Interpreting the Negative Exponential Density Gradient

This paper demonstrates for urban areas a direct relationship between the summary measures of centrography and the slope parameter of the negative exponential density gradient model. Starting with some basic assumptions about the form of urban population distributions, a mathematical relationship between the methods is derived by applying the centrographic technique to an exponentially distributed urban population. By use of data from a diverse sample of cities that vary in population, region, area, and time of data collection, the relationship is tested empirically. The results of the empirical analysis are compared with the predictions of the derived relationship, and the causes of differences between them are discussed.

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Correlation between Transit-Oriented Development (TOD), Land Use Catchment Areas, and Local Environmental Transformation

Sustainability ◽

10.3390/su10124622 ◽

2018 ◽

Vol 10 (12) ◽

pp. 4622 ◽

Cited By ~ 3

Author(s):

Xin Tong ◽

Yaowu Wang ◽

Edwin H. W. Chan ◽

Qingfeng Zhou

Keyword(s):

Land Use ◽

Density Gradient ◽

Catchment Area ◽

Primary Objective ◽

Transit Oriented Development ◽

Negative Exponential Function ◽

Future Design ◽

Catchment Areas ◽

Negative Exponential ◽

The Impact

Transit-oriented development (TOD) has been recognised as a sustainable planning approach and that is typically designed for a whole city. Individual land use characteristics and the causations have often been ignored. Therefore, the primary objective of this study was to explore the factors that influence the land use catchment area (LCA) characteristics at a station neighborhood level. First, it contributes a methodology to measure the LCA by introducing a new concept. The density gradient was introduced to generate the scale and compactness degree of each station. Second, it provides a theoretical framework for understanding the causes of different LCAs. The partial least squares (PLS) regression model was employed to explore the accessibility effects. By analysing density gradient curves, it reveals that stations grew to fit the negative exponential function. Regarding the scale and form degree of LCAs, the impact of accessibility before and after a station construction have been corroborated. Moreover, the effects of facilities function before construction, distance from main roads, and elevated stations have been emphasized. The results provide support for a more sophisticated concept of catchment area relating to land use at the level of an individual TOD station, while shedding light on the benefits of those engaged in the future design of TOD with due consideration of the local physical environments.

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Strategic population forecasting for a conurbation using the negative exponential density model

Transportation Research Part A General ◽

10.1016/0191-2607(85)90026-3 ◽

1985 ◽

Vol 19 (2) ◽

pp. 189-206 ◽

Cited By ~ 2

Author(s):

M.J.H. Mogridge

Keyword(s):

Density Model ◽

Exponential Density ◽

Population Forecasting ◽

Negative Exponential

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Residential Density Patterns in London—Any Role Left for the Exponential Density Gradient?

Environment and Planning A Economy and Space ◽

10.1068/a231007 ◽

1991 ◽

Vol 23 (7) ◽

pp. 1007-1024 ◽

Cited By ~ 7

Author(s):

G R Crampton

Keyword(s):

Density Gradient ◽

Residential Density ◽

Exponential Density

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Activated Prominences; Mechanisms for Activation and Eruption

International Astronomical Union Colloquium ◽

10.1017/s0252921100065714 ◽

1979 ◽

Vol 44 ◽

pp. 307-313

Author(s):

D.S. Spicer

Keyword(s):

Pressure Gradient ◽

Density Gradient ◽

Current Density ◽

Convective Instability ◽

Tearing Mode ◽

Magnetic Shear ◽

Long Wavelength ◽

Ideal Mhd ◽

Gradient Change ◽

Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

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Uranyl Acetate and Rotary Shadowing to Increase the Contrast of Small Aggregated Virus Particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100064037 ◽

1969 ◽

Vol 27 ◽

pp. 424-425

Author(s):

Lee F. Ellis ◽

Richard M. Van Frank ◽

Walter J. Kleinschmidt

Keyword(s):

Electron Microscopy ◽

Tissue Culture ◽

Density Gradient ◽

Density Gradient Centrifugation ◽

Gradient Centrifugation ◽

Uranyl Acetate ◽

Interferon Inducer ◽

Virus Particles ◽

Staining Methods ◽

Rotary Shadowing

The extract from Penicillum stoliniferum, known as statolon, has been purified by density gradient centrifugation. These centrifuge fractions contained virus particles that are an interferon inducer in mice or in tissue culture. Highly purified preparations of these particles are difficult to enumerate by electron microscopy because of aggregation. Therefore a study of staining methods was undertaken.

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The Combining Ability of Glycoproteins IIb, IIIa and Ca2+ in EDTA-Treated Nonaggregable Platelets

Thrombosis and Haemostasis ◽

10.1055/s-0038-1665326 ◽

1983 ◽

Vol 50 (04) ◽

pp. 848-851 ◽

Cited By ~ 11

Author(s):

Marjorie B Zucker ◽

David Varon ◽

Nicholas C Masiello ◽

Simon Karpatkin

Keyword(s):

Density Gradient ◽

Combining Ability ◽

Density Gradient Centrifugation ◽

Gradient Centrifugation ◽

Electrophoretic Pattern ◽

Sucrose Density Gradient ◽

Irreversible Loss ◽

Sucrose Density Gradient Centrifugation ◽

Crossed Immunoelectrophoresis ◽

Triton X

SummaryPlatelets deprived of calcium and incubated at 37° C for 10 min lose their ability to bind fibrinogen or aggregate with ADP when adequate concentrations of calcium are restored. Since the calcium complex of glycoproteins (GP) IIb and IIIa is the presumed receptor for fibrinogen, it seemed appropriate to examine the behavior of these glycoproteins in incubated non-aggregable platelets. No differences were noted in the electrophoretic pattern of nonaggregable EDTA-treated and aggregable control CaEDTA-treated platelets when SDS gels of Triton X- 114 fractions were stained with silver. GP IIb and IIIa were extracted from either nonaggregable EDTA-treated platelets or aggregable control platelets with calcium-Tris-Triton buffer and subjected to sucrose density gradient centrifugation or crossed immunoelectrophoresis. With both types of platelets, these glycoproteins formed a complex in the presence of calcium. If the glycoproteins were extracted with EDTA-Tris-Triton buffer, or if Triton-solubilized platelet membranes were incubated with EGTA at 37° C for 30 min, GP IIb and IIIa were unable to form a complex in the presence of calcium. We conclude that inability of extracted GP IIb and IIIa to combine in the presence of calcium is not responsible for the irreversible loss of aggregability that occurs when whole platelets are incubated with EDTA at 37° C.

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