Organic carbon deliveries and their flow related dynamics in the Fitzroy estuary     

Ford P  Tillman P  Robson B  Webster IT 《Marine pollution bulletin》2005,51(1-4):119-127

The Fitzroy estuary (Queensland, Australia) receives large, but highly episodic, river flows from a catchment (144,000 km(2)) which has undergone major land clearing. Large quantities of suspended sediments, and particulate and dissolved organic carbon are delivered. At peak flows, delta(13)C (-21.7+/-0.8 per thousand) and C/N (14.8+/-1.3) of the suspended solids indicate that the particulate organic material entering the estuary is principally soil organic carbon. At the lower beginning flows the particulate organic matter comes from in-stream producers (delta(13)C=-26 per thousand). The DOC load is about 10 times the POC load. Using the inverse method, budgets for POC and DOC were constructed for high and low flows. Under high flows, only a small portion of the POC and DOC load is lost in the estuary. Under dry season (low flow) conditions the estuary is a sink for DOC, but remains a source of POC to the coastal waters.  相似文献   

Determination of the area and mass distribution of orbital debris fragments   总被引：1，自引：0，他引：1  

Gautam D. Badhwar  Phillip D. Anz-Meador 《Earth, Moon, and Planets》1989,45(1):29-51

An important factor in modeling the orbital debris environment is the loss rate of debris due to atmospheric drag and luni/solar perturbations. An accurate knowledge of the area-to-mass ratio of debris fragments is required for the calculation of the effect of atmospheric drag. In general, this factor is unknown and assumed values are used. However, this ratio can be calculated for fragments for which changes in the orbital elements due to atmospheric drag as a function of time are known. This is the inverse of the technique used to determine the atmospheric density from the decay of satellites with accurately known area-to-mass ratios. These kinds of propagation programs are routinely used in predicting the decay of an orbiting vehicle. In this work the area-to-mass ratio of about 2600 fragments arising from the breakup of 24 artificial satellites have been determined. An analysis of the data on about 200 objects (rocket bodies, scientific satellites, etc.) with known mass, size, and shape has also been made. The value of the radar cross-section (RCS), as measured by the Eglin radar operating at 70 cm wavelength, has been correlated to the effective area of these objects. The measurements of the area-to-mass ratio of these objects then provide a calibration of the actual to the calculated mass. It has been shown that the debris mean mass, m, is related to the mean effective area, A, by a power law relation, m = k A ^1.86. However, for a given effective area the mass distribution is very broad. Moreover, the cumulative mass distribution, N(>m), can be expressed as N(>m) = D(m + b), where D, b, and c are constants. The asymptotic slope, c, of low intensity explosions is on the average lower than the slope for high intensity explosions, but there is considerable spread of this slope in each class. Part of the flattening, as indicated by the finite value of the parameter, b, can be understood as arising out of the spread in the RCS values due to the tumbling motion of the fragments and effects related to the detectability of the fragment by the Eglin radar. It has been established that the mass in a given breakup calculated using this technique is in good agreement with the expected mass value. These results can be used in modeling the breakups of other artificial earth satellites and safety analysis.  相似文献   

The use of magnetic field excursions in stratigraphy     

Ronald T. Merrill  Phillip L. McFadden 《Quaternary Research》2005,63(3):232-237

The use of magnetic field excursions in stratigraphy is difficult primarily because the excursion field is complex and not dominantly dipolar. In contrast with a reversal, which is a global event, an excursion can be evidenced at one location but not another. Although this does not by itself rule out the use of excursions in stratigraphy, it does limit the geographic area over which they may be correlated. We recommend, somewhat conservatively, that excursions can be used to correlate between sedimentary cores separated by angular distances of less than 30° on Earth's surface. Correlation between cores separated by more than 45° should not be attempted.  相似文献   

Comparing epidemic forecasts for European countries obtained from AIDS incidence and HIV prevalence data     

Phillip W Smith  Richard Thomas 《Journal of Geographical Systems》2005,7(3-4):337-359

