A correlation is demonstrated between the electrophilic superdelocalizability for the K region and carcinogenic potency for 1,2-benzanthracene and 5,6- and 7,8-benzacridine and a set of their methyl and dimethyl derivatives.

In the early 1980s, three coauthors and I published a letter ( Physics Today, Physics Today 0031-9228 37 4 1984 15 https://doi.org/10.1063/1.2916188. April 1984, page 15 ) stating that the Graduate Record Examination (GRE) aptitude tests showed that those students taking the tests and indicating physics as their intended area of study had the highest combined quantitative and verbal scores of the 98 disciplines listed. In view of evolving trends in graduate education, it seemed of interest to reexamine the quality of students planning to go to graduate school in physics, as measured by the GRE aptitude tests.The data given here appear in the GRE Guide to the Use of Scores, available online at ftp://ftp.ets.org/pub/gre/992362.pdf, and are based on exams taken between 1 October 1997 and 30 September 2000. Test takers were grouped into 50 broad fields by intended graduate major, and mean scores are reported for each of the three aptitude tests, verbal, quantitative, and analytical.For the physics and astronomy category, the mean score ranked first in quantitative aptitude, first in analytical, and tied for sixth in verbal (students who listed philosophy as their intended course of study ranked first in verbal aptitude). When the means are aggregated, students intending to study physics and astronomy easily rank first among the 50 categories. Physics graduate programs are still getting good students—so good, in fact, that the aptitude tests are of limited value in predicting first-year grades in graduate school, the one outcome for which complete data are published. The correlation of first-year graduate grades with the aggregate aptitude score is only 0.20. Moreover, the best correlation is with the verbal score, which is a little surprising until one notices that the standard deviation is largest for this test. Overall, the scores are so uniformly high that they provide little discrimination.The situation is somewhat different with the subject matter test: The correlation with first-year graduate grades is 0.27, about the same as for undergraduate grades, where the correlation is 0.28.© 2002 American Institute of Physics.

AbstractSurface energy changes of an epoxy based on tetraglycidyl diaminodiphenyl methane (TGDDM)/diaminodiphenyl sulfone (DDS), T‐300 graphite fiber, and T‐300/5208 (graphite fiber/epoxy) composites have been investigated after irradiation with 0.5 MeV electrons. The surface energy of TGDDM‐DDS epoxy increases monotonically with radiation doses up to 1,000 Mrad mainly due to increased concentration of polar groups. IR and ESCA spectral evidence indicates that carbonyl groups are formed, probably from the tertiary hydrogen at the carbon where the OH group is attached in the cured epoxy. The polarity of the graphite fiber and the graphite fiber/epoxy interface also increases with radiation dose. These results and the roles of oxygen are discussed in connection with mechanical properties of epoxy/graphite fiber composites exposed to ionizing radiation.

AbstractTGDDM/DDS epoxy and T300/NARMCO 5208 composite specimens were exposed to 0.5 MeV electrons to dose levels up to 10,000 Mrad, and the effects of radiation on the mechanical properties were characterized using dynamic mechanical analysis (DMA). In nominally cured specimens there remain unreacted epoxide groups because the epoxy system vitrifies during the cure, preventing additional reaction. DMA shows that ionizing radiation continues the reactions of epoxide groups. Also, the ultimate glass transition is shown to decrease monotonically with radiation dose. The room temperature elastic modulus of the epoxy increases slightly with radiation, but at temperatures exceeding 100°C there is a slight decrease with radiation. There is a dynamic loss phenomena associated with the composites, not seen in the epoxy, that is thought to be due to the interphase region between the fiber and the matrix.

