently accepted benchmark age of the KkT, which we deem to be erroneous. 相似文献
114.
Modelling the poroelasticity of rocks and ice 总被引:1,自引:0,他引:1
For many geophysical and astrophysical applications the relationship between physical bulk properties and porosity is needed. As part of the preparation for the 'Rosetta' comet rendezvous mission, a simple model for the porosity dependence of the elastic properties of granular media, i.e. the elastic moduli and the propagation velocities of elastic waves, has been developed based on textural properties and the contact stiffness of the constituent particles. It is shown that the derived relationships fit very well with sandstone data. The model is also consistent with data for snow and ice and is in agreement with the transformation mechanisms from snow to ice. A short review shows the relevance to another physical bulk property, the thermal conductivity. 相似文献
115.
The extent to which a water body can support submerged macrophytic vegetation provides an indicator of its degree of eutrophication. Regular, quantitative assessment of macrophyte populations enables changes in the trophic state of the system to be observed. A combination of aerial photography and underwater videography has proved to be an efficient method for calculating macrophyte coverage of large coastal areas. 相似文献
116.
Seasonal to interannual climate predictability in mid and high northern latitudes in a global coupled model 总被引:1,自引:2,他引:1
The upper limit of climate predictability in mid and high northern latitudes on seasonal to interannual time scales is investigated
by performing two perfect ensemble experiments with the global coupled atmosphere–ocean–sea ice model ECHAM5/MPI-OM. The ensembles
consist of six members and are initialized in January and July from different years of the model’s 300-year control integration.
The potential prognostic predictability is analyzed for a set of oceanic and atmospheric climate parameters. The predictability
of the atmospheric circulation is small except for southeastern Europe, parts of North America and the North Pacific, where
significant predictability occurs with a lead time of up to half a year. The predictability of 2 m air temperature shows a
large land–sea contrast with highest predictabilities over the sub polar North Atlantic and North Pacific. A combination of
relatively high persistence and advection of sea surface temperature anomalies into these areas leads to large predictability.
Air temperature over Europe, parts of North America and Asia shows significant predictability of up to half a year in advance.
Over the ice-covered Arctic, air temperature is not predictable at time scales exceeding 2 months. Sea ice thickness is highly
predictable in the central Arctic mainly due to persistence and in the Labrador Sea due to dynamics. Surface salinity is highly
predictable in the Arctic Ocean, northern North Atlantic and North Pacific for several years in advance. We compare the results
to the predictability due to persistence and show the importance of dynamical processes for the predictability. 相似文献
117.
Another Simple Method of Spectral Correction to Obtain Robust Eddy-Covariance Results 总被引:3,自引:0,他引:3
The eddy-covariance method is the state-of-the-art tool to measure mass and energy fluxes, though many measuring systems (particularly
closed-path systems) show strong spectral attenuation that causes significant underestimates of actual mass fluxes. The standard
way to correct these underestimates is to use theoretically derived transfer functions. Practical implementation has shown
that the attenuation, especially of closed-path systems, is underestimated by this method, even when the additional tube damping
is considered. This paper introduces and tests three alternative site-specific and hardware specific correction methods based
on spectral analysis, which typically enhance—additionally to the classical correction—the calculated mass fluxes based on
closed-path analysers, as their inevitable tubing and the filters used cause additional flow attenuation. Two of the three
methods are based on a site-specific and hardware specific transfer functions, the third uses direct comparison of cospectra.
Primarily the methods based on transfer functions proved to be easy-to-handle once established for the specific set-up and
measurement site. They represent practical and robust methods to correct for spectral attenuation. 相似文献
118.
119.
Joanne H. Shorter J. Barry Mcmanus Charles E. Kolb Eugene J. Allwine Brian K. Lamb Byard W. Mosher Robert C. Harriss Uwe Partchatka Horst Fischer Geoffrey W. Harris Paul J. Crutzen Hans-Josef Karbach 《Journal of Atmospheric Chemistry》1996,24(2):121-140
We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 g/m2/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States. 相似文献
120.
Impact of data assimilation of glider observations in the Ionian Sea (Eastern Mediterranean) 总被引:1,自引:0,他引:1
Glider observations of temperature, salinity and vertically averaged velocity in the Ionian Sea (Eastern Mediterranean Sea), made in the period October 2004–December 2004, were assimilated into an operational forecasting model together with other in situ and satellite observations. The study area has a high spatial and temporal variability of near surface dynamics, characterized by the entrance of the Atlantic Ionian Stream (AIS) into the Northern Ionian Sea. The impact of glider observations on the estimation of the circulation is studied, and it is found that their assimilation locally improves the prediction of temperature, salinity, velocity and surface elevation fields. However, only the assimilation of temperature and salinity together with the vertically averaged velocity improves the forecast of all observed parameters. It is also found that glider observations rapidly impact the analyses even remotely, and the remote impacts on the analyses remain several months after the presence of the glider. The study emphasizes the importance of assimilating as much as possible all available information from gliders, especially in dynamically complex areas. 相似文献