Previously, the diffusion of HIV/AIDS among the countries of Europe has been reconstructed using a multiregion epidemic modelling system (Thomas 2000; Smith and Thomas 2001). This model was calibrated to WHO AIDS incidence series for each country which, in most instances, were replicated with a high degree of fit. The size of the epidemic implied by this procedure, however, did not conform to point estimates of cumulative HIV prevalence which indicate an eventual size at least three times greater than that attributable to recorded AIDS cases. This paper, therefore, investigates the consequences of this discrepancy for the space–time structure that is estimated for the epidemic in Europe. The first part considers how the modelling system is adapted to take account of national HIV statistics. To this end, an optimisation method is described for identifying disease transmission rates that are consistent with current cumulative HIV prevalence in each country. This method generates a range of feasible solutions where the eventual size of the epidemic is inversely related to this infectivity rate. The second part derives multiregion simulations for European countries using parameter sets calibrated according to both AIDS incidence and HIV prevalence. The outputs for each set include the predicted starting pathway of the epidemic together with a graph recording the direction of the principal infection vector for each country at the forecast time of peak HIV prevalence. For AIDS based scenarios, the diffusion of the epidemic generally flows across Europe from west to east. In contrast, for HIV scenarios at peak prevalence the direction of flow is partially reversed from east to west. The discussion considers the implications of these findings for disease control in the light of issues concerning the recording of HIV and AIDS statistics.

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Dynamic analysis of column-supported hyperboloidal shells     

Phillip L. Gould  Subir K. Sen  Herman Suryoutomo 《地震工程与结构动力学》1973,2(3):269-280

The dynamic response of hyperboloidal shells on discrete column supports is studied using a curved rotational shell finite element. In this finite element formulation, the displacement field over each element domain is approximated by polynomial functions in which the coefficients of the linear terms correspond to the nodal values of the displacements and the higher order terms vanish at the nodal circles. The stiffness and mass matrices associated with the equations of motion are derived from Hamilton's variational principle and include the effects of transverse shearing deformation and rotatory inertia. Since the formulation, as such, involves a great many degrees of freedom because of the use of higher order displacement functions, the kinematic condensation technique is employed to reduce the order of the dynamic problem The dynamic analysis indicates the importance of realistically modelling the base region of the shell. Studies on a prototype tower indicates that the base flexibility reduces the natural frequencies of the shell and increases the displacements near the base. The magnitude of this reduction, which could be significant, depends primarily on the tangential stiffnesses of the supporting columns and is hardly affected by the thickened ring beam at the base.  相似文献   

Complex response analysis of shells of revolution including uniform base translation and rocking     

Bor-Jen Lee  Phillip L. Gould 《地震工程与结构动力学》1984,12(4):507-519

A complex response algorithm for the dynamic analysis of axisymmetric thin shells supported on an interactive foundation is developed. The substructure deletion method is employed through the utilization of a dynamic boundary system at the contact area between the superstructure and the substructure. A new mathematical formulation in conjunction with the shell behaviour is developed to deal with rigid body motions due to the negation of the fixed base assumption. Four foundation conditions, that is, a fixed base, two pile foundation cases and a flexible base, are to examine the effect of base flexibility on the seismic response of cooling towers. Also, excellent comparative results between the frequency domain solution and a time domain solution are obtained.  相似文献   

Thermodynamic and Turbulence Characteristics of the Southern Great Plains Nocturnal Boundary Layer Under Differing Turbulent Regimes     

Timothy A. Bonin  William G. Blumberg  Petra M. Klein  Phillip B. Chilson 《Boundary-Layer Meteorology》2015,157(3):401-420

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Movement Patterns and Distributional Shifts of Dungeness Crab (Metacarcinus magister) and English Sole (Parophrys vetulus) During Seasonal Hypoxia     

Halley E. Froehlich  Timothy E. Essington  Anne H. Beaudreau  Phillip S. Levin 《Estuaries and Coasts》2014,37(2):449-460

Hypoxia (dissolved oxygen?<?2 mg L^–1) has emerged as a worldwide threat to coastal and estuarine ecosystems. Beyond direct mortality, secondary ecological impacts caused by hypoxia-driven distributional shifts may be equally important. From July–November 2009 and June–September 2010, we quantified the movement patterns of Dungeness crab (Metacarcinus magister) and English sole (Parophrys vetulus) in Hood Canal, Washington USA, a seasonally hypoxic estuary. Although highly mobile (mean cumulative distance?±?SD?=?11.0?±?25.6 km, N?=?60), there was little evidence of either species exhibiting large-scale directional movement out of the hypoxic region. However, Dungeness crab showed significant shifts towards shallower waters and elevation in activity in the hypoxic region, potentially increasing their vulnerability to crabbing and other indirect ecological consequences. Our findings suggest hypoxia could have a more localized impact on the mobile fauna in Hood Canal. However, more detailed information concerning the local-scale oxygen dynamics and responses of these species, such as English sole vertical movement, is essential for grasping the population and community level effects of hypoxia.  相似文献   

