28,095 research outputs found
Autonomous rendezvous and capture development infrastructure
In the development of the technology for autonomous rendezvous and docking, key infrastructure capabilities must be used for effective and economical development. This involves facility capabilities, both equipment and personnel, to devise, develop, qualify, and integrate ARD elements and subsystems into flight programs. One effective way of reducing technical risks in developing ARD technology is the use of the ultimate test facility, using a Shuttle-based reusable free-flying testbed to perform a Technology Demonstration Test Flight which can be structured to include a variety of additional sensors, control schemes, and operational approaches. This conceptual testbed and flight demonstration will be used to illustrate how technologies and facilities at MSFC can be used to develop and prove an ARD system
Gaia DR2 Distances and Peculiar Velocities for Galactic Black Hole Transients
We report on a first census of Galactic black hole X-ray binary (BHXRB)
properties with the second data release (DR2) of {\em Gaia}, focusing on
dynamically confirmed and strong candidate black hole transients. DR2 provides
five-parameter astrometric solutions including position, parallax and proper
motion for 11 of a sample of 24 systems. Distance estimates are tested with
parallax inversion as well as Bayesian inference. We derive an empirically
motivated characteristic scale length of =2.170.12 kpc for this BHXRB
population to infer distances based upon an exponentially decreasing space
density prior. Geometric DR2 parallaxes provide new, independent distance
estimates, but the faintness of this population in quiescence results in
relatively large fractional distance uncertainties. Despite this, DR2 estimates
generally agree with literature distances. The most discrepant case is BW Cir,
for which detailed studies of the donor star have suggested a distant location
at >~25 kpc. A large DR2 measured parallax and relatively high proper motion
instead prefer significantly smaller distances, suggesting that the source may
instead be amongst the nearest of XRBs. However, both distances create problems
for interpretation of the source, and follow-up data are required to resolve
its true nature. DR2 also provides a first distance estimate to one source,
MAXI J1820+070, and novel proper motion estimates for 7 sources. Peculiar
velocities relative to Galactic rotation exceed 50 km s for the
bulk of the sample, with a median system kinetic energy of peculiar motion of
5 10 erg. BW Cir could be a new high-velocity BHXRB if
its astrometry is confirmed. A putative anti-correlation between peculiar
velocity and black hole mass is found, as expected in mass-dependent BH kick
formation channels, but this trend remains weak in the DR2 data.Comment: MNRAS in pres
Micro-CT Image-Derived Metrics Quantify Arterial Wall Distensibility Reduction in a Rat Model of Pulmonary Hypertension
We developed methods to quantify arterial structural and mechanical properties in excised rat lungs and applied them to investigate the distensibility decrease accompanying chronic hypoxia-induced pulmonary hypertension. Lungs of control and hypertensive (three weeks 11% O2) animals were excised and a contrast agent introduced before micro-CT imaging with a special purpose scanner. For each lung, four 3D image data sets were obtained, each at a different intra-arterial contrast agent pressure. Vessel segment diameters and lengths were measured at all levels in the arterial tree hierarchy, and these data used to generate features sensitive to distensibility changes. Results indicate that measurements obtained from 3D micro-CT images can be used to quantify vessel biomechanical properties in this rat model of pulmonary hypertension and that distensibility is reduced by exposure to chronic hypoxia. Mechanical properties can be assessed in a localized fashion and quantified in a spatially-resolved way or as a single parameter describing the tree as a whole. Micro-CT is a nondestructive way to rapidly assess structural and mechanical properties of arteries in small animal organs maintained in a physiological state. Quantitative features measured by this method may provide valuable insights into the mechanisms causing the elevated pressures in pulmonary hypertension of differing etiologies and should become increasingly valuable tools in the study of complex phenotypes in small-animal models of important diseases such as hypertension
Synthetic perspective optical flow: Influence on pilot control tasks
One approach used to better understand the impact of visual flow on control tasks has been to use synthetic perspective flow patterns. Such patterns are the result of apparent motion across a grid or random dot display. Unfortunately, the optical flow so generated is based on a subset of the flow information that exists in the real world. The danger is that the resulting optical motions may not generate the visual flow patterns useful for actual flight control. Researchers conducted a series of studies directed at understanding the characteristics of synthetic perspective flow that support various pilot tasks. In the first of these, they examined the control of altitude over various perspective grid textures (Johnson et al., 1987). Another set of studies was directed at studying the head tracking of targets moving in a 3-D coordinate system. These studies, parametric in nature, utilized both impoverished and complex virtual worlds represented by simple perspective grids at one extreme, and computer-generated terrain at the other. These studies are part of an applied visual research program directed at understanding the design principles required for the development of instruments displaying spatial orientation information. The experiments also highlight the need for modeling the impact of spatial displays on pilot control tasks
