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At least 289 records · Page 16

Active Region Magnetic Structure Observed in the Photosphere and Chromosphere

The magnetic flux above sunspots and plage in NOAA (National Oceanic and Atmospheric Administration) Active Region 8299 has been measured in the photosphere and the chromosphere. We investigate the vertical magnetic structure above the umbrae, penumbrae and plage regions using quantitative statistical comparisons of the photospheric and chromospheric vector magnetic flux data. The results include: (1) a decrease in flux with height, (2) the direct detection of the superpenumbral canopy in the chromosphere, (3) values for dB/dz which are consistent with earlier investigations when derived from a straight difference between the two datasets but quite low when derived from the delta x B = 0 condition, (4) a monolithic structure in the umbra which extends well into the upper chromosphere with a very complex and varied structure in the penumbra and plage, as evidenced by (5) a uniform magnetic scale height in the umbrae with an abrupt jump to widely varying scale heights in the penumbral and plage regions. Further, we find (6) evidence for a very large (delta z approximately equals 3Mm) height difference between the atmospheric layers sampled in the two magnetograms, almost a factor of three larger than that implied by atmospheric models. We additionally test the apropriateness of using photospheric magnetic flux as a boundary for field-line extrapolations, and find a better agreement with observed coronal structure when the chromospheric flux is used as a boundary.

Leka, K. D.↗

Extending the ICRF to Higher Radio Frequencies: Imaging and Source Structure

We present imaging results and source structure analysis of extragalactic radio sources observed using the Very Long Baseline Array (VLBA) at 24 GHz and 43 GHz as part of an ongoing NASA, USNO, NRAO and Bordeaux Observatory collaboration to extend the International Celestial Reference Frame (ICRF) to higher radio frequencies. The K/Q-band image database now includes images of 108 sources at 43 GHz (Q-braid) and images of 230 sources at 24 GHz (K-band). Preliminary analysis of the observations taken to date shows that the sources are generally more compact as one goes from the ICRF frequency of 8.4 GHz to 24 GHz. This result is consistent with the standard theory of compact extragalactic radio sources and suggests that reference frames defined at these higher radio frequencies will be less susceptible to the effects of intrinsic source structure than those defined at lower frequencies.

Boboltz, David A.↗

Skeletal Structural Consequences of Reduced Gravity Environments

The overall goal of this project is to provide structurally meaningful data on bone loss after exposure to reduced gravity environments so that more precise estimates of fracture risk and the effectiveness of countermeasures in reducing fracture risk can be developed. The project has three major components: (1) measure structural changes in the limb bones of rats subjected to complete and partial nonweightbearing, with and without treatment with ibandronate and periodic full weightbearing; (2) measure structural changes in the limb bones of human bedrest subjects, with and without treatment with alendronate and resistive exercise, and Russian cosmonauts flying on the Mir Space Station; and (3) validate and extend the 2-dimensional structural analyses currently possible in the second project component (bedrest and Mir subjects) using 3-dimensional finite element modeling techniques, and determine actual fracture-producing loads on earth and in space.

Ruff, Christropher B.↗

Coronal Structures Observed by Radio Propagation Measurements

This paper summarizes (1) advances in our knowledge of coronal structures inferred from radio propagation measurements, and (2) gains in our understanding of the relationship between radio propagation and white-light coronagraph measurements. Radio propagation measurements confirm that streamers are ray-like structures as depicted in coronagraph pictures, but also reveal a hierarchy of filamentary structures throughout the corona, extending from the size of streamers down to scale sizes as small as about 1 km at the Sun (10(ghe) arcsec). Doppler scintillation measurements, therefore, open a new window on small-scale structure that has long eluded coronagraph measurements. In addition, high precision ranging measurements make it possible to investigate large-scale structures not yet observed in corona graphs, such as plumes in equatorial coronal regions.

Sun↗

Jet induced star formation in centrally dominant galaxies?

Using U-I CCD color maps of two centrally dominant cluster galaxies, we find unusual color structures which may be due to star formation which has been induced by their radio sources. These objects, located in the clusters A1795 and A2597, have blue central colors to radii of 20 kpc, spatially extended emission-line structures, and powerful radio sources. They reside at the centers of cooling flows with mass-accretion rates which are estimated to be approximately greater than 300 solar mass/yr. The regions of bluest local color are superposed on or along their radio-source structures. Our observations suggest that the radio sources associated with these objects may be inducing massive star formation in their central 20 kpc. The star formation may be the result of the radio plasma interacting with the warm emission-line gas and dense, x-ray emitting filaments similar to those recently discovered in two other clusters with the ROSAT Observatory. Since radio jets are likely to be transient, this may help to explain the scatter in the correlations between color and mass-accretion rate, although other factors may also contribute. Alternatively, scattered radiation from a hidden active nucleus or recent mergers may be responsible for the color structure. The color and radio properties of these objects are qualitatively similar but smaller in luminosity and spatial extent to those found in high redshift radio galaxies. Our observations of galaxies at z approximately = 0.06-0.1 show that processes similar to 'the alignment effect' found in high redshift radio galaxies occur at more recent epochs.

