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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Could Road Constructions Be More Hazardous Than an Earthquake in Terms of Mass Movement?

Roads can have a significant impact on the frequency of mass wasting events in mountainous areas. However, characterizing the extent and pervasiveness of mass movements over time has rarely been documented due to limitations in available data sources to consistently map such events. We monitored the evolution of a road network and assessed its effect on mass movements for a 11-year window in Arhavi, Turkey. The main road construction projects run in the area are associated with a hydroelectric power plant as well as other road extension works and are clearly associated with the vast majority (90.1%) of mass movements in the area. We also notice that the overall number and size of the mass movements are much larger than in the naturally-occurring comparison area. This means that the sediment load originating from the anthropogenically induced mass movements is larger than its counterpart associated with naturally occurred landslides. Notably, this extra sediment load could cause river channel aggregation, reduce accommodation space and as a consequence, it could lead to an increase in the probability and severity of flooding along the river channel. This marks a strong and negative effect of human activities on the natural course of earth surface processes. We also compare frequency-area distributions of human-induced mass movements mapped in this study and co-seismic landslide inventories from the literature. By doing so, we aim to better understand the consequences of human effects on mass movements in a comparative manner. Our findings show that the damage generated by the road construction in terms of sediment loads to river channels is compatible with the possible effect of a theoretical earthquake with a magnitude greater than Mw=6.0.

Hakan Tanyas↗
NASA NTRS1990

Masses and radii for thirteen chromospherically active ellipsoidal variables

The amplitude of the ellipticity effect, the mass function, and the V sin i in ten long-period RS CVn SB1 binaries are used to compute limits on the masses of the two stars and the radius of the primary: zeta And, UV CrB, V1764 Cyg, V826 Her, V350 Lac, GX Lib, V1197 Ori, AP Psc, 33 Psc, and EE UMa. Explicit masses and radii are computed for three SB2 systems: BL CVn, V1817 Cyg, and TZ Tri. The primary in several is found to fill 95 percent or more of its Roche lobe. The two minima produced by the ellipticity effect are unequal in depth, with the effect largest when i is near 90 deg and the primary nearly fills its Roche lobe. The greatest inequality found, in UV CrB, was 0.08 mag.

Hall, Douglas S.↗
NASA NTRS1994

X-ray sources in regions of star formation. 5: The low mass stars of the Upper Scorpius association

We report followup investigations of Einstein x-ray observations of the Upper Scorpius OB association. We identify 28 low mass pre-main sequence stars as counterparts of x-ray sources in the approximately = 7 square degrees of the OB association observed. Based on kinematics and lithium abundances, these stars are low mass members of the OB association. We use optical spectra and optical and near-IR photometry to determine the stellar luminosities, effective temperatures, masses, and ages. We show that the bolometric corrections and effective temperatures of the G and K stars are consistent with those of subgiants. The low mass stars have isochronal ages of 1-2 Myr, depending on the choice of evolutionary models, with very small dispersion (sigma approximately = 1 Myr). This age is significantly younger than the 5-6 Myr found for the more massive B stars. The small dispersion in stellar ages, less than 10% the sound-crossing time of the association, suggests that star formation was triggered. We present two scenarios for star formation in this association. In the two-episode scenario, formation of the low mass stars was triggered by a supernova explosion, and the low mass stars form quickly, with high efficiency. Alternatively, high and low mass star formation was all initiated at the same time, some 5-6 Myr ago, and the apparent systematic age difference is an artifact of how the isochrones are dated. The effect of the supernova is to terminate mass accretion and yield an apparently coeval population. We show that the incompleteness in the x-ray sampling is about 65%, and is strongly dependent on stellar mass. After correction for incompleteness, we estimate there are about 2000 low mass members (stellar mass less than 2 solar mass) of this association. The mass function in this association is indistinguishable from that of the field. The ratio of naked to classical T Tauri stars is much larger than in Tau-Aur, and may be attributable to the local environment. We also present observations of eight ROX sources associated with the rho Oph cloud, and observations of non-pre-main sequence (PMS) stars in our fields.

Walter, Frederick M.↗
NASA NTRS1984

Engineering correlations of variable-property effects on laminar forced convection mass transfer for dilute vapor species and small particles in air

A simple engineering correlation scheme is developed to predict the variable property effects on dilute species laminar forced convection mass transfer applicable to all vapor molecules or Brownian diffusing small particle, covering the surface to mainstream temperature ratio of 0.25 T sub W/T sub e 4. The accuracy of the correlation is checked against rigorous numerical forced convection laminar boundary layer calculations of flat plate and stagnation point flows of air containing trace species of Na, NaCl, NaOH, Na2SO4, K, KCl, KOH, or K2SO4 vapor species or their clusters. For the cases reported here the correlation had an average absolute error of only 1 percent (maximum 13 percent) as compared to an average absolute error of 18 percent (maximum 54 percent) one would have made by using the constant-property results.

