Data bases for LDEF results

The Long Duration Exposure Facility (LDEF) carried 57 experiments and 10,000 specimens for some 200 LDEF experiment investigators. The external surface of LDEF had a large variety of materials exposed to the space environment which were tested preflight, during flight, and post flight. Thermal blankets, optical materials, thermal control paints, aluminum, and composites are among the materials flown. The investigations have produced an abundance of analysis results. One of the responsibilities of the Boeing Support Contract, Materials and Systems Special Investigation Group, is to collate and compile that information into an organized fashion. The databases developed at Boeing to accomplish this task is described

Long Duration Exposure Facility (LDEF) optical systems SIG summary and database

The main objectives of the Long Duration Exposure Facility (LDEF) Optical Systems Special Investigative Group (SIG) Discipline are to develop a database of experimental findings on LDEF optical systems and elements hardware, and provide an optical system overview. Unlike the electrical and mechanical disciplines, the optics effort relies primarily on the testing of hardware at the various principal investigator's laboratories, since minimal testing of optical hardware was done at Boeing. This is because all space-exposed optics hardware are part of other individual experiments. At this time, all optical systems and elements testing by experiment investigator teams is not complete, and in some cases has hardly begun. Most experiment results to date, document observations and measurements that 'show what happened'. Still to come from many principal investigators is a critical analysis to explain 'why it happened' and future design implications. The original optical system related concerns and the lessons learned at a preliminary stage in the Optical Systems Investigations are summarized. The design of the Optical Experiments Database and how to acquire and use the database to review the LDEF results are described

Analysis of systems hardware flown on LDEF. Results of the systems special investigation group

The Long Duration Exposure Facility (LDEF) was retrieved after spending 69 months in low Earth orbit (LEO). LDEF carried a remarkable variety of mechanical, electrical, thermal, and optical systems, subsystems, and components. The Systems Special Investigation Group (Systems SIG) was formed to investigate the effects of the long duration exposure to LEO on systems related hardware and to coordinate and collate all systems analysis of LDEF hardware. Discussed here is the status of the LDEF Systems SIG investigation through the end of 1991

Frequency‐Dependent Moment Tensors of Induced Microearthquakes

Analysis of 984 induced microearthquakes from The Geysers geothermal reservoir in California reveals that the retrieved moment tensors depend on the frequency band of the inverted waveforms. The observed dependence is more significant for the percentages of the double‐couple, compensated linear vector dipole, and isotropic (ISO) components than for the focal mechanisms. The average root‐mean‐square of the moment tensors obtained in different frequency bands is correlated with spectra of ambient noise. The percentages of double‐couple and ISO components tend to decrease and increase with the upper cutoff frequency (fu), respectively. This suggests that shear rupture radiates energy preferentially in a lower frequency band and tensile rupture in a higher frequency band. Events displaying a strong increase of the ISO with fu are confined within the same depth interval as the injection points. This might be related to the strong thermoelastic effects in the vicinity of injection points that promote opening of small cracks adjacent to the main fractures

Analysis of microseismicity framing ML > 2.5 earthquakes at The Geysers geothermal field, California

Preparatory mechanisms accompanying or leading to nucleation of larger earthquakes have been observed at both laboratory and field scales, but conditions favoring the occurrence of observable preparatory processes are still largely unknown. In particular, it remains a matter of debate why some earthquakes occur spontaneously without noticeable precursors as opposed to events that are preceded by an extended failure process. In this study, we have generated new high‐resolution seismicity catalogs framing the occurrence of 20 ML > 2.5 earthquakes at The Geysers geothermal field in California. To this end, a seismicity catalog of the 11 days framing each large event was created. We selected 20 sequences sampling different hypocentral depths and hydraulic conditions within the field. Seismic activity and magnitude frequency distributions displayed by the different earthquake sequences are correlated with their location within the reservoir. Sequences located in the northwestern part of the reservoir show overall increased seismic activity and low b values, while the southeastern part is dominated by decreased seismic activity and higher b values. Periods of high injection coincide with high b values and vice versa. These observations potentially reflect varying differential and mean stresses and damage of the reservoir rocks across the field. About 50% of analyzed sequences exhibit no change in seismicity rate in response to the large main event. However, we find complex waveforms at the onset of the main earthquake, suggesting that small ruptures spontaneously grow into or trigger larger events

Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations

International audienceThe most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ) in northwestern Turkey were the 1999 Izmit (Mw=7.4) and Düzce (Mw=7.1) events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the Düzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal) and 400m (vertical). Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-Düzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the Düzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault

Teat Lesions Resulting from Fungus Infection

In dairy cattle teat lesions are often frustrating. Not only do they interfere with proper milking procedure, but also increase the incidence of mastitis

