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31.
J. Rogers 《Bulletin of Volcanology》1966,29(1):173-175
The temperatures at which melting begins of three New Zealand greywackes and two argillites were determined as a function of water pressure up to 3000 atmospheres. The purpose of these experiments was to provide data possibly relevant to the genesis of the North Island ignimbrites and for comparison with the experiments ofBowen andTuttle (1958) on the melting temperatures of granites and the ternary minimum system (NaAlSi3O8 — KAlSi3O8 — SiO2 — H2O). Powdered samples of the rocks were heated in unsealed silver tubes in cold seal bombs, the water pressure being measured on a Bourdon gauge and applied during heating. Temperature control was ± 5°C. Twelve days was the longest heating period, most being for 24 hours, which was sufficient for apparent reaction. At the end of an experiment, the pressure was released, and the sample quickly cooled by removal from the bomb. The samples were crushed and examined by X-ray diffraction and the petrographic microscope. The PT curve for the beginning of melting of the greywackes and argillites is very close toBowen andTuttle’s for granites and the ternary minimum to 1000 atmospheres water pressure. Above this pressure the greywackes melt at slightly higher temperatures than on the granite curve with the argillites a little higher still. These observations are similar to those reported for shales byWyllie andTuttle 1960, 1961, for greywackes byWinkler andvon Platen 1961, and pelitic sediments byWyart andSabatier, 1959. The amount of anatectic melt increases rapidly above the temperature of initial melting and is inversely related to the quartz present in the greywackes. The partially melted products were often notably vesicular. Cordierite, mullite, hypersthene, scapolite and mica were identified in the X-ray diffractograms as coexisting with the melt. These experiments are in agreement with published work in showing that the quartz and alkali feldspars of granites, shales and arkosic sediments can in the presence of water react and begin to melt at 20–25 kilometres depth in the earth assuming a geothermal gradient of 30°C/km. The melt is granitic or granodioritic in composition. 相似文献
32.
A possible suture between an old craton in West Africa and the Arabian—Nubian shield is marked by a persistent zone of Phanerozoic weakness. This zone extends between the Nile and Niger deltas and passes through the Qattara embayment, along the Bahariya fault, through the Kufra basin, between the Tibesti and Jabal al Uwaynat massifs, through the Bahr el Ghazal and Lake Chad areas, and along the Benoue trough. 相似文献
33.
The tall sea pen Funiculina quadrangularis has a patchy distribution around the UK, being found in sheltered waters below 20 m depth on the northwest coast of Scotland and Ireland. The limited distribution and sensitivity to bottom fishing activities make F. quadrangularis vulnerable to reduction in population numbers that may lead to genetic isolation and reduced diversity. Because of this vulnerability and low resilience to physical disturbance, the tall sea pen is recognised as a Species of Principle Importance under the Natural Environment and Rural Communities Act, 2006, UK. ( http://www.legislation.gov.uk/ukpga/2006/16/contents ) and is also on the Biodiversity Action Plan list of Priority Species for the UK. In the Mediterranean it is recognised as a sensitive and essential fish habitat because it forms habitat for several commercially important crustaceans. The aim of this study was to understand the current state of the genetic structure and gene flow of F. quadrangularis in areas of NW Scotland. We developed 10 microsatellite markers and used them to genotype 176 samples from four populations. Overall, our results suggest that there is high genetic diversity and high gene flow between colonies of F. quadrangularis in and among locations in Loch Linnhe and Loch Duich. As a result of the high rates of gene flow, genetic differentiation between sites was low. This may provide resilience to human impacts if distant populations have a high connectivity. However, care must be taken, as small but significant isolation by distance was found between the most geographically distant sites and only a small part of the species range was examined in this study. The genetic tools developed here will provide a foundation for wider studies of this vulnerable species. 相似文献
34.
Internal gravity waves excited by overshoot at the bottom of the convection zone can be influenced by rotation and by the
strong toroidal magnetic field that is likely to be present in the solar tachocline. Using a simple Cartesian model, we show
how waves with a vertical component of propagation can be reflected when traveling through a layer containing a horizontal
magnetic field with a strength that varies with depth. This interaction can prevent a portion of the downward traveling wave
energy flux from reaching the deep solar interior. If a highly reflecting magnetized layer is located some distance below
the convection zone base, a duct or wave guide can be set up, wherein vertical propagation is restricted by successive reflections
at the upper and lower boundaries. The presence of both upward and downward traveling disturbances inside the duct leads to
the existence of a set of horizontally propagating modes that have significantly enhanced amplitudes. We point out that the
helical structure of these waves makes them capable of generating an α-effect, and briefly consider the possibility that propagation in a shear of sufficient strength could lead to instability,
the result of wave growth due to over-reflection. 相似文献
35.