Mcnamara, Brian R.↗

Aircraft Structural Mass Property Prediction Using Conceptual-Level Structural Analysis

This paper describes a methodology that extends the use of the Equivalent LAminated Plate Solution (ELAPS) structural analysis code from conceptual-level aircraft structural analysis to conceptual-level aircraft mass property analysis. Mass property analysis in aircraft structures has historically depended upon parametric weight equations at the conceptual design level and Finite Element Analysis (FEA) at the detailed design level ELAPS allows for the modeling of detailed geometry, metallic and composite materials, and non-structural mass coupled with analytical structural sizing to produce high-fidelity mass property analyses representing fully configured vehicles early in the design process. This capability is especially valuable for unusual configuration and advanced concept development where existing parametric weight equations are inapplicable and FEA is too time consuming for conceptual design. This paper contrasts the use of ELAPS relative to empirical weight equations and FEA. ELAPS modeling techniques are described and the ELAPS-based mass property analysis process is detailed Examples of mass property stochastic calculations produced during a recent systems study are provided This study involved the analysis of three remotely piloted aircraft required to carry scientific payloads to very high altitudes at subsonic speeds. Due to the extreme nature of this high-altitude flight regime,few existing vehicle designs are available for use in performance and weight prediction. ELAPS was employed within a concurrent engineering analysis process that simultaneously produces aerodynamic, structural, and static aeroelastic results for input to aircraft performance analyses. The ELAPS models produced for each concept were also used to provide stochastic analyses of wing structural mass properties. The results of this effort indicate that ELAPS is an efficient means to conduct multidisciplinary trade studies at the conceptual design level.

Sexstone, Matthew G.↗

Aircraft Structural Mass Property Prediction Using Conceptual-Level Structural Analysis

This paper describes a methodology that extends the use of the Equivalent LAminated Plate Solution (ELAPS) structural analysis code from conceptual-level aircraft structural analysis to conceptual-level aircraft mass property analysis. Mass property analysis in aircraft structures has historically depended upon parametric weight equations at the conceptual design level and Finite Element Analysis (FEA) at the detailed design level. ELAPS allows for the modeling of detailed geometry, metallic and composite materials, and non-structural mass coupled with analytical structural sizing to produce high-fidelity mass property analyses representing fully configured vehicles early in the design process. This capability is especially valuable for unusual configuration and advanced concept development where existing parametric weight equations are inapplicable and FEA is too time consuming for conceptual design. This paper contrasts the use of ELAPS relative to empirical weight equations and FEA. ELAPS modeling techniques are described and the ELAPS-based mass property analysis process is detailed. Examples of mass property stochastic calculations produced during a recent systems study are provided. This study involved the analysis of three remotely piloted aircraft required to carry scientific payloads to very high altitudes at subsonic speeds. Due to the extreme nature of this high-altitude flight regime, few existing vehicle designs are available for use in performance and weight prediction. ELAPS was employed within a concurrent engineering analysis process that simultaneously produces aerodynamic, structural, and static aeroelastic results for input to aircraft performance analyses. The ELAPS models produced for each concept were also used to provide stochastic analyses of wing structural mass properties. The results of this effort indicate that ELAPS is an efficient means to conduct multidisciplinary trade studies at the conceptual design level.

Sexstone, Matthew G.↗

Configuration design sensitivity analysis of built-up structures

In the design of complex built-up structures that are made of truss, beam, membrane, shell, and solid, there are five different kinds of design variables: material property, sizing, shape, configuration, and topological variables. Previous research has shown that the improvement in performances obtained by altering the configuration of structural components can be much more significant than those obtained when the geometry is assumed to be fixed. Using the variational approach, a unified design sensitivity was developed for the first three kinds of design variables, and was further extended recently in many structural analysis problems such as nonlinear, structural dynamics, and frequency response analysis. A continuum design sensitivity analysis method is developed for the configuration design variable of built-up structures.

