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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Analysis of multifastener composite joints

A new numerical procedure for determining load proportioning in multiple-hole mechanical joints in composite plates is presented. The joints are loaded in double lap fashion in tension with pins through the holes. The commercial finite-element program ABAQUS is used to predict the load proportioning among holes using two independent plane stress finite-element models, one representing the composite inner lap and one representing the two steel outer laps, interacting through rigid circular surfaces. The circular surfaces effectively represent rigid pins. Load proportioning is predicted for a number of geometries. Excellent correlation with experimental data is obtained. Experimental and computed surface strains are also found to compare well. The assumption of a radial cosine distribution of contact stress between pin and hole is shown to be substantially in error for some holes.

Griffin, O. H., Jr.↗
DOE OSTI2021

Holes in Optical Lightning Flashes: Identifying Poorly Transmissive Clouds in Lightning Imager Data

Space-based optical lightning sensors including the lightning imaging sensor (LIS) and geostationary lightning mapper (GLM) are pixelated imagers that detect lightning as transient increases in cloud top illumination. Detection requires optical emissions to escape the cloud top to space with sufficient energy to trigger a pixel on the imaging array. Through scattering and absorption, certain clouds are able to block most light from reaching the instrument, causing a reduction in detection efficiency (DE) and possibly location accuracy (LA). Radiant lightning emissions that illuminate large cloud top areas are used to examine scenarios where clouds block light from reaching orbit. In some cases, these anomalies in the spatial radiance distribution from the lightning pulse lead to “holes” in the optical lightning flash where certain pixels fail to trigger. Such holes are identified algorithmically in the Tropical Rainfall Measuring Mission satellite LIS record and the microphysical properties of the coincident storm region are queried. We find that holes primarily occur in tall (IR T b < 235 K) convection (87%) and overhanging anvil clouds (10%). The remaining 3% of holes occur in moderate-to-weak convection or in clear air breaks between stormclouds. We further demonstrate how an algorithm that assesses the spatial radiance patterns from energetic lightning pulses might be used to construct an optical transmission gridded stoplight product for GLM that could help operators identify clouds with a potentially reduced DE and LA.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Beyond universal behavior in the one-dimensional chain with random nearest-neighbor hopping

Here, we study the one-dimensional nearest-neighbor tight-binding model of electrons with independently distributed random hopping and no on-site potential (i.e., off-diagonal disorder with particle-hole symmetry, leading to sublattice symmetry, for each realization). For nonsingular distributions of the hopping, it is known that the model exhibits a universal, singular behavior of the density of states $ρ(E) ~ 1/|E\: \text{ln}^3 |E||$ and of the localization length $ξ(E) ~ |\text{ln}|E||$, near the band center $\textit{E}$ = 0 . (This singular behavior is also applicable to random $\textit{XY}$ and Heisenberg spin chains; it was first obtained by Dyson for a specific random harmonic oscillator chain.) Simultaneously, the state at$\textit{E}$ = 0 shows a universal, subexponential decay at large distances $\sim \text{exp}[–\sqrt{r/r_0}]$. In this study, we consider singular, but normalizable, distributions of hopping, whose behavior at small $\textit{t}$ is of the form $\sim 1/[t \text{ln}^{λ+1}(1/t)]$, characterized by a single, continuously tunable parameter λ > 0. We find, using a combination of analytic and numerical methods, that while the universal result applies for λ > 2, it no longer holds in the interval 0 < λ < 2. In particular, we find that the form of the density of states singularity is enhanced (relative to the Dyson result) in a continuous manner depending on the nonuniversal parameter λ; simultaneously, the localization length shows a less divergent form at low energies and ceases to diverge below λ = 1. For λ < 2, the fall-off of the $\textit{E}$ = 0 state at large distances also deviates from the universal result and is of the form $\sim\text{exp}[–(r/r_0)^{1/λ}]$ , which decays faster than an exponential for λ < 1.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1977

Extreme-ultraviolet observations of coronal holes. I - Locations, sizes and evolution of coronal holes, June 1973-January 1974

The disk boundaries of coronal holes have been systematically determined from XUV observations taken during the manned Skylab missions (June 1973-January 1974). The resulting atlas was used to find the sizes, global distributions, differential rotation rates, growth/decay rates and lifetimes of holes during this period. The polar cap holes together covered 15% of the sun's total surface area, a number which remained surprisingly constant throughout Skylab despite the fact that each pole was independently evolving in time. Lower latitude holes contributed another 2 to 5%.

