A typical FID generated by a simulation using these equations is shown in Figure 2. The general resolution of the FID can he altered in one of three wavs. More severe dampine can be introduced into the spectrum by increasing the i r e f k t o r exoonential term. exo ( - ~ 1 5 )which . will lead to a decrease in the resolution. he apparentresolution of the spectrum can he reduced by decreasing the acquisition time to values less than one, and by taking data in bigger steps than 0.001. Poly(methylmethac~late)Spectra In the simulation of PMMA, the ester methyl was assumed to he unaffected hy changes in tacticity. The methylene group dinplaya tetrad tacticity, while the a-methyl protons show oentad tacticitv. Such differences are actuallv observed in the 220-MHZ-NMR spectrum of PMMA that was used as a model. In this case. the peaks raneina from 6 2.4 to 1.6 are due to the methylene protons, whili tKe peaks at lower 6 are to the a-methvl arouo. Shown in Figure 3 are spectra of varying degrees of taiticiiy. Note that aspectrum with as little as 10%meso diad shows peaks not present in the 100%syndiotactic PMMA spectrum with 0% meso diad. As an example of a possihle student exercise, two FID's of PMMA with different different tacticities were generated. The data was then stored in read-only files accessible to the students. I t was possible for the students to Fourier transform the files, and to then integrate the resulting spectra. After integration, the students could determine the tacticities of the simulated spectra using the Bernouillian relationships for oentad and tetrad chain seements. fn conclusion, such simulations permit teaching of the measurement of tacticitv bv NMR spectroscoov and expose the students to concep~as&iated with NMR spectroscopy itself. In principle, this approach can also he used to simulate '3C-NMR spectra. The described simulation was modelled using the chemical shifts observed in a spectrum of PMMA made with a 220-MHz instrument, hut this approach can he modified in terms of chemical shift and coupling constants with the operator ahle to specify the instrument frequency. In terms of educational excercises, it is also possihle to chanee orohlems annuallv without sacrificine anv of the concepts to he communic&ed by simply supphinithe student withanew FID. As a final note. this method of simulating NMR spectra has heen used in exercises to study changes in copolymer composition as a function of both comonomer composition and reactivity ratios. Acknowledgment The author would like to thank Mike Thompson for help in writing the subroutines used for the simulations and for reading this manuscript. The use of the Materials Science Center Computer Facility is also acknowledged.
Teaching Magnetic Resonance Imaging Using Computer Animation Davld S. Browne, Presley E. Ellsworth IV,9 and Joseph P. Hornak4 Rochesler lnstihm of Technol~gy Rocheater, NY 14623
Magnetic renonnnre imnging (MRI) is n relatively new tomographic imaging technique that is finding use in the medical settinesand thescientific research laboratorv. .17.8). . , The technique"is based on the principles of nuclear magnetic resonance (NMR) soectroscoDv and as a result much of the basic and applied iesearch in this field is conducted by chemists. Involving undergraduate students in magnetic resonance research requires a carefully planned education program in the principles of magnetic resonance. Such a program often requires the student to learn the principles inde-
pendently, as there are usually no appropriate courses at the sophomore and junior level. Modern-day NMR spectroscopy and imaging is performed in the pulsed model (9). The conventional energylevel diagrams used to describe the continuous wave NMR experiment are inadequate for giving the full picture of the pulsed methods. Pulsed methods require an understanding of the behavior of angular momentum in a force field. The student must he ahle to picture not only the macroscopic three-dimensional behavior of magnetization from the nuclear spins hut also the complex pulse and data processing schemes. Several dynamic aspects of magnetic resonance spectroscoov and imaeine are difficult for a student to understand w i i n texthooL i i t h static diagrams are used. Some of these dynamic concepts are precession of the net magnetization in a static magnetic field, the rotating frame of reference, rotation of maenetization by the radio frequency photons, dephasing ofltransverse magnetization, G i n relaxation, slice selection, and two-dimensional Fourier transform imaging. Other aspects of the technique