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The toxicity of the pyrolysis gases from some samples of polyurethane flexible foams appears to have decreased with age, while other samples seem to exhibit no significant change with age in this respect. The changes observed were greater than could be accounted for by variations in the material, or test variations or artifacts.
The Rb-Sr data reported for Apollo 17 mare basalts and for KREEP basalt 15386 is used to determine mineral isochrons. The weighted average age of four Apollo 17 basalts is 3.76 + or - 0.06 AE, while the age determined for 15386 is 3.94 + or - 0.04 AE. The isotopic data for the Apollo 17 basalts are discussed in the context of Sm and Eu data for the same samples. The Sr-isotopic data are fit best by a three-stage model evolution involving evolution of Sr-87/Sr-86 in an environment with Rb/Sr greater than in the basalts, production of mare basalt source regions of lower but variable Rb/Sr sometime in the interval 4.6 to 3.75 AE ago, and extraction of lavas from these sources 3.75 AE ago. Other possibilities are considered.
Exposure age information on lunar rocks and regolith turnover rates are correlated. If plotted in a cumulative fashion, the distribution of spallogenic noble-gas exposure ages is remarkably parallel to the rate at which various fractions of the regolith surface are cratered and/or excavated. It appears that the rate at which lunar rocks are excavated from within the regolith is strongly controlled by the impact environment. Some suggestions for future refinement of regolith dynamics are presented.
The optic nerves of C57BL/6J mice ranging from 3 to 30 months were examined by electron microscopy. At all ages investigated, optic nerve axons contained enlarged mitochondria with abnormal cristae. With increasing age, a large number of necrotic axons were observed and were in the process of being phagocytized. The abnormal mitochondria may represent preliminary changes that eventually lead to necrosis of the axon.
Topographic profiles and depth-diameter ratios from the crater Camelot and craters of the central cluster in the Apollo 17 landing area suggest that these craters are of the same age. Therefore, layers that can be recognized in the deep-drill core and that can be identified as ejecta deposits from Camelot or from the cluster craters should yield similar emplacement ages.
Age related cracks in the graphite phenolic linear and/or ATJ insert in several nine year old Altair IIA solid rocket nozzles were investigated and determined to be limited to a single lot of nozzles. Test results and photomicrographs of fracture surfaces are presented which establish that in the discrepant nozzles the bond between the graphite fibers and the phenolic resin was tenacious, resulting in a nearly homogenous behavior. These materials are shown to have a relatively weak resin - fiber bond and behave more like a released fiber composite. Lot qualification fiber directional tensile strength and the chemical composition of the two materials were comparable, indicating that standard acceptance testing could not have differentiated between the desirable and undesirable material. Review of processing records failed to reveal any cause for the difference in the aging characteristics.
A Pb-Pb internal isochron for the Barwell L5-6 chondrite yields an age of 4.530 plus or minus 0.005 billion years, using the measured U-238/U-235 ratio of 135.24 plus or minus .17. If the terrestrial U isotope composition is used, an age of 4.559 billion years is obtained. The Pb isotopic composition is distinctly different from that of a terrestrial contaminant found in the fusion crust of the Barwell stone. When the U-Th-Pb data are plotted on the concordia diagram, the data define a line that intersects the concordia curve at approximately 4.53 and 0 billion years, and nearly all of the data plot above the concordia curve, regardless of the initial Pb correction. This discordancy and the Pb isotopic composition of the triolite are attributed to a recent reequilibration of Pb and not to terrestrial contamination.
Model low-mass globular-cluster stars were evolved with their helium allowed to diffuse under the influence of gravity, thermal diffusion, and concentration gradient. The evolution tended to speed up. Also, the turnoff point moved toward lower luminosity and slightly lower surface temperature. If the luminosity at turnoff is used as the sole criterion for determining the age of a globular cluster, the inferred ages of such clusters are reduced by about 22% from starting values in the vicinity of 15 billion years.
It is shown that previous astrophysical methods of dating the young pulsar in Vela, PSR 0833-45, have effectively given upper limits to the true age. A value of 5000-8000 yr is found here to be not inconsistent with all available observational data. The historical significance of such a young age is briefly discussed.
The paper deals with a study investigating the nature and rates of the hydrolic aging of a wide-band instrumentation magnetic recording tape which employs oxide and backcoat binders made of a polyester urethane elastomer. It was found that the primary mechanism of tape aging and degradation resulted from hydrolysis of its polyester urethane binder.
Polyurethane-modified high impact anaerobic adhesives have been chosen for a bonding application where impact cushion is critical. These adhesives meet all the requirements for high rate production and automatic assembly techniques. With aluminum adherends, one selected adhesive cured at room temperature with the recommended activator retained sixty percent of its original impact strength after twenty-six week aging at 100 C. The impact strength aging, the thermogravimetric analysis results, the outgassing data, and other observations made in this work indicate that the adhesives cured by simple heating give a more durable bond than that cured with an activator at room temperature.
Calibration of the production rate of the Ne-21 nuclide was accomplished by 4 methods based on (Al-26)-age, (Mn-53)-age, Kr-81/Kr-83, and Na-22/Ne-22. These production rates are normalized to a shielding parameter ratio Ne-22/Ne-21 = 1.11 and to the chemical composition of L chondrites; a value of P(21)(1.11) = 0.31 is suggested, and a production rate equation derived in terms of the 'F' parameters for L, LL, and H chondrites. The Al-26 half-life measurements are considered to evaluate the effects resulting from preirradiation of meteorites and to examine the data on the constancy of the cosmic ray flux in the light of current astronomical observations.
Lu-Hf total-rock data for the Amitsoq gneisses of West Greenland yield an age of 3.55 + or - 0.22 billion years, based on the decay constant for Lu-176 of 1.96 x 10 to the -11th/year, and an initial Hf-176/Hf-177 ratio of 0.280482 + or - 33. The result is in good agreement with Rb-Sr total-rock and U-Pb zircon ages. In spite of severe metamorphism of the area at 2.9 billion years, zircons from two of the samples have remained on the total-rock line, and define points close to the initial Hf ratio. The initial Hf-176/Hf-177 lies close to a chondritic Hf isotopic evolution curve from 4.55 billion years to present. This is consistent with the igneous precursors to the Amitsoq gneisses having been derived from the mantle at or shortly before 3.6 billion years. Anomalous relationships between Hf concentration and the Lu-176/Hf-177 ratio may suggest that trace element abundances in the Amitsoq gneisses are partly controlled by processes related to metamorphism.
Chemical, trace element, and isotopic compositions of tektites are consistent with production by melting of sediments derived from the old terrestrial continental crust. Each tektite group is characterized by a uniform Nd model age, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites. Sr model ages are variable within each group, reflecting Rb-Sr fractionation, and, in the favorable limit of very high Rb/Sr ratios, approach the time of sedimentation of the parent material which melted to form the tektites. Unlike tektites, which are dense homogeneous objects, sanidine spherules are porous, fine grained inhomogeneous objects. The leaching experiment employed by the present study shows that the sanidine spherules could have been formed by an oceanic impact involving basaltic crust and overlying sediments or seawater.
The similarity of detrimental effects of normal aging and of exposure to space weightlessness is discussed. The effects include: the reduction in cardiac output, increase in blood pressure, decrease in respiratory vital capacity, decrease in lean body weight and muscle mass, collagen and fat infiltration of muscle, bone demineralization, and a decrease in urinary excretion of total 17-hydroxicorticosteroids. It is also noted that dispite the accelerated aging of organisms, if animals or human subjects were to spend their entire lives in weightlessness, their lifespans might be significantly increased because of a reduction in metabolic rate. Experimental results are cited.
Ultraviolet data obtained with the IUE spacecraft are presented for a dozen solar-type stars in the field. The stars are of spectral type F6 V - G1 V; on the basis of their high Li content, they range in age from 0.1 to 2.8 Gyr. The evolution of transition regions and chromospheric emission with stellar age is studied along with the surface distribution of magnetically active regions as revealed by rotational modulation of UV emission line fluxes.
Annealing in nitrogen below the glass transition temperature T(g) is found to affect the matrix-dominated physical properties of postcured, (+ and -45)2s specimens of Thornel 300 carbon fiber/Fiberite 934 epoxy composite as well as neat Fiberite 934 epoxy resin. The damping behavior, stress-relaxation rate and enthalpic state of the matrix material are found to decrease as functions of annealing time. The time-dependent change in physical properties is explained on the basis of free-volume collapse related to the physical aging of the nonequilibrium glassy network of epoxy. Such physical aging in network epoxy has been demonstrated to be thermoreversible through the monitoring of its kinetics by differential scanning calorimetry, stress relaxation tests, and dynamic mechanical analysis.
Argon analyses were performed for five coarse-grained, Ca-Al-rich inclusions from the Allende meteorite. The samples were neutron-irradiated in evacuated ampuoles, and the Ar in the ampuoles and in the samples was analyzed. Up to 60 percent of Ar-39 was lost from the samples into the ampuoles due to recoil during neutron-irradiation; this loss resulted in substantial increases in the apparent Ar-40-Ar-39 ages of the samples. Substantial amounts of trapped Ar-36 of unknown origin were found in the inclusions, and the presence of trapped Ar-40 could not be ruled out. It is inferred that the interpretation of high Ar-40/K-40 ratios as very high (presolar) ages may be subject to question. It is noted that the degrees of Ar-39 recoil loss reported is comparable to recoil loss in terrestrial rocks and cannot be attributed to KCl contamination of the samples.