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91.
Michael E. Hough 《Celestial Mechanics and Dynamical Astronomy》1989,47(1):57-85
A reversible dynamical system with two degrees-of-freedom is reduced to a second-order, Hamiltonian system under a change of independent variable. In certain circumstances, the reduced order system may be integrated following an orthogonal curvilinear transformation from Cartesian x,y to intrinsic orbital coordinates , . Solutions for the orbit position and true time variables are expressed by: % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGGipm0dc9vqaqpepu0xbbG8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiEaiabg2 % da9iaadAgacaGGOaGaeqOVdGNaaiilaiabeE7aOjaacMcacaGGSaGa % aeiiaiaadMhacqGH9aqpcaWGNbGaaiikaiabe67a4jaacYcacqaH3o % aAcaGGPaGaaiilaiaabccacaWGKbGaamiDaiabg2da9iabgglaXoaa % dmaabaWaaSaaaeaacaWGibWaa0baaKqaahaacqaH+oaEaeaacaqGYa % aaaOGaam4raiabgUcaRiaadIeadaqhaaqcbaCaaiabeE7aObqaaiaa % ikdaaaGccaWGfbaabaGaaGOmaiaacIcacaWGibGaey4kaSIaamyvai % aacMcaaaaacaGLBbGaayzxaaWaaWbaaSqabKqaGhaacaaIXaGaai4l % aiaaikdaaaGccaWGKbGaeqiXdqhaaa!6498! \[ x = f(\xi ,\eta ),{\rm{ }}y = g(\xi ,\eta ),{\rm{ }}dt = \pm \left[ {\frac{{_\xi ^{\rm{2}} {\ie} + _\eta ^2 }}{{2( + U)}}} \righ \]1446 1040 where U is the potential function, and z is the new independent variable. The functions f, g may be expressed by quadratures when the metric coefficients {\er},{\ie} are specified. Two second-order, partial differential equations specify {\er}, {\ie} and Hamiltonian {\tH}. Auxiliary conditions are needed because the solutions are underdetermined. For example, both sets of curvilinear coordinate lines are orbits when certain dynamical compatibility conditions between U and {\ie} (or {\er}) are satisfied. Alternatively, when orbits cross the parametric curves, the auxiliary condition {\er} = {\ie} specifies a conformal transformation, and the partial differential equation for {\tH} may be reduced to an ordinary differential equation for the orbit curve. In either case, integrability is guaranteed for Lionville dynamical systems. Specific applications are presented to illustrate direct solution for the orbit (e.g., two fixed centers) and inverse solution for the potential. 相似文献
92.
93.
Stratigraphy of total metals in PIRLA sediment cores 总被引:1,自引:0,他引:1
Stephen A. Norton Ray W. Bienert Jr. Michael W. Binford Jeffrey S. Kahl 《Journal of Paleolimnology》1992,7(3):191-214
Sediment cores from 30 low-alkalinity lakes in northern New England (NE), New York (NY), the northern Great Lakes States (NGLS) of Minnesota, Michigan, and Wisconsin, and Florida (FL) have been dated by 210Pb and analyzed for water and organic content, eight major elements (Al, Ti, Fe, Mn, Ca, Mg, Na, K) plus four trace metals (Pb, Zn, Cu, and V). Variations in the percentages of major elements through time are dominated by long-term independent variations in the abundance of SiO2, FeO, and to a lesser extent Ca and Al. Additional variations are caused by varying proportions of inorganic matter. Major variations in chemistry are generally unrelated to documented distrubances in the watersheds; most disturbances are minor fires or selective logging.Accelerated accumulation of Pb from atmospheric sources into sediment first occurs in sediment dated between 1800 and 1850 in NY and NE, slightly later in the NGLS region, and about 1900 in FL. Modern accumulation rates in all areas are comparable (ca. 1 to 4 g cm–2 yr–1). Accumulation rates of Pb in some lakes have declined significantly from 1975 to 1985. Atmospheric deposition of anthropogenic Zn and Cu is also indicated by generally increasing accumulation rates in sediment cores, but the record is not as clear nor are chemical profiles in all lakes parallel to the trends in atmospheric emissions inferred on the basis of fossil fuel consumption, smelting, and other industrial activities. Inter-lake variations in profiles of Cu and Zn are large. Vanadium accumulation rates increase by the 1940s in NY and NE, but not until the 1950s in the NGLS region. This timing correlates with regional trends in the combustion of fuel oil, a major source of atmospheric V.Acidification of some of the lakes is suggested by decreases in the concentration and accumulation rates of Mn, Ca, and Zn in recent sediment, relative to other elements of catchment origin. The decreases generally occur slightly before the onset of acidification as indicated by diatoms. Increased sediment accumulation rates for Fe may indicate the acidification of watershed soils. The use of the accumulation rate of TiO2 as an indicator of rates of erosion and for normalization of trace metal accumulation rates is in question for lakes where the flux of TiO2 from the atmosphere varies and is a significant fraction of the total flux of TiO2 to the sediment.This is the thirteenth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series. 相似文献
94.
