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Constant Slope (constant + slope)
Selected AbstractsNegative per capita effects of purple loosestrife and reed canary grass on plant diversity of wetland communitiesDIVERSITY AND DISTRIBUTIONS, Issue 4 2006Shon S. Schooler ABSTRACT Invasive plants can simplify plant community structure, alter ecosystem processes and undermine the ecosystem services that we derive from biotic diversity. Two invasive plants, purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinacea), are becoming the dominant species in many wetlands across temperate North America. We used a horizontal, observational study to estimate per capita effects (PCEs) of purple loosestrife and reed canary grass on plant diversity in 24 wetland communities in the Pacific Northwest, USA. Four measures of diversity were used: the number of species (S), evenness of relative abundance (J), the Shannon,Wiener index (H,) and Simpson's index (D). We show that (1) the PCEs on biotic diversity were similar for both invasive species among the four measures of diversity we examined; (2) the relationship between plant diversity and invasive plant abundance ranges from linear (constant slope) to negative exponential (variable slope), the latter signifying that the PCEs are density-dependent; (3) the PCEs were density-dependent for measures of diversity sensitive to the number of species (S, H,, D) but not for the measure that relied solely upon relative abundance (J); and (4) invader abundance was not correlated with other potential influences on biodiversity (hydrology, soils, topography). These results indicate that both species are capable of reducing plant community diversity, and management strategies need to consider the simultaneous control of multiple species if the goal is to maintain diverse plant communities. [source] Processes and mechanisms of dynamic channel adjustment to delta progradation: the case of the mouth channel of the Yellow River, ChinaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2003Changxing Shi Abstract This paper analyses the processes and mechanisms of a three-stage channel adjustment over a cycle of the Yellow River mouth channel extension based on data comprising hydrologic measurements and channel geometric surveys. Rapid siltation in the mouth channel takes place in the young stage when the channel is being built by deposits and in the old stage when the channel cannot further adjust itself to keep sediment transport in equilibrium. It is disclosed that the bankfull width,depth ratio, bed material size and slope decrease in the young and mature stages but do not change in the old stage. The reduction of bankfull width,depth ratio and bed material size during the young and mature stages is found to be able to offset the effect of the slope reduction on sediment transport due to continuous mouth progradation. They reach their limits in old stage, and a constant slope is kept by unceasing sediment accumulation. The grain size composition of incoming sediment and the fining mechanism are responsible for the occurrence of lower limit of bed material size. The reason for the existence of a limit of bankfull cross-sectional shape is that the large flows can fully transport the sediment load they are carrying, and siltation in the channel in the old stage takes place mainly in the low flows. It is suggested that the bankfull discharge plays an important role in shaping the channel but that the entire channel form is the product of both the large and low flows plus the effects of interaction between them. Channel pattern change shows a process from a braided pattern in the young stage to a straight pattern in the mature and old stages, and the straight channel becomes gradually sinuous. The occurrence and transformation of the channel patterns are supported by two planform predictors, but are also facilitated by some other conditions. Copyright © 2003 John Wiley & Sons, Ltd. [source] Substituent effects in solvolysis of 1,1-diphenylethyl p -nitrobenzoates.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2002Symmetrically disubstituted, monosubstituted systems Abstract The rates of solvolysis of 1,1-diarylethyl p -nitrobenzoates and chlorides were determined conductimetrically at 25,°C in 80% (v/v) aqueous acetone. Applying the Yukawa,Tsuno (Y,T) equation, the symmetrical (X,=,Y) subseries gave a precise additivity relationship for the whole substituent range with a ,sym value of ,3.78 and an rsym value of 0.77. While any Y subsets gave statistically less reliable Y,T correlations, the apparent , value changed significantly depending on the fixed Y substituents; the , value decreases with the more electron-donating fixed substituents Y, which is compatible with the Hammond shift of the transition state coordinate. Nevertheless, the concave correlations of the More O'Ferrall non-linearity relationship for any Y subsets are not in line with what is expected from the reactivity,selectivity relationship suggesting an anti-Hammond shift of transition state. However, we found a precise extended Brønsted relationship between the pK values of 1,1-diarylethylenes and solvolysis rate process with a constant slope of ,,=,1.03,±,0.03. This is direct evidence indicating that there is no significant shift of the transition-state coordinate over the whole range of substituent change. Copyright © 2002 John Wiley & Sons, Ltd. [source] Multidimensional density estimation and phase-space structure of dark matter haloesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Sanjib Sharma ABSTRACT We present a method to numerically estimate the densities of a discretely sampled data based on a binary space partitioning tree. We start with a root node containing all the particles and then recursively divide each node into two nodes each containing roughly equal number of particles, until each of the nodes contains only one particle. The volume of such a leaf node provides an estimate of the local density and its shape provides an estimate of the variance. We implement an entropy-based node splitting criterion that results in a significant improvement in the estimation of densities compared to earlier work. The method is completely metric free and can be applied to arbitrary number of dimensions. We use this method to determine the appropriate metric at each point in space and then use kernel-based methods for calculating the density. The kernel-smoothed estimates were found to be more accurate and have lower dispersion. We apply this method to determine the phase-space densities of dark matter haloes obtained from cosmological N -body simulations. We find that contrary to earlier studies, the volume distribution function v(f) of phase-space density f does not have a constant slope but rather a small hump at high phase-space densities. We demonstrate that a model in which a halo is made up by a superposition of Hernquist spheres is not capable in explaining the shape of v(f) versus f relation, whereas a model which takes into account the contribution of the main halo separately roughly reproduces the behaviour as seen in simulations. The use of the presented method is not limited to calculation of phase-space densities, but can be used as a general purpose data-mining tool and due to its speed and accuracy it is ideally suited for analysis of large multidimensional data sets. [source] Color constancy from invariant wavelength ratios: I. The empirical spectral mechanismCOLOR RESEARCH & APPLICATION, Issue 3 2008Ralph W. PridmoreArticle first published online: 10 APR 200 Abstract The wavelengths of several constant hues over four illuminants (D95, D65, D50, A) are derived from several sets of published data. In the plane of wavelength and reciprocal illuminant color temperature (MK,1), the wavelengths of constant hues plot straight approximately parallel lines whose mean slope is about 87°. Parallel lines give invariant wavelength ratios, hence constant hues in this plane are near-invariant wavelength ratios across illuminants. As recently demonstrated, the complementary wavelengths to a constant hue (across illuminants) represent the complementary constant hue; these complementary wavelengths also plot a near-parallel line to the first constant hue. To confirm and further define the constant slope of these lines, it is shown that complementary wavelength pairs, per CIE data, can only plot parallel straight lines at the angle of 87° ± 1. In summary, near-parallel sloping lines represent constant hues at near-invariant wavelength ratios. This mechanism of color constancy is shown to relate to the well-known theory of relational color constancy from invariant cone-excitation ratios. In the visual process, the latter ratios are presumably the source of the former (invariant wavelength ratios). © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 238,249, 2008 [source] | ||||||||||