The optical polarization of spiral galaxies     

John F. L. Simmons  Edouard Audit 《Monthly notices of the Royal Astronomical Society》2000,319(2):497-509

Scattering of starlight by dust, molecules and electrons in spiral galaxies will produce a modification of the direct intensity and a polarization in the observed light. We treat the case where the distribution of scatterers can be considered to be optically thin, and derive semi-analytic expressions for the resolved intensity and polarized intensity for Thomson, Rayleigh, and more general scattering mechanisms. These expressions are applied to a parametric model for spiral galaxies. It is further shown that in the case of Thomson and Rayleigh scattering, and when scatterers and stars are distributed with rotational symmetry, the total polarized flux depends on the inclination, i , of the galactic axis to the line of sight according to a simple sin²  i law. This generalizes the well-known result for point-like and spherical light sources. By using a method based on spherical harmonics, we generalize this law for more general mechanisms, and show that to good approximation, the sin²  i law still holds for the class of models considered.  相似文献   

Mesozooplankton biomass and grazing responses to Cyclone Opal, a subtropical mesoscale eddy     

Michael R. Landry  Moira Decima  Melinda P. Simmons  Cecelia C.S. Hannides  Emy Daniels 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1378

As part of E-Flux III cruise studies in March 2005, plankton net collections were made to assess the effects of a cyclonic cold-core eddy (Cyclone Opal) on the biomass and grazing of mesozooplankton. Mesozooplankton biomass in the central region of Cyclone Opal, an area of uplifted nutricline and a subsurface diatom bloom, averaged 0.80±0.24 and 1.51±0.59 g DW m⁻², for day and night tows, respectively. These biomass estimates were about 80% higher than control (OUT) stations, with increases more or less proportionately distributed among size classes from 0.2 to >5 mm. Though elevated relative to surrounding waters south of the Hawaiian Islands (Hawai’i lee), total biomass and size distribution in Cyclone Opal were almost exactly the same as contemporary measurements made at Stn. ALOHA, 100 km north of the islands, by the HOT (Hawaii Ocean Time-series) Program. Mesozooplankton biomass and community composition at the OUT stations were also similar to ALOHA values from 1994 to 1996, preceding a recent decadal increase. These comparisons may therefore provide insight into production characteristics or biomass gradients associated with decadal changes at Stn. ALOHA. Gut fluorescence estimates were higher in Opal than in ambient waters, translating to grazing impacts of 0.11±0.02 d⁻¹ (IN) versus 0.03±0.01 d⁻¹ (OUT). Over the depth-integrated euphotic zone, mesozooplankton accounted for 30% of the combined grazing losses of phytoplankton to micro- and meso-herbivores in Opal, as compared to 13% at control stations. Estimates of active export flux by migrating zooplankton averaged 0.81 mmol C m⁻² d⁻¹ in Cyclone Opal and 0.37 mmol C m⁻² d⁻¹ at OUT stations, 53% and 24%, respectively, of the carbon export measured by passive sediment traps. Migrants also exported 0.18 mmol N m⁻² d⁻¹ (117% of trap N flux) in Cyclone Opal compared to 0.08 mmol N m⁻² d⁻¹ (51% of trap flux) at control stations. Overall, the food-web importance of mesozooplankton increased in Cyclone Opal both in absolute and relative terms. Diel migrants provided evidence for enhanced export flux in the eddy that was missed by sediment trap and ²³⁴Th techniques, and migrant-mediated flux was the major export term in the observed bloom-perturbation response and N mass balance of the eddy.  相似文献   

Dawn-dusk (y) component of the interplanetary magnetic field and the local time of the harang discontinuity     

A.S. Rodger  S.W.H. Cowley  M.J. Brown  M. Pinnock  D.A. Simmons 《Planetary and Space Science》1984,32(8):1021-1027

We describe a simple method for determining the time at which the meridian of a sub-auroral magnetic observatory crosses that of the Harang discontinuity—the separation of the eastward and westward electrojets which flow in the evening and morning sectors of the auroral oval. We then consider how this time, determined from examination of magnetograms from sub-auroral observatories varies with the dawn-dusk (y) component of the Interplanetary Magnetic Field. We find that the time at which the Harang discontinuity is identified in the Northern Hemisphere is earlier for B_y > 0 than the occasions when B_y < 0, and that the converse is observed in the Southern Hemisphere. Also we suggest that there is no significant seasonal variation in the relationship between the time of the discontinuity and B_y. The sense of the azimuthal shift of the auroral electrojet currents with changes in B_y is consistent with the theory of Cowley (1981). However, the magnitude of the observed shifts is approximately an order of magnitude greater than the theoretical predictions. We suggest that this difference between observation and theory arises from the use of a dipole magnetic field model at auroral zone latitudes in the theoretical estimation of azimuthal displacement.  相似文献   

