Haze, clouds and limited sky visibility: polarotactic orientation of crickets under difficult stimulus conditions.

PubMed

Henze, Miriam J; Labhart, Thomas

2007-09-01

Field crickets (Gryllus campestris L.) are able to detect the orientation of the electric vector (e-vector) of linearly polarized light. They presumably use this sense to exploit the celestial polarization pattern for course control or navigation. Polarization vision in crickets can be tested by eliciting a spontaneous polarotactic response. Previously, wide and 100% polarized stimuli were employed to induce this behavior. However, field crickets live on meadows where the observation of the sky is strongly limited by surrounding vegetation. Moreover, degrees of polarization (d) in the natural sky are much lower than 100%. We have therefore investigated thresholds for the behavioral response to polarized light under conditions mimicking those experienced by the insects in the field. We show that crickets are able to rely on polarized stimuli of just 1 degrees diameter. We also provide evidence that they exploit polarization down to an (average) polarization level of less than 7%, irrespective of whether the stimulus is homogeneous, such as under haze, or patched, such as a sky spotted by clouds. Our data demonstrate that crickets can rely on skylight polarization even under unfavorable celestial conditions, emphasizing the significance of polarized skylight orientation for insects.

Celestial orientation with the sun not in view: lizards use a time-compensated sky polarization compass.

PubMed

Maoret, Francesco; Beltrami, Giulia; Bertolucci, Cristiano; Foà, Augusto

2014-04-01

The present investigation was aimed at testing whether the lizard sky polarization compass is time compensated. For this purpose, ruin lizards, Podarcis sicula, were both trained and tested for orientation inside a Morris water maze under clear skies with the sun not in view. During training, lizards showed a striking bimodal orientation along the training axis, demonstrating their capability of determining the symmetry plane of the sky polarization pattern and thus the use of polarization information in orientation. After reaching criteria, lizards were kept 7 days in a 6-h fast clock-shift treatment and then released with the sun not in view. Six-hour clock-shifted lizards showed a bimodal distribution of directional choices, which was oriented perpendicularly to the training axis, as it was expected on the basis of the clock-shift. The results show that the only celestial diurnal compass mechanism that does not need a direct vision of the sun disk (i.e., the sky polarization compass) is a time-compensated compass.

The Role of Celestial Compass Information in Cataglyphis Ants during Learning Walks and for Neuroplasticity in the Central Complex and Mushroom Bodies

PubMed Central

Grob, Robin; Fleischmann, Pauline N.; Grübel, Kornelia; Wehner, Rüdiger; Rössler, Wolfgang

2017-01-01

Central place foragers are faced with the challenge to learn the position of their nest entrance in its surroundings, in order to find their way back home every time they go out to search for food. To acquire navigational information at the beginning of their foraging career, Cataglyphis noda performs learning walks during the transition from interior worker to forager. These small loops around the nest entrance are repeatedly interrupted by strikingly accurate back turns during which the ants stop and precisely gaze back to the nest entrance—presumably to learn the landmark panorama of the nest surroundings. However, as at this point the complete navigational toolkit is not yet available, the ants are in need of a reference system for the compass component of the path integrator to align their nest entrance-directed gazes. In order to find this directional reference system, we systematically manipulated the skylight information received by ants during learning walks in their natural habitat, as it has been previously suggested that the celestial compass, as part of the path integrator, might provide such a reference system. High-speed video analyses of distinct learning walk elements revealed that even exclusion from the skylight polarization pattern, UV-light spectrum and the position of the sun did not alter the accuracy of the look back to the nest behavior. We therefore conclude that C. noda uses a different reference system to initially align their gaze directions. However, a comparison of neuroanatomical changes in the central complex and the mushroom bodies before and after learning walks revealed that exposure to UV light together with a naturally changing polarization pattern was essential to induce neuroplasticity in these high-order sensory integration centers of the ant brain. This suggests a crucial role of celestial information, in particular a changing polarization pattern, in initially calibrating the celestial compass system. PMID:29184487

The Role of Celestial Compass Information in Cataglyphis Ants during Learning Walks and for Neuroplasticity in the Central Complex and Mushroom Bodies.

PubMed

Grob, Robin; Fleischmann, Pauline N; Grübel, Kornelia; Wehner, Rüdiger; Rössler, Wolfgang

2017-01-01

Central place foragers are faced with the challenge to learn the position of their nest entrance in its surroundings, in order to find their way back home every time they go out to search for food. To acquire navigational information at the beginning of their foraging career, Cataglyphis noda performs learning walks during the transition from interior worker to forager. These small loops around the nest entrance are repeatedly interrupted by strikingly accurate back turns during which the ants stop and precisely gaze back to the nest entrance-presumably to learn the landmark panorama of the nest surroundings. However, as at this point the complete navigational toolkit is not yet available, the ants are in need of a reference system for the compass component of the path integrator to align their nest entrance-directed gazes. In order to find this directional reference system, we systematically manipulated the skylight information received by ants during learning walks in their natural habitat, as it has been previously suggested that the celestial compass, as part of the path integrator, might provide such a reference system. High-speed video analyses of distinct learning walk elements revealed that even exclusion from the skylight polarization pattern, UV-light spectrum and the position of the sun did not alter the accuracy of the look back to the nest behavior. We therefore conclude that C. noda uses a different reference system to initially align their gaze directions. However, a comparison of neuroanatomical changes in the central complex and the mushroom bodies before and after learning walks revealed that exposure to UV light together with a naturally changing polarization pattern was essential to induce neuroplasticity in these high-order sensory integration centers of the ant brain. This suggests a crucial role of celestial information, in particular a changing polarization pattern, in initially calibrating the celestial compass system.

