Pyroxene-melt equilibria: an updated model     

Roger L. Nielsen  Paula M. Davidson  Timothy L. Grove 《Contributions to Mineralogy and Petrology》1988,100(3):361-373

An updated model for pyroxene-melt equilibria at 1 atm has been developed and calibrated using new and existing experimental data in order to refine calculations of liquid lines of descent, which simulate the effect of igneous differentiation processes. We combine the Davidson and Lindsley (1985) model for activities of components in clinopyroxene and orthopyroxene solid solutions, a _i ^p , where i represents a quadrilateral endmember, with the Nielsen and Drake (1979) expressions for component activities in the melt, a _i ^L (two-lattice melt model). The chemical potential differences for pyroxene-melt equilibria are expressed in the form: $$\Delta \mu _{\iota } = 0 = In \left( {{{a_i^p } \mathord{\left/{\vphantom {{a_i^p } {a_i^L }}} \right.\kern-\nulldelimiterspace} {a_i^L }}} \right) + A_i + {{B_i } \mathord{\left/{\vphantom {{B_i } T}} \right.\kern-\nulldelimiterspace} T}$$ Pyroxene compositions were projected to quadrilateral compositions with the method of Lindsley and Anderson (1983). The regression constants A _i and B _i were calculated from experimental data that consists of 282 pyroxene-melt pairs, including 83 orthopyroxene-melt pairs. These experiments were all performed at 1 atm and represent compositions ranging from basalts (alkali to lunar) to dacites (42–66 wt% SiO₂). The model is calibrated for 1000相似文献   

Body force circulations in a compressible atmosphere: Key concepts     

Timothy J. Dunkerton 《Pure and Applied Geophysics》1989,130(2-3):243-262

The body force circulation problem of Eliassen is extended to spherical geometry and a quasi-compressible atmosphere using the zonally symmetric tidal theory. The concept of body force circulation is generalized to include the effects of mechanical friction and Newtonian cooling. This viewpoint is conceptually advantageous when the circulation is driven by body forces against radiative relaxation. The resulting linear theory is qualitatively useful in middle atmosphere applications, including the equatorial momentum source for which an analytic solution has not been given previously. Further generalizations of the theory are possible by including dynamical and photochemical feedback effects.  相似文献   

Multiple Residence and Cyclical Migration: A Life Course Perspective*   总被引：1，自引：0，他引：1  

Kevin E. McHugh  Timothy D. Hogan  Stephen K. Happel 《The Professional geographer》1995,47(3):251-267

As a result of restrictive time-space bounds in viewing migration, surprisingly little is known about the tempos and rhythms of geographical mobility in America. We discuss limitations of the conventional definition of migration and develop a life course framework of multiple residence and cyclical migration. Results of an Arizona-based case study reveal that multiple residence is common and more diverse than the annual influx of elderly snowbirds. Coming to grips with multiple residence and recurrent mobility in the United States represents a fundamental challenge in population and migration studies.  相似文献   

Two Approaches to Design of Monitoring Networks   总被引：5，自引：0，他引：5  

Timothy B. Spruill  Lucila Candela 《Ground water》1990,28(3):430-442

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Atrazine Used as a Tracer of Induced Recharge     

Diana Duncan  Darryll T. Pederson  Timothy R. Shepherd  James D. Can 《Ground Water Monitoring & Remediation》1991,11(4):144-150

The city of Lincoln draws water from a well field along the banks of the Platte River in east-central Nebraska. We have been able to follow the infusion of atrazine into this well field under induced recharge. Samples of water from the river, several monitoring wells and a production well were analyzed by GC/MS and solid phase extraction and found to change in concentration over the range 0.1 and 5.0 ppb of atrazine through the spring, summer, and fall 1989. Increases in the concentration of atrazine relating to precipitation events in the Platte River Basin were observable in the well water samples and ultimately in Lincoln municipal tap water. Atrazine from the river was seen to move via induced recharge and into well field ground water and away from the river at an observable rate. The concentration of atrazine in the river is dependent upon time of year and precipitation in the river basin.  相似文献   

Memorial to Felix Chayes     

E. H. Timothy Whitten 《Mathematical Geology》1994,26(2):157-160

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Late Holocene history of Waldsea Lake,Saskatchewan, Canada     