Bohlin, J. D.↗
DOE OSTI2025

Phenomenology of bubble size distributions in a first-order phase transition

In a cosmological first-order phase transition (FOPT), the true and false vacuum bubble radius distributions are not expected to be monochromatic, as is usually assumed. Consequently, Fermi balls (FBs) and primordial black holes (PBHs) produced in a dark FOPT will have extended mass distributions. We show how gravitational wave (GW), microlensing and Hawking evaporation signals for extended bubble radius/mass distributions deviate from the case of monochromatic distributions. The peak of the GW spectrum is shifted to lower frequencies, and the spectrum is broadened at frequencies below the peak frequency. Thus, the radius distribution of true vacuum bubbles introduces another uncertainty in the evaluation of the GW spectrum from a FOPT. The extragalactic gamma-ray signal at AMEGO-X/e-ASTROGAM from PBH evaporation may evince a break in the power-law spectrum between 5 MeV and 10 MeV for an extended PBH mass distribution. Optical microlensing surveys may observe PBH mass distributions with average masses below 10 -10 M ⊙ , which is not possible for monochromatic mass distributions. This expands the FOPT parameter space that can be explored with microlensing.

Marfatia, Danny [Univ. of Hawaii at Manoa, Honolul↗
NASA NTRS1988

The threee-dimensional morphology of the Antarctic ozone hole

The three-dimensional morphology of the spring antarctic ozone distribution as determined by the Nimbus 7 Solar Backscatter Ultraviolet (SBUV) spectrometer instrument is presented for the period 1 to 11 October in 1986. The data show that a clearly defined minimum in ozone relative to the local ozone field extends throughout the stratosphere from the tropopause to above 50 km, though decreasing in intensity with altitude. Near 18 km ozone in the ozone hole is 50 percent less than the average surrounding ozone. But even at 50 km the ozone is 20 percent less than the surrounding ozone field. The ozone minimum in the upper stratosphere is displaced about 6 degrees toward the equator so that observations at a fixed station may provide the illusion that the ozone minimum is restricted only to low altitudes. While the ozone minimum is spatially coherent throughout the stratosphere, there are differences in the behavior of ozone at different altitudes that suggest the existence of at least three distinct altitude domains. Below 30 km ozone is characterized by classic ozone hole behavior. Between 33 and 43 km ozone is more stable, actually increasing during September and October. Above 43 km ozone has always decreased during September to a minimum in October, but it has suffered a long term decrease of 7 to 12 percent since 1979 similar to that seen at low altitudes.

Aikin, Arthur C.↗
DOE OSTI2020

Bremsstrahlung in GRMHD Models of Accreting Black Holes

Here, the role of bremsstrahlung in the emission from hot accretion flows around slowly accreting supermassive black holes is not thoroughly understood. In order to appraise the importance of bremsstrahlung relative to other radiative processes, we compute spectral energy distributions (SEDs) of accretion disks around slowly accreting supermassive black holes including synchrotron radiation, inverse Compton scattering, and bremsstrahlung. We compute SEDs for (i) four axisymmetric radiative general relativistic magnetohydrodynamics (RadGRMHD) simulations of 10 8 M ⊙ black holes with accretion rates between 10 -8 $\dot{M}$ Edd and 10 -5 $\dot{M}$ Edd , (ii) four axisymmetric RadGRMHD simulations of M87* with varying dimensionless spin a$_*$ and black hole mass, and (iii) a 3D GRMHD simulation scaled for Sgr A*. At 10 -8 $\dot{M}$ Edd , most of the luminosity is synchrotron radiation, while at 10 -5 $\dot{M}$ Edd the three radiative processes have similar luminosities. In most models, bremsstrahlung dominates the SED near 512 keV. In the M87* models, bremsstrahlung dominates this part of the SED if a$_*$ = 0.5, but inverse Compton scattering dominates if a$_*$ = 0.9375. Since scattering is more variable than bremsstrahlung, this result suggests that 512 keV variability could be a diagnostic of black hole spin. In the appendix, we compare some bremsstrahlung formulæ found in the literature.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

Decending motion of particle and its effect on ozone hole chemistry

Particle descending motion is one possible process which causes ozone loss near the tropopause in the Antarctic spring. However, this particle size distribution has not yet been measured. Particle settling is an important redistribution process of the chemical constituents contained in the particles. To understand particle settling effects on the Ozone Hole, information on the size distribution and the chemical composition of the particles is necessary.

