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Re: letter from J.K.Parida, India

  • Subject: Re: letter from J.K.Parida, India
  • From: "John D. Barnes" <john.barnes@nist.gov>
  • Date: Thu, 05 Apr 2001 21:27:25 -0400
  • In-Reply-To: <20010405114101.24427.qmail@mailweb22.rediffmail.com>
  • reply-to: JDB.Science, LLC.jbdsci@speakeasy.org

on 4/5/01 7:55, jk  parida at jkparida@rediffmail.com wrote:

> Sender: "jk  parida" <jkparida@rediffmail.com>
> Subject: letter from J.K.Parida, India
> Dear colleagues,
> Please pay attention to the following points.
> 1. what is the criterian to be followed in order to know whether a sample is
> dense / dilute system. Will we consider all solids as dense and all liquids as
> dilute ? please explain.
> Note : In the past work had been done on silk and jute considering those as
> dilute systems though these are solid fibres.
> 2. suppose we prepared a sample. How to know it is monodisperse / polydisperse
> ? 
> Note : if Mn = Mw then the system is monodisperse otherwise it is
> polydisperse. Hence I think without estimating Mn and Mw from experimental
> data of scattered intensity it is not possible to say what type of system the
> sample is. Please explain.
> Kindly reply early.
> With regards,
> Yours sincerely,
> Mr.J.K.Parida,
> India

Dear Mr. Parida;
    Your questions define almost the entire field of small-angle scattering.
It is too bad that you do not seem to have a textbook such as the one by
Glatter and Kratky or the one by Feigin and Svergun. These are unfortunately
out of print at this time, but perhaps there is someone who can find a copy
for you. You should also search the available literature for review articles
on the modeling of SAS data. Perhaps one of the list members will point you
to some of these.

    The decision as to dense or dilute, polydisperse or monodisperse, etc.
is made on the basis of a careful analysis of the fit of the data to various
models. These are chosen on the basis of what is known about the composition
of the samples and the likely character of its microstructure.

    I suggest that you share your data with someone who has worked in the
same area that you are pursuing. Their experience should be able to help
guide you to a more fruitful analysis. Your questions are too vague to allow
anyone to answer them without a detailed knowledge of your data and the
systems from which they are derived.

Dr. John D. Barnes            phone: 301-652-0667
JDB Science, LLC              email: jdbsci@speakeasy.org
7710 Chatham Rd               url: http://www.jdbscience.com
Chevy Chase, MD 20815, USA

"Time is fun when you are having flies." - Kermit the Frog