Mohr circles of the First and Second Kind and their use to represent tensor operations     

Declan G. de Paor  Winthrop D. Means 《Journal of Structural Geology》1984,6(6):693-701

Since their introduction to the geological literature by Brace (1959, 1960, 1961), Mohr circles for large irrotational deformations have proved valuable as aids to our understanding of deformation geometry. However, confusion persists regarding sign conventions. We show that there are two basic kinds of Mohr circles, each with its distinct set of sign conventions. These two divisions, which we call Mohr circles of the First and Second Kind, are not merely reflections of one another in Mohr space. They represent two distinct aspects of the relationship between the space of tensor components (Mohr space) and the space of geological structures (geographical space). The distinction between Mohr circles of the First and Second Kind is critical when the circles are drawn in off-axis positions for asymmetric tensors. Constructions in Mohr space are described which correspond to various standard tensor operations including transposition, inversion, addition and various kinds of multiplication. For some of these operations Mohr circles of one kind or the other offer advantages.  相似文献   

Sediment accumulation at a fringe marsh during transgression,Oyster, Virginia     

G. F. Oertel  G. T. F. Wong  J. D. Conway 《Estuaries and Coasts》1989,12(1):18-26

A variety of processes and sources account for the total accumulation of sediment on a fringe marsh. The rates of accretion across Brockenberry fringe marsh at the south end of the Delmarva Peninsula, Virginia, were determined by Pb-210 radiogeochronology. Rates are governed by the surface elevation with respect to midtide elevation, the rate of sea-level rise, and outwash from the mainland. Only some portions of the fringe marsh are able to keep pace with sea-level rise and thus migrate up the mainland slope during transgression.  相似文献   

The impact of land use change on soil water holding capacity and river flow modelling in the Nakambe River, Burkina-Faso   总被引：3，自引：0，他引：3  

Gil Mahe  Jean-Emmanuel Paturel  Eric Servat  Declan Conway  Alain Dezetter 《Journal of Hydrology》2005,300(1-4):33-43

The annual hydrological regime of the Nakambe River shows substantial changes during the period 1955–1998 with a shift occurring around 1970. From 1970 to the mid-1990s, despite a reduction in rainfall and an increase in the number of dams in the basin, average runoff and maximum daily discharges increased. This paper reviews the hydrological behaviour of the Nakambe River from 1955 to 1998 and examines the potential role of land use change on soil water holding capacity (WHC) in producing the counter-intuitive change in runoff observed after 1970. We compare the results of two monthly hydrological models using different rainfall, potential evapotranspiration and WHC data sets. Model simulations with soil WHC values modified over time based upon historical maps of land use, are compared against simulations with a constant value for WHC. The extent of natural vegetation declined from 43 to 13% of the total basin area between 1965 and 1995, whilst the cultivated areas increased from 53 to 76% and the area of bare soil nearly tripled from 4 to 11%. The total reduction in WHC is estimated to range from 33 to 62% depending on the method used, either considering that the WHC values given by the FAO stand for the environmental situation in 1965 or before. There is a marked improvement in river flow simulation using the time-varying values of soil WHC. The paper ends with a discussion of the role of other factors such as surface runoff processes and groundwater trends in explaining the hydrological behaviour of the Nakambe River.  相似文献   

Further comment on Titan's atmospheric scaling     

Conway B. Leovy  James B. Pollack 《Icarus》1975,24(1):76-77

In discussions of the circulation of planetary atmospheres, the atmospheric efficiency factor η is overestimated when the atmosphere is very thin, or when latent heat transfer is neglected.  相似文献   

Observations of methanol masers in star-forming regions     

V. Minier  R. S. Booth  J. E. Conway 《New Astronomy Reviews》1999,43(8-10)

We present VLBI observations of 6.7 and 12.2 GHz methanol masers in three star-forming regions, NGC7538, W75N and S252. Our results reveal linear structures in the VLBI maps and monotonic velocity gradients in the three sources. All these results are consistent with Keplerian disks of diameter of 1000–2000 AU around young stars of mass (10–30) M.  相似文献   

Analytical solution from vector potentials for the gravitational field of a general polyhedron   总被引：4，自引：0，他引：4  

John T. Conway 《Celestial Mechanics and Dynamical Astronomy》2015,121(1):17-38

  相似文献   

Getting Charlie off the MTA: a multiobjective optimization method to account for cost constraints in public transit accessibility metrics     

Matthew Wigginton Conway  Anson F. Stewart 《International journal of geographical information science》2019,33(9):1759-1787