Membrane behavior, diffusion, and compatibility of a polymerized bentonite for containment barrier applications

2012 Fall.Includes bibliographical references.Conventional (untreated or unmodified) bentonites are commonly used in hydraulic containment barriers to contain liquid flow and contaminant transport, because of the ability of bentonite to swell and achieve low hydraulic conductivity to water, substantial membrane behavior, and low solute diffusion coefficients. However, conventional bentonites also have been shown to be affected adversely by environmental conditions that promote multivalent-for-monovalent cation exchange. In this study, the membrane behavior and diffusive properties of a polyacrylic acid modified bentonite referred to as a bentonite polymer nanocomposite, or BPN, were determined through the simultaneous measurement of membrane efficiency coefficients, ω, and solute diffusion coefficients, D*, during combined multi-stage membrane and diffusion tests using either potassium chloride (KCl) with concentrations ranging from 4.7 mM to 54 mM or calcium chloride (CaCl2) with concentrations ranging from 5 mM to 20 mM. The BPN exhibited substantial membrane behavior when exposed to KCl with values of ω that were higher than those previously reported for conventional (unmodified) bentonite under similar testing conditions. For example, the ω value measured in this study for a BPN specimen contained within a rigid-wall cell and based on circulation of 20 mM KCl was 0.43, whereas that previously reported for a GCL specimen containing a conventional bentonite under similar testing conditions except at a lower porosity (0.74 vs. 0.92) was only 0.30. Also, in contrast to previously reported results for conventional bentonite, the membrane behavior of the BPN was sustained when exposed to 5 mM CaCl2, and values of ω for the BPN were higher than those previously reported for conventional and other modified bentonites. For example, the value of ω for the BPN tested in a rigid-wall cell with 5 mM CaCl2 was 0.95, whereas the ω values for an anionic polymer modified bentonite, known as Hyper clay, and a GCL were 0.13 and 0, respectively. However, exposure of specimens of the BPN to 10 mM CaCl2 for a test conducted in a rigid-wall cell and 20 mM CaCl2 for a test conducted in a flexible-wall cell did ultimately result in complete destruction of the membrane behavior. The destruction of the membrane behavior of the specimen in the rigid-wall test was attributed to short-circuiting along the side-walls of the rigid cell after shrinkage of the BPN specimen, whereas the destruction of the membrane behavior of the specimen in the flexible-wall test correlated with the time to reach steady-state diffusion of calcium (Ca2+). Similar to a previous study involving a conventional bentonite, the diffusive properties of the BPN also were shown to correlate well with the membrane behavior of the BPN, such that that the diffusive solute mass flux decreased as the membrane efficiency of the BPN increased. However, in contrast to previous test results, the steady-state values of D* for K+ and Ca2+ were not only not equal to but also lower than the D* value for Cl- at steady state, although the differences between the D* for K+ or Ca2+ versus that for Cl- diminished with increasing source concentration of KCl or CaCl2, respectively. This inequality between salt cation and salt anion D* values at steady state was attributed to the complicating existence of significant excess Na+ that was initially present within the specimen of BPN prior to testing and contributed to satisfying the requirement for electroneutrality, a contribution that diminished with time as the Na+ diffused out of the specimen. Finally, the use of BPN in soil-bentonite (SB) backfills of vertical cutoff walls was investigated. The hydraulic conductivity, k, to tap water, the consolidation behavior, and the chemical compatibility (Δk) based on permeation with CaCl2 solutions of SB backfills amended with BPN were evaluated and compared with those for a backfill comprised of a conventional bentonite. Although the backfills containing BPN were more sensitive to stress conditions than the backfill containing conventional bentonite, the overall hydraulic performance of a backfill containing 5 % dry BPN was better than that of the backfill containing 5 % dry conventional bentonite by approximately two orders of magnitude in terms of k. Overall, the BPN exhibited improved membrane and diffusion properties relative to conventional and other modified bentonites previously tested under similar conditions. However, the improved membrane behavior of the BPN was ultimately destroyed upon exposure to 10 mM CaCl2 in a rigid-wall cell and 20 mM CaCl2 in a flexible-wall cell. Also, despite an overall lower k of the sand-BPN backfills relative to a backfill comprised of the same sand but a conventional bentonite upon permeation with a 50 mM CaCl2 solution, the chemical resistance of the sand-BPN backfills in terms of changes in k was not any better than that for the sand-conventional bentonite backfill. Thus, the beneficial behavior of the BPN was not unlimited nor without issues, such that any perceived benefit of polymerized bentonites must first be properly characterized on a case-by-case basis prior to use