Activity–composition relations for phases in petrological calculations: an asymmetric multicomponent formulation     

Tim?HollandEmail author  Roger?Powell 《Contributions to Mineralogy and Petrology》2003,145(4):492-501

For petrological calculations, including geothermobarometry and the calculation of phase diagrams (for example, P–T petrogenetic grids and pseudosections), it is necessary to be able to express the activity–composition (a–x) relations of minerals, melt and fluid in multicomponent systems. Although the symmetric formalism—a macroscopic regular model approach to a–x relations—is an easy-to-formulate, general way of doing this, the energetic relationships are a symmetric function of composition. We allow asymmetric energetics to be accommodated via a simple extension to the symmetric formalism which turns it into a macroscopic van Laar formulation. We term this the asymmetric formalism (ASF). In the symmetric formalism, the a–x relations are specified by an interaction energy for each of the constituent binaries amongst the independent set of end members used to represent the phase. In the asymmetric formalism, there is additionally a "size parameter" for each of the end members in the independent set, with size parameter differences between end members accounting for asymmetry. In the case of fluid mixtures, for example, H₂O–CO₂, the volumes of the end members as a function of pressure and temperature serve as the size parameters, providing an excellent fit to the a–x relations. In the case of minerals and silicate liquid, the size parameters are empirical parameters to be determined along with the interaction energies as part of the calibration of the a–x relations. In this way, we determine the a–x relations for feldspars in the systems KAlSi₃O₈–NaAlSi₃O₈ and KAlSi₃O₈–NaAlSi₃O₈–CaAl₂Si₂O₈, for carbonates in the system CaCO₃–MgCO₃, for melt in the melting relationships involving forsterite, protoenstatite and cristobalite in the system Mg₂SiO₄–SiO₂, as well as for fluids in the system H₂O–CO₂. In each case the a–x relations allow the corresponding, experimentally determined phase diagrams to be reproduced faithfully. The asymmetric formalism provides a powerful and flexible way of handling a–x relations of complex phases in multicomponent systems for petrological calculations.  相似文献   

Rerouting the stakeholder express   总被引：1，自引：0，他引：1  

Roger E. Kasperson   《Global Environmental Change》2006,16(4):320-322

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Linking vulnerability, adaptation, and resilience science to practice: Pathways, players, and partnerships   总被引：7，自引：1，他引：7  

Coleen Vogel  Susanne C. Moser  Roger E. Kasperson  Geoffrey D. Dabelko 《Global Environmental Change》2007,17(3-4):349-364

Vulnerability, adaptation and resilience are concepts that are finding increasing currency in several fields of research as well as in various policy and practitioner communities engaged in global environmental change science, climate change, sustainability science, disaster risk-reduction and famine interventions. As scientists and practitioners increasingly work together in this arena a number of questions are emerging: What is credible, salient and legitimate knowledge, how is this knowledge generated and how is it used in decision making? Drawing on important science in this field, and including a case study from southern Africa, we suggest an alternative mode of interaction to the usual one-way interaction between science and practice often used. In this alternative approach, different experts, risk-bearers, and local communities are involved and knowledge and practice is contested, co-produced and reflected upon. Despite some successes in the use and negotiation of such knowledge for ‘real’ world issues, a number of problems persist that require further investigation including the difficulties of developing consensus on the methodologies used by a range of stakeholders usually across a wide region (as the case study of southern Africa shows, particularly in determining and identifying vulnerable groups, sectors, and systems); slow delivery of products that could enhance resilience to change that reflects not only a lack of data, and need for scientific credibility, but also the time-consuming process of coming to a negotiated understanding in science–practice interactions and, finally, the need to clarify the role of ‘external’ agencies, stakeholders, and scientists at the outset of the dialogue process and subsequent interactions. Such factors, we argue, all hinder the use of vulnerability and resilience ‘knowledge’ that is being generated and will require much more detailed investigation by both producers and users of such knowledge.  相似文献   

Mistreatment of the economic impacts of extreme events in the Stern Review Report on the Economics of Climate Change   总被引：1，自引：0，他引：1  

