On the phenomenon of mixed dynamics in Pikovsky-Topaj system of coupled rotators

NASA Astrophysics Data System (ADS)

Gonchenko, A. S.; Gonchenko, S. V.; Kazakov, A. O.; Turaev, D. V.

2017-07-01

A one-parameter family of time-reversible systems on three-dimensional torus is considered. It is shown that the dynamics is not conservative, namely the attractor and repeller intersect but not coincide. We explain this as the manifestation of the so-called mixed dynamics phenomenon which corresponds to a persistent intersection of the closure of the stable periodic orbits and the closure of the completely unstable periodic orbits. We search for the stable and unstable periodic orbits indirectly, by finding non-conservative saddle periodic orbits and heteroclinic connections between them. In this way, we are able to claim the existence of mixed dynamics for a large range of parameter values. We investigate local and global bifurcations that can be used for the detection of mixed dynamics.

The role of invariant manifolds in lowthrust trajectory design (part III)

NASA Technical Reports Server (NTRS)

Lo, Martin W.; Anderson, Rodney L.; Lam, Try; Whiffen, Greg

2006-01-01

This paper is the third in a series to explore the role of invariant manifolds in the design of low thrust trajectories. In previous papers, we analyzed an impulsive thrust resonant gravity assist flyby trajectory to capture into Europa orbit using the invariant manifolds of unstable resonant periodic orbits and libration orbits. The energy savings provided by the gravity assist may be interpreted dynamically as the result of a finite number of intersecting invariant manifolds. In this paper we demonstrate that the same dynamics is at work for low thrust trajectories with resonant flybys and low energy capture. However, in this case, the flybys and capture are effected by continuous families of intersecting invariant manifolds.

SEAHT: A computer program for the use of intersecting arcs of altimeter data for sea surface height refinement

NASA Technical Reports Server (NTRS)

Allen, C. P.; Martin, C. F.

1977-01-01

The SEAHT program is designed to process multiple passes of altimeter data with intersecting ground tracks, with the estimation of corrections for orbital errors to each pass such that the data has the best overall agreement at the crossover points. Orbit error for each pass is modeled as a polynomial in time, with optional orders of 0, 1, or 2. One or more passes may be constrained in the adjustment process, thus allowing passes with the best orbits to provide the overall level and orientation of the estimated sea surface heights. Intersections which disagree by more than an input edit level are not used in the error parameter estimation. In the program implementation, passes are grouped into South-North passes and North-South passes, with the North-South passes partitioned out for the estimation of orbit error parameters. Computer core utilization is thus dependent on the number of parameters estimated for the set of South-North arcs, but is independent on the number of North-South passes. Estimated corrections for each pass are applied to the data at its input data rate and an output tape is written which contains the corrected data.

Scout: orbit analysis and hazard assessment for NEOCP objects

NASA Astrophysics Data System (ADS)

Farnocchia, Davide; Chesley, Steven R.; Chamberlin, Alan B.

2016-10-01

It typically takes a few days for a newly discovered asteroid to be officially recognized as a real object. During this time, the tentative discovery is published on the Minor Planet Center's Near-Earth Object Confirmation Page (NEOCP) until additional observations confirm that the object is a real asteroid rather than an observational artifact or an artificial object. Also, NEOCP objects could have a limited observability window and yet be scientifically interesting, e.g., radar and lightcurve targets, mini-moons (temporary Earth captures), mission accessible targets, close approachers or even impactors. For instance, the only two asteroids discovered before an impact, 2008 TC3 and 2014 AA, both reached the Earth less than a day after discovery. For these reasons we developed Scout, an automated system that provides an orbital and hazard assessment for NEOCP objects within minutes after the observations are available. Scout's rapid analysis increases the chances of securing the trajectory of interesting NEOCP objects before the ephemeris uncertainty grows too large or the observing geometry becomes unfavorable. The generally short observation arcs, perhaps only a few hours or even less, lead severe degeneracies in the orbit estimation process. To overcome these degeneracies Scout relies on systematic ranging, a technique that derives possible orbits by scanning a grid in the poorly constrained space of topocentric range and range rate, while the plane-of-sky position and motion are directly tied to the recorded observations. This scan allows us to derive a distribution of the possible orbits and in turn identify the NEOCP objects of most interest to prioritize followup efforts. In particular, Scout ranks objects according to the likelihood of an impact, estimates the close approach distance, the Earth-relative minimum orbit intersection distance and v-infinity, and computes scores to identify objects more likely to be an NEO, a km-sized NEO, a Potentially Hazardous Asteroid, and those on a geocentric orbit. Moreover, Scout provides an ephemeris service that makes use of the statistical information to support observers in their followup efforts.

Surprise! The oft-ignored Moon might actually be important for changing the spins of asteroids during Earth flybys

NASA Astrophysics Data System (ADS)

Tuttle Keane, James; Siu, Hosea C.; Moskovitz, Nicholas A.; Binzel, Richard P.

2015-11-01

Analysis near-Earth asteroid archival data has revealed that asteroids with Earth MOIDs (minimum orbit intersection distance; a proxy for flyby distance) smaller than 1.0-1.5 lunar distances have a systematically larger dispersion in spin rate than more distant flybys (Siu, et al. 2015, DPS). While tidal torques during close encounters are expected to alter the spin states of asteroids (e.g. Scheeres et al. 2000, Icarus), there is no intrinsic reason to expect the observed sharp transition in spin rate distribution at 1.0-1.5 lunar distances, as tidal forces drop off smoothly with distance.While the Moon itself is too diminutive to directly alter the spin-states of asteroids, we show that its presence is enough to significantly affect asteroid encounter trajectories. Asteroids entering the Earth-Moon system are subject to three-body dynamics (due to the combined gravitational effects of the Earth and Moon). Depending on the flyby geometry, the Moon can act as a temporary sink for the asteroid's geocentric orbital energy. This allows some fraction of asteroids to have closer approaches with the Earth than expected when considering the Earth-Moon barycenter alone. In rare cases (~0.1%) this process enables the capture of temporary moons around the Earth (Granvik et al. 2012, Icarus). Asteroids that undergo these "enhanced" flybys can have both closer-than-expected encounter distances (resulting in more significant tidal perturbations), and repeated encounters with the Earth and Moon before leaving the system (resulting in the accumulation of multiple tidal interactions). By numerically solving the circular restricted three-body problem, we show that this process naturally produces a sharp transition in the asteroid population: asteroids with MOIDs less than 1.5 lunar distances can undergo these enhanced close approaches, possibly explaining the sharp transition in the dispersion of asteroid spin rates at this distance. Future work will investigate the efficiency of this process, and the relationship between the physical response of the asteroid to tidal perturbations and the statistical distribution of asteroid spin rates.

Collar grids for intersecting geometric components within the Chimera overlapped grid scheme

NASA Technical Reports Server (NTRS)

Parks, Steven J.; Buning, Pieter G.; Chan, William M.; Steger, Joseph L.

1991-01-01

A method for overcoming problems with using the Chimera overset grid scheme in the region of intersecting geometry components is presented. A 'collar grid' resolves the intersection region and provides communication between the component grids. This approach is validated by comparing computed and experimental data for a flow about a wing/body configuration. Application of the collar grid scheme to the Orbiter fuselage and vertical tail intersection in a computation of the full Space Shuttle launch vehicle demonstrates its usefulness for simulation of flow about complex aerospace vehicles.

Development of next generation intersection control.

DOT National Transportation Integrated Search

2013-03-01

A reservation-based autonomous intersection control system, named Autonomous Control of Urban : TrAffic (ACUTA), was developed as a part of this research effort. ACUTA allows centralized management : of autonomous vehicles within a certain distance f...

General Relativistic Precession in Small Solar System Bodies

NASA Astrophysics Data System (ADS)

Sekhar, Aswin; Werner, Stephanie; Hoffmann, Volker; Asher, David; Vaubaillon, Jeremie; Hajdukova, Maria; Li, Gongjie

2016-10-01

Introduction: One of the greatest successes of the Einstein's General Theory of Relativity (GR) was the correct prediction of the precession of perihelion of Mercury. The closed form expression to compute this precession tells us that substantial GR precession would occur only if the bodies have a combination of both moderately small perihelion distance and semi-major axis. Minimum Orbit Intersection Distance (MOID) is a quantity which helps us to understand the closest proximity of two orbits in space. Hence evaluating MOID is crucial to understand close encounters and collision scenarios better. In this work, we look at the possible scenarios where a small GR precession in argument of pericentre (ω) can create substantial changes in MOID for small bodies ranging from meteoroids to comets and asteroids.Analytical Approach and Numerical Integrations: Previous works have looked into neat analytical techniques to understand different collision scenarios and we use those standard expressions to compute MOID analytically. We find the nature of this mathematical function is such that a relatively small GR precession can lead to drastic changes in MOID values depending on the initial value of ω. Numerical integrations were done with package MERCURY incorporating the GR code to test the same effects. Numerical approach showed the same interesting relationship (as shown by analytical theory) between values of ω and the peaks/dips in MOID values. Previous works have shown that GR precession suppresses Kozai oscillations and this aspect was verified using our integrations. There is an overall agreement between both analytical and numerical methods.Summary and Discussion: We find that GR precession could play an important role in the calculations pertaining to MOID and close encounter scenarios in the case of certain small solar system bodies (depending on their initial orbital elements). Previous works have looked into impact probabilities and collision scenarios on planets from different small body populations. This work aims to find certain sub-sets of orbits where GR could play an interesting role. Certain parallels are drawn between the cases of asteroids, comets and small perihelion distance meteoroid streams.

Protactinium and the intersection of actinide and transition metal chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, Richard E.; De Sio, Stephanie; Vallet, Valérie

The role of the 5f and 6d orbitals in the chemistry of the actinide elements has been of considerable interest since their discovery and synthesis. Relativistic effects cause the energetics of the 5f and 6d orbitals to change as the actinide series is traversed left to right imparting a rich and complex chemistry. The 5f and 6d atomic states cross in energy at protactinium (Pa), making it a potential intersection between transition metal and actinide chemistries. Herein, we report the synthesis of a Pa-peroxo cluster, A(6)(Pa4O(O-2)(6)F-12) [A = Rb, Cs, (CH3)(4)N], formed in pursuit of an actinide polyoxometalate. Quantum chemicalmore » calculations at the density functional theory level demonstrate equal 5f and 6d orbital participation in the chemistry of Pa and increasing 5f orbital participation for the heavier actinides. Periodic changes in orbital character to the bonding in the early actinides highlights the influence of the 5f orbitals in their reactivity and chemical structure.« less

Worst-case space radiation environments for geocentric missions

NASA Technical Reports Server (NTRS)

Stassinopoulos, E. G.; Seltzer, S. M.

1976-01-01

Worst-case possible annual radiation fluences of energetic charged particles in the terrestrial space environment, and the resultant depth-dose distributions in aluminum, were calculated in order to establish absolute upper limits to the radiation exposure of spacecraft in geocentric orbits. The results are a concise set of data intended to aid in the determination of the feasibility of a particular mission. The data may further serve as guidelines in the evaluation of standard spacecraft components. Calculations were performed for each significant particle species populating or visiting the magnetosphere, on the basis of volume occupied by or accessible to the respective species. Thus, magnetospheric space was divided into five distinct regions using the magnetic shell parameter L, which gives the approximate geocentric distance (in earth radii) of a field line's equatorial intersect.

Particle acceleration at shocks with surface ripples

NASA Technical Reports Server (NTRS)

Decker, R. B.

1990-01-01

The present treatment of superthermal-ion acceleration on the surface of a fast-mode hydromagnetic shock gives attention to (1) small-amplitude surface ripples characterized by width L and amplitude A that are large relative to the energetic-ion gyroradius, and (2) shocks which are on average quasi-perpendicular. An investigation is made of the effects of the confinement, evolving geometry, and finite shock curvature associated with the ripple, by integrating along the orbits of the proton test particles. As an upstream magnetic field line convects through the surface ripple, it intersects the shock at two points, thereby forming a temporary magnetic trap. Flux-line profiles and angular distributions in a given ripple differ substantially, depending on the path it takes through the ripple and its distance from the shock.

Effectiveness of transverse grooves in rigid pavement

NASA Astrophysics Data System (ADS)

Gurney, G. F.; Bryden, J. E.

1982-10-01

Transverse grooves were installed at 11 intersection approaches on worn rigid pavement to reduce a high rate of wet road accidents. In most cases, accident reductions were experienced only at intersections with multiple negative operational characteristics, including higher approach speeds, limited sight distances, and frequent vehicle stopping for turns or stop signs. Intersections with no more than one negative characteristic generally did not benefit from grooving.

Large-size space debris flyby in low earth orbits

NASA Astrophysics Data System (ADS)

Baranov, A. A.; Grishko, D. A.; Razoumny, Y. N.

2017-09-01

the analysis of NORAD catalogue of space objects executed with respect to the overall sizes of upper-stages and last stages of carrier rockets allows the classification of 5 groups of large-size space debris (LSSD). These groups are defined according to the proximity of orbital inclinations of the involved objects. The orbits within a group have various values of deviations in the Right Ascension of the Ascending Node (RAAN). It is proposed to use the RAANs deviations' evolution portrait to clarify the orbital planes' relative spatial distribution in a group so that the RAAN deviations should be calculated with respect to the concrete precessing orbital plane of the concrete object. In case of the first three groups (inclinations i = 71°, i = 74°, i = 81°) the straight lines of the RAAN relative deviations almost do not intersect each other. So the simple, successive flyby of group's elements is effective, but the significant value of total Δ V is required to form drift orbits. In case of the fifth group (Sun-synchronous orbits) these straight lines chaotically intersect each other for many times due to the noticeable differences in values of semi-major axes and orbital inclinations. The intersections' existence makes it possible to create such a flyby sequence for LSSD group when the orbit of one LSSD object simultaneously serves as the drift orbit to attain another LSSD object. This flyby scheme requiring less Δ V was called "diagonal." The RAANs deviations' evolution portrait built for the fourth group (to be studied in the paper) contains both types of lines, so the simultaneous combination of diagonal and successive flyby schemes is possible. The value of total Δ V and temporal costs were calculated to cover all the elements of the 4th group. The article is also enriched by the results obtained for the flyby problem solution in case of all the five mentioned LSSD groups. The general recommendations are given concerned with the required reserve of total Δ V and with amount of detachable de-orbiting units onboard the maneuvering platform and onboard the refueling vehicle.

Accuracy of WAAS-Enabled GPS-RF Warning Signals When Crossing a Terrestrial Geofence

PubMed Central

Grayson, Lindsay M.; Keefe, Robert F.; Tinkham, Wade T.; Eitel, Jan U. H.; Saralecos, Jarred D.; Smith, Alistair M. S.; Zimbelman, Eloise G.

2016-01-01

Geofences are virtual boundaries based on geographic coordinates. When combined with global position system (GPS), or more generally global navigation satellite system (GNSS) transmitters, geofences provide a powerful tool for monitoring the location and movements of objects of interest through proximity alarms. However, the accuracy of geofence alarms in GNSS-radio frequency (GNSS-RF) transmitter receiver systems has not been tested. To achieve these goals, a cart with a GNSS-RF locator was run on a straight path in a balanced factorial experiment with three levels of cart speed, three angles of geofence intersection, three receiver distances from the track, and three replicates. Locator speed, receiver distance and geofence intersection angle all affected geofence alarm accuracy in an analysis of variance (p = 0.013, p = 2.58 × 10−8, and p = 0.0006, respectively), as did all treatment interactions (p < 0.0001). Slower locator speed, acute geofence intersection angle, and closest receiver distance were associated with reduced accuracy of geofence alerts. PMID:27322287

Accuracy of WAAS-Enabled GPS-RF Warning Signals When Crossing a Terrestrial Geofence.

PubMed

Grayson, Lindsay M; Keefe, Robert F; Tinkham, Wade T; Eitel, Jan U H; Saralecos, Jarred D; Smith, Alistair M S; Zimbelman, Eloise G

2016-06-18

Geofences are virtual boundaries based on geographic coordinates. When combined with global position system (GPS), or more generally global navigation satellite system (GNSS) transmitters, geofences provide a powerful tool for monitoring the location and movements of objects of interest through proximity alarms. However, the accuracy of geofence alarms in GNSS-radio frequency (GNSS-RF) transmitter receiver systems has not been tested. To achieve these goals, a cart with a GNSS-RF locator was run on a straight path in a balanced factorial experiment with three levels of cart speed, three angles of geofence intersection, three receiver distances from the track, and three replicates. Locator speed, receiver distance and geofence intersection angle all affected geofence alarm accuracy in an analysis of variance (p = 0.013, p = 2.58 × 10(-8), and p = 0.0006, respectively), as did all treatment interactions (p < 0.0001). Slower locator speed, acute geofence intersection angle, and closest receiver distance were associated with reduced accuracy of geofence alerts.

Characterizing Longitude-Dependent Orbital Debris Congestion in the Geosynchronous Orbit Regime

NASA Astrophysics Data System (ADS)

Anderson, Paul V.

The geosynchronous orbit (GEO) is a unique commodity of the satellite industry that is becoming increasingly contaminated with orbital debris, but is heavily populated with high-value assets from the civil, commercial, and defense sectors. The GEO arena is home to hundreds of communications, data transmission, and intelligence satellites collectively insured for an estimated 18.3 billion USD. As the lack of natural cleansing mechanisms at the GEO altitude renders the lifetimes of GEO debris essentially infinite, conjunction and risk assessment must be performed to safeguard operational assets from debris collisions. In this thesis, longitude-dependent debris congestion is characterized by predicting the number of near-miss events per day for every longitude slot at GEO, using custom debris propagation tools and a torus intersection metric. Near-miss events with the present-day debris population are assigned risk levels based on GEO-relative position and speed, and this risk information is used to prioritize the population for debris removal target selection. Long-term projections of debris growth under nominal launch traffic, mitigation practices, and fragmentation events are also discussed, and latitudinal synchronization of the GEO debris population is explained via node variations arising from luni-solar gravity. In addition to characterizing localized debris congestion in the GEO ring, this thesis further investigates the conjunction risk to operational satellites or debris removal systems applying low-thrust propulsion to raise orbit altitude at end-of-life to a super-synchronous disposal orbit. Conjunction risks as a function of thrust level, miss distance, longitude, and semi-major axis are evaluated, and a guidance method for evading conjuncting debris with continuous thrust by means of a thrust heading change via single-shooting is developed.

Post-traumatic orbital reconstruction: anatomical landmarks and the concept of the deep orbit.

PubMed

Evans, B T; Webb, A A C

2007-04-01

Dissection deep within the orbit is a cause for concern to surgeons because of the perceived risks of injuring critical structures such as the contents of the superior orbital fissure and the optic nerve. Although "safe distances" (those distances within which it is considered safe to dissect within the orbit) have been described, these are of limited value if the orbit is severely disrupted or is congenitally shallow. In addition, traumatic defects in the orbital floor, in particular, often extend beyond these distances. Reliable landmarks based on the relations between anatomical structures within the orbit, rather than absolute distances, are described that permit safe dissection within the orbit. We present the concept of the deep orbit and describe its relevance to repair of injuries.

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

NASA Astrophysics Data System (ADS)

Chiang, Eugene; Fung, Jeffrey

2017-10-01

We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star’s wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the “avalanche zone”—located on AU Mic’s primary “birth” ring at a true distance of ˜35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind’s magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiang, Eugene; Fung, Jeffrey, E-mail: echiang@astro.berkeley.edu, E-mail: jeffrey.fung@berkeley.edu

We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star’s wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the “avalanche zone”—located on AU Mic’s primary “birth” ring at a true distance of ∼35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanchemore » zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind’s magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.« less

Minimum impulse transfers to rotate the line of apsides

NASA Technical Reports Server (NTRS)

Phong, Connie; Sweetser, Theodore H.

2005-01-01

Transfer between two coplanar orbits can be accomplished via a single impulse if the two orbits intersect. Optimization of a single-impulse transfer, however, is not possible since the transfer orbit is completely constrained by the initial and final orbits. On the other hand, two-impulse transfers are possible between any two terminal orbits. While optimal scenarios are not known for the general two-impulse case, there are various approximate solutions to many special cases. We consider the problem of an inplane rotation of the line of apsides, leaving the size and shape of the orbit unaffected.

Solution of the flyby problem for large space debris at sun-synchronous orbits

NASA Astrophysics Data System (ADS)

Baranov, A. A.; Grishko, D. A.; Medvedevskikh, V. V.; Lapshin, V. V.

2016-05-01

the paper considers the flyby problem related to large space debris (LSD) objects at low earth orbits. The data on the overall dimensions of known last and upper stages of launch vehicles makes it possible to single out five compact groups of such objects from the NORAD catalog in the 500-2000 km altitude interval. The orbits of objects of each group have approximately the same inclinations. The features of the mutual distribution of the orbital planes of LSD objects in the group are shown in a portrait of the evolution of deviations of the right ascension of ascending nodes (RAAN). In the case of the first three groups (inclinations of 71°, 74°, and 81°), the straight lines of relative RAAN deviations of object orbits barely intersect each other. The fourth (83°) and fifth (97°-100°) LSD groups include a considerable number of objects whose orbits are described by straight lines (diagonals), which intersect other lines many times. The use of diagonals makes it possible to significantly reduce the temporal and total characteristic velocity expenditures required for object flybys, but it complicates determination of the flyby sequence. Diagonal solutions can be obtained using elements of graph theory. A solution to the flyby problem is presented for the case of group 5, formed of LSD objects at sun-synchronous orbits.

Watching Electrons at Conical Intersections and Funnels

NASA Astrophysics Data System (ADS)

Jonas, David M.; Smith, Eric R.; Peters, William K.; Kitney, Katherine A.

2009-06-01

The electronic motion at conical intersections and funnels is probed after polarized excitation of aligned electronic wavepackets. The pulses have bandwidth sufficient to observe vibrations mainly through their effect on the electrons. Vibrational symmetry can be identified by the polarization anisotropy of vibrational quantum beats. The polarized transients show signatures of electronic wavepacket motion (due to the energy gaps) and of electron transfer between orbitals (due to the couplings) driven by the conical intersection. For a conical intersection in a four-fold symmetric symmetry silicon naphthalocyanine molecule, electronic motions on a 100 fs timescale are driven by couplings of 1 meV. In the lower symmetry free-base naphthalocyanine, the conical intersection may be missed or missing (conical funnel), and the motions are nearly as rapid, but electronic equilibration is incomplete for red-edge excitation. These experiments probe non-adiabatic electronic dynamics with near-zero nuclear momentum - the electronic motions are determined by the principal slopes of the conical intersection and the width of the vibrational wavepacket.

The globe and orbit in Laron syndrome.

PubMed

Kornreich, L; Konen, O; Lilos, P; Laron, Z

2011-09-01

Patients with LS have an inborn growth hormone resistance, resulting in failure to generate IGF-1. The purpose of this study was to evaluate the size of the eye and orbit in LS. We retrospectively reviewed the MR imaging of the brain in 9 patients with LS for the following parameters: axial diameter of the globe, interzygomatic distance, perpendicular distance from the interzygomatic line to margins of the globe, medial-to-lateral diameter of the orbit at the anterior orbital rim, distance from the anterior orbital rim to the anterior globe, maximal distance between the medial walls of the orbits, lateral orbital wall angle, lateral orbital wall length, and mediolateral thickness of the intraorbital fat in the most cranial image of the orbit. All measurements were made bilaterally. Twenty patients referred for MR imaging for unrelated reasons served as control subjects. Compared with the control group, the patients with LS had a significantly smaller maximal globe diameter and shallower but wider orbits due to a shorter lateral wall, a smaller medial distance between the orbits, and a larger angle of the orbit. The ratio between the most anterior orbital diameter and the globe was greater than that in controls. The position of the globe was more anterior in relation to the interzygomatic line. Shallow and wide orbits and small globes relative to orbital size are seen in LS and may be secondary to IGF-1 deficiency.

Interplanetary baseline observations of type 3 solar radio bursts. [by Helios satellites

NASA Technical Reports Server (NTRS)

Weber, R. R.; Fitzenreiter, R. J.; Novaco, J. C.; Fainberg, J.

1977-01-01

Simultaneous observations of type III radio bursts using spacecraft separated by several tenths of an AU were made using the solar orbiters HELIOS-A and -B. The burst beginning at 1922 UT on March 28, 1976, was located from the intersection of the source directions measured at each spacecraft, and from the burst arrival time differences. Wide baseline observations give the radial distance of the source at each observing frequency. Consequently, coronal electron densities and exciter velocity were determined directly, without the need to assume a density model as is done with single spacecraft observations. The separation of HELIOS-A and -B also provided the first measurements of burst directivity at low frequencies. For the March 28 burst, the intensity observed from near the source longitude (HELIOS-B) was significantly greater than from 60 W of the source (HELIOS-A).

Parental perceptions of barriers to active commuting to school in Spanish children and adolescents.

PubMed

Huertas-Delgado, Francisco Javier; Herrador-Colmenero, Manuel; Villa-González, Emilio; Aranda-Balboa, María Jesús; Cáceres, María Victoria; Mandic, Sandra; Chillón, Palma

2017-06-01

: Understanding parental barriers is crucial to promote active commuting to school since the parental perceptions influence how young people commute. This study examined parental barriers to active commuting to school among Spanish children and adolescents, and their association with their gender and the usual mode of commuting. Parents of children ( n = 628) and parents of adolescents ( n = 151) from Granada (Spain) completed a paper-based questionnaire about perceived parental barriers to active commuting to school and mode of commuting. Data were analyzed using the Chi-square test. Among Spanish parents, the most common barriers reported by parents of children were traffic volume and dangerous intersections, whereas the most frequent barriers reported by parents of adolescents were distance to school and dangerous intersections. Compared to parents of children, a greater proportion of parents of adolescents reported distance to school and crime and smaller proportion reported traffic volume as barriers to active commuting to school. Among parents of children, crime was a more commonly reported as a barrier by parents of girls. Although some barriers reported by parents of passive commuters were similar for children and adolescents (such as distance to school and absence of a policeman at crosswalks), other barriers were specific to parents of children. The main parental barriers to active commuting in children were traffic volume and dangerous intersections whereas for adolescents were distance and dangerous intersections. Among Spanish parents, parental barriers to active commuting are influenced by children's age, gender and mode of commuting to school. © The Author 2017. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.

27 CFR 9.233 - Kelsey Bench-Lake County.

Code of Federal Regulations, 2014 CFR

2014-04-01

... mile to the point where the road intersects a straight line drawn westward from the marked 2,493-foot..., approximately 0.8 mile to the first intersection of the eastern boundary of section 26 and the 1,720-foot..., a total distance of approximately 3.25 miles, to the marked 1,439-foot elevation point in section 29...

Influences of motorcycle rider and driver characteristics and road environment on red light running behavior at signalized intersections.

PubMed

Jensupakarn, Auearree; Kanitpong, Kunnawee

2018-04-01

In Thailand, red light running is considered as one of the most dangerous behaviors at intersection. Red light running (RLR) behavior is the failure to obey the traffic control signal. However, motorcycle riders and car drivers who are running through red lights could be influenced by human factors or road environment at intersection. RLR could be advertent or inadvertent behavior influenced by many factors. Little research study has been done to evaluate the contributing factors influencing the red-light violation behavior. This study aims to determine the factors influencing the red light running behavior including human characteristics, physical condition of intersection, traffic signal operation, and traffic condition. A total of 92 intersections were observed in Chiang Mai, Nakhon Ratchasima, and Chonburi, the major provinces in each region of Thailand. In addition, the socio-economic characteristics of red light runners were obtained from self-reported questionnaire survey. The Binary Logistic Regression and the Multiple Linear Regression models were used to determine the characteristics of red light runners and the factors influencing rates of red light running respectively. The results from this study can help to understand the characteristics of red light runners and factors affecting them to run red lights. For motorcycle riders and car drivers, age, gender, occupation, driving license, helmet/seatbelt use, and the probability to be penalized when running the red light significantly affect RLR behavior. In addition, the results indicated that vehicle travelling direction, time of day, existence of turning lane, number of lanes, lane width, intersection sight distance, type of traffic signal pole, type of traffic signal operation, length of yellow time interval, approaching speed, distance from intersection warning sign to stop line, and pavement roughness significantly affect RLR rates. Copyright © 2018 Elsevier Ltd. All rights reserved.

Medial orbital wall landmarks in three different North American populations.

PubMed

Mehta, Milap P; Perry, Julian D

2015-04-01

We sought to measure the medial orbital wall foramina distances in two previously unstudied populations, to describe a new bony medial wall feature, and to validate the accuracy of a new coordinate measurement device within the orbit. Dried, well-preserved, complete human skulls without orbital defects were studied. Age, gender, birthplace, ethnicity, and laterality of the orbit were recorded for each skull. Supranumerary ethmoidal foramina were recorded, and the fronto-ethmoidal groove depth was measured. The distances between the anterior lacrimal crest (ALC) - anterior ethmoidal foramen (AEF), AEF - posterior ethmoidal foramen (PEF), and PEF - optic canal (OC) were measured first by surgical ruler and wire and then by the Microscribe coordinate measurement device. One hundred and forty-six orbits were studied. Fifty-seven orbits were of European or Caucasian descent, 68 orbits of African American descent, 2 orbits of West African descent, 11 orbits of Eskimo descent, and 8 orbits of unknown origin. No significant differences existed between the manual and Microscribe measurements for the ALC-AEF, AEF-PEF, and PEF-OF distances (p < 0.0001). A significant frontoethmoidal groove was observed in 27/146 (19%) orbits, in 6/57 (11%) Caucasian orbits, in 17/70 (24%) African American orbits, and in 4/11 (36%) Eskimo orbits. Supranumerary ethmoidal foramina were found in 50/146 orbits (34.2%) and in 17/27 (63%) orbits with a significant frontoethmoidal grooves. No significant differences in medial wall foramina distances exist between African American and Caucasian orbits; however, a frontoethmoidal groove occurs more commonly in African American orbits. This groove often occurs in the presence of supernumerary ethmoidal foramina. The Microscribe coordinate measurement system represents a valid tool to measure distances within the orbit.

The Innisfree meteorite: Dynamical history of the orbit - Possible family of meteor bodies

NASA Astrophysics Data System (ADS)

Galibina, I. V.; Terent'eva, A. K.

1987-09-01

Evolution of the Innisfree meteorite orbit caused by secular perturbations is studied over the time interval of 500000 yrs (from the current epoch backwards). Calculations are made by the Gauss-Halphen-Gorjatschew method taking into account perturbations from the four outer planets - Jupiter, Saturn, Uranus and Neptune. In the above mentioned time interval the meteorite orbit has undergone no essential transformations. The Innisfree orbit intersected in 91 cases the Earth orbit and in 94 - the Mars orbit. A system of small and large meteor bodies (producing ordinary meteors and fireballs) which may be genetically related to the Innisfree meteorite has been found, i.e. there probably exists an Innisfree family of meteor bodies.

View looking aft along the starboard side of the midfuselage ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

View looking aft along the starboard side of the mid-fuselage of the Orbiter Discovery. This view shows the wing profile as it intersects with the fuselage. Also note in the foreground the panels protecting the Reinforced Carbon-Carbon leading edge of the wing. This view was taken from the service platform in the Orbiter Processing Facility at Kennedy Space Center. - Space Transportation System, Orbiter Discovery (OV-103), Lyndon B. Johnson Space Center, 2101 NASA Parkway, Houston, Harris County, TX

Unraveling the strands of Saturn's F ring

USGS Publications Warehouse

Murray, C.D.; Gordon, M.K.; Giuliatti, Winter S.M.

1997-01-01

Several high-resolution Voyager 2 images of Saturn's F ring show that it is composed of at least four separate, non-intersecting strands extending ~45?? in longitude. Voyager 1 images show that the two brightest strands appear to intersect, giving rise to a "braided" morphology. From a study of all available Voyager images the detectable radial structure is cataloged and reviewed. Previous indications that there is fine material interior to the orbit of the F ring are confirmed. Evidence is presented that a model of four strands with comparable eccentricities and nearly aligned perichrones is consistent with all the Voyager observations. The observed perichrone offset of the two brightest strands suggests a minimum radial separation of ~20 km, which implies intersection of these strands when their finite radial widths are taken into account. The longitude range of such an intersection includes that observed in the Voyager 1 "braid" images. The proximity of these two strands at some longitudes may account for the apparent differences in the ring between the Voyager encounters, as well as provide a source for the short-lived features detected in the Hubble Space Telescope images of the F ring. There is no evidence that the locations of the individual strands are determined by resonant perturbations with known satellites. It is proposed that the radial structure is formed by the localized action of small satellites orbiting within the strand region. ?? 1997 Academic Press.

Monte Carlo methods to calculate impact probabilities

NASA Astrophysics Data System (ADS)

Rickman, H.; Wiśniowski, T.; Wajer, P.; Gabryszewski, R.; Valsecchi, G. B.

2014-09-01

Context. Unraveling the events that took place in the solar system during the period known as the late heavy bombardment requires the interpretation of the cratered surfaces of the Moon and terrestrial planets. This, in turn, requires good estimates of the statistical impact probabilities for different source populations of projectiles, a subject that has received relatively little attention, since the works of Öpik (1951, Proc. R. Irish Acad. Sect. A, 54, 165) and Wetherill (1967, J. Geophys. Res., 72, 2429). Aims: We aim to work around the limitations of the Öpik and Wetherill formulae, which are caused by singularities due to zero denominators under special circumstances. Using modern computers, it is possible to make good estimates of impact probabilities by means of Monte Carlo simulations, and in this work, we explore the available options. Methods: We describe three basic methods to derive the average impact probability for a projectile with a given semi-major axis, eccentricity, and inclination with respect to a target planet on an elliptic orbit. One is a numerical averaging of the Wetherill formula; the next is a Monte Carlo super-sizing method using the target's Hill sphere. The third uses extensive minimum orbit intersection distance (MOID) calculations for a Monte Carlo sampling of potentially impacting orbits, along with calculations of the relevant interval for the timing of the encounter allowing collision. Numerical experiments are carried out for an intercomparison of the methods and to scrutinize their behavior near the singularities (zero relative inclination and equal perihelion distances). Results: We find an excellent agreement between all methods in the general case, while there appear large differences in the immediate vicinity of the singularities. With respect to the MOID method, which is the only one that does not involve simplifying assumptions and approximations, the Wetherill averaging impact probability departs by diverging toward infinity, while the Hill sphere method results in a severely underestimated probability. We provide a discussion of the reasons for these differences, and we finally present the results of the MOID method in the form of probability maps for the Earth and Mars on their current orbits. These maps show a relatively flat probability distribution, except for the occurrence of two ridges found at small inclinations and for coinciding projectile/target perihelion distances. Conclusions: Our results verify the standard formulae in the general case, away from the singularities. In fact, severe shortcomings are limited to the immediate vicinity of those extreme orbits. On the other hand, the new Monte Carlo methods can be used without excessive consumption of computer time, and the MOID method avoids the problems associated with the other methods. Appendices are available in electronic form at http://www.aanda.org

Traffic as a source of organophosphorus flame retardants and plasticizers in snow.

PubMed

Marklund, Anneli; Andersson, Barbro; Haglund, Peter

2005-05-15

Snow samples collected in northern Sweden at a road intersection and an airport indicated that traffic is a source of organophosphorus flame retardants and plasticizers (OPs) in the outdoor environment. Analysis of snow samples taken at distances of 2, 100, and 250 m from the road intersection showed that the total amount of OPs declined as distance increased. Of the 11 analyzed substances, tris-(2-chloroisopropyl) phosphate (TCPP) dominated in the snow samples from the intersection, with levels of 170, 130, and 110 ng/kg snow at distances of 2, 100, and 250 m. Similar amounts of TCPP were found at the airport (100-220 ng/kg). These levels are approximately twice as high as the level found in the reference snow sample from a remote area (70 ng/kg). A possible explanation for the higher levels of TCPP found close to the road intersection is that it may be emitted from the interior of cars via their ventilation systems. Triphenyl phosphate (TPP) was identified in lubricants and in waste oil from vehicles, and thus, leakage of transmission and motor oils is a probable source of TPP found at the sampled sites. Ten OPs were detected in the three samples from the airport, of which tributyl phosphate (TBP) was the most abundant, at levels 3 orders of magnitude higher than in the reference sample, that is, 25 000 compared to 19 ng/kg. The main source of TBP at the airport was traced to aircraft hydraulic fluid. Analysis of background air and deposition samples indicated that some OPs are subject to long-range air transportation.

Three-dimensional and topographic relationships between the orbital margins with reference to assessment of eyeball protrusion.

PubMed

Shin, Kang-Jae; Lee, Shin-Hyo; Koh, Ki-Seok; Song, Wu-Chul

2017-03-01

This study investigated the topographic relationships among the eyeball and four orbital margins with the aim of identifying the correlation between orbital geometry and eyeball protrusion in Koreans. Three-dimensional (3D) volume rendering of the face was performed using serial computed-tomography images of 141 Koreans, and several landmarks on the bony orbit and the cornea were directly marked on the 3D volumes. The anterior-posterior distances from the apex of the cornea to each orbital margin and between the orbital margins were measured in both eyes. The distances from the apex of the cornea to the superior, medial, inferior, and lateral orbital margins were 5.8, 5.8, 12.0, and 17.9 mm, respectively. Differences between sides were observed in all of the orbital margins, and the distances from the apex of the cornea to the superior and inferior orbital margins were significantly greater in females than in males. The anterior-posterior distance between the superior and inferior orbital margins did not differ significantly between males (6.3 mm) and females (6.2 mm). The data obtained in this study will be useful when developing practical guidelines applicable to forensic facial reconstruction and orbitofacial surgeries.

Hephaestus Fossae

NASA Image and Video Library

2015-09-02

The intersecting linear depressions in this VIS image are part of Hephaestus Fossae. Orbit Number: 60373 Latitude: 21.9161 Longitude: 122.075 Instrument: VIS Captured: 2015-07-24 20:50 http://photojournal.jpl.nasa.gov/catalog/PIA19765

NEA impactors: what direction to they come from?

NASA Astrophysics Data System (ADS)

Harris, Alan

2018-04-01

One might expect, if Earth-crossing NEAs are "thermalized" by prior close scattering encounters with the Earth, that final impact trajectories would be isotropic in direction. But orbital perturbations and other sources of entry and exit to the Earth-crossing zone are faster acting that thermalization, so the actual distribution of impacting orbits is quite anisotropic. I have studied impactor directions by adjusting the orbits of known Earth-crossing PHAs slightly to put them on intersecting orbits and then computed the direction of approach to the Earth. This arguably suffers from "looking under the lamp post", since NEAs are mostly discovered close to the opposition direction, so I also took the distribution of NEA orbits recently derived by Granvik and others and extracted, from a set of 100,000 synthetic orbits they provided, a subset of Earth-crossing PHAs and similarly adjusted them to be intersecting orbits. This should represent an unbiased set of orbits. I then weighted the impact directions by the individual Opik impact probability to obtain a distribution of impact directions weighted by actual impact probabilities. The result was that more than 40% of incoming trajectories clustered within 60 degrees of the opposition direction, and a similar fraction come from within 60 degrees of the solar direction. Thus ~80% of impactors come from only about 1/3 of the sky area, with almost none coming from 60-120 degrees solar elongation. The message is that existing ground-based surveys can hardly be improved upon by greater sky coverage with respect to detecting "death plunge" objects, and even space-based instruments offer very little improvement due to the very low solar elongation of most objects approaching from the solar direction.

On a possible cometary origin of the object 2015TB145

NASA Astrophysics Data System (ADS)

Kokhirova, G. I.; Babadzhanov, P. B.; Khamroev, U. H.

2017-09-01

The Earth-crossing asteroid 2015TB145 was discovered on 10 October 2015 and on 31 October 2015 it already approached close to the Earth at the minimal distance. On the base of obtained radio images of the asteroid, the value of an albedo has estimated as p=0.06. Coming from the albedo value and the comet-like orbit, it was suggested, that the object is a dead comet. In order to verify the supposition, the orbital evolution of 2015TB145 was investigated under the perturbing action of major planets for the time interval of 50 kyrs. As a result, it was found that one cycle of variations of the argument of perihelion is equal to nearly 40 kyrs and during this period the object intersects the Earth's orbit eight times, i.e. it is the octuple crosser. Consequently, if the object has a cometary origin, then it can be associated with a meteoroid stream producing eight meteor showers which should be observable on the Earth. Features of the predicted meteor showers, theoretically associated with 2015TB145, were calculated and a search for observable showers identical to predicted ones was realized using all published catalogues. It turned out, that seven of eight predicted showers were identified with the active observable meteor showers. So, comet-like orbit, low value of an albedo and association with the meteoroid stream producing identified showers are strong evidences pointing that 2015TB145 is really inactive comet. A conclusion was made that the potentially hazardous object 2015TB145 is very likely extinct nucleus of a parent comet of the found meteoroid stream.

Image subregion querying using color correlograms

DOEpatents

Huang, Jing; Kumar, Shanmugasundaram Ravi; Mitra, Mandar; Zhu, Wei-Jing

2002-01-01

A color correlogram (10) is a representation expressing the spatial correlation of color and distance between pixels in a stored image. The color correlogram (10) may be used to distinguish objects in an image as well as between images in a plurality of images. By intersecting a color correlogram of an image object with correlograms of images to be searched, those images which contain the objects are identified by the intersection correlogram.

Closeup detail of the jackstand head and the attach mechanism ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Close-up detail of the jack-stand head and the attach mechanism connection to the hoist attach point on the starboard forward fuselage of the Orbiter Discovery. Note the profile of the wing intersection with the fuselage and the payload bay door in an open position with the strongback support structure attached. This view was taken from a service platform in the Orbiter Processing Facility at Kennedy Space Center. - Space Transportation System, Orbiter Discovery (OV-103), Lyndon B. Johnson Space Center, 2101 NASA Parkway, Houston, Harris County, TX

The Intersection of Dialogue and Low Transactional Distance: Considerations for Higher Education

ERIC Educational Resources Information Center

Farquhar, Lynn

2013-01-01

The theory of transactional distance has been subjected to a variety of empirical tests and philosophical critiques. Throughout this process, the variable of dialogue has attracted much attention. Although dialogue has proven difficult to measure and define, it is widely regarded as an ideal outcome of the teacher-learner transaction. Considered…

Compromising Composition: Articulating Quality and Practice in Distance Education Policy.

ERIC Educational Resources Information Center

Carnegie, Teena A. M.

Policies exist in every aspect of people's lives from the landlord's policy on pets to the government's policy on literacy. As such, policy becomes the ideal place to begin to examine the articulation of distance education because policy inevitably marks the site where different kinds of political discourses and social practices intersect. By…

Multiuse trail intersection safety analysis: A crowdsourced data perspective.

PubMed

Jestico, Ben; Nelson, Trisalyn A; Potter, Jason; Winters, Meghan

2017-06-01

Real and perceived concerns about cycling safety are a barrier to increased ridership in many cities. Many people prefer to bike on facilities separated from motor vehicles, such as multiuse trails. However, due to underreporting, cities lack data on bike collisions, especially along greenways and multiuse paths. We used a crowdsourced cycling incident dataset (2005-2016) from BikeMaps.org for the Capital Regional District (CRD), BC, Canada. Our goal was to identify design characteristics associated with unsafe intersections between multiuse trails and roads. 92.8% of mapped incidents occurred between 2014 and 2016. We extracted both collision and near miss incidents at intersections from BikeMaps.org. We conducted site observations at 32 intersections where a major multiuse trail intersected with roads. We compared attributes of reported incidents at multiuse trail-road intersections to those at road-road intersections. We then used negative binomial regression to model the relationship between the number of incidents and the infrastructure characteristics at multiuse trail-road intersections. We found a higher proportion of collisions (38%, or 17/45 total reports) at multiuse trail-road intersections compared to road-road intersections (23%, or 62/268 total reports). A higher proportion of incidents resulted in an injury at multiuse trail-road intersections compared to road-road intersections (33% versus 15%). Cycling volumes, vehicle volumes, and trail sight distance were all associated with incident frequency at multiuse trail-road intersections. Supplementing traditional crash records with crowdsourced cycling incident data provides valuable evidence on cycling safety at intersections between multiuse trails and roads, and more generally, when conflicts occur between diverse transportation modes. Copyright © 2017. Published by Elsevier Ltd.

KSC-98pc1166

NASA Image and Video Library

1998-09-28

The orbiter Atlantis, being towed from the Shuttle Landing Facility toward the Vehicle Assembly Building (VAB) , intersects the morning sun's rays. In the background, to the right of the VAB, are the Orbiter Processing Facility 1 and 2. Atlantis spent 10 months in Palmdale, CA, undergoing extensive inspections and modifications in the orbiter processing facility there. The modifications included several upgrades enabling it to support International Space Station missions, such as adding an external airlock for ISS docking missions and installing thinner, lighter thermal protection blankets for weight reduction which will allow it to haul heavier cargo. Atlantis will undergo preparations at KSC in Orbiter Processing Facility 2 for its planned flight in June 1999

Three-dimensional and topographic relationships between the orbital margins with reference to assessment of eyeball protrusion

PubMed Central

Shin, Kang-Jae; Lee, Shin-Hyo; Koh, Ki-Seok

2017-01-01

This study investigated the topographic relationships among the eyeball and four orbital margins with the aim of identifying the correlation between orbital geometry and eyeball protrusion in Koreans. Three-dimensional (3D) volume rendering of the face was performed using serial computed-tomography images of 141 Koreans, and several landmarks on the bony orbit and the cornea were directly marked on the 3D volumes. The anterior-posterior distances from the apex of the cornea to each orbital margin and between the orbital margins were measured in both eyes. The distances from the apex of the cornea to the superior, medial, inferior, and lateral orbital margins were 5.8, 5.8, 12.0, and 17.9 mm, respectively. Differences between sides were observed in all of the orbital margins, and the distances from the apex of the cornea to the superior and inferior orbital margins were significantly greater in females than in males. The anterior-posterior distance between the superior and inferior orbital margins did not differ significantly between males (6.3 mm) and females (6.2 mm). The data obtained in this study will be useful when developing practical guidelines applicable to forensic facial reconstruction and orbitofacial surgeries. PMID:28417054

Comparisons among a new soil index and other two- and four-dimensional vegetation indices

NASA Technical Reports Server (NTRS)

Wiegand, C. L.; Richardson, A. J. (Principal Investigator)

1982-01-01

The 2-D difference vegetation index (DVI) and perpendicular vegetation index (PVI), and the 4-D green vegetation index (GVI) are compared in LANDSAT MSS data from grain sorghum (Sorghum bicolor, L. Moench) fields for the years 1973 to 1977. PVI and DVI were more closely related to LAI than was GVI. A new 2-D soil line index (SLI), the vector distance from the soil line origin to the point of intersection of PVI with the soil line, is defined and compared with the 4-D soil brightness index, SBI. SLI (based on MSS and MSS7) and SL16 (based on MSS 5 and MSS 6) were smaller in magnitude than SBI but contained similar information about the soil background. These findings indicate that vegetation and soil indices calculated from the single visible and reflective infrared band sensor systems, such as the AVHRR of the TIROS-N polar orbiting series of satellites, will be meaningful for synoptic monitoring of renewable vegetation.

MRI study of minor physical anomaly in childhood autism implicates aberrant neurodevelopment in infancy.

PubMed

Cheung, Charlton; McAlonan, Grainne M; Fung, Yee Y; Fung, Germaine; Yu, Kevin K; Tai, Kin-Shing; Sham, Pak C; Chua, Siew E

2011-01-01

MPAs (minor physical anomalies) frequently occur in neurodevelopmental disorders because both face and brain are derived from neuroectoderm in the first trimester. Conventionally, MPAs are measured by evaluation of external appearance. Using MRI can help overcome inherent observer bias, facilitate multi-centre data acquisition, and explore how MPAs relate to brain dysmorphology in the same individual. Optical MPAs exhibit a tightly synchronized trajectory through fetal, postnatal and adult life. As head size enlarges with age, inter-orbital distance increases, and is mostly completed before age 3 years. We hypothesized that optical MPAs might afford a retrospective 'window' to early neurodevelopment; specifically, inter-orbital distance increase may represent a biomarker for early brain dysmaturation in autism. We recruited 91 children aged 7-16; 36 with an autism spectrum disorder and 55 age- and gender-matched typically developing controls. All children had normal IQ. Inter-orbital distance was measured on T1-weighted MRI scans. This value was entered into a voxel-by-voxel linear regression analysis with grey matter segmented from a bimodal MRI data-set. Age and total brain tissue volume were entered as covariates. Intra-class coefficient for measurement of the inter-orbital distance was 0.95. Inter-orbital distance was significantly increased in the autism group (p = 0.03, 2-tailed). The autism group showed a significant relationship between inter-orbital distance grey matter volume of bilateral amygdalae extending to the unci and inferior temporal poles. Greater inter-orbital distance in the autism group compared with healthy controls is consistent with infant head size expansion in autism. Inter-orbital distance positively correlated with volume of medial temporal lobe structures, suggesting a link to "social brain" dysmorphology in the autism group. We suggest these data support the role of optical MPAs as a "fossil record" of early aberrant neurodevelopment, and potential biomarker for brain dysmaturation in autism.

Determining partial differential cross sections for low-energy electron photodetachment involving conical intersections using the solution of a Lippmann-Schwinger equation constructed with standard electronic structure techniques.

PubMed

Han, Seungsuk; Yarkony, David R

2011-05-07

A method for obtaining partial differential cross sections for low energy electron photodetachment in which the electronic states of the residual molecule are strongly coupled by conical intersections is reported. The method is based on the iterative solution to a Lippmann-Schwinger equation, using a zeroth order Hamiltonian consisting of the bound nonadiabatically coupled residual molecule and a free electron. The solution to the Lippmann-Schwinger equation involves only standard electronic structure techniques and a standard three-dimensional free particle Green's function quadrature for which fast techniques exist. The transition dipole moment for electron photodetachment, is a sum of matrix elements each involving one nonorthogonal orbital obtained from the solution to the Lippmann-Schwinger equation. An expression for the electron photodetachment transition dipole matrix element in terms of Dyson orbitals, which does not make the usual orthogonality assumptions, is derived.

Space vehicle approach velocity judgments under simulated visual space conditions

NASA Technical Reports Server (NTRS)

Haines, Richard F.

1987-01-01

Thirty-five volunteers responded when they first perceived an increase in apparent size of a collimated, 2-D image of an Orbiter vehicle. The test variables of interest included the presence of a fixed angular reticle within the field of view (FOV); three initial Orbiter distances; three constant Orbiter approach velocities corresponding to 1.6, 0.8, and 0.4 percent of the initial distance per second; and two background starfield velocities. It was found that: (1) at each initial range, increasing approach velocity led to a larger distance between the eye and Orbiter image at threshold; (2) including the fixed reticle in the FOV produced a smaller distance between the eye and Orbiter image at threshold; and (3) increasing background star velocity during this judgment led to a smaller distance between the eye and Orbiter image at threshold. The last two findings suggest that other detail within the FOV may compete for available attention which otherwise would be available for judging image expansion; thus, the target has to approach the observer nearer than otherwise if these details were present. These findings are discussed in relation to previous research and possible underlying mechanisms.

New method for estimating low-earth-orbit collision probabilities

NASA Technical Reports Server (NTRS)

Vedder, John D.; Tabor, Jill L.

1991-01-01

An unconventional but general method is described for estimating the probability of collision between an earth-orbiting spacecraft and orbital debris. This method uses a Monte Caralo simulation of the orbital motion of the target spacecraft and each discrete debris object to generate an empirical set of distances, each distance representing the separation between the spacecraft and the nearest debris object at random times. Using concepts from the asymptotic theory of extreme order statistics, an analytical density function is fitted to this set of minimum distances. From this function, it is possible to generate realistic collision estimates for the spacecraft.

Characterizing omega-limit sets which are closed orbits

NASA Astrophysics Data System (ADS)

Bautista, S.; Morales, C.

Let X be a vector field in a compact n-manifold M, n⩾2. Given Σ⊂M we say that q∈M satisfies (P) Σ if the closure of the positive orbit of X through q does not intersect Σ, but, however, there is an open interval I with q as a boundary point such that every positive orbit through I intersects Σ. Among those q having saddle-type hyperbolic omega-limit set ω(q) the ones with ω(q) being a closed orbit satisfy (P) Σ for some closed subset Σ. The converse is true for n=2 but not for n⩾4. Here we prove the converse for n=3. Moreover, we prove for n=3 that if ω(q) is a singular-hyperbolic set [C. Morales, M. Pacifico, E. Pujals, On C robust singular transitive sets for three-dimensional flows, C. R. Acad. Sci. Paris Sér. I 26 (1998) 81-86], [C. Morales, M. Pacifico, E. Pujals, Robust transitive singular sets for 3-flows are partially hyperbolic attractors or repellers, Ann. of Math. (2) 160 (2) (2004) 375-432], then ω(q) is a closed orbit if and only if q satisfies (P) Σ for some Σ closed. This result improves [S. Bautista, Sobre conjuntos hiperbólicos-singulares (On singular-hyperbolic sets), thesis Uiversidade Federal do Rio de Janeiro, 2005 (in Portuguese)] and [C. Morales, M. Pacifico, Mixing attractors for 3-flows, Nonlinearity 14 (2001) 359-378].

The flight of Newton's cannonball

NASA Astrophysics Data System (ADS)

Pesnell, W. Dean

2018-05-01

Newton's Cannon is a thought experiment used to motivate orbital motion. Cannonballs were fired from a high mountain at increasing muzzle velocity until they orbit the Earth. We will use the trajectories of these cannonballs to describe the shape of orbital tunnels that allow a cannonball fired from a high mountain to pass through the Earth. A sphere of constant density is used as the model of the Earth to take advantage of the analytic solutions for the interior trajectories that exist for that model. For the example shown, the cannonball trajectories that pass through the Earth intersect near the antipodal point of the cannon.

Theory of electronic and spin-orbit proximity effects in graphene on Cu(111)

NASA Astrophysics Data System (ADS)

Frank, Tobias; Gmitra, Martin; Fabian, Jaroslav

2016-04-01

We study orbital and spin-orbit proximity effects in graphene adsorbed to the Cu(111) surface by means of density functional theory (DFT). The proximity effects are caused mainly by the hybridization of graphene π and copper d orbitals. Our electronic structure calculations agree well with the experimentally observed features. We carry out a graphene-Cu(111) distance dependent study to obtain proximity orbital and spin-orbit coupling parameters, by fitting the DFT results to a robust low energy model Hamiltonian. We find a strong distance dependence of the Rashba and intrinsic proximity induced spin-orbit coupling parameters, which are in the meV and hundreds of μ eV range, respectively, for experimentally relevant distances. The Dirac spectrum of graphene also exhibits a proximity orbital gap, of about 20 meV. Furthermore, we find a band inversion within the graphene states accompanied by a reordering of spin and pseudospin states, when graphene is pressed towards copper.

Balancing single- and multi-reference correlation in the chemiluminescent reaction of dioxetanone using the anti-Hermitian contracted Schrödinger equation.

PubMed

Greenman, Loren; Mazziotti, David A

2011-05-07

Direct computation of energies and two-electron reduced density matrices (2-RDMs) from the anti-Hermitian contracted Schrödinger equation (ACSE) [D. A. Mazziotti, Phys. Rev. Lett. 97, 143002 (2006)], it is shown, recovers both single- and multi-reference electron correlation in the chemiluminescent reaction of dioxetanone especially in the vicinity of the conical intersection where strong correlation is important. Dioxetanone, the light-producing moiety of firefly luciferin, efficiently converts chemical energy into light by accessing its excited-state surface via a conical intersection. Our previous active-space 2-RDM study of dioxetanone [L. Greenman and D. A. Mazziotti, J. Chem. Phys. 133, 164110 (2010)] concluded that correlating 16 electrons in 13 (active) orbitals is required for realistic surfaces without correlating the remaining (inactive) orbitals. In this paper we pursue two complementary goals: (i) to correlate the inactive orbitals in 2-RDMs along dioxetanone's reaction coordinate and compare these results with those from multireference second-order perturbation theory (MRPT2) and (ii) to assess the size of the active space-the number of correlated electrons and orbitals-required by both MRPT2 and ACSE for accurate energies and surfaces. While MRPT2 recovers very different amounts of correlation with (4,4) and (16,13) active spaces, the ACSE obtains a similar amount of correlation energy with either active space. Nevertheless, subtle differences in excitation energies near the conical intersection suggest that the (16,13) active space is necessary to determine both energetic details and properties. Strong electron correlation is further assessed through several RDM-based metrics including (i) total and relative energies, (ii) the von Neumann entropy based on the 1-electron RDM, as well as the (iii) infinity and (iv) squared Frobenius norms based on the cumulant 2-RDM.

Halo orbit transfer trajectory design using invariant manifold in the Sun-Earth system accounting radiation pressure and oblateness

NASA Astrophysics Data System (ADS)

Srivastava, Vineet K.; Kumar, Jai; Kushvah, Badam Singh

2018-01-01

In this paper, we study the invariant manifold and its application in transfer trajectory problem from a low Earth parking orbit to the Sun-Earth L1 and L2-halo orbits with the inclusion of radiation pressure and oblateness. Invariant manifold of the halo orbit provides a natural entrance to travel the spacecraft in the solar system along some specific paths due to its strong hyperbolic character. In this regard, the halo orbits near both collinear Lagrangian points are computed first. The manifold's approximation near the nominal halo orbit is computed using the eigenvectors of the monodromy matrix. The obtained local approximation provides globalization of the manifold by applying backward time propagation to the governing equations of motion. The desired transfer trajectory well suited for the transfer is explored by looking at a possible intersection between the Earth's parking orbit of the spacecraft and the manifold.

Capacity Estimation Model for Signalized Intersections under the Impact of Access Point

PubMed Central

Zhao, Jing; Li, Peng; Zhou, Xizhao

2016-01-01

Highway Capacity Manual 2010 provides various factors to adjust the base saturation flow rate for the capacity analysis of signalized intersections. No factors, however, is considered for the potential change of signalized intersections capacity caused by the access point closeing to the signalized intersection. This paper presented a theoretical model to estimate the lane group capacity at signalized intersections with the consideration of the effects of access points. Two scenarios of access point locations, upstream or downstream of the signalized intersection, and impacts of six types of access traffic flow are taken into account. The proposed capacity model was validated based on VISSIM simulation. Results of extensive numerical analysis reveal the substantial impact of access point on the capacity, which has an inverse correlation with both the number of major street lanes and the distance between the intersection and access point. Moreover, among the six types of access traffic flows, the access traffic flow 1 (right-turning traffic from major street), flow 4 (left-turning traffic from access point), and flow 5 (left-turning traffic from major street) cause a more significant effect on lane group capacity than others. Some guidance on the mitigation of the negative effect is provided for practitioners. PMID:26726998

Dormant Comets in the Near-Earth Asteroid Population

NASA Astrophysics Data System (ADS)

Mommert, Michael; Harris, Alan W.; Mueller, Michael; Hora, Joseph L.; Trilling, David E.; Knight, Matthew; Bottke, William F.; Thomas, Cristina; Delbo', Marco; Emery, Josh P.; Fazio, Giovanni; Smith, Howard A.

2015-11-01

The population of near-Earth objects comprises active comets and asteroids, covering a wide range of dynamical parameters and physical properties. Dormant (or extinct) comets, masquerading as asteroids, have long been suspected of supplementing the near-Earth asteroid (NEA) population. We present a search for asteroidal objects of cometary origin based on dynamical and physical considerations. Our study is based on albedos derived within the ExploreNEOs program and is extended by adding data from NEOWISE and the Akari asteroid catalog. We use a statistical approach to identify asteroids on orbits that resemble those of short-period near-Earth comets using the Tisserand parameter with respect to Jupiter, the aphelion distance, and the minimum orbital intersection distance with respect to Jupiter. We identify a total of 23 near-Earth asteroids from our sample that are likely to be dormant short-period near-Earth comets and, based on a de-biasing procedure applied to the cryogenic NEOWISE survey, estimate both magnitude-limited and size-limited fractions of the NEA population that are dormant short-period comets. We find that 0.3-3.3% of the NEA population with H <= 21, and 9(+2/-5)% of the population with diameters d >= 1 km, are dormant short-period near-Earth comets. We also present an observation program that utilizes the 1.8m Vatican Advanced Technology Telescope (VATT) on Mt. Graham, AZ, to identify dormant comet candidates and search for activity in these objects. Our targets are NEAs on comet-like orbits, based on the dynamical criteria derived in the above study, that are accessible with the VATT (V <= 22). We identify dormant comets based on their optical spectral slope, represented by V-R color measurements, as albedo measurements for most of these objects are not available. For each target we measure and monitor its V magnitude in order to reveal activity outbreaks. We also search for extended emission around our targets using deep imaging and a point-spread-function subtraction technique that allows us to obtain an upper limit on the dust production rate in each target. We present preliminary results from this program. This work is supported in part by funding from the Spitzer Science Center.

The Intersection of Dreams and Reality: An Expansion of Temporal Distance Theory to Experiential Purchases

ERIC Educational Resources Information Center

Grube, Ann M.

2014-01-01

This research was designed to expand the applications of Psychological Distance (PD) Theory by studying the effects of time on the importance of criteria used to evaluate institutions of higher learning. It is intended to help administrators market more effectively by determining how future intentions (to go back to school someday) transition into…

The Eccentric Behavior of Nearly Frozen Orbits

NASA Technical Reports Server (NTRS)

Sweetser, Theodore H.; Vincent, Mark A.

2013-01-01

Frozen orbits are orbits which have only short-period changes in their mean eccentricity and argument of periapse, so that they basically keep a fixed orientation within their plane of motion. Nearly frozen orbits are those whose eccentricity and argument of periapse have values close to those of a frozen orbit. We call them "nearly" frozen because their eccentricity vector (a vector whose polar coordinates are eccentricity and argument of periapse) will stay within a bounded distance from the frozen orbit eccentricity vector, circulating around it over time. For highly inclined orbits around the Earth, this distance is effectively constant over time. Furthermore, frozen orbit eccentricity values are low enough that these orbits are essentially eccentric (i.e., off center) circles, so that nearly frozen orbits around Earth are bounded above and below by frozen orbits.

Trajectory Options for a Potential Mars Mission Combining Orbiting Science, Relay and a Sample Return Rendezvous Demonstration

NASA Technical Reports Server (NTRS)

Guinn, Joseph R.; Kerridge, Stuart J.; Wilson, Roby S.

2012-01-01

Mars sample return is a major scientific goal of the 2011 US National Research Council Decadal Survey for Planetary Science. Toward achievement of this goal, recent architecture studies have focused on several mission concept options for the 2018/2020 Mars launch opportunities. Mars orbiters play multiple roles in these architectures such as: relay, landing site identification/selection/certification, collection of on-going or new measurements to fill knowledge gaps, and in-orbit collection and transportation of samples from Mars to Earth. This paper reviews orbiter concepts that combine these roles and describes a novel family of relay orbits optimized for surface operations support. Additionally, these roles provide an intersection of objectives for long term NASA science, human exploration, technology development and international collaboration.

Computing Rydberg Electron Transport Rates Using Periodic Orbits

NASA Astrophysics Data System (ADS)

Sattari, Sulimon; Mitchel, Kevin

2017-04-01

Electron transport rates in chaotic atomic systems are computable from classical periodic orbits. This technique allows for replacing a Monte Carlo simulation launching millions of orbits with a sum over tens or hundreds of properly chosen periodic orbits using a formula called the spectral determiant. A firm grasp of the structure of the periodic orbits is required to obtain accurate transport rates. We apply a technique called homotopic lobe dynamics (HLD) to understand the structure of periodic orbits to compute the ionization rate in a classically chaotic atomic system, namely the hydrogen atom in strong parallel electric and magnetic fields. HLD uses information encoded in the intersections of stable and unstable manifolds of a few orbits to compute relevant periodic orbits in the system. All unstable periodic orbits are computed up to a given period, and the ionization rate computed from periodic orbits converges exponentially to the true value as a function of the period used. Using periodic orbit continuation, the ionization rate is computed over a range of electron energy and magnetic field values. The future goal of this work is to semiclassically compute quantum resonances using periodic orbits.

Meteor-Shower on Mars Indicates Cometary Activity Far Away From the Sun

NASA Astrophysics Data System (ADS)

Sekhar, Aswin; ASHER, DAVID

2015-08-01

Introduction: The close encounter of Comet C/2013 A1 (Siding Spring) with Mars on 2014 Oct 19 at 1830h (UT) generated a lot of interest and modelling work [1] [2] [3] in the solar system community. A recent (on 2014 Nov 7) press release from NASA implied that a meteor shower was detected on Mars by their space instruments some hours after the comet-Mars close encounter. Various work [4] [5] [6] has suggested that very specific meteoroid sizes and ejection conditions may be required to produce meteor phenomena at Mars at the given times.Stream dynamics: Meteoroid stream modelling and their orbital geometry calculations have gained high precision over the years. In this work, we compute in detail the structure of the cloud of meteoroids released by C/2013 A1, showing its dependence on heliocentric ejection distances, 3-dimensional ejection velocities, and particle sizes. Our calculations using numerical integrator MERCURY, [7], incorporating radiation pressure, [8], show that ejection of particles at large heliocentric distances (about 7 au to 13 au) from C/2013 A1 could lead to evolution of a dense meteoroid cloud which intersects Mars a few hours after the comet-Mars close encounter. Hence this detection of a meteor shower on Mars by space instruments is an indirect confirmation of cometary activity at large distances which has rarely been observed directly by telescopes so far. Furthermore it shows that comprehensive threat estimation needs to be done for satellites orbiting the Earth when dynamically new comets come very close to the Earth in future.References:[1] Vaubaillon J., Macquet L., Soja R. 2014. MNRAS. 439: 3294.[2] Moorhead A. V., Wiegert P. A., Cooke W. J. 2014. Icarus. 231:13.[3] Ye Q.-Z., Hui M.-T., 2014, ApJ, 787: 115.[4] Farnocchia D. et al. 2014. ApJL. 790: 114.[5] Kelley M. S. P. et al. 2014, ApJL, 792: 16.[6] Tricarico P. et al., 2014, ApJL, 787: 35.[7] Chambers J. E. 1999. MNRAS. 304: 793.[8] Burns J. A, Lamy P. L., Soter S. 1979. Icarus. 40: 1.

Distance majorization and its applications.

PubMed

Chi, Eric C; Zhou, Hua; Lange, Kenneth

2014-08-01

The problem of minimizing a continuously differentiable convex function over an intersection of closed convex sets is ubiquitous in applied mathematics. It is particularly interesting when it is easy to project onto each separate set, but nontrivial to project onto their intersection. Algorithms based on Newton's method such as the interior point method are viable for small to medium-scale problems. However, modern applications in statistics, engineering, and machine learning are posing problems with potentially tens of thousands of parameters or more. We revisit this convex programming problem and propose an algorithm that scales well with dimensionality. Our proposal is an instance of a sequential unconstrained minimization technique and revolves around three ideas: the majorization-minimization principle, the classical penalty method for constrained optimization, and quasi-Newton acceleration of fixed-point algorithms. The performance of our distance majorization algorithms is illustrated in several applications.

Where to locate transit stops: Cross-intersection profiles of ultrafine particles and implications for pedestrian exposure.

PubMed

Choi, Wonsik; Ranasinghe, Dilhara; DeShazo, J R; Kim, Jae-Jin; Paulson, Suzanne E

2018-02-01

Epidemiological studies have shown that exposure to traffic-related pollutants increases incidence of adverse health outcomes. Transit users in cities across the globe commonly spend 15-45 min or more waiting at transit stops each day, often at locations with high levels of pollution from traffic. Here, we investigate the characteristics of concentration profiles of ultrafine particles (UFP) with 5 m spatial resolution across intersections, to determine the best place to site transit stops to minimize exposures. Cross-intersection UFP profiles were derived from 1744 profiles covering 90 m before and after each intersection center with a mobile monitoring platform. Measurements were made at 10 signalized intersections located at six urban sites, each with a distinct built environment, during both mornings and afternoons. Measurements were made within 1.5 m of the sidewalk and approximately at breathing height (1.5 m above ground level) to approximate sidewalk exposures. UFP profiles were strongly influenced by high emissions from vehicle stops and accelerations, and peaked within 30 m of intersection centers; from there concentrations decreased sharply with distance. Peak concentrations averaged about 90% higher than the minima along the block. They were accompanied by more frequent and larger transient concentration spikes, increasing the chance of people near the intersection being exposed to both short-term extremely high concentration spikes and higher average concentrations. The decays are somewhat larger before the intersection than after the intersection, however as siting transit stops after intersections is preferred for smooth traffic flow, we focus on after the intersection. Simple time-duration exposure calculations combined with breathing rates suggest moving a bus stop from 20 to 40-50 m after the intersection can reduce transit-users' exposure levels to total UFP substantially, in proportion to the reciprocal of the magnitude of elevation at the intersection. Copyright © 2017 Elsevier Ltd. All rights reserved.

Cygnus sunrise premate

NASA Image and Video Library

2014-07-16

ISS040-E-063769 (16 July 2014) --- Intersecting the thin line of Earth?s atmosphere, the Orbital Sciences? Cygnus cargo craft attached to the end of the Canadarm2 robotic arm of the International Space Station is photographed by an Expedition 40 crew member after the two spacecraft converged at 6:36 a.m. (EDT) on July 16, 2014. The red color on Cygnus is a spectral effect from one of Cygnus? strobe lights against the fading light heading into an orbital sunset following grapple.

The fate of scattered planets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bromley, Benjamin C.; Kenyon, Scott J., E-mail: bromley@physics.utah.edu, E-mail: skenyon@cfa.harvard.edu

2014-12-01

As gas giant planets evolve, they may scatter other planets far from their original orbits to produce hot Jupiters or rogue planets that are not gravitationally bound to any star. Here, we consider planets cast out to large orbital distances on eccentric, bound orbits through a gaseous disk. With simple numerical models, we show that super-Earths can interact with the gas through dynamical friction to settle in the remote outer regions of a planetary system. Outcomes depend on planet mass, the initial scattered orbit, and the evolution of the time-dependent disk. Efficient orbital damping by dynamical friction requires planets atmore » least as massive as the Earth. More massive, longer-lived disks damp eccentricities more efficiently than less massive, short-lived ones. Transition disks with an expanding inner cavity can circularize orbits at larger distances than disks that experience a global (homologous) decay in surface density. Thus, orbits of remote planets may reveal the evolutionary history of their primordial gas disks. A remote planet with an orbital distance ∼100 AU from the Sun is plausible and might explain correlations in the orbital parameters of several distant trans-Neptunian objects.« less

An optimization approach for observation association with systemic uncertainty applied to electro-optical systems

NASA Astrophysics Data System (ADS)

Worthy, Johnny L.; Holzinger, Marcus J.; Scheeres, Daniel J.

