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At least 145 records · Page 8

A Comparison of the Extra Nuclear X-ray and Radio Features in M87

ROSAT High Resolution Imager (HRI) data from eight observations have been co-added to obtain an effective exposure of 230 ksec. We have identified a number of features and regions with excess X-ray brightness over that from a circularly symmetric model of the well known hot gas component. A prominent 'spur' extends 4feet from the vicinity of knot A towards the south-west. The brightness to the south and east of this spur is significantly higher than that to the north and west. Excess brightness is also found to the East of the nucleus, with a local maximum centered on the eastern radio lobe 3 feet from the core. There are two well known relationships between radio and X-ray emission for radio galaxies in clusters: coincidence of emissions because the X-rays come from inverse Compton or synchrotron processes; and anti-coincidence caused by exclusion of hot gas from radio entities. We present a radio/X-ray comparison to determine if either of these relationships can be isolated in M87. The greatest obstacle we face is the unknown projection which affects both bands.

Harris, D. E.↗

Birth of millisecond pulsars in globular clusters

It is argued here that accretion-induced collapse of white dwarfs in binaries can form millisecond pulsars directly without requiring a precursor low-mass X-ray binary stage. Ablation of the precollapse binary companion by the millisecond pulsar's radiation field, a process invoked to explain some of the characteristics of the recently discovered eclipsing millisecond pulsar, can then yield isolated neutron stars witout requiring an additional stellar encounter.

Grindlay, J. E.↗

The Dense, Warm Interstellar Medium (D-WIM): Unravelling a New Phase of the ISM A PRIMA FIR Probe Mission Project

We propose a study of the Dense Warm Interstellar Medium (D-WIM) via the two fine structure lines of ionized nitrogen (\NII). This new phase of the interstellar medium (ISM) has density 10 $\cmv \le n(e) \le$ 100 $\cmv$, and has effectively been identified throughout much of the Milky Way and in nearby galaxies. :The unexpected conditiosn in the D-WIM immediately raise important questions both about this phase of the ISM and its relationship to the ISM as a while. These include: what is the structure of the D-WIM -- e.g. filling factor, distribution, and morphology?; what is the origin of the D-WIM?; what supports its ionization and what is its evolution given huge overpressure relative to the $\ge$ 100 times more diffuse Warm Ionized Medium (WIM)?; what is its possible relationship to stars - is it the the remnants of very old HII regions that were produced by clusters of masive stars? The PRIMA survey requires a coverage of a large fraction of the plane, plus selected regions at high galactic latitudes. A sensitivity of 10$^{-9}$ $Wm^{-2}sr^{-1}$ would be highly desirable. A spectral resolution $R$ of 10$^4$ will isolate individual spectral features. $R$ = 10$^3$ would be acceptable to measure the total intensity. This PRIMA survey could be part of a broader survey of the ISM, and include a number of other important ISM tracers such as [CII] 158 \um, [OI] 63 \um\ and [OI] 146 \um, depending on wavelength coverage of the instrument. The sensitivity requirement for study of the D-WIM is likely more stringent than for the other lines, and may require special consideration for successful implementation as well as for determining the area that can be observed.

Lis, Dariusz↗

Fault Diagnosis of Power Systems Using Intelligent Systems

The power system operator's need for a reliable power delivery system calls for a real-time or near-real-time Al-based fault diagnosis tool. Such a tool will allow NASA ground controllers to re-establish a normal or near-normal degraded operating state of the EPS (a DC power system) for Space Station Alpha by isolating the faulted branches and loads of the system. And after isolation, re-energizing those branches and loads that have been found not to have any faults in them. A proposed solution involves using the Fault Diagnosis Intelligent System (FDIS) to perform near-real time fault diagnosis of Alpha's EPS by downloading power transient telemetry at fault-time from onboard data loggers. The FDIS uses an ANN clustering algorithm augmented with a wavelet transform feature extractor. This combination enables this system to perform pattern recognition of the power transient signatures to diagnose the fault type and its location down to the orbital replaceable unit. FDIS has been tested using a simulation of the LeRC Testbed Space Station Freedom configuration including the topology from the DDCU's to the electrical loads attached to the TPDU's. FDIS will work in conjunction with the Power Management Load Scheduler to determine what the state of the system was at the time of the fault condition. This information is used to activate the appropriate diagnostic section, and to refine if necessary the solution obtained. In the latter case, if the FDIS reports back that it is equally likely that the faulty device as 'start tracker #1' and 'time generation unit,' then based on a priori knowledge of the system's state, the refined solution would be 'star tracker #1' located in cabinet ITAS2. It is concluded from the present studies that artificial intelligence diagnostic abilities are improved with the addition of the wavelet transform, and that when such a system such as FDIS is coupled to the Power Management Load Scheduler, a faulty device can be located and isolated from the rest of the system. The benefit of these studies provides NASA with the ability to quickly restore the operating status of a space station from a critical state to a safe degraded mode, thereby saving costs in experimentation rescheduling, fault diagnostics, and prevention of loss-of-life.

