Surface-structure-controlled sectoral zoning of the rare earth elements in fluorite from Long Lake, New York, and Bingham, New Mexico, USA   总被引：1，自引：0，他引：1  

Stephanie BoszeJohn Rakovan 《Geochimica et cosmochimica acta》2002,66(6):997-1009

The concentration and distribution of rare earth elements (REE) in sectorally zoned fluorite crystals from Long Lake, New York, and the Hansonburg Mining District, Bingham, New Mexico, have been studied using cathodoluminescence and synchrotron X-ray fluorescence microanalysis (SXRFMA). In cubo-octahedral samples from Long Lake, New York, Ce, Nd, Gd, Dy, Ho, Er, and Tm are preferentially partitioned into the |111| sector relative to the |100| sector. Partition coefficients (K_d = concentration in |111| sector/concentration in |100| sector) range between 3.5 for Ce, to 1.4 for Tm, with a general decrease in K_d as elements deviated from the ionic radius of Ca²⁺, for which REE substitute in fluorite. Diffusion of the REE has occurred, as evidenced by gradual changes in composition over distances of 0.2 to 0.3 mm at sector boundaries.In Bingham samples, three different partition coefficients were determined for Dy: K_d|100|/|111| = 2.83, K_{d |100|/|110|} = 1.77, and K_{d |110|/|111|} = 1.60. These are mean K_d values for a 95% confidence interval. In another sample from the same deposit, Dy, Er, and Gd were found to be preferentially incorporated into the |100| sector relative to the |210| sector with average K_{d |100|/|210|} of 3.1, 2.4, and 2.9, respectively. In a third sample, Nd was found to be preferentially incorporated into the |110| sector relative to the |321| sector with an average K_{d |110|/|321|} value of 2.3.Compositional heterogeneities in a given sector (concentric zoning) have been resolved using SXRFMA but are significantly less than the concentration difference across sector boundaries. Often fluorite exists in a wide variety of morphologies, as is the case in the Hansonburg Mining District of Bingham. We suggest caution when using the REE as petrogenetic indicators because fluorite trace element chemistry can vary greatly among crystals within a deposit depending on the internal morphology of a particular crystal.  相似文献   

Fine-scale volume heterogeneity measurements in sand     

Dajun Tang Briggs  K.B. Williams  K.L. Jackson  D.R. Thorsos  E.I. Percival  D.B. 《Oceanic Engineering, IEEE Journal of》2002,27(3):546-560

As part of the effort to characterize the acoustic environment during the high frequency sediment acoustics experiment (SAX99), fine-scale variability of sediment density was measured by an in situ technique and by core analysis. The in situ measurement was accomplished by a newly developed instrument that measures sediment conductivity. The conductivity measurements were conducted on a three-dimensional (3-D) grid, hence providing a set of data suited for assessing sediment spatial variability. A 3-D sediment porosity matrix is obtained from the conductivity data through an empirical relationship (Archie's Law). From the porosity matrix, sediment bulk density is estimated from known average grain density. A number of cores were taken at the SAX99 site, and density variations were measured using laboratory techniques. The power spectra were estimated from both techniques and were found to be appropriately fit by a power-law. The exponents of the horizontal one-dimensional (1-D) power-law spectra have a depth-dependence and range from 1.72 to 2.41. The vertical 1-D spectra have the same form, but with an exponent of 2.2. It was found that most of the density variability is within the top 5 mm of the sediment, which suggests that sediment volume variability will not have major impact on acoustic scattering when the sound frequency is below 100 kHz. At higher frequencies, however, sediment volume variability is likely to play an important role in sound scattering.  相似文献   

Four years of BATSE gamma-ray burst observations     

Michael S. Briggs 《Astrophysics and Space Science》1995,231(1-2):3-10

In four years BATSE has observed more than 1000 gamma-ray bursts, making unprecedented measurements of their spatial and brightness distributions. These measurements and their implications for the origin of gamma-ray bursts are reviewed.  相似文献   

The BATSE search for absorption lines     

D. L. Band  L. A. Ford  J. L. Matteson  D. M. Palmer  B. J. Teegarden  M. S. Briggs  G. N. Pendleton  R. D. Preece  W. S. Paciesas 《Astrophysics and Space Science》1995,231(1-2):145-148

No absorption lines between 15 and 100 keV have been detected in burst spectra accumulated by BATSE. Almost 250 bursts have been inspected visually, and a computerized search has begun. Our simulations show that BATSE could indeed detect lines similar to those observed byGinga in strong bursts, and our tests of the detectors' actual capabilities demonstrate they function as understood. The apparent discrepancy between BATSE andGinga is not yet compelling, and therefore the BATSE nondetections do not invalidate theGinga detections. Nonetheless, the absence of BATSE line detections indicates a low line-occurrence frequency.  相似文献   

THE IMPACT OF FEDERAL LOCAL PUBLIC TRANSPORTATION ASSISTANCE UPON TRAVEL BEHAVIOR     

Ronald Briggs 《The Professional geographer》1980,32(3):316-325

Despite substantial amounts of federal assistance to local public transportation, ridership has declined considerably in the country as a whole since 1964, suggesting an ineffective government program. A city-by-city comparison of assistance received with changes in transit ridership shows that declines in transit usage were least in cities receiving the most federal aid, and greatest in cities receiving the least aid. This demonstrates that federal aid has had an impact upon travel behavior. Indeed, it is the single most important factor explaining differences between cities in travel behavior changes in the 1970's.  相似文献   