2018-06-01

The observation to observation measurement association problem for dynamical systems can be addressed by determining if the uncertain admissible regions produced from each observation have one or more points of intersection in state space. An observation association method is developed which uses an optimization based approach to identify local Mahalanobis distance minima in state space between two uncertain admissible regions. A binary hypothesis test with a selected false alarm rate is used to assess the probability that an intersection exists at the point(s) of minimum distance. The systemic uncertainties, such as measurement uncertainties, timing errors, and other parameter errors, define a distribution about a state estimate located at the local Mahalanobis distance minima. If local minima do not exist, then the observations are not associated. The proposed method utilizes an optimization approach defined on a reduced dimension state space to reduce the computational load of the algorithm. The efficacy and efficiency of the proposed method is demonstrated on observation data collected from the Georgia Tech Space Object Research Telescope.

A Cooperative Traffic Control of Vehicle–Intersection (CTCVI) for the Reduction of Traffic Delays and Fuel Consumption

PubMed Central

Li, Jinjian; Dridi, Mahjoub; El-Moudni, Abdellah

2016-01-01

The problem of reducing traffic delays and decreasing fuel consumption simultaneously in a network of intersections without traffic lights is solved by a cooperative traffic control algorithm, where the cooperation is executed based on the connection of Vehicle-to-Infrastructure (V2I). This resolution of the problem contains two main steps. The first step concerns the itinerary of which intersections are chosen by vehicles to arrive at their destination from their starting point. Based on the principle of minimal travel distance, each vehicle chooses its itinerary dynamically based on the traffic loads in the adjacent intersections. The second step is related to the following proposed cooperative procedures to allow vehicles to pass through each intersection rapidly and economically: on one hand, according to the real-time information sent by vehicles via V2I in the edge of the communication zone, each intersection applies Dynamic Programming (DP) to cooperatively optimize the vehicle passing sequence with minimal traffic delays so that the vehicles may rapidly pass the intersection under the relevant safety constraints; on the other hand, after receiving this sequence, each vehicle finds the optimal speed profiles with the minimal fuel consumption by an exhaustive search. The simulation results reveal that the proposed algorithm can significantly reduce both travel delays and fuel consumption compared with other papers under different traffic volumes. PMID:27999333

THE ARCHES CLUSTER: EXTENDED STRUCTURE AND TIDAL RADIUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hosek, Matthew W. Jr.; Lu, Jessica R.; Anderson, Jay

At a projected distance of ∼26 pc from Sgr A*, the Arches cluster provides insight into star formation in the extreme Galactic center (GC) environment. Despite its importance, many key properties, such as the cluster’s internal structure and orbital history, are not well known. We present an astrometric and photometric study of the outer region of the Arches cluster ( R > 6.″25) using Hubble Space Telescope WFC3IR. Using proper motions, we calculate membership probabilities for stars down to F153M = 20 mag (∼2.5 M {sub ⊙}) over a 120″ × 120″ field of view, an area 144 times largermore » than previous astrometric studies of the cluster. We construct the radial profile of the Arches to a radius of 75″ (∼3 pc at 8 kpc), which can be well described by a single power law. From this profile we place a 3 σ lower limit of 2.8 pc on the observed tidal radius, which is larger than the predicted tidal radius (1–2.5 pc). Evidence of mass segregation is observed throughout the cluster, and no tidal tail structures are apparent along the orbital path. The absence of breaks in the profile suggests that the Arches has not likely experienced its closest approach to the GC between ∼0.2 and 1 Myr ago. If accurate, this constraint indicates that the cluster is on a prograde orbit and is located in front of the sky plane that intersects Sgr A*. However, further simulations of clusters in the GC potential are required to interpret the observed profile with more confidence.« less

The Orbit and Distance of WR140

NASA Astrophysics Data System (ADS)

Dougherty, S. M.; Trenton, V.; Beasley, A. J.

2011-01-01

A campaign of 35 epochs of milli-arcsecond resolution VLBA observations of the archetype colliding-wind WR+O star binary system WR 140 show the wind-collision region (WCR) as a bow-shaped arc of emission that rotates as the highly eccentric orbit progresses. The observations comprise 21 epochs from the 1993-2001 orbit, discussed by Dougherty et al. (2005), and 14 epochs from the 2001-2009 orbit, and span orbital phase 0.43 to 0.95. Assuming the WCR is symmetric about the line-of-centres of the two stars and ``points'' at the WR star, this rotation shows the O star moving from SE to E of the WR star between these orbital phases. Using IR interferometry observations from IOTA that resolve both stellar components at phase 0.297 in conjunction with orbital parameters derived from radial velocity variations, the VLBA observations constrain the inclination of the orbit plane as 120°±4°, the longitude of the ascending node as 352°±2°, and the orbit semi-major axis as 9.0±0.1 mas. This leads to a distance estimate to WR 140 of 1.81±0.08 kpc. Further refinements of the orbit and distance await more IR interferometric observations of the stellar components directly.

Kepler-36: a pair of planets with neighboring orbits and dissimilar densities.

PubMed

Carter, Joshua A; Agol, Eric; Chaplin, William J; Basu, Sarbani; Bedding, Timothy R; Buchhave, Lars A; Christensen-Dalsgaard, Jørgen; Deck, Katherine M; Elsworth, Yvonne; Fabrycky, Daniel C; Ford, Eric B; Fortney, Jonathan J; Hale, Steven J; Handberg, Rasmus; Hekker, Saskia; Holman, Matthew J; Huber, Daniel; Karoff, Christopher; Kawaler, Steven D; Kjeldsen, Hans; Lissauer, Jack J; Lopez, Eric D; Lund, Mikkel N; Lundkvist, Mia; Metcalfe, Travis S; Miglio, Andrea; Rogers, Leslie A; Stello, Dennis; Borucki, William J; Bryson, Steve; Christiansen, Jessie L; Cochran, William D; Geary, John C; Gilliland, Ronald L; Haas, Michael R; Hall, Jennifer; Howard, Andrew W; Jenkins, Jon M; Klaus, Todd; Koch, David G; Latham, David W; MacQueen, Phillip J; Sasselov, Dimitar; Steffen, Jason H; Twicken, Joseph D; Winn, Joshua N

2012-08-03

In the solar system, the planets' compositions vary with orbital distance, with rocky planets in close orbits and lower-density gas giants in wider orbits. The detection of close-in giant planets around other stars was the first clue that this pattern is not universal and that planets' orbits can change substantially after their formation. Here, we report another violation of the orbit-composition pattern: two planets orbiting the same star with orbital distances differing by only 10% and densities differing by a factor of 8. One planet is likely a rocky "super-Earth," whereas the other is more akin to Neptune. These planets are 20 times more closely spaced and have a larger density contrast than any adjacent pair of planets in the solar system.

Configuration interaction singles natural orbitals: An orbital basis for an efficient and size intensive multireference description of electronic excited states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shu, Yinan; Levine, Benjamin G., E-mail: levine@chemistry.msu.edu; Hohenstein, Edward G.

2015-01-14

Multireference quantum chemical methods, such as the complete active space self-consistent field (CASSCF) method, have long been the state of the art for computing regions of potential energy surfaces (PESs) where complex, multiconfigurational wavefunctions are required, such as near conical intersections. Herein, we present a computationally efficient alternative to the widely used CASSCF method based on a complete active space configuration interaction (CASCI) expansion built from the state-averaged natural orbitals of configuration interaction singles calculations (CISNOs). This CISNO-CASCI approach is shown to predict vertical excitation energies of molecules with closed-shell ground states similar to those predicted by state averaged (SA)-CASSCFmore » in many cases and to provide an excellent reference for a perturbative treatment of dynamic electron correlation. Absolute energies computed at the CISNO-CASCI level are found to be variationally superior, on average, to other CASCI methods. Unlike SA-CASSCF, CISNO-CASCI provides vertical excitation energies which are both size intensive and size consistent, thus suggesting that CISNO-CASCI would be preferable to SA-CASSCF for the study of systems with multiple excitable centers. The fact that SA-CASSCF and some other CASCI methods do not provide a size intensive/consistent description of excited states is attributed to changes in the orbitals that occur upon introduction of non-interacting subsystems. Finally, CISNO-CASCI is found to provide a suitable description of the PES surrounding a biradicaloid conical intersection in ethylene.« less

Evaluation of the Prince William County collision countermeasure system.

DOT National Transportation Integrated Search

2001-02-01

The Collision Countermeasure System (CCS) is an ITS application intended to reduce side-impact accident potential at rural, limited sight-distance intersections. It consists of activated warning signs and pavement loop detectors designed to enhance d...

Distance majorization and its applications

PubMed Central

Chi, Eric C.; Zhou, Hua; Lange, Kenneth

2014-01-01

The problem of minimizing a continuously differentiable convex function over an intersection of closed convex sets is ubiquitous in applied mathematics. It is particularly interesting when it is easy to project onto each separate set, but nontrivial to project onto their intersection. Algorithms based on Newton’s method such as the interior point method are viable for small to medium-scale problems. However, modern applications in statistics, engineering, and machine learning are posing problems with potentially tens of thousands of parameters or more. We revisit this convex programming problem and propose an algorithm that scales well with dimensionality. Our proposal is an instance of a sequential unconstrained minimization technique and revolves around three ideas: the majorization-minimization principle, the classical penalty method for constrained optimization, and quasi-Newton acceleration of fixed-point algorithms. The performance of our distance majorization algorithms is illustrated in several applications. PMID:25392563

Optimal solar sail planetocentric trajectories

NASA Technical Reports Server (NTRS)

Sackett, L. L.

1977-01-01

The analysis of solar sail planetocentric optimal trajectory problem is described. A computer program was produced to calculate optimal trajectories for a limited performance analysis. A square sail model is included and some consideration is given to a heliogyro sail model. Orbit to a subescape point and orbit to orbit transfer are considered. Trajectories about the four inner planets can be calculated and shadowing, oblateness, and solar motion may be included. Equinoctial orbital elements are used to avoid the classical singularities, and the method of averaging is applied to increase computational speed. Solution of the two-point boundary value problem which arises from the application of optimization theory is accomplished with a Newton procedure. Time optimal trajectories are emphasized, but a penalty function has been considered to prevent trajectories which intersect a planet's surface.

32 CFR 634.49 - Standards for impoundment.

Code of Federal Regulations, 2010 CFR

2010-07-01

... locate the owner of the POV and have the vehicle removed. (2) The vehicle may be moved a short distance... traffic. (ii) On a sidewalk, within an intersection, on a cross-walk, on a railroad track, in a fire lane...

Exploring the impact of signal types and adjacent vehicles on drivers' choices after the onset of yellow

NASA Astrophysics Data System (ADS)

Bao, Ji; Chen, Qun; Luo, Dandan; Wu, Yuli; Liang, Zuli

2018-06-01

Drivers' choices at signalized intersections may be made in great uncertainty after the onset of yellow, which creates potential hazards for road safety. These choices are analyzed and modeled based on field observations at three comparable signalized intersections in Changsha, China. The results show that intersections without monitoring devices widen the indecision zone, which can increase the risk of rear-end collisions and the uncertainty of drivers' decision-making. In addition, drivers are more likely to stop during the yellow interval at intersections equipped with a green signal countdown device (GSCD) than at those with a green signal flashing device (GSFD). Subsequently, according to the results of a binary logistic regression model (BLRM), drivers' decision making at the onset of the yellow indication is greatly influenced by the vehicle's spot speed, the distance to the stop line, and signal and monitoring devices. The presence of an adjacent vehicle with a short space headway can particularly motivate the following driver to make a go-decision after the first driver chooses to pass the intersection. However, a stop-decision by a driver in an adjacent lane can also prompt the following driver to stop.

Predicting Driver Behavior during the Yellow Interval Using Video Surveillance

PubMed Central

Li, Juan; Jia, Xudong; Shao, Chunfu

2016-01-01

At a signalized intersection, drivers must make a stop/go decision at the onset of the yellow signal. Incorrect decisions would lead to red light running (RLR) violations or crashes. This study aims to predict drivers’ stop/go decisions and RLR violations during yellow intervals. Traffic data such as vehicle approaching speed, acceleration, distance to the intersection, and occurrence of RLR violations are gathered by a Vehicle Data Collection System (VDCS). An enhanced Gaussian Mixture Model (GMM) is used to extract moving vehicles from target lanes, and the Kalman Filter (KF) algorithm is utilized to acquire vehicle trajectories. The data collected from the VDCS are further analyzed by a sequential logit model, and the relationship between drivers’ stop/go decisions and RLR violations is identified. The results indicate that the distance of vehicles to the stop line at the onset of the yellow signal is an important predictor for both drivers’ stop/go decisions and RLR violations. In addition, vehicle approaching speed is a contributing factor for stop/go decisions. Furthermore, the accelerations of vehicles after the onset of the yellow signal are positively related to RLR violations. The findings of this study can be used to predict the probability of drivers’ RLR violations and improve traffic safety at signalized intersections. PMID:27929447

Predicting Driver Behavior during the Yellow Interval Using Video Surveillance.

PubMed

Li, Juan; Jia, Xudong; Shao, Chunfu

2016-12-06

At a signalized intersection, drivers must make a stop/go decision at the onset of the yellow signal. Incorrect decisions would lead to red light running (RLR) violations or crashes. This study aims to predict drivers' stop/go decisions and RLR violations during yellow intervals. Traffic data such as vehicle approaching speed, acceleration, distance to the intersection, and occurrence of RLR violations are gathered by a Vehicle Data Collection System (VDCS). An enhanced Gaussian Mixture Model (GMM) is used to extract moving vehicles from target lanes, and the Kalman Filter (KF) algorithm is utilized to acquire vehicle trajectories. The data collected from the VDCS are further analyzed by a sequential logit model, and the relationship between drivers' stop/go decisions and RLR violations is identified. The results indicate that the distance of vehicles to the stop line at the onset of the yellow signal is an important predictor for both drivers' stop/go decisions and RLR violations. In addition, vehicle approaching speed is a contributing factor for stop/go decisions. Furthermore, the accelerations of vehicles after the onset of the yellow signal are positively related to RLR violations. The findings of this study can be used to predict the probability of drivers' RLR violations and improve traffic safety at signalized intersections.

Near-Earth asteroids orbits using Gaia and ground-based observations

NASA Astrophysics Data System (ADS)

Bancelin, D.; Hestroffer, D.; Thuillot, W.

2011-05-01

Potentially Hazardous Asteroids (PHAs) are Near-Earth Asteroids caraterised by a Minimum Orbital Intersection Distance (MOID) with Earth less to 0.05 A.U and an absolute magnitude H<22. Those objects have sometimes a so significant close approach with Earth that they can be put on a chaotic orbit. This kind of orbit is very sensitive for exemple to the initial conditions, to the planetary theory used (for instance JPL's model versus IMCCE's model) or even to the numerical integrator used (Lie Series, Bulirsch-Stoer or Radau). New observations (optical, radar, flyby or satellite mission) can improve those orbits and reduce the uncertainties on the Keplerian elements.The Gaia mission is an astrometric mission that will be launched in 2012 and will observe a large number of Solar System Objects down to magnitude V≤20. During the 5-year mission, Gaia will continuously scan the sky with a specific strategy: objects will be observed from two lines of sight separated with a constant basic angle. Five constants already fixed determinate the nominal scanning law of Gaia: The inertial spin rate (1°/min) that describe the rotation of the spacecraft around an axis perpendicular to those of the two fields of view, the solar-aspect angle (45°) that is the angle between the Sun and the spacecraft rotation axis, the precession period (63.12 days) which is the precession of the spin axis around the Sun-Earth direction. Two other constants are still free parameters: the initial spin phase, and the initial precession angle that will be fixed at the start of the nominal science operations. These latter are constraint by scientific outcome (e.g. possibility of performing test of fundamental physics) together with operational requirements (downlink to Earth windows). Several sets of observations of specific NEOs will hence be provided according to the initial precession angle. The purpose here is to study the statistical impact of the initial precession angle on the error propagation and on the collision probability, especially for PHAs. We will also analyse the advantage of combining space-based to ground-based observation over long term, as well as in short term from observations in alert.

Orbital infections: a complete cycle 7-year audit and a management guideline.

PubMed

Atfeh, Mihiar Sami; Singh, Kathryn; Khalil, Hisham Saleh

2018-06-04

Orbital infections are regularly encountered and are managed by various healthcare disciplines. Sepsis of the orbit and adjacent tissues can be associated with considerable acute complication and long-term sequelae. Therefore, prompt recognition and management of this condition are crucial. This article presents the outcomes of a 7-year complete cycle audit project and describes the development of the new local guideline on the management of orbital infections in our tertiary centre. (1) A retrospective 5-year audit cycle on patients with orbital infections. (2) A review of available evidence on the management of orbital infections. (3) A new local multidisciplinary guideline on the management of orbital infections. (4) A retrospective 2-year second audit cycle to assess the clinical outcomes. Various disciplines intersect in the management of orbital infections. Standardising the management of this condition proved to be achievable through the developed guideline. However, room for improvement in practice exists in areas such as the promptness in referring patients to specialist care, the multidisciplinary assessment of patients on admission, and the improvement of scanning requests of patients.

Self-organizing systems in planetary physics: Harmonic resonances of planet and moon orbits

NASA Astrophysics Data System (ADS)

Aschwanden, Markus J.

2018-01-01

The geometric arrangement of planet and moon orbits into a regularly spaced pattern of distances is the result of a self-organizing system. The positive feedback mechanism that operates a self-organizing system is accomplished by harmonic orbit resonances, leading to long-term stable planet and moon orbits in solar or stellar systems. The distance pattern of planets was originally described by the empirical Titius-Bode law, and by a generalized version with a constant geometric progression factor (corresponding to logarithmic spacing). We find that the orbital periods Ti and planet distances Ri from the Sun are not consistent with logarithmic spacing, but rather follow the quantized scaling (Ri + 1 /Ri) =(Ti + 1 /Ti) 2 / 3 =(Hi + 1 /Hi) 2 / 3 , where the harmonic ratios are given by five dominant resonances, namely (Hi + 1 :Hi) =(3 : 2) ,(5 : 3) ,(2 : 1) ,(5 : 2) ,(3 : 1) . We find that the orbital period ratios tend to follow the quantized harmonic ratios in increasing order. We apply this harmonic orbit resonance model to the planets and moons in our solar system, and to the exo-planets of 55 Cnc and HD 10180 planetary systems. The model allows us a prediction of missing planets in each planetary system, based on the quasi-regular self-organizing pattern of harmonic orbit resonance zones. We predict 7 (and 4) missing exo-planets around the star 55 Cnc (and HD 10180). The accuracy of the predicted planet and moon distances amounts to a few percents. All analyzed systems are found to have ≈ 10 resonant zones that can be occupied with planets (or moons) in long-term stable orbits.

Traffic Sign Detection System for Locating Road Intersections and Roundabouts: The Chilean Case.

PubMed

Villalón-Sepúlveda, Gabriel; Torres-Torriti, Miguel; Flores-Calero, Marco

2017-05-25

This paper presents a traffic sign detection method for signs close to road intersections and roundabouts, such as stop and yield (give way) signs. The proposed method relies on statistical templates built using color information for both segmentation and classification. The segmentation method uses the RGB-normalized (ErEgEb) color space for ROIs (Regions of Interest) generation based on a chromaticity filter, where templates at 10 scales are applied to the entire image. Templates consider the mean and standard deviation of normalized color of the traffic signs to build thresholding intervals where the expected color should lie for a given sign. The classification stage employs the information of the statistical templates over YCbCr and ErEgEb color spaces, for which the background has been previously removed by using a probability function that models the probability that the pixel corresponds to a sign given its chromaticity values. This work includes an analysis of the detection rate as a function of the distance between the vehicle and the sign. Such information is useful to validate the robustness of the approach and is often not included in the existing literature. The detection rates, as a function of distance, are compared to those of the well-known Viola-Jones method. The results show that for distances less than 48 m, the proposed method achieves a detection rate of 87.5 % and 95.4 % for yield and stop signs, respectively. For distances less than 30 m, the detection rate is 100 % for both signs. The Viola-Jones approach has detection rates below 20 % for distances between 30 and 48 m, and barely improves in the 20-30 m range with detection rates of up to 60 % . Thus, the proposed method provides a robust alternative for intersection detection that relies on statistical color-based templates instead of shape information. The experiments employed videos of traffic signs taken in several streets of Santiago, Chile, using a research platform implemented at the Robotics and Automation Laboratory of PUC to develop driver assistance systems.

Traffic Sign Detection System for Locating Road Intersections and Roundabouts: The Chilean Case

PubMed Central

Villalón-Sepúlveda, Gabriel; Torres-Torriti, Miguel; Flores-Calero, Marco

2017-01-01

This paper presents a traffic sign detection method for signs close to road intersections and roundabouts, such as stop and yield (give way) signs. The proposed method relies on statistical templates built using color information for both segmentation and classification. The segmentation method uses the RGB-normalized (ErEgEb) color space for ROIs (Regions of Interest) generation based on a chromaticity filter, where templates at 10 scales are applied to the entire image. Templates consider the mean and standard deviation of normalized color of the traffic signs to build thresholding intervals where the expected color should lie for a given sign. The classification stage employs the information of the statistical templates over YCbCr and ErEgEb color spaces, for which the background has been previously removed by using a probability function that models the probability that the pixel corresponds to a sign given its chromaticity values. This work includes an analysis of the detection rate as a function of the distance between the vehicle and the sign. Such information is useful to validate the robustness of the approach and is often not included in the existing literature. The detection rates, as a function of distance, are compared to those of the well-known Viola–Jones method. The results show that for distances less than 48 m, the proposed method achieves a detection rate of 87.5% and 95.4% for yield and stop signs, respectively. For distances less than 30 m, the detection rate is 100% for both signs. The Viola–Jones approach has detection rates below 20% for distances between 30 and 48 m, and barely improves in the 20–30 m range with detection rates of up to 60%. Thus, the proposed method provides a robust alternative for intersection detection that relies on statistical color-based templates instead of shape information. The experiments employed videos of traffic signs taken in several streets of Santiago, Chile, using a research platform implemented at the Robotics and Automation Laboratory of PUC to develop driver assistance systems. PMID:28587071

Fluctuations in Conjunction Miss Distance Projections as Time Approaches Time of Closest Approach

NASA Technical Reports Server (NTRS)

Christian, John A., III

2005-01-01

A responsibility of the Trajectory Operations Officer is to ensure that the International Space Station (ISS) avoids colliding with debris. United States Space Command (USSPACECOM) tracks and catalogs a portion of the debris in Earth orbit, but only objects with a perigee less than 600 km and a radar cross section (RCS) greater than 10 cm-objects that, in fact, represent only a small fraction of the objects in Earth orbit. To accommodate for this, the ISS uses shielding to protect against collisions with smaller objects. This study provides a better understanding of how quickly, and to what degree, USSPACECOM projections tend to converge to the final, true miss distance. The information included is formulated to better predict the behavior of miss distance data during real-time operations. It was determined that the driving components, in order of impact on miss distance fluctuations, are energy dissipation rate (EDR), RCS, and inclination. Data used in this analysis, calculations made, and conclusions drawn are stored in Microsoft Excel log sheets. A separate log sheet, created for each conjunction, contains information such as predicted miss distances, apogee and perigee of debris orbit, EDR, RCS, inclination, tracks and observations, statistical data, and other evaluation/orbital parameters.

The relationship of the globe to the orbital rim.

PubMed

Eckstein, Lauren A; Shadpour, Joseph M; Menghani, Ravi; Goldberg, Robert A

2011-01-01

To present a novel method for accurately characterizing the position of the globe relative to the orbital rim. The appearance and function of the eyelids are dependent on the underlying orbital bony architecture and globe position; however, no comprehensive language to describe these complex 3-dimensional relationships exists. Three-dimensional orbital reconstructions were generated from computed tomographic scans of 15 Occidental and 12 Oriental orbits without orbital pathologic disease. Globe and orbital rim anatomy were identified and outlined. Reference points were measured along 2 independent axes: (1) the distance between a plane defined by the corneal apex and the sagittal projection of the orbital rim and (2) the distance between the circumference of the globe and the coronal projection of the orbital rim. For Occidental orbits, the mean (SD) elevation of the sagittal projection of the orbital rim relative to the anterior projection of the globe was 4.6 (4.2) mm superiorly, 5.9 (3.0) mm nasally, 12.6 (3.7) mm inferiorly, and 20.6 (2.6) mm laterally. The mean (SD) radial distance between the coronal projection of the orbital rim and the circumference of the globe was 3.7 (2.1) mm superiorly, 7.6 (1.8) mm nasally, 6.6 (2.2) mm inferiorly, and 4.6 (2.3) mm laterally. For Oriental orbits, the mean (SD) elevation of the sagittal projection of the orbital rim relative to the anterior projection of the globe was 5.0 (4.5) mm superiorly, 6.8 (4.1) mm nasally, 11.1 (4.3) mm inferiorly, and 17.5 (3.3) mm laterally. The mean (SD) radial distance between the coronal projection of the orbital rim and the circumference of the globe was 2.1 (1.2) mm superiorly, 8.2 (2.0) mm nasally, 6.5 (1.9) mm inferiorly, and 4.5 (1.7) mm laterally. Comparison of Occidental and Oriental orbital rim and globe configurations revealed quantitative and qualitative differences. In addition to differences in soft-tissue anatomy, bony architectural variations may contribute substantially to racial differences in the surface anatomy of the periorbital area. Anatomic analysis, based on 3-dimensional orbital imaging, may provide a rational approach to surgical planning for aesthetic and reconstructive orbitofacial surgery.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeffries, C.; Perez, J.

For a driven nonlinear oscillator we report direct evidence for three cases of an interior crisis of the attractor, as conjectured by Grebogi, Ott, and Yorke. These crises are sudden and discontinuous changes in the attractor, observed directly from bifurcation diagrams and attractor diagrams (Poincare sections) in real time. The crises arise from intersection of an unstable orbit with the chaotic attractor.

IMS/Satellite Situation Center report

NASA Technical Reports Server (NTRS)

1973-01-01

Services planned by the Satellite Situation Center during the International Magnetospheric Study are briefly described. User requirements are emphasized. The following data are presented: orbital parameters for ISIS 2, ESRO 4, and HEOS 2; entry exit times for highly elliptical satellites; plots for highly elliptical earth satellites; and plots and flux tube intersection for low altitude satellites.

26. DIVERSION STRUCTURE WITH FORMER BASIN F IN DISTANCE (SECTION ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

26. DIVERSION STRUCTURE WITH FORMER BASIN F IN DISTANCE (SECTION 26). - Highline Canal, Sand Creek Lateral, Beginning at intersection of Peoria Street & Highline Canal in Arapahoe County (City of Aurora), Sand Creek lateral Extends 15 miles Northerly through Araphoe County, City & County of Denver, & Adams County to its end point, approximately 1/4 mile Southest of intersectioin of D Street & Ninth Avenue in Adams County (Rocky Mountain Arsenal, Commerce City Vicinity), Commerce City, Adams County, CO

Open ocean Internal Waves, Namibia Coast, Africa.

NASA Image and Video Library

1990-12-10

These open ocean Internal Waves were seen off the Namibia Coast, Africa (23.0S, 14.0E). The periodic and regularly spaced sets of internal waves most likely coincide with tidal periods about 12 hours apart. The wave length (distance from crest to crest) varies between 1.5 and 5.0 miles and the crest lengths stretch across and beyond the distance of the photo. The waves are intersecting the Namibia coastline at about a 30 degree angle.

Open ocean Internal Waves, Namibia Coast, Africa.

NASA Technical Reports Server (NTRS)

1990-01-01

These open ocean Internal Waves were seen off the Namibia Coast, Africa (23.0S, 14.0E). The periodic and regularly spaced sets of internal waves most likely coincide with tidal periods about 12 hours apart. The wave length (distance from crest to crest) varies between 1.5 and 5.0 miles and the crest lengths stretch across and beyond the distance of the photo. The waves are intersecting the Namibia coastline at about a 30 degree angle.

Conical intersection seams in polyenes derived from their chemical composition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nenov, Artur; Vivie-Riedle, Regina de

2012-08-21

The knowledge of conical intersection seams is important to predict and explain the outcome of ultrafast reactions in photochemistry and photobiology. They define the energetic low-lying reachable regions that allow for the ultrafast non-radiative transitions. In complex molecules it is not straightforward to locate them. We present a systematic approach to predict conical intersection seams in multifunctionalized polyenes and their sensitivity to substituent effects. Included are seams that facilitate the photoreaction of interest as well as seams that open competing loss channels. The method is based on the extended two-electron two-orbital method [A. Nenov and R. de Vivie-Riedle, J. Chem.more » Phys. 135, 034304 (2011)]. It allows to extract the low-lying regions for non-radiative transitions, which are then divided into small linear segments. Rules of thumb are introduced to find the support points for these segments, which are then used in a linear interpolation scheme for a first estimation of the intersection seams. Quantum chemical optimization of the linear interpolated structures yields the final energetic position. We demonstrate our method for the example of the electrocyclic isomerization of trifluoromethyl-pyrrolylfulgide.« less

On the orbit calculation of visual binaries with a very short arc: application to the PMS binary system, FW Tau AB

NASA Astrophysics Data System (ADS)

Docobo, J. A.; Tamazian, V. S.; Campo, P. P.

2018-05-01

In the vast majority of cases when available astrometric measurements of a visual binary cover a very short orbital arc, it is practically impossible to calculate a good quality orbit. It is especially important for systems with pre-main-sequence components where standard mass-spectrum calibrations cannot be applied nor can a dynamical parallax be calculated. We have shown that the analytical method of Docobo allows us to put certain constraints on the most likely orbital solutions, using an available realistic estimate of the global mass of the system. As an example, we studied the interesting PMS binary, FW Tau AB, located in the Taurus-Auriga as well as investigated a range of its possible orbital solutions combined with an assumed distance between 120 and 160 pc. To maintain the total mass of FW Tau AB in a realistic range between 0.2 and 0.6M_{⊙}, minimal orbital periods should begin at 105, 150, 335, and 2300 yr for distances of 120, 130, 140, and 150 pc, respectively (no plausible orbits were found assuming a distance of 160 pc). An original criterion to establish the upper limit of the orbital period is applied. When the position angle in some astrometric measurements was flipped by 180°, orbits with periods close to 45 yr are also plausible. Three example orbits with periods of 44.6, 180, and 310 yr are presented.

On the past orbital history of Comet P/Halley

NASA Astrophysics Data System (ADS)

Carusi, A.; Valsecchi, G. B.; Kresak, L.; Perozzi, E.

The results of backward integration of the Comet P/Halley behavior over the time span from 1585 AD to 9367 BC (a total of 4 million days) are discussed. The integration was performed on the FPS 364, using the integrator described by Everhart (1985); planets from Venus to Neptune were included, and nongravitational forces were neglected. Graphs are presented for the temporal evolution of the orbital eccentricity (computed along the barycentric orbit at each aphelion passage), orbital inclination, the argument of perihelion of the orbit, perihelion distance, and the two nodal distances of P/Halley comet. A more or less continuous decrease of the orbital eccentricity and inclination were found, as well as of the argument of perihelion. It is suggested that Comet P/Halley may have undergone strong gravitational interactions with Jupiter about 11,000 years ago, and that the time span spent by the comet in a short period orbit may be as short as that.

The Influence of Intersections on Fuel Consumption in Urban Arterial Road Traffic: A Single Vehicle Test in Harbin, China

PubMed Central

Wu, Lina; Ci, Yusheng; Chu, Jiangwei; Zhang, Hongsheng

2015-01-01

The calculating method for fuel consumption (FC) was put forward and calibrated and the characteristics of the fuel consumption on intersections were analyzed based on 18 groups of vehicular operating data which were acquired from the test experiment of a single vehicle along the urban arterial roads in Harbin, China. The results obtained show that 50.36% of the fuel consumption for the test vehicle was used at the area of intersections compared with 28.9% of the influencing distance and 68.5% of the running time; and 78.4% of them was burnt at the stages of acceleration and idling. Meanwhile, the type (c) of the vehicular operating status was illustrated to be the worst way of reducing fuel consumption, the causes were analyzed and four improvement strategies were put forward. PMID:26367012

A Cepheid Distance to NGC 4603 in the Centaurus Cluster

NASA Technical Reports Server (NTRS)

Madore, B.; Newman, J.; Zepf, S.; Davis, M.; Freedman, W.; Madore, B.; Stetson, P.; Silbermann, N.; Phelps, R.

1999-01-01

In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling 6 orbits) in the F814W filter.

A Classroom Note on: The Average Distance in an Ellipse

ERIC Educational Resources Information Center

Gordon, Sheldon P.

2011-01-01

This article presents an applied calculus exercise that can be easily shared with students. One of Kepler's greatest discoveries was the fact that the planets move in elliptic orbits with the sun at one focus. Astronomers characterize the orbits of particular planets by their minimum and maximum distances to the sun, known respectively as the…

"Dry" Mercury and "wet" Mars: comparison of two terrestrial planets with strongly differing orbital frequencies

NASA Astrophysics Data System (ADS)

Kochemasov, G.

The modern wave planetology states that "orbits make structures". It means that all celestial bodies moving in non-round keplerian elliptical (and parabolic) orbits and rotating (all bodies rotate) are subjected to warping action of inertia-gravity waves . The waves appear in bodies due to periodically changing accelerations during cyclic orbital movements; they have a stationary character, 4 intersecting ortho- and diagonal directions and various lengths. Wave intersections and superpositions produce uplifting (+), subsiding (-) and neutral (0) regularly disposed tectonic blocks. Their sizes depend on wavelengths. The longest in a globe fundamental wave1 long 2πR is responsible for ubiquitous appearance in all celestial bodies of tectonic dichotomy or segmentation (2πR-structure). The first overtone wave2 produces tectonic sectoring (πR-structure). On this already complex wave structurization are superposed individual waves whose lengths are proportional to orbital periods or inversely proportional to orbital frequencies: higher frequency - smaller waves, lower frequency - larger waves. These waves are responsible for production of tectonic granules. In a row of terrestrial planets according to their orb. fr. sizes of the granules are as follows (this row can be started with the solar photosphere that orbits around the center of the solar system with about one month period): Photosphere πR/60, Mercury πR/16, Venus πR/6, Earth πR/4, Mars πR/2, asteroids πR/1. By this way a bridging is made between planets and stars in that concerns their wave structurization. The calculated granule sizes are rather known in nature. The solar supergranulation about 30-40 thousand km across, prevailing sizes of mercurian craters ˜500 km in diameter (a radar image from Earth), venusian "blobs" ˜3000 km across, superstructures of the Earth's cratons ˜ 5000 km across (seen now on NASA image PIA04159), martian elongated shape due to 2 waves inscribed in equator, asteroids' convexo-concave shape. "Orbits make structures" - this concerns solid planetary spheres as well as gaseous ones. Tectonic granulation of lithospheres of Venus, Earth and Mars is repeated in their atmospheres. Moreover, their atmospheric masses correlate with their orbital properties: the higher orbital fr. the larger atmospheric masses, that means more complete sweeping volatiles. Venus is covered with a thick dense atmosphere, Mars possesses very weak transparent one, Earth is in the middle, Mercury is bare. Sweeping volatiles out of the planets was compared using their granulations and oscillation frequencies [1]. Venus is ˜ 60 times more outgassed than Earth, and 6000 times more outgassed than Mars. Mercury is ˜500 times more 1 outgassed than Venus [1]. The most outgassed of the terrestrial planets Mercury is the only planet bearing distinct traces of earlier planetary contraction: escarps or lobate ledges. Numerous so-called secondary craters - small and deep holes controlled by lineaments or weakness zones could speak in favor of intense degassing. The most degassed Venus and Mercury rotate very slowly. This is due to angular momenta redistribution between a solid body and its gaseous envelopes. Solid bodies slow down, atmospheres rotate faster. However, if Venus mainly keeps its atmosphere, Mercury has lost it by solar wind sweeping (remain traces of noble gases, Na, K). Mars , on the contrary, is very mildly outgassed and keeps a lot of CO2 and H2 O. Thus, two small planets - Mars and Mercury are "antipodean" bodies. Mercury is dull, heavy, Fe-rich, low relief range, contracted (squeezed), slowly rotating, without atmosphere ("candle-end"). Mars is bright, less dense, with high relief range, extended (at least partially), rapidly rotating, with an atmosphere. And this is due to different solar distances explaining not only different primary accretion compositions but also different orbiting frequencies so crucial for evolution of celestial bodies. References: [1] Kochemasov G.G. (2003) Tectonically and chemically dichotomic Mars is the least outgassed of terrestrial planets // Vernadsky-Brown microsymposium 38, Oct. 27-29, 2003, Vernadsky Inst., Moscow, Russia, Abstr.,(CD-ROM). 2

Planning-Support for Mitigation of Wildlife-Vehicle Collisions and Highway Impacts on Migration Routes in Wyoming

DOT National Transportation Integrated Search

2016-08-23

Wyoming is home to abundant big game, including long-distance migratory species such as mule deer, elk, and pronghorn. Where these animals movement patterns intersect with roads, vehicles often hit animals. This poses a threat both to highway safe...

Euclidean, Spherical, and Hyperbolic Shadows

ERIC Educational Resources Information Center

Hoban, Ryan

2013-01-01

Many classical problems in elementary calculus use Euclidean geometry. This article takes such a problem and solves it in hyperbolic and in spherical geometry instead. The solution requires only the ability to compute distances and intersections of points in these geometries. The dramatically different results we obtain illustrate the effect…

Changes in Drivers’ Visual Performance during the Collision Avoidance Process as a Function of Different Field of Views at Intersections

PubMed Central

Yan, Xuedong; Zhang, Xinran; Zhang, Yuting; Li, Xiaomeng; Yang, Zhuo

2016-01-01

The intersection field of view (IFOV) indicates an extent that the visual information can be observed by drivers. It has been found that further enhancing IFOV can significantly improve emergent collision avoidance performance at intersections, such as faster brake reaction time, smaller deceleration rate, and lower traffic crash involvement risk. However, it is not known how IFOV affects drivers’ eye movements, visual attention and the relationship between visual searching and traffic safety. In this study, a driving simulation experiment was conducted to uncover the changes in drivers’ visual performance during the collision avoidance process as a function of different field of views at an intersection by using an eye tracking system. The experimental results showed that drivers’ ability in identifying the potential hazard in terms of visual searching was significantly affected by different IFOV conditions. As the IFOVs increased, drivers had longer gaze duration (GD) and more number of gazes (NG) in the intersection surrounding areas and paid more visual attention to capture critical visual information on the emerging conflict vehicle, thus leading to a better collision avoidance performance and a lower crash risk. It was also found that female drivers had a better visual performance and a lower crash rate than male drivers. From the perspective of drivers’ visual performance, the results strengthened the evidence that further increasing intersection sight distance standards should be encouraged for enhancing traffic safety. PMID:27716824

Telemetry location error in a forested habitat

USGS Publications Warehouse

Chu, D.S.; Hoover, B.A.; Fuller, M.R.; Geissler, P.H.; Amlaner, Charles J.

1989-01-01

The error associated with locations estimated by radio-telemetry triangulation can be large and variable in a hardwood forest. We assessed the magnitude and cause of telemetry location errors in a mature hardwood forest by using a 4-element Yagi antenna and compass bearings toward four transmitters, from 21 receiving sites. The distance error from the azimuth intersection to known transmitter locations ranged from 0 to 9251 meters. Ninety-five percent of the estimated locations were within 16 to 1963 meters, and 50% were within 99 to 416 meters of actual locations. Angles with 20o of parallel had larger distance errors than other angles. While angle appeared most important, greater distances and the amount of vegetation between receivers and transmitters also contributed to distance error.

Metrics in Keplerian orbits quotient spaces

NASA Astrophysics Data System (ADS)

Milanov, Danila V.

2018-03-01

Quotient spaces of Keplerian orbits are important instruments for the modelling of orbit samples of celestial bodies on a large time span. We suppose that variations of the orbital eccentricities, inclinations and semi-major axes remain sufficiently small, while arbitrary perturbations are allowed for the arguments of pericentres or longitudes of the nodes, or both. The distance between orbits or their images in quotient spaces serves as a numerical criterion for such problems of Celestial Mechanics as search for common origin of meteoroid streams, comets, and asteroids, asteroid families identification, and others. In this paper, we consider quotient sets of the non-rectilinear Keplerian orbits space H. Their elements are identified irrespective of the values of pericentre arguments or node longitudes. We prove that distance functions on the quotient sets, introduced in Kholshevnikov et al. (Mon Not R Astron Soc 462:2275-2283, 2016), satisfy metric space axioms and discuss theoretical and practical importance of this result. Isometric embeddings of the quotient spaces into R^n, and a space of compact subsets of H with Hausdorff metric are constructed. The Euclidean representations of the orbits spaces find its applications in a problem of orbit averaging and computational algorithms specific to Euclidean space. We also explore completions of H and its quotient spaces with respect to corresponding metrics and establish a relation between elements of the extended spaces and rectilinear trajectories. Distance between an orbit and subsets of elliptic and hyperbolic orbits is calculated. This quantity provides an upper bound for the metric value in a problem of close orbits identification. Finally the invariance of the equivalence relations in H under coordinates change is discussed.

Orbital shape in intentional skull deformations and adult sagittal craniosynostoses.

PubMed

Sandy, Ronak; Hennocq, Quentin; Nysjö, Johan; Giran, Guillaume; Friess, Martin; Khonsari, Roman Hossein

2018-06-21

Intentional cranial deformations are the result of external mechanical forces exerted on the skull vault that modify the morphology of various craniofacial structures such as the skull base, the orbits and the zygoma. In this controlled study, we investigated the 3D shape of the orbital inner mould and the orbital volume in various types of intentional deformations and in adult non-operated scaphocephaly - the most common type of craniosynostosis - using dedicated morphometric methods. CT scans were performed on 32 adult skulls with intentional deformations, 21 adult skull with scaphocephaly and 17 non-deformed adult skulls from the collections of the Muséum national d'Histoire naturelle in Paris, France. The intentional deformations group included six skulls with Toulouse deformations, eight skulls with circumferential deformations and 18 skulls with antero-posterior deformations. Mean shape models were generated based on a semi-automatic segmentation technique. Orbits were then aligned and compared qualitatively and quantitatively using colour-coded distance maps and by computing the mean absolute distance, the Hausdorff distance, and the Dice similarity coefficient. Orbital symmetry was assessed after mirroring, superimposition and Dice similarity coefficient computation. We showed that orbital shapes were significantly and symmetrically modified in intentional deformations and scaphocephaly compared with non-deformed control skulls. Antero-posterior and circumferential deformations demonstrated a similar and severe orbital deformation pattern resulting in significant smaller orbital volumes. Scaphocephaly and Toulouse deformations had similar deformation patterns but had no effect on orbital volumes. This study showed that intentional deformations and scaphocephaly significantly interact with orbital growth. Our approach was nevertheless not sufficient to identify specific modifications caused by the different types of skull deformations or by scaphocephaly. © 2018 Anatomical Society.

Detection of the lunar body tide by the Lunar Orbiter Laser Altimeter.

PubMed

Mazarico, Erwan; Barker, Michael K; Neumann, Gregory A; Zuber, Maria T; Smith, David E

2014-04-16

The Lunar Orbiter Laser Altimeter instrument onboard the Lunar Reconnaissance Orbiter spacecraft collected more than 5 billion measurements in the nominal 50 km orbit over ∼10,000 orbits. The data precision, geodetic accuracy, and spatial distribution enable two-dimensional crossovers to be used to infer relative radial position corrections between tracks to better than ∼1 m. We use nearly 500,000 altimetric crossovers to separate remaining high-frequency spacecraft trajectory errors from the periodic radial surface tidal deformation. The unusual sampling of the lunar body tide from polar lunar orbit limits the size of the typical differential signal expected at ground track intersections to ∼10 cm. Nevertheless, we reliably detect the topographic tidal signal and estimate the associated Love number h 2 to be 0.0371 ± 0.0033, which is consistent with but lower than recent results from lunar laser ranging. Altimetric data are used to create radial constraints on the tidal deformationThe body tide amplitude is estimated from the crossover dataThe estimated Love number is consistent with previous estimates but more precise.

Near-Earth Asteroids Astrometry with Gaia

NASA Astrophysics Data System (ADS)

Bancelin, D.; Hestroffer, D.; Thuillot, W.

2011-05-01

Potentially Hazardous Asteroids (PHAs) are Near-Earth Asteroids caraterised by a Minimum Orbital Intersection Distance (MOID) with Earth less to 0.05 A.U and an absolute magnitude H<22. Those objects have sometimes a so significant close approach with Earth that they can be put on a chaotic orbit. This kind of orbit is very sensitive for exemple to the initial conditions, to the planetary theory used (for instance JPL's model versus IMCCE's model) or even to the numerical integrator used (Lie Series, Bulirsch-Stoer or Radau). New observations (optical, radar, flyby or satellite mission) can improve those orbits and reduce the uncertainties on the Keplerian elements.The Gaia mission is an astrometric mission that will be launched in 2012 and will observe a large number of Solar System Objects down to magnitude V≤20. During the 5-year mission, Gaia will continuously scan the sky with a specific strategy: objects will be observed from two lines of sight separated with a constant basic angle. Five constants already fixed determinate the nominal scanning law of Gaia: The inertial spin rate (1°/min) that describe the rotation of the spacecraft around an axis perpendicular to those of the two fields of view, the solar-aspect angle (45°) that is the angle between the Sun and the spacecraft rotation axis, the precession period (63.12 days) which is the precession of the spin axis around the Sun-Earth direction. Two other constants are still free parameters: the initial spin phase, and the initial precession angle that will be fixed at the start of the nominal science operations. These latter are constraint by scientific outcome (e.g. possibility of performing test of fundamental physics) together with operational requirements (downlink to Earth windows). Several sets of observations of specific NEOs will hence be provided according to the initial precession angle. The purpose here is to study the statistical impact of the initial precession angle on the error propagation and on the collision probability, especially for PHAs. We will also analyse the advantage of combining space-based to ground-based observation over long term, as well as in short term from observations in alert.

Incorporation of star measurements for the determination of orbit and attitude parameters of a geosynchronous satellite: An iterative application of linear regression

NASA Astrophysics Data System (ADS)

Phillips, D.

1980-10-01

Currently on NOAA/NESS's VIRGS system at the World Weather Building star images are being ingested on a daily basis. The image coordinates of the star locations are measured and stored. Subsequently, the information is used to determine the attitude, the misalignment angles between the spin axis and the principal axis of the satellite, and the precession rate and direction. This is done for both the 'East' and 'West' operational geosynchronous satellites. This orientation information is then combined with image measurements of earth based landmarks to determine the orbit of each satellite. The method for determining the orbit is simple. For each landmark measurement one determines a nominal position vector for the satellite by extending a ray from the landmark's position towards the satellite and intersecting the ray with a sphere with center coinciding with the Earth's center and with radius equal to the nominal height for a geosynchronous satellite. The apparent motion of the satellite around the Earth's center is then approximated with a Keplerian model. In turn the variations of the satellite's height, as a function of time found by using this model, are used to redetermine the successive satellite positions by again using the Earth based landmark measurements and intersecting rays from these landmarks with the newly determined spheres. This process is performed iteratively until convergence is achieved. Only three iterations are required.

Refining Binary Pulsar B1913+16's Gravitational Wave Test via a VLBI Parallax Measurement

NASA Astrophysics Data System (ADS)

Weisberg, Joel; Deller, Adam; Chatterjee, Shami; Nice, David

2018-01-01

The orbital decay of binary pulsar B1913+16 provided the first evidence of gravitational waves as predicted by General Relativity, and ruled out numerous previously viable alternative gravitational theories (e.g., Taylor & Weisberg, APJ, 253, 908, 1982). The gravitational wave emission and resulting orbital decay manifest themselves as an orbital period derivative. Subsequent observations (e.g., Weisberg and Huang 2016, APJ, 829, 55) have greatly refined the precision of the orbital period derivative measurement. The accuracy of the experiment is currently limited by our knowledge of the relative galactic accelerations of the binary and solar system barycenters, which make another contribution to the observed orbital period derivative. The magnitude of these accelerations depend on various galactic constants and on the pulsar distance.As our knowledge of the Galaxy and its motions has improved, the pulsar's distance has become the largest remaining source of uncertainty in the experiment.Therefore, we conducted a series of astrometric measurements of PSR B1913+16 with the Very Long Baseline Array. We report the pulsar parallax and distance derived from these measurements, and use them to correct our observed orbital period derivative for the above galactic acceleration term, thereby providing a more accurate test of gravitational radiation emission from the system.

HABITABLE ZONES OF POST-MAIN SEQUENCE STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramirez, Ramses M.; Kaltenegger, Lisa

Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (∼M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons tomore » super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.« less

Estimating rear-end accident probabilities at signalized intersections: a comparison study of intersections with and without green signal countdown devices.

PubMed

Ni, Ying; Li, Keping

2014-01-01

Rear-end accidents are the most common accident type at signalized intersections, because the diversity of actions taken increases due to signal change. Green signal countdown devices (GSCDs), which have been widely installed in Asia, are thought to have the potential of improving capacity and reducing accidents, but some negative effects on intersection safety have been observed in practice; for example, an increase in rear-end accidents. A microscopic modeling approach was applied to estimate rear-end accident probability during the phase transition interval in the study. The rear-end accident probability is determined by the following probabilities: (1) a leading vehicle makes a "stop" decision, which was formulated by using a binary logistic model, and (2) the following vehicle fails to stop in the available stopping distance, which is closely related to the critical deceleration used by the leading vehicle. Based on the field observation carried out at 2 GSCD intersections and 2 NGSCD intersections (i.e., intersections without GSCD devices) along an arterial in Suzhou, the rear-end probabilities at GSCD and NGSCD intersections were calculated using Monte Carlo simulation. The results suggested that, on the one hand, GSCDs caused significantly negative safety effects during the flashing green interval, especially for vehicles in a zone ranging from 15 to 70 m; on the other hand, GSCD devices were helpful in reducing rear-end accidents during the yellow interval, especially in a zone from 0 to 50 m. GSCDs helped shorten indecision zones and reduce rear-end collisions near the stop line during the yellow interval, but they easily resulted in risky car following behavior and much higher rear-end collision probabilities at indecision zones during both flashing green and yellow intervals. GSCDs are recommended to be cautiously installed and education on safe driving behavior should be available.

Traffic Management for Emergency Vehicle Priority Based on Visual Sensing.

PubMed

Nellore, Kapileswar; Hancke, Gerhard P

2016-11-10

Vehicular traffic is endlessly increasing everywhere in the world and can cause terrible traffic congestion at intersections. Most of the traffic lights today feature a fixed green light sequence, therefore the green light sequence is determined without taking the presence of the emergency vehicles into account. Therefore, emergency vehicles such as ambulances, police cars, fire engines, etc. stuck in a traffic jam and delayed in reaching their destination can lead to loss of property and valuable lives. This paper presents an approach to schedule emergency vehicles in traffic. The approach combines the measurement of the distance between the emergency vehicle and an intersection using visual sensing methods, vehicle counting and time sensitive alert transmission within the sensor network. The distance between the emergency vehicle and the intersection is calculated for comparison using Euclidean distance, Manhattan distance and Canberra distance techniques. The experimental results have shown that the Euclidean distance outperforms other distance measurement techniques. Along with visual sensing techniques to collect emergency vehicle information, it is very important to have a Medium Access Control (MAC) protocol to deliver the emergency vehicle information to the Traffic Management Center (TMC) with less delay. Then only the emergency vehicle is quickly served and can reach the destination in time. In this paper, we have also investigated the MAC layer in WSNs to prioritize the emergency vehicle data and to reduce the transmission delay for emergency messages. We have modified the medium access procedure used in standard IEEE 802.11p with PE-MAC protocol, which is a new back off selection and contention window adjustment scheme to achieve low broadcast delay for emergency messages. A VANET model for the UTMS is developed and simulated in NS-2. The performance of the standard IEEE 802.11p and the proposed PE-MAC is analysed in detail. The NS-2 simulation results have shown that the PE-MAC outperforms the IEEE 802.11p in terms of average end-to-end delay, throughput and energy consumption. The performance evaluation results have proven that the proposed PE-MAC prioritizes the emergency vehicle data and delivers the emergency messages to the TMC with less delay compared to the IEEE 802.11p. The transmission delay of the proposed PE-MAC is also compared with the standard IEEE 802.15.4, and Enhanced Back-off Selection scheme for IEEE 802.15.4 protocol [EBSS, an existing protocol to ensure fast transmission of the detected events on the road towards the TMC] and the comparative results have proven the effectiveness of the PE-MAC over them. Furthermore, this research work will provide an insight into the design of an intelligent urban traffic management system for the effective management of emergency vehicles and will help to save lives and property.

Controlled tether extends satellite's orbital range

NASA Astrophysics Data System (ADS)

Wigotsky, V.

1984-06-01

A low orbit satellite tethered to the Space Shuttle Orbiter's cargo bay would be able to conduct upper atmosphere experiments without fear of orbit deterioration. NASA has in light of this initiated a Tethered Satellite System program aimed at the 1987 deployment of a 1,100-lb, 5 ft-diameter satellite to a distance of 6-12 miles from the Space Shuttle on a Kevlar tether. The distance of the fully developed system will be 62 miles, representing an altitude of 80 miles above the earth. Tether diameters under consideration are in the 0.065-0.1 inch range. The satellite control system will consist of a reel drive, a deployment boom, and a boom-mounted tether control, in order to vary tether tension during gravity gradient changes.

Packed Planetary Systems

NASA Astrophysics Data System (ADS)

Barnes, R.; Greenberg, R.

2005-08-01

Planetary systems display a wide range of appearances, with apparently arbitrary values of semi-major axis, eccentricity, etc. We reduce the complexity of orbital configurations to a single value, δ , which is a measure of how close, over secular timescales ( ˜10,000 orbits), two consecutive planets come to each other. We measure this distance relative to the sum of the radii of their Hill spheres, sometimes referred to as mutual Hill radii (MHR). We determine the closest approach distance by numerically integrating the entire system on coplanar orbits, using minimum masses. For non-resonant systems, close approach occurs during apsidal alignment, either parallel or anti-parallel. For resonant pairs the distance at conjunction determines the closest approach distance. Previous analytic work found that planets on circular orbits were assuredly unstable if they came within 3.5 MHR (i.e. Gladman 1993; Chambers, Wetherill & Boss 1996). We find that most known pairs of jovian planets (including those in our solar system) come within 3.5 -- 7 MHR of each other. We also find that several systems are unstable (their closest approach distance is less than 3.5 MHR). These systems, if they are real, probably exist in an observationally permitted location somewhat different from the current best fit. In these cases, the planets' closest approach distance will most likely also be slightly larger than 3.5 MHR. Most pairs beyond 7 MHR probably experienced post-formation migration (i.e. tidal circularization, inward scattering of small bodies) which moved them further apart. This result is even more remarkable since we have used the minimum masses; most likely the systems are inclined to the line of sight, making the Hill spheres larger, and shrinking δ . This dense packing may reflect a tendency for planets to form as close together as they can without being dynamically unstable. This result further implies there may be a large number of smaller, currently undetectable companions packed in orbits around stars with known planets.

Subversion and Critical Distance: Black Speculative Fiction, White Pre-Service Teachers, and Anti-Racist Pedagogy

ERIC Educational Resources Information Center

Roue, Bevin

2016-01-01

This dissertation examines representations of black lives in adolescent speculative fiction and explores what the genre offers to anti-racist teacher education. Situating my study at the intersections of literacy education and children's literature studies, I interrogate assumptions surrounding genre conventions adopted in multicultural education.…

Cutting Solid Figures by Plane--Analytical Solution and Spreadsheet Implementation

ERIC Educational Resources Information Center

Benacka, Jan

2012-01-01

In some secondary mathematics curricula, there is a topic called Stereometry that deals with investigating the position and finding the intersection, angle, and distance of lines and planes defined within a prism or pyramid. Coordinate system is not used. The metric tasks are solved using Pythagoras' theorem, trigonometric functions, and sine and…

When Life and Learning Do Not Fit: Challenges of Workload and Communication in Introductory Computer Science Online

ERIC Educational Resources Information Center

Benda, Klara; Bruckman, Amy; Guzdial, Mark

2012-01-01

We present the results of an interview study investigating student experiences in two online introductory computer science courses. Our theoretical approach is situated at the intersection of two research traditions: "distance and adult education research," which tends to be sociologically oriented, and "computer science education…

Complete elliptical ring geometry provides energy and instrument calibration for synchrotron-based two-dimensional X-ray diffraction

PubMed Central

Hart, Michael L.; Drakopoulos, Michael; Reinhard, Christina; Connolley, Thomas

2013-01-01

A complete calibration method to characterize a static planar two-dimensional detector for use in X-ray diffraction at an arbitrary wavelength is described. This method is based upon geometry describing the point of intersection between a cone’s axis and its elliptical conic section. This point of intersection is neither the ellipse centre nor one of the ellipse focal points, but some other point which lies in between. The presented solution is closed form, algebraic and non-iterative in its application, and gives values for the X-ray beam energy, the sample-to-detector distance, the location of the beam centre on the detector surface and the detector tilt relative to the incident beam. Previous techniques have tended to require prior knowledge of either the X-ray beam energy or the sample-to-detector distance, whilst other techniques have been iterative. The new calibration procedure is performed by collecting diffraction data, in the form of diffraction rings from a powder standard, at known displacements of the detector along the beam path. PMID:24068840

Validating a driving simulator using surrogate safety measures.

PubMed

Yan, Xuedong; Abdel-Aty, Mohamed; Radwan, Essam; Wang, Xuesong; Chilakapati, Praveen

2008-01-01

Traffic crash statistics and previous research have shown an increased risk of traffic crashes at signalized intersections. How to diagnose safety problems and develop effective countermeasures to reduce crash rate at intersections is a key task for traffic engineers and researchers. This study aims at investigating whether the driving simulator can be used as a valid tool to assess traffic safety at signalized intersections. In support of the research objective, this simulator validity study was conducted from two perspectives, a traffic parameter (speed) and a safety parameter (crash history). A signalized intersection with as many important features (including roadway geometries, traffic control devices, intersection surroundings, and buildings) was replicated into a high-fidelity driving simulator. A driving simulator experiment with eight scenarios at the intersection were conducted to determine if the subjects' speed behavior and traffic risk patterns in the driving simulator were similar to what were found at the real intersection. The experiment results showed that speed data observed from the field and in the simulator experiment both follow normal distributions and have equal means for each intersection approach, which validated the driving simulator in absolute terms. Furthermore, this study used an innovative approach of using surrogate safety measures from the simulator to contrast with the crash analysis for the field data. The simulator experiment results indicated that compared to the right-turn lane with the low rear-end crash history record (2 crashes), subjects showed a series of more risky behaviors at the right-turn lane with the high rear-end crash history record (16 crashes), including higher deceleration rate (1.80+/-1.20 m/s(2) versus 0.80+/-0.65 m/s(2)), higher non-stop right-turn rate on red (81.67% versus 57.63%), higher right-turn speed as stop line (18.38+/-8.90 km/h versus 14.68+/-6.04 km/h), shorter following distance (30.19+/-13.43 m versus 35.58+/-13.41 m), and higher rear-end probability (9/59=0.153 versus 2/60=0.033). Therefore, the relative validity of driving simulator was well established for the traffic safety studies at signalized intersections.

A Computer Program for Mapping Satellite-borne Narrow-Beam Antenna Footprints on Earth. Memorandum Number 72/3.

ERIC Educational Resources Information Center

Stagl, Thomas W.; Singh, Jai P.

Written primarily to define the area of the earth covered by a narrow-beam antenna carried on a synchronous satellite in circular, near equatorial orbits, a computer program has been developed that computes the locus of intersection of a quadric cone and a sphere. The program, which outputs a list of the longitude and latitude coordinates of the…

Activity spaces among injection drug users in San Francisco.

PubMed

Martinez, Alexis N; Lorvick, Jennifer; Kral, Alex H

2014-05-01

Representations of activity spaces, defined as the local areas within which people move or travel in the course of their daily activities, are unexplored among injection drug users (IDUs). The purpose of this paper is to use an activity space framework to study place and drug user health. Data for this analysis is from an epidemiological study of street-recruited IDUs in San Francisco (N=1084). Study participants reported geographic intersections of where they most often slept at night, hung out during the day, and used drugs during a 6 month time period. We used GIS software to construct and map activity space routes of street-based network paths between these intersections. We further identified if syringe exchange program (SEP) locations intersected with, participant activity space routes. We used logistic regression to estimate associations between activity space variables and HIV serostatus, syringe sharing, and non-fatal overdose, after adjusting for individual and Census tract covariates. Mean activity space distance for all participants was 1.5miles. 9.6% of participants had a SEP located along their activity space. An increase in activity space distance was associated with a decrease in odds of being HIV positive. An increase in residential transience, or the number of different locations slept in by participants in a 6 month time period, was associated with higher odds of syringe sharing. Activity space distance was not independently associated with overdose or syringe sharing. Research that locates individuals in places of perceived importance is needed to inform placement and accessibility of HIV and overdose prevention programs. More attention needs to be given to the logistics of collecting sensitive geospatial data from vulnerable populations as well as how to maximize the use of GIS software for visualizing and understanding how IDUs interact with their environment. Copyright © 2013. Published by Elsevier B.V.

Orbits of Selected Globular Clusters in the Galactic Bulge

NASA Astrophysics Data System (ADS)

Pérez-Villegas, A.; Rossi, L.; Ortolani, S.; Casotto, S.; Barbuy, B.; Bica, E.

2018-05-01

We present orbit analysis for a sample of eight inner bulge globular clusters, together with one reference halo object. We used proper motion values derived from long time base CCD data. Orbits are integrated in both an axisymmetric model and a model including the Galactic bar potential. The inclusion of the bar proved to be essential for the description of the dynamical behaviour of the clusters. We use the Monte Carlo scheme to construct the initial conditions for each cluster, taking into account the uncertainties in the kinematical data and distances. The sample clusters show typically maximum height to the Galactic plane below 1.5 kpc, and develop rather eccentric orbits. Seven of the bulge sample clusters share the orbital properties of the bar/bulge, having perigalactic and apogalatic distances, and maximum vertical excursion from the Galactic plane inside the bar region. NGC 6540 instead shows a completely different orbital behaviour, having a dynamical signature of the thick disc. Both prograde and prograde-retrograde orbits with respect to the direction of the Galactic rotation were revealed, which might characterise a chaotic behaviour.

On the origin of the unusual orbit of Comet 2P/Encke

NASA Astrophysics Data System (ADS)

Levison, Harold F.; Terrell, Dirk; Wiegert, Paul A.; Dones, Luke; Duncan, Martin J.

2006-05-01

The orbit of Comet 2P/Encke is difficult to understand because it is decoupled from Jupiter—its aphelion distance is only 4.1 AU. We present a series of orbital integrations designed to determine whether the orbit of Comet 2P/Encke can simply be the result of gravitational interactions between Jupiter-family comets and the terrestrial planets. To accomplish this, we integrated the orbits of a large number of objects from the trans-neptunian region, through the realm of the giant planets, and into the inner Solar System. We find that at any one time, our model predicts that there should be roughly 12 objects in Encke-like orbits. However, it takes roughly 200 times longer to evolve onto an orbit like this than the typical cometary physical lifetime. Thus, we suggest that (i) 2P/Encke became dormant soon after it was kicked inward by Jupiter, (ii) it spent a significant amount of time inactive while rattling around the inner Solar System, and (iii) it only became active again as the ν secular resonance drove down its perihelion distance.

Detection of the lunar body tide by the Lunar Orbiter Laser Altimeter

PubMed Central

Mazarico, Erwan; Barker, Michael K; Neumann, Gregory A; Zuber, Maria T; Smith, David E

2014-01-01

The Lunar Orbiter Laser Altimeter instrument onboard the Lunar Reconnaissance Orbiter spacecraft collected more than 5 billion measurements in the nominal 50 km orbit over ∼10,000 orbits. The data precision, geodetic accuracy, and spatial distribution enable two-dimensional crossovers to be used to infer relative radial position corrections between tracks to better than ∼1 m. We use nearly 500,000 altimetric crossovers to separate remaining high-frequency spacecraft trajectory errors from the periodic radial surface tidal deformation. The unusual sampling of the lunar body tide from polar lunar orbit limits the size of the typical differential signal expected at ground track intersections to ∼10 cm. Nevertheless, we reliably detect the topographic tidal signal and estimate the associated Love number h2 to be 0.0371 ± 0.0033, which is consistent with but lower than recent results from lunar laser ranging. Key Points Altimetric data are used to create radial constraints on the tidal deformationThe body tide amplitude is estimated from the crossover dataThe estimated Love number is consistent with previous estimates but more precise PMID:26074646

Circular features with predictable size on Xanadu region of Titan

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

2008-09-01

Planets' satellites in the Solar system (rocky and icy) have in common one fundamental property: all of them move simultaneously in two orbits - around Sun and around their planets (planets have only one orbit in the Solar system). As was shown by the wave planetology [1-6] " orbits make structures'. This means that movements in elliptical keplerian orbits imply periodically changing increasing and decreasing accelerations. Multiplied by celestial body mass this produces inertia-gravity forces (Newton: F=m • a). These forces warp celestial bodies in form of standing waves propagating in rotating bodies in four interfering orthogonal and diagonal directions. This interference gives three kinds of regularly disposed tectonic blocks: uprising (+), subsiding (-), neutral (0)(Fig. 1). Their size depends on warping wavelengths. The fundamental wave1 and its first overtone wave2 (and weaker ones) are responsible for ubiquitous tectonic dichotomy - two hemispheres - segments and sectoring. These superimposed global tectonic features are adorned by tectonic granulations size of which is inversely proportional to orbital frequencies: higher frequency - smaller granule, lower frequency - larger granule. A row of the planets granulations is as follows: Mercury πR/16, Venus πR/6, Earth πR/4, Mars πR/2, asteroids πR/1, Jupiter 3πR, Saturn 7.5πR, Uranus 21πR, Neptune 41πR, Pluto 62πR (a granule size is a half of a wavelength; a scale is Earth with πR/4 granule corresponding to 1/1 year orbital frequency; R-radius). So, orbits make structures. They are simpler for planets, but much more complicated for moons. Their surfaces are saturated with granules related to two main frequencies and at least two modulated side frequencies. Two orbits imply a wave modulation. The lower circum-Sun frequency modulates the higher circum-planet frequency by dividing and multiplying it thus producing two side frequencies with corresponding waves and granules. In case of Titan for the first time the larger modulated granules were reported in pre-Cassini era in the Hubble ST images [5] (Fig. 2, 3). Titan rather extensively studied by imaging systems and radar presents now a good example of the wave modulations. It has two orbiting frequencies: around Sun -1/30 years, around Saturn -1/16 days. The corresponding main granule sizes are 7.5πR and πR/91, or 60641 and 88 km, the former size is too large to be directly observed (its wave probably influences only the whole shape of the satellite) and the latter is visible in the near IR image PIA06154 as chains and grids of hollows (about 70 to 100 km across) at intersections of crosscutting tight lineations covering the whole Titan's surface. This mode of granulation is also clearly presented in PIA03567. The modulated side frequencies give granules 662 and 12 km across (πR/12 and πR/667). Both sizes are discernable on Titan's radar image PIA08454. The first as roundish white and dark areas (these granules were discerned and calculated earlier on the Hubble image of Titan in pre-Cassini era [5]). The second size is produced by an intersection of regular wavings-ripples (erroneously interpreted as dunes) with spacing about 10- 20 km covering mainly smooth dark equatorial parts of the satellite. Thus, three granule sizes (662, 88, 12 km) are detected on Titan's surface by imaging from various distances and using different wave diapasons. The Xanadu water ice mountaneous equatorial area was imaged by radar on May 12, 2008 (Fig. 4, PIA10654). Three prominent ridges trending west-to-east are spaced about 25 km apart. In many places of the image are seen not very clear but discernable roundish spots about 10 to 20 km in diameter. Sometimes they are arranged in a row touching each other as in the area between two upper ridges. The best visible darkest spot at bottom center is about 20 km in diameter and shows polygonal outlines as do some other circular spots. Such structures could be interpreted as a manifestation of a wave woven pattern with granules belonging to the modulated ones - πR/667.

Orbital Transfer Vehicle Oxygen Turbopump Technology. Final Report, Volume 1. Design, Fabrication, and Hydrostatic Bearing Testing

DTIC Science & Technology

1990-12-01

Temperature Distance Sensors -. ...................... 188 Start Transient 4.5-7 Distance Sensor Signal as a Function of Speed...189 4.5-8 Distance Sensor Signal as a Function of Speed ......................................... 190 4.5-9 Cryogenic Operation of...Distance Sensors at 72,000 RPM ........................ 192 Steady State 4.5-10 Cryogenic Operation of Distance Sensor Through Start

Support requirements for remote sensor systems on unmanned planetary missions. Appendix A: Support requirement summary tables, phase 3

NASA Technical Reports Server (NTRS)

1971-01-01

An appendix containing one page summary tables of sensor observation objectives, measurement capabilities, support requirments, and worth values is presented. Tables are arranged according to (1) sensor type number, (2) flyby mission number, (3) for multi-planet missions, in order of increasing distance from the sun, (4) for orbiter mission, by planets in order of increasing distance from the sun, and (5) by orbit number.

Near-Earth Objects. Chapter 27

NASA Technical Reports Server (NTRS)

Harris, Alan W.; Drube, Line; McFadden, Lucy A.; Binzel, Richard P.

2014-01-01

A near-Earth object (NEO) is an asteroid or comet orbiting the Sun with a perihelion distance of less than 1.3 Astronomical Units (AU) (1 AU, an astronomical unit, is the mean distance between the Earth and the Sun, around 150 million kilometers). If the orbit of an NEO can bring it to within 0.05 AU of the Earth's orbit, and it is larger than about 120 meters, it is termed a potentially hazardous object (PHO); an object of this size is likely to survive passage through the atmosphere and cause extensive damage on impact. (The acronyms NEA and PHO are used when referring specifically to asteroids.)

Field results for line intersect distance sampling of coarse woody debris

Treesearch

David L. R. Affleck

2009-01-01

A growing recognition of the importance of downed woody materials in forest ecosystem processes and global carbon budgets has sharpened the need for efficient sampling strategies that target this resource. Often the aggregate volume, biomass, or carbon content of the downed wood is of primary interest, making recently developed probability proportional-to-volume...

78 FR 70321 - Petitions for Modification of Application of Existing Mandatory Safety Standards

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-25

.... (9) Keep the working place free from accumulations of coal dust and coal spillages, and place rock... been intersected and the working place determined safe, continue mining inby the well at a distance... perforating multiple strings. (3) Place a mechanical bridge plug in the well if a cleaned-out well emits...

