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The space exposure age of the unique Portales Valley H-chondrite is approx. 40-45 Myr. The 39 Ar-40 Ar ages of two samples are 4.477 +/- 0.016 and 4.46 +/- 0.02 Ga and show no evidence of more recent disturbance, in contrast to previous radiometric determinations Additional information is contained in the original extended abstract..
A precise Rb-Sr age of 174+/-3 Ma was determined for EET79001B. A Sm-Nd age of 169+/-23 Ma also was determined, but the Nd isotopic systematics are disturbed. This disturbance is attributed to incomplete isotopic equilibration during petrogenesis. Additional information is contained in the original extended abstract.
The funds in this grant were used to support costs for observing and data analysis over the past two years. During this time I have been obtaining low-resolution (R-2,000) spectra for about 5,000 solar-type stars (late-F and G dwarfs) that are within 60 parsecs of the Sun. The sample was defined with results from the Hipparcos mission, and the spectra were obtained at Kitt Peak National Observatory, using the Coude Feed telescope, and at Cerro Tololo Interamerican Observatory, using their 1.5 m telescopes for stars below -40 declination. Nearly all the observed spectra have been reduced and analyzed. What is determined is R-prime, an index of the chromospheric emission in the cores of the Ca II H and K lines relative to the nearby continuum, and normalized for the color of the star. Chromospheric emission arises from magnetic activity on the star, and that is turn is driven by rotation. Solar-type stars spin down as they age, and so they get weaker in their chromospheric emission as well. Thus this R-prime index can be used to estimate the ages of stars. A few stars remain to be observed at Kitt Peak, and follow-up high-resolution spectra are being obtained of the most active stars seen, but the majority of the starting sample have been completed. The spectra obtained are also being analyzed to yield an index of overall metallicity for each star, and this will be used to study Galactic evolution questions. These metallicities will form the first large dataset of high and consistent quality. Initial results from this work have been used to define targets for a SIRTF Legacy program, for stars to study for planetary transits, and for SETI efforts. Because of the large number of stars involved, most of the data will be made available on the web, although some specific papers about the results are in preparation. The web database is being constructed.
Integrins specifically recognize and bind extracellular matrix components, providing physical anchor points and functional setpoints. Focal adhesion complexes, containing integrin and cytoskeletal proteins, are potential mechanoreceptors, poised to distribute applied forces through the cytoskeleton. Pursuing the hypothesis that cells both perceive and respond to external force, we applied a stretch/relaxation regimen to normal human fetal and aged dermal fibroblast monolayers cultured on flexible membranes. The frequency and magnitude of the applied force is precisely controlled by the Flexercell Unit(Trademark). A protocol of stretch (20% elongation of the monolayer) at a frequency of 6 cycles/min caused a progressive change from a randomly distributed pattern of cells to a symmetric, radial distribution with cells aligned parallel to the applied force. We have coined the term 'orienteering' as the process of active alignment of cells in response to applied force. Cytochalasin D was added in graded doses to investigate the role of the actin cytoskeleton in force perception and transmission. A clear dose response was found; at high concentrations orienteering was abolished; and the drug's impact was reversible. The two cell strains used were similar in their alignment behavior and in their responses to cytochalasin D. Orienteering was influenced by cell density, and the cell strains studied differed in this respect. Fetal cells, unlike their aged counterparts, failed to orient at high cell density. In both cell strains, mid-density cultures aligned rapidly and sparse cultures lagged. These results indicate that both cell-cell adhesion and cytoskeleton integrity are critical in mediating the orienteering response. Differences between these two cell strains may relate to their expression of extracellular matrix molecules (fibronectin, collagen type 1) integrins and their relative binding affinities.
I-Xe and Pb-Pb ages of individual Richardton chondrules and different mineral phases were compared in order to test the absolute I-Xe age normalization. Additional information is contained in the original extended abstract.
The rodent bone response to spaceflight may be influenced by a multitude of actors including flight duration, strain, and housing. Review of bone formation rates during spaceflight suggests that age may also play a role in the response. Weanling rats show fewer bone changes than older rats. To determine if the long bones of weanling rats were insensitive to weight-bearing, a hindlimb unloading experiment was conducted simultaneously with a 9d shuttle flight in 34d old group-housed male rats. All animals were injected with bone markers 7d and 1d before flight and euthanized at landing, 24hr, and 72hr following recovery. If no differences in body weight, bone length, or bone formation at the tibiofibular junction were noted at the different time points, data were combined for each group. No significant differences in body weight were found at any time period among the groups. The humerus, tibia, and femur elongated significantly during the flight period with no difference in lengths between groups at the end of the flight period. The group-housed flight rats showed no change in cortical bone formation rate compared to preflight values, flight controls, or vivarium controls. However, the hindlimb unloading group showed a significant 30% decrease in bone formation rate compared to all other groups. Individually-housed 38d old animals flown for 14d showed approx. 10% suppression of cortical growth. We speculate that the mechanical threshold required for cross-sectional bone growth is reached in group-house weanling rats during spaceflight, perhaps, through physical interactions, and that the weanling animals are sensitive to loading. However, the threshold is not fully reached in either singly-housed flight or hindlimb unloaded weanling rats. Older singly-housed flight animals appear to show equal or greater bone changes compared to hindlimb unloaded rats. We conclude that age, flight duration, strain, and housing have important roles in rodent skeletal responses to spaceflight.