Choi, Kyung K.↗

The Spectroscopic Evolution of the Symbiotic-like Recurrent Nova V407 Cygni During Its 2010 Outburst. 2. The Circumstellar Environment and the Aftermath

The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at gamma-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development of the photoionized Mira wind, circumstellar medium, and shocked circumstellar environment to derive their physical parameters and how they relate to large scale structure of the environment, extending the previous coverage to more than 500 days after outburst. We use optical spectra obtained at high resolution with the Nordic Optical Telescope (NOT) (R approx. =.45000 to 65000) and medium resolution Ondrejov Observatory (R approx. = 12000) data and compare the line variations with publicly available archival measurements at 30 GHz OVNR and at X-rays with Swift during the first four months of the outburst, through the end of the epoch of strong XR emission. We use nebular diagnostics and high resolution profile variations to derive the densities and locations of the extended emission. We find that the higher the ionization and/or the higher the excitation energy, the more closely the profiles resemble the He II/Ca V-type high velocity shock profile discussed in Paper I. This also accounts for the comparative development of the [N II] and [O III] isoelectronic transitions: the [O III] 4363A profile does not show the low velocity peaks while the excited [N II] 5754A does. If nitrogen is mainly N(+3) or higher in the shock, the upper state of the [N II] nebular lines will contribute but if the oxygen is O(+2) then this line is formed by recombination, masking the nebular contributor, and the lower states are collisionally quenched but emit from the low density surroundings. Absorption lines of Fe-peak ions formed in the Mira wind were visible as P Cyg profiles at low velocity before Day 69, around the time of the X-ray peak and we identified many absorption transitions without accompanying emission for metal lines. The H Balmer lines showed strong P Cyg absorption troughs that weakened during the 2010 observing period, through Day 128. The Fe-peak line profiles and flux variations were different for permitted and forbidden transitions: the E1 transitions were not visible after Day 128 but had shown a narrow peak superimposed on an extended (200 km/s) blue wing, while the M1 and E2 transitions persisted to Day 529, the last observation, and showed extended redshifted wings up of the same velocity. We distinguish the components from the shock, the photoionized environment, and the chromosphere and inner Mira wind using spectra taken more than one year after outburst. The multiple shells and radiative excitation phenomenology are similar to those recently cited for GRBs and SNIa .

Shore, S. N.↗

Mineral exploration potential of ERTS-1 data

The author has identified the following significant results. Further analysis of ERTS-1 MSS imagery of Arizona has led to division of the earlier reported three major regional fault/fracture systems into eight subdivisions. These are: System A - N40E to N50E; System B - N50W; System C - N35W; System D - N65E to N75E; System E - N-E; System F - N25W average; System G - N75W average; and System H - close to E-W. Their individual significance to known porphyry coppers and correlation to the Wasatch-Jerome and Front Orogens, the Texas Zone and Basin Range topography is postulated in the report. In this study area of Arizona the ERTS-1 mapped structural trends confirm and greatly extend some concepts of porphyry copper distribution based on prior geologic knowledge of major structural trends.

Brewer, W. A.↗

Tuned grid generation with ICEM CFD

ICEM CFD is a CAD based grid generation package that supports multiblock structured, unstructured tetrahedral and unstructured hexahedral grids. Major development efforts have been spent to extend ICEM CFD's multiblock structured and hexahedral unstructured grid generation capabilities. The modules added are: a parametric grid generation module and a semi-automatic hexahedral grid generation module. A fully automatic version of the hexahedral grid generation module for around a set of predefined objects in rectilinear enclosures has been developed. These modules will be presented and the procedures used will be described, and examples will be discussed.

Wulf, Armin↗

The X-ray structure of the Perseus cluster of galaxies

The X-ray source in the Perseus cluster has been studied both by the Copernicus satellite and by sounding-rocket instruments flown by Columbia University. The spatial and spectral data from these observations are examined. A surface brightness distribution is obtained which shows that the source consists of a compact core associated with NGC 1275 and a more extended emission volume. The structure of the central core region has been examined by means of an image reconstruction technique, revealing a steeply declining luminosity function and north-south elongation. The spectrum of the emission of the core region is distinguished from that of the surrounding area and found to be consistent with a hydrogen column density of 2.5 x 10 to the 21th/sq cm. A comparison between the isothermal and adiabatic gas sphere models is presented which shows the need for at least two components to provide the X-ray emission.

Wolff, R. S.↗

Thermal characterization and toughness of ethynyl containing blends

As part of an effort to develop high performance structural resins with an attractive combination of properties for aerospace applications, a series of ethynyl-terminated polysulfones of different molecular weights were prepared and blended with a low molecular weight ethynyl-terminated coreactant. Upon heating above 200 C, these ethynyl containing materials react to form a chain extended and crosslinked network structure. This reaction renders the materials insoluble in common solvents, but also reduces the toughness as compared to high molecular weight linear polysulfones. The thermal characterization of these blends and the toughness of the resulting cured materials are discussed.