such as the timing diagrams for pulse sequences and two-dimensional Fourier transform data processing are easy to understand once the student has been walked through each and every one of the steps. Unfortunately most textbooks do not have the space to devote to such an endeavor. Consequently, significant amounts of time are snent hv the research advisor ex~laininathese concepts,whichcouid hetter he taught by other means. A logical solution to this problem is to utilize dynamic diagrams of these concepts. The prohlem then becomes how best to create the dynamic material and to make it availahle to the student. Today this material is best generated by computer animation. Three video display modes are then possible. TV video presentations utilize material recorded on videotape for playback using a VCR and TV comhination. The advantage of this technique is the availability of the playback equipment. The disadvantages are that random access of the recorded material is difficult, and picture quality varies from VCR to VCR. Interactive video combines prerecorded video and real-time computer sequences in one display (10).The presentations are of superior quality; however. the s~ecializeddisolav- eauipment is expensive and not . . readily available. ~ e a i - t i m ecomputer animation on a computer maphics monitor is the third option (11).Programs h a y he designed to operate on readiiy availahle pe&onal computers or on a mainframe computer. The advantages of chis&hnique are the ahility to access the material randomly and customize the presentation to a particular viewer. The presentation is limited by the capabilities of the computer on which it is running. We have developed a comouter-based teachine ~ a c k a e e readiy for the pr~nciplesi f NMR lm&ing that operates available IBM PC with color monitor and sinele flooov d ~ s k drive. The IBM PC was chosen because it is readily &ilahle in our department for use by students. The package was written in Turbo Pascal, Borland Associates, because of its graphics capabilities and speed. The approximately 15,000 lines of software code were written by two RIT students on their co-op blocks in a total of 1200 h. The parkage is composed of 15 sequences that are equivalent to chapters in a book. l'he sequences are further divided into screens, which are a series of images and text describing a given ropic. Hoth the sequences and screens are selrctal~lt. from menus. The screens contain text and accom~anvine . . .. animated diagrams that appear simultaneously, thus allow. ine" the reader to oicture the process beine described. l'he 15 sequences available from the main menu are listed next.
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Present address: FONAR Corporation. Melville. NY. 'Corresponding author. Volume 66 Number 8 August 1989
647
Basic NMR Spectroscopy NMRTerminology The laboratory vs. rotating frame of reference Response of spins to pulsed magnetic field NMR pulse sequences The Fourier transform Measuring relaxation times 8. Imaging using the hack projection 9. Slice selection in MRI 10. Partial saturation Fourier transform imaging sequence I I . Imaging data and the iwo-dimensionalFourier transform 12. Additional MRI pulsesequences 13. l'hr magnetic resonance image 14. List oi rquations 15. Lirt of rrnding materials 1. 2. 3. 4. 5. 6. 7.
The package is suitable as a stand-alone teaching package or as part of a lecture presentation. Although the package was intended to introduce the principles of MRI, the first half is suitable for teaching the basics of modern NMR techniques. ~ a c k a e ehas been used at RIT at the underThis teachine-. graduate and introductory graduate levels with much success. Students may use the package a t RIT in our departmental computer room or check it out for use a t home. Students have found the seauences describine - the soin echo and two-dimensional Fourier transform imaging techniques esneciallvuseful. Thev have commented that the material is i k m e d i a k y comprehendible on viewing the sequences. From the instructor's point of view the time needed to explain the dynamic processes of MR is significantly reduced. The menu selection of topics allows the viewer to treat the material as a formal course by viewing topics in order or as a review by viewing individual topics. creation of this software was supported by the Rochester Institute of Technology under its productivity grant program. This software package is entitled "The Basics of NMR Imaging, A Computer Based Teaching Package" and is available from RIT Instructional Media Services for $50.