AbstractElectron spin resonance (ESR) investigations of line shapes and radical decay behavior have been made on an epoxy based on tetraglycidyl diaminodiphenyl methane (TGDDM)/diaminodiphenyl sulfone (DDS), T‐300 graphite fiber, and T‐300/5208 (graphite fiber/epoxy) composites after irradiation with Co60 γ‐radiation or 0.5 MeV electrons. Two kinetically distinct radical species are found in the irradiated epoxy as the temperature is raised beyond 120 K following irradiation of samples at 77 K with Co60 γ. One has been termed a fast‐decaying species and the other a slow‐decaying species. The ratio of fast‐decaying/slow‐decaying radicals increases as the decay temperature rises. The fast‐decaying radicals at room temperature are attributed largely to alkyl type radicals residing in regions of relatively low crosslink density, while the long‐lived radicals are attributed to radicals residing in the highly crosslinked regions of the epoxy. A large concentration (ca. 1020 to 1021 spins/g) of unpaired electrons was found in unirradiated graphite fiber which masked the ESR spectral change in irradiated composites.

The effects of radiation on graphite fiber reinforced composites, particularly those using an epoxy matrix, are reviewed. Specifically, it is concluded that there is no catastrophic deterioration of mechanical properties for doses up to thousands of Mrad, provided the irradiation occurs in an oxygen-free environment.

The epoxy resin formed by tetraglycidyl 4,4'-diamino diphenyl methane and 4,4'-diamino diphenyl sulfone was characterized by dynamic mechanical analysis. Epoxy specimens were exposed to varying dose levels of ionizing radiation (0.5 MeV electrons) up to 10,000 Mrads to assess their endurance in long-term space applications. Ionizing radiation has a limited effect on the mechanical properties of the epoxy. The most notable difference was a decrease of approximately 40°C in Tg after an absorbed dose of 10,000 Mrads. Sorption/desorption studies revealed that plasticization by degradation products was responsible for a portion of the decrease in Tg.

Journal of Applied Polymer ScienceVolume 31, Issue 5 p. 1531-1535 NoteFree Access Thermogravimetric analysis of water-epoxy interaction A. N. Netravali, A. N. Netravali North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this authorR. E. Fornes, R. E. Fornes North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this authorR. D. Gilbert, R. D. Gilbert North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this authorJ. D. Memory, J. D. Memory North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this author A. N. Netravali, A. N. Netravali North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this authorR. E. Fornes, R. E. Fornes North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this authorR. D. Gilbert, R. D. Gilbert North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this authorJ. D. Memory, J. D. Memory North Caroline State University, Department of Physics, Box 8202, Raleigh, North Carolina 27605Search for more papers by this author First published: April 1986 https://doi.org/10.1002/app.1986.070310535Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL References 1 A. N. Netravali, R. E. Fornes, R. D. Gilbert, and J. D. Memory, J. Appl. Polym. Sci., 29, 311 (1984). 2 C. E. Browning and J. M. Whitney, ACS, Org. Coatings and Plastics Chemistry, 33(2) (1972.) 3 A. N. Netravali, R. E. Fornes, R. D. Gilbert, and J. D. Memory, J. Appl. Polym. Sci., 30, 1573 (1985). 4 T. S. Ellis and F. E. Karasz, Polymer, 25, 664 (1984). 5 J. L. Illinger and J. F. Sprouse, Org. Coatings and Plastics Chemistry, 175th ACS meeting, 38, 497 (1978). 6 K. W. Thompson, T. Wong, and L. S. Broutman, Poly. Eng. Sci., 24, 1270 (1984). 7 F. Yang, Ph.D. dissertation, NCSU, Raleigh, N.C. (1984). 8 C. M. Fisher, R. D. Gilbert, R. E. Fornes, and J. D. Memory, Reduction in the moisture sensitivity of cured MY720/DDS epoxy resins by treatment with organic blocking agents, J. Polym. Sci., Chem. Ed. (in press). 9 R. T. Fuller, R. E. Fornes, and J. D. Memory, J. Appl. Polym. Sci., 23, 1871 (1979). 10 P. Moy and F. Karasz, Polym. Eng. Sci., 20, 315 (1980). 11 R. T. Fuller, R. E. Fornes, and J. D. Memory, J. Appl. Polym. Sci., 24, 1383 (1980). 12 D. A. Lawing, Ph.D. dissertation, NCSU, Raleigh, NC (1982). Citing Literature Volume31, Issue5April 1986Pages 1531-1535 ReferencesRelatedInformation

