Comparison of ground-based and spacecraft observations of the infrared emission from Venus: The nature of thermal contrasts     

David J. Diner  Jerome Apt  Lee S. Elson 《Icarus》1982,52(2):301-319

Comparisons are made between observations of spatial variations in the thermal emission from Venus obtained with ground-based telescopes and those from spacecraft. In particular, we concentrate on measurements of solar-related structure at low and mid-latitudes, limb-darkening, and on the high-contrast polar structure. We conclude that (1) the solar-related emission is predominantly wavenumber 2, although it contains a significant diurnal component; (2) the relative amplitudes of the semidiurnal and diurnal components vary with latitude; (3) thermally excited temperature waves or, alternatively, solar-driven vertical motions of the cloud top are better able to account for the magnitude of the solar-locked emission than brightness temperature contrasts resulting from variations in aerosol microphysical properties; (4) the equatorial limb-darkening shows the top of the main cloud to be diffuse and approximately uniformly mixed with the gas; (5) polar collars are persistent at least for several months but disappear on occasion; and (6) collars have been observed at both poles simultaneously, but whether simultaneous appearance is the exception or the rule is still in question.  相似文献   

A critical evaluation of the boron isotope-pH proxy: The accuracy of ancient ocean pH estimates     

M. Pagani  Damien Lemarchand  Jérôme Gaillardet 《Geochimica et cosmochimica acta》2005,69(4):953-961

The boron isotope-pH technique is founded on a theoretical model of carbonate δ¹¹B variation with pH that assumes that the boron isotopic composition of carbonates mirrors the boron isotopic composition of borate in solution (δ¹¹B_carb = δ¹¹B_borate). Knowledge of the fractionation factor for isotope exchange between boric acid and borate in solution (α_4-3), the equilibrium constant for the dissociation of boric acid (pK_B*), as well as the isotopic composition of boron in seawater (δ¹¹B_sw) are required parameters of the model.The available data suggests that both the value of α_4-3 and the history of δ¹¹B_sw are poorly constrained. However, if one assumes that δ¹¹B_carb = δ¹¹B_borate, an empirical value for α_4-3 can be estimated from the results of inorganic carbonate precipitation experiments. This exercise yields an α_4-3 value of ∼0.974 in accordance with recent theoretical estimates, but substantially deviates from the theoretical value of 0.981 often used to estimate paleo-ocean pH. Re-evaluation of ocean pH using an α_4-3 value of 0.974 and published foraminiferal δ¹¹B values for the Cenozoic yield pH estimates that are relatively invariant, but unrealistically high (∼8.4-8.6). Uncertainty increases as foraminiferal ‘vital effects’ are considered and different models for secular changes in seawater δ¹¹B are applied.The inability to capture realistic ocean pH possibly reflects on our understanding of the isotopic relationship between carbonate and borate, as well as the mechanism of boron incorporation in carbonates. Given the current understanding of boron systematics, pH values estimated using this technique have considerable uncertainty, particularly when reconstructions exceed the residence time of boron in the ocean.  相似文献   

Numerical simulations of mesoscale variability in the Straits of Florida     

Christopher N. K. Mooers  Jerome Fiechter 《Ocean Dynamics》2005,55(3-4):309-325

The circulation in the Straits of Florida is dominated by the throughflow of the Florida Current, as modified by tidal flows, responses to atmospheric cold front and extratropical cyclone (easterly wave and tropical cyclone) passages in winter (summer), and intrinsic mesoscale variability due to instabilities of the Florida Current front and jet system. Monthly meanders of the Florida Current, persistent oceanic fronts associated with the Florida Current’s baroclinic jet, and frontal eddies shed weekly by the Florida Current are the primary mesoscale features. A limited area model (Princeton Ocean Model: POM) is implemented to cover the Straits of Florida with a curvilinear grid that resolves the mesoscale structure, especially where the baroclinic flow is locked to steep topography in a 90 degree bend of the Straits. Florida Current cyclonic frontal eddies are spawned spontaneously, grow as they translate downstream, interact with shelf waters, and exhibit the same space-time attributes that characterize their observed counterparts, as evidenced by satellite imagery, shipboard synoptic mapping, coastal HF radar, and moored time series. Here, a deeper understanding is attempted for the frontal eddy kinematics and dynamics by examining, for example, their sensitivity to model parameter values, synoptic versus monthly atmospheric forcing, and other determinants of the flow. The mean flow shears are concentrated along the shelfbreak, where these frontal eddies are trapped, favoring the formation of the eddies by mean flow instabilities. In particular, it is found that the Florida Current frontal eddies exist independent of the wind-forcing considered (i.e., no winds, monthly winds, and synoptic (but not mesoscale) winds); however, they are modulated by the synoptic wind-forcing. Nevertheless, intriguingly, the frontal eddies have the same weekly time scale as the weather cycle.  相似文献   