Lunar ferroan anorthosites (FANs) are relics of an ancient, primary feldspathic crust that is widely believed to have crystallized from a global magma ocean. Compositions and ages of FANs provide fundamental information about the origin and magmatic evolution of the Moon, while the petrology and thermal history of lunar FANs illustrate the structure and impact history of the lunar crust. Here we report petrologic, geochemical, and isotopic (Nd-Sr-Ar) studies of a ferroan noritic anorthosite clast from lunar breccia 67215 to improve our understanding of the composition, age, and thermal history of the Moon.
This viewgraph report presents an examination of the fracture toughness of aluminum-lithium alloy C458 for use in cryotank structures. Topics cover include: cryogenics, alloy composition, strengthing precipitates in C458, cryogenic fracture toughness improvements, design of experiments for measuring aging optimization of C458 plate and effects of aging of properties of C458 plate.
We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M3l), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at m(sub v) = 30.7 mag. The CMD, constructed from approx. 3 x 10(exp 5) stars, reaches more than 1.5 mag fainter than the old main-sequence turnoff. Our analysis is based on direct comparisons to ACS observations of four globular clusters through the same filters, as well as chi square fitting to a finely-spaced grid of calibrated stellar-population models. We find that the M31 halo contains a major (approx. 30% by mass) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] greater than -0.5) population, as well as a significant globular-cluster age (11-13.5 Gyr) metal-poor population. These findings support the idea that galaxy mergers played an important role in the formation of the M31 halo.
The introduction of new, advanced composite materials into aviation systems requires a thorough understanding of the long term effects of combined thermal and mechanical loading upon those materials. Analytical methods investigating the effects of intense thermal heating combined with mechanical loading have been investigated. The damage mechanisms and fatigue lives were dependent on test parameters as well as stress levels. Castelli, et al. identified matrix dominated failure modes for out-of-phase cycling and fiber dominated damage modes for in-phase cycling. In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. To help evaluate the effect of aging, a suitably designed Lamb wave measurement system is being used to obtain bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system works by exciting an antisymmetric Lamb wave and calculating the velocity at each frequency from the known transducer separation and the measured time-of-flight. The same peak in the waveforms received at various distances is used to measure the time difference between the signals. The velocity measurements are accurate and repeatable to within 1% resulting in reconstructed stiffness values repeatable to within 4%. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. A mechanical scanner is used to move the sensors over the surface to map the time-of-flight, velocity, or stiffnesses of the entire specimen. Access to only one side of the material is required and no immersion or couplants are required because the sensors are dry coupled to the surface of the plate. In this study, the elastic stiffnesses D(sub 11), D(sub 22), A(sub 44), and A(sub 55) as well as time-of-flight measurements for composite samples that have undergone combined thermal and mechanical aging for a duration of 10,000 hours are reported.
MOLA data have revealed a large population of 'Quasi-Circular Depressions' (QCDs) with little or no visible expression in image data. These likely buried impact basins have important implications for the age of the lowland crust, how that compares with original highland crust, and when and how the crustal dichotomy may have formed. The buried lowlands are of Early Noachian age, likely slightly younger than the buried highlands but older than the exposed (visible) highland surface. A depopulation of large visible basins at diameters 800 to 1300 km suggests some global scale event early in martian history, maybe related to the formation of the lowlands and/or the development of Tharsis. A suggested early disappearance of the global magnetic field can be placed within a temporal sequence of formation of the very largest impact basins. The global field appears to have disappeared at about the time the lowlands formed. It seems likely the topographic crustal dichotomy was produced very early in martian history by processes which operated very quickly. This and the preservation of large relic impact basins in the northern hemisphere, which themselves can account for the lowland topography, suggest that large impacts played the major role in the origin Mars fundamental crustal feature.
