Re: purposefully modifying a distribution to get...?

[brian whatcott <inet@INTELLISYS.NET>]

At 21:48 7/11/00 -0400, Stefan J wrote:
> Recent discussions lead me ask about a minor physics quandry I have.
> I am working on software that simulates the acquisition and analysis
> of an x-ray pulse processor data stream such as occurs in x-ray
> microanalysis using an electron microscope (EDS, Energy Dispersive
> Spectroscopy). The software will ultimately operate with a -real-
> stream of data taking the place of the simulated stream.
>
> The x-ray emission events in time are described by a Poisson process.
> This is straightforward to simulate using a computer. However,
> practicalities (limits on memory, etc) require that the pulse height
> analysis data be recorded into finite arrays....

> Stefan Jeglinski

There are several features of this equipment that are unclear to me.
 I understand there is a data stream in time, of pulses which vary
in amplitude. (correct?)

It is not clear if this time sequence is obtained by ramping up the
incident energy of the electron beam over a point, or if the sequence
represents an electron probe scanning along a direction of the sample.

 Further, I am not sure if you are assigning pulses of differing amplitude
 to different buckets (which would be a reasonable description of
spectrometry) or if the time sequence is a mapping of X ray energy with
displacement of the electron beam.

If the latter were true, you would have have ample precedents on handling
the windowing inherent in fourier transforming a number of samples forming
an even binary power in the usual way. The convolving effect of the finite
sample size is improved by using various weights for the data towards
the window sides.

But I fancy the partial pulses you need to discard are selected from the
larger amplitudes which stretch further in time (?) and have more chance
 of crossing a window edge.   If this were true, you are discounting higher
energy effects.

I would enjoy reading a simple description of the action of your device.
 Pending better information of that kind, I could offer a fire-brand to
counter the darkness of the "looks OK" school of software.

 If removing edge pulses "looks OK", can you remove 10 times as many pulses?
 Those occuring after each 1/10th of the sample window, perhaps?

If this is a statistically harmless process, it will just take longer to
arrive at comparable results to the existing ones.

 This assumes you have some standard for judging your data stream
processing - and I'm sure you do.




brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!