William M. Last  Timothy H. Schweyen 《Quaternary Research》1985,24(2):219-234

The post-Hypsithermal history of Waldsea Lake, a saline meromictic lake located in south-central Saskatchewan, has been deduced from a study of the changes in physical, mineralogical, and paleobiological parameters in sediment cores from the basin. Six lithostratigraphic units and three palynological zones are identified in the most recent sediment. These units and zones indicate that a shallow hypersaline lake with extensive mudflats existed about 4000 yr B.P. In response to the subsequent trend toward a cooler and wetter climate, deeper water conditions ensued, and by about 3000 yr ago a relatively deep stratified lake occupied the Waldsea Basin. A short climatic reversal about 2500 yr B.P. again caused low-water and mudflat conditions, but by 2000 yr ago the lake had regained its higher levels. The past 2000 yr of Waldsea's history have been relatively uneventful, except for a minor lowering of the lake about 700 yr B.P.  相似文献   

Instrumental temperature records at two sites in Central Canada: 1768 to 1910     

Timothy F. Ball  Roger A. Kingsley 《Climatic change》1984,6(1):39-56

As a result of affiliation between the Hudson's Bay Company and the Royal Society a relatively large number of instrumental temperature records are available from York Factory and Churchill Factory on the southwest of Hudson Bay beginning in 1768. The nature of these records, details of the instruments and information about the observers are presented. The major difficulty with the records is that the number of observations and the time of observation varied considerably. Adjustment factors were calculated for all of the combinations using a modern record maintained at the Churchill airport. By combining the Hudson's Bay Company record with data recorded by members of the Royal Canadian Mounted Police after 1852, and up to 1910, a long and relatively continuous record of daily and monthly average temperatures has been created for Central Canada.  相似文献   

The nursery role of seagrass meadows in the upper and lower reaches of the Chesapeake Bay     

Kenneth L. Heck  Timothy A. Thoman 《Estuaries and Coasts》1984,7(1):70-92

A two-year trawling and gill-netting study of vegetated and unvegetated bottoms near Parson’s Island, Maryland and near the mouth of the York River, Virginia was carried out to assess the nursery function of submerged vegetation for populations of fishes and decapod crustaceans in the Chesapeake Bay. Results revealed that vegetated bottoms supported substantially larger numbers of decapods, but not fishes, than unvegetated substrates. The lower Bay grassbed was an important nursery area for juvenile blue crabs, although neither of the grassbeds functioned as a nursery for commercially or recreationally valuable fishes. Our results suggest that: (1) further decreases in lower Bay Seagrass biomass would result in reduced numbers of adult blue crabs, but should not substantially affect populations of valuable fish species; (2) additional decreases in Upper Bay submerged vegetation should not produce dramatic change in the population sizes of either adult blue crabs or fishes.  相似文献   

Inverted-polarity electrical structures in thunderstorms in the Severe Thunderstorm Electrification and Precipitation Study (STEPS)     

W. David Rust  Donald R. MacGorman  Eric C. Bruning  Stephanie A. Weiss  Paul R. Krehbiel  Ronald J. Thomas  William Rison  Timothy Hamlin  Jeremiah Harlin 《Atmospheric Research》2005,76(1-4):247

Balloon-borne electric field soundings and lightning mapping data have been analyzed for three of the storms that occurred in the Severe Thunderstorm Electrification and Precipitation Study field program in 2000 to determine if the storms had inverted-polarity electrical structures. The polarities of all or some of the vertically stacked charge regions in such storms are opposite to the polarities observed at comparable heights in normal storms. Analyses compared the charge structures inferred from electric field soundings in the storms with charges inferred from three-dimensional lightning mapping data. Charge structures were inferred from electric field profiles by combining the one-dimensional approximation of Gauss's law with additional information from three-dimensional patterns in the electric field vectors. The three different ways of inferring the charge structure in the storms were found to complement each other and to be consistent overall. Charge deposition by lightning possibly occurred and increased the charge complexity of one of the storms.Many of the cloud flashes in each case were inverted-polarity flashes. Two storms produced ground flash activity comprised predominantly of positive ground flashes. One storm, which was an isolated thunderstorm, produced inverted-polarity cloud flashes, but no flashes to ground. The positive and negative thunderstorm charge regions were found at altitudes where, respectively, negative and positive charge would be found in normal-polarity storms. Thus, we conclude that these storms had anomalous and inverted-polarity electrical structures. Collectively, these three cases (along with the limited cases in the refereed literature) provide additional evidence that thunderstorms can have inverted-polarity electrical structures.  相似文献