Physical models of seismic attenuation measurements in the lab

Classical continuum mechanics with dissipation allows the description of observed creep and phase-lag attenuation effects in solids. The frequency-dependent Q or time dependent moduli, compliances, or creep functions which are often used to describe such observations may be empirical characteristics reflecting not only the properties of the materials but also the dimensions and shapes of the samples. The theoretical paradigm employed in this study is strongly different from the conventional, Q-based (often called “viscoelastic”) model. Instead of a single, but arbitrarily frequency-dependent Q attributed to a solid, a number of specific physical parameters of energy-dissipation mechanisms (such as viscosity or thermoelasticity) are considered. The model is based on first physical principles and focuses on inverting for the intrinsic (time- and frequency-independent) properties of the material. The observed frequency-dependent Q’s or time-dependent creep (“memory”) functions are generally explained by the non-linearity of solid viscosity, which can be described by selecting the Lagrangian dissipation function. This fundamental conclusion was suggested as long ago as by Knopoff (1964) but appeared to be little developed since. I only consider a specific, power-law form of this function, and show that it is consistent with the strain-rate dependence of effective viscosity used in geodynamics. Power-law nonlinearity of solid viscosity combined with thermoelastic effects allows quantitatively predicting all key observations, such as creep, stress-strain phase lags in torsional and longitudinal oscillations, and broadening of spectral amplitude peaks near resonance. Analytical and numerical modeling of longitudinal-oscillation phase-lag measurements in Plexiglas cylinders suggest the value of rheological exponent approximately 0.56. This is interpreted as a “near-dry” internal friction in solids. The physical models of internal friction also suggest methods for inverting for the in situ dissipation properties of materials. Finally, the new models suggest several ways for enhancing the theoretical knowledge about the physical properties of Earth materials

Professional Advanced Research and Analysis

Reported here is a summary of studies examining some problems in an energy conversion system. Regenerative fuel cell systems have been suggested for future manned space missions, but to meet the needed specific power requirements substantial improvements in the state-of-the-art technologies are needed. Similar improvements are needed, with emphasis on cost reduction in addition to higher conversion efficiency, for fuel cell systems that have potential for terrestrial applications. Polymer electrolyte membrane (PEM) fuel cells have been identified as promising candidates for development that would lead to the desired cost reduction and increased efficiency

Professional Advanced Research and Analysis

Reported here is a summary of studies examining some problems in an energy conversion system. Regenerative fuel cell systems have been suggested for future manned space missions, but to meet the needed specific power requirements substantial improvements in the state-of-the-art technologies are needed. Similar improvements are needed, with emphasis on cost reduction in addition to higher conversion efficiency, for fuel cell systems that have potential for terrestrial applications. Polymer Electrolyte Membrane (PEM) fuel cells have been identified as promising candidates for development that would lead to the desired cost reduction and increased efficiency

Space power systems technology

Reported here is a series of studies which examine several potential catalysts and electrodes for some fuel cell systems, some materials for space applications, and mathematical modeling and performance predictions for some solid oxide fuel cells and electrolyzers. The fuel cell systems have a potential for terrestrial applications in addition to solar energy conversion in space applications. Catalysts and electrodes for phosphoric acid fuel cell systems and for polymer electrolyte membrane (PEM) fuel cell and electrolyzer systems were examined

The history of forage cultivar testing in Saskatchewan

Non-Peer Reviewe

Influence of balanced application of N, P and S fertilizers on forage yield and quality of timothy in northeastern Saskatchewan

Non-Peer Reviewe

Standardizing vegetative propagation as a tool for polycross mating of ascending purple milkvetch (Astragalus adsurgens Pall.)

Non-Peer ReviewedThis article highlights the efficacy of plant growth regulators and nutrient solutions on root development and survival of ascending purple milkvetch (APMV) cuttings. Three auxin-like growth regulators and Hoagland solutions were used as root inducing agents. The cuttings were planted in sand medium that allowed evaluation of rooting effectiveness. The study showed that up to 100% establishment of APMV cuttings can be achieved with the application of half-strength modified Hoagland (MHL) solution and plant growth regulators such as indole-3-acetic acid (IAA), 1-naphthaleneacetic acid (NAA) and indole-3-butyric acid (IBA) at 100mg L-1 strength. To the best knowledge of the authors, this is first time documentation of the vegetative propagation of APMV

Tumbleweeds and airborne gravitational noise sources for LIGO

Gravitational-wave detectors are sensitive not only to astrophysical gravitational waves, but also to the fluctuating Newtonian gravitational forces of moving masses in the ground and air around the detector. This paper studies the gravitational effects of density perturbations in the atmosphere, and from massive airborne objects near the detector. These effects were previously considered by Saulson; in this paper I revisit these phenomena, considering transient atmospheric shocks, and the effects of sound waves or objects colliding with the ground or buildings around the test masses. I also consider temperature perturbations advected past the detector as a source of gravitational noise. I find that the gravitational noise background is below the expected noise floor even of advanced interferometric detectors, although only by an order of magnitude for temperature perturbations carried along turbulent streamlines. I also find that transient shockwaves in the atmosphere could potentially produce large spurious signals, with signal-to-noise ratios in the hundreds in an advanced interferometric detector. These signals could be vetoed by means of acoustic sensors outside of the buildings. Massive wind-borne objects such as tumbleweeds could also produce gravitational signals with signal-to-noise ratios in the hundreds if they collide with the interferometer buildings, so it may be necessary to build fences preventing such objects from approaching within about 30m of the test masses.Comment: 15 pages, 10 PostScript figures, uses REVTeX4.cls and epsfig.st