MOLA data have revealed a large population of "Quasi-Circular Depressions" (QCDs) with little or no visible expression in image data. These likely buried impact basins have important implications for the age of the lowland crust, how that compares with original highland crust, and when and how the crustal dichotomy may have formed. The buried lowlands are of Early Noachian age, likely slightly younger than the buried highlands but older than the exposed (visible) highland surface. A depopulation of large visible basins at diameters 800 to 1300 km suggests some global scale event early in martian history, maybe related to the formation of the lowlands andor the development of Tharsis. A suggested early disappearance of the global magnetic field can be placed within a temporal sequence of formation of the very largest impact basins. The global field appears to have disappeared at about the time the lowlands formed. It seems likely the topographic crustal dichotomy was produced very early in martian history by processes which operated very quickly. This and the preservation of large relic impact basins in the north- em hemisphere, which themselves can account for the lowland topography, suggest that large impacts played the major role in the origin Mars fundamental crustal feature.
Total alpha-A crystallin was purified from young versus old lens, followed by digestion with cyanogen bromide. Laser desorption mass spectrometry of the C-terminal fragment demonstrated age-dependent loss of one and five amino acids from the C-terminus of alpha-A crystallin from both bovine and human lens. These results demonstrate specific peptide bonds of alpha-A crystallin are cleaved during the aging process of the normal lens. The C-terminal region is cleaved in two places between the two hydroxyl-containing amino acids present in the sequence -P-S(T)-S-.
The behavior of a physiological system which, after displacement, returns by homeostatic mechanisms to its original condition can be described by a simple differential equation in which the "recovery time" is a parameter. Two such systems, which influence one another, can be linked mathematically by the use of "coupling" or "feedback" coefficients. These concepts are the basis for many mathematical models of physiological behavior, and we describe the general nature of such models. Next, we introduce the concept of a "fatal limit" for the displacement of a physiological system, and show how measures of such limits can be included in mathematical models. We show how the numerical values of such limits depend on the values of other system parameters, i.e., recovery times and coupling coefficients, and suggest ways of measuring all these parameters experimentally, for example by monitoring changes induced by X-irradiation. Next, we discuss age-related changes in these parameters, and show how the parameters of mortality statistics, such as the famous Gompertz parameters, can be derived from experimentally measurable changes. Concepts of onset-of-aging, critical or fatal limits, equilibrium value (homeostasis), recovery times and coupling constants are involved. Illustrations are given using published data from mouse and rat populations. We believe that this method of deriving survival patterns from model that is experimentally testable is unique.
Aging wiring has become a critical issue to the aerospace and aircraft industries due to Shuttle and aircraft incidents. The problem is that over time the insulation on wire becomes brittle and cracks. This exposes the underlying conductive wire to the potential for short circuits and fire. Popular methods of monitoring aging wire problems focuses on applying electrical sensing techniques that are sensitive to the conductor's condition, but not very sensitive to the wire insulation's condition. Measurement of wire insulation stiffness and ultrasonic properties by ultrasonic guided waves is being examined. Experimental measurements showed that the lowest order extensional mode could be sensitive to stiffness changes in the wire insulation. To test this theory conventional wire samples were heat damaged in an oven, in a range of heating conditions. The samples were 12, 16, and 20 gauge and the heat damage introduced material changes in the wire insulation that made the originally flexible insulation brittle and darker in color. Results showed that extensional mode phase velocity increased for the samples that were exposed to heat for longer duration.
Regional differences in crater retention ages (CRAs) across the Mars dichotomy boundary are compared to the global highland-lowland age difference previously determined from visible and buried impact basins based on MOLA-derived Quasi-Circular Depressions (QCDs). Here Western Arabia (WA) is compared with Ismenius Lacus (IL). We find the buried lowlands in the two regions have total CRAs essentially identical to the global average. Even more intriguing, the WA cratered terrain appears to have a CRA like that of the adjacent buried lowlands,
A high-spatial-resolution, multi-wavelength observation by the Galileo NIMS instrument has been analysed to determine the temperature and area distribution of a large portion of the ionian volcano Loki Patera. The temperatures of the cooler components from a two-temperature fit to the data can be used to determine ages of the surface. The age of the floor along a profile across the floor of the caldera ranges from ~10 to ~80 days. This puts the start of the resurfacing in July/early August 2001, yielding a resurfacing rate of approximately 1 km/day, with the new lava spreading from the SW corner of the caldera in a NE direction. This rate is consistent with resurfacing by foundering of the crust on a lava lake. However,the temperature distribution may also result from the emplacement of flows. Implied crust thicknesses (derived using a lava cooling model) range from 2.6 to 0.9 m.
A method of predicting aging of polymers operates by heating a polymer in the outdoors to an elevated temperature until a change of property is induced. The test is conducted at a plurality of temperatures to establish a linear Arrhenius plot which is extrapolated to predict the induction period for failure of the polymer at ambient temperature. An Outdoor Photo Thermal Aging Reactor (OPTAR) is also described including a heatable platen for receiving a sheet of polymer, means to heat the platen and switching means such as a photoelectric switch for turning off the heater during dark periods.