Iwasaka, Y.↗
NASA NTRS1989

Antarctic ozone hole - Possible implications for ozone trends in the Southern Hemisphere

Satellite-borne instruments (the Total Ozone Mapping Spectrometer and the Solar Backscattered Ultraviolet Instrument) show that, compared to 1979, total column ozone has a year-round decrease of more than 5 percent in the neighborhood of 60 deg S. The meteorological conditions (warmer temperatures, the absence of polar stratospheric clouds) at these latitudes do not seem to favor heterogeneous chemistry as the direct cause for the observed year-round ozone reduction. A mechanism involving the seasonal transport of ozone-poor air from within the polar vortex to lower latitudes (the so-called 'dilution effect') is proposed as a possible explanation for the observed year-round ozone reduction in subpolar regions. A two-dimensional model with an imposed springtime Antarctic ozone depletion is used to study the post-ozone hole impact on the spatial and temporal distributions of column ozone at latitudes north of 60 deg S. It is found that the time constant associated with the dilution effect in the latitude region 40-60 deg S is about 1 year, long enough to contribute to the observed year-round decrease of total ozone in that region.

Sze, N. D.↗
NASA NTRS1991

Nitrous Oxide In The Antarctic Stratosphere

Paper reports on measurements of nitrous oxide (N2O) in upper atmosphere of Southern Hemisphere, made by tunable-laser absorption spectrometer on airplane. Measurements fill gap in information about distribution of N2O over Antarctic while ozone hole forming.

Podolske, J. R.↗
NASA NTRS2004

MHD Modeling of Differential Rotation in Coronal Holes

The photosphere and the magnetic flux therein undergo differential rotation. Coronal holes appear to rotate almost rigidly. Magnetic reconnection has been invoked to reconcile these phenomena. Mechanism relevant to the formation of the slow solar wind. We have used our MHD model in spherical coordinates to study the effect of differential rotation on coronal holes. We have imposed a magnetic flux distribution similar to and applied differential rotation for the equivalent of 5 solar rotations.

Lionello, Roberto↗
NASA NTRS1998

Microblowing Technique Demonstrated to Reduce Skin Friction

One of the most challenging areas of research in aerodynamics is the reduction of skin friction, especially for turbulent flow. Reduced skin friction means less drag. For aircraft, less drag can lead to less fuel burned or to a greater flight range for a fixed amount of fuel. Many techniques and methods have been tried; however, none of them has significantly reduced skin friction in the flight environment. An innovative skin-friction reduction technique, the Microblowing Technique (MBT), was invented in 1993. This is a unique concept in which an extremely small amount of air is blown vertically at a surface through very small holes. It can be used for aircraft or marine vehicles, such as submarines (where water is blown through the holes instead of air). As shown in the figure, the outer layer, which controls vertical flow, is a plate with high-vertical holes. The inner layer, which produces evenly distributed flow, is a low-permeability porous plate. Microblowing reduces the surface roughness and changes the flow velocity profile on the surface, thereby reducing skin friction.

Hwang, Danny P.↗
NASA NTRS2012

Prospects for AGN Science using the ART-XC on the SRG Mission

The enhanced hard X-ray sensitivity provided by the Astronomical Roentgen Telescope to the Spectrum Roentgen Gamma mission facilitates the detection of heavily obscured and other hard-spectrum cosmic X-ray sources. The SRG all-sky survey will obtain large, statistically-well-defined samples of active galactic nuclei (AGN) including a significant population of local heavily-obscured AGN. In anticipation of the SRG all-sky survey, we investigate the prospects for refining the bright end of the AGN luminosity function and determination of the local black hole mass function and comparing the spatial distribution of AGN with large-scale structure defined by galaxy clusters and groups. Particular emphasis is placed on studies of the deep survey Ecliptic Pole regions.

Swartz, Douglas A.↗
NASA NTRS1982

Flow distributions and discharge coefficient effects for jet array impingement with initial crossflow

To model the impingement cooled mid-chord region of gas turbine airfoils in cases where an initial crossflow is present, the paper presents experimentally determined flow distributions for jet arrays with ten spanwise rows of holes, which range from uniform to highly nonuniform. The jet flow after impingement is constrained to exit in a single direction along the channel formed by the jet orifice plate and the impingement surface. The streamwise distributions and crossflow velocities are presented for ratios of the initial crossflow rate to the total jet flow rate ranging from zero to unity. For crossflow to jet velocity ratios greater than a value somewhat less than unity, jet orifice discharge coefficients do not remain constant, but decrease significantly, showing a secondary dependence on z/d, where z is the channel height and d is the jet hole diameter.