Measurements of skylight polarization: a case study in urban region with high-loading aerosol.

PubMed

Wu, Lianghai; Gao, Jun; Fan, Zhiguo; Zhang, Jun

2015-02-01

We investigate skylight polarization patterns in an urban region using our developed full-Stokes imaging polarimeter. A detailed description of our imaging polarimeter and its calibration are given, then, we measure skylight polarization patterns at wavelength λ=488  nm and at solar elevation between -05°10' and +35°42' in the city of Hefei, China. We show that in an urban region with high-loading aerosols: (1) the measured degree of linear polarization reaches the maximum near sunset, and large areas of unpolarized sky exist in the forward sunlight direction close to the Sun; (2) the position of neural points shifts from the local meridian plane and, if compared with a clear sky, alters the symmetrical characteristics of celestial polarization pattern; and (3) the observed circular polarization component is negligible.

Underwater refraction-polarization patterns of skylight perceived by aquatic animals through Snell's window of the flat water surface.

PubMed

Horváth, G; Varjú, D

1995-06-01

The grass shrimp (Palaemonetes vulgaris) orients itself by means of the polarization pattern of the sky visible through Snell's window of the water surface. The celestial polarization pattern viewed from water is distorted and modified because of refraction and repolarization of skylight at the air-water interface. This work provides a quantitative account of the repolarization of skylight transmitted through a flat water surface. The degree and direction of linear polarization, the transmissivity and the shape of the refraction-polarization oval are calculated at the air-water interface as functions of the polarization characteristics and the incident angle of partially linearly polarized incoming light. Two-dimensional patterns of linear polarization ellipses and of the degree and direction of polarization of skylight are presented for different zenith distances of the sun. The corresponding underwater refraction-polarization patterns are computed. Transmissivity patterns of a flat water surface are calculated for unpolarized light of an overcast sky and for partially polarized light of clear skies as a function of the zenith distance of the sun. The role of these refraction-polarization patterns in orientation and polarization vision of the grass shrimp (P. vulgaris) and rainbow trout (Oncorhyncus mykiss) is reviewed. The effects of cloud cover, surface waves and water turbidity on the refraction-polarization patterns are briefly discussed.

Integration of polarization and chromatic cues in the insect sky compass.

PubMed

el Jundi, Basil; Pfeiffer, Keram; Heinze, Stanley; Homberg, Uwe

2014-06-01

Animals relying on a celestial compass for spatial orientation may use the position of the sun, the chromatic or intensity gradient of the sky, the polarization pattern of the sky, or a combination of these cues as compass signals. Behavioral experiments in bees and ants, indeed, showed that direct sunlight and sky polarization play a role in sky compass orientation, but the relative importance of these cues are species-specific. Intracellular recordings from polarization-sensitive interneurons in the desert locust and monarch butterfly suggest that inputs from different eye regions, including polarized-light input through the dorsal rim area of the eye and chromatic/intensity gradient input from the main eye, are combined at the level of the medulla to create a robust compass signal. Conflicting input from the polarization and chromatic/intensity channel, resulting from eccentric receptive fields, is eliminated at the level of the anterior optic tubercle and central complex through internal compensation for changing solar elevations, which requires input from a circadian clock. Across several species, the central complex likely serves as an internal sky compass, combining E-vector information with other celestial cues. Descending neurons, likewise, respond both to zenithal polarization and to unpolarized cues in an azimuth-dependent way.

Sensory integration: neuronal filters for polarized light patterns.

PubMed

Krapp, Holger G

2014-09-22

Animal and human behaviour relies on local sensory signals that are often ambiguous. A new study shows how tuning neuronal responses to celestial cues helps locust navigation, demonstrating a common principle of sensory information processing: the use of matched filters. Copyright © 2014 Elsevier Ltd. All rights reserved.

Integration of celestial compass cues in the central complex of the locust brain.

PubMed

Pegel, Uta; Pfeiffer, Keram; Homberg, Uwe

2018-01-29

Many insects rely on celestial compass cues such as the polarization pattern of the sky for spatial orientation. In the desert locust, the central complex (CX) houses multiple sets of neurons, sensitive to the oscillation plane of polarized light and thus probably acts as an internal polarization compass. We investigated whether other sky compass cues like direct sunlight or the chromatic gradient of the sky might contribute to this compass. We recorded from polarization-sensitive CX neurons while an unpolarized green or ultraviolet light spot was moved around the head of the animal. All types of neuron that were sensitive to the plane of polarization ( E -vector) above the animal also responded to the unpolarized light spots in an azimuth-dependent way. The tuning to the unpolarized light spots was independent of wavelength, suggesting that the neurons encode solar azimuth based on direct sunlight and not on the sky chromatic gradient. Two cell types represented the natural 90 deg relationship between solar azimuth and zenithal E -vector orientation, providing evidence to suggest that solar azimuth information supports the internal polarization compass. Most neurons showed advances in their tuning to the E -vector and the unpolarized light spots dependent on rotation direction, consistent with anticipatory signaling. The amplitude of responses and its variability were dependent on the level of background firing, possibly indicating different internal states. The integration of polarization and solar azimuth information strongly suggests that besides the polarization pattern of the sky, direct sunlight might be an important cue for sky compass navigation in the locust. © 2018. Published by The Company of Biologists Ltd.