Although the supply and fate of suspended sediment is of fundamental importance to the functioning and morphological evolution
of muddy estuaries, reliable sediment budgets have been established in only a few cases. Especially for smaller estuaries,
inadequate bathymetric surveys and a lack of intertidal sedimentation data often preclude estimation of the sediment budget
from morphological change, while instrument-derived residual fluxes typically lie well within the errors associated with measurement
of much larger gross tidal transports. Given suitably long-term records of continuously monitored suspended sediment concentration
(SSC), however, analysis of the major scales of variation in sediment transport and their relation to hydrodynamic and meteorological
forcing permits qualitative testing of hypotheses suggested by directly measured residual fluxes. This paper analyzes data
from a 1-year acoustic Doppler profiler deployment in the Blyth estuary, a muddy mesotidal barrier-enclosed system on the
UK east coast. Flux calculations indicate a small sediment import equivalent to just 1.5% of the gross flood tide transport.
Little confidence can be assigned to either the magnitude or direction of such a small residual when considered in isolation.
However, the inference that the sediment regime is finely balanced is qualitatively supported by the close similarity between
flood-tide and ebb-tide SSC values. Singular spectrum analysis of the SSC time series shows the expectedly large contributions
to the variance in SSC at intratidal and subtidal (semimonthly and monthly) scales but also picks out intermittent variability
that is initially attributed to a combination of non-tidal surge and wind stress forcing. Closer examination of the data through
cross-correlograms and event-scale analysis indicates that local meteorological forcing is the major factor. Acting through
the resuspension of intertidal mudflat sediments at times of strong westerlies, meteorological forcing is directly implicated
in episodic sediment export from the estuary. Thresholding of tide-averaged fluxes using a range of critical wind stress values
further indicates that ‘tide-dominated’ (i.e., low wind stress) and ‘wave-dominated’ (high wind stress) conditions are associated
with sediment import and export. Sediment balance is potentially sensitive to the frequency of high wind stress events, since
the associated sediment exports are several times larger than the average import under calm conditions. Intermittent meteorological
forcing may thus exert an important control on the sedimentary balance of otherwise tidally dominated muddy estuarine systems,
and the role of wind climate should not be overlooked in studies of estuary response to environmental change. 相似文献
95.
Autumn Oczkowski Scott Nixon Kelly Henry Peter DiMilla Michael Pilson Stephen Granger Betty Buckley Carol Thornber Richard McKinney Joaquin Chaves 《Estuaries and Coasts》2008,31(1):53-69
Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one
of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage
treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third
or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary
(macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ15N) and carbon (δ13C). The δ15N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source
loading. There is also evidence of a west to east gradient of heavy to light values of δ15N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett
Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ15N values in macroalgae there reflected preferential uptake of 14N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of
dissolved C species may control the observed δ13C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ15N (13.2 ± 0.54‰ SD) and δ13C (−16.76 ± 0.61‰ SD) throughout the bay, and the δ15N values were 2–5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a
food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate
that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources. 相似文献
96.
Martin Rosner Michael Wiedenbeck Thomas Ludwig 《Geostandards and Geoanalytical Research》2008,32(1):27-38
An analytical artefact is reported here related to differences in instrumental mass fractionation between NIST SRM glasses and natural geological glasses during SIMS boron isotope determinations. The data presented demonstrated an average 3.4‰ difference between the NIST glasses and natural basaltic to rhyolitic glasses mainly in terms of their sputtering-induced fractionation of boron isotopes. As no matrix effect was found among basaltic to rhyolitic glasses, instrumental mass fractionation of most natural glass samples can be corrected by using appropriate glass reference materials. In order to confirm the existence of the compositionally induced variations in boron SIMS instrumental mass bias, the observed offset in SIMS instrumental mass bias has been independently reproduced in two laboratories and the phenomenon has been found to be stable over a period of more than one year. This study highlights the need for a close match between the chemical composition of the reference material and the samples being investigated. 相似文献
97.
