6,451 research outputs found
Image based tracking approaches to AR/C at the Johnson Space Center
Automated Rendezvous and Capture (AR&C) requires the determination of the six degrees of freedom relating two free bodies. Sensor systems that can provide such information have varying sizes, weights, power requirements, complexities and accuracies. One type of sensor system which can provide several key advantages is an image based tracking system, or better known as a machine vision system. By image based tracking we mean that the sensor is some imaging device such as one or more video cameras, from which the tracking parameters necessary to support the rendezvous and capture operations (range, attitude, etc.) can be derived. Image based tracking offers many advantages such as relative hardware simplicity and reprogrammability. These advantages must be weighed against the disadvantages of these systems, such as limited operational range, poorer accuracy at greater distances and sensitivity to lighting conditions. However, with properly designed algorithms and targets these disadvantages can be minimized for many important applications. Rigorous testing in realistic environments can further increase the robustness and reliability of these systems. This presentation describes the facilities used at JSC to support AR&C image based tracking development and the details of our binocular stereo approach to image based tracking
A binocular stereo approach to AR/C at the Johnson Space Center
Automated Rendezvous and Capture requires the determination of the 6 DOF relating two free bodies. Sensor systems that can provide such information have varying sizes, weights, power requirements, complexities, and accuracies. One type of sensor system that can provide several key advantages is a binocular stereo vision system
Pluto's Light Curve in 1933-1934
We are reporting on a new accurate photographic light curve of Pluto for
1933-1934 when the heliocentric distance was 40 AU. We used 43 B-band and
V-band images of Pluto on 32 plates taken on 15 nights from 19 March 1933 to 10
March 1934. Most of these plates were taken with the Mount Wilson 60" and 100"
telescopes, but 7 of the plates (now at the Harvard College Observatory) were
taken with the 12" and 16" Metcalf doublets at Oak Ridge. The plates were
measured with an iris diaphragm photometer, which has an average one-sigma
photometric error on these plates of 0.08 mag as measured by the repeatability
of constant comparison stars. The modern B and V magnitudes for the comparison
stars were measured with the Lowell Observatory Hall 1.1-m telescope. The
magnitudes in the plate's photographic system were converted to the Johnson B-
and V-system after correction with color terms, even though they are small in
size. We find that the average B-band mean opposition magnitude of Pluto in
1933-1934 was 15.73 +- 0.01, and we see a roughly sinusoidal modulation on the
rotational period (6.38 days) with a peak-to-peak amplitude of 0.11 +- 0.03
mag. With this, we show that Pluto darkened by 5% from 1933-1934 to 1953-1955.
This darkening from 1933-1934 to 1953-1955 cannot be due to changing viewing
geometry (as both epochs had identical sub-Earth latitudes), so our
observations must record a real albedo change over the southern hemisphere. The
later darkening trend from 1954 to the 1980s has been explained by changing
viewing geometry (as more of the darker northern hemisphere comes into view).
Thus, we now have strong evidence for albedo changes on the surface of Pluto,
and these are most easily explained by the systematic sublimation of frosts
from the sunward pole that led to a drop in the mean surface albedo.Comment: Icarus in press, 24 page
Reproductive behavior and related social organization of the muskox on Nunivak Island
Thesis (M.S.) University of Alaska Fairbanks, 1976The sexual behavior and social organization of the muskox (Ovibos moschatus wardi Zimmerman) were studied on Nunivak Island, Alaska, in fall 1972 and summer and fall 1973. Observation effort was concentrated on a single harem group for two months, during the height of courtship activity. Movements and fluctuations in the structure of this group are documented. There was no significant change in mean herd size as a result of the rut, suggesting the existence of a basic social unit independent of the influence of harem bulls. Harem bulls were in the 6-10 year age class. They exerted a stabilizing influence on the harem but did not direct its movements. The rut extended from early July to mid-October. Copulation occurred on September 4 and 5. General patterns of sexual and agonistic behavior are described. Changes in activity patterns as a result of the rut are shown. Bulls displayed more marked changes than cows or juveniles. The proportion of time allocated to sexual and agonistic behavior increased at the expense of maintenance activity as the rut progressed
Extragalactic Zeeman Detections in OH Megamasers
We have measured the Zeeman splitting of OH megamaser emission at 1667 MHz
from five (ultra)luminous infrared galaxies ([U]LIRGs) using the 305 m Arecibo
telescope and the 100 m Green Bank Telescope. Five of eight targeted galaxies
show significant Zeeman-splitting detections, with 14 individual masing
components detected and line-of-sight magnetic field strengths ranging from
~0.5-18 mG. The detected field strengths are similar to those measured in