Fine-scale estimation of carbon monoxide and fine particulate matter concentrations in proximity to a road intersection by using wavelet neural network with genetic algorithm

NASA Astrophysics Data System (ADS)

Wang, Zhanyong; Lu, Feng; He, Hong-di; Lu, Qing-Chang; Wang, Dongsheng; Peng, Zhong-Ren

2015-03-01

At road intersections, vehicles frequently stop with idling engines during the red-light period and speed up rapidly in the green-light period, which generates higher velocity fluctuation and thus higher emission rates. Additionally, the frequent changes of wind direction further add the highly variable dispersion of pollutants at the street scale. It is, therefore, very difficult to estimate the distribution of pollutant concentrations using conventional deterministic causal models. For this reason, a hybrid model combining wavelet neural network and genetic algorithm (GA-WNN) is proposed for predicting 5-min series of carbon monoxide (CO) and fine particulate matter (PM2.5) concentrations in proximity to an intersection. The proposed model is examined based on the measured data under two situations. As the measured pollutant concentrations are found to be dependent on the distance to the intersection, the model is evaluated in three locations respectively, i.e. 110 m, 330 m and 500 m. Due to the different variation of pollutant concentrations on varied time, the model is also evaluated in peak and off-peak traffic time periods separately. Additionally, the proposed model, together with the back-propagation neural network (BPNN), is examined with the measured data in these situations. The proposed model is found to perform better in predictability and precision for both CO and PM2.5 than BPNN does, implying that the hybrid model can be an effective tool to improve the accuracy of estimating pollutants' distribution pattern at intersections. The outputs of these findings demonstrate the potential of the proposed model to be applicable to forecast the distribution pattern of air pollution in real-time in proximity to road intersection.

Using periodic orbits to compute chaotic transport rates between resonance zones.

PubMed

Sattari, Sulimon; Mitchell, Kevin A

2017-11-01

Transport properties of chaotic systems are computable from data extracted from periodic orbits. Given a sufficient number of periodic orbits, the escape rate can be computed using the spectral determinant, a function that incorporates the eigenvalues and periods of periodic orbits. The escape rate computed from periodic orbits converges to the true value as more and more periodic orbits are included. Escape from a given region of phase space can be computed by considering only periodic orbits that lie within the region. An accurate symbolic dynamics along with a corresponding partitioning of phase space is useful for systematically obtaining all periodic orbits up to a given period, to ensure that no important periodic orbits are missing in the computation. Homotopic lobe dynamics (HLD) is an automated technique for computing accurate partitions and symbolic dynamics for maps using the topological forcing of intersections of stable and unstable manifolds of a few periodic anchor orbits. In this study, we apply the HLD technique to compute symbolic dynamics and periodic orbits, which are then used to find escape rates from different regions of phase space for the Hénon map. We focus on computing escape rates in parameter ranges spanning hyperbolic plateaus, which are parameter intervals where the dynamics is hyperbolic and the symbolic dynamics does not change. After the periodic orbits are computed for a single parameter value within a hyperbolic plateau, periodic orbit continuation is used to compute periodic orbits over an interval that spans the hyperbolic plateau. The escape rates computed from a few thousand periodic orbits agree with escape rates computed from Monte Carlo simulations requiring hundreds of billions of orbits.

Bianchi IX dynamics in bouncing cosmologies: homoclinic chaos and the BKL conjecture

NASA Astrophysics Data System (ADS)

Maier, Rodrigo; Damião Soares, Ivano; Valentino Tonini, Eduardo

2015-12-01

We examine the dynamics of a Bianchi IX model with three scale factors on a 4-dim Lorentzian brane embedded in a 5-dim conformally flat empty bulk with a timelike extra dimension. The matter content is a pressureless perfect fluid restricted to the brane, with the embedding consistently satisfying the Gauss-Codazzi equations. The 4-dim Einstein equations on the brane reduce to a 6-dim Hamiltonian dynamical system with additional terms (due to the bulk-brane interaction) that avoid the singularity and implement nonsingular bounces in the model. We examine the complex Bianchi IX dynamics in its approach to the neighborhood of the bounce which replaces the cosmological singularity of general relativity. The phase space of the model presents (i) two critical points (a saddle-center-center and a center-center-center) in a finite region of phase space, (ii) two asymptotic de Sitter critical points at infinity, one acting as an attractor to late-time acceleration and (iii) a 2-dim invariant plane, which together organize the dynamics of the phase space. The saddle-center-center engenders in the phase space the topology of stable and unstable 4-dim cylinders R × S 3, where R is a saddle direction and S 3 is the center manifold of unstable periodic orbits, the latter being the nonlinear extension of the center-center sector. By a proper canonical transformation the degrees of freedom of the dynamics are separated into one degree connected with the expansion/contraction of the scales of the model, and two rotational degrees of freedom associated with the center manifold S 3. The typical dynamical flow is thus an oscillatory mode about the orbits of the invariant plane. The stable and unstable cylinders are spanned by oscillatory orbits about the separatrix towards the bounce, leading to the homoclinic transversal intersection of the cylinders, as shown numerically in two distinct simulations. The homoclinic intersection manifold has the topology of R × S 2 consisting of homoclinic orbits biasymptotic to the center manifold S 3. This behavior defines a chaotic saddle associated with S 3, indicating that the intersection points of the cylinders have the nature of a Cantor set with compact support S 2. This is an invariant signature of chaos in the model. We discuss the connection between these properties of the dynamics, namely the oscillatory approach to the bounce together with its chaotic behavior, and analogous features present in the BKL conjecture in general relativity.

Stringy Gravity: Solving the Dark Problems at `short' distance

NASA Astrophysics Data System (ADS)

Park, Jeong-Hyuck

2018-01-01

Dictated by Symmetry Principle, string theory predicts not General Relativity but its own gravity which assumes the entire closed string massless sector to be geometric and thus gravitational. In terms of R/(MG), i.e. the dimensionless radial variable normalized by mass, Stringy Gravity agrees with General Relativity toward infinity, but modifies it at short distance. At far short distance, gravitational force can be even repulsive. These may solve the dark matter and energy problems, as they arise essentially from small R/(MG) observations: long distance divided by much heavier mass. We address the pertinent differential geometry for Stringy Gravity, stringy Equivalence Principle, stringy geodesics and the minimal coupling to the Standard Model. We highlight the notion of `doubled-yet-gauged' coordinate system, in which a gauge orbit corresponds to a single physical point and proper distance is defined between two gauge orbits by a path integral.

Line-drawing algorithms for parallel machines

NASA Technical Reports Server (NTRS)

Pang, Alex T.

1990-01-01

The fact that conventional line-drawing algorithms, when applied directly on parallel machines, can lead to very inefficient codes is addressed. It is suggested that instead of modifying an existing algorithm for a parallel machine, a more efficient implementation can be produced by going back to the invariants in the definition. Popular line-drawing algorithms are compared with two alternatives; distance to a line (a point is on the line if sufficiently close to it) and intersection with a line (a point on the line if an intersection point). For massively parallel single-instruction-multiple-data (SIMD) machines (with thousands of processors and up), the alternatives provide viable line-drawing algorithms. Because of the pixel-per-processor mapping, their performance is independent of the line length and orientation.

USSR and Eastern Europe Scientific Abstracts, Geophysics, Astronomy and Space, Number 394.

DTIC Science & Technology

1977-04-13

Abstracts of Scientific Articles 10 Temperature and Wind Variations in Upper Atmosphere 10 Prediction of Precipitation for Five Days 10 Short...34 Method in Sea Gravimetry ... 30 Frequency Characteristics of Filter in "Points of Intersection" Method 30 Page Gravitational Anomalies in the...Inclination of Axes of Rotation and Orbits of Planets 47 Effect of Solar Activity on Precipitation Regime 47 Gravitational Orientation Systems with Two

Solar Electric Propulsion (SEP) Tug Power System Considerations

NASA Technical Reports Server (NTRS)

Kerslake, Thomas W.; Bury, Kristen M.; Hojinicki, Jeffrey S.; Sajdak, Adam M.; Scheiddegger, Robert J.

2011-01-01

Solar electric propulsion (SEP) technology is truly at the "intersection of commercial and military space" as well as the intersection of NASA robotic and human space missions. Building on the use of SEP for geosynchronous spacecraft station keeping, there are numerous potential commercial and military mission applications for SEP stages operating in Earth orbit. At NASA, there is a resurgence of interest in robotic SEP missions for Earth orbit raising applications, 1-AU class heliocentric missions to near Earth objects (NEOs) and SEP spacecraft technology demonstrations. Beyond these nearer term robotic missions, potential future human space flight missions to NEOs with high-power SEP stages are being considered. To enhance or enable this broad class of commercial, military and NASA missions, advancements in the power level and performance of SEP technologies are needed. This presentation will focus on design considerations for the solar photovoltaic array (PVA) and electric power system (EPS) vital to the design and operation of an SEP stage. The engineering and programmatic pros and cons of various PVA and EPS technologies and architectures will be discussed in the context of operating voltage and power levels. The impacts of PVA and EPS design options on the remaining SEP stage subsystem designs, as well as spacecraft operations, will also be discussed.

Calculated dipole moment and energy in collision of a hydrogen molecule and a hydrogen atom

NASA Technical Reports Server (NTRS)

Patch, R. W.

1973-01-01

Calculations were carried out using three Slater-type 1s orbitals in the orthogonalized valencebond theory of McWeeny. Each orbital exponent was optimized, the H2 internuclear distance was varied from 7.416 x 10 to the -11th power to 7.673 x 10 to the -11th power m (1.401 to 1.450 bohrs). The intermolecular distance was varied from 1 to 4 bohrs (0.5292 to 2.117 x 10 to the 10th power). Linear, scalene, and isosceles configurations were used. A weighted average of the interaction energies was taken for each intermolecular distance. Although energies are tabulated, the principal purpose was to calculate the electric dipole moment and its derivative with respect to H2 internuclear distance.

The Orbital and Physical Parameters, and the Distance of the Eclipsing Binary System OGLE-LMC-ECL-25658 in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Elgueta, S. S.; Graczyk, D.; Gieren, W.; Pietrzyński, G.; Thompson, I. B.; Konorski, P.; Pilecki, B.; Villanova, S.; Udalski, A.; Soszyński, I.; Suchomska, K.; Karczmarek, P.; Górski, M.; Wielgórski, P.

2016-08-01

We present an analysis of a new detached eclipsing binary, OGLE-LMC-ECL-25658, in the Large Magellanic Cloud (LMC). The system consists of two late G-type giant stars on an eccentric orbit with an orbital period of ˜200 days. The system shows total eclipses and the components have similar temperatures, making it ideal for a precise distance determination. Using multi-color photometric and high resolution spectroscopic data, we have performed an analysis of light and radial velocity curves simultaneously using the Wilson-Devinney code. We derived orbital and physical parameters of the binary with a high precision of \\lt 1%. The masses and surface metallicities of the components are virtually the same and equal to 2.23+/- 0.02 {M}⊙ and [{Fe}/{{H}}]\\=\\-0.63+/- 0.10 dex. However, their radii and rates of rotation show a distinct trace of differential stellar evolution. The distance to the system was calculated using an infrared calibration between V-band surface brightness and (V-K) color, leading to a distance modulus of (m-M)\\=\\18.452+/- 0.023 (statistical) ± 0.046 (systematic). Because OGLE-LMC-ECL-25658 is located relatively far from the LMC barycenter, we applied a geometrical correction for its position in the LMC disk using the van der Marel et al. model of the LMC. The resulting barycenter distance to the galaxy is {d}{{LMC}}\\=\\50.30+/- 0.53 (stat.) kpc, and is in perfect agreement with the earlier result of Pietrzyński et al.

Invariant polygons in systems with grazing-sliding.

PubMed

Szalai, R; Osinga, H M

2008-06-01

The paper investigates generic three-dimensional nonsmooth systems with a periodic orbit near grazing-sliding. We assume that the periodic orbit is unstable with complex multipliers so that two dominant frequencies are present in the system. Because grazing-sliding induces a dimension loss and the instability drives every trajectory into sliding, the system has an attractor that consists of forward sliding orbits. We analyze this attractor in a suitably chosen Poincare section using a three-parameter generalized map that can be viewed as a normal form. We show that in this normal form the attractor must be contained in a finite number of lines that intersect in the vertices of a polygon. However the attractor is typically larger than the associated polygon. We classify the number of lines involved in forming the attractor as a function of the parameters. Furthermore, for fixed values of parameters we investigate the one-dimensional dynamics on the attractor.

Fractures on Europa - Possible response of an ice crust to tidal deformation

NASA Technical Reports Server (NTRS)

Helfenstein, P.; Parmentier, E. M.

1980-01-01

The surface of Europa contains a planetwide system of low albedo lineaments which have been interpreted as fractures in an icy crust. The pattern of fractures on the surface consists of radial and concentric fractures having the general appearance of tension cracks within a region near the antipode of the sub-Jupiter point. Outside this region, linear fractures intersect at angles near 60 deg, suggesting that they are conjugate shear fractures. The orientation of this pattern on the surface suggests that a principal axis of the deformation that produced the fractures was approximately radial to Jupiter. Fracturing may thus be consistent with an origin due to cyclical tidal deformation resulting from orbital eccentricity. Orbital eccentricity related to a relatively recent establishment of orbital resonance among the Galilean satellites may explain the presence of fractures in a relatively young, lightly cratered planetary surface.

Gate-tunable current partition in graphene-based topological zero lines

NASA Astrophysics Data System (ADS)

Wang, Ke; Ren, Yafei; Deng, Xinzhou; Yang, Shengyuan A.; Jung, Jeil; Qiao, Zhenhua

2017-06-01

We demonstrate new mechanisms for gate-tunable current partition at topological zero-line intersections in a graphene-based current splitter. Based on numerical calculations of the nonequilibrium Green's functions and Landauer-Büttiker formula, we show that the presence of a perpendicular magnetic field on the order of a few Teslas allows for carrier sign dependent current routing. In the zero-field limit the control on current routing and partition can be achieved within a range of 10-90 % of the total incoming current by tuning the carrier density at tilted intersections or by modifying the relative magnitude of the bulk band gaps via gate voltage. We discuss the implications of our findings in the design of topological zero-line networks where finite orbital magnetic moments are expected when the current partition is asymmetric.

Assessing the physical nature of near-Earth asteroids through their dynamical histories

NASA Astrophysics Data System (ADS)

Fernández, Julio A.; Sosa, Andrea; Gallardo, Tabaré; Gutiérrez, Jorge N.

2014-08-01

We analyze a sample of 139 near-Earth asteroids (NEAs), defined as those that reach perihelion distances q<1.3 au, and that also fulfill the conditions of approaching or crossing Jupiter’s orbit (aphelion distances Q>4.8 au), having Tisserand parameters 24.8 au of cometary origin, but it could be even lower if the NEAs in unstable orbits listed before turn out to be bona fide asteroids from the main belt. This study strengthens the idea that NEAs and comets essentially are two distinct populations, and that periods of dormancy in comets must be rare. Most likely, active comets in near-Earth orbits go through a continuous erosion process in successive perihelion passages until disintegration into meteoritic dust and fragments of different sizes. In this scenario, 289P/Blanpain might be a near-devolatized fragment from a by now disintegrated parent comet.

Initial results of centralized autonomous orbit determination of the new-generation BDS satellites with inter-satellite link measurements

NASA Astrophysics Data System (ADS)

Tang, Chengpan; Hu, Xiaogong; Zhou, Shanshi; Liu, Li; Pan, Junyang; Chen, Liucheng; Guo, Rui; Zhu, Lingfeng; Hu, Guangming; Li, Xiaojie; He, Feng; Chang, Zhiqiao

2018-01-01

Autonomous orbit determination is the ability of navigation satellites to estimate the orbit parameters on-board using inter-satellite link (ISL) measurements. This study mainly focuses on data processing of the ISL measurements as a new measurement type and its application on the centralized autonomous orbit determination of the new-generation Beidou navigation satellite system satellites for the first time. The ISL measurements are dual one-way measurements that follow a time division multiple access (TDMA) structure. The ranging error of the ISL measurements is less than 0.25 ns. This paper proposes a derivation approach to the satellite clock offsets and the geometric distances from TDMA dual one-way measurements without a loss of accuracy. The derived clock offsets are used for time synchronization, and the derived geometry distances are used for autonomous orbit determination. The clock offsets from the ISL measurements are consistent with the L-band two-way satellite, and time-frequency transfer clock measurements and the detrended residuals vary within 0.5 ns. The centralized autonomous orbit determination is conducted in a batch mode on a ground-capable server for the feasibility study. Constant hardware delays are present in the geometric distances and become the largest source of error in the autonomous orbit determination. Therefore, the hardware delays are estimated simultaneously with the satellite orbits. To avoid uncertainties in the constellation orientation, a ground anchor station that "observes" the satellites with on-board ISL payloads is introduced into the orbit determination. The root-mean-square values of orbit determination residuals are within 10.0 cm, and the standard deviation of the estimated ISL hardware delays is within 0.2 ns. The accuracy of the autonomous orbits is evaluated by analysis of overlap comparison and the satellite laser ranging (SLR) residuals and is compared with the accuracy of the L-band orbits. The results indicate that the radial overlap differences between the autonomous orbits are less than 15.0 cm for the inclined geosynchronous orbit (IGSO) satellites and less than 10.0 cm for the MEO satellites. The SLR residuals are approximately 15.0 cm for the IGSO satellites and approximately 10.0 cm for the MEO satellites, representing an improvement over the L-band orbits.

On Stellar Winds as a Source of Mass: Applying Bondi-Hoyle-Lyttleton Accretion

NASA Astrophysics Data System (ADS)

Detweiler, L. G.; Yates, K.; Siem, E.

2017-12-01

The interaction between planets orbiting stars and the stellar wind that stars emit is investigated and explored. The main goal of this research is to devise a method of calculating the amount of mass accumulated by an arbitrary planet from the stellar wind of its parent star via accretion processes. To achieve this goal, the Bondi-Hoyle-Lyttleton (BHL) mass accretion rate equation and model is employed. In order to use the BHL equation, various parameters of the stellar wind is required to be known, including the velocity, density, and speed of sound of the wind. In order to create a method that is applicable to arbitrary planets orbiting arbitrary stars, Eugene Parker's isothermal stellar wind model is used to calculate these stellar wind parameters. In an isothermal wind, the speed of sound is simple to compute, however the velocity and density equations are transcendental and so the solutions must be approximated using a numerical approximation method. By combining Eugene Parker's isothermal stellar wind model with the BHL accretion equation, a method for computing planetary accretion rates inside a star's stellar wind is realized. This method is then applied to a variety of scenarios. First, this method is used to calculate the amount of mass that our solar system's planets will accrete from the solar wind throughout our Sun's lifetime. Then, some theoretical situations are considered. We consider the amount of mass various brown dwarfs would accrete from the solar wind of our Sun throughout its lifetime if they were orbiting the Sun at Jupiter's distance. For very high mass brown dwarfs, a significant amount of mass is accreted. In the case of the brown dwarf 15 Sagittae B, it actually accretes enough mass to surpass the mass limit for hydrogen fusion. Since 15 Sagittae B is orbiting a star that is very similar to our Sun, this encouraged making calculations for 15 Sagittae B orbiting our Sun at its true distance from its star, 15 Sagittae. It was found that at this distance, it does not accrete enough mass to surpass the mass limit for hydrogen fusion. Finally, we apply this method to brown dwarfs orbiting a 15 solar mass star at Jupiter's distance. It is found that a significantly smaller amount of mass is accreted when compared to the same brown dwarfs orbiting our Sun at the same distance.

Traffic Management for Emergency Vehicle Priority Based on Visual Sensing

PubMed Central

Nellore, Kapileswar; Hancke, Gerhard P.

2016-01-01

Vehicular traffic is endlessly increasing everywhere in the world and can cause terrible traffic congestion at intersections. Most of the traffic lights today feature a fixed green light sequence, therefore the green light sequence is determined without taking the presence of the emergency vehicles into account. Therefore, emergency vehicles such as ambulances, police cars, fire engines, etc. stuck in a traffic jam and delayed in reaching their destination can lead to loss of property and valuable lives. This paper presents an approach to schedule emergency vehicles in traffic. The approach combines the measurement of the distance between the emergency vehicle and an intersection using visual sensing methods, vehicle counting and time sensitive alert transmission within the sensor network. The distance between the emergency vehicle and the intersection is calculated for comparison using Euclidean distance, Manhattan distance and Canberra distance techniques. The experimental results have shown that the Euclidean distance outperforms other distance measurement techniques. Along with visual sensing techniques to collect emergency vehicle information, it is very important to have a Medium Access Control (MAC) protocol to deliver the emergency vehicle information to the Traffic Management Center (TMC) with less delay. Then only the emergency vehicle is quickly served and can reach the destination in time. In this paper, we have also investigated the MAC layer in WSNs to prioritize the emergency vehicle data and to reduce the transmission delay for emergency messages. We have modified the medium access procedure used in standard IEEE 802.11p with PE-MAC protocol, which is a new back off selection and contention window adjustment scheme to achieve low broadcast delay for emergency messages. A VANET model for the UTMS is developed and simulated in NS-2. The performance of the standard IEEE 802.11p and the proposed PE-MAC is analysed in detail. The NS-2 simulation results have shown that the PE-MAC outperforms the IEEE 802.11p in terms of average end-to-end delay, throughput and energy consumption. The performance evaluation results have proven that the proposed PE-MAC prioritizes the emergency vehicle data and delivers the emergency messages to the TMC with less delay compared to the IEEE 802.11p. The transmission delay of the proposed PE-MAC is also compared with the standard IEEE 802.15.4, and Enhanced Back-off Selection scheme for IEEE 802.15.4 protocol [EBSS, an existing protocol to ensure fast transmission of the detected events on the road towards the TMC] and the comparative results have proven the effectiveness of the PE-MAC over them. Furthermore, this research work will provide an insight into the design of an intelligent urban traffic management system for the effective management of emergency vehicles and will help to save lives and property. PMID:27834924

Safe Laser Beam Propagation for Interplanetary Links

NASA Technical Reports Server (NTRS)

Wilson, Keith E.

2011-01-01

Ground-to-space laser uplinks to Earth–orbiting satellites and deep space probes serve both as a beacon and an uplink command channel for deep space probes and Earth-orbiting satellites. An acquisition and tracking point design to support a high bandwidth downlink from a 20-cm optical terminal on an orbiting Mars spacecraft typically calls for 2.5 kW of 1030-nm uplink optical power in 40 micro-radians divergent beams.2 The NOHD (nominal ocular hazard distance) of the 1030nm uplink is in excess of 2E5 km, approximately half the distance to the moon. Recognizing the possible threat of high power laser uplinks to the flying public and to sensitive Earth-orbiting satellites, JPL developed a three-tiered system at its Optical Communications Telescope Laboratory (OCTL) to ensure safe laser beam propagation through navigational and near-Earth space.

Spiderweb-like Fractures in Occator Crater

NASA Image and Video Library

2018-01-30

This image shows a complex set of fractures found in the southwestern region of the floor of Occator Crater on Ceres. In this picture, north is at the top. The two intersecting fracture systems (roughly northwest-southeast and southwest-northeast) are part of a larger fault network that extends across Occator's floor. These fractures have been interpreted as evidence that material came up from below and formed a dome shape, as if a piston was pushing Occator's floor from beneath the surface. This may be due to the upwelling of material coming from Ceres' deep interior. An alternative hypothesis is that the deformation is due to volume changes inside a reservoir of icy magma in the shallow subsurface that is in the process of freezing, similar to the change in volume that a bottle of water experiences when put in a freezer. Another set of fractures can be seen parallel to the southwestern wall and is not connected to the Occator fracture network. Dawn took this image during its extended mission on August 17, 2016, from its low-altitude mapping orbit, at a distance of about 240 miles (385 kilometers) above the surface. The image resolution is 120 feet (35 meters) per pixel. The center coordinates are 16 degrees north in latitude and 237 east in longitude. https://photojournal.jpl.nasa.gov/catalog/PIA22091

Method and apparatus for relative navigation using reflected GPS signals

NASA Technical Reports Server (NTRS)

Cohen, Ian R. (Inventor); Boegner, Jr., Gregory J. (Inventor)

2010-01-01

A method and system to passively navigate an orbiting moving body towards an orbiting target using reflected GPS signals. A pair of antennas is employed to receive both direct signals from a plurality of GPS satellites and a second antenna to receive GPS signals reflected off an orbiting target. The direct and reflected signals are processed and compared to determine the relative distance and position of the orbiting moving body relative to the orbiting target.

The orbit of Phi Cygni measured with long-baseline optical interferometry - Component masses and absolute magnitudes

NASA Technical Reports Server (NTRS)

Armstrong, J. T.; Hummel, C. A.; Quirrenbach, A.; Buscher, D. F.; Mozurkewich, D.; Vivekanand, M.; Simon, R. S.; Denison, C. S.; Johnston, K. J.; Pan, X.-P.

1992-01-01

The orbit of the double-lined spectroscopic binary Phi Cygni, the distance to the system, and the masses and absolute magnitudes of its components are presented via measurements with the Mar III Optical Interferometer. On the basis of a reexamination of the spectroscopic data of Rach & Herbig (1961), the values and uncertainties are adopted for the period and the projected semimajor axes from the present fit to the spectroscopic data and the values of the remaining elements from the present fit to the Mark III data. The elements of the true orbit are derived, and the masses and absolute magnitudes of the components, and the distance to the system are calculated.

The early history of the lunar inclination. [effect of tidal friction

NASA Technical Reports Server (NTRS)

Rubincam, D. P.

1973-01-01

The effect of tidal friction on the inclination of the lunar orbit to the earth's equator for earth-moon distances of less than 10 earth radii is examined. The results obtained bear on a conclusion drawn by Gerstenkorn and others which has been raised as a fatal objection to the fission hypothesis of lunar origin, namely, that the present nonzero inclination of the moon's orbit to the ecliptic implies a steep inclination of the moon's orbit to the earth's equatorial plane in the early history of the earth-moon system. This conclusion is shown to be valid only for particular rheological models of the earth. The earth is assumed to behave like a highly viscous fluid in response to tides raised in it by the moon. The moon is assumed to be tideless and in a circular orbit about the earth. The equations of tidal friction are integrated numerically to give inclination of the lunar orbit as a function of earth-moon distance.

Our Solar System's Cousin?

NASA Technical Reports Server (NTRS)

2007-01-01

This artist's concept illustrates two planetary systems -- 55 Cancri (top) and our own. Blue lines show the orbits of planets, including the dwarf planet Pluto in our solar system. The 55 Cancri system is currently the closest known analogue to our solar system, yet there are some fundamental differences.

The similarities begin with the stars themselves, which are about the same mass and age. Both stars also host big families of planets. Our solar system has eight planets, while 55 Cancri has five, making it the record-holder for having the most known exoplanets. In fact, 55 Cancri could have additional planets, possibly even rocky ones that are too small to be seen with current technologies. All of the planets in the two systems have nearly circular orbits.

In addition, both planetary systems have giant planets in their outer regions. The giant located far away from 55 Cancri is four times the mass of our Jupiter, and completes one orbit every 14 years at a distance of five times that between Earth and the sun (about 868 million kilometers or 539 million miles). Our Jupiter completes one orbit around the sun every 11.9 years, also at about five times the Earth-sun distance (778 million kilometers or 483 million miles). Fifty-five Cancri is still the only known star besides ours with a planet in a distant Jupiter-like orbit. Both systems also contain inner planets that are less massive than their outer planets.

The differences begin with the planets' masses. The planets orbiting 55 Cancri are all larger than Earth, and represent a 'souped-up' version of our own solar system. In fact, this is the first star that boasts more giant planets than our sun!

The arrangement of the planetary systems is also different. The inner four planets of 55 Cancri are all closer to the star than Earth is to the sun. The closest, about the mass of Uranus, whips around the star in just under three days at a distance of approximately 5.6 million kilometers (3.5 million miles). The second planet out from the star is a little smaller than Jupiter and completes one orbit every 14.7 days at a distance of approximately 17.9 million kilometers (11.2 million miles). The third planet out from the star is similar in mass to Saturn and completes one orbit every 44 days at a distance of approximately 35.9 million kilometers (22.3 million miles). The fourth planet is about half the mass of Saturn, orbits every 260 days and is approximately 116.7 million kilometers (72.5 million miles) away from the star.

Efficient Proximity Computation Techniques Using ZIP Code Data for Smart Cities †

PubMed Central

Murdani, Muhammad Harist; Hong, Bonghee

2018-01-01

In this paper, we are interested in computing ZIP code proximity from two perspectives, proximity between two ZIP codes (Ad-Hoc) and neighborhood proximity (Top-K). Such a computation can be used for ZIP code-based target marketing as one of the smart city applications. A naïve approach to this computation is the usage of the distance between ZIP codes. We redefine a distance metric combining the centroid distance with the intersecting road network between ZIP codes by using a weighted sum method. Furthermore, we prove that the results of our combined approach conform to the characteristics of distance measurement. We have proposed a general and heuristic approach for computing Ad-Hoc proximity, while for computing Top-K proximity, we have proposed a general approach only. Our experimental results indicate that our approaches are verifiable and effective in reducing the execution time and search space. PMID:29587366

Efficient Proximity Computation Techniques Using ZIP Code Data for Smart Cities †.

PubMed

Murdani, Muhammad Harist; Kwon, Joonho; Choi, Yoon-Ho; Hong, Bonghee

2018-03-24

In this paper, we are interested in computing ZIP code proximity from two perspectives, proximity between two ZIP codes ( Ad-Hoc ) and neighborhood proximity ( Top-K ). Such a computation can be used for ZIP code-based target marketing as one of the smart city applications. A naïve approach to this computation is the usage of the distance between ZIP codes. We redefine a distance metric combining the centroid distance with the intersecting road network between ZIP codes by using a weighted sum method. Furthermore, we prove that the results of our combined approach conform to the characteristics of distance measurement. We have proposed a general and heuristic approach for computing Ad-Hoc proximity, while for computing Top-K proximity, we have proposed a general approach only. Our experimental results indicate that our approaches are verifiable and effective in reducing the execution time and search space.

Calculating lunar retreat rates using tidal rhythmites

USGS Publications Warehouse

Kvale, E.P.; Johnson, H.W.; Sonett, C.P.; Archer, A.W.; Zawistoski, A.N.N.

1999-01-01

Tidal rhythmites are small-scale sedimenta??r}- structures that can preserve a hierarchy of astronomically induced tidal periods. They can also preserve a record of periodic nontidal sedimentation. If properly interpreted and understood, tidal rhjthmites can be an important component of paleoastronomy and can be used to extract information on ancient lunar orbital dynamics including changes in Earth-Moon distance through geologic time. Herein we present techniques that can be used to calculate ancient Earth-Moon distances. Each of these techniques, when used on a modern high-tide data set, results in calculated estimates of lunar orbital periods and an EarthMoon distance that fall well within 1 percent of the actual values. Comparisons to results from modern tidal data indicate that ancient tidal rhythmite data as short as 4 months can provide suitable estimates of lunar orbital periods if these tidal records are complete. An understanding of basic tidal theory allows for the evaluation of completeness of the ancient tidal record as derived from an analysis of tidal rhythmites. Utilizing the techniques presented herein, it appears from the rock record that lunar orbital retreat slowed sometime during the midPaleozoic. Copyright ??1999, SEPM (Society for Sedimentary Geology).

30 CFR 219.414 - How will MMS determine each Gulf producing State's share of the qualified OCS revenues?

Code of Federal Regulations, 2011 CFR

2011-07-01

... determine each Gulf producing State's share of the qualified OCS revenues? (a) The MMS will determine the... be disbursed to each Gulf producing State using the following procedure: (1) For each Gulf producing... intersected. (2) For each Gulf producing State, we will divide the sum of each State's inverse distances, from...

Biangular Coordinates Redux: Discovering a New Kind of Geometry

ERIC Educational Resources Information Center

Winkel, Brian; Naylor, Michael

2010-01-01

Biangular coordinates specify a point on the plane by two angles giving the intersection of two rays emanating from two fixed poles. This is a dual of Cartesian coordinates wherein a point on the plane is described by two distances. Biangular coordinates, first written about in 1803 in France, were subsequently studied in Britain at the end of the…

Reducing Conflicts between Motor Vehicles and Pedestrians: The Separate and Combined Effects of Pavement Markings and a Sign Prompt

ERIC Educational Resources Information Center

Huybers, Sherry; Van Houten, Ron; Malenfant, J.E. Louis

2004-01-01

The effects of a symbolic "yield here to pedestrians" sign and advance yield pavement markings on pedestrian/motor vehicle conflicts, motorists' yielding behavior, and the distance motorists' yield in advance of crosswalks were evaluated at multilane crosswalks at uncontrolled T intersections. In Experiment 1, the sign, when used alone, reduced…

Fair sharing of resources in a supply network with constraints.

PubMed

Carvalho, Rui; Buzna, Lubos; Just, Wolfram; Helbing, Dirk; Arrowsmith, David K

2012-04-01

This paper investigates the effect of network topology on the fair allocation of network resources among a set of agents, an all-important issue for the efficiency of transportation networks all around us. We analyze a generic mechanism that distributes network capacity fairly among existing flow demands. The problem can be solved by semianalytical methods on a nearest-neighbor graph with one source and sink pair, when transport occurs over shortest paths. For this setup, we uncover a broad range of patterns of intersecting shortest paths as a function of the distance between the source and the sink. When the number of intersections is the maximum and the distance between the source and the sink is large, we find that a fair allocation implies a decrease of at least 50% from the maximum throughput. We also find that the histogram of the flow allocations assigned to the agents decays as a power law with exponent -1. Our semianalytical framework suggests possible explanations for the well-known reduction of the throughput in fair allocations. It also suggests that the combination of network topology and routing rules can lead to highly uneven (but fair) distributions of resources, a remark of caution to network designers.

Fair sharing of resources in a supply network with constraints

NASA Astrophysics Data System (ADS)

Carvalho, Rui; Buzna, Lubos; Just, Wolfram; Helbing, Dirk; Arrowsmith, David K.

2012-04-01

This paper investigates the effect of network topology on the fair allocation of network resources among a set of agents, an all-important issue for the efficiency of transportation networks all around us. We analyze a generic mechanism that distributes network capacity fairly among existing flow demands. The problem can be solved by semianalytical methods on a nearest-neighbor graph with one source and sink pair, when transport occurs over shortest paths. For this setup, we uncover a broad range of patterns of intersecting shortest paths as a function of the distance between the source and the sink. When the number of intersections is the maximum and the distance between the source and the sink is large, we find that a fair allocation implies a decrease of at least 50% from the maximum throughput. We also find that the histogram of the flow allocations assigned to the agents decays as a power law with exponent -1. Our semianalytical framework suggests possible explanations for the well-known reduction of the throughput in fair allocations. It also suggests that the combination of network topology and routing rules can lead to highly uneven (but fair) distributions of resources, a remark of caution to network designers.

Macro-level safety analysis of pedestrian crashes in Shanghai, China.

PubMed

Wang, Xuesong; Yang, Junguang; Lee, Chris; Ji, Zhuoran; You, Shikai

2016-11-01

Pedestrian safety has become one of the most important issues in the field of traffic safety. This study aims at investigating the association between pedestrian crash frequency and various predictor variables including roadway, socio-economic, and land-use features. The relationships were modeled using the data from 263 Traffic Analysis Zones (TAZs) within the urban area of Shanghai - the largest city in China. Since spatial correlation exists among the zonal-level data, Bayesian Conditional Autoregressive (CAR) models with seven different spatial weight features (i.e. (a) 0-1 first order, adjacency-based, (b) common boundary-length-based, (c) geometric centroid-distance-based, (d) crash-weighted centroid-distance-based, (e) land use type, adjacency-based, (f) land use intensity, adjacency-based, and (g) geometric centroid-distance-order) were developed to characterize the spatial correlations among TAZs. Model results indicated that the geometric centroid-distance-order spatial weight feature, which was introduced in macro-level safety analysis for the first time, outperformed all the other spatial weight features. Population was used as the surrogate for pedestrian exposure, and had a positive effect on pedestrian crashes. Other significant factors included length of major arterials, length of minor arterials, road density, average intersection spacing, percentage of 3-legged intersections, and area of TAZ. Pedestrian crashes were higher in TAZs with medium land use intensity than in TAZs with low and high land use intensity. Thus, higher priority should be given to TAZs with medium land use intensity to improve pedestrian safety. Overall, these findings can help transportation planners and managers understand the characteristics of pedestrian crashes and improve pedestrian safety. Copyright © 2016 Elsevier Ltd. All rights reserved.

Intersecting branes, Higgs sector, and chirality from N = 4 SYM with soft SUSY breaking

NASA Astrophysics Data System (ADS)

Sperling, Marcus; Steinacker, Harold C.

2018-04-01

We consider SU( N ) N = 4 super Yang-Mills with cubic and quadratic soft SUSY breaking potential, such that the global SU(4) R is broken to SU(3) or further. As shown recently, this set-up supports a rich set of non-trivial vacua with the geometry of self-intersecting SU(3) branes in 6 extra dimensions. The zero modes on these branes can be interpreted as 3 generations of bosonic and chiral fermionic strings connecting the branes at their intersections. Here, we uncover a large class of exact solutions consisting of branes connected by Higgs condensates, leading to Yukawa couplings between the chiral fermionic zero modes. Under certain decoupling conditions, the backreaction of the Higgs on the branes vanishes exactly. The resulting physics is that of a spontaneously broken chiral gauge theory on branes with fluxes. In particular, we identify combined brane plus Higgs configurations which lead to gauge fields that couple to chiral fermions at low energy. This turns out to be quite close to the Standard Model and its constructions via branes in string theory. As a by-product, we construct a G 2-brane solution corresponding to a squashed fuzzy coadjoint orbit of G 2.

Ion cyclotron range of frequencies heating of plasma with small impurity production

DOEpatents

Ohkawa, Tihiro

1987-01-01

Plasma including plasma ions is magnetically confined by a magnetic field. The plasma has a defined outer surface and is intersected by resonance surfaces of respective common ion cyclotron frequency of a predetermined species of plasma ions moving in the magnetic field. A radio frequency source provides radio frequency power at a radio frequency corresponding to the ion cyclotron frequency of the predetermined species of plasma ions moving in the field at a respective said resonance surface. RF launchers coupled to the radio frequency source radiate radio frequency energy at the resonance frequency onto the respective resonance surface within the plasma from a plurality of locations located outside the plasma at such respective distances from the intersections of the respective resonance surface and the defined outer surface and at such relative phases that the resulting interference pattern provides substantially null net radio frequency energy over regions near and including substantial portions of the intersections relative to the radio frequency energy provided thereby at other portions of the respective resonance surface within the plasma.

Ocular adnexal asymmetry in models: a magazine photograph analysis.

PubMed

Ing, Edsel; Safarpour, Azien; Ing, Tom; Ing, Sabrina

2006-04-01

Symmetry of facial features often correlates with a perception of physical attractiveness, and ophthalmologists are sometimes consulted by patients for eyelid, eyebrow, or orbital asymmetry. Our objective was to determine the prevalence of ocular adnexal asymmetry among people generally regarded as attractive. The mean width of the horizontal palpebral fissure (MHPF) for both men and women was determined in 40 adult volunteers. Then unobscured, head-on photographs of models looking in the primary position were digitally scanned from popular magazines. Eyelid height, eyelid folds, eyebrow height, medial canthus to midline distance, pupil to midline distance, and orbital dystopia measurements were made. After the measurements from the models were scaled to size by factoring with the MHPF obtained from the volunteers, the results were analyzed by paired samples t test for right-left asymmetry of the ocular adnexal measurements. We also examined for antimongoloid slant in the models. The MHPF of the volunteers was 27+/-1.3 mm for women and 29.6+/-2.0 mm for men. Of 102 magazine photographs analyzed, 55 were women and 47 men. As a group, the models showed a statistically significant asymmetry (p<0.05) in the horizontal fissure width, upper central lid fold, upper temporal lid fold, central eyebrow height, temporal eyebrow height, medial canthal to midline distance, pupil to midline distance, and orbital dystopia. The female models had more eyebrow asymmetry. The male models had more asymmetry at the horizontal fissure and with orbital dystopia. Two male models also had a unilateral antimongoloid slant. Small to moderate amounts of eyelid, eyebrow, and orbital asymmetry were observed in faces generally perceived as attractive. This fact should be considered during preoperative discussions with patients considering oculoplastic surgery.

Disposal strategy for the geosynchronous orbits of the Beidou Navigation Satellite System

NASA Astrophysics Data System (ADS)

Tang, Jingshi; Liu, Lin

Beidou Navigation Satellite System (BDS) is China's navigation satelite system. It is now operational for navigation service in China and Asia-Pacific region and is due to be fully operational as a global navigation system by 2020. Unlike other navigation satellite systems, BDS consists of both 12-hour medium Earth orbit and 24-hour geosynchronous orbit. To sustain a safe environment for the navigation satellites, the end-of-life satellites must be disposed appropriately so they do not pose potential dangers to the operational satellites. There are currently two strategies for the disposal orbit. One is to put the disposed satellite in a graveyard orbit that has a safe distance from the operational satellites. It is often applied in geosynchronous orbits and such graveyard orbit can always maintain a safe distance even for a few centuries. This strategy is also currently adopted by GPS, yet recent researches show a re-entry orbit can sometimes be a better alternative. The interaction of Earth oblateness and lunisolar gravitation can lead to a rapid increase in the orbit eccentricity such that by proper design the disposed GPS satellite can be cleared out by re-entry into the atmosphere. In this work we focus on the disposal strategy for BDS geosynchronous orbit, which consists of the equatorial stationary orbit (GEO) and the inclined orbit (IGSO). We show that these two orbits are essentially in two different dynamical environments and evolve quite distinctly over a long period of time. Taking advantage of the dynamic nature, we apply the graveyard orbit and the re-entry orbit to GEO and IGSO respectively and propose appropriate disposal strategies accordingly.

Updating the orbital ephemeris of the dipping source XB 1254-690 and the distance to the source

NASA Astrophysics Data System (ADS)

Gambino, Angelo F.; Iaria, Rosario; Di Salvo, Tiziana; Matranga, Marco; Burderi, Luciano; Pintore, Fabio; Riggio, Alessandro; Sanna, Andrea

2017-09-01

XB 1254-690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining a more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply, for the first time, an orbital timing technique to XB 1254-690, using the arrival times of the dips present in the light curves that have been collected during 26 yr of X-ray pointed observations acquired from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254-690, improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M 2 = 0.42 ± 0.04 M ʘ for the donor star, in agreement with estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 M ʘ. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6 ± 0.8 kpc. Finally, we discuss the evolution of the system, suggesting that it is compatible with a conservative mass transfer driven by magnetic braking.

A study of pedestrian compliance with traffic signals for exclusive and concurrent phasing.

PubMed

Ivan, John N; McKernan, Kevin; Zhang, Yaohua; Ravishanker, Nalini; Mamun, Sha A

2017-01-01

This paper describes a comparison of pedestrian compliance at traffic signals with two types of pedestrian phasing: concurrent, where both pedestrians and vehicular traffic are directed to move in the same directions at the same time, and exclusive, where pedestrians are directed to move during their own dedicated phase while all vehicular traffic is stopped. Exclusive phasing is usually perceived to be safer, especially by senior and disabled advocacy groups, although these safety benefits depend upon pedestrians waiting for the walk signal. This paper investigates whether or not there are differences between pedestrian compliance at signals with exclusive pedestrian phasing and those with concurrent phasing and whether these differences continue to exist when compliance at exclusive phasing signals is evaluated as if they had concurrent phasing. Pedestrian behavior was observed at 42 signalized intersections in central Connecticut with both concurrent and exclusive pedestrian phasing. Binary regression models were estimated to predict pedestrian compliance as a function of the pedestrian phasing type and other intersection characteristics, such as vehicular and pedestrian volume, crossing distance and speed limit. We found that pedestrian compliance is significantly higher at intersections with concurrent pedestrian phasing than at those with exclusive pedestrian phasing, but this difference is not significant when compliance at exclusive phase intersections is evaluated as if it had concurrent phasing. This suggests that pedestrians treat exclusive phase intersections as though they have concurrent phasing, rendering the safety benefits of exclusive pedestrian phasing elusive. No differences were observed for senior or non-senior pedestrians. Published by Elsevier Ltd.

An Earth-mass planet orbiting α Centauri B.

PubMed

Dumusque, Xavier; Pepe, Francesco; Lovis, Christophe; Ségransan, Damien; Sahlmann, Johannes; Benz, Willy; Bouchy, François; Mayor, Michel; Queloz, Didier; Santos, Nuno; Udry, Stéphane

2012-11-08

Exoplanets down to the size of Earth have been found, but not in the habitable zone--that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water-carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth-Sun distance).

Temporal orientation.

PubMed

Maglio, Sam J; Trope, Yaacov

2018-05-18

Time in the mind orients people in one of two directions. An inward orientation points to the present, contracting the scope of thought to immediate concerns. An outward orientation, in contrast, points away from the present to the past or the future, expanding the scope of thought to a wider consideration set. These oriented arrows need not solely be used for mental time travel, as a similar inward/outward orientation can apply to social distance, spatial distance, and probability. We review recent findings illuminated by this broad form distancing, as illustrated in how people learn from and compare themselves to others, before concluding with a discussion of how change necessarily transpires over time, providing opportunities for future research at the intersection of future thought and present behavior. Copyright © 2018 Elsevier Ltd. All rights reserved.

High Capacity Communications From Martian Distances. Part 1; Spacecraft Link Design Analysis

NASA Technical Reports Server (NTRS)

Vyas, Hemali N.; Schuchman, Leonard; Orr, Richard; Williams, Wallace Dan; Collins, Michael; Noreen, Gary

2006-01-01

High capacity space communications has been a desire for Human Exploration and Science missions. Current Mars missions operate at data rates of 120 kbps for telemetry downlink and it is desirable to study high rate communication links in the range of 100 Mbps to 1 Gbps data rates from Martian distances. This paper will present some assumed scenarios along with link design assumptions and link analysis for high capacity communications from Mars. The paper will focus on RF subsystems namely antenna and power for the downlink communication from a relay orbiter at Mars. The relay orbiter will communicate with the low orbit spacecrafts at Mars or any Martian surface elements such as robots, and relay the data back to the ground networks on Earth. The study will dive into the spacecraft downlink system design and communication link analysis between the relay orbiter and ground network on Earth for data rates ranging from 100 Mbps to 1 Gbps based on the assumed scenarios and link assumptions. With high rate links at larger distances, there will be a significant impact on the antenna and power requirements and the link design will make an attempt to minimize the mass of the RF subsystem on the spacecraft. The results of this study will be presented for three data rates 1 Gbps, 500 Mbps and 100 Mbps at maximum Mars to Earth distance of 2.67AU. The design will use a Ka-band downlink with 90% link availability, along with various ground network G/T assumptions and possible bandwidth efficient modulations. The paper will conclude with what types of high rate communication links are feasible from Martian distances and also identify a range of requirements for antenna and power technologies for these high capacity communications from Mars.

Active Asteroids in the NEO Population

NASA Astrophysics Data System (ADS)

Jenniskens, Peter

2016-01-01

Some main-belt asteroids evolve into near-Earth objects. They can then experience the same meteoroid-producing phenomena as active asteroids in the main belt. If so, they would produce meteoroid streams, some of which evolve to intersect Earth's orbit and produce meteor showers at Earth. Only few of those are known. Meteoroid streams that move in orbits with Tisserand parameter well in excess of 3 are the Geminids and Daytime Sextantids of the Phaethon complex and the lesser known epsilon Pegasids. The observed activity appears to be related to nearly whole scale disintegrations, rather than dust ejection from volatile outgassing as observed in active comets. There is only a small population of asteroids with a main-belt origin that recently disintegrated into meteoroid streams.

Bond angle variations in XH3 [X = N, P, As, Sb, Bi]: the critical role of Rydberg orbitals exposed using a diabatic state model.

PubMed

Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

2015-10-14

Ammonia adopts sp(3) hybridization (HNH bond angle 108°) whereas the other members of the XH3 series PH3, AsH3, SbH3, and BiH3 instead prefer octahedral bond angles of 90-93°. We use a recently developed general diabatic description for closed-shell chemical reactions, expanded to include Rydberg states, to understand the geometry, spectroscopy and inversion reaction profile of these molecules, fitting its parameters to results from Equation of Motion Coupled-Cluster Singles and Doubles (EOM-CCSD) calculations using large basis sets. Bands observed in the one-photon absorption spectrum of NH3 at 18.3 eV, 30 eV, and 33 eV are reassigned from Rydberg (formally forbidden) double excitations to valence single-excitation resonances. Critical to the analysis is the inclusion of all three electronic states in which two electrons are placed in the lone-pair orbital n and/or the symmetric valence σ* antibonding orbital. An illustrative effective two-state diabatic model is also developed containing just three parameters: the resonance energy driving the high-symmetry planar structure, the reorganization energy opposing it, and HXH bond angle in the absence of resonance. The diabatic orbitals are identified as sp hybrids on X; for the radical cations XH3(+) for which only 2 electronic states and one conical intersection are involved, the principle of orbital following dictates that the bond angle in the absence of resonance is acos(-1/5) = 101.5°. The multiple states and associated multiple conical intersection seams controlling the ground-state structure of XH3 renormalize this to acos[3 sin(2)(2(1/2)atan(1/2))/2 - 1/2] = 86.7°. Depending on the ratio of the resonance energy to the reorganization energy, equilibrium angles can vary from these limiting values up to 120°, and the anomalously large bond angle in NH3 arises because the resonance energy is unexpectedly large. This occurs as the ordering of the lowest Rydberg orbital and the σ* orbital swap, allowing Rydbergization to compresses σ* to significantly increase the resonance energy. Failure of both the traditional and revised versions of the valence-shell electron-pair repulsion (VSEPR) theory to explain the ground-state structures in simple terms is attributed to exclusion of this key physical interaction.

Fuel-Optimal Trajectories in a Planet-Moon Environment Using Multiple Gravity Assists

NASA Technical Reports Server (NTRS)

Ross, Shane D.; Grover, Piyush

2007-01-01

For low energy spacecraft trajectories such as multi-moon orbiters for the Jupiter system, multiple gravity assists by moons could be used in conjunction with ballistic capture to drastically decrease fuel usage. In this paper, we outline a procedure to obtain a family of zero-fuel multi-moon orbiter trajectories, using a family of Keplerian maps derived by the first author previously. The maps capture well the dynamics of the full equations of motion; the phase space contains a connected chaotic zone where intersections between unstable resonant orbit manifolds provide the template for lanes of fast migration between orbits of different semimajor axes. Patched three body approach is used and the four body problem is broken down into two three-body problems, and the search space is considerably reduced by the use of properties of the Keplerian maps. We also introduce the notion of Switching Region where the perturbations due to the two perturbing moons are of comparable strength, and which separates the domains of applicability of the corresponding two Keplerian maps.

A lateral guidance algorithm to reduce the post-aerobraking burn requirements for a lift-modulated orbital transfer vehicle. M.S. Thesis

NASA Technical Reports Server (NTRS)

Herman, G. C.

1986-01-01

A lateral guidance algorithm which controls the location of the line of intersection between the actual and desired orbital planes (the hinge line) is developed for the aerobraking phase of a lift-modulated orbital transfer vehicle. The on-board targeting algorithm associated with this lateral guidance algorithm is simple and concise which is very desirable since computation time and space are limited on an on-board flight computer. A variational equation which describes the movement of the hinge line is derived. Simple relationships between the plane error, the desired hinge line position, the position out-of-plane error, and the velocity out-of-plane error are found. A computer simulation is developed to test the lateral guidance algorithm for a variety of operating conditions. The algorithm does reduce the total burn magnitude needed to achieve the desired orbit by allowing the plane correction and perigee-raising burn to be combined in a single maneuver. The algorithm performs well under vacuum perigee dispersions, pot-hole density disturbance, and thick atmospheres. The results for many different operating conditions are presented.

On the possible relation between the Tunguska bolide and comet Encke

NASA Astrophysics Data System (ADS)

Asher, D. J.; Steel, D. I.

1998-02-01

Almost two decades ago Ľ. Kresák ( Bull. Astron. Inst. Czechoslov.29, 129-134, 1978) suggested that the Tunguska bolide might be a fragment of comet Encke, a hypothesis that Z. Sekanina criticized in a publication a few years later ( Astron. J.88, 1382-1414, 1983). One aspect of the proposed genetic relationship is investigated, namely the required differential orbital precession of the two objects so as to make an impact upon our planet possible for the Tunguska projectile, even though the comet's orbit in the current epoch is far from the condition of Earth intersection. This work was foreshadowed in a previous paper in which it was shown how theoretical meteor radiants may be calculated for objects with orbits similar to 2P/Encke ( Earth, Moon and Planets68, 155-164, 1995). By applying appropriate secular perturbation theory and numerical integration techniques, it is shown that the necessary dispersion can be attained within 10 kyr if the semi-major axes of the orbits differ by ˜0.05 AU, an amount easily achieved even under the presently observed non-gravitational forces of 2P/Encke.

Refocusing distance of a standard plenoptic camera.

PubMed

Hahne, Christopher; Aggoun, Amar; Velisavljevic, Vladan; Fiebig, Susanne; Pesch, Matthias

2016-09-19

Recent developments in computational photography enabled variation of the optical focus of a plenoptic camera after image exposure, also known as refocusing. Existing ray models in the field simplify the camera's complexity for the purpose of image and depth map enhancement, but fail to satisfyingly predict the distance to which a photograph is refocused. By treating a pair of light rays as a system of linear functions, it will be shown in this paper that its solution yields an intersection indicating the distance to a refocused object plane. Experimental work is conducted with different lenses and focus settings while comparing distance estimates with a stack of refocused photographs for which a blur metric has been devised. Quantitative assessments over a 24 m distance range suggest that predictions deviate by less than 0.35 % in comparison to an optical design software. The proposed refocusing estimator assists in predicting object distances just as in the prototyping stage of plenoptic cameras and will be an essential feature in applications demanding high precision in synthetic focus or where depth map recovery is done by analyzing a stack of refocused photographs.

Analysis of orbital configurations for geocenter determination with GPS and low-Earth orbiters

NASA Astrophysics Data System (ADS)

Kuang, Da; Bar-Sever, Yoaz; Haines, Bruce

2015-05-01

We use a series of simulated scenarios to characterize the observability of geocenter location with GPS tracking data. We examine in particular the improvement realized when a GPS receiver in low Earth orbit (LEO) augments the ground network. Various orbital configurations for the LEO are considered and the observability of geocenter location based on GPS tracking is compared to that based on satellite laser ranging (SLR). The distance between a satellite and a ground tracking-site is the primary measurement, and Earth rotation plays important role in determining the geocenter location. Compared to SLR, which directly and unambiguously measures this distance, terrestrial GPS observations provide a weaker (relative) measurement for geocenter location determination. The estimation of GPS transmitter and receiver clock errors, which is equivalent to double differencing four simultaneous range measurements, removes much of this absolute distance information. We show that when ground GPS tracking data are augmented with precise measurements from a GPS receiver onboard a LEO satellite, the sensitivity of the data to geocenter location increases by more than a factor of two for Z-component. The geometric diversity underlying the varying baselines between the LEO and ground stations promotes improved global observability, and renders the GPS technique comparable to SLR in terms of information content for geocenter location determination. We assess a variety of LEO orbital configurations, including the proposed orbit for the geodetic reference antenna in space mission concept. The results suggest that a retrograde LEO with altitude near 3,000 km is favorable for geocenter determination.

The origin and evolution of terrestrial and Martian rock labyrinths

NASA Technical Reports Server (NTRS)

Brook, G. A.

1984-01-01

The morphological characteristics and evolutionary development of rock labyrinths on Earth (in sandstone, volcanics, and carbonates) are compared with those on Mars. On Earth rock labyrinths originate as parallel, an echelon, or intersecting narrow grabens, or develop where fault and joint networks are selectively eroded. Labyrinths frequently contain both downfaulted and erosional elements. Closed labyrinths contain depressions; open labyrinths do not, they are simple part of a fluvial network generally of low order. As closed labyrinths made up of intersecting grabens or made up of connected erosional depressions are extremely common on Mars, the research focussed on an understanding of these labyrinth types. Field investigations were carried out in Canyonlands National Park, Utah, and in the Chirachahua Mountains of Arizona. Martian labyrinths were investigated using Viking orbiter images. In addition, research was undertaken on apparent thermokarst features in Lunae Planum and Chryse Planitia where closed depressions are numerous and resemble atlas topography.

Seven Experiment Designs Addressing Problems of Safety and Capacity on Two-Lane Rural Highways : Volume 8. Experimental Design and Evaluate Remedial Aids for Intersections with Inadequate Sight Distance

DOT National Transportation Integrated Search

2007-01-01

Americans lose 3.7 billion hours and 2.3 billion gallons of fuel every year sitting in traffic jams, and nearly 24 percent of non-recurring freeway delay, or about 482 million hours, is attributed to work zones. To combat the country's growing transp...

AN IMPROVED DISTANCE AND MASS ESTIMATE FOR SGR A* FROM A MULTISTAR ORBIT ANALYSIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boehle, A.; Ghez, A. M.; Meyer, L.

2016-10-10

We present new, more precise measurements of the mass and distance of our Galaxy’s central supermassive black hole, Sgr A*. These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A*, combining 2 decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star’s orbit from the deep adaptive optics data (2005–2013) to inform the search for the star in the speckle years (1995–2005). When this new analysis technique is combined with the first complete re-reduction ofmore » Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 ( K -band magnitude = 17, orbital period = 19 yr) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass ( M {sub bh}) and distance ( R {sub o} ) of Sgr A*: M {sub bh} = (4.02 ± 0.16 ± 0.04) × 10{sup 6} M {sub ⊙} and 7.86 ± 0.14 ± 0.04 kpc. The uncertainties in M {sub bh} and R {sub o} as determined by the combined orbital fit of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared to an orbital fit of S0-2 alone and a factor of ∼2.5 compared to previous results from stellar orbits. This analysis also limits the extended dark mass within 0.01 pc to less than 0.13 × 10{sup 6} M {sub ⊙} at 99.7% confidence, a factor of 3 lower compared to prior work.« less

How Different Variants of Orbit Diagrams Influence Student Explanations of the Seasons

ERIC Educational Resources Information Center

Lee, Victor R.

2010-01-01

The cause of the seasons is often associated with a very particular alternative conception: That the earth's orbit around the sun is highly elongated, and the differences in distance result in variations in temperature. It has been suggested that the standard diagrams used to depict the earth's orbit may be in some way responsible for the initial…

Lessons learned from the 705-km fleet

NASA Astrophysics Data System (ADS)

Vincent, Mark A.

2012-10-01

The scientific benefits generated from the synergy of the satellites in the AM and PM (A-Train) Constellations are unprecedented. Constellation Flying in this context refers to each satellite flying independently in their own control box with acceptable minimum buffers ensuring that the control boxes do not intersect each other. Recently it is has been realized that rather than two separate constellations, they should be considered as one entity called the "705-km Fleet" named for their common nominal altitude over the equator. This realization partly comes from the recent events with the USGS satellite Landsat-5 which is in the AM Constellation, but for a period of time was overlapping with the A-Train. A fundamental concept is the Triad consisting of Alongtrack Phasing, Groundtrack and Mean Local Time of Ascending Node. Another related lesson learned is that to maintain the buffers, phasing at the two intersection points where each pair of orbits cross near the poles should be considered, as opposed to the relative phasing of the times they cross the equator. These types of geometric considerations are presented after presenting an introduction and history of the constellations. Other topics include: reference ground tracks, the process of handling the growing concern of conjunctions with other orbiting bodies, CloudSat and CALIPSO satellites performing Formation Flying, and the general ascent and exit methods for satellites entering/leaving a constellation.

Debris perturbed by radiation pressure: relative velocities across circular orbits

NASA Astrophysics Data System (ADS)

Celestino, C.; Winter, O.; Prado, A.

It is widely know that there is a large amount of space debris and meteoroid particles around the Earth. The objects larger than 10 cm can be tracked by radar and others means allowing the satellites/ships to be maneuvered to avoid collisions. However, the detection and the attendance of the orbital dynamics of objects smaller than 10 cm (particles) is very difficult. These particles can be generated by explosions of larger objects, collisions between large objects, or simply for the reaction of the oxygen in the wall of an object could generate the escape of paint pieces. The importance of studying the dynamics of these particles is that they can have relative high speeds and their effects in a collision could cause damages and even compromise the space missions. In this present work we considered a dynamical system of mm size particles around the Earth subject to the effects of radiation pressure. Our main goal is to study the evolution of its relative velocity to the circular orbits that it crosses.Firstly, it is considered that the particle is initially in circular orbit. The effect of the radiation pressure produces variations in its eccentricity, resulting in a change in its orbital velocity. The results show that the variation of the radial distance and the relative velocity can be divided in three parts: secular, long period and short period. For the radial distance the secular variation is constant, because the semi-axis is constant. The long period variation presents a configuration that repeats with period inferior to the orbital period of the Earth. And, finally, the short period variation presents points of local maxima and minima for the variation of the width of the radial distance. When considering the variation of the relative velocity we have that the secular behavior and of long period are similar to those obtained for the variation of the radial distance. However, for the short period variation, we have a larger number of local maxima and minima in comparison to the radial distance. The relative velocity for particles initially geostationary of size 5,0 mm are around 4,0 km/s. Acknowledgments: The authors thank FAPESP, CNPq and FUNDUNESP for the financial support.

6-DoF Haptic Rendering Using Continuous Collision Detection between Points and Signed Distance Fields.

PubMed

Hongyi Xu; Barbic, Jernej

2017-01-01

We present an algorithm for fast continuous collision detection between points and signed distance fields, and demonstrate how to robustly use it for 6-DoF haptic rendering of contact between objects with complex geometry. Continuous collision detection is often needed in computer animation, haptics, and virtual reality applications, but has so far only been investigated for polygon (triangular) geometry representations. We demonstrate how to robustly and continuously detect intersections between points and level sets of the signed distance field. We suggest using an octree subdivision of the distance field for fast traversal of distance field cells. We also give a method to resolve continuous collisions between point clouds organized into a tree hierarchy and a signed distance field, enabling rendering of contact between rigid objects with complex geometry. We investigate and compare two 6-DoF haptic rendering methods now applicable to point-versus-distance field contact for the first time: continuous integration of penalty forces, and a constraint-based method. An experimental comparison to discrete collision detection demonstrates that the continuous method is more robust and can correctly resolve collisions even under high velocities and during complex contact.

First Visual Orbit for the Prototypical Colliding-wind Binary WR 140

NASA Astrophysics Data System (ADS)

Monnier, John D.; Zhao, M.; Pedretti, E.; Millan-Gabet, R.; Berger, J.; Schloerb, F.; Traub, W.; ten Brummelaar, T.; McAlister, H.; Ridgway, S.; Turner, N.; Sturmann, L.; Sturmann, J.; Baron, F.; Tannirkulam, A.; Kraus, S.; Williams, P.

2012-01-01

Wolf-Rayet stars represent one of the final stages of massive stellar evolution. Relatively little is known about this short-lived phase and we currently lack reliable mass, distance, and binarity determinations for a representative sample. Here we report the first visual orbit for WR 140 (=HD193793), a WC7+O5 binary system known for its periodic dust production episodes triggered by intense colliding winds near periastron passage. The IOTA and CHARA interferometers resolved the pair of stars in each year from 2003--2009, covering most of the highly-eccentric, 7.9 year orbit. Combining our results with the recent improved double-line spectroscopic orbit of Fahed et al. (2011), we can estimate the distance to WR 140 with about 2% error and estimate component masses with about 4% error. Our precision orbit yields key parameters with uncertainties about 6 times smaller than previous work and paves the way for detailed modeling of the system. Our newly measured flux ratios at the near-infrared H and Ks bands allow an SED decomposition and analysis of the component evolutionary states.

Asteroid Apophis: Evaluating the impact hazards of such bodies

NASA Astrophysics Data System (ADS)

Shuvalov, V. V.; Svettsov, V. V.; Artem'eva, N. A.; Trubetskaya, I. A.; Popova, O. P.; Glazachev, D. O.

2017-01-01

Soon after the discovery of asteroid 99942 Apophis, it was classified as a potentially hazardous object with a high probability of an impact on the Earth in 2029. Although subsequent observations have substantially reduced the probability of a collision, it has not been ruled out; moreover, similar-sized asteroids in orbits intersecting the Earth's orbit may well be discovered in the near future. We conduct a numerical simulation of an atmospheric passage and an impact on the Earth's surface of a stony cosmic body with a diameter of 300 m and kinetic energy of about 1000 Mt, which roughly corresponds to the parameters of the asteroid Apophis, at atmospheric entry angles of 90° (vertical stroke), 45°, and 30°. The simulation is performed by solving three-dimensional equations of hydrodynamics and radiative transfer equations in the approximations of radiative heat conduction and volume emission. The following hazards are considered: an air shock wave, ejecta from the crater, thermal radiation, and ionospheric disturbances. Our calculations of the overpressure and wind speed on the Earth's surface show that the zone of destruction of the weakest structures can be as large as 700-1000 km in diameter; a decrease in the flight path angle to the surface leads to a marked increase in the area affected by the shock wave. The ionospheric disturbances are global in nature and continue for hours: at distances of several thousand kilometers at altitudes of more than 100 km, air density disturbances are tens of percent and the vertical and horizontal velocity components reach hundreds of meters per second. The impact of radiation on objects on the Earth's surface is estimated by solving the equation of radiative transfer along rays passing through a luminous area. In clear weather, the size of the zone where thermal heating may ignite wood can be as large as 200 km, and the zone of individual fire outbreaks associated with the ignition of flammable materials can be twice as large. In the 100-km central area, which is characterized by very strong thermal damage, there is ignition of structures, roofs, clothes, etc. The human hazardous area increases with the decrease in the trajectory angle, and people may experience thermal effects at distances of up to 250-400 km from the crater.

Dynamical study of low Earth orbit debris collision avoidance using ground based laser

NASA Astrophysics Data System (ADS)

Khalifa, N. S.

2015-06-01

The objective of this paper was to investigate the orbital velocity changes due to the effect of ground based laser force. The resulting perturbations of semi-major axis, miss distance and collision probability of two approaching objects are studied. The analytical model is applied for low Earth orbit debris of different eccentricities and area to mass ratio and the numerical test shows that laser of medium power ∼5 kW can perform a small change Δ V ‾ of an average magnitude of 0.2 cm/s which can be accumulated over time to be about 3 cm/day. Moreover, it is confirmed that applying laser Δ V ‾ results in decreasing collision probability and increasing miss distance in order to avoid collision.

Parametric study of the Orbiter rollout using an approximate solution

NASA Technical Reports Server (NTRS)

Garland, B. J.

1979-01-01

An approximate solution to the motion of the Orbiter during rollout is used to perform a parametric study of the rollout distance required by the Orbiter. The study considers the maximum expected dispersions in the landing speed and the touchdown point. These dispersions are assumed to be correlated so that a fast landing occurs before the nominal touchdown point. The maximum rollout distance is required by the maximum landing speed with a 10 knot tailwind and the center of mass at the forward limit of its longitudinal travel. The maximum weight that can be stopped within 15,000 feet on a hot day at Kennedy Space Center is 248,800 pounds. The energy absorbed by the brakes would exceed the limit for reuse of the brakes.

A three-dimensional orbit for the binary star Alpha Andromedae

NASA Astrophysics Data System (ADS)

Branham, Richard L., Jr.

2017-01-01

Stars that are both spectroscopic and optical binaries present a means to determine simultaneously the masses of the components and the distance of the system independent of trigonometric parallax. Alpha Andromedae (Alpheratz) represents such a system and, moreover, the primary is the brightest of the mercury-manganese stars. An orbit, based on 42 interferometric observations and 378 radial velocities, is calculated to solve for 10 parameters: the six coefficients of the apparent ellipse, the constant of areal velocity, the systemic velocity, and the semi-amplitudes. From these, one calculates the orbit of the binary, its period and time of periastron passage, the masses of the components, and the distance of the system. The dynamical parallax does not differ greatly from the trigonometric parallax found from Hipparcos.

Accidental degeneracy in k-space, geometrical phase, and the perturbation of π by spin-orbit interactions

NASA Astrophysics Data System (ADS)

Allen, Philip B.; Pickett, Warren E.

2018-06-01

Since closed lines of accidental electronic degeneracies were demonstrated to be possible, even frequent, by Herring in 1937, no further developments arose for eight decades. The earliest report of such a nodal loop in a real material - aluminum - is recounted and elaborated on. Nodal loop semimetals have become a focus of recent activity, with emphasis on other issues. Band degeneracies are, after all, the origin of topological phases in crystalline materials. Spin-orbit interaction lifts accidental band degeneracies, with the resulting spectrum being provided here. The geometric phase γ(C) = ± π for circuits C surrounding a line of such degeneracy cannot survive completely unchanged. The change depends on how the spin is fixed during adiabatic evolution. For spin fixed along the internal spin-orbit field, γ(C) decreases to zero as the circuit collapses around the line of lifted degeneracy. For spin fixed along a perpendicular axis, the conical intersection persists and γ(C) = ± π is unchanged.

Theoretical study of actinide monocarbides (ThC, UC, PuC, and AmC)

NASA Astrophysics Data System (ADS)

Pogány, Peter; Kovács, Attila; Visscher, Lucas; Konings, Rudy J. M.

2016-12-01

A study of four representative actinide monocarbides, ThC, UC, PuC, and AmC, has been performed with relativistic quantum chemical calculations. The two applied methods were multireference complete active space second-order perturbation theory (CASPT2) including the Douglas-Kroll-Hess Hamiltonian with all-electron basis sets and density functional theory with the B3LYP exchange-correlation functional in conjunction with relativistic pseudopotentials. Beside the ground electronic states, the excited states up to 17 000 cm-1 have been determined. The molecular properties explored included the ground-state geometries, bonding properties, and the electronic absorption spectra. According to the occupation of the bonding orbitals, the calculated electronic states were classified into three groups, each leading to a characteristic bond distance range for the equilibrium geometry. The ground states of ThC, UC, and PuC have two doubly occupied π orbitals resulting in short bond distances between 1.8 and 2.0 Å, whereas the ground state of AmC has significant occupation of the antibonding orbitals, causing a bond distance of 2.15 Å.

The potentially hazardous asteroid 2007CA19 as the parent of the η-Virginids meteoroid stream

NASA Astrophysics Data System (ADS)

Babadzhanov, P. B.; Kokhirova, G. I.; Obrubov, Yu. V.

2015-07-01

The orbit of the potentially hazardous near-Earth asteroid 2007CA19 is classified as comet-like according to the Tisserand parameter with a value of Tj = 2.8, therefore the object can be empirically considered as an extinct or dormant Jupiter-family comet. If 2007CA19 is really a former comet, it could have formed a meteoroid stream in the past in the period of its cometary activity. Investigation of the asteroid's orbital evolution shows that 2007CA19 is a quadruple-crosser of the Earth's orbit. Consequently, the meteoroid stream that is supposedly associated with the object can produce four meteor showers if, as expected, the perihelia arguments of the meteoroids are very distributed over the orbit. Theoretical radiants of the predicted showers were calculated using elements of the 2007CA19 osculating orbit that correspond to the positions of intersections with the Earth's orbit. A search for the predicted night-time showers has shown that the Northern and Southern η-Virginids can be associated to 2007CA19. Using the MOID IAU database, we identify two other daytime showers that can be associated with this asteroid. Thus, we confirm that 2007CA19 has an associated meteoroid stream that produces four active meteor showers in the Earth's atmosphere. This relationship supports the dynamical classification of the object and also points to the possibility of its cometary origin.

