An experimental correlation of the nonreactive properties of injection schemes and combustion effects in a liquid-propellant rocket engine. Part II. Instrumentation, experimental apparatus, and experimental techniques

Apparatus, techniques, and instrumentation for experimental correlation of nonreactive injection schemes and combustion effects in liquid propellant rocket engin

Integral throat entrance development, qualification and production for the Antares 3 nozzle

Although design analyses of a G-90 graphite integral throat entrance for the Antares 3 solid rocket motor nozzle indicated acceptable margins of safety, the nozzle throat insert suffered a thermostructural failure during the first development firing. Subsequent re-analysis using properties measured on material from the same billet as the nozzle throat insert showed negative margins. Carbon-carbon was investigated and found to result in large positive margins of safety. The G-90 graphite was replaced by SAI fast processed 4-D material which uses Hercules HM 10000 fiber as the reinforcement. Its construction allows powder filling of the interstices after preform fabrication which accelerates the densification process. Allied 15V coal tar pitch is then used to complete densification. The properties were extensively characterized on this material and six nozzles were subjected to demonstration, development and qualification firings

Rayleigh wave dispersion measurements reveal low-velocity zones beneath the new crust in the Gulf of California

Rayleigh wave tomography provides images of the shallow mantle shear wave velocity structure beneath the Gulf of California. Low-velocity zones (LVZs) are found on axis between 26 and 50 km depth beneath the Guaymas Basin but mostly off axis under the other rift basins, with the largest feature underlying the Ballenas Transform Fault. We interpret the broadly distributed LVZs as regions of partial melting in a solid mantle matrix. The pathway for melt migration and focusing is more complex than an axis-centered source aligned above a deeper region of mantle melt and likely reflects the magmatic evolution of rift segments. We also consider the existence of solid lower continental crust in the Gulf north of the Guaymas Basin, where the association of the LVZs with asthenospheric upwelling suggests lateral flow assisted by a heat source. These results provide key constraints for numerical models of mantle upwelling and melt focusing in this young oblique rift

Seismic structure beneath the Gulf of California: a contribution from group velocity measurements

Rayleigh wave group velocity dispersion measurements from local and regional earthquakes are used to interpret the lithospheric structure in the Gulf of California region. We compute group velocity maps for Rayleigh waves from 10 to 150 s using earthquakes recorded by broad-band stations of the Network of Autonomously Recording Seismographs in Baja California and Mexico mainland, UNM in Mexico, BOR, DPP and GOR in southern California and TUC in Arizona. The study area is gridded in 120 longitude cells by 180 latitude cells, with an equal spacing of 10 × 10 km. Assuming that each gridpoint is laterally homogeneous, for each period the tomographic maps are inverted to produce a 3-D lithospheric shear wave velocity model for the region. Near the Gulf of California rift axis, we found three prominent low shear wave velocity regions, which are associated with mantle upwelling near the Cerro Prieto volcanic field, the Ballenas Transform Fault and the East Pacific Rise. Upwelling of the mantle at lithospheric and asthenospheric depths characterizes most of the Gulf. This more detailed finding is new when compared to previous surface wave studies in the region. A low-velocity zone in northcentral Baja at ∼28ºN which extends east–south–eastwards is interpreted as an asthenospheric window. In addition, we also identify a well-defined high-velocity zone in the upper mantle beneath central-western Baja California, which correlates with the previously interpreted location of the stalled Guadalupe and Magdalena microplates. We interpret locations of the fossil slab and slab window in light of the distribution of unique post-subduction volcanic rocks in the Gulf of California and Baja California. We also observe a high-velocity anomaly at 50-km depth extending down to ∼130 km near the southwestern Baja coastline and beneath Baja, which may represent another remnant of the Farallon slab

Matching Conditions in Atomistic-Continuum Modeling of Materials

A new class of matching condition between the atomistic and continuum regions is presented for the multi-scale modeling of crystals. They ensure the accurate passage of large scale information between the atomistic and continuum regions and at the same time minimize the reflection of phonons at the interface. These matching conditions can be made adaptive if we choose appropriate weight functions. Applications to dislocation dynamics and friction between two-dimensional atomically flat crystal surfaces are described.Comment: 6 pages, 4 figure