Galactic OH masers, suggesting that the local process of massive star formation
occurs under similar conditions in (U)LIRGs and the Galaxy, in spite of the
vastly different large-scale environments. Our measured field strengths are
also similar to magnetic field strengths in (U)LIRGs inferred from synchrotron
observations, implying that milligauss magnetic fields likely pervade most
phases of the interstellar medium in (U)LIRGs. These results provide a
promising new tool for probing the astrophysics of distant galaxies.Comment: 32 pages, 14 figures, 8 tables. Accepted for publication in The
Astrophysical Journal v680n2, June 20, 2008; corrected 2 typo
Dissolved oxygen dynamics during a phytoplankton bloom in the Ross Sea polynya
The Ross Sea polynya is one of the most productive regions in the Southern Ocean. However, limited access and high spatio-temporal variability of physical and biological processes limit the use of conventional oceanographic methods to measure early season primary productivity. High-resolution observations from two Seagliders provide insights into the timing of a bloom in the southern Ross Sea polynya in December 2010. Changes in chlorophyll and oxygen concentrations are used to assess bloom dynamics. Using a ratio of dissolved oxygen to carbon, net primary production is estimated over the duration of the bloom showing a sensitive balance between net autotrophy and heterotrophy. The two gliders, observing spatially distinct regions during the same period, found net community production rates of -0.9±0.7 and 0.7±0.4 g C m-2 d-1. The difference highlights the spatial variability of biological processes and is probably caused by observing different stages of the bloom. The challenge of obtaining accurate primary productivity estimates highlights the need for increased observational efforts, particularly focusing on subsurface processes not resolved using surface or remote observations. Without an increased observational effort and the involvement of emerging technologies, it will not be possible to determine the seasonal trophic balance of the Ross Sea polynya and quantify the shelf's importance in carbon export
Conformational Behavior of Symmetrical and Unsymmetrical Mono(Alkynylpeptide)-Tungsten Complexes [post-print]
A series of N-protected amino acid alkynylesters were prepared by reaction of the amino acid carboxylate group with either propargyl alcohol (to yield the asymmetric esters 2a–c) or with 1, 4-but-2-yne diol (to yield the symmetric esters 3a–d). The alkynylesters were reacted with W(CO)3(dmtc)2 to yield monoalkyne complexes having the general formula W(CO)(dmtc)2(alkynyl ester). The monoalkyne complexes 6a–f were unstable in the presence of oxygen and had to be kept under an inert atmosphere. Analysis of the NMR spectra of the monoalkyne complexes showed that two diastereomers were formed in the synthesis, and that there was rapid rotation of the alkyne about the tungsten center at 23 °C and above with both diastereomers. At lower temperatures alkyne rotation is significantly slowed. Symmetric alkynylesters of a dipeptide (4) and tripeptide (5) were also prepared and reacted with W(CO)3(dmtc)2 to yield monoalkyne complexes. The resulting complexes (6g and 6h) also formed two diastereomers and displayed rapid rotation of the alkyne about the tungsten center at 23 °C and above, and slow rotation at lower temperatures. The amide NH protons in 6g and 6h were probed by DMSO titration to see if they were involved in intramolecular hydrogen bonds; they were not, which indicates that the peptide portions of 6g and 6h adopt an extended conformation in solution.
Two peptides linked together via ester bonds to 1,4-dihydroxy-2-butyne coordinate to a tungsten center and adopt an extended conformation
Dynamic Analysis of Executables to Detect and Characterize Malware
It is needed to ensure the integrity of systems that process sensitive
information and control many aspects of everyday life. We examine the use of
machine learning algorithms to detect malware using the system calls generated
by executables-alleviating attempts at obfuscation as the behavior is monitored
rather than the bytes of an executable. We examine several machine learning
techniques for detecting malware including random forests, deep learning
techniques, and liquid state machines. The experiments examine the effects of
concept drift on each algorithm to understand how well the algorithms
generalize to novel malware samples by testing them on data that was collected
after the training data. The results suggest that each of the examined machine
learning algorithms is a viable solution to detect malware-achieving between
90% and 95% class-averaged accuracy (CAA). In real-world scenarios, the
performance evaluation on an operational network may not match the performance
achieved in training. Namely, the CAA may be about the same, but the values for
precision and recall over the malware can change significantly. We structure
experiments to highlight these caveats and offer insights into expected
performance in operational environments. In addition, we use the induced models
to gain a better understanding about what differentiates the malware samples
from the goodware, which can further be used as a forensics tool to understand
what the malware (or goodware) was doing to provide directions for
investigation and remediation.Comment: 9 pages, 6 Tables, 4 Figure
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