Florschuetz, L. W.↗
NASA NTRS1996

Coronal Hole-Active Region-Current Sheet (CHARCS) Association with Intense Interplanetary and Geomagnetic Activity

Intense geomagnetic storms (Dst<or equal to -100nT) have been associated with interplanetary structures involving large-intensity (B(sub 3)<or equal to 10nT) and long-duration (T< or equal to 3 hours) values of the southward component of the IMF. We show that near solar maximum, the solar origin of such structures seems to be associated with active regions(flares and/or filament eruptions) ocurring close to the streamer belt and to growing low altitude coronal holes. It is also shown that such type of coronal holes had a dual-peak solar cycle distribution during solar cycle 21, similar to that previously reported for the above mentioned interplanetary and geomagnetic phenomena.

geomagnetic storms IMF solar maximum flares filame↗
NASA NTRS2002

Inclination Angles of Black Hole X-Ray Binaries Manifest Strong Gravity around Black Holes

System inclination angles have been determined for about 15 X-ray binaries, in which stellar mass black holes are considered to exist. These inclination angles range between 25 degrees and 80 degrees, but peaked between 60-70 degrees. This peak is not explained in the frame work of Newtonian gravity. However, this peak is reproduced naturally if we model the observed X-ray radiations as being produced in the accretion disks very close to the black hole horizons, where the extremely strong general and special relativistic effects, caused by the extremely strong gravity near the black hole horizons, modify the local radiation significantly as the X-rays propagate to the remote observer. Therefore the peak of the inclination angle distribution provides evidence or strong gravity around stellar mass black holes.

Zhang, S. N.↗
DOE OSTI2024

Monte Carlo evaluation of the semiclassical multi-step direct reaction series

We show how the multi-step direct reaction series can be evaluated using Monte Carlo methods. Nucleon-nucleon collisions occur according to the random selection of a nucleon’s attenuation factor along its classical trajectory. The particles and hole excited in a collision are selected from a local Fermi distribution. We assume that the particles continue to propagate and possibly collide again before leaving the nucleus. We assume that holes collide in place, to possibly produce other particles and holes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1948

Simulated Altitude Performance of Combustors for the 24C Turbojet Engine. III - Performance of Rectangular-Slot Baskets: Performance of Rectangular-Slot Baskets - 3

The performance of an annular combustion chamber from a 24C turbojet engine was investigated over a range of simulated altitudes from 20,000 to 55,000 feet and corrected engine rotor speeds from 6000 to 13,000 rpm at a simulated ram-pressure ratio of 1.04. The purpose of the investigation was to determine the effects on the altitude operational limits, combustor-outlet gas temperature distribution, combustion efficiencies, and combustor inlet-to-outlet total-pressure drops of two changes in the 24C-4B basket air-passage arrangements that were designed to improve combustor-outlet temperature distribution. These changes were: (a) replacement of the downstream secondary air holes with large rectangular slots further upstream (rectangular-slot basket), and (b) enlargement of anticoking holes in the rectangular-slot basket (modified rectangular-slot basket). The results indicate that improved outlet-gas temperature distribution of each succeeding combustor basket investigated was attained at a sacrifice in the altitude limit of operation. The altitude limits of operation of the combustor with the original basket ranged from 34,000 feet at a corrected engine speed of 6000 rpm to a maximum of 52,000 feet at 12 ' 500 rpm. The altitude limits of the rectangular-slot basket were about 2000 feet lower throughout the engine speed range than those of the original basket. The altitude limits of the combustor with the modified rectangular-slot basket were about equivalent to those of the other baskets in the corrected-engine-speed range from 12,000 to 12,500 rpm but were about 10,000 feet lower than those of the original basket in the corrected-engine-speed range from 6000 to 9000 rpm. For the same inlet-air conditions, the combustion efficiencies were highest for the original basket and progressively lower for each of the other two baskets. The combustor inlet-to-outlet pressure drops of all three combustor baskets at the same operating conditions were within +/- 10 percent of the pressure drop of the original basket.

Tischler, Adelbert O.↗