New approaches to direct gradient analysis using environmental scalars and statistical curve-fitting procedures

Vegetatio ◽  
1984 ◽  
Vol 55 (1) ◽  
pp. 11-27 ◽  
Author(s):  
M. P. Austin ◽  
R. B. Cunningham ◽  
P. M. Fleming



1969 ◽  
Vol 47 (24) ◽  
pp. 2763-2777 ◽  
Author(s):  
C. T. Tindle ◽  
E. Vogt

A comparison is made between the R-matrix and S-matrix theories of low-energy compound nucleus resonances for the particular case of two-level interference. The (p,γ) and (p,n) cross sections of 14C for proton energies between 0.7 and 1.5 MeV are analyzed using both theories. The 15N compound nucleus in this region exhibits strong two-level interference. The two theories provide equally good fits to the data, but the parameters describing the compound-nucleus levels are quite different. A general analytic method of relating the two sets of parameters is derived and shown to give good agreement with the results obtained by curve-fitting procedures. Remarks are made concerning the general behavior of the parameters under strong interference conditions and also on the inclusion of many channels into the analysis.



The Analyst ◽  
2006 ◽  
Vol 131 (10) ◽  
pp. 1145 ◽  
Author(s):  
Frank H. Stootman ◽  
Dianne M. Fisher ◽  
Alison Rodger ◽  
Janice R. Aldrich-Wright


Author(s):  
Jennifer A Nisbet ◽  
J A Owen ◽  
Gail E Ward

Data obtained from routine analytical radioimmunoassays were processed using five curve-fitting procedures, viz. ‘Amersham’, single binding site, four parameter logistic, a linear logit-log and a polynomial logit-log. The polynomial logit-log procedure gave the best fit, but this was probably due to the inherent flexibility of this curve-fitting process since the analytical precision achieved with it was no better than what was obtained with most of the other procedures. A limited study failed to show that statistical weighting of data before curve fitting had any practical advantage.



1982 ◽  
Vol 30 (6) ◽  
pp. 659 ◽  
Author(s):  
MJ Brown ◽  
FD Podger

The floristic differences found in vegetation ranging from sedgeland-heath to rainforest were sampled by the placement of 80 quadrats in an area 2 km2 near Bathurst Harbour, Tasmania. A direct gradient analysis using the time since last fire as the major axis of variation suggests that the changing species composition of sites is both gradational and fire-related. This interpretation is supported by a point- centred quarter analysis of the forested communities and by Principal Coordinates and Detrended Correspondence Analyses of the entire vegetation sequence. Previous descriptive models based on correlations between he frequency and structural formations are confirmed by this study. A broad correlation between fire frequency and floristic associations within non-forested vegetation is also demonstrated. However, explanation of detailed patterns requires consideration of the total fire regime (including duration and intensity of fire) and its interaction with edaphic factors. For example, fires which burn in peat lead to hysteresis in the successional pathways.



1979 ◽  
Vol 33 (5) ◽  
pp. 502-509 ◽  
Author(s):  
Attila E. Pavlath ◽  
Merle M. Millard

The analysis of organic and inorganic surfaces can be carried out very effectively with the aid of x-ray photoelectron spectroscopy. In many cases, however, the presently available methods and techniques for data treatment resolutions are not suitable for the qualitative and quantitative identification of the various forms of a given atom on the same surface. The number of components and a good approximation of their original position in the composite curve must be known to use the available curve fitting procedures, otherwise the evaluation can be unreliable. It is suggested that the second and higher even derivatives of the composite could provide these data. The possibility of applying even derivatives of composite curves in combination with a nonlinear least square curve fitting program was investigated. It was found that depending on the noise background of the spectra, the resolution could be improved through this method. The resolution is dependent on the half-width of the component curves, their separation, and ratio. Both Gaussian and Lorentzian curves can be resolved, but the resolution of the latter is easier. The resolution is increasing with higher derivatives; however, increased smoothing must be applied at each step to neutralize the influence of the noise background.



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