Jensen, Brian J.↗

Far infrared structure of spiral galaxies from the IRAS CPC images

Significant extended far infrared (50 micron and 100 micron) structure was found for five face-on spiral galaxies (NGC2403, M51, M83, NGC6946, and IC342) from fourteen galaxies searched in the Infrared Astronomy Satellite (IRAS) chopped photometric channel (CPC) catalogue. Images were initially processed to remove instrumental and background artifacts, the isophotal centroids of each image determined, and multiple images of each galaxy (for each wavelength) superimposed and averaged to improve signal-to-noise. Calibration of these images was performed using IRAS survey array data. Infrared isophotes were then superimposed on optical (blue) images so that direct structural comparisons could be made.

Wainscoat, Richard J.↗

Theoretical Study of the Transverse Dielectric Constant of Superlattices and Their Alloys

The optical properties of III to V binary and ternary compounds and GaAs-Al(x)Ga(1-x)As superlattices are determined by calculating the real and imaginary parts of the transverse dielectric constant. Emphasis is given to determining the influence of different material and superlattice parameters on the values of the index of refraction and absorption coefficient. In order to calculate the optical properties of a material, it is necessary to compute its electronic band structure. This was accomplished by introducing a partition band structure approach based on a combination of the vector k x vector p and nonlocal pseudopotential techniques. The advantages of this approach are that it is accurate, computationally fast, analytical, and flexible. These last two properties enable incorporation of additional effects into the model, such as disorder scattering, which occurs for alloy materials and excitons. Furthermore, the model is easily extended to more complex structures, for example multiple quantum wells and superlattices. The results for the transverse dielectric constant and absorption coefficient of bulk III to V compounds compare well with other one-electron band structure models and the calculations show that for small frequencies, the index of refraction is determined mainly by the contibution of the outer regions of the Brillouin zone.

Kahen, K. B.↗

A revised version of the transfer matrix method to analyze one-dimensional structures

A new and general method to analyze both free and forced vibration characteristics of one-dimensional structures is discussed in this paper. This scheme links for the first time the classical transfer matrix method with the recently developed integrating matrix technique to integrate systems of differential equations. Two alternative approaches to the problem are presented. The first is based upon the lumped parameter model to account for the inertia properties of the structure. The second releases that constraint allowing a more precise description of the physical system. The free vibration of a straight uniform beam under different support conditions is analyzed to test the accuracy of the two models. Finally some results for the free vibration of a 12th order system representing a curved, rotating beam prove that the present method is conveniently extended to more complicated structural dynamics problems.

Nitzsche, F.↗

Mechanical sequencer

A mechanical sequencer having a rotatable drive shaft is described. The drive shaft has a spline formed thereon. A freely rotatable shaft contains a plurality of rollers positioned thereon, the axis of the freely rotatable shaft having an axis parallel to and offset from the axis of the drive shaft. A drive fitting has an opening therein, the drive fitting being positioned on the drive shaft spline for rotating the fitting with the shaft. A finger is formed integral with the drive fitting for enabling the fitting to move the rollers and the freely rotatable shift. A crank structure is positioned in a plane in a plane perpendicular to the axis of the drive shaft and the freely rotatable shaft. The crank structure has a drive shaft opening through which the shaft passes. The crank structure further contains a slot into which the freely rotatable shaft and one of the rollers extends for driving the crank structure during movement of the freely rotatable shaft.

Appleberry, W. T.↗

Magnetosheath Filamentary Structures Formed by Ion Acceleration at the Quasi-Parallel Bow Shock

Results from 2.5-D electromagnetic hybrid simulations show the formation of field-aligned, filamentary plasma structures in the magnetosheath. They begin at the quasi-parallel bow shock and extend far into the magnetosheath. These structures exhibit anticorrelated, spatial oscillations in plasma density and ion temperature. Closer to the bow shock, magnetic field variations associated with density and temperature oscillations may also be present. Magnetosheath filamentary structures (MFS) form primarily in the quasi-parallel sheath; however, they may extend to the quasi-perpendicular magnetosheath. They occur over a wide range of solar wind Alfvénic Mach numbers and interplanetary magnetic field directions. At lower Mach numbers with lower levels of magnetosheath turbulence, MFS remain highly coherent over large distances. At higher Mach numbers, magnetosheath turbulence decreases the level of coherence. Magnetosheath filamentary structures result from localized ion acceleration at the quasi-parallel bow shock and the injection of energetic ions into the magnetosheath. The localized nature of ion acceleration is tied to the generation of fast magnetosonic waves at and upstream of the quasi-parallel shock. The increased pressure in flux tubes containing the shock accelerated ions results in the depletion of the thermal plasma in these flux tubes and the enhancement of density in flux tubes void of energetic ions. This results in the observed anticorrelation between ion temperature and plasma density.

magnetosheath↗