Momoh, James A.↗

What are cirrus point sources?

Most cirrus point sources are associated with interstellar gas. A subset of these was isolated, together with other sources showing large band 4 to 3 flux density ratios, that are not associated with interstellar gas. Most of the point sources are associated with diffuse cirrus emissions. The sources appear to be distributed randomly on the sky, with the exception of six clusters, one of which is not associated with any known object. Six sources out of seventeen that were observed for redshifted H I at Arecibo were found to be associated with relatively nondescript external galaxies. Most of the sources do not appear on the Palomar Sky Survey. Deep optical observations of eight fields revealed some fairly distant galaxies, one object with a very peculiar optical spectrum, and several blank fields.

Heiles, Carl↗

Chile Wildfires: Utilizing NASA and NOAA Earth Observations to Determine Lightning-ignited Wildfire Risks in Central Chile

In recent years, Central Chile has experienced wildfires of increasing frequency and intensity which threaten natural resources and communities. The Corporación Nacional Forestal (CONAF) responds to wildfires caused by a variety of ignitions, including lightning, but it is difficult to determine the prevalence of lightning-ignited wildfires based solely on ground observations. In collaboration with CONAF and the Embassy of Chile, Agricultural Office, the team used Earth observations to map coincidence of lightning strikes and wildfire ignitions. The Active Fire Product of Suomi NPP Visible Infrared Imaging Radiometer Suite (VIIRS) identified wildfires as thermal anomalies, which the team compared to the lightning events detected by NOAA’s GOES-16 Geostationary Lightning Mapper (GLM). Next, the team mapped lightning strike frequency and lightning related wildfires across the study area. Finally, the team calculated and mapped a relative estimate of lightning-ignited wildfire vulnerability across the year, fire season (December – March), and off-season (April – November) by summing the following factors: lightning frequency, the Normalized Difference Moisture Index (NDMI) and land surface temperature (LST). These risks were then weighted by fuel availability. Preliminary analysis of the lightning fire relationship showed a spatiotemporal coincidence, primarily in the South-central region of study, near Temuco, and isolated areas on the Andean front. The team identified areas at risk of lightning-induced wildfires, predominantly in the northern third of the study area and along the Andean front. Adjusting the relative weight of risk factors and improving the lightning and fire coincidence map by clustering VIIRS thermal anomalies into fire events could reduce discrepancies and improve risk assessments for future work.

Christopher Matechik↗

Automated Storm Tracking and the Lightning Jump Algorithm Using GOES-R Geostationary Lightning Mapper (GLM) Proxy Data

This study develops a fully automated lightning jump system encompassing objective storm tracking, Geostationary Lightning Mapper proxy data, and the lightning jump algorithm (LJA), which are important elements in the transition of the LJA concept from a research to an operational based algorithm. Storm cluster tracking is based on a product created from the combination of a radar parameter (vertically integrated liquid, VIL), and lightning information (flash rate density). Evaluations showed that the spatial scale of tracked features or storm clusters had a large impact on the lightning jump system performance, where increasing spatial scale size resulted in decreased dynamic range of the system's performance. This framework will also serve as a means to refine the LJA itself to enhance its operational applicability. Parameters within the system are isolated and the system's performance is evaluated with adjustments to parameter sensitivity. The system's performance is evaluated using the probability of detection (POD) and false alarm ratio (FAR) statistics. Of the algorithm parameters tested, sigma-level (metric of lightning jump strength) and flash rate threshold influenced the system's performance the most. Finally, verification methodologies are investigated. It is discovered that minor changes in verification methodology can dramatically impact the evaluation of the lightning jump system.