D.S.S. Lim G.L. Warman C.P. McKay M.M. Marinova D. Andersen Z. Cardman M.D. Delaney A.L. Forrest B.E. Laval P. Nuytten M. Reay D. Schulze-Makuch G.F. Slater 《Planetary and Space Science》2010,58(6):920-930
Forthcoming human planetary exploration will require increased scientific return (both in real time and post-mission), longer surface stays, greater geographical coverage, longer and more frequent EVAs, and more operational complexities than during the Apollo missions. As such, there is a need to shift the nature of astronauts’ scientific capabilities to something akin to an experienced terrestrial field scientist. To achieve this aim, the authors present a case that astronaut training should include an Apollo-style curriculum based on traditional field school experiences, as well as full immersion in field science programs. Herein we propose four Learning Design Principles (LDPs) focused on optimizing astronaut learning in field science settings. The LDPs are as follows:
- (1)
- LDP#1: Provide multiple experiences: varied field science activities will hone astronauts’ abilities to adapt to novel scientific opportunities
- (2)
- LDP#2: Focus on the learner: fostering intrinsic motivation will orient astronauts towards continuous informal learning and a quest for mastery
- (3)
- LDP#3: Provide a relevant experience—the field site: field sites that share features with future planetary missions will increase the likelihood that astronauts will successfully transfer learning
- (4)
- LDP#4: Provide a social learning experience—the field science team and their activities: ensuring the field team includes members of varying levels of experience engaged in opportunities for discourse and joint problem solving will facilitate astronauts’ abilities to think and perform like a field scientist.
36.
We present results from numerical simulations of the interaction of internal gravity waves (IGW) with a magnetic field. In accordance with the dispersion relation governing IGW in the presence of magnetism and rotation, when the IGW frequency is approximately that of the Alfvén frequency, strong reflection of the wave occurs. Such strong reflection markedly changes the angular momentum transport properties of the waves. In these simple models a strong, time-independent shear layer develops, in contrast to the oscillating shear layer that develops in the purely hydrodynamic case. 相似文献
37.
A range of biological traits of nematode species were combined to identify patterns in the functional composition of their assemblages collected at 19 soft-bottom stations in the southwestern North Sea with the primary aim to determine which environmental variables control communities. We used 19 categories of five biological traits thought or known to represent an important ecological function. These were related to buccal morphology, tail shape, body size, body shape and life history strategy. Data on trait membership was provided by biological information on species and genera. A total of 79 different trait combinations were recorded. Results from correlation analyses revealed several significant relationships between traits. Some trait combinations were shared by different species and genera, and the ratio of realised versus total number of possible trait combinations of < 1 suggested that some trait combinations were not represented by the nematode fauna from this region. The functional composition of nematodes was strongly linked to median particle diameter and silt content of the sediment and water depth. The approach adopted and our attempts at defining and analysing functional attributes of nematode communities raised a number of conceptual and methodological issues which are discussed. 相似文献
38.
Stanislav S. Shabala Jonathan G. Rogers Jamie N. McCallum Oleg A. Titov Jay Blanchard James E. J. Lovell Christopher S. Watson 《Journal of Geodesy》2014,88(6):575-586
We examine the relationship between source position stability and astrophysical properties of radio-loud quasars making up the International Celestial Reference Frame (ICRF2). Understanding this relationship is important for improving quasar selection and analysis strategies, and therefore reference frame stability. We construct flux density time series, known as light curves, for 95 of the most frequently observed ICRF2 quasars at both the 2.3 and 8.4 GHz geodetic very long baseline interferometry (VLBI) observing bands. Because the appearance of new quasar components corresponds to an increase in quasar flux density, these light curves alert us about potential changes in source structure before they appear in VLBI images. We test how source position stability depends on three astrophysical parameters: (1) flux density variability at X band; (2) time lag between flares in S and X bands; (3) spectral index root-mean-square (rms), defined as the variability in the ratio between S and X band flux densities. We find that the time lag between S and X band light curves provides a good indicator of position stability: sources with time lags $<$ 0.06 years are significantly more stable ( $>$ 20 % improvement in weighted rms) than sources with larger time lags. A similar improvement is obtained by observing sources with low $(<$ 0.12) spectral index variability. On the other hand, there is no strong dependence of source position stability on flux density variability in a single frequency band. These findings can be understood by interpreting the time lag between S and X band light curves as a measure of the size of the source structure. Monitoring of source flux density at multiple frequencies therefore appears to provide a useful probe of quasar structure on scales important to geodesy. The observed astrometric position of the brightest quasar component (the core) is known to depend on observing frequency. We show how multi-frequency flux density monitoring may allow the dependence on frequency of the relative core positions along the jet to be elucidated. Knowledge of the position–frequency relation has important implications for current and future geodetic VLBI programs, as well as the alignment between the radio and optical celestial reference frames. 相似文献
39.
40.
Raymond F. Smith K. Thomas Lorenz Darwin Ho Bruce A. Remington Alex Hamza John Rogers Stephen Pollaine Seokwoo Jeon Yun-Suk Nam J. Kilkenny 《Astrophysics and Space Science》2007,307(1-3):269-272
In recently developed laser-driven shockless compression experiments an ablatively driven shock in a primary target is transformed
into a ramp compression wave in a secondary target via unloading followed by stagnation across an intermediate vacuum gap.
Current limitations on the achievable peak longitudinal stresses are limited by the ability of shaping the temporal profile
of the ramp compression pulse. We report on new techniques using graded density reservoirs for shaping the loading profile
and extending these techniques to high peak pressures. 相似文献