4528011 Immobilization of radwastes in glass containers and products formed thereby     

Pedro B Macedo  Catherine J Simmons  Danh C Tran  Nichola Lagakos  Joseph Simmons 《Marine pollution bulletin》1985,16(12):ii

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Deglacial climate,carbon cycle and ocean chemistry changes in response to a terrestrial carbon release     

C. T. Simmons  H. D. Matthews  L. A. Mysak 《Climate Dynamics》2016,46(3-4):1287-1299

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On the testing of fully integrated surface–subsurface hydrological models     

Megan L. Sebben  Adrian D. Werner  Jessica E. Liggett  Daniel Partington  Craig T. Simmons 《水文研究》2013,27(8):1276-1285

Studies employing integrated surface–subsurface hydrological models (ISSHMs) have utilized a variety of test cases to demonstrate model accuracy and consistency between codes. Here, we review the current state of ISSHM testing and evaluate the most popular ISSHM test cases by comparing the hydrodynamic processes simulated in each case to the processes found in well‐characterized, real‐world catchments and by comparing their general attributes to those of successful benchmark problems from other fields of hydrogeology. The review reveals that (1) ISSHM testing and intercode comparison have not adopted specific test cases consistently; (2) despite the wide range of ISSHM metrics available for model testing, only two model performance diagnostics are typically adopted: the catchment outflow hydrograph and the catchment water balance; (3) in intercode comparisons, model performance is usually judged by evaluating only one performance diagnostic: the catchment outflow hydrograph; and (4) ISSHM test cases evaluate a small number of hydrodynamic processes that are largely uniform across the model domain, representing a limited selection of the processes of interest in well‐characterized, real‐world catchments. ISSHM testing would benefit from more intercode comparisons using a consistent set of test cases, aimed at evaluating more catchment processes (e.g. flooding) and using a wider range of simulation diagnostics (e.g. pressure head distributions). To achieve this, a suite of test case variations is required to capture the relevant catchment processes. Finally, there is a need for additional ISSHM test problems that compare model predictions with hydrological observations from intensively monitored field sites and controlled laboratory experiments. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

STRATA: William Smith’s Geological Maps. Foreword by Robert Macfarlane. Thames & Hudson Ltd,London (2020). Hardback., ISBN: 979-0-500-25247-5. £50.00.     

Mike Simmons 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):145-146

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Ozone as a stratospheric Lagrangian tracer     

Simmons  E. L.  Hamilton  R. A. 《Pure and Applied Geophysics》1973,106(1):1200-1207

Published papers reporting the use of ozone as a tracer are reviewed, and we conclude, as have the authors themselves, that the results are limited by lack of data. The results of a Meteorological Office experiment in which soundings were made at 12-hour intervals from four stations are also reported. In the light of these we are of the opinion that little further progress is likely unless campaigns involving sixty stations and soundings every 3 hours can be launched. This would be a formidable undertaking, and raises the question of whether it would be worth the effort and expense. A more modest approach might be to use aircraft and balloons in conjunction.  相似文献   

Tourism Alternatives: Potentials and Problems in the Development of Tourism     

D G Simmons 《New Zealand geographer》1994,50(2):57-58

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Microfractures in rocks from two geothermal areas     

Michael L. Batzle  Gene Simmons 《Earth and Planetary Science Letters》1976,30(1):71-93

Core samples from the Dunes, California, and Raft River, Idaho, geothermal areas show diagenesis superimposed on episodic fracturing and fracture sealing. The minerals that fill fractures show significant temporal variations. Sealed fractures can act as barriers to fluid flow. Sealed fractures often mark boundaries between regions of significantly different physical properties. The fracture porosities measured on several samples are less than 0.1%. This low value indicates that fractures are effectively sealed or that fracturing is confined to the relatively few large fractures visible within the samples. Fracture sealing and low fracture porosity imply that only the most recently formed fractures are open to fluids.  相似文献