Transmission of linearly polarized light in seawater: implications for polarization signaling.

PubMed

Shashar, Nadav; Sabbah, Shai; Cronin, Thomas W

2004-09-01

Partially linearly polarized light is abundant in the oceans. The natural light field is partially polarized throughout the photic range, and some objects and animals produce a polarization pattern of their own. Many polarization-sensitive marine animals take advantage of the polarization information, using it for tasks ranging from navigation and finding food to communication. In such tasks, the distance to which the polarization information propagates is of great importance. Using newly designed polarization sensors, we measured the changes in linear polarization underwater as a function of distance from a standard target. In the relatively clear waters surrounding coral reefs, partial (%) polarization decreased exponentially as a function of distance from the target, resulting in a 50% reduction of partial polarization at a distance of 1.25-3 m, depending on water quality. Based on these measurements, we predict that polarization sensitivity will be most useful for short-range (in the order of meters) visual tasks in water and less so for detecting objects, signals, or structures from far away. Navigation and body orientation based on the celestial polarization pattern are predicted to be limited to shallow waters as well, while navigation based on the solar position is possible through a deeper range.

Robust sky light polarization detection with an S-wave plate in a light field camera.

PubMed

Zhang, Wenjing; Zhang, Xuanzhe; Cao, Yu; Liu, Haibo; Liu, Zejin

2016-05-01

The sky light polarization navigator has many advantages, such as low cost, no decrease in accuracy with continuous operation, etc. However, current celestial polarization measurement methods often suffer from low performance when the sky is covered by clouds, which reduce the accuracy of navigation. In this paper we introduce a new method and structure based on a handheld light field camera and a radial polarizer, composed of an S-wave plate and a linear polarizer, to detect the sky light polarization pattern across a wide field of view in a single snapshot. Each micro-subimage has a special intensity distribution. After extracting the texture feature of these subimages, stable distribution information of the angle of polarization under a cloudy sky can be obtained. Our experimental results match well with the predicted properties of the theory. Because the polarization pattern is obtained through image processing, rather than traditional methods based on mathematical computation, this method is less sensitive to errors of pixel gray value and thus has better anti-interference performance.

Spatial integration in polarization-sensitive interneurones of crickets: a survey of evidence, mechanisms and benefits.

PubMed

Labhart, T; Petzold, J; Helbling, H

2001-07-01

Many insects exploit the polarization pattern of the sky for compass orientation in navigation or cruising-course control. Polarization-sensitive neurones (POL1-neurones) in the polarization vision pathway of the cricket visual system have wide visual fields of approximately 60 degrees diameter, i.e. these neurones integrate information over a large area of the sky. This results from two different mechanisms. (i) Optical integration; polarization vision is mediated by a group of specialized ommatidia at the dorsal rim of the eye. These ommatidia lack screening pigment, contain a wide rhabdom and have poor lens optics. As a result, the angular sensitivity of the polarization-sensitive photoreceptors is very wide (median approximately 20 degrees ). (ii) Neural integration; each POL1-neurone receives input from a large number of dorsal rim photoreceptors with diverging optical axes. Spatial integration in POL1-neurones acts as a spatial low-pass filter. It improves the quality of the celestial polarization signal by filtering out cloud-induced local disturbances in the polarization pattern and increases sensitivity.

Do monarch butterflies use polarized skylight for migratory orientation?

PubMed

Stalleicken, Julia; Mukhida, Maya; Labhart, Thomas; Wehner, Rüdiger; Frost, Barrie; Mouritsen, Henrik

2005-06-01

To test if migratory monarch butterflies use polarized light patterns as part of their time-compensated sun compass, we recorded their virtual flight paths in a flight simulator while the butterflies were exposed to patches of naturally polarized blue sky, artificial polarizers or a sunny sky. In addition, we tested butterflies with and without the polarized light detectors of their compound eye being occluded. The monarchs' orientation responses suggested that the butterflies did not use the polarized light patterns as a compass cue, nor did they exhibit a specific alignment response towards the axis of polarized light. When given direct view of the sun, migratory monarchs with their polarized light detectors painted out were still able to use their time-compensated compass: non-clockshifted butterflies, with their dorsal rim area occluded, oriented in their typical south-southwesterly migratory direction. Furthermore, they shifted their flight course clockwise by the predicted approximately 90 degrees after being advance clockshifted 6 h. We conclude that in migratory monarch butterflies, polarized light cues are not necessary for a time-compensated celestial compass to work and that the azimuthal position of the sun disc and/or the associated light-intensity and spectral gradients seem to be the migrants' major compass cue.