Managing Engineering Talent: Unique Challenges to Optimize the Best and Brightest
Most engineers are bright, hard-working, reliable, and prefer to avoid conflict. An engineering curriculum tends to self-select these characteristics. By most standards, you would expect workers exhibiting these traits to require minimal supervision. But is this true? Is this how most current engineering managers lead? Looking at some current theories on leadership combined with personal anecdotes, this presentation will look at some common misconceptions about leading engineers
Replication of Known Dental Characteristics in Porcine Skin: Emerging Technologies for the Imaging Specialist
This study demonstrates that it is sometimes possible to replicate patterns of human teeth in pig skin and determine scientifically that a given injury pattern (bite mark) correlates with the dentitions of a very small proportion of a population dataset, e.g., 5 percent or even 1 percent. The authors recommend building on the template of this research with a sufficiently large database of samples that reflects the diverse world population. They also envision the development of a sophisticated imaging software application that enables forensic examiners to insert parameters for measurement, as well as additional methods of applying force to produce bite marks for research. The authors further advise that this project is applied science for injury pattern analysis and is only foundational research that should not be cited in testimony and judicial procedures. It supplements but does not contradict current guidelines of the American Board of Forensic Odontology regarding bite mark analysis and comparisons. A much larger population database must be developed. The project’s methodology is described in detail, accompanied by 11 tables and 41 figures
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Impacts of Exhaust Transfer System Contamination on Particulate Matter Measurements
Real-time diagnostics of gas/water assisted injection moulding using integrated ultrasonic sensors
YesAn ultrasound sensor system has been applied to the mould of both the water and gas assisted
injection moulding processes. The mould has a cavity wall mounted pressure sensor and instrumentation to
monitor the injection moulding machine. Two ultrasound sensors are used to monitor the arrival of the fluid
(gas or water) bubble tip through the detection of reflected ultrasound energy from the fluid polymer
boundary and the fluid bubble tip velocity through the polymer melt is estimated. The polymer contact with
the cavity wall is observed through the reflected ultrasound energy from that boundary. A theoretically
based estimation of the residual wall thickness is made using the ultrasound reflection from the fluid (gas or
water) polymer boundary whilst the samples are still inside the mould and a good correlation with a physical
measurement is observed
Impact of Pre-Columbian Agriculture, Climate Change, and Tectonic Activity Inferred From a 5,700-Year Paleolimnological Record from Lake Nicaragua
Lake Nicaragua, the largest lake in Central America, is a promising site for paleolimnological study of past climate change, tectonic and volcanic activity, and pre-Columbian agriculture in the region. It is near the northern limit of the Intertropical Convergence Zone (ITCZ), which brings the rainy season to the tropics, so effects of decreasing precipitation due to southern migration of the ITCZ through the Holocene should be observable. Because fault zones and an active volcano lie within the lake, the long-term impact of tectonic and volcanic activity can also be examined. Finally, the fertile volcanic soils near the lake may have encouraged early agriculture. We analyzed diatoms, biogenic silica (BSi), total organic carbon (TOC), water content, volcanic glass, and magnetic susceptibility in a sediment core from Lake Nicaragua with eleven accelerator mass spectroscopy radiocarbon dates, spanning ~5,700 years. Sediment accumulation rates decreased from the bottom to the top of the core, indicating a general drying trend through the Holocene. An increase in eutrophic diatom abundance suggests that pre-Columbian agriculture impacted the lake as early as ~5,400 cal yr BP. Above a horizon of coarser grains deposited sometime between ~5,200 and 1,600 cal yr BP, planktonic diatoms increased and remained dominant to the top of the core, indicating that water depth permanently increased. Although magnetic susceptibility peaked and water content dipped at the coarse horizon, volcanic glass fragments did not increase, suggesting that the coarse horizon and subsequent increase in water depth were caused by tectonic rather than by volcanic activity. Decreased accumulation rates of BSi and TOC indicate that water became clearer when depth increased
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