Comment concerning 'On the Fréchet differentiability of the one-dimensional magnetotellurics problem' by John MacBain     

Robert Parker 《Geophysical Journal International》1986,86(2):673-674

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Reliability constrained capacity expansion planning of water resource systems     

Robert W. Hinks 《Advances in water resources》1980,3(3):99-105

Two questionable features of many existing studies of capacity expansion planning problems in water resources are (1) the modelling of the expansion as a deterministic process, and (2) the lack of control over the incidence of system failure. System failure, in this presentation, is related to the occurrence of shortfalls in water supply. A sequential decision model is used as a general framework for the formulation of stochastic demand capacity expansion problems subject to reliability constraints designed to regulate the incidence of system failure. Various different types of constraint are investigated and each is incorporated into a dynamic programming solution procedure by means of Lagrangian theory. Computational examples illustrate the potential importance of using such reliability constraints in the analysis of capacity expansion problems.  相似文献   

Active solar radio regions at metric frequencies and the interplanetary sector structures     

Kunitomo Sakurai  Robert G. Stone 《Solar physics》1971,19(1):247-256

The possible relation between type I noise active regions and the polarity distribution of the interplanetary magnetic field is examined for the period from 13 March to 21 August, 1968 (Solar Rotation Numbers 1842–1847) by using data from ground-based and satellite observations. In general four type I radio regions appeared during each solar rotation period except for Rotation No. 1842. The number of type I regions is the same as the number of sector boundaries. This result suggests that the configuration of the photospheric magnetic field extending into the interplanetary space may be related to the origin of the type I radio regions. Statistically the passage of the sector boundaries is delayed by approximately 5 days after the central meridian passage of the type I noise regions on the solar disk.The position of the source of the sector boundaries and its relation to the type I radio regions are investigated by taking into account the mean bulk velocity of solar winds as observed by space probes. A model of the large-scale structure of type I radio regions and their relation to the sector structure of the magnetic field as observed in the interplanetary space is briefly discussed.NASA Research Associate at the University of Maryland.  相似文献   

Possible production by lightning of aerosols and trace gases in Titan's atmosphere     

William J. Borucki  Christopher P. McKay  Robert C. Whitten 《Icarus》1984,60(2):260-273

Although lightning has not yet been observed in Titan's atmosphere, the presence of condensable vapors and the deposition of a significant amount of solar energy at the surface suggest the possibility of lightning activity. Based on an understanding of the relationship of lightning activity to the amount of convective energy available on Titan, a lightning energy dissipation rate of 4 × 10^?6, W/m² can be expected. This value is much lower than that for Earth or Jupiter, and is a result of both the reduced solar flux at Titan and the absorption of sunlight by the aerosols that lie above the convective layer. For this dissipation rate, the amount of HCN and C₂N₂ produced by lightning should be greater than that by solar UV, but could be less than that produced by electron precipitation and galactic cosmic rays. Equilibrium calculations indicate that large mole fractions of elemental solid phase carbon will also be produced. Using a simplified model of aerosol formation, coagulation, and settling, it is estimated that a lightning-produced aerosol could have a typical optical depth of 10^?2, with values as high as 0.1. The accumulation of soot over geological time might reach a meter or more in depth.  相似文献   

Optimal low-thrust takeoff from an orbit about an oblate planet     

Robert A. Jacobson  William F. Powers 《Celestial Mechanics and Dynamical Astronomy》1977,15(2):161-189

Future space missions to the outer planets may depend upon the use of low-thrust propulsion systems. As these planets are decidedly oblate, the question of the effect of that oblateness on a low-thrust trajectory is of some interest. In this paper the problem of optimal energy increase is attacked under the assumption that the coefficients for the second zonal harmonic, i.e.,J ₂, and the nondimensional thrust acceleration are the same order of magnitude. Using a two variable asymptotic expansion technique, a near optimal control program is generated and the first order uniformly valid approximation for the corresponding trajectory is obtained. Tangential thrust is shown to be a good near-optimal thrust program even in the presence of oblateness effects. The optimal control program is found to be oscillatory and quite similar to the optimal control for energy increase in an inverse square gravitational field.This research was supported by the National Aeronautics and Space Administration under Grant NGR-23-005-329.  相似文献   