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

NASA Astrophysics Data System (ADS)

Horváth, Gábor; Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-02-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d* for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d > d* is satisfied. Using full-sky imaging polarimetry, we measured the d-pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ. From the measured d-patterns of a given sky we determined the proportion P of the sky for which d > d*. We obtained that P is the largest at low solar elevations θ ≈ 0° and under totally or nearly clear skies with cloud coverage ρ = 0%, when the sun's position is already easily determined. If the sun is below the horizon (-5° ≤ θ < 0°) during twilight, P = 76.17 ± 4.18% for dmin∗=23 % under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.

Maplike representation of celestial E-vector orientations in the brain of an insect.

PubMed

Heinze, Stanley; Homberg, Uwe

2007-02-16

For many insects, the polarization pattern of the blue sky serves as a compass cue for spatial navigation. E-vector orientations are detected by photoreceptors in a dorsal rim area of the eye. Polarized-light signals from both eyes are finally integrated in the central complex, a brain area consisting of two subunits, the protocerebral bridge and the central body. Here we show that a topographic representation of zenithal E-vector orientations underlies the columnar organization of the protocerebral bridge in a locust. The maplike arrangement is highly suited to signal head orientation under the open sky.

Central neural coding of sky polarization in insects.

PubMed

Homberg, Uwe; Heinze, Stanley; Pfeiffer, Keram; Kinoshita, Michiyo; el Jundi, Basil

2011-03-12

Many animals rely on a sun compass for spatial orientation and long-range navigation. In addition to the Sun, insects also exploit the polarization pattern and chromatic gradient of the sky for estimating navigational directions. Analysis of polarization-vision pathways in locusts and crickets has shed first light on brain areas involved in sky compass orientation. Detection of sky polarization relies on specialized photoreceptor cells in a small dorsal rim area of the compound eye. Brain areas involved in polarization processing include parts of the lamina, medulla and lobula of the optic lobe and, in the central brain, the anterior optic tubercle, the lateral accessory lobe and the central complex. In the optic lobe, polarization sensitivity and contrast are enhanced through convergence and opponency. In the anterior optic tubercle, polarized-light signals are integrated with information on the chromatic contrast of the sky. Tubercle neurons combine responses to the UV/green contrast and e-vector orientation of the sky and compensate for diurnal changes of the celestial polarization pattern associated with changes in solar elevation. In the central complex, a topographic representation of e-vector tunings underlies the columnar organization and suggests that this brain area serves as an internal compass coding for spatial directions.

Polarization patterns of the twilight sky

NASA Astrophysics Data System (ADS)

Cronin, Thomas W.; Warrant, Eric J.; Greiner, Birgit

2005-08-01

Although natural light sources produce depolarized light, patterns of partially linearly polarized light appear in the sky due to scattering from air molecules, dust, and aerosols. Many animals, including bees and ants, orient themselves to patterns of polarization that are present in daytime skies, when the intensity is high and skylight polarization is strong and predictable. The halicitid bee Megalopta genalis inhabits rainforests in Central America. Unlike typical bees, it forages before sunrise and after sunset, when light intensities under the forest canopy are very low, and must find its way to food sources and return to its nest in visually challenging circumstances. An important cue for the orientation could be patterns of polarization in the twilight sky. Therefore, we used a calibrated digital camera to image skylight polarization in an overhead patch of sky, 87.6° across, before dawn on Barro Colorado Island in Panama, where the bees are found. We simultaneously measured the spectral properties of polarized light in a cloudless patch of sky 15° across centered on the zenith. We also performed full-sky imaging of polarization before dawn and after dusk on Lizard Island in Australia, another tropical island. During twilight, celestial polarized light occurs in a wide band stretching perpendicular to the location of the hidden sun and reaching typical degrees of polarization near 80% at wavelengths >600 nm. This pattern appears about 45 minutes before local sunrise or disappears 45 minutes after local sunset (about 20 minutes after the onset of astronomical twilight at dawn, or before its end at dusk) and extends with little change through the entire twilight period. Such a strong and reliable orientation cue could be used for flight orientation by any animal with polarization sensitivity that navigates during twilight.

Central neural coding of sky polarization in insects

PubMed Central

Homberg, Uwe; Heinze, Stanley; Pfeiffer, Keram; Kinoshita, Michiyo; el Jundi, Basil

2011-01-01

Many animals rely on a sun compass for spatial orientation and long-range navigation. In addition to the Sun, insects also exploit the polarization pattern and chromatic gradient of the sky for estimating navigational directions. Analysis of polarization–vision pathways in locusts and crickets has shed first light on brain areas involved in sky compass orientation. Detection of sky polarization relies on specialized photoreceptor cells in a small dorsal rim area of the compound eye. Brain areas involved in polarization processing include parts of the lamina, medulla and lobula of the optic lobe and, in the central brain, the anterior optic tubercle, the lateral accessory lobe and the central complex. In the optic lobe, polarization sensitivity and contrast are enhanced through convergence and opponency. In the anterior optic tubercle, polarized-light signals are integrated with information on the chromatic contrast of the sky. Tubercle neurons combine responses to the UV/green contrast and e-vector orientation of the sky and compensate for diurnal changes of the celestial polarization pattern associated with changes in solar elevation. In the central complex, a topographic representation of e-vector tunings underlies the columnar organization and suggests that this brain area serves as an internal compass coding for spatial directions. PMID:21282171

Insect Responses to Linearly Polarized Reflections: Orphan Behaviors Without Neural Circuits.