Gokoglu, S. A.↗
NASA NTRS2001

The Effects of Hypergravity and Adrenalectomy on Bone Mineral Content, Urine Calcium and Body Mass in Rats

The effects of 14 days of increased gravitational load, and the absence of adrenal stress hormones on total body bone mineral content (BMC) were examined in male Sprague-Dawley rats. Centrifugation at 2 Gs (2G) was used to increase the gravitational load, and bilateral adrenalectomy (ADX) was used to eliminate the production of adrenal stress hormones. Stationary groups at 1 G (1G) and sham operated (SHAM) animals served as controls. Thirty rats (n=6 or 8) made up the four experimental groups (1G SHAM, 1G ADX, 2G SHAM and 2G ADX). BMC was assessed by dual energy x-ray absorptiometry (DXA) which was performed to determine the total body bone mineral content, and also through bone ashing of the left femur and the left humerus. Activity was determined through biotelemetry, also body mass and food intake were measured. Multi-factorial analysis of variance (MANCOVA) and Newman Keuls post hoc tests were used to analyze significant effects (p is less than 0.05) for the primary variables. Results from both DXA and the ashed femur indicated that BMC decreased significantly with increased G for both the SHAM and ADX groups. The BMC determined by DXA for the 1G ADX group was also significantly lower than the 1G SHAM group, however the 2G SHAM and 2G ADX groups were not significantly different. However, the bone ashing results showed the femur differed significantly only between the rates of centrifugation and not between the ADX and SHAM. The humerus showed no significant difference between any of the groups. There was a significant decrease in body mass with increased G and there was no ADX effect on body mass. When DXA BMC was normalized for body mass changes, there were no significant group differences. However, with bone ashing, the femur BMC/BW still showed significant difference between rates of centrifugation, with the 2G group being lower. Activity level decreased with body mass, and food intake data showed there was significant hypophagia during the first few days of centrifugation. Urine calcium was measured and was found decrease at the start of centrifugation for the 2G groups and rise to a level higher than that of the stationary groups. Finally, the correlation between BW and BMC was determined to be highly correlated (r = .71). These results suggest that the decrease in total body BMC seen with hypergravity may be based to a large extent on the differences in body mass induced by the 2G load.

Lau, A.↗
NASA NTRS1961

A Theoretical Analysis of Effects of Ablation on Heat Transfer to an Arbitrary Axisymmetric Body

An analysis has been performed t o determine the effect of mass injection on heat transfer to an arbitrary surface of revolution. effective heat of ablation is determined, and the downstream effects of injection are investigated. It is found that the linear relation between heat of ablation and difference between wall and free-stream enthalpy, previously verified at the stagnation point, provides a useful approximation at any point on a surface of revolution. From the investigation of the downstream effects of injection it is found that an appreciable rate of heating may be obtained, even at points considerably downstream from the point at which injection ends. However, the radiation equilibrium temperature is proportional to the fourth root of the heating rate; therefore, except in particular cases, it will be difficult to make use of this effect in the design of thermal protection systems. Effects of radiation from a hot gas layer to the ablating surface are investigated by an approximate procedure. The efficiency of ablation is found to approach a maximum value which depends on the ratio of radiant heating to aerodynamic heating and is independent of the enthalpy difference across the boundary layer.

Swann, Robert T.↗
NASA NTRS1986

Mass balancing of hollow fan blades

A typical section model is used to analytically investigate the effect of mass balancing as applied to hollow, supersonic fan blades. A procedure to determine the best configuration of an internal balancing mass to provide flutter alleviation is developed. This procedure is applied to a typical supersonic shroudless fan blade which is unstable in both the solid configuration and when it is hollow with no balancing mass. The addition of an optimized balancing mass is shown to stabilize the blade at the design condition.

Kielb, R. E.↗
NASA NTRS1986

Mass balancing of hollow fan blades

A typical section model is used to analytically investigate the effect of mass balancing as applied to hollow, supersonic fan blades. A procedure to determine the best configuration of an internal balancing mass to provide flutter alleviation is developed. This procedure is applied to a typical supersonic shroudless fan blade which is unstable in both the solid configuration and when it is hollow with no balancing mass. The addition of an optimized balancing mass is shown to stabilize the blade at the design condition.

Kielb, R. E.↗
NASA NTRS1984

Apparatus for and method of compensating dynamic unbalance

An apparatus to stabilize a fine platform that carries a parabolic reflecting dish, utilized in connection with the large aperture, multichannel microwave radiometer, is discussed. It provides compensation for dynamic unbalance imparted to a fixed body by a shaft about which the rotating body rotates. Force components exerted on the fixed body by the rotating body in a plane at right angles to the axis are determined. In response to the determined force components, the rotational speed and effective direction of mass means mounted on the rotating body are controlled. The mass means has an effective axis of rotation in a plane at right angles to the longitudinal axis.