lightning jump↗

The relation of dust and atomic gas properties of galaxies

The way in which the neutral atomic hydrogen and far-IR emission from galaxies relate to their environments is shown. It is found that isolated and interacting galaxies display a fairly narrow range of a temperature-adjusted 'H I/100-micron index', suggesting that atomic gas-to-dust ratios are relatively constant among most galaxies. Isolated normal galaxies are used to develop a fiducial standard for the H I/100-micron index, against which galaxies in other environments are compared. Galaxies undergoing tidal interactions prove to have the same value for the index once the proper temperature adjustment is applied according to their FIR color. Applied to clusters, the H I/100-micron index shows a clear discrimination between galaxies whose H I is 'stripped' or 'unstripped', implying that there is about 6 times less H I in stripped galaxies relative to the 100-micron-emitting dust. The stripped galaxies also appear to have a slightly lower mean dust temperature, which is surprising since the stripping process might be expected to remove preferentially cooler than average dust from the outer disk.

Spitzak, John G.↗

Refinement of the Robert-Bonamy Formalism: Considering Effects from the Line Coupling

Since it was developed in 1979, the Robert-Bonamy (RB) formalism has been widely used in calculating pressure broadened half-widths and induced shifts for many molecular systems. However, this formalism contains several approximations whose applicability has not been thoroughly justified. One of them is that lines of interest are well isolated. When these authors developed the formalism, they have relied on this assumption twice. First, in calculating the spectral density F(ω), they have only considered the diagonal matrix elements of the relaxation operator. Due to this simplification, effects from the line mixing are ignored. Second, when they applied the linked cluster theorem to remove the cutoff, they have assumed the matrix elements of the operator exp(-iS(sub 1) - S(sub 2)) can be replaced by the exponential of the matrix elements of -iS(sub 1) - S(sub 2). With this replacement, effects from the line coupling are also ignored. Although both these two simplifications relied on the same approximation, their validity criteria are completely different and the latter is more stringent than the former. As a result, in many cases where the line mixing becomes negligible, significant effects from the line coupling have been completely missed. In the present study, we have developed a new method to evaluate the matrix elements of exp(-iS(sub 1) - S(sub 2)) and have refined the RB formalism such that line coupling can be taken into account. Our numerical calculations of the half-widths for Raman Q lines of the N(sub 2)-N(sub 2) pair have demonstrated that effects from the line coupling are important. In comparison with values derived from the RB formalism, new calculated values for these lines are significantly reduced. A recent study has shown that in comparison with the measurements and the most accurate close coupling calculations, the RB formalism overestimates the half-widths by a large amount. As a result, the refinement of the RB formalism goes in the right direction and these new calculated half-widths become closer to the "true" values.

spectra↗

Hemichordates and the Origin of Chordates

At the start of the period of the NASA grant three years ago, we had no information on the organization and development of the body axis of the hemichordate, Saccoglossus kowalevskii. Now we have substantial findings about the anteroposterior axis and dorsoventral axis, and based on this information, we have new insights about the origin of chordates from ancestral deuterostomes. We found ways to obtain and preserve large numbers of embryos and hatched juveniles. We can now collect about 40,000 embryos in the month of September, the time of S. kowalevskii spawning at Woods Hole. Excellent cDNA libraries were prepared from three developmental stages. From these libraries, we directly isolated about 30 gene ortholog sequences by screening and pcr techniques, all of these sequences of interest in the inquiry about the animal's organization and development. We also performed a mid-sized EST project (60,000 randomly picked clones, many of these arrayed). About half of these have been analyzed so far by blastx and are suitable for direct use of clones. We have obtained about 50 interesting sequences from this set. The rest still await analysis. Thus, at this time we have isolated orthologs of 80 genes that are known to be expressed in chordates in conserved domains and known to have interesting roles in chordate organization and development. The orthology of the S. kowalevskii sequences has been verified by neighbor joining and parsimony methods, with bootstrap estimates of validity. The S. kowalevskii sequences cluster with other deuterostome sequences, namely, other hemichordates, echinoderms, ascidians, amphioxus, or vertebrates, depending on what sequences are available in the database for comparison. We have used these sequences to do high quality in situ hybridization on S. kowalevskii embryos, and the results can be divided into three sections-those concerning the anteroposterior axis of S. kowalevskii in comparison to the same axis of chordates, those concerning the dorsoventral axis of S. kowalevskii in comparison to the same axis of chordates, and those concerning the signals and transcription factors found in the endoderm, of S. kowalevskii compared to the signals and transcription factors in the endo-mesodermal cells of Spemann's organizer of chordates.