AbstractIt was found that the amount of water absorbed at room temperature in cured tetraglycidyl‐4,4′‐diaminodiphenyl methane/diaminodiphenyl sulfone epoxy resins increases as the curing time or temperature increases while the amount of tetrahydrofuran‐soluble extractables and the room temperature density decreases. These data suggest that the free volume increases with the extent of cure and the resins become more accessible to water. While the driving force for water absorption is the electrostatic attraction between water and the functional groups in the epoxy, the results suggest that equilibrium H2O absorption is determined primarily by unoccupied volume of the epoxy resin.

AbstractThin films of cured MY720/DDS epoxy resins were treated with blocking reagents for hydroxyl, amine, and epoxide functional groups. Infrared spectroscopy (IR) and differential scanning calorimetry (DSC) were used to monitor the progress of the reaction. Treated films were soaked in distilled water at 30°C for 720 h, and the corresponding moisture absorption determined gravimetrically. Samples treated with N‐methyl‐N‐t‐butyldimethylsilyl trifluroacetamide (MTBSTFA) containing 1% t‐butyldimethylchlorosilane (TBDMCS) in dimethylsulfoxide (DMSO) at 30°C showed a maximum reduction in the IR peak at 3400 cm−1 (OH and NH) of 39% and a 100% reduction in the epoxide peak at 904 cm, −1. The moisture absorption was 1.9%, a reduction of 58% compared to the untreated films (ca. 4.5%). The reactions show dependencies on time and temperature and are diffusion controlled. Samples treated with trimethylsilyl isocyanate (TMSI) in DMSO a 70°C showed 72% reduction in the 3400 cm−1 IR peak; DSC thermograms do not show an exothermic energy, suggesting that all epoxide groups reacted. These reactions are primarily dependent on time and temperature. The moisture absorption of TMSI treated samples was 1.0% (75% reduction). Samples were also treated with m‐trifluoromethyl phenyliscyanate (MTFPI). The reduction in the IR peak at 3400 cm−1 was 9%, but the moisture absorption was 2.4%—a reduction of 47%.

The epoxy resin system formed by tetraglycidyl 4,4'-diamino diphenyl methane (TGDDM) and 4,4'-diamino diphenyl sulfone (DDS) was characterized by dynamic mechanical analysis and differential scanning calorimetry. Dynamic mechanical properties of graphite fiber epoxy composite specimens formulated with two different adhesive systems (NARMCO 5208, NARMCO 5209) were determined. The specimens were exposed to varying dose levels of ionizing radiation (0.5 MeV electrons) with a maximum absorbed dose of 10,000 Mrads. Following irradiation, property measurements were made to assess the influence of radiation on the epoxy and composite specimens. The results established that ionizing radiation has a limited effect on the properties of epoxy and composite specimens.

AbstractCrosslinked epoxy resins, tetraglycidyl 4,4′‐diamino diphenyl methane cured with 4,4′‐diamino diphenyl sulfone, were soaked in water at either 25°C or 70°C for varying lengths of time. The infrared spectra and DSC thermograms were obtained for samples that were soaked, or soaked and dried. There was a monotonic decrease in exothermic reaction energy with water content. The glass transition was also lowered, although samples soaked at 70°C showed a leveling in the Tg around 115°C. When the soaked samples were dried, the exothermic reaction energy showed near reversibility for samples soaked at 25°C while the 70°C samples were highly irreversible. IR of the latter samples showed that the 70°C water soaking resulted in reaction of some of the unreacted epoxide groups that remained after the initial cure.