PubMed

Heinloth, Tanja; Uhlhorn, Juliane; Wernet, Mathias F

2018-01-01

The e-vector orientation of linearly polarized light represents an important visual stimulus for many insects. Especially the detection of polarized skylight by many navigating insect species is known to improve their orientation skills. While great progress has been made towards describing both the anatomy and function of neural circuit elements mediating behaviors related to navigation, relatively little is known about how insects perceive non-celestial polarized light stimuli, like reflections off water, leaves, or shiny body surfaces. Work on different species suggests that these behaviors are not mediated by the "Dorsal Rim Area" (DRA), a specialized region in the dorsal periphery of the adult compound eye, where ommatidia contain highly polarization-sensitive photoreceptor cells whose receptive fields point towards the sky. So far, only few cases of polarization-sensitive photoreceptors have been described in the ventral periphery of the insect retina. Furthermore, both the structure and function of those neural circuits connecting to these photoreceptor inputs remain largely uncharacterized. Here we review the known data on non-celestial polarization vision from different insect species (dragonflies, butterflies, beetles, bugs and flies) and present three well-characterized examples for functionally specialized non-DRA detectors from different insects that seem perfectly suited for mediating such behaviors. Finally, using recent advances from circuit dissection in Drosophila melanogaster , we discuss what types of potential candidate neurons could be involved in forming the underlying neural circuitry mediating non-celestial polarization vision.

Polarized Light in Astronomy.

ERIC Educational Resources Information Center

King, D. J.

1983-01-01

The application of very sensitive electronic detecting devices during the last decade has revolutionized and revitalized the study of polarization in celestial objects. The nature of polarization, how polaroids work, interstellar polarization, dichroic filters, polarization by scattering, and modern polarimetry are among the topics discussed. (JN)

The polarization compass dominates over idiothetic cues in path integration of desert ants.

PubMed

Lebhardt, Fleur; Koch, Julja; Ronacher, Bernhard

2012-02-01

Desert ants, Cataglyphis, use the sky's pattern of polarized light as a compass reference for navigation. However, they do not fully exploit the complexity of this pattern, rather - as proposed previously - they assess their walking direction by means of an approximate solution based on a simplified internal template. Approximate rules are error-prone. We therefore asked whether the ants use additional cues to improve the accuracy of directional decisions, and focused on 'idiothetic' cues, i.e. cues based on information from proprioceptors. We trained ants in a channel system that was covered with a polarization filter, providing only a single e-vector direction as a directional 'celestial' cue. Then we observed their homebound runs on a test field, allowing full view of the sky. In crucial experiments, the ants were exposed to a cue conflict, in which sky compass and idiothetic information disagreed, by training them in a straight channel that provided a change in e-vector direction. The results indicated that the polarization information completely dominates over idiothetic cues. Two path segments with different e-vector orientations are combined linearly to a summed home vector. Our data provide additional evidence that Cataglyphis uses a simplified internal template to derive directional information from the sky's polarization pattern.

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

PubMed Central

Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-01-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d* for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d > d* is satisfied. Using full-sky imaging polarimetry, we measured the d-pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ. From the measured d-patterns of a given sky we determined the proportion P of the sky for which d > d*. We obtained that P is the largest at low solar elevations θ ≈ 0° and under totally or nearly clear skies with cloud coverage ρ = 0%, when the sun's position is already easily determined. If the sun is below the horizon (−5° ≤ θ < 0°) during twilight, P = 76.17 ± 4.18% for dmin∗=23% under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes. PMID:28386426

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions.

PubMed

Horváth, Gábor; Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-02-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d * for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d  >  d * is satisfied. Using full-sky imaging polarimetry, we measured the d -pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ . From the measured d -patterns of a given sky we determined the proportion P of the sky for which d  >  d *. We obtained that P is the largest at low solar elevations θ  ≈ 0° and under totally or nearly clear skies with cloud coverage ρ  = 0%, when the sun's position is already easily determined. If the sun is below the horizon (-5° ≤  θ  < 0°) during twilight, P  = 76.17 ± 4.18% for [Formula: see text] under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.

Why is it advantageous for animals to detect celestial polarization in the ultraviolet? Skylight polarization under clouds and canopies is strongest in the UV.

PubMed

Barta, András; Horváth, Gábor

2004-02-21

The perception of skylight polarization in the ultraviolet (UV) by many insect species for orientation purposes is rather surprising, because both the degree of linear polarization and the radiance of light from the clear sky are considerably lower in the UV than in the blue or green. In this work we call this the "UV-sky-pol paradox". Although in the past, several attempts have been made to resolve this paradox, none of them was convincing. We present here a possible quantitative resolution to the paradox. We show by a model calculation that if the air layer between a cloud and a ground-based observer is partly sunlit, the degree of linear polarization p of skylight originating from the cloudy region is highest in the UV, because in this spectral range the unpolarized UV-deficient cloudlight dilutes least the polarized light scattered in the air beneath the cloud. Similarly, if the air under foliage is partly sunlit, p of downwelling light from the canopied region is maximal in the UV, because in this part of spectrum the unpolarized UV-deficient green canopylight dilutes least the polarized light scattered in the air beneath the canopy. Therefore, the detection of polarization of downwelling light under clouds or canopies is most advantageous in the UV, in which spectral range the risk is the smallest that the degree of polarization p is lower than the threshold p(tr) of polarization sensitivity in animals. On the other hand, under clear skies there is no favoured wavelength for perception of celestial polarization, because p of skylight is high enough (p > p(tr)) at all wavelengths. We show that there is an analogy between the detection of UV skylight polarization and the polarotactic water detection in the UV. However, insects perceive skylight polarization by UV or blue or green receptors. The question, why they differ in the spectral channel used for the detection of celestial polarization cannot be answered at the present time, because data are insufficient. Nevertheless, we present here one possible atmospheric optical reason why certain visual systems involved in detecting celestial polarization, are specifically tuned to the UV part of the spectrum.

Insect Responses to Linearly Polarized Reflections: Orphan Behaviors Without Neural Circuits

PubMed Central

Heinloth, Tanja; Uhlhorn, Juliane; Wernet, Mathias F.

2018-01-01

The e-vector orientation of linearly polarized light represents an important visual stimulus for many insects. Especially the detection of polarized skylight by many navigating insect species is known to improve their orientation skills. While great progress has been made towards describing both the anatomy and function of neural circuit elements mediating behaviors related to navigation, relatively little is known about how insects perceive non-celestial polarized light stimuli, like reflections off water, leaves, or shiny body surfaces. Work on different species suggests that these behaviors are not mediated by the “Dorsal Rim Area” (DRA), a specialized region in the dorsal periphery of the adult compound eye, where ommatidia contain highly polarization-sensitive photoreceptor cells whose receptive fields point towards the sky. So far, only few cases of polarization-sensitive photoreceptors have been described in the ventral periphery of the insect retina. Furthermore, both the structure and function of those neural circuits connecting to these photoreceptor inputs remain largely uncharacterized. Here we review the known data on non-celestial polarization vision from different insect species (dragonflies, butterflies, beetles, bugs and flies) and present three well-characterized examples for functionally specialized non-DRA detectors from different insects that seem perfectly suited for mediating such behaviors. Finally, using recent advances from circuit dissection in Drosophila melanogaster, we discuss what types of potential candidate neurons could be involved in forming the underlying neural circuitry mediating non-celestial polarization vision. PMID:29615868

Dung beetles use the Milky Way for orientation.

PubMed

Dacke, Marie; Baird, Emily; Byrne, Marcus; Scholtz, Clarke H; Warrant, Eric J

2013-02-18

When the moon is absent from the night sky, stars remain as celestial visual cues. Nonetheless, only birds, seals, and humans are known to use stars for orientation. African ball-rolling dung beetles exploit the sun, the moon, and the celestial polarization pattern to move along straight paths, away from the intense competition at the dung pile. Even on clear moonless nights, many beetles still manage to orientate along straight paths. This led us to hypothesize that dung beetles exploit the starry sky for orientation, a feat that has, to our knowledge, never been demonstrated in an insect. Here, we show that dung beetles transport their dung balls along straight paths under a starlit sky but lose this ability under overcast conditions. In a planetarium, the beetles orientate equally well when rolling under a full starlit sky as when only the Milky Way is present. The use of this bidirectional celestial cue for orientation has been proposed for vertebrates, spiders, and insects, but never proven. This finding represents the first convincing demonstration for the use of the starry sky for orientation in insects and provides the first documented use of the Milky Way for orientation in the animal kingdom. Copyright © 2013 Elsevier Ltd. All rights reserved.

Neutral points of skylight polarization observed during the total eclipse on 11 August 1999.

PubMed

Horváth, Gábor; Pomozi, István; Gál, József

2003-01-20

We report here on the observation of unpolarized (neutral) points in the sky during the total solar eclipse on 11 August 1999. Near the zenith a neutral point was observed at 450 nm at two different points of time during totality. Around this celestial point the distribution of the angle of polarization was heterogeneous: The electric field vectors on the one side were approximately perpendicular to those on the other side. At another moment of totality, near the zenith a local minimum of the degree of linear polarization occurred at 550 nm. Near the antisolar meridian, at a low elevation another two neutral points occurred at 450 nm at a certain moment during totality. Approximately at the position of these neutral points, at another moment of totality a local minimum of the degree of polarization occurred at 550 nm, whereas at 450 nm a neutral point was observed, around which the angle-of-polarization pattern was homogeneous: The electric field vectors were approximately horizontal on both sides of the neutral point.

Spectral properties of identified polarized-light sensitive interneurons in the brain of the desert locust Schistocerca gregaria.