Topography of the Lunar Poles and Application to Geodesy with the Lunar Reconnaissance Orbiter

NASA Technical Reports Server (NTRS)

Mazarico, Erwan; Neumann, Gregory A.; Rowlands, David D.; Smith, David E.; Zuber, Maria T.

2012-01-01

The Lunar Orbiter Laser Altimeter (LOLA) [1] onboard the Lunar Reconnaissance Orbiter (LRO) [2] has been operating continuously since July 2009 [3], accumulating approx.5.4 billion measurements from 2 billion on-orbit laser shots. LRO s near-polar orbit results in very high data density in the immediate vicinity of the lunar poles, which are each sampled every 2h. With more than 10,000 orbits, high-resolution maps can be constructed [4] and studied [5]. However, this requires careful processing of the raw data, as subtle errors in the spacecraft position and pointing can lead to visible artifacts in the final map. In other locations on the Moon, ground tracks are subparallel and longitudinal separations are typically a few hundred meters. Near the poles, the track intersection angles can be large and the inter-track spacing is small (above 80 latitude, the effective resolution is better than 50m). Precision Orbit Determination (POD) of the LRO spacecraft [6] was performed to satisfy the LOLA and LRO mission requirements, which lead to a significant improvement in the orbit position knowledge over the short-release navigation products. However, with pixel resolutions of 10 to 25 meters, artifacts due to orbit reconstruction still exist. Here, we show how the complete LOLA dataset at both poles can be adjusted geometrically to produce a high-accuracy, high-resolution maps with minimal track artifacts. We also describe how those maps can then feedback to the POD work, by providing topographic base maps with which individual LOLA altimetric measurements can be contributing to orbit changes. These direct altimetry constraints improve accuracy and can be used more simply than the altimetric crossovers [6].

Field Effect Flow Control in a Polymer T-Intersection Microfluidic Network

NASA Technical Reports Server (NTRS)

Sniadecki, Nathan J.; Chang, Richard; Beamesderfer, Mike; Lee, Cheng S.; DeVoe, Don L.

2003-01-01

We present a study of induced pressure pumping in a polymer microchannel due to differential electroosmotic flow @OF) rates via field-effect flow control (FEFC). The experimental results demonstrate that the induced pressure pumping is dependent on the distance of the FEFC gate from the cathodic gate. A proposed flow model based on a linearly-decaying zeta potential profile is found to successfully predict experimental trends.

Large-Scale Urban Localisation with a Pushbroom LIDAR

DTIC Science & Technology

2012-10-01

the sole means of gen- erating full 6-DOF poses from a previously-surveyed workspace. In this approach, Normalised Information Distance is used as the...vehicle to have good knowledge of its position at system- initialization. We now turn to an overview of the use of point-based registration methods for...combination of reference vertices, and provides a convenient representation for the intersection test . Using this parametric representation, the coordinates

Space Operations Center, Shuttle Interaction Study. Volume 2: Appendices, Book 1 of 2

NASA Technical Reports Server (NTRS)

1981-01-01

The feasibility of shuttle orbiter docking to the Space Operations Center (SOC) is studied. The in-orbit relative motion of the free flying orbiter and SOC was simulated, accounting for the Orbiter RCS and digital autopilot (DAP) systems, orbital mechanics, center of gravity offset of the orbiter docking port, aero and gravity gradient effects, and other pertinent natural and man-made phenomena. Since there is no specified flight path and procedure for docking, terminal closure sensitivities were investigated. Orbiter approach direction, Orbiter approach attitude out of plane, DAP thruster compensation mode, final ballistic docking distance and time to dock, rate and excursion attitude deadbands, and selection of various thruster combinations (differing from nominal) for translational pulses are considered.

Passage of a star by a massive black hole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noltenius, R.A.; Katz, J.I.

1982-12-01

We have calculated the effects on a 1 M/sub sun/ star of passage by a 10/sup 4/ M/sub sun/ point mass (black hole) in an intially parabolic orbit with a variety of pericenter distances. Because this problem is three-dimensional, we use the gridless smoothed particle hydrodynamic method of Lucy, Gingold, and Monaghan. The tidal forces are found to induce rotation and radial and nonradial pulsations of the star. The loss of orbital energy to these internal motions leads to capture of the star by the black hole. For small pericenter distances, the outer layers of the star are disrupted, whilemore » at still smaller distances, the entire star is destroyed. These results may be applied to some X-ray sources, active galactic nuclei, and quasars.« less

Dynamical Constraints on Nontransiting Planets Orbiting TRAPPIST-1

NASA Astrophysics Data System (ADS)

Jontof-Hutter, Daniel; Truong, Vinh H.; Ford, Eric B.; Robertson, Paul; Terrien, Ryan C.

2018-06-01

We derive lower bounds on the orbital distance and inclination of a putative planet beyond the transiting seven planets of TRAPPIST-1, for a range of masses ranging from 0.08 M Jup to 3.5 M Jup. While the outer architecture of this system will ultimately be constrained by radial velocity measurements over time, we present dynamical constraints from the remarkably coplanar configuration of the seven transiting planets, which is sensitive to modestly inclined perturbers. We find that the observed configuration is unlikely if a Jovian-mass planet inclined by ≥3° to the transiting planet exists within 0.53 au, exceeding any constraints from transit timing variations (TTV) induced in the known planets from an undetected perturber. Our results will inform RV programs targeting TRAPPIST-1, and for near coplanar outer planets, tighter constraints are anticipated for radial velocity (RV) precisions of ≲140 m s‑1. At higher inclinations, putative planets are ruled out to greater orbital distances with orbital periods up to a few years.

Normal orbit skeletal changes in adolescents as determined through cone-beam computed tomography.

PubMed

Lee, B; Flores-Mir, C; Lagravère, M O

2016-11-10

To determine three-dimensional spatial orbit skeletal changes in adolescents over a 19 to 24 months observation period assessed through cone-beam computed tomography (CBCT). The sample consisted of 50 adolescents aged 11 to 17. All were orthodontic patients who had two CBCTs taken with an interval of 19 to 24 months between images. The CBCTs were analyzed using the third-party software Avizo. Sixteen anatomical landmarks resulting in 24 distances were used to measure spatial structural changes of both orbits. Reliability and measurement error of all landmarks were calculated using ten CBCTs. Descriptive and t-test statistical analyses were used to determine the overall changes in the orbits. All landmarks showed excellent reliability with the largest measurement error being the Y-coordinate of the left most medial point of the temporalis grooves at 0.95 mm. The mean differences of orbital changes between time 1 and time 2 in the transverse, antero-posterior and vertical directions were 0.97, 0.36 and 0.33 mm respectively. Right to left most antero-inferior superior orbital rim distance had the greatest overall transverse change of 4.37 mm. Right most posterior point of lacrimal crest to right most postero-lateral point of the superior orbital fissure had the greatest overall antero-posterior change of 0.52 mm. Lastly, left most antero-inferior superior orbital rim to left most antero-superior inferior orbital rim had the greatest overall vertical change of 0.63 mm. The orbit skeletal changes in a period of 19-24 months in a sample of 11-17 year olds were statistically significant, but are not considered to be clinically significant. The overall average changes of orbit measurements were less than 1 mm.

Fast focus estimation using frequency analysis in digital holography.

PubMed

Oh, Seungtaik; Hwang, Chi-Young; Jeong, Il Kwon; Lee, Sung-Keun; Park, Jae-Hyeung

2014-11-17

A novel fast frequency-based method to estimate the focus distance of digital hologram for a single object is proposed. The focus distance is computed by analyzing the distribution of intersections of smoothed-rays. The smoothed-rays are determined by the directions of energy flow which are computed from local spatial frequency spectrum based on the windowed Fourier transform. So our method uses only the intrinsic frequency information of the optical field on the hologram and therefore does not require any sequential numerical reconstructions and focus detection techniques of conventional photography, both of which are the essential parts in previous methods. To show the effectiveness of our method, numerical results and analysis are presented as well.

A Virtual Blind Cane Using a Line Laser-Based Vision System and an Inertial Measurement Unit

PubMed Central

Dang, Quoc Khanh; Chee, Youngjoon; Pham, Duy Duong; Suh, Young Soo

2016-01-01

A virtual blind cane system for indoor application, including a camera, a line laser and an inertial measurement unit (IMU), is proposed in this paper. Working as a blind cane, the proposed system helps a blind person find the type of obstacle and the distance to it. The distance from the user to the obstacle is estimated by extracting the laser coordinate points on the obstacle, as well as tracking the system pointing angle. The paper provides a simple method to classify the obstacle’s type by analyzing the laser intersection histogram. Real experimental results are presented to show the validity and accuracy of the proposed system. PMID:26771618

A New Orbit for Comet C/1865 B1 (Great Southern Comet of 1865)

NASA Astrophysics Data System (ADS)

Branham, Richard L., Jr.

2018-04-01

Comet C/1865 B1 (Great southern comet of 1865), observed only in the southern hemisphere, is one of a large number of comets with parabolic orbits. Given that there are 202 observations in right ascension and 165 in declination it proves possible to calculate a better orbit than that Körber published in 1887, the orbit used in various catalogs and data bases. C/1865 B1's orbit is hyperbolic and statistically distinguishable from a parabola. This object, therefore, cannot be considered an NEO. The comet has a small perihelion distance of 0.026 AU.

Morphology and morphometry of the meningo-orbital foramen as a result of plastic responses to the ambient temperature and its clinical relevance.

PubMed

Tomaszewska, Agnieszka; Zelaźniewicz, Agnieszka

2014-05-01

The meningo-orbital foramen (FMO) is an osteal opening, containing vessels providing an accessory blood supply to the orbit, situated close to the superior orbital fissure. Recent studies show FMO to be ubiquitous, with localization and occurrence varying, depending on a population, what may be due to environmental conditions (ie, temperature). It is often located near the operating area in surgeries in the orbital cavity, and its accurate localization allows avoiding unexpected bleeding during intervention. Because there is a lack of clarity in the literature concerning the morphology and the morphometry of the FMO, this study aimed to clarify the issue with clinical relevance. We studied dry adult human skulls (50 men and 33 women). The morphology and minimal distances between the FMO and standard anthropologic landmarks (nasion, frontomalare orbitale, supraorbital foramen, and zygomaticomaxillary suture) were measured, using MicroScribe G2L, a three-dimensional contact scanner. We compared the result with results of previous studies on populations from various climate zones. The FMO was present in 69.88% of the skulls (56.02% of orbits): in 60.34% of the skulls, the FMO was bilateral; and in 39.66%, unilateral. We observed 74 single, 10 double, and 2 triple foramina. The FMO was present mostly on the sphenoid and the frontal bone. There was no difference in minimal distances between the FMO and the anthropologic landmarks, depending on sex, except the distance to the nasion (shorter in women). The occurrence of the FMO in the population differed from that of other populations. The results show that it is possible that the morphology and the morphometry of the FMO depend on the climate zone or ambient temperature during growth, which should be considered before performing surgery in the orbital cavity.

The large-scale structure of the asteroid belt

NASA Technical Reports Server (NTRS)

Zellner, B.; Thirunagari, A.; Bender, D.

1985-01-01

The distributions of 2888 numbered minor planets over orbital inclination, eccentricity, and semimajor axis are examined, and 19 zones believed to adequately isolate the selection biases in survey programs of the physical properties of minor planets are defined. Six numbered asteroids have exceptional orbits and fall into no zone. Attention is called to rather sharp upper limits, which become increasingly stringent at larger heliocentric distances, on orbital inclinations and eccentricity.

Eye on Io.

ERIC Educational Resources Information Center

Lewis, Scott M.

1985-01-01

"Io," one of four satellites of Jupiter, orbits its mother planet in roughly the same plane as Earth orbits the sun. Guidelines for collecting data about Io using a reflecting telescope, 35mm camera, and adapter are presented. A computer program used in studying Io's maximum distance from Jupiter is available. (DH)

Distance Estimation for Eclipsing X-Ray Pulsars

NASA Astrophysics Data System (ADS)

Wilson, Robert E.; Paul, B.; Raichur, H.

2006-06-01

Recent interest in eclipsing binaries as distance indicators leads naturally into direct distance estimation for X-ray pulsars by combination of pulse arrival times, radial velocities, X-ray eclipse duration, and spectra. Optical light curves may help in some cases by measuring tides and irradiation, although dynamical tides in eccentric systems limit light curve usefulness. Pulse arrivals give an absolute scale and also orbit shape and orientation, which may be poorly known from radial velocities. For example, orbital eccentricity of 0.09 is known from Vela X1 pulse arrivals, although optical velocities are too noisy to measure eccentricity accurately. Combined pulse and optical velocity data give mass information. A lower limit to sin i from eclipse duration sets a lower limit to R2, and for the general eccentric case. A mass ratio sets lobe size and thus an upper limit to R2, so boxing R2 within a narrow range may be possible. T2 can be assessed from spectra so EB distance estimation can work if magnitude is known in one or more standard bands such as B or V. Realistic distance uncertainties are explored. In regard to new observations, Vela X-1 was observed by RXTE over about nine days in January 2005, including an eclipse of about 3.5 days. We extracted the light curves with time resolution 0.125 s. Spin period measurements by the Chi square criterion show Doppler variation with orbital phase and mean spin period 283.5 s. Pulse profiles of that period were averaged in sets of 10 at 138 phases. Cross correlation for the first 40 pulses show the expected Doppler arrival time variation. As the Vela X-1 pulse period is large compared to light travel time across the orbit, the pulses are already phase connected. Support is by U.S. National Science Foundation grant 0307561.

Small Mercury Relativity Orbiter

NASA Technical Reports Server (NTRS)

Bender, Peter L.; Vincent, Mark A.

1989-01-01

The accuracy of solar system tests of gravitational theory could be very much improved by range and Doppler measurements to a Small Mercury Relativity Orbiter. A nearly circular orbit at roughly 2400 km altitude is assumed in order to minimize problems with orbit determination and thermal radiation from the surface. The spacecraft is spin-stabilized and has a 30 cm diameter de-spun antenna. With K-band and X-band ranging systems using a 50 MHz offset sidetone at K-band, a range accuracy of 3 cm appears to be realistically achievable. The estimated spacecraft mass is 50 kg. A consider-covariance analysis was performed to determine how well the Earth-Mercury distance as a function of time could be determined with such a Relativity Orbiter. The minimum data set is assumed to be 40 independent 8-hour arcs of tracking data at selected times during a two year period. The gravity field of Mercury up through degree and order 10 is solved for, along with the initial conditions for each arc and the Earth-Mercury distance at the center of each arc. The considered parameters include the gravity field parameters of degree 11 and 12 plus the tracking station coordinates, the tropospheric delay, and two parameters in a crude radiation pressure model. The conclusion is that the Earth-Mercury distance can be determined to 6 cm accuracy or better. From a modified worst-case analysis, this would lead to roughly 2 orders of magnitude improvement in the knowledge of the precession of perihelion, the relativistic time delay, and the possible change in the gravitational constant with time.

Orbital Payload Reductions Resulting from Booster and Trajectory Modifications for Recovery of a Large Rocket Booster

NASA Technical Reports Server (NTRS)

Levin, Alan D.; Hopkins, Edward J.

1961-01-01

An analysis was made to determine the reduction in payload for a 300 nautical mile orbit resulting from the addition of inert weight, representing recovery gear, to the first-stage booster of a three-stage rocket vehicle. The values of added inert weight investigated ranged from 0 to 18 percent of gross weight at lift off. The study also included the effects on the payload in orbit and the distance from the launch site at burnout and at impact caused by variation in the vertical rise time before the programmed tilt. The vertical rise times investigated ranged from 16-7 to 100 percent of booster burning time. For a vertical rise of 16.7 percent of booster burning time it was found that a 50-percent increase in the weight of the empty booster resulted in only a 10-percent reduction of the payload in orbit. For no added booster weight, increasing vertical rise time from 16-7 to 100 percent of booster burning time (so that the spent booster would impact in the launch area) reduced the payload by 37 percent. Increasing the vertical rise time from 16-7 to 50 percent of booster burning time resulted in about a 15-percent reduction in the impact distance, and for vertical rise times greater than 50-percent the impact distance decreased rapidly.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Yoonyoung; Ishiguro, Masateru; Usui, Fumihiko

We investigated the population of asteroids in comet-like orbits using available asteroid size and albedo catalogs of data taken with the Infrared Astronomical Satellite, AKARI, and the Wide-field Infrared Survey Explorer on the basis of their orbital properties (i.e., the Tisserand parameter with respect to Jupiter, T{sub J}, and the aphelion distance, Q). We found that (1) there are 123 asteroids in comet-like orbits by our criteria (i.e., Q > 4.5 AU and T{sub J} < 3), (2) 80% of them have low albedo, p{sub v} < 0.1, consistent with comet nuclei, (3) the low-albedo objects among them have amore » size distribution shallower than that of active comet nuclei, that is, the power index of the cumulative size distribution is around 1.1, and (4) unexpectedly, a considerable number (i.e., 25 by our criteria) of asteroids in comet-like orbits have high albedo, p{sub v} > 0.1. We noticed that such high-albedo objects mostly consist of small (D < 3 km) bodies distributed in near-Earth space (with perihelion distance of q < 1.3 AU). We suggest that such high-albedo, small objects were susceptible to the Yarkovsky effect and drifted into comet-like orbits via chaotic resonances with planets.« less

On the orbits that generate the X-shape in the Milky Way bulge

NASA Astrophysics Data System (ADS)

Abbott, Caleb G.; Valluri, Monica; Shen, Juntai; Debattista, Victor P.

2017-09-01

The Milky Way (MW) bulge shows a boxy/peanut or X-shaped bulge (hereafter BP/X) when viewed in infrared or microwave bands. We examine orbits in an N-body model of a barred disc galaxy that is scaled to match the kinematics of the MW bulge. We generate maps of projected stellar surface density, unsharp masked images, 3D excess-mass distributions (showing mass outside ellipsoids), line-of-sight number count distributions, and 2D line-of-sight kinematics for the simulation as well as co-added orbit families, in order to identify the orbits primarily responsible for the BP/X shape. We estimate that between 19 and 23 per cent of the mass of the bar in this model is associated with the BP/X shape and that the majority of bar orbits contribute to this shape that is clearly seen in projected surface density maps and 3D excess mass for non-resonant box orbits, 'banana' orbits, 'fish/pretzel' orbits and 'brezel' orbits. Although only the latter two families (comprising 7.5 per cent of the total mass) show a distinct X-shape in unsharp masked images, we find that nearly all bar orbit families contribute some mass to the 3D BP/X-shape. All co-added orbit families show a bifurcation in stellar number count distribution with distance that resembles the bifurcation observed in red clump stars in the MW. However, only the box orbit family shows an increasing separation of peaks with increasing galactic latitude |b|, similar to that observed. Our analysis suggests that no single orbit family fully explains all the observed features associated with the MW's BP/X-shaped bulge, but collectively the non-resonant boxes and various resonant boxlet orbits contribute at different distances from the centre to produce this feature. We propose that since box orbits (which are the dominant population in bars) have three incommensurable orbital fundamental frequencies, their 3D shapes are highly flexible and, like Lissajous figures, this family of orbits is most easily able to adapt to evolution in the shape of the underlying potential.

Optimal graph based segmentation using flow lines with application to airway wall segmentation.

PubMed

Petersen, Jens; Nielsen, Mads; Lo, Pechin; Saghir, Zaigham; Dirksen, Asger; de Bruijne, Marleen

2011-01-01

This paper introduces a novel optimal graph construction method that is applicable to multi-dimensional, multi-surface segmentation problems. Such problems are often solved by refining an initial coarse surface within the space given by graph columns. Conventional columns are not well suited for surfaces with high curvature or complex shapes but the proposed columns, based on properly generated flow lines, which are non-intersecting, guarantee solutions that do not self-intersect and are better able to handle such surfaces. The method is applied to segment human airway walls in computed tomography images. Comparison with manual annotations on 649 cross-sectional images from 15 different subjects shows significantly smaller contour distances and larger area of overlap than are obtained with recently published graph based methods. Airway abnormality measurements obtained with the method on 480 scan pairs from a lung cancer screening trial are reproducible and correlate significantly with lung function.

Cutting solid figures by plane - analytical solution and spreadsheet implementation

NASA Astrophysics Data System (ADS)

Benacka, Jan

2012-07-01

In some secondary mathematics curricula, there is a topic called Stereometry that deals with investigating the position and finding the intersection, angle, and distance of lines and planes defined within a prism or pyramid. Coordinate system is not used. The metric tasks are solved using Pythagoras' theorem, trigonometric functions, and sine and cosine rules. The basic problem is to find the section of the figure by a plane that is defined by three points related to the figure. In this article, a formula is derived that gives the positions of the intersection points of such a plane and the figure edges, that is, the vertices of the section polygon. Spreadsheet implementations of the formula for cuboid and right rectangular pyramids are presented. The user can check his/her graphical solution, or proceed if he/she is not able to complete the section.

GPS/DR Error Estimation for Autonomous Vehicle Localization.

PubMed

Lee, Byung-Hyun; Song, Jong-Hwa; Im, Jun-Hyuck; Im, Sung-Hyuck; Heo, Moon-Beom; Jee, Gyu-In

2015-08-21

Autonomous vehicles require highly reliable navigation capabilities. For example, a lane-following method cannot be applied in an intersection without lanes, and since typical lane detection is performed using a straight-line model, errors can occur when the lateral distance is estimated in curved sections due to a model mismatch. Therefore, this paper proposes a localization method that uses GPS/DR error estimation based on a lane detection method with curved lane models, stop line detection, and curve matching in order to improve the performance during waypoint following procedures. The advantage of using the proposed method is that position information can be provided for autonomous driving through intersections, in sections with sharp curves, and in curved sections following a straight section. The proposed method was applied in autonomous vehicles at an experimental site to evaluate its performance, and the results indicate that the positioning achieved accuracy at the sub-meter level.

GPS/DR Error Estimation for Autonomous Vehicle Localization

PubMed Central

Lee, Byung-Hyun; Song, Jong-Hwa; Im, Jun-Hyuck; Im, Sung-Hyuck; Heo, Moon-Beom; Jee, Gyu-In

2015-01-01

Autonomous vehicles require highly reliable navigation capabilities. For example, a lane-following method cannot be applied in an intersection without lanes, and since typical lane detection is performed using a straight-line model, errors can occur when the lateral distance is estimated in curved sections due to a model mismatch. Therefore, this paper proposes a localization method that uses GPS/DR error estimation based on a lane detection method with curved lane models, stop line detection, and curve matching in order to improve the performance during waypoint following procedures. The advantage of using the proposed method is that position information can be provided for autonomous driving through intersections, in sections with sharp curves, and in curved sections following a straight section. The proposed method was applied in autonomous vehicles at an experimental site to evaluate its performance, and the results indicate that the positioning achieved accuracy at the sub-meter level. PMID:26307997

Planetary Protection Trajectory Analysis for the Juno Mission

NASA Technical Reports Server (NTRS)

Lam, Try; Johannesen, Jennie R.; Kowalkowski, Theresa D.

2008-01-01

Juno is an orbiter mission expected to launch in 2011 to Jupiter. Juno's science orbit is a highly eccentric orbit with a period of about 11 days and a nominal duration of one year. Initially, the equatorial crossing near apojove occurs outside Callisto's orbit, but as the mission evolves the apsidal rotation causes this distance to move much closer to Jupiter. This motion could lead to potential impacts with the Galilean satellites as the ascending node crosses the satellite orbits. In this paper, we describe the method to estimate impact probabilities with the satellites and investigate ways of reducing the probabilities for the Juno mission.

Circulating transportation orbits between earth and Mars

NASA Technical Reports Server (NTRS)

Friedlander, A. L.; Niehoff, J. C.; Byrnes, D. V.; Longuski, J. M.

1986-01-01

This paper describes the basic characteristics of circulating (cyclical) orbit design as applied to round-trip transportation of crew and materials between earth and Mars in support of a sustained manned Mars Surface Base. The two main types of nonstopover circulating trajectories are the socalled VISIT orbits and the Up/Down Escalator orbits. Access to the large transportation facilities placed in these orbits is by way of taxi vehicles using hyperbolic rendezvous techniques during the successive encounters with earth and Mars. Specific examples of real trajectory data are presented in explanation of flight times, encounter frequency, hyperbolic velocities, closest approach distances, and Delta V maneuver requirements in both interplanetary and planetocentric space.

Accuracy Assessment in Determining the Location of Corners of Building Structures Using a Combination of Various Measurement Methods

NASA Astrophysics Data System (ADS)

Krzyżek, Robert; Przewięźlikowska, Anna

2017-12-01

When surveys of corners of building structures are carried out, surveyors frequently use a compilation of two surveying methods. The first one involves the determination of several corners with reference to a geodetic control using classical methods of surveying field details. The second method relates to the remaining corner points of a structure, which are determined in sequence from distance-distance intersection, using control linear values of the wall faces of the building, the so-called tie distances. This paper assesses the accuracy of coordinates of corner points of a building structure, determined using the method of distance-distance intersection, based on the corners which had previously been determined by the conducted surveys tied to a geodetic control. It should be noted, however, that such a method of surveying the corners of building structures from linear measures is based on the details of the first-order accuracy, while the regulations explicitly allow such measurement only for the details of the second- and third-order accuracy. Therefore, a question arises whether this legal provision is unfounded, or whether surveyors are acting not only against the applicable standards but also without due diligence while performing surveys? This study provides answers to the formulated problem. The main purpose of the study was to verify whether the actual method which is used in practice for surveying building structures allows to obtain the required accuracy of coordinates of the points being determined, or whether it should be strictly forbidden. The results of the conducted studies clearly demonstrate that the problem is definitely more complex. Eventually, however, it might be assumed that assessment of the accuracy in determining a location of corners of a building using a combination of two different surveying methods will meet the requirements of the regulation [MIA, 2011), subject to compliance with relevant baseline criteria, which have been presented in this study. Observance of the proposed boundary conditions would allow for frequent performance of surveys of building structures by surveyors (from tie distances), while maintaining the applicable accuracy criteria. This would allow for the inclusion of surveying documentation into the national geodetic and cartographic documentation center database pursuant to the legal bases.

Optical Spectra of Extrasolar Giant Planets

NASA Technical Reports Server (NTRS)

Heap, Sara R.; Hubeny, Ivan; Sudarsky, David; Burrows, Adam

2004-01-01

The flux distribution of a planet relative to its host star is a critical quantity for planning space observatories to detect and characterize extrasolar giant planets (EGP's). In this paper, we present optical planet-star contrasts of Jupiter-mass planets as a function of stellar type, orbital distance, and planetary cloud characteristics. As originally shown by Sudarsky et al. (2000, 2003), the phaseaveraged brightness of an EGP does not necessarily decrease monotonically with greater orbital distance because of changes in its albedo and absorption spectrum at lower temperatures. We apply our results to Eclipse, a 1.8-m optical telescope + coronograph to be proposed as a NASA Discovery mission later this year.

A new method for solving reachable domain of spacecraft with a single impulse

NASA Astrophysics Data System (ADS)

Chen, Qi; Qiao, Dong; Shang, Haibin; Liu, Xinfu

2018-04-01

This paper develops a new approach to solve the reachable domain of a spacecraft with a single maximum available impulse. First, the distance in a chosen direction, started from a given position on the initial orbit, is formulated. Then, its extreme value is solved to obtain the maximum reachable distance in this direction. The envelop of the reachable domain in three-dimensional space is determined by solving the maximum reachable distance in all directions. Four scenarios are analyzed, including three typical scenarios (either the maneuver position or impulse direction is fixed, or both are arbitrary) and a new extended scenario (the maneuver position is restricted to an interval and the impulse direction is arbitrary). Moreover, the symmetry and the boundedness of the reachable domain are discussed in detail. The former is helpful to reduce the numerical computation, while the latter decides the maximum eccentricity of the initial orbit for a maximum available impulse. The numerical simulations verify the effectiveness of the proposed method for solving the reachable domain in all four scenarios. Especially, the reachable domain with a highly elliptical initial orbit can be determined successfully, which remains unsolved in the existing papers.

Assessment of Normal Eyeball Protrusion Using Computed Tomographic Imaging and Three-Dimensional Reconstruction in Korean Adults.

PubMed

Shin, Kang-Jae; Gil, Young-Chun; Lee, Shin-Hyo; Kim, Jeong-Nam; Yoo, Ja-Young; Kim, Soon-Heum; Choi, Hyun-Gon; Shin, Hyun Jin; Koh, Ki-Seok; Song, Wu-Chul

2017-01-01

The aim of the present study was to assess normal eyeball protrusion from the orbital rim using two- and three-dimensional images and demonstrate the better suitability of CT images for assessment of exophthalmos. The facial computed tomographic (CT) images of Korean adults were acquired in sagittal and transverse views. The CT images were used in reconstructing three-dimensional volume of faces using computer software. The protrusion distances from orbital rims and the diameters of eyeballs were measured in the two views of the CT image and three-dimensional volume of the face. Relative exophthalmometry was calculated by the difference in protrusion distance between the right and left sides. The eyeball protrusion was 4.9 and 12.5 mm in sagittal and transverse views, respectively. The protrusion distances were 2.9 mm in the three-dimensional volume of face. There were no significant differences between right and left sides in the degree of protrusion, and the difference was within 2 mm in more than 90% of the subjects. The results of the present study will provide reliable criteria for precise diagnosis and postoperative monitoring using CT imaging of diseases such as thyroid-associated ophthalmopathy and orbital tumors.

Small-Body Extensions for the Satellite Orbit Analysis Program (SOAP)

NASA Technical Reports Server (NTRS)

Carnright, Robert; Stodden, David; Coggi, John

2008-01-01

An extension to the SOAP software allows users to work with tri-axial ellipsoid-based representations of planetary bodies, primarily for working with small, natural satellites, asteroids, and comets. SOAP is a widely used tool for the visualization and analysis of space missions. The small body extension provides the same visualization and analysis constructs for use with small bodies. These constructs allow the user to characterize satellite path and instrument cover information for small bodies in both 3D display and numerical output formats. Tri-axial ellipsoids are geometric shapes the diameters of which are different in each of three principal x, y, and z dimensions. This construct provides a better approximation than using spheres or oblate spheroids (ellipsoids comprising two common equatorial diameters as a distinct polar diameter). However, the tri-axial ellipsoid is considerably more difficult to work with from a modeling perspective. In addition, the SOAP small-body extensions allow the user to actually employ a plate model for highly irregular surfaces. Both tri-axial ellipsoids and plate models can be assigned to coordinate frames, thus allowing for the modeling of arbitrary changes to body orientation. A variety of features have been extended to support tri-axial ellipsoids, including the computation and display of the spacecraft sub-orbital point, ground trace, instrument footprints, and swathes. Displays of 3D instrument volumes can be shown interacting with the ellipsoids. Longitude/latitude grids, contour plots, and texture maps can be displayed on the ellipsoids using a variety of projections. The distance along an arbitrary line of sight can be computed between the spacecraft and the ellipsoid, and the coordinates of that intersection can be plotted as a function of time. The small-body extension supports the same visual and analytical constructs that are supported for spheres and oblate spheroids in SOAP making the implementation of the more complex algorithms largely transparent to the user.

Design of Spacecraft Missions to Test Kinetic Impact for Asteroid Deflection

NASA Technical Reports Server (NTRS)

Hernandez, Sonia; Barbee, Brent W.

2011-01-01

There are currently over 8,000 known near-Earth asteroids (NEAs), and more are being discovered on a continual basis. More than 1,200 of these are classified as Potentially Hazardous Asteroids (PHAs) because their Minimum Orbit Intersection Distance (MOID) with Earth's orbit is <= 0.05 AU and their estimated diameters are >= 150 m. To date, 178 Earth impact structures have been discovered, indicating that our planet has previously been struck with devastating force by NEAs and will be struck again. Such collisions are aperiodic events and can occur at any time. A variety of techniques have been proposed to defend our planet from NEA impacts by deflecting the incoming asteroid. However, none of these techniques have been tested. Unless rigorous testing is conducted to produce reliable asteroid deflection systems, we will be forced to deploy completely untested -- and therefore unreliable -- deflection missions when a sizable asteroid on a collision course with Earth is discovered. Such missions will have a high probability of failure. We propose to address this problem with a campaign of deflection technology test missions deployed to harmless NEAs. The objective of these missions is to safely evaluate and refine the mission concepts and asteroid deflection system designs. Our current research focuses on the kinetic impactor, one of the simplest proposed asteroid deflection techniques in which a spacecraft is sent to collide with an asteroid at high relative velocity. By deploying test missions in the near future, we can characterize the performance of this deflection technique and resolve any problems inherent to its execution before needing to rely upon it during a true emergency. In this paper we present the methodology and results of our survey, including lists of NEAs for which safe and effective kinetic impactor test missions may be conducted within the next decade. Full mission designs are also presented for the NEAs which offer the best mission opportunities.

Copernican Mathematics: Calculating Periods and Distances of the Planets

ERIC Educational Resources Information Center

Rosenkrantz, Kurt J.

2004-01-01

The heliocentric, or Sun-centered model, one of the most important revolutions in scientific thinking, allowed Nicholas Copernicus to calculate the periods, relative distances, and approximate orbital shapes of all the known planets, thereby paving the way for Kepler's laws and Newton's formation of gravitation. Recreating Copernicus's…

DOE Office of Scientific and Technical Information (OSTI.GOV)

Telloni, Daniele; INFN Section in Florence, Via Giovanni Sansone 1, 50019 Sesto Fiorentino; Fabi, Michele

The aim of this work is to calculate the dose released by galactic cosmic rays (GCRs) and solar energetic particles (SEPs) in the polarimeter of the Multi Element Telescope for Imaging and Spectroscopy (METIS) coronagraph [1] aboard the Solar Orbiter. This investigation is performed with a Monte Carlo method by considering the role of SEP events of proper intensity at a heliocentric distance from the Sun averaged along the spacecraft orbit. Our approach can be extended to other space missions reaching short distances from the Sun, such as Solar Probe Plus. This study indicates that the deposited dose on themore » whole set of polarimeter lenses and filters during ten years of the Solar Orbiter mission is of about 2000 Gy. For cerium treated lenses, a dose of 10{sup 6} Gy of gamma radiation from a {sup 60}Co source causes a few percent transmittance loss.« less

Dust characteristics of dusty plasma ring of Saturn

NASA Astrophysics Data System (ADS)

Morooka, M.; Wahlund, J.-E.; Ye, S.-Y.; Persoon, A. M.; Kurth, W. S.

2017-09-01

During the Ring Grazing orbit, starting from December 2016, Cassini carried out twenty of the faint Saturn ring crossing observations at the distance of 2.45-2.51 RS (1RS 60,268 km) from Saturn center. We will show the electron and the ion density measurements of the RPWS/Langmuir Probe (LP) during these orbits. In most of the orbits significant ion/electron density differences have been observed, which indicates the presence of the charged nm and µm sized grains. The relationship between the observed charge densities and the electrical potential of the grains shows that the grains and the ambient electrons and ions are electro dynamical ensemble, a dusty plasma. The results show that characteristic dust size changes depending on the distance from the ring center. The result suggests that a dusty plasma state is related to the dynamics of the grain sizes.

Conceptual Design of a Communications Relay Satellite for a Lunar Sample Return Mission

NASA Technical Reports Server (NTRS)

Brunner, Christopher W.

2005-01-01

In 2003, NASA solicited proposals for a robotic exploration of the lunar surface. Submissions were requested for a lunar sample return mission from the South Pole-Aitken Basin. The basin is of interest because it is thought to contain some of the oldest accessible rocks on the lunar surface. A mission is under study that will land a spacecraft in the basin, collect a sample of rock fragments, and return the sample to Earth. Because the Aitken Basin is on the far side of the Moon, the lander will require a communications relay satellite (CRS) to maintain contact with the Earth during its surface operation. Design of the CRS's orbit is therefore critical. This paper describes a mission design which includes potential transfer and mission orbits, required changes in velocity, orbital parameters, and mission dates. Several different low lunar polar orbits are examined to compare their availability to the lander versus the distance over which they must communicate. In addition, polar orbits are compared to a halo orbit about the Earth-Moon L2 point, which would permit continuous communication at a cost of increased fuel requirements and longer transmission distances. This thesis also examines some general parameters of the spacecraft systems for the mission under study. Mission requirements for the lander dictate the eventual choice of mission orbit. This mission could be the first step in a period of renewed lunar exploration and eventual human landings.

Exocomet Orbit Fitting: Accelerating Coma Absorption During Transits of β Pictoris

NASA Astrophysics Data System (ADS)

Kennedy, Grant M.

2018-06-01

Comets are a remarkable feature in our night sky, visible on their passage through the inner Solar system as the Sun's energy sublimates ices and liberates surface material, generating beautiful comae, dust, and ion tails. Comets are also thought to orbit other stars, and are the most promising interpretation of sporadic absorption features (i.e. transits) seen in spectra of stars such as β Pictoris and 49 Ceti. These "exocomets" are thought to form and evolve in the same way as in the Solar system, and as in the Solar system we may gain insight into their origins by deriving their orbits. In the case of β Pictoris, orbits have been estimated indirectly, using the radial velocity of the absorption features coupled with a physical evaporation model to estimate the stellocentric distance at transit dtr. Here, we note that the inferred dtr imply that some absorption signatures should accelerate over several hours, and show that this acceleration is indeed seen in HARPS spectra. This new constraint means that orbital characteristics can be obtained directly, and the pericentre distance and longitude constrained when parabolic orbits are assumed. The results from fitting orbits to 12 accelerating features, and a handful of non-accelerating ones, are in broad agreement with previous estimates based on an evaporation model, thereby providing some validation of the exocomet hypothesis. A prediction of the evaporation model, that coma absorption is deeper for more distant transits, is also seen here.

Intelligent Patching of Conceptual Geometry for CFD Analysis

NASA Technical Reports Server (NTRS)

Li, Wu

2010-01-01

The iPatch computer code for intelligently patching surface grids was developed to convert conceptual geometry to computational fluid dynamics (CFD) geometry (see figure). It automatically uses bicubic B-splines to extrapolate (if necessary) each surface in a conceptual geometry so that all the independently defined geometric components (such as wing and fuselage) can be intersected to form a watertight CFD geometry. The software also computes the intersection curves of surface patches at any resolution (up to 10.4 accuracy) specified by the user, and it writes the B-spline surface patches, and the corresponding boundary points, for the watertight CFD geometry in the format that can be directly used by the grid generation tool VGRID. iPatch requires that input geometry be in PLOT3D format where each component surface is defined by a rectangular grid {(x(i,j), y(i,j), z(i,j)):1less than or equal to i less than or equal to m, 1 less than or equal to j less than or equal to n} that represents a smooth B-spline surface. All surfaces in the PLOT3D file conceptually represent a watertight geometry of components of an aircraft on the half-space y greater than or equal to 0. Overlapping surfaces are not allowed, but could be fixed by a utility code "fixp3d". The fixp3d utility code first finds the two grid lines on the two surface grids that are closest to each other in Hausdorff distance (a metric to measure the discrepancies of two sets); then uses one of the grid lines as the transition line, extending grid lines on one grid to the other grid to form a merged grid. Any two connecting surfaces shall have a "visually" common boundary curve, or can be described by an intersection relationship defined in a geometry specification file. The intersection of two surfaces can be at a conceptual level. However, the intersection is directional (along either i or j index direction), and each intersecting grid line (or its spine extrapolation) on the first surface should intersect the second surface. No two intersection relationships will result in a common intersection point of three surfaces. The output files of iPatch are IGES, d3m, and mapbc files that define the CFD geometry in VGRID format. The IGES file gives the NURBS definition of the outer mold line in the geometry. The d3m file defines how the outer mold line is broken into surface patches whose boundary curves are defined by points. The mapbc file specifies what the boundary condition is on each patch and the corresponding NURBS surface definition of each non-planar patch in the IGES file.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Lixin; Escala, Andres; Coppi, Paolo, E-mail: lixin.dai@yale.edu

We have carried out general relativistic particle simulations of stars tidally disrupted by massive black holes. When a star is disrupted in a bound orbit with moderate eccentricity instead of a parabolic orbit, the temporal behavior of the resulting stellar debris changes qualitatively. The debris is initially all bound, returning to pericenter in a short time about the original stellar orbital timescale. The resulting fallback rate can thus be much higher than the Eddington rate. Furthermore, if the star is disrupted close to the hole, in a regime where general relativity is important, the stellar and debris orbits display generalmore » relativistic precession. Apsidal precession can make the debris stream cross itself after several orbits, likely leading to fast debris energy dissipation. If the star is disrupted in an inclined orbit around a spinning hole, nodal precession reduces the probability of self-intersection, and circularization may take many dynamical timescales, delaying the onset of flare activity. An examination of the particle dynamics suggests that quasi-periodic flares with short durations, produced when the center of the tidal stream passes pericenter, may occur in the early-time light curve. The late-time light curve may still show power-law behavior which is generic to disk accretion processes. The detection triggers for future surveys should be extended to capture such 'non-standard' short-term flaring activity before the event enters the asymptotic decay phase, as this activity is likely to be more sensitive to physical parameters such as the black hole spin.« less

Ripples in Reality

ERIC Educational Resources Information Center

Lincoln, Don; Stuver, Amber

2016-01-01

In a deep and dark corner of space, a cataclysm loomed. Two cosmic nemeses circled one another, locked in a macabre dance of death. Unfolding over millennia, the deadly waltz began leisurely enough. But with the dance came radiation and the energy loss that it implies. Orbit after orbit, the distance between the two protagonists shrank as their…

High-Resolution Mars Camera Test Image of Moon (Infrared)

NASA Technical Reports Server (NTRS)

2005-01-01

This crescent view of Earth's Moon in infrared wavelengths comes from a camera test by NASA's Mars Reconnaissance Orbiter spacecraft on its way to Mars. The mission's High Resolution Imaging Science Experiment camera took the image on Sept. 8, 2005, while at a distance of about 10 million kilometers (6 million miles) from the Moon. The dark feature on the right is Mare Crisium. From that distance, the Moon would appear as a star-like point of light to the unaided eye. The test verified the camera's focusing capability and provided an opportunity for calibration. The spacecraft's Context Camera and Optical Navigation Camera also performed as expected during the test.

The Mars Reconnaissance Orbiter, launched on Aug. 12, 2005, is on course to reach Mars on March 10, 2006. After gradually adjusting the shape of its orbit for half a year, it will begin its primary science phase in November 2006. From the mission's planned science orbit about 300 kilometers (186 miles) above the surface of Mars, the high resolution camera will be able to discern features as small as one meter or yard across.

Late type close binary system CM Dra

NASA Astrophysics Data System (ADS)

Kalomeni, Belinda

2015-08-01

In this study, we present new observations of the close binary system CM Dra. We analyzed all the available data of the system and estimated the physical parameters of the system stars highly accurately. Using the newly obtained parameters the distance of the system is determined to be 11.6 pc. A possible giant planet orbiting the close binary system has been detected. This orbital period would likely make it one of the longest known orbital period planet.

LAREDO: LAunching, REndezvous and DOcking Simulation Tool

DTIC Science & Technology

2006-08-01

the Clohessy - Wiltshire equation for small eccentricities and relative distances, as shown in Eq. (12). z 2 y x 2 azz ax2y ay2x3x +−= +−= ++= ω ω...ωω && &&& &&& (12) In case of circular orbits, the LAREDO tool orbital maneuvers are all based on the Clohessy - Wiltshire equations4, where the set...Elliptical maneuvers guidance and control The Clohessy - Wiltshire equations described in the above section cannot be applied when the orbits have a

Preliminary Orbit and Differential Photometry of the Nearby Flare Star CR Dra

NASA Astrophysics Data System (ADS)

Tamazian, Vakhtang S.; Docobo, José A.; Balega, Yuri Y.; Melikian, Norair D.; Maximov, Alexander F.; Malogolovets, Evgeny V.

2008-09-01

New speckle measurements with the 6 m telescope of the Special Astrophysical Observatory (Russia) and the first preliminary orbit of the nearby flare star CR Dra (=Gl 616.2; WDS 16171+5516; BLA 3) with a period of 4.04 yr and a semimajor axis of 0farcs148 are reported. The Hipparcos parallax of 48.36 ± 1.16 mas (distance 20.7 pc) leads to an unusually large total mass of 1.8 M sun for a couple of red dwarfs. Meanwhile, the application of the Baize-Romani algorithm resulted in a mass sum of 1.00 M sun and a dynamical parallax of 58.43 mas (17.4 pc), which sensibly differs from that of Hipparcos. For the first time, we measured the photometric magnitude difference between the components (1.8 mag and 1.4 mag in the V and R bands, respectively) and obtained individual brightness estimates for each of them. Independently of the adopted parallax type, standard mass-luminosity relationships applied to individual components yield a total mass less than 1.2 M sun. This lends support to the use of a dynamical parallax, which is a more reliable distance estimate until a third body is discovered and/or our reported preliminary orbit is sensibly changed. CR Dra belongs to a handful of resolved short-period flare binaries, representing an excellent target to calculate a very accurate (or even definitive) orbit and a dynamical mass on a short time span. The available photometric data reveal no plausible correlation between flaring activity of CR Dra and linear distance between the components on the orbital path. Follow-up observations are needed for more detailed study of a possible relationship between dynamical and astrophysical properties of CR Dra and other similar systems.

Solar Cycle Changes in the Position of the Intermediate Transition in the Venus Ionosheath.

NASA Astrophysics Data System (ADS)

Perez De Tejada, H. A.; Lundin, R. N. A.; Durand-Manterola, H. J.; Reyes-Ruiz, M.; Barabash, S.; Zhang, T.; Sauvaud, J. A.

2014-12-01

Measurements conducted with the ASPERA plasma probe and the magnetometer of the Venus Express (VEX) spacecraft in orbits that probed by the midnight plane within the Venus wake show the presence of a sharp plasma transition outside the region where enhanced fluxes of planetary ions are observed. That transition agrees with a feature reported earlier [1] from the VEX electron measurements and that is now also characterized by a sharp change in the speed and density of the solar wind H+ ions [2]. From the analysis of the plasma data of 10 VEX orbits in two different time periods (August 2006 and September 2009) it is possible to derive the position of the VEX spacecraft at the time when the plasma transition is observed in all 10 orbits. The data show a collection of different distances downstream from Venus where the plasma transition is detected and that are grouped for each time period. As a whole the X-distance on the sun-Venus line downstream from the planet for each of the 5 orbits corresponding to the August 2006 time period is smaller than that corresponding to the 5 orbits of the September 2009 time period. The average distance difference between both sets of data points is nearly one half planetary radius thus leading to two different groups in their distribution. The position of the plasma transition downstream from Venus will vary along the solar cycle being displaced to regions that extend farther away from the inner wake under solar maximum conditions. [1] Pérez-de-Tejada, H.et al., JGR, 116, JA015216, 2011. [2] Pérez-de-Tejada, H.et al., JGR, 118, JA019029, 2013.

Werner-Wheeler mass tensor for fusionlike configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gherghescu, R.A.; Poenaru, D.N.

2005-08-01

The Werner-Wheeler approach is used to calculate the components of the mass tensor for a binary configuration of two intersected spheroids. Four free coordinates form the deformation space: the small semiaxis of the projectile, the two semiaxis ratios of the spheroids, and the distance between centers. A correction term is also calculated, due to the center of mass motion. Final results are presented for the fusion channel {sup 54}Cr+{sup 240}Pu, and all possible couplings are analyzed.

Characteristics of Organic-Metal Interaction: A Perspective from Bonding Distance to Orbital Delocalization

NASA Astrophysics Data System (ADS)

Kera, Satoshi; Hosokai, Takuya; Duhm, Steffen

2018-06-01

Understanding the mechanisms of energy-level alignment and charge transfer at the interface is one of the key issues in realizing organic electronics. However, the relation between the interface structure and the electronic structure is still not resolved in sufficient detail. An important character of materials used in organic electronics is the electronic localization of organic molecules at interfaces. To elucidate the impact of the molecular orbital distribution on the electronic structure, detailed structural information is required, particularly the vertical bonding distance at the interface, which is a signature of the interaction strength. We describe the recent progress in experimental studies on the impact of the molecule-metal interaction on the electronic structure of organic-metal interfaces by using various photoelectron spectroscopies, and review the results, focusing on the X-ray standing wave technique, to demonstrate the evaluation of the vertical bonding distance.

Detection of biomarkers for Hepatocellular Carcinoma using a hybrid univariate gene selection methods

PubMed Central

2012-01-01

Background Discovering new biomarkers has a great role in improving early diagnosis of Hepatocellular carcinoma (HCC). The experimental determination of biomarkers needs a lot of time and money. This motivates this work to use in-silico prediction of biomarkers to reduce the number of experiments required for detecting new ones. This is achieved by extracting the most representative genes in microarrays of HCC. Results In this work, we provide a method for extracting the differential expressed genes, up regulated ones, that can be considered candidate biomarkers in high throughput microarrays of HCC. We examine the power of several gene selection methods (such as Pearson’s correlation coefficient, Cosine coefficient, Euclidean distance, Mutual information and Entropy with different estimators) in selecting informative genes. A biological interpretation of the highly ranked genes is done using KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, ENTREZ and DAVID (Database for Annotation, Visualization, and Integrated Discovery) databases. The top ten genes selected using Pearson’s correlation coefficient and Cosine coefficient contained six genes that have been implicated in cancer (often multiple cancers) genesis in previous studies. A fewer number of genes were obtained by the other methods (4 genes using Mutual information, 3genes using Euclidean distance and only one gene using Entropy). A better result was obtained by the utilization of a hybrid approach based on intersecting the highly ranked genes in the output of all investigated methods. This hybrid combination yielded seven genes (2 genes for HCC and 5 genes in different types of cancer) in the top ten genes of the list of intersected genes. Conclusions To strengthen the effectiveness of the univariate selection methods, we propose a hybrid approach by intersecting several of these methods in a cascaded manner. This approach surpasses all of univariate selection methods when used individually according to biological interpretation and the examination of gene expression signal profiles. PMID:22867264

Waste Management Options for Long-Duration Space Missions: When to Reject, Reuse, or Recycle

NASA Technical Reports Server (NTRS)

Linne, Diane L.; Palaszewski, Bryan A.; Gokoglu, Suleyman; Gallo, Christopher A.; Balasubramaniam, Ramaswamy; Hegde, Uday G.

2014-01-01

The amount of waste generated on long-duration space missions away from Earth orbit creates the daunting challenge of how to manage the waste through reuse, rejection, or recycle. The option to merely dispose of the solid waste through an airlock to space was studied for both Earth-moon libration point missions and crewed Mars missions. Although the unique dynamic characteristics of an orbit around L2 might allow some discarded waste to intersect the lunar surface before re-impacting the spacecraft, the large amount of waste needed to be managed and potential hazards associated with volatiles recondensing on the spacecraft surfaces make this option problematic. A second option evaluated is to process the waste into useful gases to be either vented to space or used in various propulsion systems. These propellants could then be used to provide the yearly station-keeping needs at an L2 orbit, or if processed into oxygen and methane propellants, could be used to augment science exploration by enabling lunar mini landers to the far side of the moon.

Spin Dependence in Tidal Disruption Events

NASA Astrophysics Data System (ADS)

Kesden, Michael; Stone, Nicholas; van Velzen, Sjoert

2018-01-01

A supermassive black hole (SBH) can tidally disrupt stars when its tidal field overwhelms the stars’ self-gravity. The stellar debris produced in such tidal disruption events (TDEs) evolves into tidal streams that can self-intersect. These inelastic stream collisions dissipate orbital energy, both circularizing the tidal stream and contributing to the emission observed during the TDE. Once circularized into a disk, the stellar debris can be viscously accreted by the SBH powering additional luminous emission. We explore how SBH spin can affect the tidal disruption process. Tidal forces are spin dependent, as is the minimum orbital angular momentum below which stars are directly captured by the SBH. This implies that the TDE rate will be spin dependent, particularly for more massive SBHs for which relativistic effects are more significant. SBH spin also affects TDE light curves through the initial debris orbits, the nature of the stream collisions, the viscous evolution of the accretion disk, and the possibility of launching jets. We explore the spin dependence of these phenomena to identify promising signatures for upcoming surveys expected to discover hundreds of TDE candidates in the next decade.

Modeling left-turn crash occurrence at signalized intersections by conflicting patterns.

PubMed

Wang, Xuesong; Abdel-Aty, Mohamed

2008-01-01

In order to better understand the underlying crash mechanisms, left-turn crashes occurring at 197 four-legged signalized intersections over 6 years were classified into nine patterns based on vehicle maneuvers and then were assigned to intersection approaches. Crash frequency of each pattern was modeled at the approach level by mainly using Generalized Estimating Equations (GEE) with the Negative Binomial as the link function to account for the correlation among the crash data. GEE with a binomial logit link function was also applied for patterns with fewer crashes. The Cumulative Residuals test shows that, for correlated left-turn crashes, GEE models usually outperformed basic Negative Binomial models. The estimation results show that there are obvious differences in the factors that cause the occurrence of different left-turn collision patterns. For example, for each pattern, the traffic flows to which the colliding vehicles belong are identified to be significant. The width of the crossing distance (represented by the number of through lanes on the opposing approach of the left-turning traffic) is associated with more left-turn traffic colliding with opposing through traffic (Pattern 5), but with less left-turning traffic colliding with near-side crossing through traffic (Pattern 8). The safety effectiveness of the left-turning signal is not consistent for different crash patterns; "protected" phasing is correlated with fewer Pattern 5 crashes, but with more Pattern 8 crashes. The study indicates that in order to develop efficient countermeasures for left-turn crashes and improve safety at signalized intersections, left-turn crashes should be considered in different patterns.

Two-way laser ranging and time transfer experiments between LOLA and an Earth-based satellite laser ranging station

NASA Astrophysics Data System (ADS)

Mao, D.; Sun, X.; Neumann, G. A.; Barker, M. K.; Mazarico, E. M.; Hoffman, E.; Zagwodzki, T. W.; Torrence, M. H.; Mcgarry, J.; Smith, D. E.; Zuber, M. T.

2017-12-01

Satellite Laser Ranging (SLR) has established time-of-flight measurements with mm precision to targets orbiting the Earth and the Moon using single-ended round-trip laser ranging to passive optical retro-reflectors. These high-precision measurements enable advances in fundamental physics, solar system dynamics. However, the received signal strength suffers from a 1/R4 decay, which makes it impractical for measuring distances beyond the Moon's orbit. On the other hand, for a two-way laser transponder pair, where laser pulses are both transmitted to and received from each end of the laser links, the signal strength at both terminals only decreases by 1/R2, thus allowing a greater range of distances to be covered. The asynchronous transponder concept has been previously demonstrated by a test in 2005 between the Mercury Laser Altimeter (MLA) aboard the MESSENGER (MErcury Surface, Space ENvironment, Geochemistry, and Ranging) spacecraft and NASA's Goddard Geophysical and Astronomical Observatory (GGAO) at a distance of ˜0.16 AU. In October 2013, regular two-way transponder-type range measurements were obtained over 15 days between the Lunar Laser Communication Demonstration (LLCD) aboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft and NASA's ground station at White Sands, NM. The Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) provides us a unique capability to test time-transfer beyond near Earth orbit. Here we present results from two-way transponder-type experiments between LOLA and GGAO conducted in March 2014 and 2017. As in the time-transfer by laser link (T2L2) experiments between a ground station and an earth-orbiting satellite, LOLA and GGAO ranged to each other simultaneously in these two-way tests at lunar distance. We measured the time-of-flight while cross-referencing the spacecraft clock to the ground station time. On May 4th, 2017, about 20 minutes of two-way measurements were collected. The uplink observations were fit with a RMS residual of 9 ns, while the downlink observations yielded a RMS residual of 2 ns. The time offset between the spacecraft and ground station clocks as well as the spacecraft clock drift rate were determined from these measurements. More tests are expected in the coming months and the results will be reported.

Fast and accurate computation of system matrix for area integral model-based algebraic reconstruction technique

NASA Astrophysics Data System (ADS)

Zhang, Shunli; Zhang, Dinghua; Gong, Hao; Ghasemalizadeh, Omid; Wang, Ge; Cao, Guohua

2014-11-01

Iterative algorithms, such as the algebraic reconstruction technique (ART), are popular for image reconstruction. For iterative reconstruction, the area integral model (AIM) is more accurate for better reconstruction quality than the line integral model (LIM). However, the computation of the system matrix for AIM is more complex and time-consuming than that for LIM. Here, we propose a fast and accurate method to compute the system matrix for AIM. First, we calculate the intersection of each boundary line of a narrow fan-beam with pixels in a recursive and efficient manner. Then, by grouping the beam-pixel intersection area into six types according to the slopes of the two boundary lines, we analytically compute the intersection area of the narrow fan-beam with the pixels in a simple algebraic fashion. Overall, experimental results show that our method is about three times faster than the Siddon algorithm and about two times faster than the distance-driven model (DDM) in computation of the system matrix. The reconstruction speed of our AIM-based ART is also faster than the LIM-based ART that uses the Siddon algorithm and DDM-based ART, for one iteration. The fast reconstruction speed of our method was accomplished without compromising the image quality.

Near Earth Asteroids- Prospection, Orbit Modification and Mining

NASA Astrophysics Data System (ADS)

Grandl, W.; Bazso, A.

2014-04-01

The number of known Near Earth Asteroids (NEAs) has increased continuously during the last decades. Now we understand the role of asteroid impacts for the evolution of life on Earth. To ensure that mankind will survive in the long run, we have to face the "asteroid threat" seriously. On one hand we will have to develop methods of detection and deflection for Hazardous Asteroids, on the other hand we can use these methods to modify their orbits and exploit their resources. Rare-earth elements, rare metals like platinum group elements, etc. may be extracted more easily from NEAs than from terrestrial soil, without environmental pollution or political and social problems. In a first step NEAs, which are expected to contain resources like nickel-iron, platinum group metals or rare-earth elements, will be prospected by robotic probes. Then a number of asteroids with a minimum bulk density of 2 g/cm^3 and a diameter of 150 to 500 m will be selected for mining. Given the long duration of an individual mission time of 10-20 years, the authors propose a "pipeline" concept. While the observation of NEAs can be done in parallel, the precursor missions of the the next phase can be launched in short intervals, giving time for technical corrections and upgrades. In this way a continuous data flow is established and there are no idle times. For our purpose Potentially Hazardous Asteroids (PHAs) seem to be a favorable choice for the following reasons: They have frequent closeencounters to Earth, their minimum orbit intersection distance is less than 0.05 AU (Astronomic Units) and they have diameters exceeding 150 meters. The necessary velocity change (delta V) for a spaceship is below 12 km/s to reach the PHA. The authors propose to modify the orbits of the chosen PHAs by orbital maneuvers from solar orbits to stable Earth orbits beyond the Moon. To change the orbits of these celestial bodies it is necessary to develop advanced propulsion systems. They must be able to deliver high thrust and specific impulse to move the huge masses of the asteroids. Such a propulsion system could be the Bussard Fusion System, also known as the quiet-electricdischarge (QED) engine. It uses electrostatic fusion devices to generate electrical power. The fuel consists of Deuterium and Helium3 that are fusing to Helium4 plus protons releasing 18.3 MeV of energy per reaction. The charged protons escape from the confinement; their kinetic energy can be converted to electricity or be used directly as a plasma beam for generating thrust. For the reaction a specific energy of 3.5x1014 Joule/kg can be computed, i.e. orders-ofmagnitude higher than for any existing propulsion system. As an example we take the Asteroid with the designation 2008 EV5. It is classified as an Aten group asteroid with a mean diameter of 450 meters and belongs to spectral type S (stony asteroids). Our mass estimate (using a bulk density of 3 g/cm^3) is 1.4x1011 kg. To transfer 2008 EV5 to an Earth-like orbit the energy required is estimated to be in the order of 2.8x1018 Joule. This is the difference in Kepler energy between the NEA's current orbit and the Earth's orbit around the sun. Using the Bussard Fusion System the amount of fuel would be approx. 8000 kg of Helium3. To move an asteroid by remote control the authors propose to design unmanned space tugs which are propelled by Bussard Fusion Engines. A pair of space tugs is docked to each asteroid using drilling anchors. The fusion engines of the tugs then apply the thrust forces for the maneuvers. The first tug, which carries the main fuel quantity, applies the primary force for the orbital maneuvers. The second one adjust the flight track by short engine thrusts.

Guidance and Control System for a Satellite Constellation

NASA Technical Reports Server (NTRS)

Bryson, Jonathan Lamar; Cox, James; Mays, Paul Richard; Neidhoefer, James Christian; Ephrain, Richard

2010-01-01

A distributed guidance and control algorithm was developed for a constellation of satellites. The system repositions satellites as required, regulates satellites to desired orbits, and prevents collisions. 1. Optimal methods are used to compute nominal transfers from orbit to orbit. 2. Satellites are regulated to maintain the desired orbits once the transfers are complete. 3. A simulator is used to predict potential collisions or near-misses. 4. Each satellite computes perturbations to its controls so as to increase any unacceptable distances of nearest approach to other objects. a. The avoidance problem is recast in a distributed and locally-linear form to arrive at a tractable solution. b. Plant matrix values are approximated via simulation at each time step. c. The Linear Quadratic Gaussian (LQG) method is used to compute perturbations to the controls that will result in increased miss distances. 5. Once all danger is passed, the satellites return to their original orbits, all the while avoiding each other as above. 6. The delta-Vs are reasonable. The controller begins maneuvers as soon as practical to minimize delta-V. 7. Despite the inclusion of trajectory simulations within the control loop, the algorithm is sufficiently fast for available satellite computer hardware. 8. The required measurement accuracies are within the capabilities of modern inertial measurement devices and modern positioning devices.

Laser device

DOEpatents

Scott, Jill R [Idaho Falls, ID; Tremblay, Paul L [Idaho Falls, ID

2007-07-10

A laser device includes a target position, an optical component separated a distance J from the target position, and a laser energy source separated a distance H from the optical component, distance H being greater than distance J. A laser source manipulation mechanism exhibits a mechanical resolution of positioning the laser source. The mechanical resolution is less than a spatial resolution of laser energy at the target position as directed through the optical component. A vertical and a lateral index that intersect at an origin can be defined for the optical component. The manipulation mechanism can auto align laser aim through the origin during laser source motion. The laser source manipulation mechanism can include a mechanical index. The mechanical index can include a pivot point for laser source lateral motion and a reference point for laser source vertical motion. The target position can be located within an adverse environment including at least one of a high magnetic field, a vacuum system, a high pressure system, and a hazardous zone. The laser source and an electro-mechanical part of the manipulation mechanism can be located outside the adverse environment. The manipulation mechanism can include a Peaucellier linkage.

Laser device

DOEpatents

Scott, Jill R.; Tremblay, Paul L.

2004-11-23

A laser device includes a target position, an optical component separated a distance J from the target position, and a laser energy source separated a distance H from the optical component, distance H being greater than distance J. A laser source manipulation mechanism exhibits a mechanical resolution of positioning the laser source. The mechanical resolution is less than a spatial resolution of laser energy at the target position as directed through the optical component. A vertical and a lateral index that intersect at an origin can be defined for the optical component. The manipulation mechanism can auto align laser aim through the origin during laser source motion. The laser source manipulation mechanism can include a mechanical index. The mechanical index can include a pivot point for laser source lateral motion and a reference point for laser source vertical motion. The target position can be located within an adverse environment including at least one of a high magnetic field, a vacuum system, a high pressure system, and a hazardous zone. The laser source and an electro-mechanical part of the manipulation mechanism can be located outside the adverse environment. The manipulation mechanism can include a Peaucellier linkage.

Determination of celestial bodies orbits and probabilities of their collisions with the Earth

NASA Astrophysics Data System (ADS)

Medvedev, Yuri; Vavilov, Dmitrii

In this work we have developed a universal method to determine the small bodies orbits in the Solar System. In the method we consider different planes of body’s motion and pick up which is the most appropriate. Given an orbit plane we can calculate geocentric distances at time of observations and consequence determinate all orbital elements. Another technique that we propose here addresses the problem of estimation probability of collisions celestial bodies with the Earth. This technique uses the coordinate system associated with the nominal osculating orbit. We have compared proposed technique with the Monte-Carlo simulation. Results of these methods exhibit satisfactory agreement, whereas, proposed method is advantageous in time performance.

New Hypervelocity Terminal Intercept Guidance Systems for Deflecting/Disrupting Hazardous Asteroids

NASA Astrophysics Data System (ADS)

Lyzhoft, Joshua Richard

Computational modeling and simulations of visual and infrared (IR) sensors are investigated for a new hypervelocity terminal guidance system of intercepting small asteroids (50 to 150 meters in diameter). Computational software tools for signal-to-noise ratio estimation of visual and IR sensors, estimation of minimum and maximum ranges of target detection, and GPU (Graphics Processing Units)-accelerated simulations of the IR-based terminal intercept guidance systems are developed. Scaled polyhedron models of known objects, such as the Rosetta mission's Comet 67P/C-G, NASA's OSIRIS-REx Bennu, and asteroid 433 Eros, are utilized in developing a GPU-based simulation tool for the IR-based terminal intercept guidance systems. A parallelized-ray tracing algorithm for simulating realistic surface-to-surface shadowing of irregular-shaped asteroids or comets is developed. Polyhedron solid-angle approximation is also considered. Using these computational models, digital image processing is investigated to determine single or multiple impact locations to assess the technical feasibility of new planetary defense mission concepts of utilizing a Hypervelocity Asteroid Intercept Vehicle (HAIV) or a Multiple Kinetic-energy Interceptor Vehicle (MKIV). Study results indicate that the IR-based guidance system outperforms the visual-based system in asteroid detection and tracking. When using an IR sensor, predicting impact locations from filtered images resulted in less jittery spacecraft control accelerations than conducting missions with a visual sensor. Infrared sensors have also the possibility to detect asteroids at greater distances, and if properly used, can aid in terminal phase guidance for proper impact location determination for the MKIV system. Emerging new topics of the Minimum Orbit Intersection Distance (MOID) estimation and the Full-Two-Body Problem (F2BP) formulation are also investigated to assess a potential near-Earth object collision risk and the proximity gravity effects of an irregular-shaped binary-asteroid target on a standoff nuclear explosion mission.

An orbital angular momentum radio communication system optimized by intensity controlled masks effectively: Theoretical design and experimental verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Xinlu; Applied Optics Beijing Area Major Laboratory, Department of Physics, Beijing Normal University, Beijing 100875; Huang, Shanguo, E-mail: shghuang@bupt.edu.cn

A system of generating and receiving orbital angular momentum (OAM) radio beams, which are collectively formed by two circular array antennas (CAAs) and effectively optimized by two intensity controlled masks, is proposed and experimentally investigated. The scheme is effective in blocking of the unwanted OAM modes and enhancing the power of received radio signals, which results in the capacity gain of system and extended transmission distance of the OAM radio beams. The operation principle of the intensity controlled masks, which can be regarded as both collimator and filter, is feasible and simple to realize. Numerical simulations of intensity and phasemore » distributions at each key cross-sectional plane of the radio beams demonstrate the collimated results. The experimental results match well with the theoretical analysis and the receive distance of the OAM radio beam at radio frequency (RF) 20 GHz is extended up to 200 times of the wavelength of the RF signals, the measured distance is 5 times of the original measured distance. The presented proof-of-concept experiment demonstrates the feasibility of the system.« less

An introduction to shuttle/LDEF retrieval operations: The R-bar approach option. [orbital mechanics and braking schedule

NASA Technical Reports Server (NTRS)

Hall, W. M.

1978-01-01

Simulated orbiter direct approaches during long duration exposure facility (LDEF) retrieval operations reveal that the resultant orbiter jet plume fields can significantly disturb LDEF. An alternate approach technique which utilizes orbital mechanics forces in lieu of jets to brake the final orbiter/LDEF relative motion during the final approach, is described. Topics discussed include: rendezvous operations from the terminal phase initiation burn through braking at some standoff distance from LDEF, pilot and copilot activities, the cockpit instrumentation employed, and a convenient coordinate frame for studying the relative motion between two orbiting bodies. The basic equations of motion for operating on the LDEF radius vector are introduced. Practical considerations of implementing an R-bar approach, namely, orbiter/LDEF relative state uncertainties and orbiter control system limitations are explored. A possible R-bar approach strategy is developed and demonstrated.

The asteroid 2014 JO25

NASA Astrophysics Data System (ADS)

Vodniza, Alberto; Pereira, Mario

2017-10-01

The asteroid 2014 JO25 was discovered by A. D. Grauer at the Mt. Lemmon Survey on May 2014, and Joe Masiero used observations from the NEOWISE in 2014 to estimate a diameter of 650 meters [1]. However, using the radio telescope at Arecibo-Puerto Rico, astronomers obtained radar images on April 17-2017 and Edgar Rivera Valentín (scientist at Arecibo) said: “We found 2014 JO25 is a contact binary asteroid, two space rocks that were originally separate bodies, and each segment is about 640 meters and 670 meters, for a total of about 1.3 km long. Its rotation is of 3.5 hours” [2]. This asteroid flew past Earth on April 19 at a distance of about 4.6 lunar distances from the Earth. This was the closest approach by an asteroid since 4179 Toutatis. Toutatis flew past Earth on September 2004 at a distance of about 4 lunar distances from the Earth [3]. In April 12-2020 the asteroid will be at a minimum possible distance of 0.1617280 A.U from Earth [4]. From our observatory, located in Pasto-Colombia, we obtained a lot of pictures. Our data was published by the Minor Planet Center [5] and also appears at the web page of NEODyS [6]. Astrometry and photometry were carried out, and we calculated the orbital elements. We obtained the following orbital parameters: eccentricity=0.88454+/-0.00152, semi-major axis= 2.0573+/- 0.0216 A.U, orbital inclination=25.22+/-0.10 deg, longitude of the ascending node =30.6530+/-0.0032 deg, argument of perihelion=49.586+/-0.012 deg, mean motion = 0.33402+/-0.00527 deg/d, perihelion distance=0.237524+/-0.000644 A.U, aphelion distance=3.8770+/-0.0449 A.U, absolute magnitude =18.1. The parameters were calculated based on 164 observations. Dates: 2017 April: 22 to 24 with mean residual=0.22 arcseconds.The asteroid has an orbital period of 2.95 years.[1] https://echo.jpl.nasa.gov/asteroids/2014JO25/2014JO25_planning.html[2] http://earthsky.org/astronomy-essentials/large-asteroid-2014-jo25-close-april-19-2017-how-to-see[3] https://cneos.jpl.nasa.gov/news/news196.html[4] http://newton.dm.unipi.it/neodys/index.php?pc=1.1.8&n=2014JO25[5] http://www.minorplanetcenter.net/db_search/show_object?utf8=%E2%9C%93&object_id=2014+JO25[6] http://newton.dm.unipi.it/neodys/index.php?pc=2.1.2&o=H78&ab=8

Restricted Hartree Fock using complex-valued orbitals: A long-known but neglected tool in electronic structure theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Small, David W.; Sundstrom, Eric J.; Head-Gordon, Martin

2015-01-14

Restricted Hartree Fock using complex-valued orbitals (cRHF) is studied. We introduce an orbital pairing theorem, with which we obtain a concise connection between cRHF and real-valued RHF, and use it to uncover the close relationship between cRHF, unrestricted Hartree Fock, and generalized valence bond perfect pairing. This enables an intuition for cRHF, contrasting with the generally unintuitive nature of complex orbitals. We also describe an efficient computer implementation of cRHF and its corresponding stability analysis. By applying cRHF to the Be + H{sub 2} insertion reaction, a Woodward-Hoffmann violating reaction, and a symmetry-driven conical intersection, we demonstrate in genuine molecularmore » systems that cRHF is capable of removing certain potential energy surface singularities that plague real-valued RHF and related methods. This complements earlier work that showed this capability in a model system. We also describe how cRHF is the preferred RHF method for certain radicaloid systems like singlet oxygen and antiaromatic molecules. For singlet O{sub 2}, we show that standard methods fail even at the equilibrium geometry. An implication of this work is that, regardless of their individual efficacies, cRHF solutions to the HF equations are fairly commonplace.« less

Advanced Strain-Isolation-Pad Material with Bonded Fibrous Construction

NASA Technical Reports Server (NTRS)

Seibold, R. W.; Saito, C. A.; Buller, B. W.

