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Department of Chemistry
North Eastern Hill University
Shillong 793022 Meghalaya
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Superannuation on 30-11-2006
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To enumerate the cumulative impacts of the topic on which papers are being contributed at international conferences it is necessary to recall that the poster presented at the Joint ISMAR-CA�98 was the material presented at the NMRS(India) Symposia at IIT/Delhi (1997) and at IISc., Bangalore (1998) which even in India evoked an interest and later found acceptable alsoto be presented at International conference. This work has yet to be pursued for better results to be conclusive. This effort was to use a Magnetic dipole for Shielding (Induced Fields) calculations and the results till now on this could further substantiate the reproducibility of the Deagnetization factor Calculations by using the same approach and equations for induced field calculations with an additional constraints and equations used for summing over semimicrovolume elements for the whole macroscopic specimen.
While presenting these approaches for the Macroscopic Magnetized Specimen in India at the Dehradun,IIP (1999) Symposium the abstract could be presented giving the rationale for the necessity of semimicro volume elements and the derived equations inquiring as to whether all these are only a mere mathematical simplification OR can there be more to it. Later the interest from the audience and viewres of posters resulted in presenting the Full explanations and calculation of Demagnetization factor and its reproducibility and these were the considerations at the NMRS Symposia at TIFR,Mumbai (2000) and at Chennai,CLRI/IITM (2001) which were summarised as POSTER presentation at the 2nd Alpine Conference on Solid State NMR ,Chamonix Mont-Blanc,France (2001). Soon after there were messages received from the participants expressing much interest in the material and these materials are being more carefully studied by them as per the messages, from the point of view of the posiible applications indicated.
The presentations at XIII International Biophysics Congress, New Delhi (1999) and in the XIV IBC at Buenos Aires,Argentina (2002) have highlighted and explained the induced fields and their calculations from the point of view of Membrane transport studies by NMR methods and further efforts to improve the applicability are being pursued. The purpose of all the national and international presentations are being more and more substantiated by the interest of the Organizers (National &International) of Conferences. The explanations for the workability of this simple procedure for induced calculations raises a few questions which must be clarified and explained before detailed application of the method. In Feb 2003 in the National Symposium on Biophysics, a typical consideration of a aromatic-ring susceptibility tensor was used to illustrate the consequences of induced fields calculated in the tensor form at a point nearby the ring.
On the basis of the simple procedure being used for the calculation of Induced Fields due to the magnetized specimen in the regions inside and outside this Uniformly magnetized Specimen and the inferences based on the already known demagnetization effects, an inquiry was put forth as to what really are the criteria for the specimen shape and the shape for the semimicro volume element (a cavity) would apply to know the trends of field distributions inside a magnetized specimen. This was the content of the oral presentation at the NMRS2003 in IISc., Bangalore. A suggestion could be made in these considerations that if the Lorentz cavity is chosen to be a nonspherical shape , an ellipsoid for that matter, then within this volume element the discrete dipoles would contribute at a nuclear site inside induced fields and, will these trends be the same as it is for spherically shaped Lorentz Cavity?
At the 3rd Alpine Conference on Solid State NMR, France during Sept 14-18,2003 the above question could be certain extent answered from the numerical trends from a simple lattice sum calculations for CUBIC & NONCUBIC lattices when a spherical and nonspherical (ellipsoidal) inner volume elements are considered. it seems the Lorentz Cavity need not be only spherical since even for an ellipsoidal shape of comparable semimicro volume element the discrete poit dipoles yielded the same limiting sum value for the total contribution from all the dipoles within the volume element. Hence the Lorentz cavity need not be only of spherical shape. Then for the same dimensions for all cases the CUBIC lattice yielded the same numerical value indicating a near zero contribution but for noncubic lattice the limiting sum varied significantly depending on the relative ratios/magnitudes of the lattice parameters. And even in this ellipsoidal case the limiting values did not depend on the elliticities for the ellipsoids and all values were close to the nonzero values obtained for the spherical case.
Thus having carified for the situations with regard to the intermolecular lattice contributions at proton sites in the single crystal specimen, now it seems more confidence can be placed while using the magnetic dipole ( the Joint ISMAR CA'98 POSTER presentation) for the intramolecular shielding calculations since the comparison with experimentally measured Shielding tensor values would be available with much more certainty.Further reconciliatons of the situation inside the Lorentz Ellipsoids for solid state and liquid state HR PMR studies seems to be due