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EmerllencY Response J. Shofstahl, D. Jencen, G. Chansa, and J. Hardy The University of Akron Akron. OH 44325
Safetv in the chemical laboratorv is alwavs a concern. precautions to take ~ t u d e n i a a r einstructed as to the as to ~rotectiveclothine and safe handline of chemicals. ~ h e n ' s ~ e c i aprecautions l are required, this is also noted. However. i t is not alwavs oossible to nresent much information as to health hazids'and procedures in the event of a laree soill or fire. system has been developed t o provide information on over 1900 chemicals, mixtures, and general material classes in a form that is easy t o retrieve -and use. Students can rapidly locate hazard-related information on chemicals they will be using with little or no instruction. The system contains a range or information for each material where available and appropriate.
A
Name and up to four synonyms Formula Description Chemleal and storage incompatibilities Chemical Ahslracta Registry number (CAS) NlOSH Remtryof Tonic Effects of ChemicalSubstances (RTECS) number Environmental Protection Agency (EPA) Hazsrdous Waste Codes Department of Transportation (DOT) Numbers and Guides National Fire Protection Association (NFPA) values for Health, Flammability, and Reactivity hazards. Physical properties including: weight, vapor pressure, melting paint, boiling point, flash point, explosive limits, and solubility. 648
Journal of Chemical Education
All information has been taken from the following standard sources on hazardous materials. NFPA No. 49-Hazardous Materials, 1975. DOT-P 58000.2-Hazardous Materials, Emergency Response Guidebook. 1980. DHEW ~ubiicationNo. 78-210-NIOSH Pocket Guidebook to Chemical Hazards, 1985. Federal Register, Vol. 45, No. 229. The student can locate a chemical based on names. formula, or registry numbers. Wildcards may be used tb locate materials based on oartial entries. Once an entrv has been identified, the data screen is displayed withalldaro pertainine to the chemiral. Svecific definitions for the NFPA haza& values and a compiete DOT Emergency Response Guide can be obtained with a single key stroke. The Emergency Response Guide gives the student a list of any health, fire, and explosive hazards and corrective actions they can take in the event of a spill or fire. A second benefit of the system is that i t provides a crossreference of the various reeistrv numbers assiened to a chemical. This should prove-usef;l to stockroom-personnel faced with the res~onsibilitvof hazardous waste dis~osal. The program is h i t t e n incompiled BASIC and runsonan 1BM PC (orcomvatible) withal least 512 K RAMand a hard disk containing at least 2.5 MB of free space. The system is distributed on either two 360 K 5 W n . disks or one 720 K 3'f2-in. disk. A copy of the system and the 63-page user manual may be obtained by sending $50 (to cover postage and duplication costs) to J. K. Hardy, Department of Chemistry, The University of Akron, Akron, OH 44325. Please specify the disk format desired.
An X-ray Diffraction Pattern Simulator Gonzalo Rodriguez and Silvlo Rodrfguez University of the Pacific Stockion. CA 95211 Most textbooks on experimental physical chemistry include the analysis of an X-ray powder diffraction pattern from which students determine the cubic lattice type and the lattice constant of a crystalline substance. The density of the substance is then calculated from these data (12-15). Currently, structural determinations by X-ray diffraction are highly computerized, and powder pattern photographs are verv ~" rarelv used. Because manv educational institutions donot have X-ray equipment avaiiable, usually each student is eiven a neeative or nrint of a film and asked to oerform c e h n calcu~atioos. here is a clear pedagogical val"e in the determination o f a cwstal structure hv this method, and the experiment is usualiy included in experimental physical chemistry rourses. Although powder patterns for all alkali halides are available in the literature (16), it is desirahle to be able to eenerate the X-ray powder diffraction pattern of a substancefrom a knowledge bf its density and cubic structure. This increases the variety of "unknowns" available for student usage and allows a comparison of the diffraction patterns of a substance hypothetically crystallizing in a simple (primitive), face-centered, or body-centered cubic lattice. We have develooed a microcom~uteraroeram that simulates X-ray powder diffraction for many substances and oroduces realistic spectra from the input of (1) the atomic or ?ormula weight o f t h e compound, (2) the density of the compound, and (3) the lattice type. The program, written in Microsoft BASIC Version 1.31, for execution on the Sanyo MBC-555 microcomputer, consists of 85 lines, including 10 remark statements, and can be easily converted for use on any other version of BASIC. The program calculates the ~
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