Roger Pielke Jr.   《Global Environmental Change》2007,17(3-4):302-310

The Stern Review on the Economics of Climate Change has focused debate on the costs and benefits of alternative courses of action on climate change. This refocusing has helped to move debate away from science of the climate system and on to issues of policy. However, a careful examination of the Stern Review's treatment of the economics of extreme events in developed countries, such as floods and tropical cyclones, shows that the report is selective in its presentation of relevant impact studies and repeats a common error in impacts studies by confusing sensitivity analyses with projections of future impacts. The Stern Review's treatment of extreme events is misleading because it overestimates the future costs of extreme weather events in developed countries by an order of magnitude. Because the Stern Report extends these findings globally, the overestimate propagates through the report's estimate of future global losses. When extreme events are viewed more comprehensively the resulting perspective can be used to expand the scope of choice available to decision makers seeking to grapple with future disasters in the context of climate change. In particular, a more comprehensive analysis underscores the importance of adaptation in any comprehensive portfolio of responses to climate change.  相似文献   

Effects of mesoscale sea-surface temperature fronts on the marine atmospheric boundary layer   总被引：1，自引：0，他引：1  

Eric D. Skyllingstad  Dean Vickers  Larry Mahrt  Roger Samelson 《Boundary-Layer Meteorology》2007,123(2):219-237

A numerical modelling study is presented focusing on the effects of mesoscale sea-surface temperature (SST) variability on surface fluxes and the marine atmospheric boundary-layer structure. A basic scenario is examined having two regions of SST anomaly with alternating warm/cold or cold/warm water regions. Conditions upstream from the anomaly region have SST values equal to the ambient atmosphere temperature, creating an upstream neutrally stratified boundary layer. Downstream from the anomaly region the SST is also set to the ambient atmosphere value. When the warm anomaly is upstream from the cold anomaly, the downstream boundary layer exhibits a more complex structure because of convective forcing and mixed layer deepening upstream from the cold anomaly. An internal boundary layer forms over the cold anomaly in this case, generating two distinct layers over the downstream region. When the cold anomaly is upstream from the warm anomaly, mixing over the warm anomaly quickly destroys the shallow cold layer, yielding a more uniform downstream boundary-layer vertical structure compared with the warm-to- cold case. Analysis of the momentum budget indicates that turbulent momentum flux divergence dominates the velocity field tendency, with pressure forcing accounting for only about 20% of the changes in momentum. Parameterization of surface fluxes and boundary-layer structure at these scales would be very difficult because of their dependence on subgrid-scale SST spatial order. Simulations of similar flow over smaller scale fronts (<5 km) suggest that small-scale SST variability might be parameterized in mesoscale models by relating the effective heat flux to the strength of the SST variance.  相似文献   

Spectral Diagnostics of an Active Region Observed by the Solar EUV Rocket Telescope and Spectrograph (SERTS)     

Dwivedi  Bhola  Mohan  Anita  Thomas  Roger 《Solar physics》1998,180(1-2):157-178

The EUV spectrum of a solar active region observed by SERTS-89 is used to estimate physical parameters such as electron density, elemental abundance and inhomogeneity in the emitting source. A total of 13 ions, namely, Neiv-vi, Mgv-ix, Sivii-x and Sx, are studied in the SERTS spectral range 170-450 Ú, providing plasma diagnostics at temperatures between10₅ –10⁶ K. Attention is called to results derived from ion pairs of different elements that are formed over similar temperature regimes, which allow special checks on the standard assumptions of spectral analyses. Some EUV lines, not originally reported in the SERTS-89 spectrum, are shown to have measureable intensities and are indicated for future observations.  相似文献   

Using Strong Solar Coronal Emission Lines as Coronal Flux Proxies     

Falconer  David A.  Jordan  Stuart D.  Brosius  Jeffrey W.  Davila  Joseph M.  Thomas  Roger J.  Andreatta  Vicenzo  Hara  Hirohisa 《Solar physics》1998,180(1-2):179-191

We investigate the possibility that strong EUV lines observed with the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) provide good proxies for estimating the total coronal flux over shorter wavelength ranges. We use coordinated SERTS and Yohkoh observations to obtain both polynomial and power-law fits relating the broad-band soft X-ray fluxes to the intensities of Fexvi 335 Ú and 361 Ú, Fexv 284 Ú and 417 Ú, and Mgix 368 Ú measured with SERTS. We found that the power-law fits best cover the full range of solar conditions from quiet Sun through active region, though not surprisingly the cooler Mgix 368 Ú line proves to be a poor proxy. The quadratic polynomial fits yield fair agreement over a large range for all but the Mgix line. However, the linear fits fail conspicuously when extrapolated into the quiet-Sun regime. The implications of this work for the Heii 304 Ú line formation problem are also briefly considered.  相似文献   

Separation of local and regional information in distorted GDS response functions by hypothetical event analysis   总被引：2，自引：0，他引：2  