Most analyses of accessibility by public transit have focused on travel time and not considered the cost of transit fares. It is difficult to include fares in shortest-path algorithms because fares are often path-dependent. When fare policies allow discounted transfers, for example, the fare for a given journey segment depends on characteristics of previous journey segments. Existing methods to characterize tradeoffs between travel time and monetary cost objectives do not scale well to complex networks, or they rely on approximations. Additionally, they often require assumed values of time, which may be problematic for evaluating the equity of service provision. We propose a new method that allows us to find Pareto sets of paths, jointly minimizing fare and travel time. Using a case study in greater Boston, Massachusetts, USA, we test the algorithm’s performance as part of an interactive web application for computing accessibility metrics. Potential extensions for journey planning and route choice models are also discussed.  相似文献   

Rural livelihoods and climate variability in Ningxia, Northwest China     

Yue Li  D. Conway  Yanjuan Wu  Qingzhu Gao  S. Rothausen  Wei Xiong  Hui Ju  Erda Lin 《Climatic change》2013,119(3-4):891-904

This study addresses the role of climate variability in the livelihoods of agricultural communities in Ningxia, Northwest China. Data sources comprise meteorological observations and official reports, complemented by questionnaires and focus group discussions designed around a livelihoods framework. Sample villages were located in three different agricultural systems: irrigated, mixed irrigated/grazing, and rainfed. Much of Ningxia is perennially dry and this is a significant limiting factor to agricultural production in the region, exacerbated by drought and buffered by irrigation mainly supplied from the Yellow River. Climate observations show stable temperatures from the 1950s to the 1980s followed by a positive trend (0.38°C/decade 1961–2010). Precipitation shows very modest trends and low decadal variability. Recent climate variability, particularly a drought from 2004–2006, was perceived to have had a significant effect on agricultural production and access to water, but it was not the only challenge respondents had faced. Susceptibility to drought was higher in the mixed irrigated and grazing and rainfed areas, due to farmers’ greater exposure to climatic hazards and because a higher proportion of their income originated from farming activities. Respondents were using a wide range of measures to retain and enhance soil moisture and maintain agricultural production. The discussion examines challenges in disentangling the role of climate within rapidly changing livelihood systems.  相似文献   

Sea-level change and paleogeographic reconstructions,southern Vancouver Island,British Columbia,Canada     

Thomas James  Evan J. Gowan  Ian Hutchinson  John J. Clague  J. Vaughn Barrie  Kim W. Conway 《Quaternary Science Reviews》2009,28(13-14):1200-1216

Forty-eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern Vancouver Island, British Columbia. Sea level fell rapidly from its high stand of about +75 m elevation just before 14 000 cal BP (12 000 radiocarbon yrs BP) to below the present shoreline by 13 200 cal BP (11 400 radiocarbon years BP). The sea fell below its present level 1000 years later in the central Strait of Georgia and 2000 years later in the northern Strait of Georgia, reflecting regional differences in ice sheet retreat and downwasting. Direct observations only constrain the low stand to be below ?11 m and above ?40 m. Analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the Cascadia subduction zone, however, places the low stand at ?30 ± 5 m at about 11 200 cal BP (9800 BP). The inferred low stand for southern Vancouver Island, when compared to the sea-level curve previously derived for the central Strait of Georgia to the northwest, generates differential isostatic depression that is consistent with the expected crustal response between the two regions. Morphologic and sub-bottom features previously interpreted to indicate a low stand of ?50 to ?65 m are re-evaluated and found to be consistent with a low stand of ?30 ± 5 m. Submarine banks in eastern Juan de Fuca Strait were emergent at the time of the low stand, but marine passages persisted between southern Vancouver Island and the mainland. The crustal uplift presently occurring in response to the Late Pleistocene collapse of the southwestern sector of the Cordilleran Ice Sheet amounts to about 0.1 mm/yr. The small glacial isostatic adjustment rate is a consequence of low-viscosity mantle in this tectonically active region.  相似文献   

Atmospheric CO2 variations at Barrow,Alaska, 1973–1982     

Peterson  James T.  Komhyr  W. D.  Waterman  L. S.  Gammon  R. H.  Thoning  K. W.  Conway  T. J. 《Journal of Atmospheric Chemistry》1986,4(4):491-510

The first 10 years (1973–1982) of atmospheric CO₂ measurements at Barrow, Alaska, by the NOAA/GMCC program are described. The paper updates and extends the Barrow CO₂ record presented in Tellus (1982). The data are given in final form, based on recent calibrations of the Scripps Institution of Oceanography, with selected values identified as representative of large, spacescale conditions. Analyses of the data show: (1) a long-term CO₂ average increase of 1.3 ppm per year, but with large year-to-year variations in that growth rate; (2) a suggestion, not statistically significant, of a secular increase in the amplitude of the annual cycle, presumably a reflection of global-scale biospheric variability; and (3) good absolute agreement between the Barrow results and those from four neighboring high latitude sites between 50 and 82°N.  相似文献