1982-01-01

The feasibility of utilizing air lay and liquid lay felt deposition techniques to fabricate strain isolation pad (SIP) materials for the Space Shuttle Orbiter was demonstrated. These materials were developed as candidate replacements for the present needled felt SIP used between the ceramic tiles and the aluminum skin on the undersurface of the Orbiter. The SIP materials that were developed consisted of high temperature aramid fibers deposited by controlled fluid (air or liquid) carriers to form low density unbonded felts. The deposited felts were then bonded at the fiber intersections with a small amount of high temperature polyimide resin. This type of bonded felt construction can potentially eliminate two of the problems associated with the present SIP, viz., transmittal of localized stresses into the tiles and load history dependent mechanical response. However, further work is needed to achieve adequate through thickness tensile strength in the bonded felts.

Flow-field surveys on the windward side of the NASA 040A space shuttle orbiter at 31 deg angle of attack and Mach 20 in helium

NASA Technical Reports Server (NTRS)

Ashby, G. C., Jr.; Helms, V. T., III

1977-01-01

Pitot pressure and flow angle distributions in the windward flow field of the NASA 040A space shuttle orbiter configuration and surface pressures were measured, at a Mach number of 20 and an angle of attack of 31 deg. The free stream Reynolds number, based on model length, was 5.39 x 10 to the 6th power. Results show that cores of high pitot pressure, which are related to the body-shock-wing-shock intersections, occur on the windward plane of symmetry in the vicinity of the wing-body junction and near midspan on the wing. Theoretical estimates of the flow field pitot pressures show that conical flow values for the windward plane of symmetry surface are representative of the average level over the entire lower surface.

Communication: Multiple-property-based diabatization for open-shell van der Waals molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karman, Tijs; Avoird, Ad van der; Groenenboom, Gerrit C., E-mail: gerritg@theochem.ru.nl

2016-03-28

We derive a new multiple-property-based diabatization algorithm. The transformation between adiabatic and diabatic representations is determined by requiring a set of properties in both representations to be related by a similarity transformation. This set of properties is determined in the adiabatic representation by rigorous electronic structure calculations. In the diabatic representation, the same properties are determined using model diabatic states defined as products of undistorted monomer wave functions. This diabatic model is generally applicable to van der Waals molecules in arbitrary electronic states. Application to locating seams of conical intersections and collisional transfer of electronic excitation energy is demonstrated formore » O{sub 2} − O{sub 2} in low-lying excited states. Property-based diabatization for this test system included all components of the electric quadrupole tensor, orbital angular momentum, and spin-orbit coupling.« less

Nanoscale multireference quantum chemistry: full configuration interaction on graphical processing units.

PubMed

Fales, B Scott; Levine, Benjamin G

2015-10-13

Methods based on a full configuration interaction (FCI) expansion in an active space of orbitals are widely used for modeling chemical phenomena such as bond breaking, multiply excited states, and conical intersections in small-to-medium-sized molecules, but these phenomena occur in systems of all sizes. To scale such calculations up to the nanoscale, we have developed an implementation of FCI in which electron repulsion integral transformation and several of the more expensive steps in σ vector formation are performed on graphical processing unit (GPU) hardware. When applied to a 1.7 × 1.4 × 1.4 nm silicon nanoparticle (Si72H64) described with the polarized, all-electron 6-31G** basis set, our implementation can solve for the ground state of the 16-active-electron/16-active-orbital CASCI Hamiltonian (more than 100,000,000 configurations) in 39 min on a single NVidia K40 GPU.

Former 9th and possible future 9th planet in the Solar system

NASA Astrophysics Data System (ADS)

Vidmachenko, A. P.

2016-12-01

4 terrestrial planets and 4 giant planets were formed in the Solar system. The Main asteroid belt is located between them, and the Kuiper belt and Oort cloud are located beyond the giant planets. Therefore, the planetary system is surrounded by a swarm of rocky-icy bodies up to a distance of 105 AU. The former 9th planet in the Solar system, Pluto, is the first known object of the Kuiper Belt. Due to data from the spacecraft "New Horizons" we made significant progress in the study of the physical characteristics of the object and its surface. Numerous observations have shown that the Kuiper belt itself is dynamically stable. And the source of cometary nuclei is a disk scattered by the gravitational perturbation of the giant planets more than 4 billion years ago. Recently, it was reported on indirect evidence of the existence of a new 9th planet in the Solar system with a mass 10 times greater than the mass of the Earth, a distance from the Sun ∼200 AU at perihelion, 600-1200 AU at aphelion, and an orbital period of ∼15000 years. These conclusions are based on the calculation of the orbits of 6 presently known objects of the scattered disc. We pay attention that, in moments close to their discovery, they were located near the perihelion, had a maximum brightness and a maximum orbital velocity. On the basis of probabilistic assumptions, we estimated that the probable number of the same bodies with eccentric orbits should be estimated at many thousands rather than at a few. For the initial evaluation, we used observational data from the Infrared Space Telescope "WISE". They showed that any Saturn's analog has not been registered at distances up to 30 000 AU. Therefore, a super-Earth with a radius of <11000 km (with a mass of ∼10 Earth masses) would have been seen at a distance up to 1000 AU. Thus, either unknown 9th planet is now at a greater distance, or these results cannot be directly scaled to the super-Earth with a disproporti! onately lower internal heat reserves.

Hydrodynamic interaction of trapped active Janus particles in two dimensions

NASA Astrophysics Data System (ADS)

Debnath, Tanwi; Li, Yunyun; Ghosh, Pulak K.; Marchesoni, Fabio

2018-04-01

The dynamics of a pair of identical artificial microswimmers bound inside two harmonic traps, in a thin sheared fluid film, is numerically investigated. In a two-dimensional Oseen approximation, the hydrodynamic pair coupling is long-ranged and proportional to the particle radius to film thickness ratio. On increasing such ratio above a certain threshold, a transition occurs between a free regime, where each swimmer orbits in its own trap with random phase, and a strong synchronization regime, where the two swimmers strongly repel each other to an average distance larger than both the trap distance and their free orbit diameter. Moreover, the swimmers tend to synchronize their positions opposite the center of the system.

Effects of perturbations on space debris in supersynchronous storage orbits

NASA Astrophysics Data System (ADS)

Luu, Khanh Kim

1998-12-01

Accumulation of space debris in the geosynchronous region (GEO) has raised attention among spacefaring nations. The current mitigation measure supported is to boost satellites into supersynchronous orbits in the time before station-keeping fuel is expected to be exhausted. Because this solution does not remove mass from space, debris generation by fragmentation events remains a possibility. The collision hazard between inactive satellites in the supersynchronous region raises questions about the consequences of collisions in this regime and possible interaction with GEO. In considering the use of supersynchronous orbits for satellite disposal, the first concern is to determine the minimum safe distance above GEO such that objects in the disposal orbits will not interfere with the GEO population in the future. This involves defining the useful GEO area and studying the perturbation effects on objects in supersynchronous orbits. Thus far, research has focused on propagating the orbits of intact objects. However, in the aftermath of a collision, pieces of varying sizes and shapes can be found in orbits quite different from the parent objects' orbits. This document summarizes background information on debris in the GEO region, sources and management strategies, and then addresses the problem: Will orbits of fragments from a collision in a storage orbit occupy GEO altitudes at some time after the collision? If so, at what altitude should the storage orbit occupy such that collision fragments will not interfere with the GEO population? The methods and tools by which the effects of collisions in the supersynchronous region can be analyzed are discussed. A low-velocity collision model is employed to provide delta-velocities imparted to the fragments. An analytical study of perturbation effects, including solar and lunar third body gravitation, Earth oblateness through degree and order four, and solar radiation pressure, follows in order to evaluate the magnitude of these disturbing forces on the fragmentation debris. Validation of these results by numerical analysis using proven numerical and semianalytical orbit propagators is discussed. The results show that currently practiced reorbiting distances above GEO do not isolate debris from GEO after the occurrence of collisions in the storage orbit.

Signatures Of A Putative Planetary Mass Solar Companion On The Orbital Distribution Of Tno's And Centaurs

NASA Astrophysics Data System (ADS)

Gomes, Rodney S.; Soares, J. S.

2012-05-01

Gomes et al. 2006 (Icarus 184, 589) show that a planetary mass solar companion (PMSC) can produce orbits in an inner Oort cloud that can account for Sedna's orbit. On the other hand, one should expect that this faraway planet would also produce some peculiar orbital distribution for distant TNO's and Centaurs. A pair of interesting orbits in this respect are those of 2006 SQ372 and 2000 OO67. These objects have very large semimajor axes and perihelion between Uranus and Neptune orbits. It has been claimed that a likely source for 2006 SQ372 is the Oort cloud. Yet a PMSC has an important effect on objects at inner Oort cloud distances, say between 300 AU and 2000 AU, to make their perihelion distances to continually oscillate with a large enough amplitude to account for objects both inside and outside Neptune's orbit. This naturally produces an extra amount of TNO's with semimajor axes between 300 and 2000 AU and perihelion inside Neptune's orbit, like 2006 SQ372 and 2000 OO67. This signature should be found in present observations. To deal with this problem we construct a numerical simulator and apply it to populations of distant TNO's produced by numerical integration of planetesimals and planets according to the Nice model, either including or not a PMSC. With the results from the numerical simulator we compare the model with and without the PMSC with observations. We conclude that a PMSC is compatible with the existence of 2006 SQ372 and 2000 OO67 and, in fact, although not conclusively, we can also claim that the observations of 2006 SQ372 and 2000 OO67, compared to all other scattered objects, would be lucky events if no PMSC exists.

Atomic-scale visualization of surface-assisted orbital order

PubMed Central

Kim, Howon; Yoshida, Yasuo; Lee, Chi-Cheng; Chang, Tay-Rong; Jeng, Horng-Tay; Lin, Hsin; Haga, Yoshinori; Fisk, Zachary; Hasegawa, Yukio

2017-01-01

Orbital-related physics attracts growing interest in condensed matter research, but direct real-space access of the orbital degree of freedom is challenging. We report a first, real-space, imaging of a surface-assisted orbital ordered structure on a cobalt-terminated surface of the well-studied heavy fermion compound CeCoIn5. Within small tip-sample distances, the cobalt atoms on a cleaved (001) surface take on dumbbell shapes alternatingly aligned in the [100] and [010] directions in scanning tunneling microscopy topographies. First-principles calculations reveal that this structure is a consequence of the staggered dxz-dyz orbital order triggered by enhanced on-site Coulomb interaction at the surface. This so far overlooked surface-assisted orbital ordering may prevail in transition metal oxides, heavy fermion superconductors, and other materials. PMID:28948229

15. CONCRETE CHECK DAM NORTHWEST OF SOUTHEAST LAKE LADORA (SECTION ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

15. CONCRETE CHECK DAM NORTHWEST OF SOUTHEAST LAKE LADORA (SECTION 2) WITH THE FORMER EGLI FARM IN THE DISTANCE. - Highline Canal, Sand Creek Lateral, Beginning at intersection of Peoria Street & Highline Canal in Arapahoe County (City of Aurora), Sand Creek lateral Extends 15 miles Northerly through Araphoe County, City & County of Denver, & Adams County to its end point, approximately 1/4 mile Southest of intersectioin of D Street & Ninth Avenue in Adams County (Rocky Mountain Arsenal, Commerce City Vicinity), Commerce City, Adams County, CO

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

NASA Astrophysics Data System (ADS)

Jones, Geraint H.; Knight, Matthew M.; Battams, Karl; Boice, Daniel C.; Brown, John; Giordano, Silvio; Raymond, John; Snodgrass, Colin; Steckloff, Jordan K.; Weissman, Paul; Fitzsimmons, Alan; Lisse, Carey; Opitom, Cyrielle; Birkett, Kimberley S.; Bzowski, Maciej; Decock, Alice; Mann, Ingrid; Ramanjooloo, Yudish; McCauley, Patrick

2018-02-01

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun's centre, equal to half of Mercury's perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics.

The Generation of the Distant Kuiper Belt by Planet Nine from an Initially Broad Perihelion Distribution

NASA Astrophysics Data System (ADS)

Khain, Tali; Batygin, Konstantin; Brown, Michael E.

2018-04-01

The observation that the orbits of long-period Kuiper Belt objects are anomalously clustered in physical space has recently prompted the Planet Nine hypothesis - the proposed existence of a distant and eccentric planetary member of our Solar System. Within the framework of this model, a Neptune-like perturber sculpts the orbital distribution of distant Kuiper Belt objects through a complex interplay of resonant and secular effects, such that the surviving orbits get organized into apsidally aligned and anti-aligned configurations with respect to Planet Nine's orbit. We present results on the role of Kuiper Belt initial conditions on the evolution of the outer Solar System using numerical simulations. Intriguingly, we find that the final perihelion distance distribution depends strongly on the primordial state of the system, and demonstrate that a bimodal structure corresponding to the existence of both aligned and anti-aligned clusters is only reproduced if the initial perihelion distribution is assumed to extend well beyond 36 AU. The bimodality in the final perihelion distance distribution is due to the permanently stable objects, with the lower perihelion peak corresponding to the anti-aligned orbits and the higher perihelion peak corresponding to the aligned orbits. We identify the mechanisms that enable the persistent stability of these objects and locate the regions of phase space in which they reside. The obtained results contextualize the Planet Nine hypothesis within the broader narrative of solar system formation, and offer further insight into the observational search for Planet Nine.

Flyby of large-size space debris objects and their transition to the disposal orbits in LEO

NASA Astrophysics Data System (ADS)

Baranov, Andrey A.; Grishko, Dmitriy A.; Razoumny, Yury N.; Jun, Li

2017-06-01

The article focuses on the flyby issue involving large-size space debris (LSSD) objects in low Earth orbits. The data on overall sizes of the known upper-stages and last stages of launch-vehicles make it possible to emphasize five compact groups of such objects from the Satellite catalogue in 600-2000 km altitude interval. The flyby maneuvers are executed by a single space vehicle (SV) that transfers the current captured LSSD object to the specially selected circular or elliptical disposal orbit (DO) and after a period of time returns to capture a new one. The flight is always realized when a value of the Right Ascension of the Ascending Node (RAAN) is approximately the same for the current DO and for an orbit of the following LSSD object. Distinctive features of changes in mutual distribution of orbital planes of LSSD within a group are shown on the RAAN deviations' evolution portrait. In case of the first three groups (inclinations 71°, 74° and 81°), the lines describing the relative orientation of orbital planes are quasi-parallel. Such configuration allows easy identification of the flyby order within a group, and calculation of the mission duration and the required total ΔV. In case of the 4th and the 5th groups the RAAN deviations' evolution portrait represents a conjunction of lines chaotically intersecting. The article studies changes in mission duration and in the required ΔV depending on the catalogue number of the first object in the flyby order. The article also contains a comparative efficiency analysis of the two world-wide known schemes applicable to LSSD objects' de-orbiting; the analysis is carried out for all 5 distinguished LSSD groups.

The on-orbit calibration of geometric parameters of the Tian-Hui 1 (TH-1) satellite

NASA Astrophysics Data System (ADS)

Wang, Jianrong; Wang, Renxiang; Hu, Xin; Su, Zhongbo

2017-02-01

The on-orbit calibration of geometric parameters is a key step in improving the location accuracy of satellite images without using Ground Control Points (GCPs). Most methods of on-orbit calibration are based on the self-calibration using additional parameters. When using additional parameters, different number of additional parameters may lead to different results. The triangulation bundle adjustment is another way to calibrate the geometric parameters of camera, which can describe the changes in each geometric parameter. When triangulation bundle adjustment method is applied to calibrate geometric parameters, a prerequisite is that the strip model can avoid systematic deformation caused by the rate of attitude changes. Concerning the stereo camera, the influence of the intersection angle should be considered during calibration. The Equivalent Frame Photo (EFP) bundle adjustment based on the Line-Matrix CCD (LMCCD) image can solve the systematic distortion of the strip model, and obtain high accuracy location without using GCPs. In this paper, the triangulation bundle adjustment is used to calibrate the geometric parameters of TH-1 satellite cameras based on LMCCD image. During the bundle adjustment, the three-line array cameras are reconstructed by adopting the principle of inverse triangulation. Finally, the geometric accuracy is validated before and after on-orbit calibration using 5 testing fields. After on-orbit calibration, the 3D geometric accuracy is improved to 11.8 m from 170 m. The results show that the location accuracy of TH-1 without using GCPs is significantly improved using the on-orbit calibration of the geometric parameters.

September epsilon Perseid cluster as a result of orbital fragmentation

NASA Astrophysics Data System (ADS)

Koten, P.; Čapek, D.; Spurný, P.; Vaubaillon, J.; Popek, M.; Shrbený, L.

2017-04-01

Context. A bright fireball was observed above the Czech Republic on September 9, 2016, at 23:06:59 UT. Moreover, the video cameras at two different stations recorded eight fainter meteors flying on parallel atmospheric trajectories within less than 2 s. All the meteors belong to the September epsilon Perseid meteor shower. The measured proximity of all meteors during a very low activity meteor shower suggests that a cluster of meteors was observed. Aims: The goal of the paper is first to determine whether this event was a random occurrence or a real meteor cluster and second, if it was a cluster, to determine the epoch and at what distance from the Earth the separation of the particles occurred. Methods: The atmospheric trajectories of the observed meteors, masses, and relative distances of individual particles were determined using a double-station observation. According to the distances and masses of the particles, the most probable distance and time of fragmentation is determined. Results: The observed group of meteors is interpreted as the result of the orbital fragmentation of a bigger meteoroid. The fragmentation happened no earlier than 2 or 3 days before the encounter with the Earth at a distance smaller than 0.08 AU from the Earth.

Migration of comets to near-Earth space

NASA Astrophysics Data System (ADS)

Ipatov, S. I.

The orbital evolution of more than 21000 Jupiter-crossing objects under the gravitational influence of planets was investigated. For orbits close to that of Comet 2P, the mean collision probabilities of Jupiter-crossing objects with the terrestrial planets were greater by two orders of magnitude than for some other comets. For initial orbital elements close to those of Comets 2P, 10P, 44P, and 113P, a few objects (<0.1%) got Earth-crossing orbits with semi-major axes a<2 AU and aphelion distances Q<4.2 AU and moved in such orbits for more than 1 Myr (up to tens or even hundreds of Myrs). Some of them even got inner-Earth orbits (Q<0.983 AU) and Aten orbits for millions of years. Most former trans-Neptunian objects that have typical near-Earth object orbits moved in such orbits for millions of years, so during most of this time they were extinct comets or disintegrated into mini-comets.

Road facilitation of trematode infections in snails of northern Alaska.

PubMed

Urban, Mark C

2006-08-01

Road disturbances can influence wildlife health by spreading disease agents and hosts or by generating environmental conditions that sustain these agent and host populations. I evaluated field patterns of trematode infections in snails inhabiting ponds at varying distances from the Dalton Highway, a wilderness road that intersects northern Alaska. I also assessed the relationships between trematode infections and snail densities and six environmental variables: calcium concentration, aquatic vegetative cover canopy cover temperature, pond size, and community structure. Presence of trematode infections and snail density were negatively correlated with distance from the highway. Of the pond characteristics measured, only calcium concentration and vegetation density declined with distance from road. However neither variable was positively associated with snail density or trematode presence. One potential explanation for observed patterns is that vehicles, road maintenance, or vertebrate vectors attracted to the highway facilitate colonization of snails or trematodes. Emerging disease threats to biological diversity in northern ecosystems highlight the importance of understanding how roads affect disease transmission.

Distance-Based Phylogenetic Methods Around a Polytomy.

PubMed

Davidson, Ruth; Sullivant, Seth

2014-01-01

Distance-based phylogenetic algorithms attempt to solve the NP-hard least-squares phylogeny problem by mapping an arbitrary dissimilarity map representing biological data to a tree metric. The set of all dissimilarity maps is a Euclidean space properly containing the space of all tree metrics as a polyhedral fan. Outputs of distance-based tree reconstruction algorithms such as UPGMA and neighbor-joining are points in the maximal cones in the fan. Tree metrics with polytomies lie at the intersections of maximal cones. A phylogenetic algorithm divides the space of all dissimilarity maps into regions based upon which combinatorial tree is reconstructed by the algorithm. Comparison of phylogenetic methods can be done by comparing the geometry of these regions. We use polyhedral geometry to compare the local nature of the subdivisions induced by least-squares phylogeny, UPGMA, and neighbor-joining when the true tree has a single polytomy with exactly four neighbors. Our results suggest that in some circumstances, UPGMA and neighbor-joining poorly match least-squares phylogeny.

Evolution of the orbit of asteroid 4179 Toutatis over 11,550 years.

NASA Astrophysics Data System (ADS)

Zausaev, A. F.; Pushkarev, A. N.

1994-05-01

The Everhart method is used to study evolution of the orbit of the asteroid 4179 Toutatis, a member of the Apollo group, over the time period 9300 B.C. to 2250 A.D. Minimum asteroid-Earth distances during the evolution process are calculated. It is shown that the asteroid presents no danger to the Earth over the interval studied.

TRAPPIST-1 Statistics Table

NASA Image and Video Library

2017-02-22

This chart shows, on the top row, artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. On the bottom row, the same numbers are displayed for the bodies of our inner solar system: Mercury, Venus, Earth and Mars. The TRAPPIST-1 planets orbit their star extremely closely, with periods ranging from 1.5 to only about 20 days. This is much shorter than the period of Mercury, which orbits our sun in about 88 days. The artist concepts show what the TRAPPIST-1 planetary system may look like, based on available data about their diameters, masses and distances from the host star. The system has been revealed through observations from NASA's Spitzer Space Telescope and the ground-based TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) telescope, as well as other ground-based observatories. The system was named for the TRAPPIST telescope. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial, according to research published in 2017 in the journal Nature. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. http://photojournal.jpl.nasa.gov/catalog/PIA21425

Multiple attractors and boundary crises in a tri-trophic food chain.

PubMed

Boer, M P; Kooi, B W; Kooijman, S A

2001-02-01

The asymptotic behaviour of a model of a tri-trophic food chain in the chemostat is analysed in detail. The Monod growth model is used for all trophic levels, yielding a non-linear dynamical system of four ordinary differential equations. Mass conservation makes it possible to reduce the dimension by 1 for the study of the asymptotic dynamic behaviour. The intersections of the orbits with a Poincaré plane, after the transient has died out, yield a two-dimensional Poincaré next-return map. When chaotic behaviour occurs, all image points of this next-return map appear to lie close to a single curve in the intersection plane. This motivated the study of a one-dimensional bi-modal, non-invertible map of which the graph resembles this curve. We will show that the bifurcation structure of the food chain model can be understood in terms of the local and global bifurcations of this one-dimensional map. Homoclinic and heteroclinic connecting orbits and their global bifurcations are discussed also by relating them to their counterparts for a two-dimensional map which is invertible like the next-return map. In the global bifurcations two homoclinic or two heteroclinic orbits collide and disappear. In the food chain model two attractors coexist; a stable limit cycle where the top-predator is absent and an interior attractor. In addition there is a saddle cycle. The stable manifold of this limit cycle forms the basin boundary of the interior attractor. We will show that this boundary has a complicated structure when there are heteroclinic orbits from a saddle equilibrium to this saddle limit cycle. A homoclinic bifurcation to a saddle limit cycle will be associated with a boundary crisis where the chaotic attractor disappears suddenly when a bifurcation parameter is varied. Thus, similar to a tangent local bifurcation for equilibria or limit cycles, this homoclinic global bifurcation marks a region in the parameter space where the top-predator goes extinct. The 'Paradox of Enrichment' says that increasing the concentration of nutrient input can cause destabilization of the otherwise stable interior equilibrium of a bi-trophic food chain. For a tri-trophic food chain enrichment of the environment can even lead to extinction of the highest trophic level.

Detail view of the lower portion of the vertical stabilizer ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Detail view of the lower portion of the vertical stabilizer of the Orbiter Discovery. The section below the rudder, often referred to as the "stinger", is used to house the orbiter drag chute assembly. The system consisted of a mortar deployed pilot chute, the main drag chute, a controller assembly and an attach/jettison mechanism. This system was a modification to the original design of the Orbiter Discovery to safely reduce the roll to stop distance without adversely affecting the vehicle handling qualities. This view was taken from a service platform in the Orbiter Processing Facility at Kennedy Space Center. - Space Transportation System, Orbiter Discovery (OV-103), Lyndon B. Johnson Space Center, 2101 NASA Parkway, Houston, Harris County, TX

Radio Remote Sensing of Coronal Mass Ejections: Implications for Parker Solar Probe and Solar Orbiter

NASA Astrophysics Data System (ADS)

Kooi, J. E.; Thomas, N. C.; Guy, M. B., III; Spangler, S. R.

2017-12-01

Coronal mass ejections (CMEs) are fast-moving magnetic field structures of enhanced plasma density that play an important role in space weather. The Solar Orbiter and Parker Solar Probe will usher in a new era of in situ measurements, probing CMEs within distances of 60 and 10 solar radii, respectively. At the present, only remote-sensing techniques such as Faraday rotation can probe the plasma structure of CMEs at these distances. Faraday rotation is the change in polarization position angle of linearly polarized radiation as it propagates through a magnetized plasma (e.g. a CME) and is proportional to the path integral of the electron density and line-of-sight magnetic field. In conjunction with white-light coronagraph measurements, Faraday rotation observations have been used in recent years to determine the magnetic field strength of CMEs. We report recent results from simultaneous white-light and radio observations made of a CME in July 2015. We made radio observations using the Karl G. Jansky Very Large Array (VLA) at 1 - 2 GHz frequencies of a set of radio sources through the solar corona at heliocentric distances that ranged between 8 - 23 solar radii. These Faraday rotation observations provide a priori estimates for comparison with future in situ measurements made by the Solar Orbiter and Parker Solar Probe. Similar Faraday rotation observations made simultaneously with observations by the Solar Orbiter and Parker Solar Probe in the future could provide information about the global structure of CMEs sampled by these probes and, therefore, aid in understanding the in situ measurements.

Collisions with meteoroid streams as one possible mechanism for the formation of hyperbolic cometary orbits

NASA Astrophysics Data System (ADS)

Guliyev, Ayyub; Nabiyev, Shaig

2017-07-01

This paper presents the results of a statistical analysis of the dynamic parameters of 300 comets that have osculating hyperbolic orbits. It is shown that such comets differ from other comets by their large perihelion distances and by a predominance of retrograde motion. It is shown that the values of i, the inclination of the hyperbolic comets, are in comparative excess over the interval 90-120°. The dominance by q, the perihelion distance, renders it difficult to suggest that the excess hyperbolic velocity of these comets can be the result of physical processes that take place in their nuclei. Aspects of the following working hypothesis, that the hyperbolic excess of parameter e might be formed after comets pass through meteoroid streams, are also studied. To evaluate this hypothesis, the distribution of the orbits of hyperbolic comets relative to the plane of motion of 112 established meteoroid streams are analyzed. The number (N) of orbit nodes for hyperbolic comets with respect to the plane of each stream at various distances is calculated. To determine the degree of redundancy of N, a special computing algorithm was applied that provided the expected value nav as well as the standard deviation σ for the number of cometary nodes at the plane of each stream. A comparative analysis of the N and nav values that take σ into account suggests an excess in 40 stream cases. This implies that the passage of comets through meteoroid streams can lead to an acceleration of the comets' heliocentric velocity.

Some considerations on measuring the Newtonian gravitational constant G in an orbiting laboratory

NASA Technical Reports Server (NTRS)

Baker, Stephen D.

1986-01-01

A common suggestion for measuring the Newtonian gravitational constant G in a near-earth orbiting laboratory is simply to put two balls in orbit around each other and observe the resulting motion, thereby determining G. However, the radial variation with distance of the gravitational field of the earth is so large that tidal forces on the balls in near-earth orbit can be several times greater than the gravitational attraction between the two masses, leading some writers to assume that two objects will not stably orbit about each other and that this method of measuring G in low-earth is impossible, or at least impractical. Certain orbits were identified which are stable (at least over many periods of the spacecraft about the earth). In this case, the objects experience their gravitational interaction for a long time, and it becomes reasonable to consider such orbits as candidates for measurements of G.

Safety and Convergence Analysis of Intersecting Aircraft Flows Under Decentralized Collision Avoidance

NASA Astrophysics Data System (ADS)

Dallal, Ahmed H.

Safety is an essential requirement for air traffic management and control systems. Aircraft are not allowed to get closer to each other than a specified safety distance, to avoid any conflicts and collisions between aircraft. Forecast analysis predicts a tremendous increase in the number of flights. Subsequently, automated tools are needed to help air traffic controllers resolve air born conflicts. In this dissertation, we consider the problem of conflict resolution of aircraft flows with the assumption that aircraft are flowing through a fixed specified control volume at a constant speed. In this regard, several centralized and decentralized resolution rules have been proposed for path planning and conflict avoidance. For the case of two intersecting flows, we introduce the concept of conflict touches, and a collaborative decentralized conflict resolution rule is then proposed and analyzed for two intersecting flows. The proposed rule is also able to resolved airborne conflicts that resulted from resolving another conflict via the domino effect. We study the safety conditions under the proposed conflict resolution and collision avoidance rule. Then, we use Lyapunov analysis to analytically prove the convergence of conflict resolution dynamics under the proposed rule. The analysis show that, under the proposed conflict resolution rule, the system of intersecting aircraft flows is guaranteed to converge to safe, conflict free, trajectories within a bounded time. Simulations are provided to verify the analytically derived conclusions and study the convergence of the conflict resolution dynamics at different encounter angles. Simulation results show that lateral deviations taken by aircraft in each flow, to resolve conflicts, are bounded, and aircraft converged to safe and conflict free trajectories, within a finite time.

The geology of the Oceanographer Transform: The ridge-transform intersection

NASA Astrophysics Data System (ADS)

Karson, J. A.; Fox, P. J.; Sloan, H.; Crane, K. T.; Kidd, W. S. F.; Bonatti, E.; Stroup, J. B.; Fornari, D. J.; Elthon, D.; Hamlyn, P.; Casey, J. F.; Gallo, D. G.; Needham, D.; Sartori, R.

1984-06-01

Seven dives in the submersible ALVIN and four deep-towed (ANGUS) camera lowerings have been made at the eastern ridge-transform intersection of the Oceanographer Transform with the axis of the Mid-Atlantic Ridge. These data constrain our understanding of the processes that create and shape the distinctive morphology that is characteristic of slowly-slipping ridge-transform-ridge plate boundaries. Although the geological relationships observed in the rift valley floor in the study area are similar to those reported for the FAMOUS area, we observe a distinct change in the character of the rift valley floor with increasing proximity to the transform. Over a distance of approximately ten kilometers the volcanic constructional terrain becomes increasingly more disrupted by faulting and degraded by mass wasting. Moreover, proximal to the transform boundary, faults with orientations oblique to the trend of the rift valley are recognized. The morphology of the eastern rift valley wall is characterized by inward-facing scarps that are ridge-axis parallel, but the western rift valley wall, adjacent to the active transform zone, is characterized by a complex fault pattern defined by faults exhibiting a wide range of orientations. However, even for transform parallel faults no evidence for strike-slip displacement is observed throughout the study area and evidence for normal (dip-slip) displacement is ubiquitous. Basalts, semi-consolidated sediments (chalks, debris slide deposits) and serpentinized ultramafic rocks are recovered from localities within or proximal to the rift valley. The axis of accretion-principal transform displacement zone intersection is not clearly established, but appears to be located along the E-W trending, southern flank of the deep nodal basin that defines the intersection of the transform valley with the rift floor.

A conceptual framework for dynamic extension of the red clearance interval as a countermeasure for red-light-running.

PubMed

Gates, Timothy J; Noyce, David A

2016-11-01

This manuscript describes the development and evaluation of a conceptual framework for real-time operation of dynamic on-demand extension of the red clearance interval as a countermeasure for red-light-running. The framework includes a decision process for determining, based on the real-time status of vehicles arriving at the intersection, when extension of the red clearance interval should occur and the duration of each extension. A zonal classification scheme was devised to assess whether an approaching vehicle requires additional time to safely clear the intersection based on the remaining phase time, type of vehicle, current speed, and current distance from the intersection. Expected performance of the conceptual framework was evaluated through modeling of replicated field operations using vehicular event data collected as part of this research. The results showed highly accurate classification of red-light-running vehicles needing additional clearance time and relatively few false extension calls from stopping vehicles, thereby minimizing the expected impacts to signal and traffic operations. Based on the recommended parameters, extension calls were predicted to occur once every 26.5cycles. Assuming a 90scycle, 1.5 extensions per hour were expected per approach, with an estimated extension time of 2.30s/h. Although field implementation was not performed, it is anticipated that long-term reductions in targeted red-light-running conflicts and crashes will likely occur if red clearance interval extension systems are implemented at locations where start-up delay on the conflicting approach is generally minimal, such as intersections with lag left-turn phasing. Copyright © 2015 Elsevier Ltd. All rights reserved.

Tracking multiple surgical instruments in a near-infrared optical system.

PubMed

Cai, Ken; Yang, Rongqian; Lin, Qinyong; Wang, Zhigang

2016-12-01

Surgical navigation systems can assist doctors in performing more precise and more efficient surgical procedures to avoid various accidents. The near-infrared optical system (NOS) is an important component of surgical navigation systems. However, several surgical instruments are used during surgery, and effectively tracking all of them is challenging. A stereo matching algorithm using two intersecting lines and surgical instrument codes is proposed in this paper. In our NOS, the markers on the surgical instruments can be captured by two near-infrared cameras. After automatically searching and extracting their subpixel coordinates in the left and right images, the coordinates of the real and pseudo markers are determined by the two intersecting lines. Finally, the pseudo markers are removed to achieve accurate stereo matching by summing the codes for the distances between a specific marker with the other two markers on the surgical instrument. Experimental results show that the markers on the different surgical instruments can be automatically and accurately recognized. The NOS can accurately track multiple surgical instruments.

Development of Model for Pedestrian Gap Based on Land Use Pattern at Midblock Location and Estimation of Delay at Intersections

NASA Astrophysics Data System (ADS)

Ramesh, Adepu; Ashritha, Kilari; Kumar, Molugaram

2018-04-01

Walking has always been a prime source of human mobility for short distance travel. Traffic congestion has become a major problem for safe pedestrian crossing in most of the metropolitan cities. This has emphasized for providing a sufficient pedestrian gap for safe crossing on urban road. The present works aims in understanding factors that influence pedestrian crossing behaviour. Four locations were chosen for identification of pedestrian crossing behaviour, gap characteristics, waiting time etc., in Hyderabad city. From the study it was observed that pedestrian behaviour and crossing patterns are different and is influenced by land use pattern. A gap acceptance model was developed from the data for improving pedestrian safety at mid-block location; the model was validated using the existing data. Pedestrian delay was estimated at intersection using Highway Capacity Manual (HCM). It was observed that field delays are less when compared to delay arrived from HCM method.

Simulation of the effect of a magnetically insulated anode on a low-power cylindrical Hall thruster

NASA Astrophysics Data System (ADS)

Yongjie, DING; Hong, LI; Boyang, JIA; Peng, LI; Liqiu, WEI; Yu, XU; Wuji, PENG; Hezhi, SUN; Yong, CAO; Daren, YU

2018-03-01

The intersection point of the characteristic magnetic field line (CMFL) crossing the anode boundary with the discharge channel wall, and its influence on thruster performance and the energy and flux of ions bombarding the channel wall, have been studied numerically. The simulation results demonstrate that with the increase in distance from the crossover point of the CMFL with the channel wall to the bottom of the thruster channel, the ionization rate in the discharge channel gradually increases; meanwhile, the ion energy and ion current density bombarding the channel wall decreases. When the point of the CMFL with the channel wall is at the channel outlet, the thrust, specific impulse, and efficiency are at a maximum, while the ion energy and ion current density bombarding the channel wall are at a minimum. Therefore, to improve the performance and lifetime of the thruster, it is important to control the point of intersection of the CMFL with the channel wall.

Origin of the non-monotonic variance of Tc in the 1111 iron based superconductors with isovalent doping

PubMed Central

Usui, Hidetomo; Suzuki, Katsuhiro; Kuroki, Kazuhiko

2015-01-01

Motivated by recent experimental investigations of the isovalent doping iron-based superconductors LaFe(AsxP1-x)O1-yFy and NdFe(AsxP1-x)O1-yFy, we theoretically study the correlation between the local lattice structure, the Fermi surface, the spin fluctuation-mediated superconductivity, and the composition ratio. In the phosphides, the dXZ and dYZ orbitals barely hybridize around the Γ point to give rise to two intersecting ellipse shape Fermi surfaces. As the arsenic content increases and the Fe-As-Fe bond angle is reduced, the hybridization increases, so that the two bands are mixed to result in concentric inner and outer Fermi surfaces, and the orbital character gradually changes to dxz and dyz, where x–y axes are rotated by 45 degrees from X–Y. This makes the orbital matching between the electron and hole Fermi surfaces better and enhances the spin fluctuation within the dxz/yz orbitals. On the other hand, the hybridization splits the two bands, resulting in a more dispersive inner band. Hence, there is a trade-off between the density of states and the orbital matching, thereby locally maximizing the dxz/yz spin fluctuation and superconductivity in the intermediate regime of As/P ratio. The consistency with the experiment strongly indicate the importance of the spin fluctuation played in this series of superconductors. PMID:26073071

Lunar shadow eclipse prediction models for the Earth orbiting spacecraft: Comparison and application to LEO and GEO spacecrafts

NASA Astrophysics Data System (ADS)

Srivastava, Vineet K.; Kumar, Jai; Kulshrestha, Shivali; Srivastava, Ashutosh; Bhaskar, M. K.; Kushvah, Badam Singh; Shiggavi, Prakash; Vallado, David A.

2015-05-01

A solar eclipse occurs when the Sun, Moon and Earth are aligned in such a way that shadow of the Moon falls on the Earth. The Moon's shadow also falls on the Earth orbiting spacecraft. In this case, the alignment of the Sun, Moon, and spacecraft is similar to that of the Sun, Moon, and Earth but this phenomenon is often referred as a lunar eclipse falling on the spacecraft. Lunar eclipse is not as regular in terms of times of occurrence, duration, and depth as the Earth shadow eclipse and number of its occurrence per orbital location per year ranges from zero to four with an average of two per year; a spacecraft may experience two to three lunar eclipses within a twenty-four hour period [2]. These lunar eclipses can cause severe spacecraft operational problems. This paper describes two lunar shadow eclipse prediction models using a projection map approach and a line of intersection method by extending the Earth shadow eclipse models described by Srivastava et al. [10,11] for the Earth orbiting spacecraft. The attractive feature of both models is that they are much easier to implement. Both mathematical models have been simulated for two Indian low Earth orbiting spacecrafts: Oceansat-2, Saral-1, and two geostationary spacecrafts: GSAT-10, INSAT-4CR. Results obtained by the models compare well with lunar shadow model given by Escobal and Robertson [12], and high fidelity commercial software package, Systems Tool Kit (STK) of AGI.

Evaluation of minimum coverage size and orbital accuracy at different orbital regimes for one order of magnitude reduction of the catastrophic collision risk

NASA Astrophysics Data System (ADS)

Sánchez-Ortiz, Noelia; Domínguez-González, Raúl; Krag, Holger

2015-03-01

One of the main objectives of Space Surveillance and Tracking (SST) systems is to support space collision avoidance activities. This collision avoidance capability aims to significantly reduce the catastrophic collision risk of space objects. In particular, for the case of the future European SST, the objective is translated into a risk reduction of one order of magnitude whilst keeping a low number of false alarm events. In order to translate this aim into system requirements, an evaluation of the current catastrophic collision risk for different orbital regimes is addressed. The reduction of such risk depends on the amount of catalogued objects (coverage) and the knowledge of the associated orbits in the catalogue (accuracy). This paper presents an analysis of the impact of those two aspects in the capability to reduce the catastrophic collision risk at some orbital regimes. A reliable collision avoidance support depends on the accuracy of the predicted miss-events. The assessment of possible conjunctions is normally done by computing the estimated miss-distances between objects (which is compared with a defined distance threshold) or by computing the associated collision risk (which is compared with the corresponding accepted collision probability level). This second method is normally recommended because it takes into account the reliability of the orbits and allows reducing false alarm events. The collision risk depends on the estimated miss-distance, the object sizes and the accuracy of the two orbits at the time of event. This accuracy depends on the error of the orbits at the orbit determination epoch and the error derived from the propagation from that epoch up to the time of event. The modified DRAMA ARES (Domínguez-González et al., 2012, 2013a,b; Gelhaus et al., 2014) provides information on the expected number of encounters for a given mission and year. It also provides information on the capacity to reduce the risk of collision by means of avoidance manoeuvres as a function of the accepted collision probability level and the cataloguing performance of the surveillance system (determined by the limiting coverage size-altitude function and the orbital data accuracy). The assessment of avoidance strategies takes into account statistical models of the space object environment, as provided by ESA's MASTER-2009 model, and a mathematical framework for the collision risk estimation as used in satellite operations. In this papers, results are provided for some orbit types, covering different orbital regimes. The analysis is done for different cataloguing capacity levels (accuracy and coverage), concluding that 5 cm are to be covered at LEO for diminishing the catastrophic collision risk by one order of magnitude. For MEO and GEO regime, coverage down to 40 and 100 cm respectively allow similar reduction of risk.

The COS revolution of AGN outflow science

NASA Astrophysics Data System (ADS)

Arav, Nahum

2016-10-01

HST/COS has opened a new discovery space for quasar outflow science. Specifically, it provides high quality FUV spectra covering the diagnostic-rich 500A-1050A rest-frame of medium redshift objects. We have published three refereed papers based on the analysis of such data that were supported by our concluded COS archive program, in which we reported: a) a new population of very high ionization outflows, b) robust cases of two-ionization-phase outflows, which are the missing link between UV AGN outflows and x-ray warm absorbers, and most importantly c) spectral diagnostics that allowed us to determine the distance of the outflows from the central source. The latter is a cardinal issue in the field as many researchers believe that most outflows are situated close to the accretion disk ( 0.01 pc) while the few reliable measurements show distances of 10-10,000 pc. Therefore, every empirical distance measurement is of importance. Our archive based publication also demonstrates that quasar outflows have sufficient energy to match theoretical predictions for AGN feedback influencing galaxy evolution.We propose to continue this successful archive program. Thus far we've analyzed about 300 COS G130M and G160M orbits of AGN observations. There are roughly 900 additional orbits that satisfy our criteria and will be available within a year. Based on our published survey, we expect that these 900 orbits will yield about 20-30 additional very-high ionization outflows and 4-6 cases of distance and kinetic luminosity determinations, all in cosmologically important luminous-quasars.

Annual variations in the Martian bow shock location as observed by the Mars Express mission

NASA Astrophysics Data System (ADS)

Hall, B. E. S.; Lester, M.; Sánchez-Cano, B.; Nichols, J. D.; Andrews, D. J.; Edberg, N. J. T.; Opgenoorth, H. J.; Fränz, M.; Holmström, M.; Ramstad, R.; Witasse, O.; Cartacci, M.; Cicchetti, A.; Noschese, R.; Orosei, R.

2016-11-01

The Martian bow shock distance has previously been shown to be anticorrelated with solar wind dynamic pressure but correlated with solar extreme ultraviolet (EUV) irradiance. Since both of these solar parameters reduce with the square of the distance from the Sun, and Mars' orbit about the Sun increases by ˜0.3 AU from perihelion to aphelion, it is not clear how the bow shock location will respond to variations in these solar parameters, if at all, throughout its orbit. In order to characterize such a response, we use more than 5 Martian years of Mars Express Analyser of Space Plasma and EneRgetic Atoms (ASPERA-3) Electron Spectrometer measurements to automatically identify 11,861 bow shock crossings. We have discovered that the bow shock distance as a function of solar longitude has a minimum of 2.39RM around aphelion and proceeds to a maximum of 2.65RM around perihelion, presenting an overall variation of ˜11% throughout the Martian orbit. We have verified previous findings that the bow shock in southern hemisphere is on average located farther away from Mars than in the northern hemisphere. However, this hemispherical asymmetry is small (total distance variation of ˜2.4%), and the same annual variations occur irrespective of the hemisphere. We have identified that the bow shock location is more sensitive to variations in the solar EUV irradiance than to solar wind dynamic pressure variations. We have proposed possible interaction mechanisms between the solar EUV flux and Martian plasma environment that could explain this annual variation in bow shock location.

Mission Analysis and Orbit Control of Interferometric Wheel Formation Flying

NASA Astrophysics Data System (ADS)

Fourcade, J.

Flying satellite in formation requires maintaining the specific relative geometry of the spacecraft with high precision. This requirement raises new problem of orbit control. This paper presents the results of the mission analysis of a low Earth observation system, the interferometric wheel, patented by CNES. This wheel is made up of three receiving spacecraft, which follow an emitting Earth observation radar satellite. The first part of this paper presents trades off which were performed to choose orbital elements of the formation flying which fulfils all constraints. The second part presents orbit positioning strategies including reconfiguration of the wheel to change its size. The last part describes the station keeping of the formation. Two kinds of constraints are imposed by the interferometric system : a constraint on the distance between the wheel and the radar satellite, and constraints on the distance between the wheel satellites. The first constraint is fulfilled with a classical chemical station keeping strategy. The second one is fulfilled using pure passive actuators. Due to the high stability of the relative eccentricity of the formation, only the relative semi major axis had to be controlled. Differential drag due to differential attitude motion was used to control relative altitude. An autonomous orbit controller was developed and tested. The final accuracy is a relative station keeping better than few meters for a wheel size of one kilometer.

Accretional evolution of a planetesimal swarm. I - A new simulation

NASA Technical Reports Server (NTRS)

Spaute, Dominique; Weidenschilling, Stuart J.; Davis, Donald R.; Marzari, Francesco

1991-01-01

This novel simulation of planetary accretion simultaneously treats many interacting heliocentric distance zones and characterizes planetesimals via Keplerian elements. The numerical code employed, in addition to following the size distribution and the orbit-element distribution of a planetesimal swarm from arbitrary size and orbit distributions, treats a small number of the largest bodies as discrete objects with individual orbits. The accretion algorithm used yields good agreement with the analytic solutions; agreement is also obtained with the results of Weatherill and Stewart (1989) for gravitational accretion of planetesimals having equivalent initial conditions.

Periastron shifts of stellar orbits near the Galactic Center

NASA Astrophysics Data System (ADS)

Rubilar, G. F.; Eckart, A.

2001-07-01

The presence of a 2.9+/-0.4 million solar mass object in the central stellar cluster of the Milky Way has recently been demonstrated via measurements of the stellar proper motions and radial velocities. This mass is located at the position of the compact radio source Sagittarius A* (Sgr A*) at a distance of Ro=8.0 kpc and is most likely present in the form of a massive black hole (BH). Some of the stars have a projected distance to Sgr A* of <=0.005 pc and have proper motion velocities of up to 1400 km s-1. Recent measurements indicate that their orbits show significant curvatures indicating that the stars indeed orbit the central compact object. Detailed measurements of the stellar orbits close to Sgr A* will allow us to precisely determine the distribution of this mass. With an increased point source sensitivity due to the combination of large telescope apertures, adaptive optics, and - in the very near future - NIR interferometry it is likely that stars with orbital time scales of the order of one year will be detected. Theses sources, however, will most likely not be on simple Keplerian orbits. The effects of measurable prograde relativistic and retrograde Newtonian periastron shifts will result in rosetta shaped orbits. A substantial Newtonian periastron rotation can already be expected if only a few percent of the central mass are extended. We discuss the conditions under which an extended mass can (over-) compensate the relativistic periastron shift. We also demonstrate that measuring a single periastron shift is not sufficient to determine the distribution of an extended mass component. A periastron shift will allow us to determine the inclination of the stellar orbits and to derive inclination corrected shift values. These have to be acquired for three stars on orbits with different energy or angular momentum in order to unambiguously solve for the compactness, extent and shape of any extended mass contribution.

Orbiter/External Tank Mate 3-D Solid Modeling

NASA Technical Reports Server (NTRS)

Godfrey, G. S.; Brandt, B.; Rorden, D.; Kapr, F.

2004-01-01

This research and development project presents an overview of the work completed while attending a summer 2004 American Society of Engineering Education/National Aeronautics and Space Administration (ASEE/NASA) Faculty Fellowship. This fellowship was completed at the Kennedy Space Center, Florida. The scope of the project was to complete parts, assemblies, and drawings that could be used by Ground Support Equipment (GSE) personnel to simulate situations and scenarios commonplace to the space shuttle Orbiter/External Tank (ET) Mate (50004). This mate takes place in the Vehicle Assembly Building (VAB). These simulations could then be used by NASA engineers as decision-making tools. During the summer of 2004, parts were created that defined the Orbiter/ET structural interfaces. Emphasis was placed upon assemblies that included the Orbiter/ET forward attachment (EO-1), aft left thrust strut (EO-2), aft right tripod support structure (EO-3), and crossbeam and aft feedline/umbilical supports. These assemblies are used to attach the Orbiter to the ET. The Orbiter/ET Mate assembly was then used to compare and analyze clearance distances using different Orbiter hang angles. It was found that a 30-minute arc angle change in Orbiter hang angle affected distance at the bipod strut to Orbiter yoke fitting 8.11 inches. A 3-D solid model library was established as a result of this project. This library contains parts, assemblies, and drawings translated into several formats. This library contains a collection of the following files: sti for sterolithography, stp for neutral file work, shrinkwrap for compression. tiff for photoshop work, jpeg for Internet use, and prt and asm for Pro/Engineer use. This library was made available to NASA engineers so that they could access its contents to make angle, load, and clearance analysis studies. These decision-making tools may be used by Pro/Engineer users and non-users.

Toward a comprehensive theory for the sweeping of trapped radiation by inert orbiting matter

NASA Technical Reports Server (NTRS)

Fillius, Walker

1988-01-01

There is a need to calculate loss rates when trapped Van Allen radiation encounters inert orbiting material such as planetary rings and satellites. An analytic expression for the probability of a hit in a bounce encounter is available for all cases where the absorber is spherical and the particles are gyrotropically distributed on a cylindrical flux tube. The hit probability is a function of the particle's pitch angle, the size of the absorber, and the distance between the flux tube and the absorber when distances are scaled to the gyroradius of a particle moving perpendicular to the magnetic field. Using this expression, hit probabilities in drift encounters were computed for all regimes of particle energies and absorber sizes.

Optimal flight initiation distance.

PubMed

Cooper, William E; Frederick, William G

2007-01-07

Decisions regarding flight initiation distance have received scant theoretical attention. A graphical model by Ydenberg and Dill (1986. The economics of fleeing from predators. Adv. Stud. Behav. 16, 229-249) that has guided research for the past 20 years specifies when escape begins. In the model, a prey detects a predator, monitors its approach until costs of escape and of remaining are equal, and then flees. The distance between predator and prey when escape is initiated (approach distance = flight initiation distance) occurs where decreasing cost of remaining and increasing cost of fleeing intersect. We argue that prey fleeing as predicted cannot maximize fitness because the best prey can do is break even during an encounter. We develop two optimality models, one applying when all expected future contribution to fitness (residual reproductive value) is lost if the prey dies, the other when any fitness gained (increase in expected RRV) during the encounter is retained after death. Both models predict optimal flight initiation distance from initial expected fitness, benefits obtainable during encounters, costs of escaping, and probability of being killed. Predictions match extensively verified predictions of Ydenberg and Dill's (1986) model. Our main conclusion is that optimality models are preferable to break-even models because they permit fitness maximization, offer many new testable predictions, and allow assessment of prey decisions in many naturally occurring situations through modification of benefit, escape cost, and risk functions.

The limits of local correlation theory: electronic delocalization and chemically smooth potential energy surfaces.

PubMed

Subotnik, Joseph E; Sodt, Alex; Head-Gordon, Martin

2008-01-21

Local coupled-cluster theory provides an algorithm for measuring electronic correlation quickly, using only the spatial locality of localized electronic orbitals. Previously, we showed [J. Subotnik et al., J. Chem. Phys. 125, 074116 (2006)] that one may construct a local coupled-cluster singles-doubles theory which (i) yields smooth potential energy surfaces and (ii) achieves near linear scaling. That theory selected which orbitals to correlate based only on the distances between the centers of different, localized orbitals, and the approximate potential energy surfaces were characterized as smooth using only visual identification. This paper now extends our previous algorithm in three important ways. First, locality is now based on both the distances between the centers of orbitals as well as the spatial extent of the orbitals. We find that, by accounting for the spatial extent of a delocalized orbital, one can account for electronic correlation in systems with some electronic delocalization using fast correlation methods designed around orbital locality. Second, we now enforce locality on not just the amplitudes (which measure the exact electron-electron correlation), but also on the two-electron integrals themselves (which measure the bare electron-electron interaction). Our conclusion is that we can bump integrals as well as amplitudes, thereby gaining a tremendous increase in speed and paradoxically increasing the accuracy of our LCCSD approach. Third and finally, we now make a rigorous definition of chemical smoothness as requiring that potential energy surfaces not support artificial maxima, minima, or inflection points. By looking at first and second derivatives from finite difference techniques, we demonstrate complete chemical smoothness of our potential energy surfaces (bumping both amplitudes and integrals). These results are significant both from a theoretical and from a computationally practical point of view.

Two-Body Orbit Expansion Due to Time-Dependent Relative Acceleration Rate of the Cosmological Scale Factor

NASA Astrophysics Data System (ADS)

Iorio, Lorenzo

2014-01-01

By phenomenologically assuming a slow temporal variation of the percent acceleration rate S̈S -1 of the cosmic scale factor S(t), it is shown that the orbit of a local binary undergoes a secular expansion. To first order in the power expansion of S̈S -1 around the present epoch t0, a non-vanishing shift per orbit (Δr) of the two-body relative distance r occurs for eccentric trajectories. A general relativistic expression, which turns out to be cubic in the Hubble parameter H0 at the present epoch, is explicitly calculated for it in the case of matter-dominated epochs with Dark Energy. For a highly eccentric Oort comet orbit with period Pb ≈ 31 Myr, the general relativistic distance shift per orbit turns out to be of the order of (Δr) ≈ 70 km. For the Large Magellanic Cloud, assumed on a bound elliptic orbit around the Milky Way, the shift per orbit is of the order of (Δr) ≈ 2-4 pc. Our result has a general validity since it holds in any cosmological model admitting the Hubble law and a slowly varying S̈S-1(t). More generally, it is valid for an arbitrary Hooke-like extra-acceleration whose "elastic" parameter κ is slowly time-dependent, irrespectively of the physical mechanism which may lead to it. The coefficient κ1 of the first-order term of the power expansion of κ(t) can be preliminarily constrained in a model-independent way down to a κ1 ≤ 2 x 10-13 year-3 level from latest Solar System's planetary observations. The radial velocities of the double lined spectroscopic binary ALPHA Cen AB yield κ1 ≤ 10-8 year-3.

Geographically correlated orbit error

NASA Technical Reports Server (NTRS)

Rosborough, G. W.

1989-01-01

The dominant error source in estimating the orbital position of a satellite from ground based tracking data is the modeling of the Earth's gravity field. The resulting orbit error due to gravity field model errors are predominantly long wavelength in nature. This results in an orbit error signature that is strongly correlated over distances on the size of ocean basins. Anderle and Hoskin (1977) have shown that the orbit error along a given ground track also is correlated to some degree with the orbit error along adjacent ground tracks. This cross track correlation is verified here and is found to be significant out to nearly 1000 kilometers in the case of TOPEX/POSEIDON when using the GEM-T1 gravity model. Finally, it was determined that even the orbit error at points where ascending and descending ground traces cross is somewhat correlated. The implication of these various correlations is that the orbit error due to gravity error is geographically correlated. Such correlations have direct implications when using altimetry to recover oceanographic signals.

Atmospheric trajectory and heliocentric orbit of the Ejby meteorite fall in Denmark on February 6, 2016

NASA Astrophysics Data System (ADS)

Spurný, P.; Borovička, J.; Baumgarten, G.; Haack, H.; Heinlein, D.; Sørensen, A. N.

2017-09-01

A very bright bolide illuminated the sky over Denmark and neighboring countries on February 6th, 2016 at 21:07:18-23UT. It terminated by a multiple meteorite fall in the heavily populated area of the western outskirts of Copenhagen. Several meteorites classified as the H5/6 ordinary chondrites have been found shortly after the fall and total recovered mass reached almost 9 kg (Haack, 2016). Although this spectacular bolide has been reported by many casual witnesses, the instrumental records are very scarce, mainly due to bad weather over Denmark and neighboring countries. Despite it we were able to collect five instrumental records taken from different locations which were useful for the analysis of this event. We used three high resolution digital photographic images taken in Germany, one high resolution radiometric light curve taken by the northernmost Czech automated fireball observatory and one video record taken by a surveillance camera on the Danish west coast where a part of the fireball trajectory was recorded. It allowed us to reliably determine basic parameters defining the luminous trajectory of the bolide in the atmosphere and also heliocentric orbit of the initial meteoroid causing this spectacular meteorite fall. We found that this event was caused by a relatively fragile 50 cm meteoroid with initial mass about 250 kg. It entered the atmosphere with velocity of 14.5 km s-1 and quite steep entry angle of 62°. Its luminous flight started at 85.5 km and after 76 km long trajectory it terminated at 18.3 km. The heliocentric orbit of this meteoroid was of Apollo type with low inclination of 1° and perihelion distance just inside the Earth's orbit. It had a relatively large semimajor axis of 2.8 AU and aphelion distance 4.64 AU. It is the second largest aphelion distance among all meteorites with known orbits and the orbit had the same character as that of the Košice meteorite (H5 ordinary chondrite), which fell on February 28, 2010 (Borovička et al., 2013).

CONSTRAINING THE MILKY WAY POTENTIAL WITH A SIX-DIMENSIONAL PHASE-SPACE MAP OF THE GD-1 STELLAR STREAM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koposov, Sergey E.; Rix, Hans-Walter; Hogg, David W., E-mail: koposov@ast.cam.ac.u

2010-03-20

The narrow GD-1 stream of stars, spanning 60{sup 0} on the sky at a distance of {approx}10 kpc from the Sun and {approx}15 kpc from the Galactic center, is presumed to be debris from a tidally disrupted star cluster that traces out a test-particle orbit in the Milky Way halo. We combine Sloan Digital Sky Survey (SDSS) photometry, USNO-B astrometry, and SDSS and Calar Alto spectroscopy to construct a complete, empirical six-dimensional (6D) phase-space map of the stream. We find that an eccentric orbit in a flattened isothermal potential describes this phase-space map well. Even after marginalizing over the streammore » orbital parameters and the distance from the Sun to the Galactic center, the orbital fit to GD-1 places strong constraints on the circular velocity at the Sun's radius V{sub c} = 224 +- 13 km s{sup -1} and total potential flattening q{sub P}HI = 0.87{sup +0.07}{sub -0.04}. When we drop any informative priors on V{sub c} , the GD-1 constraint becomes V{sub c} = 221 +- 18 km s{sup -1}. Our 6D map of GD-1, therefore, yields the best current constraint on V{sub c} and the only strong constraint on q{sub P}HI at Galactocentric radii near R {approx} 15 kpc. Much, if not all, of the total potential flattening may be attributed to the mass in the stellar disk, so the GD-1 constraints on the flattening of the halo itself are weak: q{sub P}HI{sub ,halo} > 0.89 at 90% confidence. The greatest uncertainty in the 6D map and the orbital analysis stems from the photometric distances, which will be obviated by GAIA.« less

A comprehensive analysis of ion cyclotron waves in the equatorial magnetosphere of Saturn

NASA Astrophysics Data System (ADS)

Meeks, Zachary; Simon, Sven; Kabanovic, Slawa

2016-09-01

We present a comprehensive analysis of ion cyclotron waves in the equatorial magnetosphere of Saturn, considering all magnetic field data collected during the Cassini era (totaling to over 4 years of data from the equatorial plane). This dataset includes eight targeted flybys of Enceladus, three targeted flybys of Dione, and three targeted flybys of Rhea. Because all remaining orbits of Cassini are high-inclination, our study provides the complete map of ion cyclotron waves in Saturn's equatorial magnetosphere during the Cassini era. We provide catalogs of the radial and longitudinal dependencies of the occurrence rate and amplitude of the ion cyclotron fundamental and first harmonic wave modes. The fundamental wave mode is omnipresent between the orbits of Enceladus and Dione and evenly distributed across all Local Times. The occurrence rate of the fundamental mode displays a Fermi-Dirac-like profile with respect to radial distance from Saturn. Detection of the first harmonic mode is a rare event occurring in only 0.49% of measurements taken and always in conjunction with the fundamental mode. We also search for a dependency of the ion cyclotron wave field on the orbital positions of the icy moons Enceladus, Dione, and Rhea. On magnetospheric length scales, the wave field is independent of the moons' orbital positions. For Enceladus, we analyze wave amplitude profiles of seven close flybys (E9, E12, E13, E14, E17, E18, and E19), which occurred during the studied trajectory segments, to look for any local effects of Enceladan plume variability on the wave field. We find that even in the close vicinity of Enceladus, the wave amplitudes display no discernible dependency on Enceladus' angular distance to its orbital apocenter. Thus, the correlation between plume activity and angular distance to apocenter proposed by Hedman et al. (2013) does not leave a clearly distinguishable imprint in the ion cyclotron wave field.

Exact Analytic Solution for a Ballistic Orbiting Wind

NASA Astrophysics Data System (ADS)

Wilkin, Francis P.; Hausner, Harry

2017-07-01

Much theoretical and observational work has been done on stellar winds within binary systems. We present a new solution for a ballistic wind launched from a source in a circular orbit. The solution is that of a single wind—no second wind is included in the system and the shocks that arise are those due to the orbiting wind interacting with itself. Our method emphasizes the curved streamlines in the corotating frame, where the flow is steady-state, allowing us to obtain an exact solution for the mass density at all pre-shock locations. Assuming an initially isotropic wind, fluid elements launched from the interior hemisphere of the wind will be the first to cross other streamlines, resulting in a spiral structure bounded by two shock surfaces. Streamlines from the outer wind hemisphere later intersect these shocks as well. An analytic solution is obtained for the geometry of the two shock surfaces. Although the inner and outer shock surfaces asymptotically trace Archimedean spirals, our tail solution suggests many crossings where the shocks overlap, beyond which the analytic solution cannot be continued. Our solution can be readily extended to an initially anisotropic wind.

Formation flying for electric sails in displaced orbits. Part I: Geometrical analysis

NASA Astrophysics Data System (ADS)

Wang, Wei; Mengali, Giovanni; Quarta, Alessandro A.; Yuan, Jianping

2017-09-01

We present a geometrical methodology for analyzing the formation flying of electric solar wind sail based spacecraft that operate in heliocentric, elliptic, displaced orbits. The spacecraft orbit is maintained by adjusting its propulsive acceleration modulus, whose value is estimated using a thrust model that takes into account a variation of the propulsive performance with the sail attitude. The properties of the relative motion of the spacecraft are studied in detail and a geometrical solution is obtained in terms of relative displaced orbital elements, assumed to be small quantities. In particular, for the small eccentricity case (i.e. for a near-circular displaced orbit), the bounds characterized by the extreme values of relative distances are analytically calculated, thus providing an useful mathematical tool for preliminary design of the spacecraft formation structure.

The Generation of the Distant Kuiper Belt by Planet Nine from an Initially Broad Perihelion Distribution

NASA Astrophysics Data System (ADS)

Khain, Tali; Batygin, Konstantin; Brown, Michael E.

2018-06-01

The observation that the orbits of long-period Kuiper Belt objects (KBOs) are anomalously clustered in physical space has recently prompted the Planet Nine hypothesis—the proposed existence of a distant and eccentric planetary member of our solar system. Within the framework of this model, a Neptune-like perturber sculpts the orbital distribution of distant KBOs through a complex interplay of resonant and secular effects, such that in addition to perihelion-circulating objects, the surviving orbits get organized into apsidally aligned and anti-aligned configurations with respect to Planet Nine’s orbit. In this work, we investigate the role of Kuiper Belt initial conditions on the evolution of the outer solar system using numerical simulations. Intriguingly, we find that the final perihelion distance distribution depends strongly on the primordial state of the system, and we demonstrate that a bimodal structure corresponding to the existence of both aligned and anti-aligned clusters is only reproduced if the initial perihelion distribution is assumed to extend well beyond ∼36 au. The bimodality in the final perihelion distance distribution is due to the existence of permanently stable objects, with the lower perihelion peak corresponding to the anti-aligned orbits and the higher perihelion peak corresponding to the aligned orbits. We identify the mechanisms that enable the persistent stability of these objects and locate the regions of phase space in which they reside. The obtained results contextualize the Planet Nine hypothesis within the broader narrative of solar system formation and offer further insight into the observational search for Planet Nine.

NEOPROP: A NEO Propagator for Space Situational Awareness

NASA Astrophysics Data System (ADS)

Zuccarelli, Valentino; Bancelin, David; Weikert, Sven; Thuillot, William; Hestroffer, Daniel; Yabar Valle, Celia; Koschny, Detlef

2013-09-01

The overall aim of the Space Situational Awareness (SSA) Preparatory Programme is to support the European independent utilisation of and access to space for research or services, through providing timely and quality data, information, services and knowledge regarding the environment, the threats and the sustainable exploitation of the outer space surrounding our planet Earth. The SSA system will comprise three main segments:• Space Weather (SWE) monitoring and forecast• Near-Earth Objects (NEO) survey and follow-up• Space Surveillance and Tracking (SST) of man-made space objectsCurrently, there are over 600.000 asteroids known in our Solar System, where more than 9.500 of these are NEOs. These could potentially hit our planet and depending on their size could produce considerable damage. For this reason NEOs deserve active detection and tracking efforts.The role of the SSA programme is to provide warning services against potential asteroid impact hazards, including discovery, identification, orbit prediction and civil alert capabilities. ESA is now working to develop a NEO Coordination Centre which will later evolve into a SSA-NEO Small Bodies Data Centre (SBDC), located at ESA/ESRIN, Italy. The Software prototype developed in the frame of this activity may be later implemented as a part of the SSA-NEO programme simulators aimed at assessing the trajectory of asteroids. There already exist different algorithms to predict orbits for NEOs. The objective of this activity is to come up with a different trajectory prediction algorithm, which allows an independent validation of the current algorithms within the SSA-NEO segment (e.g. NEODyS, JPL Sentry System).The key objective of this activity was to design, develop, test, verify, and validate trajectory prediction algorithm of NEOs in order to be able to computeanalytically and numerically the minimum orbital intersection distances (MOIDs).The NEOPROP software consists of two separate modules/tools:1. The Analytical Module makes use of analytical algorithms in order to rapidly assess the impact risk of a NEO. It is responsible for the preliminary analysis. Orbit Determination algorithms, as the Gauss and the Linear Least Squares (LLS) methods, will determine the initial state (from MPC observations), along with its uncertainty, and the MOID of the NEO (analytically).2. The Numerical Module makes use of numerical algorithms in order to refine and to better assess the impact probabilities. The initial state provided by the orbit determination process will be used to numerically propagate the trajectory. The numerical propagation can be run in two modes: one faster ("fast analysis"), in order to get a fast evaluation of the trajectory and one more precise ("complete analysis") taking into consideration more detailed perturbation models. Moreover, a configurable number of Virtual Asteroids (VAs) will be numerically propagated in order to determine the Earth closest approach. This new "MOID" computation differs from the analytical one since it takes into consideration the full dynamics of the problem.

EVOLUTIONARY MODELS OF SUPER-EARTHS AND MINI-NEPTUNES INCORPORATING COOLING AND MASS LOSS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howe, Alex R.; Burrows, Adam, E-mail: arhowe@astro.princeton.edu, E-mail: burrows@astro.princeton.edu

We construct models of the structural evolution of super-Earth- and mini-Neptune-type exoplanets with H{sub 2}–He envelopes, incorporating radiative cooling and XUV-driven mass loss. We conduct a parameter study of these models, focusing on initial mass, radius, and envelope mass fractions, as well as orbital distance, metallicity, and the specific prescription for mass loss. From these calculations, we investigate how the observed masses and radii of exoplanets today relate to the distribution of their initial conditions. Orbital distance and the initial envelope mass fraction are the most important factors determining planetary evolution, particularly radius evolution. Initial mass also becomes important belowmore » a “turnoff mass,” which varies with orbital distance, with mass–radius curves being approximately flat for higher masses. Initial radius is the least important parameter we study, with very little difference between the hot start and cold start limits after an age of 100 Myr. Model sets with no mass loss fail to produce results consistent with observations, but a plausible range of mass-loss scenarios is allowed. In addition, we present scenarios for the formation of the Kepler-11 planets. Our best fit to observations of Kepler-11b and Kepler-11c involves formation beyond the snow line, after which they moved inward, circularized, and underwent a reduced degree of mass loss.« less

Electronic origin of structural transition in 122 Fe based superconductors

NASA Astrophysics Data System (ADS)

Ghosh, Haranath; Sen, Smritijit; Ghosh, Abyay

2017-03-01

Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies Edxz, Edyz of Fe at the high symmetry points of the Brillouin zone. The fractional co-ordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.

Secure satellite communication using multi-photon tolerant quantum communication protocol

NASA Astrophysics Data System (ADS)

Darunkar, Bhagyashri; Punekar, Nikhil; Verma, Pramode K.

2015-09-01

This paper proposes and analyzes the potential of a multi-photon tolerant quantum communication protocol to secure satellite communication. For securing satellite communication, quantum cryptography is the only known unconditionally secure method. A number of recent experiments have shown feasibility of satellite-aided global quantum key distribution (QKD) using different methods such as: Use of entangled photon pairs, decoy state methods, and entanglement swapping. The use of single photon in these methods restricts the distance and speed over which quantum cryptography can be applied. Contemporary quantum cryptography protocols like the BB84 and its variants suffer from the limitation of reaching the distances of only Low Earth Orbit (LEO) at the data rates of few kilobits per second. This makes it impossible to develop a general satellite-based secure global communication network using the existing protocols. The method proposed in this paper allows secure communication at the heights of the Medium Earth Orbit (MEO) and Geosynchronous Earth Orbit (GEO) satellites. The benefits of the proposed method are two-fold: First it enables the realization of a secure global communication network based on satellites and second it provides unconditional security for satellite networks at GEO heights. The multi-photon approach discussed in this paper ameliorates the distance and speed issues associated with quantum cryptography through the use of contemporary laser communication (lasercom) devices. This approach can be seen as a step ahead towards global quantum communication.