Gerhart, John↗

Harmonic oscillator representation in the theory of scattering and nuclear reactions

The following questions, concerning the application of the harmonic oscillator representation (HOR) in the theory of scattering and reactions, are discussed: the formulation of the scattering theory in HOR; exact solutions of the free motion Schroedinger equation in HOR; separable expansion of the short range potentials and the calculation of the phase shifts; 'isolated states' as generalization of the Wigner-von Neumann bound states embedded in continuum; a nuclear coupled channel problem in HOR; and the description of true three body scattering in HOR. As an illustration the soft dipole mode in the (11)Li nucleus is considered in a frame of the (9)Li+n+n cluster model taking into account of three body continuum effects.

Smirnov, Yuri F.↗

From Stars to Super-Planets: The Low-Mass IMF in the Young Cluster IC348

We investigate the low-mass population of the young cluster IC348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrow-band imaging, that measure the strength of the 1.9 micron water band, we determine the spectral type and reddening for every M-type star in the field, thereby separating cluster members from the interloper population. Due to the efficiency of our spectral classification technique, our study is complete from approximately 0.7 solar mass to 0.015 solar mass. The mass function derived for the cluster in this interval, dN/d log M alpha M(sup 0.5), is similar to that obtained for the Pleiades, but appears significantly more abundant in brown dwarfs than the mass function for companions to nearby sun-like stars. This provides compelling observational evidence for different formation and evolutionary histories for substellar objects formed in isolation vs. as companions. Because our determination of the IMF is complete to very low masses, we can place interesting constraints on the role of physical processes such as fragmentation in the star and planet formation process and the fraction of dark matter in the Galactic halo that resides in substellar objects.

Najita, Joan R.↗

Observational properties of compact groups of galaxies

Compact groups are small, relatively isolated, systems of galaxies with projected separations comparable to the diameters of the galaxies themselves. Two well-known examples are Stephan's Quintet (Stephan, 1877) and Seyfert's Sextet (Seyfert 1948a,b). In groups such as these, the apparent space density of galaxies approaches 10(exp 6) Mpc(sub -3), denser even than the cores of rich clusters. The apparent unlikeliness of the chance occurrence of such tight groupings lead Ambartsumyan (1958, 1975) to conclude that compact groups must be physically dense systems. This view is supported by clear signs of galaxy interactions that are seen in many groups. Spectroscopic observations reveal that typical relative velocities of galaxies in the groups are comparable to their internal stellar velocities. This should be conducive to strong gravitational interactions - more so than in rich clusters, where galaxy velocities are typically much higher. This suggests that compact groups could be excellent laboratories in which to study galaxy interactions and their effects. Compact groups often contain one or more galaxies whose redshift differs greatly from those of the other group members. If these galaxies are at the same distance as the other members, either entire galaxies are being ejected at high velocities from these groups, or some new physical phenomena must be occurring. If their redshifts are cosmological, we must explain why so many discordant galaxies are found in compact groups. In recent years much progress has been made in addressing these questions. Here, the author discusses the current observational data on compact groups and their implications.

Hickson, Paul↗

Resurrecting hot dark matter - Large-scale structure from cosmic strings and massive neutrinos

These are the results of a numerical simulation of the formation of large-scale structure from cosmic-string loops in a universe dominated by massive neutrinos (hot dark matter). This model has several desirable features. The final matter distribution contains isolated density peaks embedded in a smooth background, producing a natural bias in the distribution of luminous matter. Because baryons can accrete onto the cosmic strings before the neutrinos, the galaxies will have baryon cores and dark neutrino halos. Galaxy formation in this model begins much earlier than in random-phase models. On large scales the distribution of clustered matter visually resembles the CfA survey, with large voids and filaments.

Scherrer, Robert J.↗

Evolution of wide binary millisecond pulsars in globular clusters

The evolution of a binary radio pulsar in a wide orbit about a low-mass degenerate dwarf companion in a globular cluster environment is investigated. An extensive series of numerical scattering experiments is used to study encounters between such a pulsar and passing cluster field stars. A wide range of initial orbital periods from 3 to 1000 days is considered with a corresponding range of masses for the degenerate dwarf companions. The calculative results are summarized in the form of scattering cross sections. In particular, cross sections are presented for three final 'channels' in which the end product of the encounter is an isolated neutron star. Cross sections for inducing various orbital eccentricities into initially circular orbits are also derived. The implications of the results for the formation of the single millisecond pulsars in M28 and M15 and for the nearly circular obit of the M4 binary radio pulsar are discussed.

Rappaport, S.↗

Clusters of DNA damage induced by ionizing radiation: formation of short DNA fragments. II. Experimental detection

The basic 30-nm chromatin fiber in the mammalian cell consists of an unknown (possibly helical) arrangement of nucleosomes, with about 1.2 kb of DNA per 10-nm length of fiber. Track-structure considerations suggest that interactions of single delta rays or high-LET particles with the chromatin fiber might result in the formation of multiple lesions spread over a few kilobases of DNA (see the accompanying paper: W.R. Holley and A. Chatterjee, Radiat. Res. 145, 188-199, 1996). In particular, multiple DNA double-strand breaks and single-strand breaks may form. To test this experimentally, primary human fibroblasts were labeled with [3H]thymidine and exposed at 0 degrees C to X rays or accelerated nitrogen or iron ions in the LET range of 97-440 keV/microns. DNA was isolated inside agarose plugs and subjected to agarose gel electrophoresis under conditions that allowed good separation of 0.1-2 kb size DNA. The bulk of DNA remained in the well or migrated only a small distance into the gel. It was found that DNA fragments in the expected size range were formed linearly with dose with an efficiency that increased with LET. A comparison of the yield of such fragments with the yield of total DNA double-strand breaks suggests that for the high-LET ions a substantial proportion (20-90%) of DNA double-strand breaks are accompanied within 0.1-2 kb by at least one additional DNA double-strand break. It is shown that these results are in good agreement with theoretical calculations based on treating the 30-nm chromatin fiber as the target for ionizing particles. Theoretical considerations also predict that the clusters will contain numerous single-strand breaks and base damages. It is proposed that such clusters be designated "regionally multiply damaged sites." Postirradiation incubation at 37 degrees C resulted in a decline in the number of short DNA fragments, suggesting a repair activity. The biological significance of regionally multiply damaged sites is presently unknown.

Non-NASA Center↗

Optical observations of NGC 2915: A nearby blue compact dwarf galaxy

This paper presents B and R band Charge Coupled Device (CCD) images and medium resolution spectroscopy of NGC 2915, a relatively isolated BCD (blue compact dwarf) galaxy at a distance of approximately 5 Mpc. NGC 2915 contains two stellar populations: a high surface brightness blue core population and a red diffuse population. The core population contains all of the H II, and numerous embedded objects. It is the locus of current high mass star formation. The brightest embedded objects are likely to be young ionizing clusters, while many of the fainter objects are likely to be individual supergiant stars with masses up to approximately 25 solar mass, or blends of a few such stars. Curious aligned structures on the SE side of the galaxy are seen and their nature discussed. The spectrum of the core is dominated by bright narrow emission lines like that of a high excitation and low metallicity (less than half solar) H II region. The continuum is flat, with Balmer and Ca II features seen in absorption. The velocity of the Ca II features suggest contamination by galactic interstellar absorption. There is a significant velocity gradient in the spectra, probably indicative of rotation. Outside of its core, NGC 2915 resembles a dE (dwarf elliptical) galaxy, in that it has an exponential surface brightness profile, is red ((B-R)(sub 0) = 1.65), and has a low extrapolated central surface brightness (B(0)(sub c) = 22.44). NGC 2915's properties are compared with other BCDs, concentrating on two morphologically similar BCDs that are near enough to resolve into stars: NGC 1705 and NGC 5253. It is noted that the presence of winds in BCDs invalidates closed box chemical evolution models and the remaining constraints on star formation duration are relatively weak. Some BCDs, including NGC 2915, may be able to maintain their present star formation rate for Gyr time scales. This suggests that the overall evolution of these BCDs may be much slower than the approximately 10 Myr burst time scales commonly quoted. However, shortly after the formation of a massive (10(exp 6) solar mass) cluster a BCD will have all the properties of strong starburst galaxy).