PubMed

Kinoshita, Michiyo; Pfeiffer, Keram; Homberg, Uwe

2007-04-01

Many migrating animals employ a celestial compass mechanism for spatial navigation. Behavioral experiments in bees and ants have shown that sun compass navigation may rely on the spectral gradient in the sky as well as on the pattern of sky polarization. While polarized-light sensitive interneurons (POL neurons) have been identified in the brain of several insect species, there are at present no data on the neural basis of coding the spectral gradient of the sky. In the present study we have analyzed the chromatic properties of two identified POL neurons in the brain of the desert locust. Both neurons, termed TuTu1 and LoTu1, arborize in the anterior optic tubercle and respond to unpolarized light as well as to polarized light. We show here that the polarized-light response of both types of neuron relies on blue-sensitive photoreceptors. Responses to unpolarized light depended on stimulus position and wavelength. Dorsal unpolarized blue light inhibited the neurons, while stimulation from the ipsilateral side resulted in opponent responses to UV light and green light. While LoTu1 was inhibited by UV light and was excited by green light, one subtype of TuTu1 was excited by UV and inhibited by green light. In LoTu1 the sensitivity to polarized light was at least 2 log units higher than the response to unpolarized light stimuli. Taken together, the spatial and chromatic properties of the neurons may be suited to signal azimuthal directions based on a combination of the spectral gradient and the polarization pattern of the sky.

On some basic principles of the wave planetology illustrated by real shapes and tectonic patterns of celestial bodies

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

2011-10-01

The physical background. Celestial bodies move in orbits and keep them due to equality of centrifugal and attractio n forces. These forces are oppositely directed. There is a third force -the inert ia-gravity one directed at the right angle to mentioned above and, thus, not interfering with them (Fig. 1). This force is caused by moving all celestial bodies in non -circular keplerian orbits with periodically changing accelerations. A clear illustration of status of this third force is a stretched rope never achieving a straight line because of the not compensated rope weight acting at the right angle to the stretching force s. In the cas e of cosmic bodies this "not compens ated" inertia-gravity force is absorbed in a cosmic body mass making this mass to warp, undulate. This warping in form of standing waves in rotating bodies is decomposed in four interfering direct ions (ortho - and diagonal) (Fig. 2) producing uplifted (+, ++), subsided (-, --) and neutral (0) blocks (Fig. 2). An interfe rence of fundamental waves 1 long 2π R ma kes always pres ent in bodies tectonic dichotomy: an oppos ition of two hemispheres-segments - one uplifted, another subsided (Fig. 2-6). The first overtone of the wave 1 - wave 2 long πR ma kes tectonic sectors superimposed on segments -hemispheres (Fig. 2, 7, 8). Along with the segment -sectoral pattern in cosmic bodies tectonic granulation develops (Fig. 9, 10). The granule sizes are inversely proportional to orbital frequencies [1-3]. The sectoral tectonic blocks are clearly visible also on Venus and icy satellites of Saturn, especially on polar views. Earth and photosphere are remarkable reference points of this fundamental dependence: orbits - tectonic granulation (Fig. 9, 10).

Polarization-sensitive descending neurons in the locust: connecting the brain to thoracic ganglia.

PubMed

Träger, Ulrike; Homberg, Uwe

2011-02-09

Many animal species, in particular insects, exploit the E-vector pattern of the blue sky for sun compass navigation. Like other insects, locusts detect dorsal polarized light via photoreceptors in a specialized dorsal rim area of the compound eye. Polarized light information is transmitted through several processing stages to the central complex, a brain area involved in the control of goal-directed orientation behavior. To investigate how polarized light information is transmitted to thoracic motor circuits, we studied the responses of locust descending neurons to polarized light. Three sets of polarization-sensitive descending neurons were characterized through intracellular recordings from axonal fibers in the neck connectives combined with single-cell dye injections. Two descending neurons from the brain, one with ipsilaterally and the second with contralaterally descending axon, are likely to bridge the gap between polarization-sensitive neurons in the brain and thoracic motor centers. In both neurons, E-vector tuning changed linearly with daytime, suggesting that they signal time-compensated spatial directions, an important prerequisite for navigation using celestial signals. The third type connects the suboesophageal ganglion with the prothoracic ganglion. It showed no evidence for time compensation in E-vector tuning and might play a role in flight stabilization and control of head movements.

A Snapshot-Based Mechanism for Celestial Orientation.

PubMed

El Jundi, Basil; Foster, James J; Khaldy, Lana; Byrne, Marcus J; Dacke, Marie; Baird, Emily

2016-06-06

In order to protect their food from competitors, ball-rolling dung beetles detach a piece of dung from a pile, shape it into a ball, and roll it away along a straight path [1]. They appear to rely exclusively on celestial compass cues to maintain their bearing [2-8], but the mechanism that enables them to use these cues for orientation remains unknown. Here, we describe the orientation strategy that allows dung beetles to use celestial cues in a dynamic fashion. We tested the underlying orientation mechanism by presenting beetles with a combination of simulated celestial cues (sun, polarized light, and spectral cues). We show that these animals do not rely on an innate prediction of the natural geographical relationship between celestial cues, as other navigating insects seem to [9, 10]. Instead, they appear to form an internal representation of the prevailing celestial scene, a "celestial snapshot," even if that scene represents a physical impossibility for the real sky. We also find that the beetles are able to maintain their bearing with respect to the presented cues only if the cues are visible when the snapshot is taken. This happens during the "dance," a behavior in which the beetle climbs on top of its ball and rotates about its vertical axis [11]. This strategy for reading celestial signals is a simple but efficient mechanism for straight-line orientation. Copyright © 2016 Elsevier Ltd. All rights reserved.