Juba / music by R. Nathaniel Dett

Cover: description reads dance from the suite In the Bottoms for piano, As played by the world renowned pianist Percy Grainger; Publisher: Clayton F. Summy Co. (Chicago)https://egrove.olemiss.edu/sharris_c/1055/thumbnail.jp

S wave velocity structure below central Mexico using high-resolution surface wave tomography

Shear wave velocity of the crust below central Mexico is estimated using surface wave dispersion measurements from regional earthquakes recorded on a dense, 500 km long linear seismic network. Vertical components of regional records from 90 well-located earthquakes were used to compute Rayleigh-wave group-velocity dispersion curves. A tomographic inversion, with high resolution in a zone close to the array, obtained for periods between 5 and 50 s reveals significant differences relative to a reference model, especially at larger periods (>30 s). A 2-D S wave velocity model is obtained from the inversion of local dispersion curves that were reconstructed from the tomographic solutions. The results show large differences, especially in the lower crust, among back-arc, volcanic arc, and fore-arc regions; they also show a well-resolved low-velocity zone just below the active part of the Trans Mexican Volcanic Belt (TMVB) suggesting the presence of a mantle wedge. Low densities in the back arc, inferred from the low shear wave velocities, can provide isostatic support for the TMVB

Homothetic Wyman Spacetimes

The time-dependent, spherically symmetric, Wyman sector of the Unified Field Theory is shown to be equivalent to a self-gravitating scalar field with a positive-definite, repulsive self-interaction potential. A homothetic symmetry is imposed on the fundamental tensor, and the resulting autonomous system is numerically integrated. Near the critical point (between the collapsing and non-collapsing spacetimes) the system displays an approximately periodic alternation between collapsing and dispersive epochs.Comment: 15 pages with 6 figures; requires amsart, amssymb, amsmath, graphicx; formatted for publication in Int. J. Mod. Phys.

Completion Report: Pesticide and Nitrate Monitoring Results for Craighead, Mississippi, and Poinsett Counties, Arkansas: Phase II

Because of the concern for potential contamination of ground water by agricultural chemicals, 38 wells drilled in the Mississippi River Valley alluvial aquifer in Mississippi County and the eastern parts of Craighead and Poinsett Counties, Arkansas were analyzed for pesticides and nitrate. The pesticide, fluometuron, was detected in one sample at a concentration of 0.5 mg/L. Bentazon was detected in three samples at concentrations of 2.5, 0.3, and 0.3 mg/L. The occurrences of the pesticides appear to represent isolated incidents rather than a widespread aquifer contamination. All detections were below health and safety standards. Nitrate is present in several wells at concentrations above 0.15 mg/L, one of which exceeded the EPA established maximum contaminant level for drinking water of 10 milligrams per liter as nitrogen. Except for two wells nitrate and iron are not present together at concentrations above 0.15 mg!L. This is probably due to microbially mediated reactions. Nitrate concentrations above 0.15 mg/L is only present in wells that are less than 60 feet deep and near permeable soils. Iron is present in wells that are not near permeable soils or wells that are greater than 40 feet deep, and may exceed 1 mg/L in some cases

Freshly ionized matter around the final Helium shell flash object V4334 Sgr (Sakurai's object)

We report on the discovery of recently ionized hydrogen-deficient gas in the immediate circumstellar environment of the final helium shell flash star V4334 Sgr (Sakurai's object). On spectra obtained with FORS2 multi-object spectroscopy we have found spatially extended (about 2") emission from [N II], [O I], [O II] and very faint Halpha and [S II]. In the [N II] (ll6548,83) lines we have identified two components located at velocities -350 +/-50 and +200 +/-50 km/s, relative to V4334 Sgr itself. The full width of the [N II] l6583 feature at zero intensity corresponds to a velocity spread of about 1500 km/s. Based on the available data it is not possible to conclusively determine the mechanism of ionization. Both photo-ionization, from a rapidly evolving central star, and shock excitation, as the result of the collision of the fast ouflows with slower circumstellar matter, could account for the observed lines. The central star is still hidden behind strong dust absorption, since only a faint highly reddened continuum is apparent in the spectra. Theory states that it will become hotter and will retrace its post-asymptotic giant branch evolution towards the planetary nebula domain. Our detection of the ionized ejecta from the very late helium shell flash marks the beginning of a new phase in this star's amazingly rapid evolution.Comment: 11 pages, 2 figures. Accepted by ApJ