An improved program has been developed that inverts data obtained from an electrical differential mobility analyzer (DMA)to obtain the particle size sistribution.The central problem for data inversion is to find a smooth particle size sistribution function,N(x),from the instrument response,R(t).Linear data inversion techniquews for this problem,as developed by Hagen and Alofs (1983)work by usign a small numbe of size channels arefully selected so that data channels for multiply-charged particles overlap channels for smaller single-charged particles.However,these techniques fail whtn a large number of data channels are used.The program developed here typically used 300 data channels,making it particularly appropriate for inverting data obtained in scanning mode,where the number of channels can be made arbitrarily large.It is based on regularization procedures like those described by Wolfenbarger and seinfeld (1990)and Lesnic et al.(1996).To estimated the optimal value of hte regularization parameter,and automated L-curve based method has been selected,as describes by Hansen and O'Leary (1993).The large number of data channels used ensures that the resolutin of hte measurements is limited by te capabilities of te instrument and not by the selectin of te soze channels to be used.Efficient implementation of hte inversion program is made possible by supplying analytical experssions for the gradient and hessian of the objective function that is minimized to solve the regularized problem.
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