Jeremy M. Testa W. Michael Kemp Walter R. Boynton James D. Hagy III 《Estuaries and Coasts》2008,31(6):1021-1037
We conducted a quantitative assessment of estuarine ecosystem responses to reduced phosphorus and nitrogen loading from sewage
treatment facilities and to variability in freshwater flow and nonpoint nutrient inputs to the Patuxent River estuary. We
analyzed a 19-year dataset of water quality conditions, nutrient loading, and climatic forcing for three estuarine regions
and also computed monthly rates of net production of dissolved O2 and physical transport of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) using a salt- and water-balance model.
Point-source loading of DIN and DIP to the estuary declined by 40–60% following upgrades to sewage treatment plants and correlated
with parallel decreases in DIN and DIP concentrations throughout the Patuxent. Reduced point-source nutrient loading and concentration
resulted in declines in phytoplankton chlorophyll-a (chl-a) and light-saturated carbon fixation, as well as in bottom-layer O2 consumption for upper regions of the estuary. Despite significant reductions in seaward N transport from the middle to lower
estuary, chl-a, turbidity, and surface-layer net O2 production increased in the lower estuary, especially during summer. This degradation of water quality in the lower estuary
appears to be linked to a trend of increasing net inputs of DIN into the estuary from Chesapeake Bay and to above-average
river flow during the mid-1990s. In addition, increased abundance of Mnemiopsis leidyi significantly reduced copepod abundance during summer from 1990 to 2002, which favored increases in chl-a and allowed a shift in total N partitioning from DIN to particulate organic nitrogen. These analyses illustrate (1) the value
of long-term monitoring data, (2) the need for regional scale nutrient management that includes integrated estuarine systems,
and (3) the potential water quality impacts of altered coastal food webs. 相似文献
98.
There has been increasing concern about the lack of involvement by social scientists and humanists in a global change program,
although many social scientists are already directly involved in various aspects of research on environmental change, and
their research interests are clearly central to a global change research agenda. Based on a historical review, the role of
social science disciplines as well as social science institutes in an emerging multidecadal global change program is discussed.
Both “plan of action” and “plan of inaction” are suggested to avoid potential pitfalls due to the rush development of a social
science program into the existing global climate change problem. 相似文献
99.
100.
We present an updated model for the photochemistry of Io's atmosphere and ionosphere and use this model to investigate the sensitivity of the chemical structure to vertical transport rates. SO2is assumed to be the dominant atmospheric gas, with minor molecular sodium species such as Na2S or Na2O released by sputtering or venting from the surface. Photochemical products include SO, O2, S, O, Na, NaO, NaS, and Na2. We consider both “thick” and “thin” SO2atmospheres that encompass the range allowed by recent HST and millimeter-wave observations, and evaluate the possibility that O2and/or SO may be significant minor dayside constituents and therefore likely dominant nightside gases. The fast reaction between S and O2limits the column abundance of O2to ∼104less than that calculated by Kumar (J. Geophys. Res.87, 1677–1684, 1982; 89(A9), 7399–7406, 1984) for a pure sulfur/oxygen atmosphere. If a significant source of NaO2or Na2O were supplied by the surface and mixed rapidly upward, then oxygen liberated in the chemical reactions which also liberate free Na would provide an additional source of O2. Fast eddy mixing will enhance the transport of molecular sodium species to the exobase, in addition to increasing the vertical transport rate of ions. Ions produced in the atmosphere will be accelerated by the reduced corotation electric field penetrating the atmosphere. These ions experience collisions with the neutral gas, leading to enhanced vertical ion diffusion. The dominant ion, Na+, is lost primarily by charge exchange with Na2O and/or Na2S in the lower atmosphere and by diffusion through the ionopause in the upper atmosphere. The atmospheric column abundance of SO, O2, and the upper atmosphere escape rates of Na, S, O, and molecular sodium species are all strong functions of the eddy mixing rate. Most atmospheric escape, including that of molecular sodium species, probably occurs from the low density “background” SO2atmosphere, while a localized high density “volcanic” SO2atmosphere can yield an ionosphere consistent with that detected by the Pioneer 10 spacecraft. 相似文献