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51.
Jere H. Jenkins Ephraim Fischbach John B. Buncher John T. Gruenwald Dennis E. Krause Joshua J. Mattes 《Astroparticle Physics》2009,32(1):42-46
Unexplained periodic fluctuations in the decay rates of 32Si and 226Ra have been reported by groups at Brookhaven National Laboratory (32Si), and at the Physikalisch–Technische–Bundesanstalt in Germany (226Ra). We show from an analysis of the raw data in these experiments that the observed fluctuations are strongly correlated in time, not only with each other, but also with the time of year. We discuss both the possibility that these correlations arise from seasonal influences on the detection system, as well as the suggestion of an annual modulation of the decay rates themselves which vary with Earth–Sun distance. 相似文献
52.
53.
Mean streamwise and vertical velocities as well as streamwise and vertical turbulence intensities were measured in a combustion wind tunnel used to collect pollutant emission data for agricultural field burning. Objectives were to compare the flow field upstream of a fire to that without a fire present and to compare the wind tunnel flow upstream of a fire to field conditions. Vertical centerline traverses with an anemometer were conducted for 32 separate wind tunnel operating configurations (wind speed, position in the tunnel, with or without fire, ceiling position, and floor condition) with one replication for each configuration (total of 64 traverses). Certain configurational changes in the wind tunnel had substantial effects on the flow field. Turbulence intensities and velocity profiles (as modeled by the log law-of-the-wall to determinez
0 andu
* values) in the wind tunnel were comparable to those in the field as reported in the literature. Velocities and turbulence intensities were generally higher, however, with a fire present in the tunnel and all other conditions constant. 相似文献
54.
John Michael Jenkins 《GeoJournal》1993,29(3):281-290
This paper examines tourism policies and actions in rural New South Wales. It explaines the roles of the New South Wales Tourism Commission, the New England Tourism Development Authority, and New South Wales State and Local Government planning legislation. In response to what is clearly a complex and neglected public policy sector, several suggestions are made as to rural tourism policy and research priorities. Particular attention is given to aspects of co-ordination and power in rural tourism policy formulation and implementation. 相似文献
55.
We have determined the concentrations and isotopic composition of helium in oceanic basaltic glass both by melting and by crushing in vacuo. A significant fraction of the helium is released by crushing, confirming that it resides within the vesicles. Comparison of volume percent vesicles to the fraction of helium contained in the vesicles gives qualitative agreement with experimental gas-melt partitioning studies. Measured concentrations are therefore, a function of original helium content, magmatic history, vesicle size and quantity, and grain size analyzed. Helium released by crushing is isotopically indistinguishable from that contained in the glass. Diffusion rates for helium in basaltic glass (in the temperature range 125–400°C) determined using the method of stepwise heating, yielded an activation energy of 19.9 ± 1 kcal/mole andlnD0 = ?2.7 ± 0.6 (cgs units). Extrapolation of these results to ocean floor temperatures (0°C) gives a diffusivity of 1.0 ± 0.6 × 10?17 cm2/s, indicating that diffusion is an insignificant mechanism for helium loss from fresh basaltic glasses. The3He/4He ratios are remarkably constant (at 1.10 ± 0.03 × 10?5) for samples from the Mid-Atlantic Ridge (FAMOUS area and 23°N), the Juan de Fuca Ridge, the Galapagos spreading center, the Mid-Cayman Rise, and the Central Indian Ocean Ridge. This result is interpreted in terms of similar geochemical histories within the source regions for these samples. 相似文献
56.
Helium isotopes in geothermal systems: Iceland,The Geysers,Raft River and Steamboat Springs 总被引:1,自引:0,他引:1
Helium isotope ratios have been measured in geothermal fluids from Iceland, The Geysers, Raft River, Steamboat Springs and Hawaii. These ratios have been interpreted in terms of the processes which supply He in distinct isotopic ratios (i.e. magmatic He, ~10 Ra; atmospheric He, Ra; and crustal He, ~0.1 Ra) and in terms of the processes which can alter the isotopic ratio (hydrologic mixing, U-Th series alpha production and weathering release of crustal He, magma aging and tritiugenic addition of 3He). Using this interpretational scheme, Iceland is found to be an area of hot-spot magmatic He implying an active volcanic source although the data are suggestive of high-temperature weathering release of crustal He incorporated in the geothermal fluids. By comparison to fumarolic gases from Hawaii and Juan De Fuca and Cayman Trench basaltic glass samples, The Geysers contains MOR type magmatic He again implying an active volcanic source possibly a “leaky” transform related to the San Andreas Fault System. Raft River contains only crustal He indicating no active volcanic sources. Steamboat Springs He isotope ratios are distinctly less than typical plate margin volcanics but must still have a magmatic source. A preliminary assessment of the cause for this low ratio is made assuming an “aging” magma source. 相似文献
57.
58.
David M. Jenkins 《Contributions to Mineralogy and Petrology》1983,83(3-4):375-384
Calcic amphiboles are observed in ultramafic rocks that have equilibrated under a broad span of geological conditions and might prove to be good indicators of metamorphic grade if their stabilities could be determined as a function of their compositions. Experiments were performed on the stability of tremolite plus forsterite in the system H2O-CaO-MgO-SiO2 from 5 to 20 kbar. A univariant curve was fitted to the experimental brackets using volume, water fugacity, and heat capacity data. The results indicate that the maximum stability of tremolite in the presence of forsterite is about 825° C at 5 kbar. Addition of Al2O3 to this system increases the stability of tremolitic amphibole by only 20°–40° C and induces solubility of 5–7 wt.% Al2O3 in the amphibole, as determined from quantitative SEM analyses of individual amphibole crystals. Thus substitution of the tschermakite component (Ca2(Mg3Al2) (Si6Al2) O22(OH)2) alone cannot lead to the greatly enhanced Al2O3 contents or thermal stability of natural calcic amphiboles. Comparison of the results from this study with experimental results from other studies on synthetic calcic amphiboles indicates that the high thermal stability of natural amphiboles is strongly linked with the substitution of alkalies (Na in particular) in the form of the component Na-Ca2(Mg4Al) (Si6Al2)O22(OH)2 (pargasite). Accordingly, experimental data from studies on pargasite have been combined with the appropriate univariant curves to obtain a phase diagram for amphibole-bearing ultramafic rocks modelled by the system H2O-Na2O-CaO-MgO-Al2O3-SiO2. 相似文献
59.
Volume Contents
Contents to Volume 7 相似文献60.
A non-local parameterisation of shear turbulence is proposed, which includes a dimensionless multiplicative constant as the
sole tunable parameter. Analytical and numerical solutions in the case of plane Couette flow exhibit sheared velocity profiles
with logarithmic behaviour near the boundaries, and the classical logarithmic flow profile is reproduced for a semi-infinite
domain. We also prove that the families of analytical solutions obtained are locally unique: if the velocity is a strictly-increasing
function of the distance from the boundary, a small perturbation of the velocity profile must be of the same functional form
as the basic flow. 相似文献