Patricia Ritter  Roger J. Banks 《Geophysical Journal International》1998,135(3):923-942

Electromagnetic investigations are usually intended to examine regional structures where induction takes place at a given period range. However, the regional information is often distorted by galvanic effects at local conductivity boundaries. Bahr (1985) and Groom & Bailey (1989) developed a physical distortion model for decomposing the MT impedance tensor, based upon local galvanic distortion of a regional 2-D electromagnetic field. We have extended their method to predict the magnetic variation fields created at an array of sites. The magnetic response functions at periods around 1000 s may be distorted by large-scale inhomogeneities in the upper or middle crust. In this period range, the data measured by a magnetometer array contain common information that can be extracted if the data set is treated as a unit, for example by using hypothetical event analysis. With this technique it is always possible to recover the regional strike direction from distorted data, even if a strong, spatially varying regional vertical field component is present in the data set. The determination of the regional impedance phases, on the other hand, is far more sensitive to deviations from the physical distortion model.
The approach has been used to investigate the Iapetus data set. For the array, which covers an area of 200  km × 300  km in northern England/southern Scotland, the technique revealed a common regional strike azimuth of ca . N125° E in the period range 500–2000  s. This direction differs from the strike indicated by the induction arrows, which seem influenced mainly by local current concentrations along the east–west-striking Northumberland Trough and a NE–SW-striking mid-crustal conductor. Both impedance phases are positive and differ by ca . 10°, which supports the assumptions of distortion fields in the data set and that the regional structure is 2-D.  相似文献   

The use of infauna by juvenile Penaeus aztecus Ives and Penaeus setiferus (Linnaeus)     

Teresa Ann McTigue  Roger J. Zimmerman 《Estuaries and Coasts》1998,21(1):160-175

Penaeus aztecus Ives, the brown shrimp, and Penaeus setiferus (Linnaeus), the white shrimp, co-occur in Texas salt marshes as juveniles. Although their life cycles are similar, evidence indicates that the species utilize different resources for the primary faunal element of their diets. Prey selection and growth studies have shown that brown shrimp successfully remove infauna from natural sediment. Further, a diet of polychaetes, whether alone or in combination with algae, produced growth in the species. Brown shrimp appear to be trophically linked to infaunal populations, thus the structure and dynamics of the benthic community may directly affect local brown shrimp productivity. Areas dominated by surface-dwelling polychaetes as opposed to deep burrowers may provide more accessible foraging opportunities for juvenile brown shrimp. By contrast, white shrimp neither removed infauna nor grew to a significant degree when provided polychaetes or amphipods as food. White shrimp are omnivorous but do not rely on infaunal material to the same extent as brown shrimp. The primary faunal element in the diet of white shrimp has not yet been identified. The dietary differences between the two species may play a role in determining which species dominates in regions with varying marsh accessibility. Although not the only factors influencing penaeid survival and growth, prey choice and availability may greatly affect production and local success of penaeid populations. *** DIRECT SUPPORT *** A01BY081 00013  相似文献   

Food habits and growth of juvenile striped bassMorone saxatilis, in Albemarle Sound, North Carolina     

John E. Cooper  Roger A. Rulifson  J. Jeffrey Isely  Sara E. Winslow 《Estuaries and Coasts》1998,21(2):307-317

Juvenile striped bass,Morone saxatilis, collected in Albemarle Sound, North Carolina, during 1988–1992 were examined for food habits and growth. Ages estimated from otoliths collected in 1990–1992 were used to determine individual spawning dates and growth in total length and weight. The majority of striped bass examined had been spawned in mid-May 1990, mid-May to early June 1991, and June to early July 1992. Mysid shrimp was the dominant prey taxon and was consumed in all size classes examined. Mysid shrimp were consumed at twice the rate of copepods and 10 times more frequently than cladocerans. Fishes were a minor prey taxon. The number of mysid shrimp consumed increased with increasing length of striped bass. A higher percentage of mysid shrimp were consumed in the more saline waters of the central sound than in the less saline western sound. The opposite trend was found for consumed fishes. Increases in total length were linear from July to October, but increases in weight were not. Weight increased less rapidly in younger striped bass and more rapidly in older striped bass than either length or age. Quadratic and logarithmic equations accurately predicted weight from measures of total length but weight could not be predicted from age nor could age be predicted from total length. Estimating growth from total length at time of capture may be comparing fish of different ages. Age estimation from otoliths allowed us to determine that growth rates were similar among years and that differences in observed total length over time were due to different spawning times and not growth rates.  相似文献