Theoretical backgrounds of durability analysis by normalized equivalent stress functionals

Generalized durability diagrams and their properties are considered for a material under a multiaxial loading given by an arbitrary function of time. Material strength and durability under such loading are described in terms of durability, safety factor and normalized equivalent stress. Relations between these functionals are analysed. We discuss some material properties including time and load stability, self-degradation (ageing), and monotonic damaging. Phenomenological strength conditions are presented in terms of the normalized equivalent stress. It is shown that the damage based durability analysis is reduced to a particular case of such strength conditions. Examples of the reduction are presented for some known durability models. The approach is applicable to the strength and durability description at creep and impact loading and their combination

Publications of the space physiology and countermeasures program, Musculoskeletal Discipline: 1980-1990

A 10-year cumulative bibliography of publications resulting from research supported by the musculoskeletal discipline of the space physiology and countermeasures program of NASA's Life Sciences Division is provided. Primary subjects are bone, mineral, and connective tissue, and muscle. General physiology references are also included. Principal investigators whose research tasks resulted in publication are identified by asterisk. Publications are identified by a record number corresponding with their entry in the life sciences bibliographic database, maintained by the George Washington University

Linear polarization of light by two wheat canopies measured at many view angles

The linear polarization and reflection of visible light by wheat as a function of sun-view directions, crop development stage, and wavelength were examined. Two-hundred spectra were taken continuously in wave-lengths from 0.45 to 0.72 Micron in 33 view directions using an Exotech model 20C spectroradiometer six meters above two wheat canopies in the boot and fully headed maturity stages. The analysis results show that the amount of linearly polarized light from the wheat canopies is greatest in the blue spectral region and decreases gradually with increasing wavelength. The results also show that the linearly polarized light from the canopies is generally greatest in the azimuth direction of the Sun and tends toward zero as the view direction tends toward the direction of the hot spot or anti-solar point. It is demonstrated that the single, angle of incidence of sunlight on the leaf, explains almost all of the variation of the amount of polarized light with Sun-view direction

Simulated response of a multispectral scanner over wheat as a function of wavelength and view/illumination direction

The reflectance response with view angle of wheat, was analyzed. The analyses, which assumes there are no atmospheric effects, and otherwise simulates the response of a multispectral scanner, is based upon spectra taken continuously in wavelength from 0.45 to 2.4 micrometers at more than 1200 view/illumination directions using an Exotech model 20C spectra radiometer. Data were acquired six meters above four wheat canopies, each at a different growth stage. The analysis shows that the canopy reflective response is a pronounced function of illumination angle, scanner view angle and wavelength. The variation is greater at low solar elevations compared to high solar elevations

Coverage-dependent adsorption sites for K/Cu(001) and Cs/Cu(001) determined by surface X-ray diffraction

Surface X-ray diffraction has been used to analyze in situ the room-temperature adsorption behaviour and the structure of K and Cs on Cu(100) at submonolayer coverages. Adsorption of K takes place in fourfold hollow sites up to coverages of about 0.25 monolayers (ML), where 1 ML corresponds to 1.53 × 1015 atoms/cm2. At higher coverages the formation of a quasi-hexagonal incommensurate adlayer is observed. In contrast, for Cs adsorption we observe from the very beginning the formation of the quasi-hexagonal structure up to the completion of the adlayer at about 0.30 ML. For K adsorption in the hollow sites we determine an adsorption height, d = 2.25(15) Å, corresponding to an effective K radius of reff = 1.6(1) Å close to the ionic radius of 1.33 Å. We do not observe a change in the effective radius as a function of coverage. For the quasi-hexagonal Cs structure we find an (average) adsorption height d = 2.94 Å corresponding to an effective radius of reff = 2.18 and 1.93 Å, for the limiting ca hollow- and bridge-site adsorption, respectively. The analysis of the superlattice reflections corresponding to the quasi-hexagonal incommensurate structures indicated that the K adlayer is strongly modulated. The first Fourier component of the substrate-induced modulation was determined to u01 = 1.29(3) Å. In contrast, for Cs/Cu(001) static modulation is much less important (u01 0.2 Å). Variation of the Cs adlayer density by changing the substrate temperature allows continuous expansion and contraction of the adsorbate unit cell. No commensurate-incommensurate transition has been observed

Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of $^{85}$Rb and $^{87}$Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers