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NASA NTRS1989

An alternative design for a sparse distributed memory

A new design for a Sparse Distributed Memory, called the selected-coordinate design, is described. As in the original design, there are a large number of memory locations, each of which may be activated by many different addresses (binary vectors) in a very large address space. Each memory location is defined by specifying ten selected coordinates (bit positions in the address vectors) and a set of corresponding assigned values, consisting of one bit for each selected coordinate. A memory location is activated by an address if, for all ten of the locations's selected coordinates, the corresponding bits in the address vector match the respective assigned value bits, regardless of the other bits in the address vector. Some comparative memory capacity and signal-to-noise ratio estimates for the both the new and original designs are given. A few possible hardware embodiments of the new design are described.

Jaeckel, Louis A.↗

NASA NTRS2022

The Long-stable Hard State of XTE J1752-223 and the Disk Truncation Dilemma

The degree to which the thin accretion disks of black hole X-ray binaries are truncated during hard spectral states remains a contentious open question in black hole astrophysics. During its singular observed outburst in 2009–2010, the black hole X-ray binary XTE J1752−223 spent ∼1 month in a long-stable hard spectral state at a luminosity of ∼0.02–0.1 L Edd . It was observed with 56 RXTE pointings during this period, with simultaneous Swift-XRT daily coverage during the first 10 days of the RXTE observations. While reflection modeling has been extensively explored in the analysis of these data, there is disagreement surrounding the geometry of the accretion disk and corona implied by the reflection features. We reexamine the combined, high signal-to-noise, simultaneous Swift and RXTE observations, and perform extensive reflection modeling with the latest relxill suite of reflection models, including newer high disk density models. We show that reflection modeling requires that the disk be within ∼5 R ISCO during the hard spectral state, while weaker constraints from the thermal disk emission imply higher truncation (Rin = 6–80 R ISCO ). We also explore more complex coronal continuum models, allowing for two Comptonization components instead of one, and show that the reflection features still require only a mildly truncated disk. Finally we present a full comparison of our results to previous constraints found from analyses of the same data set.

Accretion↗

NASA NTRS1993

Dynamics of the young binary LMC cluster NGC 1850

BV CCD images and echelle spectra of 52 supergiants are used to examine the age and internal dynamics of the young binary LMC cluster NGC 1850. A color-magnitude diagram was constructed and found to contain three distinct populations of stars. Using star-subtracted, median filtered BV images, attempts were made to determine ellipticity parameters, BV luminosity profiles were constructed to project radii greater than 40. A power law model was applied to test for the presence of a tidal cutoff in the luminosity profile. Of the 52 stars with echelle spectra, a subset of 36 were used to study the cluster dynamics. A rotational signal in the radial velocities has been detected at the 93-percent confidence level, implying a rotation axis at a position angle of 100 +/- 40 deg. Values for the slope of the mass function were determined using mass luminosity relationships and different forms for the IMF. The current cluster age is similar to its central relaxation time.

Fischer, Philippe↗

NASA NTRS2020

The Multiplanet System TOI-421: A Warm Neptune and a Super Puffy Mini-Neptune Transiting a G9 V Star in a Visual Binary

We report the discovery of a warm Neptune and a hot sub-Neptune transiting TOI-421 (BD-14 1137, TIC 94986319), a bright (V = 9.9) G9 dwarf star in a visual binary system observed by the Transiting Exoplanet Survey Satellite (TESS) space mission in Sectors 5 and 6. We performed ground-based follow-up observations—comprised of Las Cumbres Observatory Global Telescope transit photometry, NIRC2 adaptive optics imaging, and FIbre-fed Echellé Spectrograph, CORALIE, High Accuracy Radial velocity Planet Searcher, High Resolution Échelle Spectrometer, and Planet Finder Spectrograph high-precision Doppler measurements—and confirmed the planetary nature of the 16 day transiting candidate announced by the TESS team. We discovered an additional radial velocity signal with a period of five days induced by the presence of a second planet in the system, which we also found to transit its host star. We found that the inner mini-Neptune, TOI-421 b, has an orbital period of P(b) = 5.19672 ± 0.00049 days, a mass of M(b) = 7.17 ± 0.66 Mꚛ, and a radius of R(b) = 2.68 (+0.19,-0.18) Rꚛ, whereas the outer warm Neptune, TOI-421 c, has a period of P(c) = 16.06819 ± 0.00035 days, a mass of M(c) = 16.42 (+1.06,-1.04) Mꚛ, a radius of R(c) = 5.09{+0.16,-0.15) Rꚛ, and a density of ρ(c) = 0.685 (+0.080,-0.072) g/cu. cm. With its characteristics, the outer planet (ρ(c) = .685 {+0.080,-0.072) g/cu cm) is placed in the intriguing class of the super-puffy mini-Neptunes. TOI-421 b and TOI-421 c are found to be well-suited for atmospheric characterization. Our atmospheric simulations predict significant Lyα transit absorption, due to strong hydrogen escape in both planets, as well as the presence of detectable CH4 in the atmosphere of TOI-421 c if equilibrium chemistry is assumed.

Ilaria Carleo↗

NASA NTRS1992

A proposed study of multiple scattering through clouds up to 1 THz

A rigorous computation of the electromagnetic field scattered from an atmospheric liquid water cloud is proposed. The recent development of a fast recursive algorithm (Chew algorithm) for computing the fields scattered from numerous scatterers now makes a rigorous computation feasible. A method is presented for adapting this algorithm to a general case where there are an extremely large number of scatterers. It is also proposed to extend a new binary PAM channel coding technique (El-Khamy coding) to multiple levels with non-square pulse shapes. The Chew algorithm can be used to compute the transfer function of a cloud channel. Then the transfer function can be used to design an optimum El-Khamy code. In principle, these concepts can be applied directly to the realistic case of a time-varying cloud (adaptive channel coding and adaptive equalization). A brief review is included of some preliminary work on cloud dispersive effects on digital communication signals and on cloud liquid water spectra and correlations.

Gerace, G. C.↗

NASA NTRS1999

Carrier Estimation Using Classic Spectral Estimation Techniques for the Proposed Demand Assignment Multiple Access Service

In any satellite communication, the Doppler shift associated with the satellite's position and velocity must be calculated in order to determine the carrier frequency. If the satellite state vector is unknown then some estimate must be formed of the Doppler-shifted carrier frequency. One elementary technique is to examine the signal spectrum and base the estimate on the dominant spectral component. If, however, the carrier is spread (as in most satellite communications) this technique may fail unless the chip rate-to-data rate ratio (processing gain) associated with the carrier is small. In this case, there may be enough spectral energy to allow peak detection against a noise background. In this thesis, we present a method to estimate the frequency (without knowledge of the Doppler shift) of a spread-spectrum carrier assuming a small processing gain and binary-phase shift keying (BPSK) modulation. Our method relies on an averaged discrete Fourier transform along with peak detection on spectral match filtered data. We provide theory and simulation results indicating the accuracy of this method. In addition, we will describe an all-digital hardware design based around a Motorola DSP56303 and high-speed A/D which implements this technique in real-time. The hardware design is to be used in NMSU's implementation of NASA's demand assignment, multiple access (DAMA) service.

Scaife, Bradley James↗

NASA NTRS1974

Omega flight-test data reduction sequence

Computer programs for Omega data conversion, summary, and preparation for distribution are presented. Program logic and sample data formats are included, along with operational instructions for each program. Flight data (or data collected in flight format in the laboratory) is provided by the Ohio University Omega receiver base in the form of 6-bit binary words representing the phase of an Omega station with respect to the receiver's local clock. All eight Omega stations are measured in each 10-second Omega time frame. In addition, an event-marker bit and a time-slot D synchronizing bit are recorded. Program FDCON is used to remove data from the flight recorder tape and place it on data-processing cards for later use. Program FDSUM provides for computer plotting of selected LOP's, for single-station phase plots, and for printout of basic signal statistics for each Omega channel. Mean phase and standard deviation are printed, along with data from which a phase distribution can be plotted for each Omega station. Program DACOP simply copies the Omega data deck a controlled number of times, for distribution to users.

Lilley, R. W.↗

NASA NTRS1999

The LISA Mission Design

The proposed Laser Interferometer Space Antenna (LISA) is designed to observe gravitational radiation from galactic binaries and massive black holes in other galaxies. LISA will observe waves in the frequency range 0.1 mHz to 1 Hz, which can never be observed on Earth due to background noise. The three LISA spacecraft will be located at the vertices of an equilateral triangle with side length 5 million km. The orbits are chosen so that the triangle formation trails the Earth by 20 degrees. Each spacecraft will contain two independent instruments containing a proof mass, laser and 30 cm diameter telescope for the transmission and reception of laser signals. Two independent Michelson interferometers will be formed, allowing both polarizations of gravitational waves to be detected. The observed signals will yield unique information about the formation of massive black holes and the nature of gravity in the high-field limit.

Folkner, W. M.↗

NASA NTRS2019

Fermi-GBM GRBs with Characteristics Similar to GRB 170817A

We present a search for gamma-ray bursts in the Fermi-GBM (Gamma Burst Monitor) 10-year catalog that show similar characteristics to GRB170817A, the first electromagnetic counterpart to a GRB (Gamma-Ray Burst) identified as a binary neutron star (BNS) merger via gravitational wave observations. Our search is focused on a nonthermal pulse, followed by a thermal component,as observed for GRB 170817A. We employ search methods based on the measured catalog parameters and Bayesian Block analysis. Our multipronged approach, which includes examination of the localization and spectral properties of the thermal component, yields a total of 13 candidates, including GRB170817A and the previously reported similar burst, GRB 150101B. The similarity of the candidates is likely caused by the same processes that shaped the gamma-ray signal of GRB170817A, thus providing evidence of a nearby sample of short GRBs resulting from BNS merger events. Some of the newly identified counterparts were observed by other space telescopes and ground observatories, but none of them have a measured redshift. We present an analysis of this subsample, and we discuss two models. From uncovering 13 candidates during a time period of 10 years we predict that Fermi-GBM will trigger on-board on about one burst similar to GRB170817A per year.

von Kienlin, A.↗

NASA NTRS2021

The X-ray Bursts of XTE J1739-285: A NICER Sample

In this work, we report on observations with the Neutron Star Interior Composition Explorer of the known neutron star X-ray transient XTE J1739–285. We observed the source in 2020 February and March, finding it in a highly active bursting state. Across a 20 day period, we detected 32 thermonuclear X-ray bursts, with an average burst recurrence time of-+2.0 hr0.30.4. A timing and spectral analysis of the ensemble of X-ray bursts reveals homogeneous burst properties, evidence for short-recurrence time bursts, and the detection of a 386.5 Hz burst oscillation candidate. The latter is especially notable, given that a previous study of this source claimed a 1122 Hz burst oscillation candidate. We did not find any evidence of variability near 1122 Hz and instead find that the 386.5 Hz oscillation is the more prominent signal of the two burst oscillation candidates. Hence, we conclude it is unlikely that XTE J1739–285 has a submillisecond rotation period.

X-ray burst↗

NASA NTRS2022

X-Ray Imaging Observations of the High-Mass γ-Ray Binary HESS J0632+057

The Chandra X-ray Observatory (CXO)imaged the high-massγ-ray binary (HMGB) HESS8J0632+057 with the Advanced CCD Imaging Spectrometer (ACIS). We analyzed the CXO data to-9gether with 967 ks of archival imaging Swift-XRT observations. On arcsecond scales we find a hint10of asymmetric extended emission. On arcminute scales, there is a region of extended emission (“the11blob”) which is located≈5.5′east of the binary. The blob is seen in both the CXO-ACIS and the12Swift-XRT images but it does not have a counterpart in the radio, NIR, IR, or optical images. The13ACIS spectrum of the blob fits either an absorbed power-law model with Γ'2.6, or a thermal plasma14model withkT'3 keV. Since the blob’s NH is significantly larger than that of the binary we conclude15that the blob and binary are not directly related. The somewhat larger very deep XRT image suggests16that the binary may be located within a shell (or cavity). The four ACIS spectra taken within the∼2017day interval near the light curve minimum suggests that the NH is varying on timescales of days, pos-18sibly due to the inhomogenous circumbinary environment. The XRT spectra extracted from the wider19orbital phase intervals support significant changes in NH near the light curve maximum/minimum,20which may be responsible for the substantial systematic residuals seen near 1 keV, and provide tenta-21tive evidence for a Fe line at 6.4 keV. We find no significant periodic signal in the ACIS data up to 0.156 Hz.

O Kargaltsev↗

NASA NTRS1986

A 6 second periodic X-ray source in Carina

A serendipitous source, 1E 1048.1-5937, was discovered during Einstein imaging observations of the Carina nebula. On July 13, 1979, this source had an intensity of 0.14 IPC counts/s, and the signal was 65 percent pulsed with a period of 6.44 s. An earlier observation failed to detect any source with strength greater than 1/10 the above signal. The source is therefore highly variable, perhaps transient. An Exosat observation of this source on June 20, 1985 confirmed the pulse period and refined the source position to an accuracy of 10 arcsec. On the basis of the position, the source is tentatively identified with a V = 19 optical counterpart. The X-ray spectrum is best fitted by a power law with photon index = 2.26 and a column density of 1.6 x 10 to the 22nd atoms/sq cm. The X-ray characteristics are consistent with an accretion-powered Be star binary.

Seward, F. D.↗

NASA NTRS2021

A variable magnetic disc wind in the black hole X-ray binary GRS 1915+105?

Context. GRS 1915+105 being one of the brightest transient black hole binaries (BHBs) in the X-rays offers a unique testbed for the study of the connection between accretion and ejection mechanisms in BHBs. In particular, this source can be used to study the accretion disc wind and its dependence on the state changes in BHBs. Aims. Our aim is to investigate the origin and geometry of the accretion disc wind in GRS 1915+105. This study will provide a basis for planning future observations with the X-ray Imaging Spectroscopy Mission (XRISM), and may also provide important parameters for estimating the polarimetric signal with the upcoming Imaging X-ray Polarimetry Explorer (IXPE). Methods. We analysed the spectra of GRS 1915+105 in the soft ϕ and hard χ classes using the high-resolution spectroscopy offered by Chandra HETGS. In the soft state, we find a series of wind absorption lines that follow a non-linear dependence of velocity width, velocity shift, and equivalent width with respect to ionisation, indicating a multiple component or stratified outflow. In the hard state we find only a faint Fe XXVI absorption line. We model the absorption lines in both the states using a dedicated magneto-hydrodynamic (MHD) wind model to investigate a magnetic origin of the wind and to probe the cause of variability in the observed line flux between the two states. Conclusions. The MHD disc wind model provides a good fit for both states, indicating the possibility of a magnetic origin of the wind. The multiple ionisation components of the wind are well characterised as a stratification of the same magnetic outflow. We find that the observed variability in the line flux between soft and hard states cannot be explained by photo-ionisation alone but is most likely due to a large (three orders of magnitude) increase in the wind density. We find the mass outflow rate of the wind to be comparable to the accretion rate, suggesting an intimate link between accretion and ejection processes that lead to state changes in BHBs.

A. Ratheesh↗

NASA NTRS1981

Discovery and observation of BY Draconis variables

The discovery of BY Draconis variables was efficiently accomplished by a spectroscopic survey of dK-M stars for weak H-alpha emissions, using 1-2 A resolution. The four BY Dra variables discovered are all spectroscopic binaries with P values lower than about 10 d, in light of which, it is noted that the onset of high surface activity and appearance of H-alpha emission occur sharply at v(equator) of approximately 5 km/sec. At v(equator) of about 3 km/sec, dK-M stars have low levels of surface activity. It is found that while there is a range of Ca II emission strength, and only the strongest emitters of this line are BY Dra and/or flare stars, the H-alpha feature changes abruptly to an emission feature signaling the onset of flaring and/or the BY Dra syndrome. An increase of the rotation rate above v(equator) 5 km/sec does not appear to increase the level of surface activity.

Bopp, B. W.↗

NASA NTRS1984

On the passage of high-level pulsed radio frequency interference through a nonlinear satellite transponder

Attention is given to the uncoded bit error rate (BER) performance of a satellite communications system whose modulation scheme is binary PSK and whose transponder contains an arbitrary amplitude nonlinearity, all in the presence of high level pulsed radio frequency interference (RFI). A general approach is presented for direct BER evaluations, in contrast to other approaches which may employ SNR suppression factors. The computed results are based on arbitrarily specified RFI scenarios, in the presence of hard limiter, clipper, or blanker amplitude nonlinearities. Performance curves demonstrate the superiority of an appropriately chosen blanker when the RFI environment is most severe. The results obtained also pertain to the sensitivity of performance to the information bit rate, signal power variations, and the ratio of CW to noise content. The CW effects are found to be the most severe.

Weinberg, A.↗

NASA NTRS1987

IECON '87: Industrial applications of control and simulation; Proceedings of the 1987 International Conference on Industrial Electronics, Control, and Instrumentation, Cambridge, MA, Nov. 3, 4, 1987

Recent advances in control-system design and simulation are discussed in reviews and reports. Among the topics considered are fast algorithms for generating near-optimal binary decision programs, trajectory control of robot manipulators with compensation of load effects via a six-axis force sensor, matrix integrators for real-time simulation, a high-level control language for an autonomous land vehicle, and a practical engineering design method for stable model-reference adaptive systems. Also addressed are the identification and control of flexible-limb robots with unknown loads, adaptive control and robust adaptive control for manipulators with feedforward compensation, adaptive pole-placement controllers with predictive action, variable-structure strategies for motion control, and digital signal-processor-based variable-structure controls.

Hartley, Tom T.↗

NASA NTRS1995

Phase-Dependent Observations of Intermediate Polars and The Broad Emission and Absorption Line Region in NGC 3516

The Intermediate Polars (IP's) constitute a class of Cataclysmic Variables (CV's), which are binary star systems in which mass is transferred from a late-type main-sequence star to a white dwarf via Roche lobe overflow. In the IP's, the inner accretion disk is evidently disrupted by the magnetic field of the white dwarf. High-temperature shocks at the white dwarf's magnetic poles (where accretion occurs) produce X-rays, which are reprocessed into photons over a broad energy band across the electromagnetic spectrum. Because the white dwarf typically spins rapidly (rotation periods a few 10s to a few 100s of seconds), the signals due to both the X-rays and reprocessed photons are pulsed. The shape of the spectrum of pulse amplitude as a function of wavelength yields information about both the temperature and size of the pulse-emitting region. It has been noted by several investigators that the optical pulsation amplitudes rise steeply toward short wavelengths. It is therefore a fair surmise that pulsation amplitudes peak in the ultraviolet. The scientific goal of this project was to observe a representative sample of IP's, using IUE, in search of the expected strong UV pulsations, and hence to further our understanding of pulse-producing mechanisms.

Koratkar, Anuradha↗

NASA NTRS1981

E-beam generated holographic masks for optical vector-matrix multiplication

An optical vector matrix multiplication scheme that encodes the matrix elements as a holographic mask consisting of linear diffraction gratings is proposed. The binary, chrome on glass masks are fabricated by e-beam lithography. This approach results in a fairly simple optical system that promises both large numerical range and high accuracy. A partitioned computer generated hologram mask was fabricated and tested. This hologram was diagonally separated outputs, compact facets and symmetry about the axis. The resultant diffraction pattern at the output plane is shown. Since the grating fringes are written at 45 deg relative to the facet boundaries, the many on-axis sidelobes from each output are seen to be diagonally separated from the adjacent output signals.

Arnold, S. M.↗