Market‐based control of linear structural systems     

Jerome Peter Lynch  Kincho H. Law 《地震工程与结构动力学》2002,31(10):1855-1877

To limit the response of structures during external disturbances such as strong winds or large seismic events, structural control systems can be used. In the structural engineering field, attention has been shifted from active control to semi‐active control systems. Unlike active control system devices, semi‐active devices are compact, have efficient power consumption characteristics and are less expensive. As a result, an environment of a large number of actuators and sensors will result, rendering a complex large‐scale dynamic system. Such a system is best controlled by a decentralized approach such as market‐based control (MBC). In MBC, the system is modelled as a market place of buyers and sellers that leads to an efficient allocation of control power. The resulting MBC solution is shown to be locally Pareto optimal. This novel control approach is applied to three linear structural systems ranging from a one‐storey structure to a 20‐storey structure, all controlled by semi‐active hydraulic dampers. It is shown that MBC is competitive in the reduction of structural responses during large seismic loadings as compared to the centralized control approach of the linear quadratic regulation controller. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Arsenic enrichment in lakes near the smelters at Sudbury,Ontario     

Jerome O. Nriagu 《Geochimica et cosmochimica acta》1983,47(8):1523-1526

Roughly 200 tonnes of arsenic are produced annually with the base metal ores at Sudbury about 125 tonnes of which are released to the ambient environment via the atmosphere. The dispersion of this highly toxic element in lakes around the smelters is described. The total As concentrations in unfiltered lake waters vary from 0.2 to 0.6 ug 1^?1. The suspended particulates in the water column (with As contents of 2–6 ug g^?1) play a major role in the flux of arsenic to the lake sediments. The present-day rates of As accumulation in the sediments are found to be 1.5–6.4 mg m^?2 yr^?1; these rates exceed those of precolonial times by factors of 5–47. The changes in the rates of As flux to the sediments are shown to parallel the history of Cu and Ni production in the district.  相似文献   

Tertiary systems     

Alan G. Hernried  Jerome L. Sackman 《地震工程与结构动力学》1985,13(4):467-479

Through perturbation theory, results are obtained for the dynamic response of the very light equipment component(s) of tertiary equipment-structure systems. Both the three-degree-of-freedom and multi-degree-of-freedom models are examined. The case of all natural frequencies of the subsystems distinct (detuning) as well as a natural frequency of each subsystem close or equal to one another (tuning) are examined. The results should serve as a reliable and economical alternative to expensive numerical time-integration schemes which may mask significant response due to ill-conditioning of the combined system property matrices.  相似文献   

Distribution and isotopic composition of sulfur in lake sediments of northern Ontario   总被引：1，自引：0，他引：1  

Jerome O. Nriagu  Yoong K. Soon 《Geochimica et cosmochimica acta》1985,49(3):823-834

Sediments from unpolluted and highly polluted lakes in northern Ontario have been fractionated into acid volatile sulfide, HCl-soluble sulfur, elemental sulfur, pyrite sulfur, ester sulfate and carbon-bonded sulfur and the isotopic composition of each fraction determined. In general, reduced inorganic S constitutes 25–50% of the total S in the polluted surficial sediments, but is <20% in the unpolluted samples, with pyrite formation being a minor process of S diagenesis in lake sediment ecosystems. Organic S in the form of ester sulfate and carbon-bonded S predominates and both the C/S ratios and the isotopic data suggest that, in unpolluted lakes, plant detritus can be a major contributor of organic-S to the sediments. The depth profiles observed suggest that the more labile ester sulfate is diagenetically converted to the carbon-bonded form. For the polluted sediments from the Sudbury basin, the isotopic data suggest that (a) the elemental S is derived from the oxidation of acid volatile sulfide in the aerobic surficial sediments, and (b) the isotopically light reduced S species are incorporated into the organic material. S diagenesis in lake sediments generally results in the release of ³⁴S to the overlying water. The suggestion is made that sulfate concentrations over 5 mg/1 accompanied by an enrichment of surficial sediments with isotopically different S may signal significant inputs of pollutant S into the lake and its basin.  相似文献   

Some methods for the analysis of equipment-structure interaction     

Tim J. Ingham  Jerome L. Sackman 《地震工程与结构动力学》1984,12(5):583-601

We present some numerical methods which simplify the analysis of equipment-structure systems composed of an equipment component which is light with respect to the structure component. We consider completely general forms of equipment-structure interaction. In particular, we consider that an arbitrary number of natural frequencies of the equipment and the structure are nearly equal (or equal) to each other. We show that this coincidence of natural frequencies implies that the equipment-structure system will itself have several closely spaced natural frequencies. The essence of equipment-structure interaction is the formation of beats, with slowly varying amplitude in each degree of freedom, between these natural frequencies-at least in response to a δ-function ground motion. We derive some differential equations, the solutions of which are a slowly varying envelope function (a vector) which yields the above slowly varying amplitudes. It is obtained by numerical integration using some conventional, but modified, methods and using a step size appropriate to capture its slowly varying nature. This envelope function defines the response to a δ-function ground motion. We show how it may be combined with the properties of an arbitrary ground motion (acceleration record or response spectrum) to yield the response to such a ground motion.  相似文献   

Chemical oceanography: J. P. Riley and G. Skirrow (editors), second edition. Academic Press, 1975, vol. 3, 564 pp., £18.20 ($32.25)     

Jerome O. Nriagu 《Geochimica et cosmochimica acta》1976,40(12):1583

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A Rationale for the National Center for Geographic Information and Analysis     

Jerome E. Dobson 《The Professional geographer》1993,45(2):207-215

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