Electronic Coupling Calculations for Bridge-Mediated Charge Transfer Using Constrained Density Functional Theory (CDFT) and Effective Hamiltonian Approaches at the Density Functional Theory (DFT) and Fragment-Orbital Density Functional Tight Binding (FODFTB) Level

DOE PAGES

Gillet, Natacha; Berstis, Laura; Wu, Xiaojing; ...

2016-09-09

In this paper, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesizedmore » by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated p-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. Finally, these four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.« less

Electronic Coupling Calculations for Bridge-Mediated Charge Transfer Using Constrained Density Functional Theory (CDFT) and Effective Hamiltonian Approaches at the Density Functional Theory (DFT) and Fragment-Orbital Density Functional Tight Binding (FODFTB) Level

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gillet, Natacha; Berstis, Laura; Wu, Xiaojing

In this paper, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesizedmore » by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated p-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. Finally, these four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.« less

Lazy orbits: An optimization problem on the sphere

NASA Astrophysics Data System (ADS)

Vincze, Csaba

2018-01-01

Non-transitive subgroups of the orthogonal group play an important role in the non-Euclidean geometry. If G is a closed subgroup in the orthogonal group such that the orbit of a single Euclidean unit vector does not cover the (Euclidean) unit sphere centered at the origin then there always exists a non-Euclidean Minkowski functional such that the elements of G preserve the Minkowskian length of vectors. In other words the Minkowski geometry is an alternative of the Euclidean geometry for the subgroup G. It is rich of isometries if G is "close enough" to the orthogonal group or at least to one of its transitive subgroups. The measure of non-transitivity is related to the Hausdorff distances of the orbits under the elements of G to the Euclidean sphere. Its maximum/minimum belongs to the so-called lazy/busy orbits, i.e. they are the solutions of an optimization problem on the Euclidean sphere. The extremal distances allow us to characterize the reducible/irreducible subgroups. We also formulate an upper and a lower bound for the ratio of the extremal distances. As another application of the analytic tools we introduce the rank of a closed non-transitive group G. We shall see that if G is of maximal rank then it is finite or reducible. Since the reducible and the finite subgroups form two natural prototypes of non-transitive subgroups, the rank seems to be a fundamental notion in their characterization. Closed, non-transitive groups of rank n - 1 will be also characterized. Using the general results we classify all their possible types in lower dimensional cases n = 2 , 3 and 4. Finally we present some applications of the results to the holonomy group of a metric linear connection on a connected Riemannian manifold.

Accurate analytical periodic solution of the elliptical Kepler equation using the Adomian decomposition method

NASA Astrophysics Data System (ADS)

Alshaery, Aisha; Ebaid, Abdelhalim

2017-11-01

Kepler's equation is one of the fundamental equations in orbital mechanics. It is a transcendental equation in terms of the eccentric anomaly of a planet which orbits the Sun. Determining the position of a planet in its orbit around the Sun at a given time depends upon the solution of Kepler's equation, which we will solve in this paper by the Adomian decomposition method (ADM). Several properties of the periodicity of the obtained approximate solutions have been proved in lemmas. Our calculations demonstrated a rapid convergence of the obtained approximate solutions which are displayed in tables and graphs. Also, it has been shown in this paper that only a few terms of the Adomian decomposition series are sufficient to achieve highly accurate numerical results for any number of revolutions of the Earth around the Sun as a consequence of the periodicity property. Numerically, the four-term approximate solution coincides with the Bessel-Fourier series solution in the literature up to seven decimal places at some values of the time parameter and nine decimal places at other values. Moreover, the absolute error approaches zero using the nine term approximate Adomian solution. In addition, the approximate Adomian solutions for the eccentric anomaly have been used to show the convergence of the approximate radial distances of the Earth from the Sun for any number of revolutions. The minimal distance (perihelion) and maximal distance (aphelion) approach 147 million kilometers and 152.505 million kilometers, respectively, and these coincide with the well known results in astronomical physics. Therefore, the Adomian decomposition method is validated as an effective tool to solve Kepler's equation for elliptical orbits.

Local stellar kinematics from RAVE data—VIII. Effects of the Galactic disc perturbations on stellar orbits of red clump stars

NASA Astrophysics Data System (ADS)

Önal Taş, Ö.; Bilir, S.; Plevne, O.

2018-02-01

We aim to probe the dynamic structure of the extended Solar neighborhood by calculating the radial metallicity gradients from orbit properties, which are obtained for axisymmetric and non-axisymmetric potential models, of red clump (RC) stars selected from the RAdial Velocity Experiment's Fourth Data Release. Distances are obtained by assuming a single absolute magnitude value in near-infrared, i.e. M_{Ks}=-1.54±0.04 mag, for each RC star. Stellar orbit parameters are calculated by using the potential functions: (i) for the MWPotential2014 potential, (ii) for the same potential with perturbation functions of the Galactic bar and transient spiral arms. The stellar age is calculated with a method based on Bayesian statistics. The radial metallicity gradients are evaluated based on the maximum vertical distance (z_{max}) from the Galactic plane and the planar eccentricity (ep) of RC stars for both of the potential models. The largest radial metallicity gradient in the 0< z_{max} ≤0.5 kpc distance interval is -0.065±0.005 dex kpc^{-1} for a subsample with ep≤0.1, while the lowest value is -0.014±0.006 dex kpc^{-1} for the subsample with ep≤0.5. We find that at z_{max}>1 kpc, the radial metallicity gradients have zero or positive values and they do not depend on ep subsamples. There is a large radial metallicity gradient for thin disc, but no radial gradient found for thick disc. Moreover, the largest radial metallicity gradients are obtained where the outer Lindblad resonance region is effective. We claim that this apparent change in radial metallicity gradients in the thin disc is a result of orbital perturbation originating from the existing resonance regions.

Electronic Coupling Calculations for Bridge-Mediated Charge Transfer Using Constrained Density Functional Theory (CDFT) and Effective Hamiltonian Approaches at the Density Functional Theory (DFT) and Fragment-Orbital Density Functional Tight Binding (FODFTB) Level.

PubMed

Gillet, Natacha; Berstis, Laura; Wu, Xiaojing; Gajdos, Fruzsina; Heck, Alexander; de la Lande, Aurélien; Blumberger, Jochen; Elstner, Marcus

2016-10-11

In this article, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesized by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated π-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. These four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.

Diabatic models with transferrable parameters for generalized chemical reactions

NASA Astrophysics Data System (ADS)

Reimers, Jeffrey R.; McKemmish, Laura K.; McKenzie, Ross H.; Hush, Noel S.

2017-05-01

Diabatic models applied to adiabatic electron-transfer theory yield many equations involving just a few parameters that connect ground-state geometries and vibration frequencies to excited-state transition energies and vibration frequencies to the rate constants for electron-transfer reactions, utilizing properties of the conical-intersection seam linking the ground and excited states through the Pseudo Jahn-Teller effect. We review how such simplicity in basic understanding can also be obtained for general chemical reactions. The key feature that must be recognized is that electron-transfer (or hole transfer) processes typically involve one electron (hole) moving between two orbitals, whereas general reactions typically involve two electrons or even four electrons for processes in aromatic molecules. Each additional moving electron leads to new high-energy but interrelated conical-intersection seams that distort the shape of the critical lowest-energy seam. Recognizing this feature shows how conical-intersection descriptors can be transferred between systems, and how general chemical reactions can be compared using the same set of simple parameters. Mathematical relationships are presented depicting how different conical-intersection seams relate to each other, showing that complex problems can be reduced into an effective interaction between the ground-state and a critical excited state to provide the first semi-quantitative implementation of Shaik’s “twin state” concept. Applications are made (i) demonstrating why the chemistry of the first-row elements is qualitatively so different to that of the second and later rows, (ii) deducing the bond-length alternation in hypothetical cyclohexatriene from the observed UV spectroscopy of benzene, (iii) demonstrating that commonly used procedures for modelling surface hopping based on inclusion of only the first-derivative correction to the Born-Oppenheimer approximation are valid in no region of the chemical parameter space, and (iv), demonstrating the types of chemical reactions that may be suitable for exploitation as a chemical qubit in some quantum information processor.

Aeroassisted manned transfer vehicle (TAXI) for advanced Mars Transportation: NASA/USRA 1987 Senior Design Project

NASA Technical Reports Server (NTRS)

1987-01-01

A conceptual design study of an aeroassisted orbital transfer vehicle is discussed. Nicknamed TAXI, it will ferry personnel and cargo: (1) between low Earth orbit and a spacecraft circling around the Sun in permanent orbit intersecting gravitational fields of Earth and Mars, and (2) between the cycling spacecraft and a Mars orbiting station, co-orbiting with Phobos. Crew safety and mission flexibility (in terms of ability to provide a wide range of delta-V) were given high priority. Three versions were considered, using the same overall configuration based on a low L/D aerobrake with the geometry of a raked off elliptical cone with ellipsoidal nose and a toroidal skirt. The propulsion system consists of three gimballed LOX/LH2 engines firing away from the aerobrake. The versions differ mainly in the size of the aeroshields and propellant tanks. TAXI A version resulted from an initial effort to design a single transfer vehicle able to meet all delta-V requirements during the 15-year period (2025 to 2040) of Mars mission operations. TAXI B is designed to function with the cycling spacecraft moving in a simplified, nominal trajectory. On Mars missions, TAXI B would be able to meet the requirements of all the missions with a relative approach velocity near Mars of less than 9.3 km/sec. Finally, TAXI C is a revision of TAXI A, a transfer vehicle designed for missions with a relative velocity near Mars larger than 9.3 km/sec. All versions carry a crew of 9 (11 with modifications) and a cargo of 10000 lbm. Trip duration varies from 1 day for transfer from LEO to the cycling ship to nearly 5 days for transfer from the ship to the Phobos orbit.

Solar Dynamics Observatory High Gain Antenna Handover Planning

NASA Technical Reports Server (NTRS)

Hashmall, Joseph A.; Mann, Laurie

2007-01-01

The Solar Dynamics Observatory (SDO) is planned to launch in early 2009 as a mission to study the solar variability and its impact on Earth. To best satisfy its science goal, SDO will fly in a geosynchronous orbit with an inclination of approximately 29 deg. The spacecraft attitude is designed so that the science instruments point directly at the Sun with high accuracy. One of SDO s principal requirements is to obtain long periods of uninterrupted observations. The observations have an extremely high data volume so SDO must be in continuous contact with the ground during the observation periods. To maintain this contact, SDO is equipped with a pair of high gain antennas (HGAs) transmitting to a pair of ground antennas at the SDO ground station (SDOGS) located in White Sands, New Mexico. Either HGA can transmit to either SDOGS antenna. Neither HGA can be powered down. During a portion of each year, each of the HGA beams will intersect with the SDO body for a portion of the orbit. The original SDO antenna contact plan used each HGA for the half of each year during which its beam would not intersect the spacecraft. No data would be lost except, possibly, when switching from one antenna to another. After this plan was adopted, further analysis showed that daily handovers would be necessary for significant periods of the year. This unexpected need for extensive handovers necessitated that a handover design be developed to minimize the impact on the mission. This antenna handover design was developed and successfully tested with simulated data using the slew rate limits from preliminary jitter analysis. Subsequent analysis provided significant revision of allowed rates requiring modification of the handover plans.

Solar Dynamics Observatory High Gain Antenna Handover Planning

NASA Technical Reports Server (NTRS)

Hashmall, Joseph A.; Mann, Laurie

2007-01-01

The Solar Dynamics Observatory (SDO) is planned to launch in early 2009 as a mission to study the solar variability and its impact on Earth. To best satisfy its science goal, SDO will fly in a geosynchronous orbit with an inclination of approximately 29 deg. The spacecraft attitude is designed so that the science instruments point directly at the Sun with high accuracy. One of SDO's principal requirements is to obtain long periods of uninterrupted observations. The observations have an extremely high data volume so SDO must be in continuous contact with the ground during the observation periods. To maintain this contact, SDO is equipped with a pair of high gain antennas (HGAs) transmitting to a pair of ground antennas at the SDO ground station (SDOGS) located in White Sands, New Mexico. Either HGA can transmit to either SDOGS antenna. Neither HGA can be powered down. During a portion of each year, each of the HGA beams will intersect with the SDO body for a portion of the orbit. The original SDO antenna contact plan used each HGA for the half of each year during which its beam would not intersect the spacecraft. No data would be lost except, possibly, when switching from one antenna to another. After this plan was adopted, further analysis showed that daily handovers would be necessary for significant periods of the year. This unexpected need for extensive handovers necessitated that a handover design be developed to minimize the impact on the mission. This antenna handover design was developed and successfully tested with simulated data using the slew rate limits from preliminary jitter analysis. Subsequent analysis provided significant revision of allowed rates requiring modification of the handover plans.

Two-craft Coulomb formation study about circular orbits and libration points

NASA Astrophysics Data System (ADS)

Inampudi, Ravi Kishore

This dissertation investigates the dynamics and control of a two-craft Coulomb formation in circular orbits and at libration points; it addresses relative equilibria, stability and optimal reconfigurations of such formations. The relative equilibria of a two-craft tether formation connected by line-of-sight elastic forces moving in circular orbits and at libration points are investigated. In circular Earth orbits and Earth-Moon libration points, the radial, along-track, and orbit normal great circle equilibria conditions are found. An example of modeling the tether force using Coulomb force is discussed. Furthermore, the non-great-circle equilibria conditions for a two-spacecraft tether structure in circular Earth orbit and at collinear libration points are developed. Then the linearized dynamics and stability analysis of a 2-craft Coulomb formation at Earth-Moon libration points are studied. For orbit-radial equilibrium, Coulomb forces control the relative distance between the two satellites. The gravity gradient torques on the formation due to the two planets help stabilize the formation. Similar analysis is performed for along-track and orbit-normal relative equilibrium configurations. Where necessary, the craft use a hybrid thrusting-electrostatic actuation system. The two-craft dynamics at the libration points provide a general framework with circular Earth orbit dynamics forming a special case. In the presence of differential solar drag perturbations, a Lyapunov feedback controller is designed to stabilize a radial equilibrium, two-craft Coulomb formation at collinear libration points. The second part of the thesis investigates optimal reconfigurations of two-craft Coulomb formations in circular Earth orbits by applying nonlinear optimal control techniques. The objective of these reconfigurations is to maneuver the two-craft formation between two charged equilibria configurations. The reconfiguration of spacecraft is posed as an optimization problem using the calculus of variations approach. The optimality criteria are minimum time, minimum acceleration of the separation distance, minimum Coulomb and electric propulsion fuel usage, and minimum electrical power consumption. The continuous time problem is discretized using a pseudospectral method, and the resulting finite dimensional problem is solved using a sequential quadratic programming algorithm. The software package, DIDO, implements this approach. This second part illustrates how pseudospectral methods significantly simplify the solution-finding process.

Model-based approaches to deal with detectability: a comment on Hutto (2016)

USGS Publications Warehouse

Marques, Tiago A.; Thomas, Len; Kéry, Marc; Buckland, Steve T.; Borchers, David L.; Rexstad, Eric; Fewster, Rachel M.; MacKenzie, Darryl I.; Royle, Andy; Guillera-Arroita, Gurutzeta; Handel, Colleen M.; Pavlacky, David C.; Camp, Richard J.

2017-01-01

In a recent paper, Hutto (2016a) challenges the need to account for detectability when interpreting data from point counts. A number of issues with model-based approaches to deal with detectability are presented, and an alternative suggested: surveying an area around each point over which detectability is assumed certain. The article contains a number of false claims and errors of logic, and we address these here. We provide suggestions about appropriate uses of distance sampling and occupancy modeling, arising from an intersection of design- and model-based inference.

27. DIVERSION STRUCTURE WITH CONCRETE SIDEWALLS AND CONCRETE CHANNEL BEYOND, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

27. DIVERSION STRUCTURE WITH CONCRETE SIDEWALLS AND CONCRETE CHANNEL BEYOND, A SHORT DISTANCE WEST OF D STREET ABOUT ONE-QUARTER MILE SOUTH OF 9TH AVENUE (SECTION 26). - Highline Canal, Sand Creek Lateral, Beginning at intersection of Peoria Street & Highline Canal in Arapahoe County (City of Aurora), Sand Creek lateral Extends 15 miles Northerly through Araphoe County, City & County of Denver, & Adams County to its end point, approximately 1/4 mile Southest of intersectioin of D Street & Ninth Avenue in Adams County (Rocky Mountain Arsenal, Commerce City Vicinity), Commerce City, Adams County, CO

Golf Aerodynamics

NASA Technical Reports Server (NTRS)

1995-01-01

A former Martin Marietta Manned Space Systems engineer, Robert T. Thurman went from analyzing airloads on the Space Shuttle External Tank to analyzing airloads on golf balls for Wilson Sporting Goods Company. Using his NASA know-how, Thurman designed the Ultra 500 golf ball, which has three different-sized dimples in 60 triangular faces (instead of the usual 20) formed by a series of intersecting "parting" lines. This balances the asymmetry caused by the molding line in all golf balls. According to Wilson, the ball sustains initial velocity longer and produces the most stable ball flight for "unmatched" accuracy and distance.

Gaussian-Beam/Physical-Optics Design Of Beam Waveguide

NASA Technical Reports Server (NTRS)

Veruttipong, Watt; Chen, Jacqueline C.; Bathker, Dan A.

1993-01-01

In iterative method of designing wideband beam-waveguide feed for paraboloidal-reflector antenna, Gaussian-beam approximation alternated with more nearly exact physical-optics analysis of diffraction. Includes curved and straight reflectors guiding radiation from feed horn to subreflector. For iterative design calculations, curved mirrors mathematically modeled as thin lenses. Each distance Li is combined length of two straight-line segments intersecting at one of flat mirrors. Method useful for designing beam-waveguide reflectors or mirrors required to have diameters approximately less than 30 wavelengths at one or more intended operating frequencies.

Ground Target Overflight and Orbital Maneuvering via Atmospheric Maneuvers

DTIC Science & Technology

2014-03-27

Total deceleration m ∙ s−2 Gravitational acceleration m ∙ s−2 ℎ Altitude m Inclination angle rad Vehicle mass kg Geocentric ...determine the longitude. By expanding and simplifying Eqs. (3.1) and (3.5) for a circular orbit, the position can be written in the Geocentric Equatorial...Altitude m Inclination angle rad Vehicle mass kg Geocentric radial distance from planet center of mass to vehicle m General time s

Potential SPOT-1 R/B-Cosmos 1680 R/B collision

NASA Technical Reports Server (NTRS)

Henize, Karl G.; Rast, Richard H.

1989-01-01

Detailed NORAD data have revealed updated orbital elements for the Ariane third-stage rocket body that underwent breakup on November 13, 1986, as well as for the Cosmos 1680 rocket body. Applying the maximum expected error due to the extrapolation of orbital elements to the date of the possible collision between the two bodies shows the smallest possible distance between bodies to have been 380 km, thereby precluding collision.

Alternative Transfer to the Earth-Moon Lagrangian Points L4 and L5 Using Lunar Gravity assist

NASA Astrophysics Data System (ADS)

Salazar, Francisco; Winter, Othon; Macau, Elbert; Bertachini de Almeida Prado, Antonio Fernando

2012-07-01

Lagrangian points L4 and L5 lie at 60 degrees ahead of and behind Moon in its orbit with respect to the Earth. Each one of them is a third point of an equilateral triangle with the base of the line defined by those two bodies. These Lagrangian points are stable for the Earth-Moon mass ratio. Because of their distance electromagnetic radiations from the Earth arrive on them substantially attenuated. As so, these Lagrangian points represent remarkable positions to host astronomical observatories. However, this same distance characteristic may be a challenge for periodic servicing mission. This paper studies transfer orbits in the planar restricted three-body problem. To avoid solving a two-boundary problem, the patched-conic approximation is used to find initial conditions to transfer a spacecraft between an Earth circular parking orbit and the Lagrangian points L4, L5 (in the Earth-Moon system), such that a swing-by maneuver is applied using the lunar gravity. We also found orbits that can be used to make a tour to the Lagrangian points L4, L5 based on the theorem of image trajectories. Keywords: Stable Lagrangian points, L4, L5, Three-Body problem, Patched Conic, Swing-by

Imaging molecular interaction of NO on Cu(110) with a scanning tunneling microscope.

PubMed

Okuyama, Hiroshi

2014-10-01

Molecular interaction on metal surfaces is one of the central issues of surface science for the microscopic understanding of heterogeneous catalysis. In this Personal Account, I review the recent studies on NO/Cu(110) employing a scanning tunneling microscope (STM) to probe and control the molecule-molecule interaction on the surface. An individual NO molecule was observed as a characteristic dumbbell-shaped protrusion, visualizing the 2π* orbital. By manipulating the intermolecular distance with the STM, the overlap of the 2π* orbital between two NO molecules was controlled. The interaction causes the formation of the bonding and antibonding orbitals below and above the Fermi level, respectively, as a function of the intermolecular distance. The 2π* orbital also plays a role in the reaction of NO with water molecules. A water molecule donates a H-bond to NO, giving rise to the down-shift of the 2π* level below the Fermi level. This causes electron transfer from the substrate to NO, weakening, and eventually rupturing, the N-O bond. The facile bond cleavage by water molecules has implications for the catalytic reduction of NO under ambient conditions. Copyright © 2014 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

TRANSITING PLANETS WITH LSST. II. PERIOD DETECTION OF PLANETS ORBITING 1 M{sub ⊙} HOSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacklin, Savannah; Lund, Michael B.; Stassun, Keivan G.

2015-07-15

The Large Synoptic Survey Telescope (LSST) will photometrically monitor ∼10{sup 9} stars for 10 years. The resulting light curves can be used to detect transiting exoplanets. In particular, as demonstrated by Lund et al., LSST will probe stellar populations currently undersampled in most exoplanet transit surveys, including out to extragalactic distances. In this paper we test the efficiency of the box-fitting least-squares (BLS) algorithm for accurately recovering the periods of transiting exoplanets using simulated LSST data. We model planets with a range of radii orbiting a solar-mass star at a distance of 7 kpc, with orbital periods ranging from 0.5more » to 20 days. We find that standard-cadence LSST observations will be able to reliably recover the periods of Hot Jupiters with periods shorter than ∼3 days; however, it will remain a challenge to confidently distinguish these transiting planets from false positives. At the same time, we find that the LSST deep-drilling cadence is extremely powerful: the BLS algorithm successfully recovers at least 30% of sub-Saturn-size exoplanets with orbital periods as long as 20 days, and a simple BLS power criterion robustly distinguishes ∼98% of these from photometric (i.e., statistical) false positives.« less

The habitable zone and extreme planetary orbits.

PubMed

Kane, Stephen R; Gelino, Dawn M

2012-10-01

The habitable zone for a given star describes the range of circumstellar distances from the star within which a planet could have liquid water on its surface, which depends upon the stellar properties. Here we describe the development of the habitable zone concept, its application to our own solar system, and its subsequent application to exoplanetary systems. We further apply this to planets in extreme eccentric orbits and show how they may still retain life-bearing properties depending upon the percentage of the total orbit which is spent within the habitable zone. Key Words: Extrasolar planets-Habitable zone-Astrobiology.

Compact two-electron wave function for bond dissociation and Van der Waals interactions: a natural amplitude assessment.

PubMed

Giesbertz, Klaas J H; van Leeuwen, Robert

2014-05-14

Electron correlations in molecules can be divided in short range dynamical correlations, long range Van der Waals type interactions, and near degeneracy static correlations. In this work, we analyze for a one-dimensional model of a two-electron system how these three types of correlations can be incorporated in a simple wave function of restricted functional form consisting of an orbital product multiplied by a single correlation function f (r12) depending on the interelectronic distance r12. Since the three types of correlations mentioned lead to different signatures in terms of the natural orbital (NO) amplitudes in two-electron systems, we make an analysis of the wave function in terms of the NO amplitudes for a model system of a diatomic molecule. In our numerical implementation, we fully optimize the orbitals and the correlation function on a spatial grid without restrictions on their functional form. Due to this particular form of the wave function, we can prove that none of the amplitudes vanishes and moreover that it displays a distinct sign pattern and a series of avoided crossings as a function of the bond distance in agreement with the exact solution. This shows that the wave function ansatz correctly incorporates the long range Van der Waals interactions. We further show that the approximate wave function gives an excellent binding curve and is able to describe static correlations. We show that in order to do this the correlation function f (r12) needs to diverge for large r12 at large internuclear distances while for shorter bond distances it increases as a function of r12 to a maximum value after which it decays exponentially. We further give a physical interpretation of this behavior.

Eccentric Capitellar Ossification Limits the Utility of the Radiocapitellar Line in Young Children.

PubMed

Fader, Lauren M; Laor, Tal; Eismann, Emily A; Cornwall, Roger; Little, Kevin J

2016-03-01

The radiocapitellar line (RCL) has long been used for the radiographic evaluation of elbow alignment. In children, the capitellar ossific nucleus serves as a proxy for the entire capitellum, but this substitution has not been verified. Using magnetic resonance imaging (MRI), we sought to understand how maturation of the ossific nucleus of the capitellum affects the utility of RCL throughout skeletal maturation of the elbow. The RCL was drawn on coronal and sagittal MRIs in 82 children (43 boys, 39 girls; age range, 1 to 13 y) with at least 3 patients in each 1-year interval age group. The perpendicular distance of the RCL from the center of both the cartilaginous capitellum and the capitellar ossific nucleus was measured relative to its total width, and a percent offset for each measurement was calculated. Logarithmic regression analysis was performed to analyze the effect of age and sex on percent offset. The RCL reliably intersected with the central third of the cartilaginous capitellum at all ages in both planes. Although the RCL intersected with the ossified capitellum in all but 3 measurements, it intersected with the central third of the ossified capitellum less often in younger children in both sagittal (B=0.47, P<0.001) and coronal (B=0.31, P=0.002) planes. Percent offset decreased significantly with age in a logarithmic manner in both sagittal (r=0.57, P<0.001) and coronal (r=-0.47, P<0.001) planes. 95% confidence intervals predict that the sagittal plane RCL will accurately intersect the central third of the ossified capitellum by age 10 years in girls and age 11 years in boys but not in the coronal plane. Eccentric ossification of the capitellum explains RCL variability in young children. The RCL does not reliably intersect the central third of the ossified capitellum until ages 10 years in girls and 11 years in boys in the sagittal plane. The RCL should be used within its limitations in skeletally immature children and should be combined with advanced imaging if necessary.

Models of Angular Momentum Input to a Circumterrestrial Swarm from Encounters with Heliocentric Planetesimals

NASA Technical Reports Server (NTRS)

Davis, D. R.; Greenberg, R.; Hebert, F.

1985-01-01

Models of lunar origin in which the Moon accretes in orbit about the Earth from material approaching the Earth from heliocentric orbits must overcome a fundamental problem: the approach orbits of such material would be, in the simplest approximation, equally likely to be prograde or retrograde about the Earth, with the result that accretion of such material adds mass but not angular momentum to circumterrestrial satellites. Satellite orbits would then decay due to the resulting drag, ultimately impacting onto the Earth. One possibility for adding both material and angular momentum to Earth orbit is investigated: imbalance in the delivered angular momentum between pro and retrograde Earth passing orbits which arises from the three body dynamics of planetesimals approaching the Earth from heliocentric space. In order to study angular momentum delivery to circumterrestrial satellites, the near Earth velocities were numerically computed as a function of distance from the Earth for a large array of orbits systematically spanning heliocentric phase space.

Effective orbital volume and eyeball position: an MRI study.

PubMed

Detorakis, Efstathios T; Drakonaki, Eleni; Papadaki, Efrosini; Pallikaris, Ioannis G; Tsilimbaris, Miltiadis K

2010-10-01

Previous studies have examined factors affecting the position of the eyeball to the orbit. This study examined the role of effective orbital volume (EOV), defined as the difference between orbital and eyeball volume, as a determinant of eyeball position, using MRI scans. Forty-six patients were recruited from the Department of Ophthalmology of the University Hospital of Heraklion, Crete Greece. Patients with a history of orbital disease were excluded. Distances between eyeball poles and orbital landmarks were measured in T1 weighted transverse, sagittal and coronal orbital images. The protrusion of the eyeball in the sagittal and transverse planes was recorded. The volume of the eyeball and bony orbit, the EOV, the volume of the extraocular muscles as well as clinical information (age, gender, Hertel exophthalmometry) were also recorded. EOV was significantly associated with orbital volume but not with eyeball volume. EOV was also significantly associated with transverse and sagittal globe protrusions. Females displayed significantly lower orbital and eyeball volumes as well as EOV than males but higher transverse globe protrusion than males. Variations in EOV are associated with orbital volume rather than with eyeball volume. EOV is associated with globe protrusion and may be taken into account in the planning of various procedures, including orbital decompression, treatment of enophthalmos or the size of orbital implants following enucleation.

Pre-flight and On-orbit Geometric Calibration of the Lunar Reconnaissance Orbiter Camera

NASA Astrophysics Data System (ADS)

Speyerer, E. J.; Wagner, R. V.; Robinson, M. S.; Licht, A.; Thomas, P. C.; Becker, K.; Anderson, J.; Brylow, S. M.; Humm, D. C.; Tschimmel, M.

2016-04-01

The Lunar Reconnaissance Orbiter Camera (LROC) consists of two imaging systems that provide multispectral and high resolution imaging of the lunar surface. The Wide Angle Camera (WAC) is a seven color push-frame imager with a 90∘ field of view in monochrome mode and 60∘ field of view in color mode. From the nominal 50 km polar orbit, the WAC acquires images with a nadir ground sampling distance of 75 m for each of the five visible bands and 384 m for the two ultraviolet bands. The Narrow Angle Camera (NAC) consists of two identical cameras capable of acquiring images with a ground sampling distance of 0.5 m from an altitude of 50 km. The LROC team geometrically calibrated each camera before launch at Malin Space Science Systems in San Diego, California and the resulting measurements enabled the generation of a detailed camera model for all three cameras. The cameras were mounted and subsequently launched on the Lunar Reconnaissance Orbiter (LRO) on 18 June 2009. Using a subset of the over 793000 NAC and 207000 WAC images of illuminated terrain collected between 30 June 2009 and 15 December 2013, we improved the interior and exterior orientation parameters for each camera, including the addition of a wavelength dependent radial distortion model for the multispectral WAC. These geometric refinements, along with refined ephemeris, enable seamless projections of NAC image pairs with a geodetic accuracy better than 20 meters and sub-pixel precision and accuracy when orthorectifying WAC images.

Radio Astronomers Set New Standard for Accurate Cosmic Distance Measurement

NASA Astrophysics Data System (ADS)

1999-06-01

A team of radio astronomers has used the National Science Foundation's Very Long Baseline Array (VLBA) to make the most accurate measurement ever made of the distance to a faraway galaxy. Their direct measurement calls into question the precision of distance determinations made by other techniques, including those announced last week by a team using the Hubble Space Telescope. The radio astronomers measured a distance of 23.5 million light-years to a galaxy called NGC 4258 in Ursa Major. "Ours is a direct measurement, using geometry, and is independent of all other methods of determining cosmic distances," said Jim Herrnstein, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. The team says their measurement is accurate to within less than a million light-years, or four percent. The galaxy is also known as Messier 106 and is visible with amateur telescopes. Herrnstein, along with James Moran and Lincoln Greenhill of the Harvard- Smithsonian Center for Astrophysics; Phillip Diamond, of the Merlin radio telescope facility at Jodrell Bank and the University of Manchester in England; Makato Inoue and Naomasa Nakai of Japan's Nobeyama Radio Observatory; Mikato Miyoshi of Japan's National Astronomical Observatory; Christian Henkel of Germany's Max Planck Institute for Radio Astronomy; and Adam Riess of the University of California at Berkeley, announced their findings at the American Astronomical Society's meeting in Chicago. "This is an incredible achievement to measure the distance to another galaxy with this precision," said Miller Goss, NRAO's Director of VLA/VLBA Operations. "This is the first time such a great distance has been measured this accurately. It took painstaking work on the part of the observing team, and it took a radio telescope the size of the Earth -- the VLBA -- to make it possible," Goss said. "Astronomers have sought to determine the Hubble Constant, the rate of expansion of the universe, for decades. This will in turn lead to an estimate of the age of the universe. In order to do this, you need an unambiguous, absolute distance to another galaxy. We are pleased that the NSF's VLBA has for the first time determined such a distance, and thus provided the calibration standard astronomers have always sought in their quest for accurate distances beyond the Milky Way," said Morris Aizenman, Executive Officer of the National Science Foundation's (NSF) Division of Astronomical Sciences. "For astronomers, this measurement is the golden meter stick in the glass case," Aizenman added. The international team of astronomers used the VLBA to measure directly the motion of gas orbiting what is generally agreed to be a supermassive black hole at the heart of NGC 4258. The orbiting gas forms a warped disk, nearly two light-years in diameter, surrounding the black hole. The gas in the disk includes water vapor, which, in parts of the disk, acts as a natural amplifier of microwave radio emission. The regions that amplify radio emission are called masers, and work in a manner similar to the way a laser amplifies light emission. Determining the distance to NGC 4258 required measuring motions of extremely small shifts in position of these masers as they rotate around the black hole. This is equivalent to measuring an angle one ten-thousandth the width of a human hair held at arm's length. "The VLBA is the only instrument in the world that could do this," said Moran. "This work is the culmination of a 20-year effort at the Harvard Smithsonian Center for Astrophysics to measure distances to cosmic masers," said Irwin Shapiro, Director of that institution. Collection of the data for the NGC 4258 project was begun in 1994 and was part of Herrnstein's Ph.D dissertation at Harvard University. Previous observations with the VLBA allowed the scientists to measure the speed at which the gas is orbiting the black hole, some 39 million times more massive than the Sun. They did this by observing the amount of change in the wavelength of the radio waves caused by the Doppler effect. The gas is orbiting at a speed of more than two million miles per hour. The orbiting disk of gas is almost edge-on as viewed from Earth. The astronomers obtained the orbital speeds and the positions of the masers in the disk by measuring the Doppler Shift of the masers at the disk's sides, where the gas is moving almost directly away from the Earth on one side and toward the Earth on the other. Measurements of the different orbital speeds at different distances from the black hole, made in 1994, allowed them to determine the mass of the black hole. These measurements required the great resolving power, or ability to see fine detail, of the VLBA. This picture of an orbiting disk was confirmed by measurement of centrifugal acceleration, according to the scientists. The newest observations were focused on maser "spots" on the near edge of the disk, where orbital motion shifts their position in the sky, though by an extremely small amount. The VLBA, however, was able to detect this extremely small movement, called "proper motion" by astronomers. This motion was detected by observing the galaxy at 4- to 8-month intervals over more than three years. "By knowing the speed at which the gas is orbiting and then measuring its motion across the sky, we can use plain old trigonometry to calculate the distance," Greenhill said. He added, however, that "you need a bit of luck to be able to do this. So far, we know of only 22 galaxies with water masers in their nuclear regions that also are relatively nearby. Then, the geometry of the disk, relative to Earth, has to be right to allow us to make such a measurement" The VLBA measurement of NGC 4258's distance differs significantly from the distance to that galaxy determined through HST observations of Cepheid variable stars. Using such stars, a team of astronomers led by University of California-Berkeley scientist Eyal Maoz has made preliminary and as-yet unpublished estimates of the distance to NGC 4258 as either 27 or 29 million light-years, depending on assumptions about the characteristics of this type of star in that galaxy. Other Cepheid-based galaxy distances were used to calculate the expansion rate of the universe, called the Hubble Constant, announced by a team of HST observers last week. "This difference could mean that there may be more uncertainty in Cepheid-determined distances than people have realized," said Moran. "Providing this directly-determined distance to one galaxy -- a distance that can serve as a milestone -- should be helpful in determining distances to other galaxies, and thus the Hubble Constant and the size and age of the universe" The VLBA is a system of ten radio-telescope antennas, each 25 meters (82 feet) in diameter, stretching some 5,000 miles from Mauna Kea in Hawaii to St. Croix in the U.S. Virgin Islands. Operated from NRAO's Array Operations Center in Socorro, NM, the VLBA offers astronomers the greatest resolving power of any telescope anywhere. The NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Background information: Determining Cosmic Distances Determining cosmic distances obviously is vital to understanding the size of the universe. In turn, knowing the size of the universe is an important step in determining its age. "The size puts a limit on how much expansion could have occurred since the Big Bang, and thus tells us something about the age," said Moran. However, determining cosmic distances has proven to be a particularly thorny problem for astronomers. In the third century, B.C., the Greek astronomer Aristarchus devised a method of using trigonometry to determine the relative distances of the Moon and Sun, but in practice his method was difficult to use. Though a great first step, he missed the mark by a factor of 20. It wasn't until 1761 that trigonometric methods produced a relatively accurate distance to Venus, thus calibrating the size of the Solar System. The first accurate distance to another star was determined trigonometrically by Friedrich Wilhelm Bessel in 1838. Traditional trigonometric methods of measuring celestial distances require extremely accurate measurement of an object's position in the sky. By measuring the apparent shift in an object's position, called parallax, caused by the Earth's journey around the Sun, the distance to the object can be calculated. Until recent years, such measurements were limited by the atmosphere's degrading effect on optical observations. Recently, the Hipparcos satellite has measured stellar distances accurate to within 10 percent out to about 300 light-years. Beyond the range of parallax measurements, astronomers were forced to use indirect methods of estimating distances. Many of these methods make presumptions about the intrinsic brightness of objects, then estimate the distance by measuring how much fainter they appear on Earth. The faintness is presumed to be caused by the distance, according to the inverse-square law (doubling of the distance reduces brightness by a factor of four). Thus, stars of a particular spectral class are all presumed to be of the same intrinsic brightness. Such techniques have been used to estimate distances of stars out to about 25,000 light-years, still not far enough to estimate distance beyond our own Milky Way Galaxy. Early in the 20th Century, Henrietta Leavitt, of Harvard College Observatory, discovered that variable-brightness stars known as Cepheid variables showed a useful property -- the longer their pulsation periods, the brighter they are intrinsically. Once the absolute distance to a few Cepheids was determined, these stars were used to measure distances beyond the Milky Way. In the 1920s, Edwin Hubble used Cepheid-variable distance determinations to show that, contrary to then-prevalent opinion, many "nebulae" were, in fact, other galaxies far distant from our own. Distances determined using Cepheid variables, along with measurements of the Doppler shift of other galaxies' light, allowed Hubble to discover the expansion of the universe, the basis of the Big Bang theory. The Cepheid technique still is one of the building blocks of the extragalactic distance scale. However, because of absorption of light by interstellar dust and subtle differences among the stars themselves, this technique is subject to considerable uncertainty. Similarly, techniques that use a specific type of supernova (Type Ia) presumed to be of uniform intrinsic brightness, while able to make distance estimates farther than the Cepheid technique, still are subject to uncertainties. The NSF's VLBA, with resolving power hundreds of times better than even the Hubble Space Telescope, has allowed direct trigonometric techniques to be applied in measuring much greater distances than ever before. The VLBA measured the expansion of the shell of exploding debris from the supernova SN 1993J in the galaxy M81, 11 million light- years away. This information, combined with optical observations that measured the speed of the expanding debris by the Doppler shift of its emitted spectral lines, allowed a trigonometric calculation of the distance to M81. Now, with the VLBA's direct measurement of motions in the gas disk surrounding NGC 4258, trigonometric measurement, not subject to the vagaries of dust absorption and other uncertaintities in an object's brightness, has been extended to a distance of more than 23 million light-years.

A graphical approach to electric sail mission design with radial thrust

NASA Astrophysics Data System (ADS)

Mengali, Giovanni; Quarta, Alessandro A.; Aliasi, Generoso

2013-02-01

This paper describes a semi-analytical approach to electric sail mission analysis under the assumption that the spacecraft experiences a purely radial, outward, propulsive acceleration. The problem is tackled by means of the potential well concept, a very effective idea that was originally introduced by Prussing and Coverstone in 1998. Unlike a classical procedure that requires the numerical integration of the equations of motion, the proposed method provides an estimate of the main spacecraft trajectory parameters, as its maximum and minimum attainable distance from the Sun, with the simple use of analytical relationships and elementary graphs. A number of mission scenarios clearly show the effectiveness of the proposed approach. In particular, when the spacecraft parking orbit is either circular or elliptic it is possible to find the optimal performances required to reach an escape condition or a given distance from the Sun. Another example is given by the optimal strategy required to reach a heliocentric Keplerian orbit of prescribed orbital period. Finally the graphical approach is applied to the preliminary design of a nodal mission towards a Near Earth Asteroid.

Simulation and analysis of a geopotential research mission

NASA Technical Reports Server (NTRS)

White, Lisa K.

1987-01-01

Methods for the determination of the initial conditions for the two satellites that will satisfy Geopotential Research Mission (GRM) requirements are investigated. For certain gravitational recovery techniques, the satellites must remain close to a specified separation distance and their groundtracks must repeat after a specified interval of time. Since the objective of the GRM mission is to improve the gravity model, any pre-mission orbit predicted using existing gravity models will be in error. A technique has been developed to eliminate the drift between the two satellites caused by gravitational modeling errors and return them to repeating groundtracks. The concept of frozen orbits, which minimize altitude variations over given latitudes, was investigated. Finally, the effects of temporal perturbations on the relative range-rate signal were studied. At the proposed altitude of 160 km, the range-rate signal produced by perturbations other than the static geopotential field are dominated by the luni-solar effect. This study demonstrates that the combined effects of all the temporal perturbations does not prevent the orbit from being frozen or the satellites from obtaining a repeating groundtrack to within a specified closure distance.

Laplace-transformed atomic orbital-based Møller–Plesset perturbation theory for relativistic two-component Hamiltonians

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmich-Paris, Benjamin, E-mail: b.helmichparis@vu.nl; Visscher, Lucas, E-mail: l.visscher@vu.nl; Repisky, Michal, E-mail: michal.repisky@uit.no

2016-07-07

We present a formulation of Laplace-transformed atomic orbital-based second-order Møller–Plesset perturbation theory (MP2) energies for two-component Hamiltonians in the Kramers-restricted formalism. This low-order scaling technique can be used to enable correlated relativistic calculations for large molecular systems. We show that the working equations to compute the relativistic MP2 energy differ by merely a change of algebra (quaternion instead of real) from their non-relativistic counterparts. With a proof-of-principle implementation we study the effect of the nuclear charge on the magnitude of half-transformed integrals and show that for light elements spin-free and spin-orbit MP2 energies are almost identical. Furthermore, we investigate themore » effect of separation of charge distributions on the Coulomb and exchange energy contributions, which show the same long-range decay with the inter-electronic/atomic distance as for non-relativistic MP2. A linearly scaling implementation is possible if the proper distance behavior is introduced to the quaternion Schwarz-type estimates as for non-relativistic MP2.« less

Ripples in reality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lincoln, Don; Stuver, Amber

In a deep and dark corner of space, a cataclysm loomed. Two cosmic nemeses circled one another, locked in a macabre dance of death. Unfolding over millennia, the deadly waltz began leisurely enough. But with the dance came radiation and the energy loss that it implies. Orbit after orbit, the distance between the two protagonists shrank as their grip on each other tightened. Radiation carried away energy, but not angular momentum, so the orbital velocity grew to incomprehensible levels—well into the realm where Einstein's theory of special relativity reigns supreme. With the closing distances, the inevitable occurred as the twomore » twisted knots of spacetime approached each other and merged in a spasm that shook the universe so violently that the energy output briefly outshone the electromagnetic energy output of the entire universe. The two adversaries become one, finally merged together for all eternity. The traces of their ordeal died away, leaving only a fading death scream that spread throughout the cosmos, growing ever fainter. That is, until they passed through Earth. Furthermore, that was the moment that changed everything.« less

Ripples in reality

DOE PAGES

Lincoln, Don; Stuver, Amber

2016-10-01

In a deep and dark corner of space, a cataclysm loomed. Two cosmic nemeses circled one another, locked in a macabre dance of death. Unfolding over millennia, the deadly waltz began leisurely enough. But with the dance came radiation and the energy loss that it implies. Orbit after orbit, the distance between the two protagonists shrank as their grip on each other tightened. Radiation carried away energy, but not angular momentum, so the orbital velocity grew to incomprehensible levels—well into the realm where Einstein's theory of special relativity reigns supreme. With the closing distances, the inevitable occurred as the twomore » twisted knots of spacetime approached each other and merged in a spasm that shook the universe so violently that the energy output briefly outshone the electromagnetic energy output of the entire universe. The two adversaries become one, finally merged together for all eternity. The traces of their ordeal died away, leaving only a fading death scream that spread throughout the cosmos, growing ever fainter. That is, until they passed through Earth. Furthermore, that was the moment that changed everything.« less

Elliptical-like orbits on a warped spandex fabric: A theoretical/experimental undergraduate research project

NASA Astrophysics Data System (ADS)

Middleton, Chad A.; Weller, Dannyl

2016-04-01

We present a theoretical and experimental analysis of the elliptical-like orbits of a marble rolling on a warped spandex fabric. We arrive at an expression describing the angular separation between successive apocenters, or equivalently successive pericenters, in both the small and large slope regimes. We find that a minimal angular separation of ˜197° is predicted for orbits with small radial distances when the surface is void of a central mass. We then show that for small radii and large central masses, when the orbiting marble is deep within the well, the angular separation between successive apocenters transitions to values greater than 360°. We lastly compare these expressions to those describing elliptical-like orbits about a static, spherically symmetric massive object in the presence of a constant vacuum energy, as described by general relativity.

Theoretical treatment of the spin-orbit coupling in the rare gas oxides NeO, ArO, KrO, and XeO

NASA Technical Reports Server (NTRS)

Langhoff, S. R.

1980-01-01

Off-diagonal spin-orbit matrix elements are calculated as a function of internuclear distance for the rare gas oxides NeO, ArO, KrO, and XeO using the full microscopic spin-orbit Hamiltonian, including all one- and two-electron integrals, and POL-CI wave functions comparable to those of Dunning and Hay (1977). A good agreement was found when comparing these results in detail with the calculations of Cohen, Wadt and Hay (1979) that utilize an effective one-electron one-center spin-orbit operator. For the rare gas oxide molecules, it is suggested that the numerical results are a more sensitive test of the wave functions (particularly to the extent of charge transfer) than the exact evaluation of all terms in the full spin-orbit operator.

Effects of solar radiation on the orbits of small particles

NASA Technical Reports Server (NTRS)

Lyttleton, R. A.

1976-01-01

A modification of the Robertson (1937) equations of particle motion in the presence of solar radiation is developed which allows for partial reflection of sunlight as a result of rapid and varying particle rotations caused by interaction with the solar wind. The coefficients and forces in earlier forms of the equations are compared with those in the present equations, and secular rates of change of particle orbital elements are determined. Orbital dimensions are calculated in terms of time, probable sizes and densities of meteoric and cometary particles are estimated, and times of infall to the sun are computed for a particle moving in an almost circular orbit and a particle moving in an elliptical orbit of high eccentricity. Changes in orbital elements are also determined for particles from a long-period sun-grazing comet. The results show that the time of infall to the sun from a highly eccentric orbit is substantially shorter than from a circular orbit with a radius equal to the mean distance in the eccentric orbit. The possibility is considered that the free orbital kinetic energy of particles drawn into the sun may be the energy source for the solar corona.

Solar Orbiter Status Update

NASA Astrophysics Data System (ADS)

Zouganelis, Y.; Mueller, D.; St Cyr, O. C.; Gilbert, H. R.

2016-12-01

Solar Orbiter, the first mission of ESA's Cosmic Vision 2015-2025 programme, promises to deliver groundbreaking science with previously unavailable observational capabilities provided by a suite of in-situ and remote-sensing instruments in a unique orbit. The mission will address the central question of heliophysics: How does the Sun create and control the heliosphere? The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. In this talk, we highlight the scientific goals of Solar Orbiter, address the synergy between this joint ESA/NASA mission and other new space and ground-based observatories, and present the mission's development status.

Nontraditional method for determining unperturbed orbits of unknown space objects using incomplete optical observational data

NASA Astrophysics Data System (ADS)

Perov, N. I.

1985-02-01

A physical-geometrical method for computing the orbits of earth satellites on the basis of an inadequate number of angular observations (N3) was developed. Specifically, a new method has been developed for calculating the elements of Keplerian orbits of unidentified artificial satellites using two angular observations (alpha sub k, S sub k, k = 1). The first section gives procedures for determining the topocentric distance to AES on the basis of one optical observation. This is followed by description of a very simple method for determining unperturbed orbits using two satellite position vectors and a time interval which is applicable even in the case of antiparallel AED position vectors, a method designated the R sub 2 iterations method.

Mission Steering Profiles of Outer Planetary Orbiters Using Radioisotope Electric Propulsion

NASA Technical Reports Server (NTRS)

Fiehler, Douglas; Oleson, Steven

2004-01-01

Radioisotope Electric Propulsion (REP) has the potential to enable small spacecraft to orbit outer planetary targets with trip times comparable to flyby missions. The ability to transition from a flyby to an orbiter mission lies in the availability of continuous low power electric propulsion along the entire trajectory. The electric propulsion system s role is to add and remove energy from the spacecraft s trajectory to bring it in and out of a heliocentric hyperbolic escape trajectory for the outermost target bodies. Energy is added and the trajectory is reshaped to rendezvous with the closer-in target bodies. Sample REP trajectories will be presented for missions ranging for distances from Jupiter orbit to the Pluto-Kuiper Belt.

Orbital effect for the Fulde-Ferrell-Larkin-Ovchinnikov phase in a quasi-two-dimensional superconductor in a parallel magnetic field

NASA Astrophysics Data System (ADS)

Lebed, A. G.

2018-04-01

We theoretically study the orbital destructive effect against superconductivity in a parallel magnetic field in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO or LOFF) phase at zero temperature in a quasi-two-dimensional (Q2D) conductor. We demonstrate that at zero temperature a special parameter, λ =l⊥(H ) /d , is responsible for strength of the orbital effect, where l⊥(H ) is a typical "size" of the quasiclassical electron orbit in a magnetic field and d is the interplane distance. We discuss applications of our results to the existing experiments on the FFLO phase in the organic Q2D conductors κ -(ET) 2Cu (NCS) 2 and κ -(ET) 2Cu [N (CN) 2] Cl .

Orbital Evolution of Jupiter-family Comets

NASA Astrophysics Data System (ADS)

Ipatov, S. I.; Mather, J. C.

2004-05-01

The orbital evolution of more than 25,000 Jupiter-family comets (JFCs) under the gravitational influence of planets was studied. After 40 Myr one considered object (with initial orbit close to that of Comet 88P) got aphelion distance Q<3.5 AU, and it moved in orbits with semi-major axis a=2.60-2.61 AU, perihelion distance 1.71.4 AU, Q<2.6 AU, e=0.2-0.3, and i=9-33 deg for 8 Myr (and it had Q<3 AU for 100 Myr). So JFCs can rarely get typical asteroid orbits and move in them for Myrs. In our opinion, it can be possible that Comet 133P (Elst--Pizarro) moving in a typical asteroidal orbit was earlier a JFC and it circulated its orbit also due to non-gravitational forces. JFCs got near-Earth object (NEO) orbits more often than typical asteroidal orbits. A few JFCs got Earth-crossing orbits with a<2 AU and Q<4.2 AU and moved in such orbits for more than 1 Myr (up to tens or even hundreds of Myrs). Three considered former JFCs even got inner-Earth orbits (with Q<0.983 AU) or Aten orbits for Myrs. The probability of a collision of one of such objects, which move for millions of years inside Jupiter's orbit, with a terrestrial planet can be greater than analogous total probability for thousands other objects. Results obtained by the Bulirsch-Stoer method and by a symplectic method were mainly similar (except for probabilities of close encounters with the Sun when they were high). Our results show that the trans-Neptunian belt can provide a significant portion of NEOs, or the number of trans-Neptunian objects migrating inside solar system could be smaller than it was earlier considered, or most of 1-km former trans-Neptunian objects that had got NEO orbits disintegrated into mini-comets and dust during a smaller part of their dynamical lifetimes if these lifetimes are not small. The obtained results show that during the accumulation of the giant planets the total mass of icy bodies delivered to the Earth could be about the mass of water in Earth's oceans. Several our papers on this problem were put in http://arXiv.org/format/astro-ph/ (e.g., 0305519, 0308448). This work was supported by NASA (NAG5-10776) and INTAS (00-240).

Precise Distances for Main-belt Asteroids in Only Two Nights

NASA Astrophysics Data System (ADS)

Heinze, Aren N.; Metchev, Stanimir

2015-10-01

We present a method for calculating precise distances to asteroids using only two nights of data from a single location—far too little for an orbit—by exploiting the angular reflex motion of the asteroids due to Earth’s axial rotation. We refer to this as the rotational reflex velocity method. While the concept is simple and well-known, it has not been previously exploited for surveys of main belt asteroids (MBAs). We offer a mathematical development, estimates of the errors of the approximation, and a demonstration using a sample of 197 asteroids observed for two nights with a small, 0.9-m telescope. This demonstration used digital tracking to enhance detection sensitivity for faint asteroids, but our distance determination works with any detection method. Forty-eight asteroids in our sample had known orbits prior to our observations, and for these we demonstrate a mean fractional error of only 1.6% between the distances we calculate and those given in ephemerides from the Minor Planet Center. In contrast to our two-night results, distance determination by fitting approximate orbits requires observations spanning 7-10 nights. Once an asteroid’s distance is known, its absolute magnitude and size (given a statistically estimated albedo) may immediately be calculated. Our method will therefore greatly enhance the efficiency with which 4m and larger telescopes can probe the size distribution of small (e.g., 100 m) MBAs. This distribution remains poorly known, yet encodes information about the collisional evolution of the asteroid belt—and hence the history of the Solar System.

Low-energy ballistic lunar transfers

NASA Astrophysics Data System (ADS)

Parker, Jeffrey S.

A systematic method is developed that uses dynamical systems theory to model, analyze, and construct low-energy ballistic lunar transfers (BLTs). It has been found that low-energy BLTs may be produced by intersecting the stable manifold of an unstable Earth-Moon three-body orbit with the Earth. A spacecraft following such a trajectory is only required to perform a single maneuver, namely, the Trans-Lunar Injection maneuver, in order to complete the transfer. After the Trans-Lunar Injection maneuver, the spacecraft follows an entirely ballistic trajectory that asymptotically approaches and arrives at the target lunar three-body orbit. Because these orbit transfers require no orbit insertion maneuver at the three-body orbit, the transfers may be used to send spacecraft 25--40% more massive than spacecraft sent to the same orbits via conventional, direct transfers. From the targeted three-body orbits, the spacecraft may transfer to nearly any region within the Earth-Moon system, including any location on the surface of the Moon. The systematic methods developed in this research allow low-energy BLTs to be characterized by six parameters. It has been found that BLTs exist in families, where a family of BLTs consists of transfers whose parameters vary in a continuous fashion from one end of the family to the other. The families are easily identified and studied using a BLT State Space Map (BLT Map). The present research studies BLT Maps and has surveyed a wide variety of BLTs that exist in the observed families. It has been found that many types of BLTs may be constructed between 185-km low Earth parking orbits and lunar three-body orbits that require less than 3.27 km/s and fewer than 120 days of transfer time. Under certain conditions, BLTs may be constructed that require less than 3.2 km/s and fewer than 100 days of transfer time. It has been found that BLTs may implement LEO parking orbits with nearly any combination of altitude and inclination; they may depart from their LEO parking orbits nearly any day of each month; and they may target a variety of different classes of unstable Earth-Moon three-body orbits. Finally, studies are provided that address how low-energy transfers impact the design of spacecraft systems and how BLT Maps may be implemented as pragmatic tools in the design of practical lunar missions.

Survey of Galileo Plasma Observations in Jupiter's Plasma Sheet

NASA Technical Reports Server (NTRS)

Bagenal, Fran; Wilson, Robert J.; Siler, Scott; Paterson, William R.; Kurth, William S.

2016-01-01

The plasma science (PLS) Instrument on the Galileo spacecraft (orbiting Jupiter from December 1995 to September 2003) measured properties of the ions that were trapped in the magnetic field. The PLS data provide a survey of the plasma properties between approx. 5 and 30 Jupiter radii [R(sub J)] in the equatorial region. We present plasma properties derived via two analysis methods: numerical moments and forward modeling. We find that the density decreases with radial distance by nearly 5 orders of magnitude from approx. 2 to 3000 cm(exp.-3) at 6R(sub j) to approx. 0.05cm(sub -3) at 30 R(sub j). The density profile did not show major changes from orbit to orbit, suggesting that the plasma production and transport remained constant within about a factor of 2. The radial profile of ion temperature increased with distance which implied that contrary to the concept of adiabatic cooling on expansion, the plasma heats up as it expands out from Io's orbit (where TI is approx.60-80 eV) at approx. 6R(sub j) to a few keV at 30R(sub j).There does not seem to be a long-term, systematic variation in ion temperature with either local time or longitude. This latter finding differs from earlier analysis of Galileo PLS data from a selection of orbits. Further examination of all data from all Galileo orbits suggests that System Ill variations are transitory on timescales of weeks, consistent with the modeling of Cassini Ultraviolet Imaging Spectrograph observations. The plasma flow is dominated by azimuthal flow that is between 80% and 100% of corotation out to 25 R(sub j).

Globular Clusters: Absolute Proper Motions and Galactic Orbits

NASA Astrophysics Data System (ADS)

Chemel, A. A.; Glushkova, E. V.; Dambis, A. K.; Rastorguev, A. S.; Yalyalieva, L. N.; Klinichev, A. D.

2018-04-01

We cross-match objects from several different astronomical catalogs to determine the absolute proper motions of stars within the 30-arcmin radius fields of 115 Milky-Way globular clusters with the accuracy of 1-2 mas yr-1. The proper motions are based on positional data recovered from the USNO-B1, 2MASS, URAT1, ALLWISE, UCAC5, and Gaia DR1 surveys with up to ten positions spanning an epoch difference of up to about 65 years, and reduced to Gaia DR1 TGAS frame using UCAC5 as the reference catalog. Cluster members are photometrically identified by selecting horizontal- and red-giant branch stars on color-magnitude diagrams, and the mean absolute proper motions of the clusters with a typical formal error of about 0.4 mas yr-1 are computed by averaging the proper motions of selected members. The inferred absolute proper motions of clusters are combined with available radial-velocity data and heliocentric distance estimates to compute the cluster orbits in terms of the Galactic potential models based on Miyamoto and Nagai disk, Hernquist spheroid, and modified isothermal dark-matter halo (axisymmetric model without a bar) and the same model + rotating Ferre's bar (non-axisymmetric). Five distant clusters have higher-than-escape velocities, most likely due to large errors of computed transversal velocities, whereas the computed orbits of all other clusters remain bound to the Galaxy. Unlike previously published results, we find the bar to affect substantially the orbits of most of the clusters, even those at large Galactocentric distances, bringing appreciable chaotization, especially in the portions of the orbits close to the Galactic center, and stretching out the orbits of some of the thick-disk clusters.

Precision Orbit of δ Delphini and Prospects for Astrometric Detection of Exoplanets

NASA Astrophysics Data System (ADS)

Gardner, Tyler; Monnier, John D.; Fekel, Francis C.; Williamson, Mike; Duncan, Douglas K.; White, Timothy R.; Ireland, Michael; Adams, Fred C.; Barman, Travis; Baron, Fabien; ten Brummelaar, Theo; Che, Xiao; Huber, Daniel; Kraus, Stefan; Roettenbacher, Rachael M.; Schaefer, Gail; Sturmann, Judit; Sturmann, Laszlo; Swihart, Samuel J.; Zhao, Ming

2018-03-01

Combining visual and spectroscopic orbits of binary stars leads to a determination of the full 3D orbit, individual masses, and distance to the system. We present a full analysis of the evolved binary system δ Delphini using astrometric data from the MIRC and PAVO instruments on the CHARA long-baseline interferometer, 97 new spectra from the Fairborn Observatory, and 87 unpublished spectra from the Lick Observatory. We determine the full set of orbital elements for δ Del, along with masses of 1.78 ± 0.07 M ⊙ and 1.62 ± 0.07 M ⊙ for each component, and a distance of 63.61 ± 0.89 pc. These results are important in two contexts: for testing stellar evolution models and for defining the detection capabilities for future planet searches. We find that the evolutionary state of this system is puzzling, as our measured flux ratios, radii, and masses imply a ∼200 Myr age difference between the components, using standard stellar evolution models. Possible explanations for this age discrepancy include mass transfer scenarios with a now-ejected tertiary companion. For individual measurements taken over a span of two years, we achieve <10 μas precision on the differential position with 10 minute observations. The high precision of our astrometric orbit suggests that exoplanet detection capabilities are within reach of MIRC at CHARA. We compute exoplanet detection limits around δ Del and conclude that, if this precision is extended to wider systems, we should be able to detect most exoplanets >2 M J on orbits >0.75 au around individual components of hot binary stars via differential astrometry.

HABITABILITY OF EXOMOONS AT THE HILL OR TIDAL LOCKING RADIUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hinkel, Natalie R.; Kane, Stephen R., E-mail: natalie.hinkel@gmail.com

2013-09-01

Moons orbiting extrasolar planets are the next class of object to be observed and characterized for possible habitability. Like the host-planets to their host-star, exomoons have a limiting radius at which they may be gravitationally bound, or the Hill radius. In addition, they also have a distance at which they will become tidally locked and therefore in synchronous rotation with the planet. We have examined the flux phase profile of a simulated, hypothetical moon orbiting at a distant radius around the confirmed exoplanets {mu} Ara b, HD 28185 b, BD +14 4559 b, and HD 73534 b. The irradiated fluxmore » on a moon at its furthest, stable distance from the planet achieves its largest flux gradient, which places a limit on the flux ranges expected for subsequent (observed) moons closer in orbit to the planet. We have also analyzed the effect of planetary eccentricity on the flux on the moon, examining planets that traverse the habitable zone either fully or partially during their orbit. Looking solely at the stellar contributions, we find that moons around planets that are totally within the habitable zone experience thermal equilibrium temperatures above the runaway greenhouse limit, requiring a small heat redistribution efficiency. In contrast, exomoons orbiting planets that only spend a fraction of their time within the habitable zone require a heat redistribution efficiency near 100% in order to achieve temperatures suitable for habitability. This means that a planet does not need to spend its entire orbit within the habitable zone in order for the exomoon to be habitable. Because the applied systems comprise giant planets around bright stars, we believe that the transit detection method is most likely to yield an exomoon discovery.« less

On the Diversity in Mass and Orbital Radius of Giant Planets Formed via Disk Instability

NASA Astrophysics Data System (ADS)

Müller, Simon; Helled, Ravit; Mayer, Lucio

2018-02-01

We present a semi-analytical population synthesis model of protoplanetary clumps formed by disk instability at radial distances of 80–120 au. Various clump density profiles, initial mass functions, protoplanetary disk models, stellar masses, and gap opening criteria are considered. When we use more realistic gap opening criteria, we find that gaps open only rarely, which strongly affects clump survival rates and their physical properties (mass, radius, and radial distance). The inferred surviving population is then shifted toward less massive clumps at smaller radial distances. We also find that populations of surviving clumps are very sensitive to the model assumptions and used parameters. Depending on the chosen parameters, the protoplanets occupy a mass range between 0.01 and 16 M J and may either orbit close to the central star or as far out as 75 au, with a sweet spot at 10–30 au for the massive ones. However, in all of the cases we consider, we find that massive giant planets at very large radial distances are rare, in qualitative agreement with current direct imaging surveys. We conclude that caution should be taken in deriving population synthesis models as well as when comparing the models’ results with observations.

The magnetic field in the very close neighborhood of Mars according to data from the Mars 2 and Mars 3 spacecraft

NASA Technical Reports Server (NTRS)

Dolginov, S. S.; Yeroshenko, Y. G.; Zhuzgov, L. N.

1972-01-01

The magnetic field in the close proximity of planet Mars according to data from Mars 2 and Mars 3 spacecraft is discussed. The magnetometers on the spacecraft detected a field whose intensity near the orbital periapses was 7 to 10 times higher than the interplanetary field at the distance of the Martian orbit. The nature of the observed field is described.

Predicting pathologic tumor response to chemoradiotherapy with histogram distances characterizing longitudinal changes in 18F-FDG uptake patterns

PubMed Central

Tan, Shan; Zhang, Hao; Zhang, Yongxue; Chen, Wengen; D’Souza, Warren D.; Lu, Wei

2013-01-01

Purpose: A family of fluorine-18 (18F)-fluorodeoxyglucose (18F-FDG) positron-emission tomography (PET) features based on histogram distances is proposed for predicting pathologic tumor response to neoadjuvant chemoradiotherapy (CRT). These features describe the longitudinal change of FDG uptake distribution within a tumor. Methods: Twenty patients with esophageal cancer treated with CRT plus surgery were included in this study. All patients underwent PET/CT scans before (pre-) and after (post-) CRT. The two scans were first rigidly registered, and the original tumor sites were then manually delineated on the pre-PET/CT by an experienced nuclear medicine physician. Two histograms representing the FDG uptake distribution were extracted from the pre- and the registered post-PET images, respectively, both within the delineated tumor. Distances between the two histograms quantify longitudinal changes in FDG uptake distribution resulting from CRT, and thus are potential predictors of tumor response. A total of 19 histogram distances were examined and compared to both traditional PET response measures and Haralick texture features. Receiver operating characteristic analyses and Mann-Whitney U test were performed to assess their predictive ability. Results: Among all tested histogram distances, seven bin-to-bin and seven crossbin distances outperformed traditional PET response measures using maximum standardized uptake value (AUC = 0.70) or total lesion glycolysis (AUC = 0.80). The seven bin-to-bin distances were: L2 distance (AUC = 0.84), χ2 distance (AUC = 0.83), intersection distance (AUC = 0.82), cosine distance (AUC = 0.83), squared Euclidean distance (AUC = 0.83), L1 distance (AUC = 0.82), and Jeffrey distance (AUC = 0.82). The seven crossbin distances were: quadratic-chi distance (AUC = 0.89), earth mover distance (AUC = 0.86), fast earth mover distance (AUC = 0.86), diffusion distance (AUC = 0.88), Kolmogorov-Smirnov distance (AUC = 0.88), quadratic form distance (AUC = 0.87), and match distance (AUC = 0.84). These crossbin histogram distance features showed slightly higher prediction accuracy than texture features on post-PET images. Conclusions: The results suggest that longitudinal patterns in 18F-FDG uptake characterized using histogram distances provide useful information for predicting the pathologic response of esophageal cancer to CRT. PMID:24089897

Scale-dependent correlation of seabirds with schooling fish in a coastal ecosystem

USGS Publications Warehouse

Schneider, Davod C.; Piatt, John F.

1986-01-01

The distribution of piscivorous seabirds relative to schooling fish was investigated by repeated censusing of 2 intersecting transects in the Avalon Channel, which carries the Labrador Current southward along the east coast of Newfoundland. Murres (primarily common murres Uria aalge), Atlantic puffins Fratercula arctica, and schooling fish (primarily capelin Mallotus villosus) were highly aggregated at spatial scales ranging from 0.25 to 15 km. Patchiness of murres, puffins and schooling fish was scale-dependent, as indicated by significantly higher variance-to-mean ratios at large measurement distances than at the minimum distance, 0.25 km. Patch scale of puffins ranged from 2.5 to 15 km, of murres from 3 to 8.75 km, and of schooling fish from 1.25 to 15 km. Patch scale of birds and schooling fish was similar m 6 out of 9 comparisons. Correlation between seabirds and schooling birds was significant at the minimum measurement distance in 6 out of 12 comparisons. Correlation was scale-dependent, as indicated by significantly higher coefficients at large measurement distances than at the minimum distance. Tracking scale, as indicated by the maximum significant correlation between birds and schooling fish, ranged from 2 to 6 km. Our analysis showed that extended aggregations of seabirds are associated with extended aggregations of schooling fish and that correlation of these marine carnivores with their prey is scale-dependent.

Patterns and drivers for wetland connections in the Prairie Pothole Region, United States

USGS Publications Warehouse

Vanderhoof, Melanie; Christensen, Jay R.; Alexander, Laurie C.

2017-01-01

Ecosystem function in rivers, lakes and coastal waters depends on the functioning of upstream aquatic ecosystems, necessitating an improved understanding of watershed-scale interactions including variable surface-water flows between wetlands and streams. As surface water in the Prairie Pothole Region expands in wet years, surface-water connections occur between many depressional wetlands and streams. Minimal research has explored the spatial patterns and drivers for the abundance of these connections, despite their potential to inform resource management and regulatory programs including the U.S. Clean Water Act. In this study, wetlands were identified that did not intersect the stream network, but were shown with Landsat images (1990–2011) to become merged with the stream network as surface water expanded. Wetlands were found to spill into or consolidate with other wetlands within both small (2–10 wetlands) and large (>100 wetlands) wetland clusters, eventually intersecting a stream channel, most often via a riparian wetland. These surface-water connections occurred over a wide range of wetland distances from streams (averaging 90–1400 m in different ecoregions). Differences in the spatial abundance of wetlands that show a variable surface-water connection to a stream were best explained by smaller wetland-to-wetland distances, greater wetland abundance, and maximum surface-water extent. This analysis demonstrated that wetland arrangement and surface water expansion are important mechanisms for depressional wetlands to connect to streams and provides a first step to understanding the frequency and abundance of these surface-water connections across the Prairie Pothole Region.

The qualitative scoring MMSE pentagon test (QSPT): a new method for differentiating dementia with Lewy Body from Alzheimer's disease.

PubMed

Caffarra, Paolo; Gardini, Simona; Dieci, Francesca; Copelli, Sandra; Maset, Laura; Concari, Letizia; Farina, Elisabetta; Grossi, Enzo

2013-01-01

The differential diagnosis across different variants of degenerative diseases is sometimes controversial. This study aimed to validate a qualitative scoring method for the pentagons copy test (QSPT) of Mini-Mental State Examination (MMSE) based on the assessment of different parameters of the pentagons drawing, such as number of angles, distance/intersection, closure/opening, rotation, closing-in, and to verify its efficacy to differentiate dementia with Lewy Body (DLB) from Alzheimer's disease (AD). We established the reliability of the qualitative scoring method through the inter-raters and intra-subjects analysis. QSPT was then applied to forty-six AD and forty-six DLB patients, using two phases statistical approach, standard and artificial neural network respectively. DLB patients had significant lower total score in the copy of pentagons and number of angles, distance/intersection, closure/opening, rotation compared to AD. However the logistic regression did not allow to establish any suitable modeling, whereas using Auto-Contractive Map (Auto-CM) the DLB was more strongly associated with low scores in some qualitative parameters of pentagon copying, i.e. number of angles and opening/closure and, for the remaining subitems of the MMSE, in naming, repetition and written comprehension, and for demographic variables of gender (male) and education (6-13 years). Twist system modeling showed that the QSPT had a good sensitivity (70.29%) and specificity (78.67%) (ROC-AUC 0.74). The proposed qualitative method of assessment of pentagons copying used in combination with non-linear analysis, showed to be consistent and effective in the differential diagnosis between Lewy Body and Alzheimer's dementia.

