numOSL (version 1.6)

decomp: Decomposing an OSL decay curve

Description

Decomposing an OSL decay curve (type "CW" or "LM") to a given number of first-order exponential components using a combination of differential evolution and Levenberg-Marquardt algorithm.

Usage

decomp(Sigdata, ncomp = 2, constant = TRUE, 
       typ = c("cw","lm"), control.args = list(), 
       transf = TRUE, LEDpower = 60, LEDwavelength = 470, 
       plot = TRUE, xylog= FALSE, lwd = 3, outfile = NULL)

Arguments

Sigdata

matrix(required): two columns, i.e., time values and photon counts

ncomp

numeric(with default): the number of components to be decomposed

constant

logical(with default): subtract a constant component or not

typ

character(with default): type ("cw" or "lm") of a decay curve, default typ="cw"

control.args

list(with default): arguments used by the differential evolution algorithm, see details

transf

logical(with default): do not use

LEDpower

numeric(with default): LED power (mW/cm2) of the instrument

LEDwavelength

numeric(with default): LED wavelength (nm) of the instrument

plot

logical(with default): draw a plot or not

xylog

logical(with default): using both logged x-axis and y-axis or only logged x-axis

lwd

numeric(with default): the width of a line

outfile

character(optional): if specified, decomposed signal values will be written to a file named "outfile" in ".csv" format and saved to the current work directory

Value

• Return an list containing following elements:
• pars
  the decay rates, the number of trapped electrons and their standard errors
• constant
  the constant component (it will be 0 if constant=FALSE)
• value
  the minimized sum of squared residuals

Details

This function decomposes an OSL decay curve to a specified number of components using a combination of differential evolution and Levenberg-Marquardt algorithm. Both OSL decay curves of type "CW" and "LM" can be decomposed. For an CW-OSL decay curve, the fitting model (Bluszcz and Adamiec, 2006) is: I(t)=a1*b1*exp(-b1*t)+...+ak*bk*exp(-bk*t), where k=1, 2, ..., 7, I(t) is the luminescence intensity as a function of time, a is the number of trapped electrons, and b is the detrapping rate. The constant component will be c if constant=TRUE. For an LM-OSL decay curve, the fitting model (Bulur, 2000) is: I(t)=a1*b1*(t/P)*exp[-b1*t^2/(2*P)]+...+ak*bk*(t/P)*exp[-bk*t^2/(2*P)], where k=1, 2, ..., 7, and I(t) is the luminescence intensity as a function of time, P is the total stimulation time, a is the number of trapped electrons, and b is the detrapping rate. The constant component will be c*(t/P) if constant=TRUE. Parameters are initialized using a differential evolution method suggested by Bluszcz and Adamiec (2006), then the Levenberg-Marquardt algorithm (available at http://ftp.netlib.org/minpack) will be performed to fit the curve. Arguments (control.args) that control the performance of the differential evolution algorithm include: factor: control the number of parents, np=factor*ncomp, default factor=10 f: a weighting factor that lies between 0 and 1.2, default f=0.5 cr: a crossover constant that lies between 0 and 1, default cr=0.99 maxiter: the allowed maximum number of iterations, default maxiter=500 tol: a tolerance for stopping the iteration, the iteration will be terminated if the relative standard deviations of parameters are smaller than tol, defalut tol=0.1

References

Bluszcz A, 1996. Exponential function fitting to TL growth data and similar applications. Geochronometria, 13: 135-141.

Bluszcz A, Adamiec G, 2006. Application of differential evolution to fitting OSL decay curves. Radiation Measurements, 41: 886-891.

Bulur E, 2000. A simple transformation for converting CW-OSL curves to LM-OSL curves. Radiation Measurements, 32: 141-145.

Differential evolution algorithm, http://en.wikipedia.org/wiki/Differential_evolution Jain M, Murray AS, Boetter-Jensen L, 2003. Characterisation of blue-light stimulated luminescence components in different quartz samples: implications for dose measurement. Radiation Measurements, 37: 441-449.

More JJ, 1978. "The Levenberg-Marquardt algorithm: implementation and theory," in Lecture Notes in Mathematics: Numerical Analysis, Springer-Verlag: Berlin. 105-116.

Further reading

Adamiec G, 2005. OSL decay curves-relationship between single- and multiple-grain aliquots. Radiation Measurements, 39: 63-75.

Choi JH, Duller GAT, Wintle AG, 2006. Analysis of quartz LM-OSL curves. Ancient TL, 24: 9-20.

Li SH, Li B, 2006. Dose measurement using the fast component of LM-OSL signals from quartz. Radiation Measurements, 41: 534-541.

See Also

fastED

Examples

data(Signaldata)
 decomp(Signaldata$lm,ncomp=3,typ="lm",control.args=list(maxiter=10))