The rotation of active regions with differing magnetic polarity separations     

Robert F. Howard 《Solar physics》1992,142(2):233-248

The separation of the leading and following portions of plages and (multi-spot) sunspot groups is examined as a parameter in the analysis of plage and spot group rotation. The magnetic complexity of plages affects their average properties in such a study because it tends to make the polarity separations of the plages less than they really are (by the definition of polarity separation used here). Correcting for this effect, one finds a clear and very significant dependence of the total magnetic flux of a region on its polarity separation. Extrapolating this relationship to zero total flux leads to an X intercept of about 25 Mm in polarity separation. The average residual rotation rates of regions depend upon the polarity separation in the sense that larger separations correspond to slower rotation rates (except for small values of separation, which are affected by region complexity). In the case of sunspots, the result that smaller individual spots rotate faster than larger spots is confirmed and quantified. It is shown also that smaller spot groups rotate faster than larger groups, but this is a much weaker effect than that for individual spots. It is suggested that the principal effect is for spots, and that this individual spot effect is responsible for much or all of the group effect, including that attributed in the past to group age. Although larger spot groups have larger polarity separations, it is shown that the rotation rate-polarity separation effect is the opposite in groups than one finds in plages: groups with larger polarity separations rotate faster than those with smaller separations. This anomalous effect may be related to the evolution of plages and spot groups, or it may be related to connections with subsurface toroidal flux tubes. It is suggested that the polarity separation is a parameter of solar active regions that may shed some light on their origin and evolution.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.  相似文献   

A new model for barred spiral galaxies     

Robert L. Oldershaw 《Astrophysics and Space Science》1983,92(2):429-432

Computer simulations are used to demonstrate that normal spiral galaxies with symmetrically warped arms can appear to have bar and bar-within-ring structures when viewed from appropriate position angles.  相似文献   

Astronomical photometry: Arne A. Henden and Ronald H. Kaitchuck. Van Nostrand-Reinhold,New York, 1982. $29.95.     

Robert Millis 《Icarus》1983,55(3):499-500

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New Agendas in Intergovernmental Decentralization     

Robert J. Bennett 《The Professional geographer》1988,40(4):463-464

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MAJOR ELEMENT COMPOSITIONAL VARIATION WITHIN AND BETWEEN DIFFERENT LATE EOCENE MICROTEKTITE STREWNFIELDS     

Steven L. D'Hondt  Gerta Keller  Robert F. Stallard 《Meteoritics & planetary science》1987,22(1):61-79

Major element compositional overlap exists between microspherules of different microtektite layers or strewnfields. For this reason, microspherules of similar composition cannot, a priori, be assumed to belong to the same microtektite event and those of different compositions cannot, a priori, be assumed to result from different events. Nevertheless, despite major element compositional overlap between microspherules of different strewnfields, multivariate factor analysis shows microtektites and related microspherules of three stratigraphically different late Eocene layers to follow recognizably different compositional trends. The microtektite population of the North American strewnfield (Globorotalia cerroazulensis Zone) follows compositionally well defined trends and is characterized by high concentrations of SiO₂, Al₂O₃, and TiO₂. The microspherule population of the slightly older crystal-bearing Globorotalia cerroazulensis Zone microspherule layer is more heterogeneous and characterized by microspherules which are relatively enriched in FeO and MgO and relatively impoverished in SiO₂ and TiO₂. The microspherule population of the oldest microspherule layer in the uppermost Globigerapsis semiinvoluta Zone is highly heterogeneous and characterized by microspherules which are relatively enriched in CaO and impoverished in Al₂O₃ and Na₂O. Individual microspherules of this oldest late Eocene horizon often exhibit major element compositions similar to those of the lower Gl. cerroazulensis Zone layer and occasionally exhibit major element compositions similar to North American layer microtektites. Nevertheless, late Eocene microspherule occurrences can be assigned to appropriate late Eocene microtektite horizons on the basis of major element compositional trends.  相似文献