Hrastar, J. A.↗
NASA NTRS2014

Landform Evolution Modeling of Sedimentary Processes on Icy Worlds: the Cases of Hyperion and Helene

Sedimentary activity (erosion, transportation and deposition) is a major landscape-shaping process on many icy worlds of the outer solar system for which an understanding of this process is central to their geologic characterizations. Several recent studies, lead by the authors, have identified the effects of sedimentary activity on icy satellite landforms and recognized the role of mass wasting and volatile loss and redistribution in the evolution of these features. We apply state of the art, physics based, landform evolution modeling to icy satellite sedimentary landforms in order to fully quantitatively characterize how their morphologies change with time, and what their present appearances imply for the initial abundance and distribution of loose material, volatiles, and refractories in original pristine landforms. We will present results of our landform evolution modeling to the development of the landscapes of the Saturnian moons of Hyperion and Helene. Our current conclusions for Hyperion are that its unique appearance can be explained in part by the loss to space of ballistic ejecta during impact events. In order to create the smooth surfaces and the reticulate, honeycomb pattern of narrow divides between old craters, appreciable subsequent modification of crater morphology must occur through mass-wasting processes accompanied by sublimation, probably facilitated by the loss of CO2 as a component of the relief-supporting matrix of the bedrock. This mass wasting effectively destroys small craters, at least in part accounting for the paucity of sub-kilometer craters on Hyperion. Helene’s unusual morphology consists of broad depressions (modified large craters) and a generally smooth surface patterned with streaks and grooves. The streaks appear to be oriented down-gradient, as are the grooves. This pattern suggests intensive mass-wasting as a dominant process. Our initial modeling of this surface suggests a Bingham-like rheological behavior for the loose down-slope moving material. Interestingly, as a Bingham flow, the models indicate that aperiodic "intermittent" behavior to be present, suggesting that periods of quiet steady landform evolution are punctuated short periods of active surface readjustment.

Saturnian moons↗
NASA NTRS2000

Oceanic Excitation of Polar Motion During 1992-1994

Two global ocean general circulation models have been used to compute the angular momentum of nontidal oceanic current and sea level height variations: (1) the Princeton Modular Ocean Model (MOM) having 22 vertical layers and a rigid lid, and (2) the Miami Isopycnic-Coordinate Ocean Model (MICOM) having 11 vertical layers with a mixed layer and a free surface. Both models were run on the same 2 degree longitude by 1 degree latitude grid spanning 80 S to 80 N latitude. Following a 10-year spin-up with climatological air-sea fluxes, both models were forced during 1992-1994 with daily wind and heat flux from the NCEP operational analysis and sea surface salinity restoring to Levitus climatology. After correcting for the effects of mass non-conservation in these models, they are shown to predict similar effects on polar motion excitation of sea level height variations, but the effect of currents predicted by MOM is much larger than that predicted by MICOM.

Gross, R.↗
NASA NTRS2010

On the Nature of the Compact Object in SS 433. Observational Evidence of X-Ray Photon Index Saturation

We present an analysis of the X-ray spectral properties observed from black hole , candidate (BHC) binary SS 433. We have analyzed Rossi X-ray Time Explorer (RXTE) data from this source, coordinated with Green Bank Interferometer/RATAN-600. We show that SS 433 undergoes a X-ray spectral transition from the low hard state (LHS) to the intermediate state (IS). We show that the X-ray broad-band energy spectra during all spectral states are well fit by a sum of so called "Bulk Motion Comptonization (BMC) component" and by two (broad and narrow) Gaussians for the continuum and line emissions respectively. In addition to these spectral model components we also find a strong feature that we identify as a" blackbody-like (BB)" component which color temperature is in the range of 4-5 keV in 24 IS spectra during the radio outburst decay in SS 433. Our observational results on the "high temperature BB" bump leads us to suggest the presence of gravitationally redshifted annihilation line emission in this source. In fact this spectral feature has been recently reproduced in Monte Carlo simulations by Laurent and Titarchuk. We have also established the photon index saturation at about 2.3 in index vs mass accretion correlation. This index-mass accretion correlation allows us to evaluate the low limit of black hole (BH) mass of compact object in SS 433, M(sub bh) approximately > 2 solar masses, using the scaling method using BHC GX 339-4 as a reference source. Our estimate of the BH mass in SS 433 is consistent with recent BH mass measurement using the radial-velocity measurements of the binary system by Hillwig & Gies who find that M(sub x)( = (4.3 +/- 0.8) solar masses. This is the smallest BH mass found up to now among all BH sources. Moreover, the index saturation effect versus mass accretion rate revealed in SS 433, like in a number of other BH candidates, is the strong observational evidence for the presence of a BH in SS 433.

Seifina, Elena↗