Dixie Valley, Nevada playa bathymetry constructed from Landsat TM data

NASA Astrophysics Data System (ADS)

Groeneveld, David P.; Barz, David D.

2014-05-01

A bathymetry model was developed from a series of Landsat Thematic Mapper (TM) images to assist discrimination of hydrologic processes on a low-relief, stable saline playa in Dixie Valley, Nevada, USA. The slope of the playa surface, established by field survey on a reference transect, enabled calculation of relative elevation of the edges of pooled brine mapped from Landsat TM5 band 5 reflectance (TMB5) in the 1.55-1.75 μm shortwave infrared region (SWIR) of the spectrum. A 0.02 TMB5 reflectance threshold accurately differentiated the shallow (1-2 mm depth) edges of pools. Isocontours of equal elevations of pool margins were mapped with the TMB5 threshold, forming concentric rings that were assigned relative elevations according to the position that the pool edges intersected the reference transect. These data were used to fit a digital elevation model and a curve for estimating pooled volume given the distance from the playa edge to the intersection of the pool edge with the reference transect. To project pooled volume using the bathymetric model for any TM snapshot, within a geographic information system, the 0.02 TMB5 threshold is first used to define the edge of the exposed brine. The distance of this edge from the playa edge along the reference transect is then measured and input to the bathymetric equation to yield pooled volume. Other satellite platforms with appropriate SWIR bands require calibration to Landsat TMB5. The method has applicability for filling reservoirs, bodies of water that fluctuate and especially bodies of water inaccessible to acoustic or sounding methods.

The planar shape of drumlins

NASA Astrophysics Data System (ADS)

Spagnolo, Matteo; Clark, Chris D.; Hughes, Anna L. C.; Dunlop, Paul; Stokes, Chris R.

2010-12-01

The asymmetry of the planar shape of drumlins is an established paradigm in the literature and characterizes drumlins as resembling tear drops with a blunt (bullet-shaped) stoss end and a tapering (pointed) lee end. It is widely cited and never been seriously questioned. In this paper, the planar shape of 44,500 drumlins mapped in various regional settings from drumlin fields in North America and Northern Europe were objectively analysed by means of Geographic Information System tools. Two parameters were considered. The first (denoted here as Aspl) focuses on the relative position of the point of intersection between the axes of the maximum length and the maximum width. It is defined as the distance between the upstream (i.e. beginning of the drumlin) and the intersection point (measured along the longitudinal axis) divided by the entire length of the long axis. Results indicate that the intersection point of the majority of drumlins (64%) is very close to the longitudinal midpoint (0.33 < Aspl < 0.66). The second parameter ( Aspl _A) is defined as the ratio between the area of the upstream half of the drumlin to that of the entire drumlin. Results show that for most drumlins (81%), the upper half area is almost as large as the down-half (0.45 < Aspl _A < 0.55). Taken together, these results concordantly indicate that drumlin planar shape has a strong tendency to be longitudinally symmetric and that the long-established paradigm of their plan form is false.

Color-encoded distance for interactive focus positioning in laser microsurgery

NASA Astrophysics Data System (ADS)

Schoob, Andreas; Kundrat, Dennis; Lekon, Stefan; Kahrs, Lüder A.; Ortmaier, Tobias

2016-08-01

This paper presents a real-time method for interactive focus positioning in laser microsurgery. Registration of stereo vision and a surgical laser is performed in order to combine surgical scene and laser workspace information. In particular, stereo image data is processed to three-dimensionally reconstruct observed tissue surface as well as to compute and to highlight its intersection with the laser focal range. Regarding the surgical live view, three augmented reality concepts are presented providing visual feedback during manual focus positioning. A user study is performed and results are discussed with respect to accuracy and task completion time. Especially when using color-encoded distance superimposed to the live view, target positioning with sub-millimeter accuracy can be achieved in a few seconds. Finally, transfer to an intraoperative scenario with endoscopic human in vivo and cadaver images is discussed demonstrating the applicability of the image overlay in laser microsurgery.

A Practical, Robust and Fast Method for Location Localization in Range-Based Systems.

PubMed

Huang, Shiping; Wu, Zhifeng; Misra, Anil

2017-12-11

Location localization technology is used in a number of industrial and civil applications. Real time location localization accuracy is highly dependent on the quality of the distance measurements and efficiency of solving the localization equations. In this paper, we provide a novel approach to solve the nonlinear localization equations efficiently and simultaneously eliminate the bad measurement data in range-based systems. A geometric intersection model was developed to narrow the target search area, where Newton's Method and the Direct Search Method are used to search for the unknown position. Not only does the geometric intersection model offer a small bounded search domain for Newton's Method and the Direct Search Method, but also it can self-correct bad measurement data. The Direct Search Method is useful for the coarse localization or small target search domain, while the Newton's Method can be used for accurate localization. For accurate localization, by utilizing the proposed Modified Newton's Method (MNM), challenges of avoiding the local extrema, singularities, and initial value choice are addressed. The applicability and robustness of the developed method has been demonstrated by experiments with an indoor system.

Two-dimensional shape recognition using oriented-polar representation

NASA Astrophysics Data System (ADS)

Hu, Neng-Chung; Yu, Kuo-Kan; Hsu, Yung-Li

1997-10-01

To deal with such a problem as object recognition of position, scale, and rotation invariance (PSRI), we utilize some PSRI properties of images obtained from objects, for example, the centroid of the image. The corresponding position of the centroid to the boundary of the image is invariant in spite of rotation, scale, and translation of the image. To obtain the information of the image, we use the technique similar to Radon transform, called the oriented-polar representation of a 2D image. In this representation, two specific points, the centroid and the weighted mean point, are selected to form an initial ray, then the image is sampled with N angularly equispaced rays departing from the initial rays. Each ray contains a number of intersections and the distance information obtained from the centroid to the intersections. The shape recognition algorithm is based on the least total error of these two items of information. Together with a simple noise removal and a typical backpropagation neural network, this algorithm is simple, but the PSRI is achieved with a high recognition rate.

Spatial distribution of pollutants in the area of the former CHP plant

NASA Astrophysics Data System (ADS)

Cichowicz, Robert

2018-01-01

The quality of atmospheric air and level of its pollution are now one of the most important issues connected with life on Earth. The frequent nuisance and exceedance of pollution standards often described in the media are generated by both low emission sources and mobile sources. Also local organized energy emission sources such as local boiler houses or CHP plants have impact on air pollution. At the same time it is important to remember that the role of local power stations in shaping air pollution immission fields depends on the height of emitters and functioning of waste gas treatment installations. Analysis of air pollution distribution was carried out in 2 series/dates, i.e. 2 and 10 weeks after closure of the CHP plant. In the analysis as a reference point the largest intersection of streets located in the immediate vicinity of the plant was selected, from which virtual circles were drawn every 50 meters, where 31 measuring points were located. As a result, the impact of carbon dioxide, hydrogen sulfide and ammonia levels could be observed and analyzed, depending on the distance from the street intersection.

Kondo effect in single cobalt phthalocyanine molecules adsorbed on Au(111) monoatomic steps

NASA Astrophysics Data System (ADS)

Zhao, Aidi; Hu, Zhenpeng; Wang, Bing; Xiao, Xudong; Yang, Jinlong; Hou, J. G.

2008-06-01

The Kondo effect in single dehydrogenated cobalt phthalocyanine (CoPc) molecules adsorbed on Au(111) monoatomic steps was studied with a low temperature scanning tunneling microscope. The CoPc molecules adsorbed on Au(111) monoatomic steps show two typical configurations, which can be dehydrogenated to reveal Kondo effect. Moreover, the Kondo temperatures (TK) measured for different molecules vary in a large range from ~150 to ~550 K, increasing monotonically with decreasing Co-Au distance. A simple model consisting of a single Co 3dz2 orbital and a Au 6s orbital is considered and gives a qualitative explanation to the dependence. The large variation of TK is attributed to the variation of the interaction between the magnetic-active cobalt ion and the Au substrate resulted from different Co-Au distances.

Revisiting the Bohr Atom 100 Years Later

NASA Astrophysics Data System (ADS)

Wall, Ernst

2013-03-01

We use a novel electron model wherein the electron is modeled as a point charge behaving as a trapped photon revolving in a Compton wavelength orbit at light speed. The revolving point charge gives rise to spiraling Compton wavelets around the electron, which give rise to de Broglie waves. When applied to the Bohr model, the orbital radius of the electron scales to the first Bohr orbit's radius via the fine structure constant. The orbiting electron's orbital velocity, Vb, scales to that of the electron's charge's internal velocity (the velocity of light, c) via the fine structure constant. The Compton wavelets, if they reflect off the nucleus, have a round trip time just long enough to allow the electron to move one of its diameters in distance in the first Bohr orbit. The ratio of the electron's rotational frequency, fe, to its rotational frequency in the Bohr orbit fb, is fe/fb = 1/α2, which is also the number of electron rotations in single orbit. If we scale the electron's rotational energy (h*fe) to that of the orbit using this, the orbital energy value (h*fb) would be 27.2114 eV. However, the virial theorem reduces it to 13.6057, the ground state energy of the first Bohr orbit. Ref: www.tachyonmodel.com.

Precise orbit determination of the Lunar Reconnaissance Orbiter and first gravity field results

NASA Astrophysics Data System (ADS)

Maier, Andrea; Baur, Oliver

2014-05-01

The Lunar Reconnaissance Orbiter (LRO) was launched in 2009 and is expected to orbit the Moon until the end of 2014. Among other instruments, LRO has a highly precise altimeter on board demanding an orbit accuracy of one meter in the radial component. Precise orbit determination (POD) is achieved with radiometric observations (Doppler range rates, ranges) on the one hand, and optical laser ranges on the other hand. LRO is the first satellite at a distance of approximately 360 000 to 400 000 km from the Earth that is routinely tracked with optical laser ranges. This measurement type was introduced to achieve orbits of higher precision than it would be possible with radiometric observations only. In this contribution we investigate the strength of each measurement type (radiometric range rates, radiometric ranges, optical laser ranges) based on single-technique orbit estimation. In a next step all measurement types are combined in a joined analysis. In addition to POD results, preliminary gravity field coefficients are presented being a subsequent product of the orbit determination process. POD and gravity field estimation was accomplished with the NASA/GSFC software packages GEODYN and SOLVE.

Sleeping with an Elephant: Asteroids that Share a Planet's Orbit

NASA Astrophysics Data System (ADS)

Wiegert, Paul; Connors, Martin; Brasser, Ramon; Mikkola, Seppo; Stacey, Greg; Innanen, Kimmo

2005-08-01

Under special circumstances, relatively small asteroids are able to safely share the orbit of a much larger planet. The best known examples of such "co-orbital" bodies are the Trojan asteroids of Jupiter, over 1700 of which are known to travel either 60 degrees ahead of or behind this giant planet in its orbit. The stability of such configurations might be thought to depend on the asteroid giving the planet a wide berth. In reality, co-orbital asteroids may approach their planet relatively closely, to within a few times its Hill sphere (which is five times the distance to the Moon in the case of the Earth). For many co-orbital bodies such approaches occur rarely or not at all, but recently examples of co-orbital states that become trapped near their planet have been found. Such "quasi-satellites" may remain near their much larger partner for thousands of years, though in actuality they are not true satellites and continue to orbit the Sun. Here we discuss the behaviour of some recently discovered co-orbital asteroids with emphasis on 2004 GU9, recently found to have a long-lived quasi-satellite state relative to the Earth.

[Multi-wall orbital decompression for disfiguring proptosis in patients with mild or moderate thyroid eye disease].

PubMed

Wang, Y; Yang, N; Li, Y Y; Xiao, L H

2017-02-11

Objective: To evaluate the efficacy of orbital decompression by transconjunctival medial and inferior wall combined transpalpebral lateral wall for disfiguring proptosis with mild or moderate thyroid eye disease (TED). Methods: It is a retrospective case series study. The clinical data of 18 TED cases (28 orbits) between Dec 2013 and Dec 2015 at the Institute of Orbital Diseases of the General Hospital of the Armed Police were reviewed. All the patients underwent mulit-wall orbital decompression to relieve remarkable proptosis, widen eyelid fissure, and swollen eyelid. 1. Hertel value was 14-23 mm or over 2-7 mm than contralateral eye; 2.Orbitalpathy has been inactive with normal thyroid function for at least 6 months; 3.Orbital pressure is normal or (+). Clinical outcomes were recorded including best-corrected visual acuity, exophthalmometry, margin-to-central distance of upper and lower lids, diplopia, and CT scans before and 3 months after surgery. Results: The mean protosis of pre-and postoperation were (19.2±2.3) mm and (14.7±1.4) mm with mean reduction was (4.6±1.7) mm ( t= 14.08, P< 0.01). Margin-to-central distance of the upperlid of pre- and postoperation were (5.1±1.2) mm and (4.9±1.3) mm with mean reduction was (0.2±0.5) mm ( t= 1.73, P= 0.095). Margin-to-central distance of the lowerlid of pre-and postoperation were (5.9±0.9) mm and 4.3±0.7 mm with mean reduction was (1.6±0.8) mm ( t= 10.09, P< 0.01). The difference of bilateral exophthalmos after surgery is 0-2.5 mm (media n= 1 mm). None of the patients showed new-onset diplopia at primary gaze and two patient showed surrounding gaze diplopia postoperatively. Two patients with diplopia relieved after surgery ( Z= 743.00, P= 0.458). Conclusions: Transconjunctival and transpalpebral medial, inferior, and lateral walls decompression with a hidden incision was a controllable, safe, effective technique with minimal complications in relieving not only mild, moderate proptosis, but also retraction of lowerlid, and swollen eyelids. (Chin J Ophthalmol, 2017, 53: 128-135) .

Are There Many Inactive Jupiter-Family Comets among the Near-Earth Asteroid Population?

NASA Astrophysics Data System (ADS)

Fernández, Julio A.; Gallardo, Tabaré; Brunini, Adrián

2002-10-01

We analyze the dynamical evolution of Jupiter-family (JF) comets and near-Earth asteroids (NEAs) with aphelion distances Q>3.5 AU, paying special attention to the problem of mixing of both populations, such that inactive comets may be disguised as NEAs. From numerical integrations for 2×10 6 years we find that the half lifetime (where the lifetime is defined against hyperbolic ejection or collision with the Sun or the planets) of near-Earth JF comets (perihelion distances q<1.3 AU) is about 1.5×10 5 years but that they spend only a small fraction of this time (˜ a few 10 3 years) with q<1.3 AU. From numerical integrations for 5×10 6 years we find that the half lifetime of NEAs in "cometary" orbits (defined as those with aphelion distances Q>4.5 AU, i.e., that approach or cross Jupiter's orbit) is 4.2×10 5 years, i.e., about three times longer than that for near-Earth JF comets. We also analyze the problem of decoupling JF comets from Jupiter to produce Encke-type comets. To this end we simulate the dynamical evolution of the sample of observed JF comets with the inclusion of nongravitational forces. While decoupling occurs very seldom when a purely gravitational motion is considered, the action of nongravitational forces (as strong as or greater than those acting on Encke) can produce a few Enckes. Furthermore, a few JF comets are transferred to low-eccentricity orbits entirely within the main asteroid belt ( Q<4 AU and q>2 AU). The population of NEAs in cometary orbits is found to be adequately replenished with NEAs of smaller Q's diffusing outward, from which we can set an upper limit of ˜20% for the putative component of deactivated JF comets needed to maintain such a population in steady state. From this analysis, the upper limit for the average time that a JF comet in near-Earth orbit can spend as a dormant, asteroid-looking body can be estimated to be about 40% of the time spent as an active comet. More likely, JF comets in near-Earth orbits will disintegrate once (or shortly after) they end their active phases.

Tethered orbital refueling study

NASA Technical Reports Server (NTRS)

Fester, Dale A.; Rudolph, L. Kevin; Kiefel, Erlinda R.; Abbott, Peter W.; Grossrode, Pat

1986-01-01

One of the major applications of the space station will be to act as a refueling depot for cryogenic-fueled space-based orbital transfer vehicles (OTV), Earth-storable fueled orbit maneuvering vehicles, and refurbishable satellite spacecraft using hydrazine. One alternative for fuel storage at the space station is a tethered orbital refueling facility (TORF), separated from the space station by a sufficient distance to induce a gravity gradient force that settles the stored fuels. The technical feasibility was examined with the primary focus on the refueling of LO2/LH2 orbital transfer vehicles. Also examined was the tethered facility on the space station. It was compared to a zero-gravity facility. A tethered refueling facility should be considered as a viable alternative to a zero-gravity facility if the zero-gravity fluid transfer technology, such as the propellant management device and no vent fill, proves to be difficult to develop with the required performance.

Sedna Orbit Animation

NASA Technical Reports Server (NTRS)

2004-01-01

This animation shows the location of the newly discovered planet-like object, dubbed 'Sedna,' in relation to the rest of the solar system. Starting at the inner solar system, which includes the orbits of Mercury, Venus, Earth, and Mars (all in yellow), the view pulls away through the asteroid belt and the orbits of the outer planets beyond (green). Pluto and the distant Kuiper Belt objects are seen next until finally Sedna comes into view. As the field widens the full orbit of Sedna can be seen along with its current location. Sedna is nearing its closest approach to the Sun; its 10,000 year orbit typically takes it to far greater distances. Moving past Sedna, what was previously thought to be the inner edge of the Oort cloud appears. The Oort cloud is a spherical distribution of cold, icy bodies lying at the limits of the Sun's gravitational pull. Sedna's presence suggests that this Oort cloud is much closer than scientists believed.

Aeroheating Characteristics for a Two-Stage-To-Orbit Concept During Separation at Mach 6

NASA Technical Reports Server (NTRS)

Liechty, Derek S.

2005-01-01

An experimental study was conducted to determine the proximity aeroheating characteristics for a two-stage-to-orbit concept in close proximity in the NASA Langley 20-Inch Mach 6 Air Tunnel. A new hybrid discrete thin-film resistance gauge technique was evaluated in this study and used to measure experimental interference heating levels between the booster and the orbiter at a constant freestream Reynolds number of 8.25 x 10(exp 6)/m and a variety of separation and axial offset distances. It was found that, as the orbiter separates from the booster and the booster falls away, the windward centerline heating increased on the orbiter by as much as 13-times over the baseline, single model heating distribution, and on the booster by as much as 6-times. The aeroheating database developed can be used for computational fluid dynamic code validation.

Orbital motions of bubbles in an acoustic field

NASA Astrophysics Data System (ADS)

Shirota, Minori; Yamashita, Ko; Inamura, Takao

2012-09-01

This experimental study aims to clarify the mechanism of orbital motion of two oscillating bubbles in an acoustic field. Trajectory of the orbital motion on the wall of a spherical levitator was observed using a high-speed video camera. Because of a good repeatability in volume oscillation of bubbles, we were also able to observe the radial motion driven at 24 kHz by stroboscopic like imaging technique. The orbital motions of bubbles raging from 0.13 to 0.18 mm were examined with different forcing amplitude and in different viscous oils. As a result, we found that pairs of bubbles revolve along an elliptic orbit around the center of mass of the bubbles. We also found that the two bubbles perform anti-phase radial oscillation. Although this radial oscillation should result in a repulsive secondary Bjerknes force, the bubbles kept a constant separate distance of about 1 mm, which indicates the existence of centripetal primary Bjerknes force.

Stable regions around Exoplanets: the search for Exomoons

NASA Astrophysics Data System (ADS)

Fernandes Guimaraes, Ana Helena; Moretto Tusnski, Luis Ricardo; Vieira-Neto, Ernesto; Silva Valio, Adriana

2015-08-01

There are hundreds of exoplanets which the data are available to a dynamical investigation. We extracted from the data base (exoplanets.org) all planets and candidates which have the necessary data available for the numerical investigation of the orbital stability of a body around a exoplanet in a total of 2749 of those.There is a wealth diversity of exoplanets types and the expectation in find our Earth-living conditions in another planet motivates the search for extra-solar planets, and a satellite around a planet would, in addiction, help to keep a favorable climate.Using the planets class according to PHL@Arecibo, those planets were sorted out in groups. Analyses of density, distance from the primary body, and mass ratios were done beside the suggested classification to fit some no-classified planets into one of the groups.The aim of this work is to derive the upper stability limit (or upper critical orbit) of fictitious direct satellites around exoplanets of any density, or size, orbiting single stars. Our search is for stable regions around the planet, the called S-type orbits. This orbit type determines if there is any chance to exist (or not) bodies around the planets. The investigation is limited to single stars, excluding binaries.We derived such limit purely through numerical simulations. Our proposal involved long-term integration of the circular restricted three bodies problem . Basically, the cut off of the stability zone determined in the previous work by Domingos et al. (2006) were confirmed for any planet type. However, the limitation due the Roche limit of the own satellite showed to be lower. We used this to determined possible size and to adjust orbital range were a third body could orbit the exoplanet.Independently of densities, distance, and sizes of the objects involved, the idea was to delimit where to find celestial bodies in any given system around single stars. Furthermore, we aim to provide tracks to the search for exomoons using planetary transits.

Astrometry and orbits of Nix, Kerberos, AND Hydra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buie, Marc W.; Grundy, William M.; Tholen, David J., E-mail: buie@boulder.swri.edu, E-mail: grundy@lowell.edu, E-mail: tholen@ifa.hawaii.edu

We present new Hubble Space Telescope observations of three of Pluto's outer moons, Nix, Kerberos, and Hydra. This work revises previously published astrometry of Nix and Hydra from 2002 to 2003. New data from a four-month span during 2007 include observations designed to better measure the positions of Nix and Hydra. A third data set from 2010 also includes data on Nix and Hydra as well as some pre-discovery observations of Kerberos. The data were fitted using numerical point-spread function (PSF) fitting techniques to get accurate positions but also to remove the extended wings of the Pluto and Charon PSFsmore » when working on these faint satellites. The resulting astrometric data were fitted with two-body Keplerian orbits that are useful for short-term predictions of the future positions of these satellites for stellar occultation and for guiding encounter planning for the upcoming New Horizons flyby of the Pluto system. The mutual inclinations of the satellites are all within 0.°2 of the plane of Charon's orbit. The periods for all continue to show that their orbits are near but distinct from integer period ratios relative to Charon. Based on our results, the period ratios are Hydra:Charon = 5.98094 ± 0.00001, Kerberos:Charon = 5.0392 ± 0.0003, and Nix:Charon = 3.89135 ± 0.00001. Based on period ratios alone, there is a trend of increased distance from an integer period ratio with decreasing distance from Charon. Our analysis shows that orbital uncertainties for Nix and Hydra are now low enough to permit useful stellar occultation predictions and for New Horizons encounter planning. In 2015 July, our orbits predict a position error of 60 km for Nix and 38 km for Hydra, well below other limiting errors that affect targeting. The orbit for Kerberos, however, still needs a lot of work as its uncertainty in 2015 is quite large at 22,000 km based on these data.« less

Interpreting Radar View near Mars' South Pole, Orbit 1360

NASA Technical Reports Server (NTRS)

2006-01-01

A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the south pole of Mars.

The sounding radar collected the data presented here during orbit 1360 of the mission, on Nov. 10, 2006.

The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 74 degrees to 85 degrees south latitude, or about 650 kilometers (400 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse proceeds up onto a plateau formed by the layers.

The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface at one place: about 800 meters (2,600 feet) to one of the strongest subsurface reflectors. This reflector marks the base of the polar layered deposits. The color scale varies from black for weak reflections to white for strong reflections.

The middle panel shows mapping of the major subsurface reflectors, some of which can be traced for a distance of 100 kilometers (60 miles) or more. The layering manifests the recent climate history of Mars, recorded by the deposition and removal of ice and dust.

The Shallow Subsurface Radar was provided by the Italian Space Agency (ASI). Its operations are led by the University of Rome and its data are analyzed by a joint U.S.-Italian science team. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington.

The study of the physics of cometary nuclei

NASA Technical Reports Server (NTRS)

Whipple, F. L.

1985-01-01

The development and utilization of an optimized computer program to analyze orbital stabilization by repeated calculations is presented. The stability of comets in the Opik-Oort Cloud about the Sun against perturbations by the Galactic center involve the same basic type of calculation. The supposed persistence of these bodies in orbits over the life of the solar system, depends upon the stability of bodies of negligible mass in orbits around a body whose mass is small compared to the central mass about which they revolve. The question remains of preferential orientation of extremely eccentric comet orbits, possibly to explain the asymmetry observed among new comet motions. A third application of the computing programs is suited to meteoroids that may exist in orbits about asteroids and that may endanger science spacecraft making flybys too near to asteroids. As in the double-comet case, solar activity and solar gravitational perturbations limit the attendance to an asteroid by small meteroids in their orbits. It is found that the mass distances planned for asteroid fly-bys are adequate.

Simplified technique for orbital prosthesis fabrication: a clinical report.

PubMed

Veerareddy, Chandrika; Nair, K Chandrasekharan; Reddy, G Ramaswamy

2012-10-01

Loss of orbital content can cause functional impairment, disfigurement of the face, and psychological distress. Rehabilitation of an orbital defect is a complex task, and if reconstruction by plastic surgery is not possible or not desired by the patient, the defect can be rehabilitated by an orbital prosthesis. The prosthetic rehabilitation in such cases depends on the precisely retained, user-friendly removable maxillofacial prosthesis. Many times, making an impression of the orbital area with an accurate record of surface details can be a difficult procedure. The critical areas are making a facial moulage, mold preparation, and attaching the retention device, particularly when eyeglass frames are used. This case focuses on these hindrance factors. A simple basket was used for the impression tray to obtain the facial moulage. A putty mold was used, and attachment of the prosthesis to a retention device was accomplished with positional distance. This method proves to be an economical and simple way of making an orbital prosthesis. © 2012 by the American College of Prosthodontists.

Gas Flow and Star Formation in the Centre of the Milky Way : Investigations with Smoothed Particle Hydrodynamics

NASA Astrophysics Data System (ADS)

Lucas, William Evan

2015-06-01

The centre of the Milky Way, commonly referred to as the Galactic Centre, is roughly that region within 500 pc of the central black hole, Sagittarius A*. Within the innermost parsec around the supermassive black hole Sagittarius A* are more than a hundred massive young stars whose orbits align to form one or possibly two discs. At about 100 pc is a ring containing more than ten million solar masses of molecular gas which could be the origin of some of the most massive star clusters in the Galaxy. I have performed a number of numerical simulations to help us understand how it is that these structures may have been formed. I firstly describe and test an improvement to the smoothed particle hydrodynamics code I used. This improves conservation of energy and momentum in certain situations such as in strong shocks from supernovae, which were to be included in a later chapter. The discs of massive stars around Sagittarius A* are believed to have been born there within fragmenting gaseous discs. This is problematic, as the formation of two stellar discs would require two gaseous counterparts. A method is described of forming multiple discs around a black hole from a single cloud's infall and subsequent tidal destruction. This is due to its prolate shape providing a naturally large distribution in the direction of the angular momentum vectors within the cloud. The resulting discs may then go on to form stars. Energetically, it would appear that a sequence of supernovae could potentially cause a giant molecular cloud to fall inwards towards the central black hole from an originally large orbit around the Galactic Centre. I simulate the impact on a giant molecular cloud of supernovae originating from a massive stellar cluster located a parsec away. Ultimately, the supernovae are found to have little effect. Finally, I simulate the formation of the dense ring of clouds observed in the Central Molecular Zone at a distance of about 100 pc from Sgr A*. Infalling gas is shown to be subject to such extreme tidal forces that a single cloud of gas is extended to form a long stream. The ribbon grows to the point that it self-intersects and forms a ring-like structure. Its complexity depends on the orbit of the original cloud. The position-velocity data is compared with observations, and similarities are noted.

Tectonics of ridge-transform intersections at the Kane fracture zone

NASA Astrophysics Data System (ADS)

Karson, J. A.; Dick, H. J. B.

1983-03-01

The Kane Transform offsets spreading-center segments of the Mid-Atlantic Ridge by about 150 km at 24° N latitude. In terms of its first-order morphological, geological, and geophysical characteristics it appears to be typical of long-offset (>100 km), slow-slipping (2 cm yr-1) ridge-ridge transform faults. High-resolution geological observations were made from deep-towed ANGUS photographs and the manned submersible ALVIN at the ridge-transform intersections and indicate similar relationships in these two regions. These data indicate that over a distance of about 20 km as the spreading axes approach the fracture zone, the two flanks of each ridge axis behave in very different ways. Along the flanks that intersect the active transform zone the rift valley floor deepens and the surface expression of volcanism becomes increasingly narrow and eventually absent at the intersection where only a sediment-covered ‘nodal basin’ exists. The adjacent median valley walls have structural trends that are oblique to both the ridge and the transform and have as much as 4 km of relief. These are tectonically active regions that have only a thin (<200 m), highly fractured, and discontinuous carapace of volcanic rocks overlying a variably deformed and metamorphosed assemblage of gabbroic rocks. Overprinting relationships reveal a complex history of crustal extension and rapid vertical uplift. In contrast, the opposing flanks of the ridge axes, that intersect the non-transform zones appear to be similar in many respects to those examined elsewhere along slow-spreading ridges. In general, a near-axial horst and graben terrain floored by relatively young volcanics passes laterally into median valley walls with a simple block-faulted character where only volcanic rocks have been found. Along strike toward the fracture zone, the youngest volcanics form linear constructional volcanic ridges that transect the entire width of the fracture zone valley. These volcanics are continuous with the older-looking, slightly faulted volcanic terrain that floors the non-transform fracture zone valleys. These observations document the asymmetric nature of seafloor spreading near ridge-transform intersections. An important implication is that the crust and lithosphere across different portions of the fracture zone will have different geological characteristics. Across the active transform zone two lithosphere plate edges formed at ridge-transform corners are faulted against one another. In the non-transform zones a relatively younger section of lithosphere that formed at a ridge-non-transform corner is welded to an older, deformed section that initially formed at a ridge-transform corner.

The finite body triangulation: algorithms, subgraphs, homogeneity estimation and application.

PubMed

Carson, Cantwell G; Levine, Jonathan S

2016-09-01

The concept of a finite body Dirichlet tessellation has been extended to that of a finite body Delaunay 'triangulation' to provide a more meaningful description of the spatial distribution of nonspherical secondary phase bodies in 2- and 3-dimensional images. A finite body triangulation (FBT) consists of a network of minimum edge-to-edge distances between adjacent objects in a microstructure. From this is also obtained the characteristic object chords formed by the intersection of the object boundary with the finite body tessellation. These two sets of distances form the basis of a parsimonious homogeneity estimation. The characteristics of the spatial distribution are then evaluated with respect to the distances between objects and the distances within them. Quantitative analysis shows that more physically representative distributions can be obtained by selecting subgraphs, such as the relative neighbourhood graph and the minimum spanning tree, from the finite body tessellation. To demonstrate their potential, we apply these methods to 3-dimensional X-ray computed tomographic images of foamed cement and their 2-dimensional cross sections. The Python computer code used to estimate the FBT is made available. Other applications for the algorithm - such as porous media transport and crack-tip propagation - are also discussed. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society.

Orbital synchronization capture of two binaries emitting gravitational waves

NASA Astrophysics Data System (ADS)

Seto, Naoki

2018-03-01

We study the possibility of orbital synchronization capture for a hierarchical quadrupole stellar system composed by two binaries emitting gravitational waves. Based on a simple model including the mass transfer for white dwarf binaries, we find that the capture might be realized for inter-binary distances less than their gravitational wavelength. We also discuss related intriguing phenomena such as a parasitic relation between the coupled white dwarf binaries and significant reductions of gravitational and electromagnetic radiations.

Practical Method to Identify Orbital Anomaly as Breakup Event in the Geostationary Region

DTIC Science & Technology

2015-01-14

point ! Geocentric distance at the pinch point Table 4 summarizes the results of the origin identifications. One object labeled x15300 was...Table 4. The result of origin identification of the seven detected objects Object name Parent object Inclination vector Pinch point Geocentric distance...of the object. X-Y, X’-Y’, and R.A.-Dec. represent the Image Coordinate before rotating the CCD sensor, after rotation, and the Geocentric Inertial

Distance to the Center of the Milky Way Galaxy: An Experiment for Intermediate-Level Students Using Research Data and Professional Analysis Tools

ERIC Educational Resources Information Center

Fitzgerald, M. T.; Feteris, S. M.; Gillessen, S.; Eisenhauer, F.

2008-01-01

The most recent data on stars orbiting Sagittarius A*, the black hole at the center of the Milky Way galaxy, have been used in an experiment undertaken by second-year university students to determine the distance R[theta] to the center of the galaxy. Students applied each of Kepler's 17th-century laws, in turn, to 21st-century data. The…

A search of impact orbits for near-Earth objects by means of minimization of two target functions product. (Russian Title: Поиск столкновительных орбит астероидов, сближающихся с Землей, с помощью минимизации произведения двух целевых функций)

NASA Astrophysics Data System (ADS)

Baturin, A. P.

2011-07-01

The method of NEO's impact orbits search based on two target functions product minimization is presented. These functions are: a square of asteroid-Earth distance at the moment of close approach and a sum of squares of angular residuals. Besides, the method includes a minimization of asteroid-Earth distance's square in function of time alone when initial motion parameters are fixed. Both minimizations are carrying out in turn each by another. The testing of method has been made on the problem of Apophis's impact orbit search. The results of the testing have depicted an effectivity of presented method in searching of impact orbits for the Apophis's Earth encounters in 2036 and 2037.

A Comprehensive Analysis of Ion Cyclotron Waves in the Equatorial Magnetosphere of Saturn

NASA Astrophysics Data System (ADS)

Meeks, Z. C.; Simon, S.

2016-12-01

We present a comprehensive analysis of ion cyclotron waves in the equatorial magnetosphere of Saturn, considering all magnetic field data collected during the Cassini era (totaling to over 4 years of data from the equatorial plane). This dataset includes eight targeted flybys of Enceladus, three targeted flybys of Dione, and three targeted flybys of Rhea. Because all remaining orbits of Cassini are high-inclination, our study provides the complete map of ion cyclotron waves in Saturn's equatorial magnetosphere during the Cassini era. We provide catalogs of the radial and longitudinal dependencies of the occurrence rate and amplitude of the ion cyclotron fundamental and first harmonic wave modes. The fundamental wave mode is omnipresent between the orbits of Enceladus and Dione and evenly distributed across all Local Times. The occurrence rate of the fundamental mode displays a Fermi-Dirac-like profile with respect to radial distance from Saturn. Detection of the first harmonic mode is a rare event occurring in only 0.49% of measurements taken and always in conjunction with the fundamental mode. We also search for a dependency of the ion cyclotron wave field on the orbital positions of the icy moons Enceladus, Dione, and Rhea. On magnetospheric length scales, the wave field is independent of the moons' orbital positions. For Enceladus, we analyze wave amplitude profiles of seven close flybys (E9, E12, E13, E14, E17, E18, and E19), which occurred during the studied trajectory segments, to look for any local effects of Enceladan plume variability on the wave field. We find that even in the close vicinity of Enceladus, the wave amplitudes display no discernible dependency on Enceladus' angular distance to its orbital apocenter. Thus, the correlation between plume activity and angular distance to apocenter proposed by Hedman et al. (2013) does not leave a clearly distinguishable imprint in the ion cyclotron wave field. Reference: Meeks, Z., Simon, S., Kabanovic, S., 2016. A comprehensive analysis of ion cyclotron waves in the equatorial magnetosphere of Saturn. Planetary and Space Sciences 129, 47-60.

Investigating the Relativistic Motion of the Stars Near the Supermassive Black Hole in the Galactic Center

NASA Astrophysics Data System (ADS)

Parsa, M.; Eckart, A.; Shahzamanian, B.; Karas, V.; Zajaček, M.; Zensus, J. A.; Straubmeier, C.

2017-08-01

The S-star cluster in the Galactic center allows us to study the physics close to a supermassive black hole, including distinctive dynamical tests of general relativity. Our best estimates for the mass of and the distance to Sgr A* using the three stars with the shortest period (S2, S38, and S55/S0-102) and Newtonian models are M BH = (4.15 ± 0.13 ± 0.57) × 106 M ⊙ and R 0 = 8.19 ± 0.11 ± 0.34 kpc. Additionally, we aim at a new and practical method to investigate the relativistic orbits of stars in the gravitational field near Sgr A*. We use a first-order post-Newtonian approximation to calculate the stellar orbits with a broad range of periapse distance r p . We present a method that employs the changes in orbital elements derived from elliptical fits to different sections of the orbit. These changes are correlated with the relativistic parameter defined as ϒ ≡ r s /r p (with r s being the Schwarzschild radius) and can be used to derive ϒ from observational data. For S2 we find a value of ϒ = 0.00088 ± 0.00080, which is consistent, within the uncertainty, with the expected value of ϒ = 0.00065 derived from M BH and the orbit of S2. We argue that the derived quantity is unlikely to be dominated by perturbing influences such as noise on the derived stellar positions, field rotation, and drifts in black hole mass.

How Sedna and family were captured in a close encounter with a solar sibling

NASA Astrophysics Data System (ADS)

Jílková, Lucie; Portegies Zwart, Simon; Pijloo, Tjibaria; Hammer, Michael

2015-11-01

The discovery of 2012 VP113 initiated the debate on the origin of the Sedna family of planetesimals in orbit around the Sun. Sednitos roam the outer regions of the Solar system between the Egeworth-Kuiper belt and the Oort Cloud, in extraordinary wide (a > 150 au) orbits with a large perihelion distance of q > 30 au compared to the Earth's (a ≡ 1 au and eccentricity e ≡ (1 - q/a) ≃ 0.0167 or q ≃ 1 au). This population is composed of a dozen objects, which we consider a family because they have similar perihelion distance and inclination with respect to the ecliptic i = 10°-30°. They also have similar argument of perihelion ω = 340° ± 55°. There is no ready explanation for their origin. Here we show that these orbital parameters are typical for a captured population from the planetesimal disc of another star. Assuming that the orbital elements of Sednitos have not changed since they acquired their orbits, we reconstruct the encounter that led to their capture. We conclude that they might have been captured in a near miss with a 1.8 M⊙ star that impacted the Sun at ≃ 340 au at an inclination with respect to the ecliptic of 17°-34° with a relative velocity at infinity of ˜4.3 km s-1. We predict that the Sednitos region is populated by 930 planetesimals and the inner Oort Cloud acquired ˜440 planetesimals through the same encounter.

Gas Planet Orbits

NASA Image and Video Library

2008-08-19

Jupiter, Saturn, Uranus, and Neptune are known as the jovian Jupiter-like planets because they are all gigantic compared with Earth, and they have a gaseous nature. This diagram shows the approximate distance of the jovian planets from the Sun.

Infrared Spectroscopy of Symbiotic Stars. XI. Orbits for Southern S-type Systems: Hen 3-461, SY Mus, Hen 3-828, AND AR Pav

NASA Astrophysics Data System (ADS)

Fekel, Francis C.; Hinkle, Kenneth H.; Joyce, Richard R.; Wood, Peter R.

2017-01-01

Employing new infrared radial velocities, we have computed spectroscopic orbits of the cool giants in four southern S-type symbiotic systems. The orbits for two of the systems, Hen 3-461 and Hen 3-828, have been determined for the first time, while orbits of the other two, SY Mus and AR Pav, have previously been determined. For the latter two systems, we compare our results with those in the literature. The low mass of the secondary of SY Mus suggests that it has gone through a common envelope phase. Hen 3-461 has an orbital period of 2271 days, one of the longest currently known for S-type symbiotic systems. That period is very different from the orbital period proposed previously from its photometric variations. The other three binaries have periods between 600 and 700 day, values that are typical for S-type symbiotic orbits. Basic properties of the M giant components and the distance to each system are determined.

Angles-only relative orbit determination in low earth orbit

NASA Astrophysics Data System (ADS)

Ardaens, Jean-Sébastien; Gaias, Gabriella

2018-06-01

The paper provides an overview of the angles-only relative orbit determination activities conducted to support the Autonomous Vision Approach Navigation and Target Identification (AVANTI) experiment. This in-orbit endeavor was carried out by the German Space Operations Center (DLR/GSOC) in autumn 2016 to demonstrate the capability to perform spaceborne autonomous close-proximity operations using solely line-of-sight measurements. The images collected onboard have been reprocessed by an independent on-ground facility for precise relative orbit determination, which served as ultimate instance to monitor the formation safety and to characterize the onboard navigation and control performances. During two months, several rendezvous have been executed, generating a valuable collection of images taken at distances ranging from 50 km to only 50 m. Despite challenging experimental conditions characterized by a poor visibility and strong orbit perturbations, angles-only relative positioning products could be continuously derived throughout the whole experiment timeline, promising accuracy at the meter level during the close approaches. The results presented in the paper are complemented with former angles-only experience gained with the PRISMA satellites to better highlight the specificities induced by different orbits and satellite designs.

INFRARED SPECTROSCOPY OF SYMBIOTIC STARS. XI. ORBITS FOR SOUTHERN S-TYPE SYSTEMS: HEN 3-461, SY MUS, HEN 3-828, AND AR PAV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fekel, Francis C.; Hinkle, Kenneth H.; Joyce, Richard R.

Employing new infrared radial velocities, we have computed spectroscopic orbits of the cool giants in four southern S-type symbiotic systems. The orbits for two of the systems, Hen 3-461 and Hen 3-828, have been determined for the first time, while orbits of the other two, SY Mus and AR Pav, have previously been determined. For the latter two systems, we compare our results with those in the literature. The low mass of the secondary of SY Mus suggests that it has gone through a common envelope phase. Hen 3-461 has an orbital period of 2271 days, one of the longest currently known for S-type symbiotic systems.more » That period is very different from the orbital period proposed previously from its photometric variations. The other three binaries have periods between 600 and 700 day, values that are typical for S-type symbiotic orbits. Basic properties of the M giant components and the distance to each system are determined.« less

The Solar Orbiter Heliospheric Imager (SoloHI) for the Solar Orbiter Mission

NASA Astrophysics Data System (ADS)

Howard, R.; Colaninno, R. C.; Plunkett, S. P.; Thernisien, A. F.; Wang, D.; Rich, N.; Korendyke, C.; Socker, D. G.; Linton, M.; McMullin, D. R.; Vourlidas, A.; Liewer, P. C.; De Jong, E.; Velli, M.; Mikic, Z.; Bothmer, V.; Philippe, L.; Carter, M. T.

2017-12-01

The SoloHI instrument has completed its development effort and has been integrated onto the Solar Orbiter (SolO) spacecraft. The SolO mission, scheduled for launch in February 2019, will undergo gravity assist maneuvers around Venus to change both the perihelion distance as well as the plane of the orbit to ultimately achieve a minimum perihelion of 0.28 AU and an orbital inclination of about 35° relative to the ecliptic plane. The remote sensing instruments will operate for three 10-day periods out of the nominal 6-month orbit. SoloHI will observe sunlight scattered by free electrons in the corona/solar wind from 5° to 45° elongation in visible wavelengths and will provide a coupling between remote sensing and in situ observations. It is very similar to the HI-1 instrument on STEREO/SECCHI except that the FOV is twice the size at 40o. We present our efforts to prepare for the mission including our observing plans, quick-look plans and some results of the calibration activities. We gratefully acknowledge the support of the NASA Solar Orbiter Collaboration project.

Orbital revolution of a pair of bubbles in an acoustic field

NASA Astrophysics Data System (ADS)

Shirota, Minori; Yamashita, Kou; Inamura, Takao

2011-11-01

This experimental study aims to clarify the mechanism of orbital motion of two oscillating bubbles in an acoustic field. Trajectory of the orbital motion was observed using a high-speed video camera. Because of a good repeatability in volume oscillation of bubbles, we were also able to observe the radial motion driven at 24 kHz by stroboscopic like imaging; the cyclic bubble oscillation was appeared to slow down by capturing images at the framing rate close to the forcing frequency. The orbital motions of bubbles raging from 0.13 to 0.18 mm were examined with different forcing amplitude and in different viscous oils. As a result, we found that pairs of bubbles revolve along a circular orbit around the center of mass of the orbiting two bubbles. We also found that the two bubbles perform anti-phase radial oscillation. Although this radial oscillation should result in a repulsive secondary Bjerknes force, the bubbles kept a constant separate distance of about 1 mm, which indicates the existence of centripetal primary Bjerknes force. The angular velocity of orbital revolution increases linearly with the increase in Bjerknes force.

Cosine-Gauss plasmon beam: a localized long-range nondiffracting surface wave.

PubMed

Lin, Jiao; Dellinger, Jean; Genevet, Patrice; Cluzel, Benoit; de Fornel, Frederique; Capasso, Federico

2012-08-31

A new surface wave is introduced, the cosine-Gauss beam, which does not diffract while it propagates in a straight line and tightly bound to the metallic surface for distances up to 80 μm. The generation of this highly localized wave is shown to be straightforward and highly controllable, with varying degrees of transverse confinement and directionality, by fabricating a plasmon launcher consisting of intersecting metallic gratings. Cosine-Gauss beams have potential for applications in plasmonics, notably for efficient coupling to nanophotonic devices, opening up new design possibilities for next-generation optical interconnects.

The Constraint of Coplanarity: Compact multi-planet system outer architectures and formation.-UP

NASA Astrophysics Data System (ADS)

Jontof-Hutter, Daniel

The Kepler mission discovered 92 systems with 4 or more transiting exoplanets. Systems like Kepler-11 with six "mini-Neptunes" on orbital periods well inside that of Venus pose a challenge to planet formation theory which is broadly split into two competing paradigms. One theory invokes the formation of Neptunes beyond the "snow line", followed by inward migration and assembly into compact configurations near the star. The alternative is that low density planets form in situ at all distances in the protoplanetary nebula. The two paradigms disagree on the occurrence of Jovian planets at longer orbital periods than the transiting exoplanets since such massive planets would impede the inward migration of multiple volatile-rich planets to within a fraction of 1 AU. The likelihood of all the known planets at systems like Kepler-11 to be transiting is very sensitive to presence of outer Jovian planets for a wide range in orbital distance and relative inclination of the Jovian planet. This can put upper limits on the occurrence of Jovian planets by the condition that the six known planets have to have low mutual inclinations most of the time in order for their current cotransiting state to be plausible. Most of these systems have little or no RV data. Hence, our upper limits may be the best constraints on the occurrence of Jovian planets in compact co-planar systems for years to come, and may help distinguish the two leading paradigms of planet formation theory. Methodology. We propose to use an established n-body code (MERCURY) to perform long-term simulations of systems like Kepler-11 with the addition of a putative Jovian planet considering a range of orbital distances. These simulations will test for which initial conditions a Jovian planet would prevent the known planets from all transiting at the same time. We will 1) determine at what orbital distances and inclinations an outer Jovian planet would make the observed configuration of Kepler-11 very unlikely. 2) Test the effect of an undetected planet in the large dynamical space between Kepler-11 f and Kepler 11 g on our upper limits on a Jovian outer planet. 3) Repeat the analysis for all compact systems of 4 or more transiting planets with published planetary masses (including Kepler-79, Kepler-33, and Kepler-80) 5) Repeat the analysis for all systems of 4 or more transiting planets where the condition of long-term orbital stability provides useful upper limits on planetary masses, using their orbital periods and an appropriate mass-radius relation. 6) Measure an upper limit on the occurrence rate of outer Jovian planets. If we find an occurrence rate significantly lower than the known occurrence rate of Jovian planets from RV surveys, this would be evidence in support of the migration model as Jovian planets are expected impede the assembly of compact coplanar systems of low-density planets close to the host star. Relevance. According to the XRP Solicitation, investigations are expected to directly support the goal of "understanding exoplanetary systems", by doing one or more of the following..."improve understanding of the origins of exoplanetary systems". This proposal will help distinguish between competing paradigms in planet formation with dynamical modeling, and hence will improve our understanding of the origins of exoplanetary systems. This proposal will in no way require analysis of archival Kepler data, and relies only on the published masses, radii and orbital periods of high muliplicity systems discovered by Kepler. Therefore, our proposal is not appropriate for ADAP.

Improved Apparatus for Measuring Distance Between Axles

NASA Technical Reports Server (NTRS)

Willard, Douglas E.; Townsend, Ivan I., III

2003-01-01

An improved version of an optoelectronic apparatus for measuring distances of the order of tens of feet with an error no larger than a small fraction of an inch (a few millimeters) has been built. Like the previous version, the present improved version of the apparatus is designed to measure the distance approximately equal to 66 ft (approximately equal to 20 m) between the axes of rotation of the front and rear tires of the space shuttle orbiter as it rests in a ground-based processing facility. Like the previous version, the present version could also be adapted for similar purposes in other settings: Examples include measuring perpendicular distance from a wall in a building, placement of architectural foundations, and general alignment and measurement operations.

Trajectories of ballistic impact ejecta on a rotating Earth

NASA Technical Reports Server (NTRS)

Alvarez, W.

1994-01-01

On an airless, slowly rotating planetary body like the Moon, ejecta particles from an impact follow simple ballistic trajectories. If gaseous interactions in the fireball are ignored, ejecta particles follow elliptical orbits with the center of the planetary body at one focus until they encounter the surface at the point of reimpact. The partial elliptical orbit of the ejecta particle lies in a plane in inertial (galactic) coordinates. Because of the slow rotation rate (for example, 360 degrees/28 days for the Moon), the intersection of the orbital plane and the surface remains nearly a great circle during the flight time of the ejecta. For this reason, lunar rays, representing concentrations of ejecta with the same azimuth but different velocities and/or ejecta angles, lie essentially along great circles. Ejecta from airless but more rapidly rotating bodies will follow more complicated, curving trajectories when plotted in the coordinate frame of the rotating planet or viewed as rays on the planetary surface. The curvature of trajectories of ejecta particles can be treated as a manifestation of the Coriolis effect, with the particles being accelerated by Coriolis pseudoforces. However, it is more straightforward to calculate the elliptical orbit in inertial space and then determine how far the planet rotates beneath the orbiting ejecta particle before reimpact. The Earth's eastward rotation affects ballistic ejecta in two ways: (1) the eastward velocity component increases the velocity of eastbound ejecta and reduces the velocity of westbound ejecta; and (2) the Earth turns underneath inflight ejecta, so that although the latitude of reimpact is not changed, the longitude is displaced westward, with the displacement increasing as a function of the time the ejecta remains aloft.

A possible space VLBI constellation utilizing the stable orbits around the TLPs in the Earth-Moon system.

NASA Astrophysics Data System (ADS)

Liu, Bin; Tang, Jingshi; Hou, Xiyun

2016-07-01

Current studies indicate that there are stable orbits around but far away from the triangular libration points .Two special quasi-periodic orbits around each triangular libration points L4 , L5 in the Earth-Moon sys-tem perturbed by Sun are gain , and the stable orbits discussed in this work are ideal places for space colonies because no orbit control is needed. These stable orbits can also be used as nominal orbits for space VLBI (Very Long Baseline Interferometry) stations. The two stations can also form baselines with stations on the Earth and the Moon, or with stations located around another TLP. Due to the long distance between the stations, the observation precision can be greatly enhanced compared with the VLBI stations on the Earth. Such a VLBI constellation not only can advance the radio astronomy, but also can be used as a navigation system for human activities in the Earth-Moon system and even in the solar system. This paper will focus on the navigation constellation coverage issues, and the orbit determination accuracy problems within the Earth-Moon sys-tem and interplanetary space.

The Gould’s Belt Distances Survey (GOBELINS). III. The Distance to the Serpens/Aquila Molecular Complex

NASA Astrophysics Data System (ADS)

Ortiz-León, Gisela N.; Dzib, Sergio A.; Kounkel, Marina A.; Loinard, Laurent; Mioduszewski, Amy J.; Rodríguez, Luis F.; Torres, Rosa M.; Pech, Gerardo; Rivera, Juana L.; Hartmann, Lee; Boden, Andrew F.; Evans, Neal J., II; Briceño, Cesar; Tobin, John J.; Galli, Phillip A. B.

2017-01-01

We report on new distances and proper motions to seven stars across the Serpens/Aquila complex. The observations were obtained as part of the Gould’s Belt Distances Survey (GOBELINS) project between 2013 September and 2016 April with the Very Long Baseline Array (VLBA). One of our targets is the proto-Herbig AeBe object EC 95, which is a binary system embedded in the Serpens Core. For this system, we combined the GOBELINS observations with previous VLBA data to cover a total period of 8 years, and derive the orbital elements and an updated source distance. The individual distances to sources in the complex are fully consistent with each other, and the mean value corresponds to a distance of 436.0 ± 9.2 pc for the Serpens/W40 complex. Given this new evidence, we argue that Serpens Main, W40, and Serpens South are physically associated and form a single cloud structure.

Photometric follow-up of sungrazing comet C/2012 S1 ISON from OAdM and other observatories

NASA Astrophysics Data System (ADS)

Trigo-Rodríguez, J. M.; Moyano-Cambero, C. E.; Meech, K. J.; Rodríguez, D.; Sánchez, A.; Lacruz, J.

2013-09-01

Comet C/2012 S1 ISON was discovered on Sept. 21st, 2012 by Russian amateur astronomers Vitaly Nevski and Artyom Novichonok in the framework of a monitoring program called the International Scientific Optical Network (giving the acronym ISON from which the comet has been named). At discovery the comet was at a heliocentric distance of 6.29 A.U. and its magnitude was +18.8, but the computed orbit indicated that the comet was following a nearly parabolic orbit. The current orbit brings C/2012 S1 ISON to an extremely small perihelion distance of about 1 milion km on Nov. 28th, 2013. We have set up a multiband photometric monitoring of this sungrazing comet using 0.8m Telescope Joan Oró of the Montsec Astronomical Observatory (OAdM: www.oadm.cat) and several medium-size amateur telescopes with dedicated experience in cometary photometry [1, 2]. Comet sungrazers are interesting objects as they probably originate from the dynamical evolution of long period comets that typically end their lives colliding with the Sun [3]. They are though to be fragments of primitive ice-rich bodies gravitationally dispersed during the early stages of solar system evolution [4].

Depth Perception in Space Artist Concept

NASA Image and Video Library

2007-05-30

This artist concept shows how astronomers use the unique orbit of NASA Spitzer Space Telescope and a depth-perceiving trick called parallax to determine the distance of dark planets, black holes and failed stars that lurk invisibly among us.

Mars Odyssey Observes Martian Moons

NASA Image and Video Library

2018-02-22

Phobos and Deimos, the moons of Mars, are seen by the Mars Odyssey orbiter's Thermal Emission Imaging System, or THEMIS, camera. The images were taken in visible-wavelength light. THEMIS also recorded thermal-infrared imagery in the same scan. The apparent motion is due to progression of the camera's pointing during the 17-second span of the February 15, 2018, observation, not from motion of the two moons. This was the second observation of Phobos by Mars Odyssey; the first was on September 29, 2017. Researchers have been using THEMIS to examine Mars since early 2002, but the maneuver turning the orbiter around to point the camera at Phobos was developed only recently. The distance to Phobos from Odyssey during the observation was about 3,489 miles (5,615 kilometers). The distance to Deimos from Odyssey during the observation was about 12,222 miles (19,670 kilometers). An animation is available at https://photojournal.jpl.nasa.gov/catalog/PIA22248

Possible Periodic Orbit Control Maneuvers for an eLISA Mission

NASA Technical Reports Server (NTRS)

Bender, Peter L.; Welter, Gary L.

2012-01-01

This paper investigates the possible application of periodic orbit control maneuvers for so-called evolved-LISA (eLISA) missions, i.e., missions for which the constellation arm lengths and mean distance from the Earth are substantially reduced. We find that for missions with arm lengths of 106 km and Earth-trailing distance ranging from approx. 12deg to 20deg over the science lifetime, the occasional use of the spacecraft micro-Newton thrusters for constellation configuration maintenance should be able to essentially eliminate constellation distortion caused by Earth-induced tidal forces at a cost to science time of only a few percent. With interior angle variation kept to approx. +/-0:1deg, the required changes in the angles between the laser beam pointing directions for the two arms from any spacecraft could be kept quite small. This would considerably simplify the apparatus necessary for changing the transmitted beam directions.

Toward a comprehensive theory for the sweeping of trapped radiation by inert orbiting matter

NASA Technical Reports Server (NTRS)

Fillius, Walker

1988-01-01

There is a need to calculate loss rates when trapped Van Allen radiation encounters inert orbiting material such as planetary rings and satellites. An analytic expression for the probability of a hit in a bounce encounter is available for all cases where the absorber is spherical and the particles are gyrotropically distributed on a cylindrical flux tube. The hit probability is a function of the particle's pitch angle, the size of the absorber, and the distance between flux tube and absorber, when distances are scaled to the gyroradius of a particle moving perpendicular to the magnetic field. Using this expression, hit probabilities have been computed in drift encounters for all regimes of particle energies and absorber sizes. This technique generalizes the approach to sweeping lifetimes, and is particularly suitable for attacking the inverse problem, where one is given a sweeping signature and wants to deduce the properties of the absorber(s).

Janus Stands Alone

NASA Image and Video Library

2015-05-18

Although Janus should be the least lonely of all moons -- sharing its orbit with Epimetheus -- it still spends most of its orbit far from other moons, alone in the vastness of space. Janus (111 miles or 179 kilometers across) and Epimetheus have the same average distance from Saturn, but they take turns being a little closer or a little farther from Saturn, swapping positions approximately every 4 years. See PIA08348 for more. This view looks toward the sunlit side of the rings from about 19 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 4, 2015. The view was acquired at a distance of approximately 1.6 million miles (2.5 million kilometers) from Janus and at a Sun-Janus-spacecraft, or phase, angle of 91 degrees. Image scale is 9 miles (15 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/pia18315

Mass Determination of Small Bodies in the Solar System

NASA Astrophysics Data System (ADS)

Paetzold, M.

2017-12-01

The masses and gravity fields of the planetary bodies were determined by radio tracking of spacecraft flying by or orbiting that body at a suffiently close distance. Small bodies (asteroids, cometary nuclei...) of the solar system pose certain challenges in order to reveal their masses and gravity fields. Those challenges mostly concerns spacecraft safety and/or optimal instrment operations. In order to resolve an acceptable Doppler shift with regard to the frequency noise, a spacecraft shall flyby at close distances, at slow speed and at an optimal flyby geometry for a given body mass. This cannot always be achieved. The flybys of Mars Express at Phobos, the flyby of Rosetta at asteroid Lutetia, its orbiting about the nucleus of 67P/Churyumov-Gerasimenko shall be reviewed. The prospects and challenges of future flybys like New Horizons at 2016MU69 and Lucy at the Trojan asteroids shall be presented.

SODA Repuslive Function Shaping

NASA Image and Video Library

2017-06-16

SODA, Swarm Orbital Dynamics Advisor, a tool that provides the orbital maneuvers required to achieve a desired type of relative swarm motion. The SODA algorithm uses a repulsive potential that is a function of the distances between each pair of satellites. Choosing the parameters of the function is a swarm design choice, as different values can yield very different maneuvers and thus impact fuel use and mission life. This is an animation illustrating how the peaks of the repulsive potential function vary when varying certain parameters.

Media Effects on Electronic Systems in the High Latitude Region

DTIC Science & Technology

1988-09-01

oval and auroral electron densities. Essentially the ICED model is still based on a set of coefficients, but these are modified by other inputs. There...and larger. At the distance of the Earth’s orbit the speed of the solar wind is usually between 200 and 700 or 800 km s -1 , on which is superimposed a...magnetometer on IMP-I (the Interplanetary Monitoring Platform), an eccentric orbit satellite with apogee at 32 RE Although the solar wind flows out almost

Taking the Measure of the Universe: Precision Astrometry with SIM Planetquest (Preprint)

DTIC Science & Technology

2006-10-09

the orbits of nearby galaxies and groups going out to the distance of the Virgo Cluster . The orbits are in comoving coordinates. This is just a...single solution of a set of several solutions using present 3-d positions as inputs. The four massive objects ( Virgo Cluster , Coma Group, CenA Group, and... Virgo Cluster from a Numerical Action Method calculation with parameters M/L = 90 for spirals and 155 for ellipticals, Ωm = 0.24, ΩΛ = 0.76. The axes are

STS-31 Discovery, Orbiter Vehicle (OV) 103, lands on EAFB concrete runway 22

NASA Technical Reports Server (NTRS)

1990-01-01

The main landing gear (MLG) of Discovery, Orbiter Vehicle (OV) 103, rides along concrete runway 22 at Edwards Air Force Base (EAFB), California, bringing mission STS-31 to an end. The nose landing gear (NLG) is suspended above the runway prior to touchdown and wheel stop which occurred at 6:51:00 am (Pacific Daylight Time (PDT)). View shows OV-103's starboard side and deployed rudder/speedbrake. EAFB facilities are seen in the distance.

Evolution of orbits of the Apollo group asteroids over 11550 years.

NASA Astrophysics Data System (ADS)

Zausaev, A. F.; Pushkarev, A. N.

The Everhart method is used to study the evolution of the orbits of 20 asteroids of the Apollo group over the time period from 9300 B.C. to 2250 A.D. Minimum distances of the asteroids to the major planets over the evolution process are calculated. The stability of resonances with Venus and Earth over the 9300 B.C.to 2250 A.D. time period is shown. Theoretical coordinates of radiants for the initial and final integration times are presented.

Solar Orbiter: Exploring the Sun-Heliosphere Connection

NASA Technical Reports Server (NTRS)

Mueller, D.; Marsden, R. G.; St.Cyr, O. C.; Gilbert, H. R.

2013-01-01

The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. Solar Orbiter, the first mission of ESA's Cosmic Vision 2015 - 2025 programme, will address the central question of heliophysics: How does the Sun create and control the heliosphere? In this paper, we present the scientific goals of the mission and provide an overview of the mission implementation.

Solar Orbiter Exploring the Sun-Heliosphere Connection

NASA Technical Reports Server (NTRS)

Mueller, Daniel; Marsden, Richard George; Cyr, O. C. St.; Gilbert, Holly Robin

2012-01-01

The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. Solar Orbiter, the first mission of ESA's Cosmic Vision 2015 - 2025 programme, will address the central question of heliophysics: How does the Sun create and control the heliosphere? In this paper, we present the scientific goals of the mission and provide an overview of the mission implementation.

Project CHECO Southeast Asia Report. USAF Tactics Against Air & Ground Defenses in SEA, November 1968 - May 1970

DTIC Science & Technology

1970-09-25

EB-66 Orbits for Drone Flight .......................... 50 16. ( EB-66 Orbits in Support of B-52 Mission ................ 50I 3 ix I~WI ’CNON.11...outmaneuver it. During the period of this report, while SAMs were fired at several USAF aircraft and shot down several drones , the USAF lost no manned...Oblique camaras had beendesigned to allow photography from a safe distance, but the heavy tree cover in Laos usually required vertical photography for

System concepts and design examples for optical communication with planetary spacecraft

NASA Astrophysics Data System (ADS)

Lesh, James R.

Systems concepts for optical communication with future deep-space (planetary) spacecraft are described. These include not only the optical transceiver package aboard the distant spacecraft, but the earth-vicinity optical-communications receiving station as well. Both ground-based, and earth-orbiting receivers are considered. Design examples for a number of proposed or potential deep-space missions are then presented. These include an orbital mission to Saturn, a Lander and Rover mission to Mars, and an astronomical mission to a distance of 1000 astronomical units.

Multizone accretional evolution of planetesimal swarms

NASA Technical Reports Server (NTRS)

Spaute, D.; Davis, D. R.; Weidenschilling, S. J.

1990-01-01

The general features of a new numerical simulation of planetesimal accretion which models multiple heliocentric distance zones, together with a detailed model for the planetesimal size and orbital distribution in each zone, are described. A restricted version of this model which allows only a single heliocentric distance zone has been used to test the validity of the code by comparing with results from earlier authors when the same physical phenomena are included. Generally, very good agreement is found.

A millisecond pulsar in an extremely wide binary system

NASA Astrophysics Data System (ADS)

Bassa, C. G.; Janssen, G. H.; Stappers, B. W.; Tauris, T. M.; Wevers, T.; Jonker, P. G.; Lentati, L.; Verbiest, J. P. W.; Desvignes, G.; Graikou, E.; Guillemot, L.; Freire, P. C. C.; Lazarus, P.; Caballero, R. N.; Champion, D. J.; Cognard, I.; Jessner, A.; Jordan, C.; Karuppusamy, R.; Kramer, M.; Lazaridis, K.; Lee, K. J.; Liu, K.; Lyne, A. G.; McKee, J.; Osłowski, S.; Perrodin, D.; Sanidas, S.; Shaifullah, G.; Smits, R.; Theureau, G.; Tiburzi, C.; Zhu, W. W.

2016-08-01

We report on 22 yr of radio timing observations of the millisecond pulsar J1024-0719 by the telescopes participating in the European Pulsar Timing Array (EPTA). These observations reveal a significant second derivative of the pulsar spin frequency and confirm the discrepancy between the parallax and Shklovskii distances that has been reported earlier. We also present optical astrometry, photometry and spectroscopy of 2MASS J10243869-0719190. We find that it is a low-metallicity main-sequence star (K7V spectral type, [M/H] = -1.0, Teff = 4050 ± 50 K) and that its position, proper motion and distance are consistent with those of PSR J1024-0719. We conclude that PSR J1024-0719 and 2MASS J10243869-0719190 form a common proper motion pair and are gravitationally bound. The gravitational interaction between the main-sequence star and the pulsar accounts for the spin frequency derivatives, which in turn resolves the distance discrepancy. Our observations suggest that the pulsar and main-sequence star are in an extremely wide (Pb > 200 yr) orbit. Combining the radial velocity of the companion and proper motion of the pulsar, we find that the binary system has a high spatial velocity of 384 ± 45 km s-1 with respect to the local standard of rest and has a Galactic orbit consistent with halo objects. Since the observed main-sequence companion star cannot have recycled the pulsar to millisecond spin periods, an exotic formation scenario is required. We demonstrate that this extremely wide-orbit binary could have evolved from a triple system that underwent an asymmetric supernova explosion, though find that significant fine-tuning during the explosion is required. Finally, we discuss the implications of the long period orbit on the timing stability of PSR J1024-0719 in light of its inclusion in pulsar timing arrays.

Energy-level repulsion by spin-orbit coupling in two-dimensional Rydberg excitons

NASA Astrophysics Data System (ADS)

Stephanovich, V. A.; Sherman, E. Ya.; Zinner, N. T.; Marchukov, O. V.

2018-05-01

We study the effects of Rashba spin-orbit coupling on two-dimensional Rydberg exciton systems. Using analytical and numerical arguments we demonstrate that this coupling considerably modifies the wave functions and leads to a level repulsion that results in a deviation from the Poissonian statistics of the adjacent level distance distribution. This signifies the crossover to nonintegrability of the system and hints at the possibility of quantum chaos emerging. Such behavior strongly differs from the classical realization, where spin-orbit coupling produces highly entangled, chaotic electron trajectories in an exciton. We also calculate the oscillator strengths and show that randomization appears in the transitions between states with different total momenta.

On the expansion of ionospheric plasma into the near-wake of the Space Shuttle Orbiter

NASA Technical Reports Server (NTRS)

Stone, N. H.; Wright, K. H., Jr.; Samir, U.; Hwang, K. S.

1988-01-01

During the Spacelab 2 mission, while the Plasma Diagnostics Package was attached to the Remote Manipulator System, differential ion vector measurements were obtained in the near wake at a distance of 4-5 Shuttle radii. The Orbiter's wake was found to fill in at a much faster rate than can be explained by simple thermal motion. The measurements strongly suggest that filling of the Orbiter's wake is produced by the process of 'collisionless plasma expansion into a vacuum' and that, for oblique angles of the magnetic field and velocity vectors, the near wake plasma depletion a few radii downstream is not sensitive to the body scale size.

Wigner molecules: natural orbitals of strongly correlated two-electron harmonium.

PubMed

Cioslowski, Jerzy; Buchowiecki, Marcin

2006-08-14

Explicit asymptotic expressions for natural orbitals and their occupancies are derived for the harmonium atom at the strong-correlation limit at which the confinement strength omega tends to zero. Unlike in systems with moderate correlation effects, the occupancies at the omega-->0 limit (derived from occupation amplitudes with alternating sign patterns) are vanishingly small and asymptotically independent of the angular momentum, forming a geometric progression with the scale factor proportional to omega(1/3) and the common ratio of ca. 0.0186. The radial components of the natural orbitals are given by products of polynomials and Gaussian functions that, as expected, peak at approximately half of the equilibrium interelectron distance.

On the dependence on inclination of capture probability of short-period comets

NASA Astrophysics Data System (ADS)

Yabushita, S.; Tsujii, T.

1990-06-01

Calculation is made of probability of capture whereby a nearly parabolic comet with perihelion near the Jovian orbit comes to have a perihelion distance less than 2.5 AU and a period less than 200 yr. The probability is found to depend strongly on the inclination, in accordance with earlier results of Everhart and of Stagg and Bailey. It is large for orbits close to the ecliptic but decreases drastically for large inclinations. The overall probability of capture from randomly distributed orbits is 0.00044, which shows that either the presently observed short-period comets are not in a steady state or the source flux may be in the Uranus-Neptune zone.

Intersection

NASA Technical Reports Server (NTRS)

2006-01-01

9 June 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small portion of a dust-covered plain directly north of Labyrinthus Noctis which is cut by three linear troughs. The two long troughs running diagonally from the lower left (southwest) to the upper right (northeast) are connected by a third, shorter trough. Boulders derived from erosion of layered rock in the trough walls are seen perched on the sloping sidewalls and resting on the trough floors among giant windblown ripples.

Location near: 0.2oN, 105.0oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Northern Spring

Collapse Pits

NASA Technical Reports Server (NTRS)

2005-01-01

24 April 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a large and several small pits formed by collapse along the trend of a fault system in the Uranius Fossae region of Mars. Running diagonal from middle-right toward lower left is a trough that intersects the pit. The trough is a typical graben formed by faulting as the upper crust of Mars split and pulled apart at this location. The opening of the graben also led to formation of the collapse pits.

Location near: 26.2oN, 88.7oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Summer

Radial orbit error reduction and sea surface topography determination using satellite altimetry

NASA Technical Reports Server (NTRS)

Engelis, Theodossios

1987-01-01

A method is presented in satellite altimetry that attempts to simultaneously determine the geoid and sea surface topography with minimum wavelengths of about 500 km and to reduce the radial orbit error caused by geopotential errors. The modeling of the radial orbit error is made using the linearized Lagrangian perturbation theory. Secular and second order effects are also included. After a rather extensive validation of the linearized equations, alternative expressions of the radial orbit error are derived. Numerical estimates for the radial orbit error and geoid undulation error are computed using the differences of two geopotential models as potential coefficient errors, for a SEASAT orbit. To provide statistical estimates of the radial distances and the geoid, a covariance propagation is made based on the full geopotential covariance. Accuracy estimates for the SEASAT orbits are given which agree quite well with already published results. Observation equations are develped using sea surface heights and crossover discrepancies as observables. A minimum variance solution with prior information provides estimates of parameters representing the sea surface topography and corrections to the gravity field that is used for the orbit generation. The simulation results show that the method can be used to effectively reduce the radial orbit error and recover the sea surface topography.

