74,813 research outputs found
Bond Length - Bond Valence Relationships for Carbon - Carbon and Carbon - Oxygen Bonds
In the present study, relationships are developed for determining bond orders (also referred to as bond valences or bond numbers) from published bond lengths for carbon-carbon (C-C) and carbon-oxygen (C-O) bonds. The relationships are based on Pauling’s empirical formula s = exp((Ro-R)/b)), where s is the bond order, R is the corresponding bond length, Ro is the unit valence bond length, and b is a fitting parameter. We use a recently derived relationship for the b parameter in terms of the bonding atoms’ published atomic orbital exponents. The resulting equations were checked against published x-ray diffraction (XRD) data for 176 carbon systems with 540 published C-C bond lengths, and 50 oxygen systems having 72 published C-O bond lengths. The C-C and C-O bond length-valence relationships are shown to have sufficient applicability and accuracy for use in any bonding environment, regardless of physical state or oxidation number
Aerodynamic characteristics of an NASA supercritical-wing research airplane model with and without fuselage area-rule additions at Mach 0.25 to 1.00
Transonic pressure tunnel tests at Mach numbers from 0.25 to 1.00 were performed to determine the effects of area-rule additions to the sides of the fuselage on the aerodynamic characteristics of a 0.087 scale model of an NASA supercritical-wing research airplane. Presented are the longitudinal aerodynamic force and moment characteristics for horizontal-tail deflection angles of -2.5 deg and -5 deg with the side fuselage area-rule additions on and off the model. The effects of the side fuselage area-rule additions on selected wing and fuselage pressure distributions at near-cruise conditions are also presented
The Classification of Extragalactic X-ray Jets
The overall classification of X-ray jets has clung to that prevalent in the
radio: FRI vs. FRII (including quasars). Indeed, the common perception is that
X-ray emission from FRI's is synchrotron emission whereas that from FRII's may
be IC/CMB and/or synchrotron. Now that we have a sizable collection of sources
with detected X-ray emission from jets and hotspots, it seems that a more
unbiased study of these objects could yield additional insights on jets and
their X-ray emission. The current contribution is a first step in the process
of analyzing all of the relevant parameters for each detected component for the
sources collected in the XJET website. This initial effort involves measuring
the ratio of X-ray to radio fluxes and evaluating correlations with other jet
parameters. For single zone synchrotron X-ray emission, we anticipate that
larger values of fx/fr should correlate inversely with the average magnetic
field strength (if the acceleration process is limited by loss time equals
acceleration time). Beamed IC/CMB X-rays should produce larger values of fx/fr
for smaller values of the angle between the jet direction and the line of sight
but will also be affected by the low frequency radio spectral index.Comment: 4 pages; to appear in the conference proceedings: "X-Ray Astronomy
2009: Present Status, Multiwavelength Approach and Future Perspectives";
Bologna, Italy, September 2009, Editors: A. Comastri, M. Cappi, L. Angelini,
2010 AIP (in press
Effects of wing trailing-edge truncation on aerodynamic characteristics of a NASA supercritical-wing research airplane model
The Langley 8-foot transonic pressure tunnel was used at Mach numbers from 0.80 to 1.00 to determine the effects of wing trailing-edge truncation on the aerodynamic characteristics of a 0.0625-scale model of a NASA TF-8A supercritical-wing research airplane. The effects of trailing-edge truncations of 1, 2, and 3 percent of the local streamwise chord on the longitudinal aerodynamic characteristics and the wing section characteristics are presented
X-ray Emission from the Radio Jet in 3C 120
We report the discovery of X-ray emission from a radio knot at a projected
distance of 25" from the nucleus of the Seyfert galaxy, 3C 120. The data were
obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for
the knot preclude a simple power law extension of the radio spectrum and we
calculate some of the physical parameters for thermal bremsstrahlung and
synchrotron self-Compton models. We conclude that no simple model is consistent
with the data but if the knot contains small regions with flat spectra, these
could produce the observed X-rays (via synchrotron emission) without being
detected at other wavebands.Comment: 6 pages latex plus 3 ps/eps figures. Uses 10pt.sty and
emulateapj.sty. Accepted for publication in the ApJ (6 Jan 99
Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots
We report new detections of the hotspots in Cygnus A at 4.5 and 8.0 microns
with the Spitzer Space Telescope. Together with detailed published radio
observations and synchrotron self-Compton modeling of previous X-ray
detections, we reconstruct the underlying electron energy spectra of the two
brightest hotspots (A and D). The low-energy portion of the electron
distributions have flat power-law slopes (s~1.5) up to the break energy which
corresponds almost exactly to the mass ratio between protons and electrons; we
argue that these features are most likely intrinsic rather than due to
absorption effects. Beyond the break, the electron spectra continue to higher
energies with very steep slopes s>3. Thus, there is no evidence for the
`canonical' s=2 slope expected in 1st order Fermi-type shocks within the whole
observable electron energy range. We discuss the significance of these
observations and the insight offered into high-energy particle acceleration
processes in mildly relativistic shocks.Comment: 5 pages, 3 figures, in Extragalactic Jets: Theory and Observation
from Radio to Gamma Ray, Eds. T. A. Rector and D. S. De Youn
User's operating procedures. Volume 3: Projects directorate information programs
A review of the user's operating procedures for the scout project automatic data system, called SPADS is presented. SPADS is the results of the past seven years of software development on a prime mini-computer. SPADS was developed as a single entry, multiple cross-reference data management and information retrieval system for the automation of Project office tasks, including engineering, financial, managerial, and clerical support. This volume, three of three, provides the instructions to operate the projects directorate information programs in data retrieval and file maintenance via the user friendly menu drivers
Study of sample drilling techniques for Mars sample return missions
To demonstrate the feasibility of acquiring various surface samples for a Mars sample return mission the following tasks were performed: (1) design of a Mars rover-mounted drill system capable of acquiring crystalline rock cores; prediction of performance, mass, and power requirements for various size systems, and the generation of engineering drawings; (2) performance of simulated permafrost coring tests using a residual Apollo lunar surface drill, (3) design of a rock breaker system which can be used to produce small samples of rock chips from rocks which are too large to return to Earth, but too small to be cored with the Rover-mounted drill; (4)design of sample containers for the selected regolith cores, rock cores, and small particulate or rock samples; and (5) design of sample handling and transfer techniques which will be required through all phase of sample acquisition, processing, and stowage on-board the Earth return vehicle. A preliminary design of a light-weight Rover-mounted sampling scoop was also developed
An evaluation of the effects of stacking sequence and thickness on the fatigue life of quasi-isotropic graphite/epoxy laminates
Notched and unnotched geometries at 16, 32, and 64-ply thicknesses of a 90/45/0-45 (ns) laminate and a 45/0/-45/90 (ns) laminate were tested in compression-compression fatigue. The fatigue life and the initiation, type, and progression of damage were determined. Interlaminar stresses generated at straight, free edges of axially loaded laminates were used to interpret the test results. The fatigue lives of the notched specimens did not appear to be a strong function of laminate stacking sequence or specimen thickness. The stress concentration at the hole dominated over the interlaminar stresses at the straight free edge. The unnotched specimens of the 90/45/0/-45 (ns) laminate with tensile interlaminar normal stresses delaminated more readily than did the 45/0/-45/90 (ns) laminate with compressive interlaminar normal stress. The life of the 16-ply unnotched specimens was lower than the 32- and 64-ply specimens. Delaminations were located at the interface where the maximum shear stress occurred regardless of the sense or magnitude of the interlaminar normal stress. An antibuckling fixture was effective in preventing out-of-plane motion without overconstraining the specimen
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