Meurer, G. R.↗

NASA Tech Briefs, May 2009

Topics covered include: Valve-"Health"-Monitoring System; Microstrip Antenna for Remote Sensing of Soil Moisture and Sea Surface Salinity; Biomedical Wireless Ambulatory Crew Monitor; Wireless Avionics Packet to Support Fault Tolerance for Flight Applications; Aerobot Autonomy Architecture; Submillimeter Confocal Imaging Active Module; Traveling-Wave Maser for 32 GHz; System Synchronizes Recordings from Separated Video Cameras; Piecewise-Planar Parabolic Reflectarray Antenna; Reducing Interference in ATC Voice Communication; EOS MLS Level 1B Data Processing, Version 2.2; Auto-Generated Semantic Processing Services; Geospatial Authentication; Maneuver Automation Software; Event Driven Messaging with Role-Based Subscriptions; Estimating Relative Positions of Outer-Space Structures; Fabricating PFPE Membranes for Capillary Electrophoresis; Linear Actuator Has Long Stroke and High Resolution; Installing a Test Tap on a Metal Battery Case; Fabricating PFPE Membranes for Microfluidic Valves and Pumps; Room-Temperature-Cured Copolymers for Lithium Battery Gel Electrolytes; Catalysts for Efficient Production of Carbon Nanotubes; Amorphous Silk Fibroin Membranes for Separation of CO2; "Zero-Mass" Noninvasive Pressure Transducers; Radial-Electric-Field Piezoelectric Diaphragm Pumps; Ejector-Enhanced, Pulsed, Pressure-Gain Combustor; Suppressing Ghost Diffraction in E-Beam-Written Gratings; Target-Tracking Camera for a Metrology System; Polarimetric Imaging using Two Photoelastic Modulators; Miniature Wide-Angle Lens for Small-Pixel Electronic Camera; Modal Filters for Infrared Interferometry; Mo(3)Sb(7-x)Te(x) for Thermoelectric Power Generation; Two-Dimensional Quantum Model of a Nanotransistor; Scanning Miniature Microscopes without Lenses; Manipulating Neutral Atoms in Chip-Based Magnetic Traps; Expansion Compression Contacts for Thermoelectric Legs; Processing Electromyographic Signals to Recognize Words; Physical Principle for Generation of Randomness; DSN Beowulf Cluster-Based VLBI Correlator; Hybrid NN/SVM Computational System for Optimizing Designs; Criteria for Modeling in LES of Multicomponent Fuel Flow; Computerized Machine for Cutting Space Shuttle Thermal Tiles; Orbiting Depot and Reusable Lander for Lunar Transportation; FPGA-Based Networked Phasemeter for a Heterodyne Interferometer; Aquarius Digital Processing Unit; Three-Dimensional Optical Coherence Tomography; Benchtop Antigen Detection Technique using Nanofiltration and Fluorescent Dyes; Isolation of Precursor Cells from Waste Solid Fat Tissue; Identification of Bacteria and Determination of Biological Indicators; Further Development of Scaffolds for Regeneration of Nerves; Chemically Assisted Photocatalytic Oxidation System; Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications; Crashworthy Seats Would Afford Superior Protection; Open-Access, Low-Magnetic-Field MRI System for Lung Research; Microfluidic Mixing Technology for a Universal Health Sensor; Microfluidic Extraction of Biomarkers using Water as Solvent; Microwell Arrays for Studying Many Individual Cells; Droplet-Based Production of Liposomes; and Identifying and Inactivating Bacterial Spores

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