Real-time registration of airborne laser data with sub-decimeter accuracy     

Jan Skaloud  Philipp Schaer  Yannick Stebler  Phillip Tomé 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(2):208-217

This paper presents a methodology for the precise registering of airborne laser data directly in flight with an accuracy that is sufficient for the majority of derived products, such as digital terrain models. We first present the strategy that integrates GPS/INS/LiDAR data for generating laser point clouds directly in flight and analyzes their accuracy. The latter requires the implementation of a functional covariance propagation on-line for all the system components (i.e. trajectory, laser, system calibration) to which influences of scanning geometry are added at the end of a flight line. The study of scanning geometry necessitates the classification of vegetation and coarse estimation of the terrain normal. This is achieved by a method that we formerly proposed for off-line quality analysis. The second part of the paper focuses on the positioning component. In high resolution scanning performed close to the terrain, the absolute accuracy of the resulting point cloud depends mainly on the quality of the trajectory which is related to the type of GPS solution (e.g. absolute positioning, DGPS, RTK). To reach sub-decimeter accuracy for the point cloud in the real-time, an RTK-GPS solution is needed. This requires the establishment of a communication link for the transmission of GPS corrections (or measurements). We analyze the usability of RTK-GPS/ALS acquired during several flights using different communication methods in the particular context of helicopter based missions. We focus mainly on the exploitation of nation-wide reference GNSS networks and confirm experimentally that the real-time registration of airborne laser data is feasible with sub-decimeter accuracy. Such quality is sufficient not only for a wide range of applications, but it also opens new opportunities for monitoring missions that require a short reaction time. Finally, we concentrate on situations when the phase and code corrections cannot be transmitted, and the quality of the differential carrier-phase positioning needs to be predicted. We validate the previously introduced indicators of positioning quality by simulated degradation of the input data.  相似文献   

Upscaling site‐scale ecohydraulic models to inform salmonid population‐level life cycle modeling and restoration actions – Lessons from the Columbia River Basin          下载免费PDF全文

Joseph M. Wheaton  Nicolaas Bouwes  Peter Mchugh  Carl Saunders  Sara Bangen  Phillip Bailey  Matt Nahorniak  Eric Wall  Chris Jordan 《地球表面变化过程与地形》2018,43(1):21-44

With high‐resolution topography and imagery in fluvial environments, the potential to quantify physical fish habitat at the reach scale has never been better. Increased availability of hydraulic, temperature and food availability data and models have given rise to a host of species and life stage specific ecohydraulic fish habitat models ranging from simple, empirical habitat suitability curve driven models, to fuzzy inference systems to fully mechanistic bioenergetic models. However, few examples exist where such information has been upscaled appropriately to evaluate entire fish populations. We present a framework for applying such ecohydraulic models from over 905 sites in 12 sub‐watersheds of the Columbia River Basin (USA), to assess status and trends in anadromous salmon populations. We automated the simulation of computational engines to drive the hydraulics, and subsequent ecohydraulic models using cloud computing for over 2075 visits from 2011 to 2015 at 905 sites. We also characterize each site's geomorphic reach type, habitat condition, geomorphic unit assemblage, primary production potential and thermal regime. We then independently produce drainage network‐scale models to estimate these same parameters from coarser, remotely sensed data available across entire populations within the Columbia River Basin. These variables give us a basis for imputation of reach‐scale capacity estimates across drainage networks. Combining capacity estimates with survival estimates from mark–recapture monitoring allows a more robust quantification of capacity for freshwater life stages (i.e. adult spawning, juvenile rearing) of the anadromous life cycle. We use these data to drive life cycle models of populations, which not only include the freshwater life stages but also the marine and migration life stages through the hydropower system. More fundamentally, we can begin to look at more realistic, spatially explicit, tributary habitat restoration scenarios to examine whether the enormous financial investment on such restoration actions can help recover these populations or prevent their extinction. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献