Brown Dwarf Microlensing Diagram

NASA Image and Video Library

2016-11-10

For the first time, two space-based telescopes have teamed up with ground-based observatories to observe a microlensing event, a magnification of the light of a distant star due to the gravitational effects of an unseen object in the foreground. In this case, the cause of the microlensing event was a brown dwarf, dubbed OGLE-2015-BLG-1319, orbiting a star. In terms of mass, brown dwarfs fall somewhere between the size of the largest planets and the smallest stars. Curiously, scientists have found that, for stars roughly the mass of our sun, less than 1 percent have a brown dwarf orbiting within 3 AU (1 AU is the distance between Earth and the sun). This newly discovered brown dwarf may fall in that distance range. This microlensing event was observed by ground-based telescopes looking for these uncommon events, and subsequently seen by NASA's Spitzer and Swift space telescopes. As the diagram shows, Spitzer and Swift offer additional vantage points for viewing this chance alignment. While Swift orbits close to Earth, and saw (blue diamonds) essentially the same change in light that the ground-based telescopes measured (grey markers), Spitzer's location much farther away from Earth gave it a very different perspective on the event (red circles). In particular, Spitzer's vantage point resulted in a time lag in the microlensing event it observed, compared to what was seen by Swift and the ground-based telescope. This offset allowed astronomers to determine the distance to OGLE-2015-BLG-1319 as well as its mass: around 30-65 times that of Jupiter. http://photojournal.jpl.nasa.gov/catalog/PIA21077

Twisted light transmission over 143 km

PubMed Central

Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Ursin, Rupert; Zeilinger, Anton

2016-01-01

Spatial modes of light can potentially carry a vast amount of information, making them promising candidates for both classical and quantum communication. However, the distribution of such modes over large distances remains difficult. Intermodal coupling complicates their use with common fibers, whereas free-space transmission is thought to be strongly influenced by atmospheric turbulence. Here, we show the transmission of orbital angular momentum modes of light over a distance of 143 km between two Canary Islands, which is 50× greater than the maximum distance achieved previously. As a demonstration of the transmission quality, we use superpositions of these modes to encode a short message. At the receiver, an artificial neural network is used for distinguishing between the different twisted light superpositions. The algorithm is able to identify different mode superpositions with an accuracy of more than 80% up to the third mode order and decode the transmitted message with an error rate of 8.33%. Using our data, we estimate that the distribution of orbital angular momentum entanglement over more than 100 km of free space is feasible. Moreover, the quality of our free-space link can be further improved by the use of state-of-the-art adaptive optics systems. PMID:27856744

Predicting How Close Near-Earth Asteroids Will Come to Earth in the Next Five Years Using Only Kepler's Algorithm

NASA Astrophysics Data System (ADS)

Wright, Melissa J.

1998-04-01

There are estimated to be over 150,000 near-earth asteroids in our solar system that are large enough to pose a significant threat to Earth. In order to determine which of them may be a hazard in the future, their orbits must be propagated through time. The goal of this investigation was to see if using only Kepler's algorithm, which ignores the gravitational pull of other planets, our moon, and Jupiter, was sufficient to predict close encounters with Earth. The results were very rough, and about half of the closest approaches were near the dates of those predicted by more refined models. The distances were in general off by a magnitude often, showing that asteroid orbits must be very perturbed by other planets, particularly Jupiter, over time and these must be taken into account for a precise distance estimate. A noted correlation was that the difference in the angular distance from the I vector was very small when the asteroid and Earth were supposed to be closest. In conclusion, using Kepler's algorithm alone can narrow down intervals of time of nearest approaches, which can then be looked at using more accurate propagators.

Twisted light transmission over 143 km

NASA Astrophysics Data System (ADS)

Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Ursin, Rupert; Malik, Mehul; Zeilinger, Anton

2016-11-01

Spatial modes of light can potentially carry a vast amount of information, making them promising candidates for both classical and quantum communication. However, the distribution of such modes over large distances remains difficult. Intermodal coupling complicates their use with common fibers, whereas free-space transmission is thought to be strongly influenced by atmospheric turbulence. Here, we show the transmission of orbital angular momentum modes of light over a distance of 143 km between two Canary Islands, which is 50× greater than the maximum distance achieved previously. As a demonstration of the transmission quality, we use superpositions of these modes to encode a short message. At the receiver, an artificial neural network is used for distinguishing between the different twisted light superpositions. The algorithm is able to identify different mode superpositions with an accuracy of more than 80% up to the third mode order and decode the transmitted message with an error rate of 8.33%. Using our data, we estimate that the distribution of orbital angular momentum entanglement over more than 100 km of free space is feasible. Moreover, the quality of our free-space link can be further improved by the use of state-of-the-art adaptive optics systems.

Twisted light transmission over 143 km.

PubMed

Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Ursin, Rupert; Malik, Mehul; Zeilinger, Anton

2016-11-29

Spatial modes of light can potentially carry a vast amount of information, making them promising candidates for both classical and quantum communication. However, the distribution of such modes over large distances remains difficult. Intermodal coupling complicates their use with common fibers, whereas free-space transmission is thought to be strongly influenced by atmospheric turbulence. Here, we show the transmission of orbital angular momentum modes of light over a distance of 143 km between two Canary Islands, which is 50× greater than the maximum distance achieved previously. As a demonstration of the transmission quality, we use superpositions of these modes to encode a short message. At the receiver, an artificial neural network is used for distinguishing between the different twisted light superpositions. The algorithm is able to identify different mode superpositions with an accuracy of more than 80% up to the third mode order and decode the transmitted message with an error rate of 8.33%. Using our data, we estimate that the distribution of orbital angular momentum entanglement over more than 100 km of free space is feasible. Moreover, the quality of our free-space link can be further improved by the use of state-of-the-art adaptive optics systems.

First Rosetta Radio Science Bistatic Radar Observations of 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Andert, Thomas P.; Remus, Stefan; Simpson, Richard A.; Pätzold, Martin; Asmar, Sami W.; Kahan, Daniel S.; Bird, Mike K.; Häusler, Bernd; Tellmann, Silvia

2015-04-01

The Rosetta spacecraft was successfully inserted on 6th August 2014 into orbit around comet 67P/Churyumov-Gerasimenko. In September Rosetta was placed into bound orbits with an initial distance of 30 km and a decreasing distance until the end October. After lander delivery, bound orbits were maintained again at 20 km and 30 km. One of the objectives of the Rosetta Radio Science Investigations (RSI) is to address the dielectric properties, small-scale roughness, and rotational state of the nucleus of the comet, which can be determined by means of a surface scattering experiment, also known as Bistatic Radar. The radio subsystem transmitter located on board the Rosetta spacecraft beams right circularly polarized radio signals at two wavelengths -3.6 cm (X-Band) and 13 cm (S-Band) - toward the nucleus surface. Part of the impinging radiation is then scattered toward a receiver at a ground station on Earth and recorded. On September 29th, 2014 the first Bistatic Radar experiment ever at a comet was successfully conducted. The distance between 67P/Churyumov-Gerasimenko and Rosetta was 20 km and both right circularly polarized (RCP) and left circularly polarized (LCP) reflected signals from the comet's surface in X-Band were detected during the experiment at the Goldstone complex of the NASA Deep Space Network. The ultra-stable oscillator (USO) on board Rosetta served during the experiment as a very stable reference frequency source. The direct and reflected signal were separated during the experiment by only a fraction of 1 Hz. The extreme stability of the USO allowed a detection and separation of the weak signals even on the required long integration times. Five additional Bistatic Radar experiments were conducted successfully between mid-October and mid-December 2014 with the 70-m DSN ground stations in Goldstone and Canberra at different distances to the comet (10 km, 20 km and 30 km) and reflected signals were observed in each case.

Searching for some natural orbits to observe the double asteroid 2002CE26

NASA Astrophysics Data System (ADS)

Mescolotti, Bruna Yukiko Pinheiro Masago; Prado, Antonio Fernando Bertachini de Almeida; Chiaradia, Ana Paula Marins; Gomes, Vivian Martins

2017-07-01

Knowledge of the Solar System is increasing with data coming from space missions to small bodies. A mission to those bodies offers some problems, because they have several characteristics that are not well known, like their shapes, sizes and masses. The present research has the goal of searching for trajectories around the double asteroid 2002CE26, a system of Near-Earth Asteroids (NEAs) of the Apollo type. For every trajectory of the spacecraft, the evolution of the distances between the spacecraft and the two bodies that compose the system is crucial, due to its impact in the quality of the observations made from the spacecraft. Furthermore, this study has a first objective of searching for trajectories that make the spacecraft remain as long as possible near the two bodies that compose the asteroid system, without the use of orbital maneuvers. The model used here assumes elliptical orbits for the asteroids. The effect of the solar radiation pressure is also included, since it is a major perturbing force acting in spacecrafts traveling around small bodies. The natural orbits found here are useful for the mission. They can be used individually or combined in several pieces by orbital maneuvers. Another point considered here is the importance of the errors in the estimation of the physical parameters of the bodies. This task is very important, because there are great uncertainties in these values because the measurements are based on observations made from the Earth. It is shown that a variation of those parameters can make very large modifications in the times that the spacecraft remains close to the bodies of the system (called here "observational times"). Those modifications are large enough to make the best trajectories obtained under nominal conditions to be useless under some errors in the physical parameters. So, a search is made to find trajectories that have reasonable observation times for all the assumed error scenarios for the two bodies, because those orbits can be used as initial parking orbits for the spacecraft. We called these orbits "quasi-stable orbits", in the sense that they do not collide with any of the primaries nor travel to large distances from them. From these orbits, it is possible to make better observations of the bodies in any scenario, and a more accurate estimation of their sizes and masses is performed, so giving information to allow for other choices for the orbit of the spacecraft.

Localization of Southern Resident Killer Whales Using Two Star Arrays to Support Marine Renewable Energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Huiying; Deng, Zhiqun; Carlson, Thomas J.

2012-10-19

Tidal power has been identified as one of the most potential commercial-scale renewable energy sources. Puget Sound, Washington, is a potential site to deploy tidal power generating devices. The risk of injury for killer whales needs to be managed before the deployment of these types of devices can be approved by regulating authorities. A passive acoustic system consisting of two star arrays, each with four hydrophones, was designed and implemented for the detection and localization of Southern Resident killer whales. Deployment of the passive acoustic system was conducted at Sequim Bay, Washington. A total of nine test locations were chosen,more » within a radius of 250 m around the star arrays, to test our localization approach. For the localization algorithm, a least square solver was applied to obtain a bearing location from each star array. The final source location was determined by the intersection of the bearings given by each of the two star arrays. Bearing and distance errors were obtained to conduct comparison between the calculated and true (from Global Positioning System) locations. The results indicated that bearing errors were within 1.04º for eight of the test locations; one location had bearing errors slightly larger than expected due to the strong background noise at that position. For the distance errors, six of the test locations were within the range of 1.91 to 32.36 m. The other two test locations were near the intersection line between the centers of the two star arrays, which were expected to have large errors from the theoretical sensitivity analysis performed.« less

Shifting Sand in Herschel Crater

NASA Image and Video Library

2011-11-17

The eastern margin of a rippled dune in Herschel Crater on Mars moved an average distance of three meters about three yards between March 3, 2007 and December 1, 2010, in one of two images taken by NASA Mars Reconnaissance Orbiter.

NASA GRAIL Spacecraft in Science Collection Phase Artist Concept

NASA Image and Video Library

2012-03-27

An artist depiction of the twin spacecraft that comprise NASA GRAIL mission. During the GRAIL mission science phase, spacecraft Ebb and Flow transmit radio signals precisely defining the distance between them as they orbit the moon in formation.

Predicting the Atmospheric Composition of Extrasolar Giant Planets

NASA Technical Reports Server (NTRS)

Sharp, A. G.; Moses, J. I.; Friedson, A. J.; Fegley, B., Jr.; Marley, M. S.; Lodders, K.

2004-01-01

To date, approximately 120 planet-sized objects have been discovered around other stars, mostly through the radial-velocity technique. This technique can provide information about a planet s minimum mass and its orbital period and distance; however, few other planetary data can be obtained at this point in time unless we are fortunate enough to find an extrasolar giant planet that transits its parent star (i.e., the orbit is edge-on as seen from Earth). In that situation, many physical properties of the planet and its parent star can be determined, including some compositional information. Our prospects of directly obtaining spectra from extrasolar planets may improve in the near future, through missions like NASA's Terrestrial Planet Finder. Most of the extrasolar giant planets (EGPs) discovered so far have masses equal to or greater than Jupiter's mass, and roughly 16% have orbital radii less than 0.1 AU - extremely close to the parent star by our own Solar-System standards (note that Mercury is located at a mean distance of 0.39 AU and Jupiter at 5.2 AU from the Sun). Although all EGPs are expected to have hydrogen-dominated atmospheres similar to Jupiter, the orbital distance can strongly affect the planet's temperature, physical, chemical, and spectral properties, and the abundance of minor, detectable atmospheric constituents. Thermochemical equilibrium models can provide good zero-order predictions for the atmospheric composition of EGPs. However, both the composition and spectral properties will depend in large part on disequilibrium processes like photochemistry, chemical kinetics, atmospheric transport, and haze formation. We have developed a photochemical kinetics, radiative transfer, and 1-D vertical transport model to study the atmospheric composition of EGPs. The chemical reaction list contains H-, C-, O-, and N-bearing species and is designed to be valid for atmospheric temperatures ranging from 100-3000 K and pressures up to 50 bar. Here we examine the effect of stellar distance (e.g., incident ultraviolet flux, atmospheric temperature) on the chemical properties of EGPs. The model is applied to two generic Class II and III intermediate temperature EGPs located at 3.3 and 0.27 AU from a solar-like parent star, and the results are compared with a model for Jupiter at 5.2 AU.

Study of the Asteroid 2009 DL46

NASA Astrophysics Data System (ADS)

Vodniza, Alberto Quijano

2017-06-01

2009 DL46 was discovered by the Catalina Sky Survey on 2009-February 28. This asteroid has a diameter of about 194 meters (119 to 268 meters) [1], and Brian Warner has obtained a rotation period of at least 10 hours [2]. The asteroid 2009 DL46 flew past Earth on May 24/2016 at a distance of about 6.2 lunar distances (0.0158293668567628 A.U) [3]. The NEOWISE mission had a great likelihood to observing this asteroid in early May. Radiotelescopes of Goldstone and Arecibo had planned to make observations of 2009 DL46. “Using the Goldstone facility, we had planned to make radar observations of 2009 DL46” said Landis, Rob R. (HQ-DG000). This asteroid is on list for possible human mission targets. From our Observatory, located in Pasto-Colombia, we captured several pictures, videos and astrometry data during several hours during three days. Our data was published by the Minor Planet Center (MPC) and also appears at the web page of NEODyS [4]. The pictures and data of the asteroid were captured with the following equipment: CGE PRO 1400 CELESTRON (f/11 Schmidt-Cassegrain Telescope) and STL-1001 SBIG camera.. Astrometry was carried out, and we calculated the orbital elements. Summary and conclusions: We obtained the following orbital parameters: eccentricity = 0.30731 +/- 0.00025, semi-major axis = 1.460279 +/- 0.000532 A.U, orbital inclination = 7.9503 +/- 0.0048 deg, longitude of the ascending node = 63.45053 +/- 0.00034 deg, argument of perihelion = 159.8804 +/- 0.0024 deg, mean motion = 0.558535 +/- 0.000305 deg/d, perihelion distance = 1.01151363 +/- 3.39e-6 A.U, aphelion distance = 1.90904 +/- 0.00106 A.U, absolute magnitude = 22.5. The parameters were calculated based on 83 observations. Dates: 2016 May: 18 to 21 with mean residual = 0.29 arcseconds. The asteroid has an orbital period of 1.76 years (644.53 days).[1] http://newton.dm.unipi.it/neodys/index.php?pc=1.1.9&n=2009DL46.[2] http://echo.jpl.nasa.gov/asteroids/2009DL46/2009DL46_planning.html[3] http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2009%20DL46orb=1old=0cov=0log=0cad=1#cad[4] http://newton.dm.unipi.it/neodys/index.php?pc=2.1.2&o=H78&ab=7

Orbits and masses in the young triple system TWA 5

NASA Astrophysics Data System (ADS)

Köhler, R.; Ratzka, T.; Petr-Gotzens, M. G.; Correia, S.

2013-10-01

Aims: We aim to improve the orbital elements and determine the individual masses of the components in the triple system TWA 5. Methods: Five new relative astrometric positions in the H band were recorded with the adaptive optics system at the Very Large Telescope (VLT). We combine them with data from the literature and a measurement in the Ks band. We derive an improved fit for the orbit of TWA 5Aa-b around each other. Furthermore, we use the third component, TWA 5B, as an astrometric reference to determine the motion of Aa and Ab around their center of mass and compute their mass ratio. Results: We find an orbital period of 6.03 ± 0.01 years and a semi-major axis of 63.7 ± 0.2 mas (3.2 ± 0.1 AU). With the trigonometric distance of 50.1 ± 1.8 pc, this yields a system mass of 0.9 ± 0.1 M⊙, where the error is dominated by the error of the distance. The dynamical mass agrees with the system mass predicted by a number of theoretical models if we assume that TWA5 is at the young end of the age range of the TW Hydrae association. We find a mass ratio of MAb/MAa = 1.3-0.4+0.6 , where the less luminous component Ab is more massive. This result is likely to be a consequence of the large uncertainties due to the limited orbital coverage of the observations. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 079.C-0103, 081.C-0393, 386.C-0205, 087.C-0209, 088.C-0046, 089.C-0167, and 090.C-0184.

Orbital magnetic resonance imaging is useful in age-related distance esotropia.

PubMed

Gómez de Liaño Sanchez, Pilar; Olavarri González, Gloria; Merino Sanz, Pilar; Escribano Villafruela, Jose C

To describe findings for orbital magnetic resonance imaging (MRI) in patients with age-related distance esotropia (ARDE). We compared 31 orbital MRI from patients with ARDE (77±7 SD years) with 2 control groups: 32 orbits from individuals aged 18-50 years (33±8 SD years) and 16 orbits from individuals aged >60 years (77±7 SD years). MRI scans were acquired using 3D fast field echo in T1 sequence without fat saturation. Exclusion criteria for all groups were neurological or thyroid disease and a relevant ophthalmological history (e.g., high myopia, diplopia from another etiology, complicated cataract surgery, etc.). Muscle displacement and characteristics of the lateral rectus-superior rectus (LR-SR) intermuscular band were analyzed. The analysis of the muscles and angles revealed a series of statistically significant differences (p<0.07) between the groups. Subjects with ARDE had LR pulley positions 1.32±0.19mm lower than in younger controls, and the medial rectus (MR) pulley positions were 0.68±0.19mm lower than in younger. Older controls had LR and MR pulley positions 0.85±0.20mm and 0.49±0.23mm lower than in younger. ARDE subjects had LR pulley positions 0.46±0.26mm lower than in older control group. The LR-SR band was absent in 35.5% of ARDE patients and in 12.5% of older control group (p=0.168). MRI showed that displacements of LR and LR-SR band degeneration could facilitate the diagnosis of patients with ARDE. Copyright © 2017 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

ORBITAL AND PHYSICAL PROPERTIES OF THE σ Ori Aa, Ab, B TRIPLE SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simón-Díaz, S.; Caballero, J. A.; Apellániz, J. Maíz

2015-02-01

We provide a complete characterization of the astrophysical properties of the σ Ori Aa, Ab, B hierarchical triple system and an improved set of orbital parameters for the highly eccentric σ Ori Aa, Ab spectroscopic binary. We compiled a spectroscopic data set comprising 90 high-resolution spectra covering a total time span of 1963 days. We applied the Lehman-Filhés method for a detailed orbital analysis of the radial velocity curves and performed a combined quantitative spectroscopic analysis of the σ Ori Aa, Ab, B system by means of the stellar atmosphere code FASTWIND. We used our own plus other available information onmore » photometry and distance to the system for measuring the radii, luminosities, and spectroscopic masses of the three components. We also inferred evolutionary masses and stellar ages using the Bayesian code BONNSAI. The orbital analysis of the new radial velocity curves led to a very accurate orbital solution of the σ Ori Aa, Ab pair. We provided indirect arguments indicating that σ Ori B is a fast-rotating early B dwarf. The FASTWIND+BONNSAI analysis showed that the Aa, Ab pair contains the hottest and most massive components of the triple system while σ Ori B is a bit cooler and less massive. The derived stellar ages of the inner pair are intriguingly younger than the one widely accepted for the σ Orionis cluster, at 3 ± 1 Ma. The outcome of this study will be of key importance for a precise determination of the distance to the σ Orionis cluster, the interpretation of the strong X-ray emission detected for σ Ori Aa, Ab, B, and the investigation of the formation and evolution of multiple massive stellar systems and substellar objects.« less

Scattering of Planetesimals by a Planet

NASA Astrophysics Data System (ADS)

Higuchi, A.; Kokubo, E.; Mukai, T.

2004-05-01

We investigate the scattering process of planetesimals by a planet by numerical orbital integration, aiming at construction of theory for the comet (Oort) cloud formation. The standard scenario of the formation of the Oort cloud can be divided into three dynamical stages:(1)The eccentricity and the aphelion distance of planetesimals are increased by planetary perturbation. (2)The eccentricity is reduced and the perihelion distance is increased by the external forces such as the galactic tide. (3)The inclination is randomized also by the external forces. We model the first stage of this scenario as the restricted three-body problem and calculate the orbital evolution of planetesimals scattered by a planet. There are 4 kinds of outcomes for scattering of planetesimals by a planet: to collide with the planet, to fall onto the central star, to escape from the planetary system, and to remain in bound orbits. Here we consider the escape efficiency as the efficiency of formation of highly eccentric planetesimals, which are candidates for the members of the comet cloud. We obtain the dependence of the escape/collision probability on orbital parameters of the planetesimals and the planet. Using these results, we calculate the efficiencies of escaping from the planetary system and collision with the planet. For example, for the minimum-mass disk model, the inner and massive planet is more efficient to eject planetesimals and increase their eccentricities. Planetesimals with high eccentricities and low inclinations are easier to be ejected from the planetary system. We preset the empirical fitting formulae of these efficiencies as a function of the orbital parameters of the planetesimals and the planets. We apply the results to the solar system and discuss the efficiency of the outer giant planets.

Investigating the Relativistic Motion of the Stars Near the Supermassive Black Hole in the Galactic Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parsa, M.; Eckart, A.; Shahzamanian, B.

The S-star cluster in the Galactic center allows us to study the physics close to a supermassive black hole, including distinctive dynamical tests of general relativity. Our best estimates for the mass of and the distance to Sgr A* using the three stars with the shortest period (S2, S38, and S55/S0-102) and Newtonian models are M {sub BH} = (4.15 ± 0.13 ± 0.57) × 10{sup 6} M {sub ⊙} and R {sub 0} = 8.19 ± 0.11 ± 0.34 kpc. Additionally, we aim at a new and practical method to investigate the relativistic orbits of stars in the gravitationalmore » field near Sgr A*. We use a first-order post-Newtonian approximation to calculate the stellar orbits with a broad range of periapse distance r {sub p} . We present a method that employs the changes in orbital elements derived from elliptical fits to different sections of the orbit. These changes are correlated with the relativistic parameter defined as ϒ ≡ r {sub s} / r {sub p} (with r {sub s} being the Schwarzschild radius) and can be used to derive ϒ from observational data. For S2 we find a value of ϒ = 0.00088 ± 0.00080, which is consistent, within the uncertainty, with the expected value of ϒ = 0.00065 derived from M {sub BH} and the orbit of S2. We argue that the derived quantity is unlikely to be dominated by perturbing influences such as noise on the derived stellar positions, field rotation, and drifts in black hole mass.« less

Connectivity among subpopulations of Louisiana black bears as estimated by a step selection function

USGS Publications Warehouse

Clark, Joseph D.; Jared S. Laufenberg,; Maria Davidson,; Jennifer L. Murrow,

2015-01-01

Habitat fragmentation is a fundamental cause of population decline and increased risk of extinction for many wildlife species; animals with large home ranges and small population sizes are particularly sensitive. The Louisiana black bear (Ursus americanus luteolus) exists only in small, isolated subpopulations as a result of land clearing for agriculture, but the relative potential for inter-subpopulation movement by Louisiana black bears has not been quantified, nor have characteristics of effective travel routes between habitat fragments been identified. We placed and monitored global positioning system (GPS) radio collars on 8 female and 23 male bears located in 4 subpopulations in Louisiana, which included a reintroduced subpopulation located between 2 of the remnant subpopulations. We compared characteristics of sequential radiolocations of bears (i.e., steps) with steps that were possible but not chosen by the bears to develop step selection function models based on conditional logistic regression. The probability of a step being selected by a bear increased as the distance to natural land cover and agriculture at the end of the step decreased and as distance from roads at the end of a step increased. To characterize connectivity among subpopulations, we used the step selection models to create 4,000 hypothetical correlated random walks for each subpopulation representing potential dispersal events to estimate the proportion that intersected adjacent subpopulations (hereafter referred to as successful dispersals). Based on the models, movement paths for males intersected all adjacent subpopulations but paths for females intersected only the most proximate subpopulations. Cross-validation and genetic and independent observation data supported our findings. Our models also revealed that successful dispersals were facilitated by a reintroduced population located between 2 distant subpopulations. Successful dispersals for males were dependent on natural land cover in private ownership. The addition of hypothetical 1,000-m- or 3,000-m-wide corridors between the 4 study areas had minimal effects on connectivity among subpopulations. For females, our model suggested that habitat between subpopulations would probably have to be permanently occupied for demographic rescue to occur. Thus, the establishment of stepping-stone populations, such as the reintroduced population that we studied, may be a more effective conservation measure than long corridors without a population presence in between. 

Comparison of Travel-Time and Amplitude Measurements for Deep-Focusing Time-Distance Helioseismology

NASA Astrophysics Data System (ADS)

Pourabdian, Majid; Fournier, Damien; Gizon, Laurent

2018-04-01

The purpose of deep-focusing time-distance helioseismology is to construct seismic measurements that have a high sensitivity to the physical conditions at a desired target point in the solar interior. With this technique, pairs of points on the solar surface are chosen such that acoustic ray paths intersect at this target (focus) point. Considering acoustic waves in a homogeneous medium, we compare travel-time and amplitude measurements extracted from the deep-focusing cross-covariance functions. Using a single-scattering approximation, we find that the spatial sensitivity of deep-focusing travel times to sound-speed perturbations is zero at the target location and maximum in a surrounding shell. This is unlike the deep-focusing amplitude measurements, which have maximum sensitivity at the target point. We compare the signal-to-noise ratio for travel-time and amplitude measurements for different types of sound-speed perturbations, under the assumption that noise is solely due to the random excitation of the waves. We find that, for highly localized perturbations in sound speed, the signal-to-noise ratio is higher for amplitude measurements than for travel-time measurements. We conclude that amplitude measurements are a useful complement to travel-time measurements in time-distance helioseismology.

Cities and regions in Britain through hierarchical percolation

NASA Astrophysics Data System (ADS)

Arcaute, Elsa; Molinero, Carlos; Hatna, Erez; Murcio, Roberto; Vargas-Ruiz, Camilo; Masucci, A. Paolo; Batty, Michael

2016-04-01

Urban systems present hierarchical structures at many different scales. These are observed as administrative regional delimitations which are the outcome of complex geographical, political and historical processes which leave almost indelible footprints on infrastructure such as the street network. In this work, we uncover a set of hierarchies in Britain at different scales using percolation theory on the street network and on its intersections which are the primary points of interaction and urban agglomeration. At the larger scales, the observed hierarchical structures can be interpreted as regional fractures of Britain, observed in various forms, from natural boundaries, such as National Parks, to regional divisions based on social class and wealth such as the well-known North-South divide. At smaller scales, cities are generated through recursive percolations on each of the emerging regional clusters. We examine the evolution of the morphology of the system as a whole, by measuring the fractal dimension of the clusters at each distance threshold in the percolation. We observe that this reaches a maximum plateau at a specific distance. The clusters defined at this distance threshold are in excellent correspondence with the boundaries of cities recovered from satellite images, and from previous methods using population density.

The Julia sets of basic uniCremer polynomials of arbitrary degree

NASA Astrophysics Data System (ADS)

Blokh, Alexander; Oversteegen, Lex

Let P be a polynomial of degree d with a Cremer point p and no repelling or parabolic periodic bi-accessible points. We show that there are two types of such Julia sets J_P . The red dwarf J_P are nowhere connected im kleinen and such that the intersection of all impressions of external angles is a continuum containing p and the orbits of all critical images. The solar J_P are such that every angle with dense orbit has a degenerate impression disjoint from other impressions and J_P is connected im kleinen at its landing point. We study bi-accessible points and locally connected models of J_P and show that such sets J_P appear through polynomial-like maps for generic polynomials with Cremer points. Since known tools break down for d>2 (if d>2 , it is not known if there are small cycles near p , while if d=2 , this result is due to Yoccoz), we introduce wandering ray continua in J_P and provide a new application of Thurston laminations.

Hypersonic shock wave interaction and impingement

NASA Technical Reports Server (NTRS)

Kessler, W. C.; Reilly, J. F.; Sampatacos, E.

1971-01-01

An experimental investigation was conducted on space shuttle type, body-wing configurations. The purpose of the investigation was to determine the effects of body and wing geometry on the hypersonic shock structure about these vehicles and on the resulting surface impingement of interior flow field shock and expansion waves. Schlieren photographs and thermographic phosphor paint data were obtained on three body cross sections with three wing planforms at 40, 50 and 60 degree angles of attack. Specific configuration data were obtained at 0 and 30 degree angles of attack to develop trends. These data were obtained at a nominal Mach number of 13.5 and a freestream unit Reynolds number of 0.7 million per foot. For comparison with these straight wing configurations, data were also obtained on a model of a point design, high cross-range, delta wing orbiter at 40, 50 and 60 degree angles of attack. As expected, the data on this delta wing orbiter indicated that the shock intersection/impingement phenomena associated with straight wing vehicles are considerably more complex than, and result in both windward and leeward surface heating regions not present on, the delta configuration.

Experimental and ab initio characterization of HC3N+ vibronic structure. II. High-resolution VUV PFI-ZEKE spectroscopy.

PubMed

Gans, Bérenger; Lamarre, Nicolas; Broquier, Michel; Liévin, Jacques; Boyé-Péronne, Séverine

2016-12-21

Vacuum-ultraviolet pulsed-field-ionization zero-kinetic-energy photoelectron spectra of X + Π2←XΣ+1 and B + Π2←XΣ+1 transitions of the HC 3 14 N and HC 3 15 N isotopologues of cyanoacetylene have been recorded. The resolution of the photoelectron spectra allowed us to resolve the vibrational structures and the spin-orbit splittings in the cation. Accurate values of the adiabatic ionization potentials of the two isotopologues (E I /hc(HC 3 14 N)=93 909(2) cm -1 and E I /hc(HC 3 15 N)=93 912(2) cm -1 ), the vibrational frequencies of the ν 2 , ν 6 , and ν 7 vibrational modes, and the spin-orbit coupling constant (A SO = -44(2) cm -1 ) of the X + Π2 cationic ground state have been derived from the measurements. Using ab initio calculations, the unexpected structure of the B + Π2←XΣ+1 transition is tentatively attributed to a conical intersection between the A + and B + electronic states of the cation.

Launch Window Analysis for the Magnetospheric Multiscale Mission

NASA Technical Reports Server (NTRS)

Williams, Trevor W.

2012-01-01

The NASA Magnetospheric Multiscale (MMS) mission will fly four spinning spacecraft in formation in highly elliptical orbits to study the magnetosphere of the Earth. This paper describes the development of an MMS launch window tool that uses the orbitaveraged Variation of Parameter equations as the basis for a semi-analytic quantification of the dominant oblateness and lunisolar perturbation effects on the MMS orbit. This approach, coupled with a geometric interpretation of all of the MMS science and engineering constraints, allows a scan of 180(sup 2) = 32,400 different (RAAN, AOP) pairs to be carried out for a specified launch day in less than 10 s on a typical modern laptop. The resulting plot indicates the regions in (RAAN, AOP) space where each constraint is satisfied or violated: their intersection gives, in an easily interpreted graphical manner, the final solution space for the day considered. This tool, SWM76, is now used to provide launch conditions to the full fidelity (but far slower) MMS simulation code: very good agreement has been observed between the two methods.

A Real-Time Orbit Determination Method for Smooth Transition from Optical Tracking to Laser Ranging of Debris

PubMed Central

Li, Bin; Sang, Jizhang; Zhang, Zhongping

2016-01-01

A critical requirement to achieve high efficiency of debris laser tracking is to have sufficiently accurate orbit predictions (OP) in both the pointing direction (better than 20 arc seconds) and distance from the tracking station to the debris objects, with the former more important than the latter because of the narrow laser beam. When the two line element (TLE) is used to provide the orbit predictions, the resultant pointing errors are usually on the order of tens to hundreds of arc seconds. In practice, therefore, angular observations of debris objects are first collected using an optical tracking sensor, and then used to guide the laser beam pointing to the objects. The manual guidance may cause interrupts to the laser tracking, and consequently loss of valuable laser tracking data. This paper presents a real-time orbit determination (OD) and prediction method to realize smooth and efficient debris laser tracking. The method uses TLE-computed positions and angles over a short-arc of less than 2 min as observations in an OD process where simplified force models are considered. After the OD convergence, the OP is performed from the last observation epoch to the end of the tracking pass. Simulation and real tracking data processing results show that the pointing prediction errors are usually less than 10″, and the distance errors less than 100 m, therefore, the prediction accuracy is sufficient for the blind laser tracking. PMID:27347958

The detection of impact regions of asteroids' orbits by means of constrained minimization of confidence coefficient. (Russian Title: Выявление областей столкновительных орбит астероидов с помощью условной минимизации доверительного коэффициента)

NASA Astrophysics Data System (ADS)

Baturin, A. P.

2014-12-01

The theme of NEO's impact orbits' regions detecting has been considered. The regions have been detected in the space of initial motion parameters. The detecting has been done by means of constrained minimization of so called "confidence coefficient". This coefficient determines the position of an orbit inside its confidence ellipsoid obtained from a least-square orbit fitting. As a condition the constraining of an asteroid-Earth distance at considered encounter has been used. By means of random variation of initial approximations for the minimization and of the parameter constraining an asteroid-Earth distance it has been demonstrated that impact regions usually have a form of some long tubes in the space of initial motion parameters. The demonstration has been done for the asteroids 2009 FD, 2011 TO and 2012 PB20 at their waited closest encounters to the Earth.

Model calculations of the interaction of two parallel antiaromatic 4n π-electron systems

PubMed Central

Böhm, Michael C.; Bickert, Peter; Hafner, Klaus; Boekelheide, V.

1984-01-01

The nature of the interaction between decks of a pentalene dimer and an s-indacene dimer has been studied by semi-empirical MNDO/1 and MINDO/3 calculations for distances between decks of from 5 Å to 2 Å. In contradiction to qualitative predictions from a frontier orbital analysis, it is found that the 4n-4n π-electron interaction between decks for such dimers is destabilizing for distances exceeding about 2.5 Å. PMID:16593458

Phenomenology of a Water Venting in Low Earth Orbit

DTIC Science & Technology

1992-01-01

of the transport of outgas , the interaction of the vehicle with the ionospheric plasma, the energy balance of cometary material, and the uses of...l 4.04 100 ZA Ic 50 o)o 200 250 300 350 400 Distance along profile (pixels) Fig. 8. (a) Equi-photocurrent plot of the water trail from the aft...distance of the onboard camera’s short ONBOARD-CANIERA IMAGES focal length lens. their corresponding mean irradiance at the focal plane is - Xs we have

Black Hole With Jet (Artist's Concept)

NASA Image and Video Library

2017-11-02

This artist's concept shows a black hole with an accretion disk -- a flat structure of material orbiting the black hole -- and a jet of hot gas, called plasma. Using NASA's NuSTAR space telescope and a fast camera called ULTRACAM on the William Herschel Observatory in La Palma, Spain, scientists have been able to measure the distance that particles in jets travel before they "turn on" and become bright sources of light. This distance is called the "acceleration zone." https://photojournal.jpl.nasa.gov/catalog/PIA22085

Spectral observations of 19 weathered and 23 fresh NEAs and their correlations with orbital parameters

NASA Astrophysics Data System (ADS)

Fevig, Ronald A.; Fink, Uwe

2007-05-01

Results of our visible to near-infrared spectrophotometric observations of 41 near-Earth asteroids (NEAs) are reported. These moderate-resolution spectra, along with 14 previously published spectra from our earlier survey [Hicks, M.D., Fink, U., Grundy, W.M., 1998. Icarus 133, 69-78] show a preponderance of spectra consistent with ordinary chondrites (23 NEAs with this type of spectrum, along with 19 S-types and 13 in other taxonomic groups). There exists statistically significant evidence for orbit-dependent trends in our data. While S-type NEAs from our survey reside primarily in (1) Amor orbits or (2) Aten or Apollo orbits which do not cross the asteroid main-belt, the majority of objects with spectra consistent with ordinary chondrites in our survey are in highly eccentric Apollo orbits which enter the asteroid main-belt. This trend toward fresh, relatively unweathered NEAs with ordinary chondrite type spectra in highly eccentric Apollo orbits is attributed to one or a combination of three possible causes: (1) the chaotic nature of NEA orbits can easily result in high eccentricity orbits/large aphelion distances so that they can enter the collisionally enhanced environment in the main-belt, exposing fresh surfaces, (2) they have recently been injected into such orbits after a collision in the main-belt, or (3) such objects cross the orbits of several terrestrial planets, causing tidal disruption events that expose fresh surfaces.

The Orbital Evolution of Near-Earth Asteroid 3753

NASA Astrophysics Data System (ADS)

Wiegert, Paul A.; Innanen, Kimmo A.; Mikkola, Seppo

1998-06-01

Asteroid 3753 (1986 TO) is in a 1:1 mean motion resonance with Earth, on a complex horseshoe-type orbit. Numerical experiments are performed to determine its medium-term stability and the means by which it may have entered its current orbit. Though 3753 moves primarily under the influence of the Sun and Earth, the giant planets (and Jupiter especially) play an important role by influencing, through torque-induced precession, the position of the asteroid's nodes. Variations in the nodal distance strongly affect the interaction of 3753 with Earth and may change or destroy the horseshoe-like behavior currently seen. This precession of the nodes provides a mechanism for placing minor planets into, or removing them from, a variety of horseshoe-type orbits. The chaotic nature of this asteroid's orbit makes predictions difficult on timescales longer than its Lyapunov time (~150 yr); therefore, ensembles of particles on orbits near that of 3753 are considered. The asteroid has a high probability of passing close to Venus and/or Mars on 10^4 yr timescales, pointing to a dynamical age much shorter than that of the solar system.

The Phase Space Structure Near Neptune Resonances in the Kuiper Belt

NASA Technical Reports Server (NTRS)

Malhotra, Renu

1996-01-01

The Solar system beyond Neptune is believed to house a population of small primordial bodies left over from the planet formation process. The region up to heliocentric distance -50 AU (a.k.a. the Kuiper Belt) may be the source of the observed short-period comets. In this region, the phase space structure near orbital resonances with Neptune is of special interest for the long-term stability of orbits. There is reason to believe that a significant fraction (perhaps most) of the Kuiper Belt objects reside preferentially in these resonance locations. This paper describes the dynamics of small objects near the major orbital resonances with Neptune. Estimates of the widths of stable resonance zones as well as the properties of resonant orbits are obtained from the circular, planar restricted three-body model. Although this model does not contain the full complexity of the long-term orbital dynamics of Kuiper Belt objects subject to the full N-body perturbations of all the planets, it does provide a baseline for the phase space structure and properties of resonant orbits in the trans-Neptunian Solar system.

Sedna Orbit Comparisons

NASA Image and Video Library

2004-03-15

These four panels show the location of the newly discovered planet-like object, dubbed "Sedna," which lies in the farthest reaches of our solar system. Each panel, moving counterclockwise from the upper left, successively zooms out to place Sedna in context. The first panel shows the orbits of the inner planets, including Earth, and the asteroid belt that lies between Mars and Jupiter. In the second panel, Sedna is shown well outside the orbits of the outer planets and the more distant Kuiper Belt objects. Sedna's full orbit is illustrated in the third panel along with the object's current location. Sedna is nearing its closest approach to the Sun; its 10,000 year orbit typically takes it to far greater distances. The final panel zooms out much farther, showing that even this large elliptical orbit falls inside what was previously thought to be the inner edge of the Oort cloud. The Oort cloud is a spherical distribution of cold, icy bodies lying at the limits of the Sun's gravitational pull. Sedna's presence suggests that this Oort cloud is much closer than scientists believed. http://photojournal.jpl.nasa.gov/catalog/PIA05569

Sedna Orbit Comparisons

NASA Technical Reports Server (NTRS)

2004-01-01

These four panels show the location of the newly discovered planet-like object, dubbed 'Sedna,' which lies in the farthest reaches of our solar system. Each panel, moving counterclockwise from the upper left, successively zooms out to place Sedna in context. The first panel shows the orbits of the inner planets, including Earth, and the asteroid belt that lies between Mars and Jupiter. In the second panel, Sedna is shown well outside the orbits of the outer planets and the more distant Kuiper Belt objects. Sedna's full orbit is illustrated in the third panel along with the object's current location. Sedna is nearing its closest approach to the Sun; its 10,000 year orbit typically takes it to far greater distances. The final panel zooms out much farther, showing that even this large elliptical orbit falls inside what was previously thought to be the inner edge of the Oort cloud. The Oort cloud is a spherical distribution of cold, icy bodies lying at the limits of the Sun's gravitational pull. Sedna's presence suggests that this Oort cloud is much closer than scientists believed.

Searching for orbits around the triple system 45 Eugenia

NASA Astrophysics Data System (ADS)

Mescolotti, B. Y. P. M.; Prado, A. F. B. A.; Chiaradia, A. P. M.; Gomes, V. M.

2017-10-01

Asteroids are small bodies that raises high interest, because they have unknown characteristics. The present research aims to study orbits for a spacecraft around the triple asteroid 45 Eugenia. The quality of the observations made by the spacecraft depends on the distance the spacecraft remains from the bodies of the system. It is used a semi-analytical model that is simple but able to represent the main characteristics of that system. This model is called “Precessing Inclined Bi-Elliptical Problem” (PIBEP). A reference system centered on the main body (Eugenia) and with the reference plane assumed to be in the orbital plane of the second more massive body, here called Petit-Prince, is used. The secondary bodies are assumed to be in elliptical orbits. In addition, it is assumed that the orbits of the smaller bodies are precessing due to the presence of the flattening of the main body (J2). This work analyzes orbits for the spacecraft with passages near Petit-Prince and Princesses, which are the two smaller bodies of the triple system.

Radio Telescopes' Precise Measurements Yield Rich Scientific Payoffs

NASA Astrophysics Data System (ADS)

2008-01-01

Having the sharpest pictures always is a big advantage, and a sophisticated radio-astronomy technique using continent-wide and even intercontinental arrays of telescopes is yielding extremely valuable scientific results in a wide range of specialties. That's the message delivered to the American Astronomical Society's meeting in Austin, Texas, by Mark Reid of the Harvard-Smithsonian Center for Astrophysics, a leading researcher in the field of ultra-precise astronomical position measurements. Very Long Baseline Interferometry provides extremely high precision that can extend use of the parallax technique to many more celestial objects. Parallax is a direct means of measuring cosmic distances by detecting the slight shift in an object’s apparent position in the sky caused by Earth’s orbital motion. Credit: Bill Saxton, NRAO/AUI/NSF "Using radio telescopes, we are measuring distances and motions of celestial bodies with unprecedented accuracy. That's helping us better understand many processes ranging from star formation to the scale of the entire Universe," Reid said. The observing technique, called Very Long Baseline Interferometry (VLBI), was pioneered in 1967, but has come into continuous use only in the past 10-15 years. The National Science Foundation's Very Long Baseline Array (VLBA), a system of 10 radio-telescope antennas ranging from Hawaii to the Caribbean, was dedicated in 1993. There are other VLBI systems in Europe and Asia, and large radio telescopes around the world cooperate regularly to increase sensitivity. VLBI observations routinely produce images hundreds of times more detailed than those made at visible-light wavelengths by the Hubble Space Telescope. Several groups of researchers from across the globe use the VLBA to study stellar nurseries in our own Milky Way Galaxy and measure distances to regions where new stars are forming. The key has been to improve measurement accuracy to a factor of a hundred times better than that produced by the highly successful Hipparcos satellite. Using small clouds of gas in star-forming regions that strongly amplify radio waves, called cosmic masers, the astronomers measured the tiny shift in the object's position in the sky caused by the Earth's orbit around the sun. This, in turn, yielded highly-accurate distances by the simple surveying technique of triangulation, the "gold standard" of distance measuring techniques available to astronomers. Dr. Mark Reid Dr. Mark Reid Credit: CfA Click image for high-resolution file (1.02 MB) "Knowing the distance accurately means we also know the luminosities, masses and ages of the young stars much more accurately, and that is vital to understanding how star formation works," Reid said. In addition, he pointed out, the VLBA observations have shown the motions of the young stars in the Milky Way are much more complicated than simple circular motion. Massive young stars appear to be born orbiting the Milky Way considerably slower than older stars. "This might be explained by the interaction of giant molecular clouds, the ultimate sites of massive star formation, as they "surf" spiral density waves in the Milky Way." An international team of scientists led by Reid has used VLBI to detect the slight change in apparent position of the object at the Milky Way's center caused by our Solar System's orbit around that center. "It takes our Solar System more than 200 million years to circle the center of our Galaxy, and yet we can detect that motion in only a couple weeks with the VLBA -- truly astounding!" Reid said. The VLBA studies of the Galactic Center have shown that an object called Sagittarius A* is at the exact gravitational center of our Galaxy. That means, the scientists say, that the object must be incredibly massive. "The VLBA measurements, combined with infrared observations of stellar orbits around this object, provide overwhelming evidence that it's a supermassive black hole," Reid explained. "These observations are also going to make it possible to re-define the coordinate system used to map the entire Galaxy," Reid added. Looking farther outward, astronomers achieved a longstanding goal of measuring the spin of another galaxy. In 2005, Reid and his colleagues measured both the rotational spin and the motion in space of the galaxy M33, nearly 2.4 million light-years from Earth. Astronomers in the 1920s had attempted such a feat, but their results were not accurate enough. "This achievement had to wait for the VLBA," Reid said. This and subsequent work has put strong limits on the amount of unseen "dark matter" around the giant Andromeda galaxy, which M33 orbits. A continuing goal is to use VLBI observations to measure the orbits of these and other galaxies within the Local Group of galaxies to which our own Milky Way belongs. VLBA The Very Long Baseline Array (VLBA), the National Radio Astronomy Observatory’s continent-wide radio-telescope system. The VLBA provides the greatest resolving power, or ability to see detail, of any instrument in astronomy. Credit: NRAO/AUI/NSF In 1999, astronomers set a new standard for a distance measurement outside the Local Group of galaxies when they used the VLBA to make a direct geometric distance measurement to a galaxy called NGC 4258, 23.5 million light-years from Earth. That measurement, accurate to within 7 percent, caused other scientists to revise their indirect-measurement techniques for the rest of the Universe. The NGC 4258 distance was calculated by measuring the motion of masers in a disk of gas containing water molecules and orbiting a supermassive black hole at the galaxy's center. "Now, other galaxies are being observed in hopes of extending direct distance measurement even farther out in the Universe," Reid said. "One candidate, called UGC 3789, at a distance of about 160 million light-years, will be measured with about 10 percent accuracy. Our goal is to further improve these measurements and to measure 5 to 10 other galaxies in order to determine the Hubble constant (the expansion rate of the Universe) to 3 percent accuracy. This would put limits on key parameters of the dark energy that apparently is accelerating the expansion of the Universe," Reid added. The kind of accurate measurement of distances and motions that VLBI observations provide can benefit numerous other areas of astronomy, Reid pointed out. For example, the distances to pulsars have been measured directly with the VLBA, yielding better understanding of their characteristics. The technique also could reveal planets circling some nearby stars. "Anytime you can do something as dramatic as improving measurement accuracy by a hundredfold, you're bound to get a great scientific payoff," Reid said. "We're looking forward to exciting new results in the coming years," he added. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Temporary satellite capture of comets by Jupiter

NASA Astrophysics Data System (ADS)

Emel'yanenko, N. Yu.

2012-05-01

This paper studies the dynamical evolution of 97 Jupiter-family comets over an 800-year time period. More than two hundred encounters with Jupiter are investigated, with the observed comets moving during a certain period of time in an elliptic jovicentric orbit. In most cases this is an ordinary temporary satellite capture of a comet in Everhart's sense, not associated with a transition of the small body into Jupiter's family of satellites. The phenomenon occurs outside the Hill sphere with comets with a high Tisserand constant relative to Jupiter; the comets' orbits have a small inclination to the ecliptic plane. An analysis of 236 encounters has allowed the determination within the planar pair two-body problem of a region of orbits in the plane ( a, e) whose semimajor axes and eccentricities contribute to the phenomenon under study. Comets with orbits belonging to this region experience a temporary satellite capture during some of their encounters; the jovicentric distance function has several minima; and the encounters are characterized by reversions of the line of apsides and some others features of their combination that are intrinsic to comets in this region. Therefore, this region is called a region of comets with specific features in their encounters with Jupiter. Twenty encounters (out of 236), whereby the comet enters an elliptic jovicentric orbit in the Hill sphere, are identified and investigated. The size and shape of the elliptic heliocentric orbits enabling this transition are determined. It is found that in 11 encounters the motion of small bodies in the Hill sphere has features the most important of which is multiple minima of the jovicentric distance function. The study of these 20 encounters has allowed the introduction of the concept of temporary gravitational capture of a small body into the Hill sphere. An analysis of variations in the Tisserand constant in these (20) encounters of the observable comets shows that their motion is unstable in Hill's sense.

Dynamic behavior of solar wind as revealed by a correlation study of magnetic fields observed at the Venus and Earth orbits

NASA Technical Reports Server (NTRS)

Marubashi, K.

1995-01-01

Correlations between interplanetary magnetic fields (IMFs) at 0.72 AU and 1.0 AU have been examined using data sets obtained from the Pioneer Venus orbiter and Earth-orbiting spacecraft. While the two-sector structures are evident in long-term variations at these two heliocentric distances, the corresponding auto-correlation coefficients are consistently smaller at 1.0 AU than at 0.72 AU. This suggests that the IMF structures become less persistent at 1.0 AU due to the effects of changing solar wind dynamics between the Venus and Earth orbits. Short-term variations exhibit generally poor correlations between IMFs near Venus and those near Earth, though good correlations are sometimes obtained for well-defined structures when the Sun, Venus, and Earth are closely aligned. The rather poor correlations in the background streams indicate that the IMFs are still changing between the Venus and Earth orbits under the strong influence of solar wind dynamics.

Resolution and Orbit Reconstruction of Spectroscopic Binary Stars with the Palomar Testbed Interferometer

NASA Astrophysics Data System (ADS)

Boden, A. F.; Lane, B. F.; Creech-Eakman, M. J.; Queloz, D.; Koresko, C. D.

2000-05-01

The Palomar Testbed Interferometer (PTI) is a long-baseline near-infrared interferometer located at Palomar Observatory. For the past several years we have had an ongoing program of resolving and reconstructing the visual and physical orbits of spectroscopic binary stars with PTI, with the goal of obtaining precise dynamical mass estimates and other physical parameters. We will present a number of new visual and physical orbit determinations derived from integrated reductions of PTI visibility and archival and new spectroscopic radial velocity data. The systems for which we will discuss our orbit models are: iota Pegasi (HD 210027), 64 Psc (HD 4676), 12 Boo (HD 123999), 75 Cnc (HD 78418), 47 And (HD 8374), HD 205539, BY Draconis (HDE 234677), and 3 Boo (HD 120064), and 3 Boo (HD 120064). All of these systems are double-lined binary systems (SB2), and integrated astrometric/radial velocity orbit modeling provides precise fundamental parameters (mass, luminosity) and system distance determinations comparable with Hipparcos precisions.

A possible experiment with two counter-orbiting drag-free satellites to obtain a new test of Einstein's general theory of relativity and improved measurements in geodesy

NASA Technical Reports Server (NTRS)

Van Patten, R. A.; Everitt, C. W. F.

1976-01-01

In 1918, Lense and Thirring calculated that a moon in orbit around a massive rotating planet would experience a nodal dragging effect due to general relativity. We describe an experiment to measure this effect by means of two counter-orbiting drag-free satellites in polar orbit about the earth. For a 2-1/2 year experiment, the measurement should approach an accuracy of 1%. An independent measurement of the geodetic precession of the orbit plane due to the motion about the sun may also be possible to about 10% accuracy. In addition to precision tracking data from existing ground stations, satellite-to-satellite Doppler data are taken at points of passing near the poles to yield an accurate measurement of the separation distance between the two satellites. New geophysical information on both earth harmonics and tidal effects is inherent in this polar ranging data.

Lunatics in Introductory Physics: Using Collectivized Student Moon Position Observations To Teach Basic Orbital Mechanics In Calculus Based Introductory Physics.

NASA Astrophysics Data System (ADS)

Bottorff, Mark

2012-01-01

A large (74 student) calculus based physics class was required to make observations of the moon over two lunar cycles using a small telescope equipped with mechanical setting circles. The data was collectivized and then analyzed in the laboratory to determine the period of the moon and to search for evidence of the eccentricity of the moon's orbit. These results were used in conjunction with the simple pendulum experiment in which the students inferred the acceleration due to gravity. The student inferred lunar orbital period and acceleration due to gravity (augmented with the radius of the Earth) enabled the students to infer the average Earth to moon distance. Class lectures, activities, and homework on gravitation and orbits were tailored to this observational activity thereby forming a learning module. A basic physics and orbital mechanics knowledge questionnaire was administered before and after the learning module. The resulting learning gains are reported here.

NEMESIS: Near Encounters with M-dwarfs from an Enormous Sample and Integrated Simulations

NASA Astrophysics Data System (ADS)

Bochanski, John J.; Sanderson, R. E.; West, A. A.; Burgasser, A. J.

2011-01-01

The latest spectroscopic catalog of M dwarfs identified in the Sloan Digital Sky Survey provides radial velocities, proper motions and distances for nearly 40,000 low-mass stars. Using the full 6D phase space coverage and a realistic Galactic potential, we calculated orbits for each star in the sample. The sample consists of stars from both the thin and thick disks, and the orbital properties between the two groups are compared. We also examine trends in orbital properties with spectroscopic features, such as Balmer emission and molecular bands, that should correlate with age. In addition, we have identified a number of stars that will pass very close to the Sun within the next 1000 Myrs. These stars form the "Nemesis" family of orbits. Potential encounters with these stars could have a significant impact on orbits of Oort Cloud and Kuiper Belt members as well as the planets. We comment on the probability of a catastrophic encounter within the next 1000 Myrs.

Epimetheus Above the Rings

NASA Image and Video Library

2015-11-09

Although Epimetheus appears to be lurking above the rings here, it's actually just an illusion resulting from the viewing angle. In reality, Epimetheus and the rings both orbit in Saturn's equatorial plane. Inner moons and rings orbit very near the equatorial plane of each of the four giant planets in our solar system, but more distant moons can have orbits wildly out of the equatorial plane. It has been theorized that the highly inclined orbits of the outer, distant moons are remnants of the random directions from which they approached the planets they orbit. This view looks toward the unilluminated side of the rings from about -0.3 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 26, 2015. The view was obtained at a distance of approximately 500,000 miles (800,000 kilometers) from Epimetheus and at a Sun-Epimetheus-spacecraft, or phase, angle of 62 degrees. Image scale is 3 miles (5 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18342

Saturn's Magnetic Field from the Cassini Grand Finale orbits

NASA Astrophysics Data System (ADS)

Dougherty, M. K.; Cao, H.; Khurana, K. K.; Hunt, G. J.; Provan, G.; Kellock, S.; Burton, M. E.; Burk, T. A.

2017-12-01

The fundamental aims of the Cassini magnetometer investigation during the Cassini Grand Finale orbits were determination of Saturn's internal planetary magnetic field and the rotation rate of the deep interior. The unique geometry of the orbits provided an unprecedented opportunity to measure the intrinsic magnetic field at close distances never before encountered. The surprising close alignment of Saturn's magnetic axis with its spin axis, known about since the days of Pioneer 11, has been a focus of the team's analysis since Cassini Saturn Orbit Insertion. However, the varying northern and southern magnetospheric planetary period oscillations, which fill the magnetosphere, has been a factor in masking the field signals from the interior. Here we describe an overview of the magnetometer results from the Grand Finale orbits, including confirmation of the extreme axisymmetric nature of the planetary magnetic field, implications for knowledge of the rotation rate and the behaviour of external magnetic fields (arising from the ring current, field aligned currents both at high and low latitudes and the modulating effect of the planetary period oscillations).

The spectroscopic orbits and physical parameters of GG Carinae

NASA Astrophysics Data System (ADS)

Marchiano, P.; Brandi, E.; Muratore, M. F.; Quiroga, C.; Ferrer, O. E.; García, L. G.

2012-04-01

Aims: GG Car is an eclipsing binary classified as a B[e] supergiant star. The aims of our study are to improve the orbital elements of the binary system in order to obtain the actual orbital period of this system. We also compare the spectral energy distribution of the observed fluxes over a wide wavelength range with a model of a circumstellar envelope composed of gas and dust. This fitting allows us to derive the physical parameters of the system and its environment, as well as to obtain an estimation of the distance to GG Car. Methods: We analyzed about 55 optical and near infrared spectrograms taken during 1996-2010. The spectroscopic orbits were obtained by measuring the radial velocities of the blueshifted absorptions of the He I P-Cygni profiles, which are very representative of the orbital motion of both stars. On the other hand, we modeled the spectral energy distribution of GG Car, proposing a simple model of a spherical envelope consisting of a layer close to the central star composed of ionized gas and other outermost layers composed of dust. Its effect on the spectral energy distribution considering a central B-type star is presented. Comparing the model with the observed continuum energy distribution of GG Car, we can derive fundamental parameters of the system, as well as global physical properties of the gas and dust envelope. It is also possible to estimate the distance taking the spectral regions into account where the theoretical data fit the observational data very well and using the set of parameters obtained and the value of the observed flux for different wavelengths. Results: For the first time, we have determined the orbits for both components of the binary through a detailed study of the He I lines, at λλ4471, 5875, 6678, and 7065 Å, thereby obtaining an orbital period of 31.033 days. An eccentric orbit with e = 0.28 and a mass ratio q = 2.2 ± 0.9 were calculated. Comparing the model with the observed continuum energy distribution of GG Car, we obtain Teff = 23 000 K and log g = 3. The central star is surrounded by a spherical envelope consisting of a layer of 3.5 stellar radii composed of ionized gas and other outermost dust layers with EB - V = 0.39. These calculations are not strongly modified if we consider two similar B-type stars instead of a central star, provided our model suggests that the second star might contribute less than 10% of the primary flux. The calculated effective temperature is consistent with an spectral type B0-B2 and a distance to the object of 5 ± 1 kpc was determined. Based on observations taken at Complejo Astronómico EL LEONCITO, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Addison, B. C.; Tinney, C. G.; Wright, D. J.

We have measured the sky-projected spin–orbit alignments for three transiting hot Jupiters, WASP-103b, WASP-87b, and WASP-66b, using spectroscopic measurements of the Rossiter–McLaughlin effect, with the CYCLOPS2 optical fiber bundle system feeding the UCLES spectrograph on the Anglo-Australian Telescope. The resulting sky-projected spin–orbit angles of λ = 3° ± 33°, λ = −8° ± 11°, and λ = −4° ± 22° for WASP-103b, WASP-87b, and WASP-66b, respectively, suggest that these three planets are likely on nearly aligned orbits with respect to their host star’s spin axis. WASP-103 is a particularly interesting system as its orbital distance is only 20% larger thanmore » its host star’s Roche radius and the planet likely experiences strong tidal effects. WASP-87 and WASP-66 are hot ( T {sub eff} = 6450 ± 120 K and T {sub eff} = 6600 ± 150 K, respectively) mid-F stars, making them similar to the majority of stars hosting planets on high-obliquity orbits. Moderate spin–orbit misalignments for WASP-103b and WASP-66b are consistent with our data, but polar and retrograde orbits are not favored for these systems.« less

SRMS Assisted Docking and Undocking for the Orbiter Repair Maneuver

NASA Technical Reports Server (NTRS)

Quiocho, Leslie J.; Briscoe, Timothy J.; Schliesing, John A.; Braman, Julia M.

2005-01-01

As part of the Orbiter Repair Maneuver (ORM) planned for Return to Flight (RTF) operations, the Shuttle Remote Manipulator System (SRMS) must undock the Orbiter, maneuver it through a complex trajectory at extremely low rates, present it to an EVA crewman at the end of the Space Station Remote Manipulator System to perform the Thermal Protection System (TPS) repair, and then retrace back through the trajectory to dock the Orbiter with the Orbiter Docking System (ODs). The initial and final segments of this operation involve the interaction between the SRMS, ISS, Orbiter and ODs. This paper first provides an overview of the Monte-Carlo screening analysis for the installation (both nominal and contingency), including the variation of separation distance, misalignment conditions, SRMS joint/brake parameter characteristics, and PRCS jet combinations and corresponding thrust durations. The resulting 'optimum' solution is presented based on trade studies between predicted capture success and integrated system loads. This paper then discusses the upgrades to the APAS math model associated with the new SRMS assisted undocking technique and reviews simulation results for various options investigated for either the active and passive separation of the ISS from the Orbiter.

Orbital Evolution of Jupiter-Family Comets

NASA Technical Reports Server (NTRS)

Ipatov, S. I.; Mather, J. S.; Oegerle, William R. (Technical Monitor)

2002-01-01

We investigated the evolution for periods of at least 5-10 Myr of 2500 Jupiter-crossing objects (JCOs) under the gravitational influence of all planets, except for Mercury and Pluto (without dissipative factors). In the first series we considered N=2000 orbits near the orbits of 30 real Jupiter-family comets with period less than 10 yr, and in the second series we took 500 orbits close to the orbit of Comet 10P Tempel 2. We calculated the probabilities of collisions of objects with the terrestrial planets, using orbital elements obtained with a step equal to 500 yr and then summarized the results for all time intervals and all bodies, obtaining the total probability P(sub sigma) of collisions with a planet and the total time interval T(sub sigma) during which perihelion distance of bodies was less than a semimajor axis of the planet. The values of P = 10(exp 6)P(sub sigma)/N and T = T(sub sigma)/1000 yr are presented in Table together with the ratio r of the total time interval when orbits were of Apollo type (at e less than 0.999) to that of Amor type.

Migration of Trans-Neptunian Objects to a Near-Earth Space

NASA Technical Reports Server (NTRS)

Ipatov, S. I.; Mather, J. C.; Oegerle, William (Technical Monitor)

2002-01-01

Our estimates of the migration of trans-Neptunian objects (TNOs) to a near-Earth space are based on the results of investigations of orbital evolution of TNOs and Jupiter-crossing objects (JCOs). The orbital evolution of TNOs was considered in many papers. Recently we investigated the evolution for intervals of at least 5-10 Myr of 2500 JCOs under the gravitational influence of all planets, except for Mercury and Pluto (without dissipative factors). In the first series we considered N=2000 orbits near the orbits of 30 real Jupiter-family comets with period P(sub alpha)less than 10 yr, and in the second series we took N=500 orbits close to the orbit of Comet 10P Tempel 2 (alpha=3.1 AU, e=0.53, i=12 deg). We calculated the probabilities of collisions of objects with the terrestrial planets, using orbital elements obtained with a step equal to 500 yr, and then summarized the results for all time intervals and all bodies, obtaining the total probability P(sub sigma) of collisions with a planet and the total time interval T(sub sigma) during which perihelion distance q of bodies was less than a semimajor axis of the planet.

Resonance capture and dynamics of three-planet systems

NASA Astrophysics Data System (ADS)

Charalambous, C.; Martí, J. G.; Beaugé, C.; Ramos, X. S.

2018-06-01

We present a series of dynamical maps for fictitious three-planet systems in initially circular coplanar orbits. These maps have unveiled a rich resonant structure involving two or three planets, as well as indicating possible migration routes from secular to double resonances or pure three-planet commensurabilities. These structures are then compared to the present-day orbital architecture of observed resonant chains. In a second part of the paper, we describe N-body simulations of type-I migration. Depending on the orbital decay time-scale, we show that three-planet systems may be trapped in different combinations of independent commensurabilities: (i) double resonances, (ii) intersection between a two-planet and a first-order three-planet resonances, and (iii) simultaneous libration in two first-order three-planet resonances. These latter outcomes are found for slow migrations, while double resonances are almost always the final outcome in high-density discs. Finally, we discuss an application to the TRAPPIST-1 system. We find that, for low migration rates and planetary masses of the order of the estimated values, most three-planet sub-systems are able to reach the observed double resonances after following evolutionary routes defined by pure three-planet resonances. The final orbital configuration shows resonance offsets comparable with present-day values without the need of tidal dissipation. For the 8/5 resonance proposed to dominate the dynamics of the two inner planets, we find little evidence of its dynamical significance; instead, we propose that this relation between mean motions could be a consequence of the interaction between a pure three-planet resonance and a two-planet commensurability between planets c and d.

Deep-Space Test of a Neutrino Detector

NASA Astrophysics Data System (ADS)

Solomey, N.; Barghouty, N.; Christl, M.; Johnson, L.; Meyer, H.

2018-02-01

Changes in solar neutrino flux make it advantageous to take a detector into space since it changes as the inverse square of the distance from the Sun. A space-craft with a neutrino detector in solar orbit would perform science study opportunities.

Meter-scale thermal contraction crack polygons on the nucleus of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Auger, A.-T.; Groussin, O.; Jorda, L.; El-Maarry, M. R.; Bouley, S.; Séjourné, A.; Gaskell, R.; Capanna, C.; Davidsson, B.; Marchi, S.; Höfner, S.; Lamy, P. L.; Sierks, H.; Barbieri, C.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; Agarwal, J.; A'Hearn, M. F.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Fornasier, S.; Fulle, M.; Gutiérrez, P. J.; Güttler, C.; Hviid, S.; Ip, W.-H.; Knollenberg, J.; Kramm, J.-R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; Lopez Moreno, J. J.; Marzari, F.; Massironi, M.; Michalik, H.; Naletto, G.; Oklay, N.; Pommerol, A.; Sabau, L.; Thomas, N.; Tubiana, C.; Vincent, J.-B.; Wenzel, K.-P.

2018-02-01

We report on the detection and characterization of more than 6300 polygons on the surface of the nucleus of comet 67P/Churyumov-Gerasimenko, using images acquired by the OSIRIS camera onboard Rosetta between August 2014 and March 2015. They are found in consolidated terrains and grouped in localized networks. They are present at all latitudes (from North to South) and longitudes (head, neck, and body), sometimes on pit walls or following lineaments. About 1.5% of the observed surface is covered by polygons. Polygons have an homogeneous size across the nucleus, with 90% of them in the size range 1 - 5 m and a mean size of 3.0 ± 1.4 m. They show different morphologies, depending on the width and depth of their trough. They are found in networks with 3- or 4-crack intersection nodes. The polygons observed on 67P are consistent with thermal contraction crack polygons formed by the diurnal or seasonal temperature variations in a hard (MPa) and consolidated sintered layer of water ice, located a few centimeters below the surface. Our thermal analysis shows an evolution of thermal contraction crack polygons according to the local thermal environment, with more evolved polygons (i.e. deeper and larger troughs) where the temperature and the diurnal and seasonal temperature range are the highest. Thermal contraction crack polygons are young surface morphologies that probably formed after the injection of 67P in the inner solar system, typically 100,000 years ago, and could be as young as a few orbital periods, following the decreasing of its perihelion distance in 1959 from 2.7 to 1.3 a.u. Meter scale thermal contraction crack polygons should be common features on the nucleus of Jupiter family comets.

Analysis of chaotic saddles in a nonlinear vibro-impact system

NASA Astrophysics Data System (ADS)

Feng, Jinqian

2017-07-01

In this paper, a computational investigation of chaotic saddles in a nonlinear vibro-impact system is presented. For a classical Duffing vibro-impact oscillator, we employ the bisection procedure and an improved stagger-and-step method to present evidence of visual chaotic saddles on the fractal basin boundary and in the internal basin, respectively. The results show that the period saddles play an important role in the evolution of chaotic saddle. The dynamics mechanics of three types of bifurcation such as saddle-node bifurcation, chaotic saddle crisis bifurcation and interior chaotic crisis bifurcation are discussed. The results reveal that the period saddle created at saddle-node bifurcation is responsible for the switch of the internal chaotic saddle to the boundary chaotic saddle. At chaotic saddle crisis bifurcation, a large chaotic saddle can divide into two different chaotic saddle connected by a period saddle. The intersection points between stable and unstable manifolds of this period saddle supply access for chaotic orbits from one chaotic saddle to another and eventually induce the coupling of these two chaotic saddle. Interior chaotic crisis bifurcation is associated with the intersection of stable and unstable manifolds of the period saddle connecting two chaotic invariant sets. In addition, the gaps in chaotic saddle is responsible for the fractal structure.

Low-lying excited states by constrained DFT

NASA Astrophysics Data System (ADS)

Ramos, Pablo; Pavanello, Michele

2018-04-01

Exploiting the machinery of Constrained Density Functional Theory (CDFT), we propose a variational method for calculating low-lying excited states of molecular systems. We dub this method eXcited CDFT (XCDFT). Excited states are obtained by self-consistently constraining a user-defined population of electrons, Nc, in the virtual space of a reference set of occupied orbitals. By imposing this population to be Nc = 1.0, we computed the first excited state of 15 molecules from a test set. Our results show that XCDFT achieves an accuracy in the predicted excitation energy only slightly worse than linear-response time-dependent DFT (TDDFT), but without incurring into problems of variational collapse typical of the more commonly adopted ΔSCF method. In addition, we selected a few challenging processes to test the limits of applicability of XCDFT. We find that in contrast to TDDFT, XCDFT is capable of reproducing energy surfaces featuring conical intersections (azobenzene and H3) with correct topology and correct overall energetics also away from the intersection. Venturing to condensed-phase systems, XCDFT reproduces the TDDFT solvatochromic shift of benzaldehyde when it is embedded by a cluster of water molecules. Thus, we find XCDFT to be a competitive method among single-reference methods for computations of excited states in terms of time to solution, rate of convergence, and accuracy of the result.