Use of composite data sets for source-tracking enterococci in the water column and shoreline interstitial waters on Pensacola Beach, Florida     

Genthner FJ  James JB  Yates DF  Friedman SD 《Marine pollution bulletin》2005,50(7):724-732

Sources of Enterococcus faecalis isolates from Pensacola Beach, FL. were identified using a library-based approach by applying the statistical method of average similarity to single and composite data sets generated from separate analyses. Data sets included antibiotic resistance analysis (ARA), rep-fingerprints, and fatty acid methyl ester (FAME) profiles. Use of a composite data set composed of ARA and rep-fingerprints, added to the confidence of the identifications. The addition of FAME data to composite data sets did not add to the confidence of identifications. Source identification was performed to better understand risk associated with higher densities of enterococci found in swash zone interstitial water (SZIW) as compared to adjacent bathing water on Pensacola Beach, FL. The "swash zone" is that area of the beach continually washed over by waves. As the potential sources of enterococci were limited in this environment, only two library units, sea gull and human, were constructed. Identification of the beach isolates using a composite data set indicated a sea gull origin. The clonality of the beach isolates suggested that the beach environment selects certain subspecies of E. faecalis.  相似文献   

AUTOMOBILE ESTABLISHMENTS IN LIVERPOOL: A STEADY STATE DISTRIBUTION     

Wayne K. D. Davies  Ronald Briggs 《The Professional geographer》1967,19(6):323-329

  相似文献   

A new class of steady solutions of the barotropic vorticity equation     

William L. Briggs 《Dynamics of Atmospheres and Oceans》1980,4(2):67-99

Early studies of the wind-driven ocean problem were concerned with finding steady solutions of the equations of motion, first by analytic, and later by numerical methods. The problem is characterized by an Ekman number (?) and a Rossby number (α). Prior to this study, steady solutions were confined to the ranges α, ? < < 1.In this work the problem is considered in a circular domain with lateral friction and a partial-slip boundary condition. Steady solutions are found analytically in the new regime α > 1. Furthermore, for large enough values of ?, steady solutions are determined numerically in the intermediate range between this high-α regime and the classical low-α regime. That is, for some values of ?, steady solutions can be found through all values of α. Numerical evidence suggests that below a critical value of ?, steady solutions in this intermediate range exist, but cease to be stable. Similar results have been obtained with bottom friction and with different boundary conditions.  相似文献   

A case study of coping strategies and landslides in two villages of Central-Eastern Nepal     

Karen Sudmeier-Rieux  Stephanie Jaquet 《Applied geography (Sevenoaks, England)》2012,32(2):680-690

Landslides are an increasing problem in Nepal’s Middle Hills due to both natural and human phenomena: mainly increasingly intense monsoon rains and a boom in rural road construction. This problem has largely been neglected due to underreporting of losses and the dispersed nature of landslides. Understanding how populations cope with landslides is a first step toward developing more effective landslide risk management programs. The present research focuses on two villages in Central-Eastern Nepal, both affected by active landslides but with different coping strategies. Research methods are interdisciplinary, based on a geological assessment of landslide risk and a socio-economic study of the villages using household questionnaires, focus group discussions and transect walks. Community risk maps are compared with geological landslide risk maps to better understand and communicate community risk perceptions, priorities and coping strategies. A modified typology of coping strategies is presented, based on previous work by Burton, Kates, and White (1993) that is useful for decision-makers for designing more effective programs for landslide mitigation. Main findings underscore that coping strategies, mainly seeking external assistance and outmigration, are closely linked to access to resources, ethnicity/social status and levels of community organization. Conclusions include the importance of investing in organizational skills, while building on local knowledge about landslide mitigation for reducing landslide risk. There is great potential to increase coping strategies by incorporating skills training on landslide mitigation in existing agricultural outreach and community forest user group training.  相似文献   

Public policy, institutional investors and climate change: a UK case-study     

Stephanie Pfeifer  Rory Sullivan 《Climatic change》2008,89(3-4):245-262

Institutional investors have two important roles to play in encouraging companies to address the risks and take advantage of the opportunities presented by climate change. The first is through using their influence as shareholders to encourage companies to adopt more proactive approaches to managing the risks and opportunities presented by climate change. The second is through explicitly factoring climate change risks and opportunities into ‘mainstream’ investment analysis processes. While there is growing investor activity on the former, the integration of climate change into investment analysis remains confined to sectors where there are strong government incentives (e.g. for renewable energy) or where greenhouse gas emissions have a market price. This article reviews the evolution of UK institutional investor interest in climate change from 1990 to 2005, focusing in particular on the relative contributions of ‘soft’ policy measures such as information-disclosure and awareness raising, and ‘hard’ policy measures such as regulation and market-based instruments. The article concludes that, over this period, soft policy measures played an important role in encouraging investors to discuss climate change issues with companies, but had minimal influence on investment decisions. It was only with the introduction of hard policy measures that climate change started to be systematically factored into investment analysis. The article canvasses the implications of these findings for government efforts in the UK and elsewhere to encourage investors to play a more proactive role in the climate change debate. It also considers the role that institutional investors themselves can play in strengthening public policy measures to reduce greenhouse gas emissions.  相似文献