The lizard celestial compass detects linearly polarized light in the blue.

PubMed

Beltrami, Giulia; Parretta, Antonio; Petrucci, Ferruccio; Buttini, Paola; Bertolucci, Cristiano; Foà, Augusto

2012-09-15

The present study first examined whether ruin lizards, Podarcis sicula, are able to orientate using plane-polarized light produced by an LCD screen. Ruin lizards were trained and tested indoors, inside a hexagonal Morris water maze positioned under an LCD screen producing white polarized light with a single E-vector, which provided an axial cue. White polarized light did not include wavelengths in the UV. Lizards orientated correctly either when tested with E-vector parallel to the training axis or after 90 deg rotation of the E-vector direction, thus validating the apparatus. Further experiments examined whether there is a preferential region of the light spectrum to perceive the E-vector direction of polarized light. For this purpose, lizards reaching learning criteria under white polarized light were subdivided into four experimental groups. Each group was tested for orientation under a different spectrum of plane-polarized light (red, green, cyan and blue) with equalized photon flux density. Lizards tested under blue polarized light orientated correctly, whereas lizards tested under red polarized light were completely disoriented. Green polarized light was barely discernible by lizards, and thus insufficient for a correct functioning of their compass. When exposed to cyan polarized light, lizard orientation performances were optimal, indistinguishable from lizards detecting blue polarized light. Overall, the present results demonstrate that perception of linear polarization in the blue is necessary - and sufficient - for a proper functioning of the sky polarization compass of ruin lizards. This may be adaptively important, as detection of polarized light in the blue improves functioning of the polarization compass under cloudy skies, i.e. when the alternative celestial compass based on detection of the sun disk is rendered useless because the sun is obscured by clouds.

Polarization characteristics of an altazimuth sky scanner

NASA Technical Reports Server (NTRS)

Garrison, L. M.; Blaszczak, Z.; Green, A. E. S.

1980-01-01

A theoretical description of the polarization characteristics of an altazimuth sky scanner optical system based on Mueller-Stokes calculus is presented. This computer-driven optical system was designed to perform laboratory studies of skylight and of celestial objects during day or night, and has no space limitations; however, the two parallel 45 deg tilt mirrors introduce some intrinsic polarization. Therefore, proper data interpretation requires a theoretical understanding of the polarization features of the instrument and accurate experimental determination of the Mueller-Stokes matrix elements describing the polarizing and depolarizing action of the system.

Perceptual Strategies of Pigeons to Detect a Rotational Centre—A Hint for Star Compass Learning?

PubMed Central

Helduser, Sascha; Mouritsen, Henrik; Güntürkün, Onur

2015-01-01

Birds can rely on a variety of cues for orientation during migration and homing. Celestial rotation provides the key information for the development of a functioning star and/or sun compass. This celestial compass seems to be the primary reference for calibrating the other orientation systems including the magnetic compass. Thus, detection of the celestial rotational axis is crucial for bird orientation. Here, we use operant conditioning to demonstrate that homing pigeons can principally learn to detect a rotational centre in a rotating dot pattern and we examine their behavioural response strategies in a series of experiments. Initially, most pigeons applied a strategy based on local stimulus information such as movement characteristics of single dots. One pigeon seemed to immediately ignore eccentric stationary dots. After special training, all pigeons could shift their attention to more global cues, which implies that pigeons can learn the concept of a rotational axis. In our experiments, the ability to precisely locate the rotational centre was strongly dependent on the rotational velocity of the dot pattern and it crashed at velocities that were still much faster than natural celestial rotation. We therefore suggest that the axis of the very slow, natural, celestial rotation could be perceived by birds through the movement itself, but that a time-delayed pattern comparison should also be considered as a very likely alternative strategy. PMID:25807499

Panoramic Stokes-polarimeter

NASA Astrophysics Data System (ADS)

Syniavskyi, I. I.; Ivanov, Yu. S.; Vidmachenko, A. P.; Karpov, N. V.

2013-12-01

This article proposes optical layout of the imaging polarimeter based on the polarization films to measure the linear polarization of point and extended celestial objects. The spectral range of device is 420-850 nm, field of view 0.25°x0.25°. The device is designed to equip the telescope with a diameter of primary mirror about 400 mm and aperture f/12.

A New View on an Old Debate: Type of Cue-Conflict Manipulation and Availability of Stars Can Explain the Discrepancies between Cue-Calibration Experiments with Migratory Songbirds.

PubMed

Sjöberg, Sissel; Muheim, Rachel

2016-01-01

Migratory birds use multiple compass systems for orientation, including a magnetic, star and sun/polarized light compass. To keep these compasses in register, birds have to regularly update them with respect to a common reference. However, cue-conflict studies have revealed contradictory results on the compass hierarchy, favoring either celestial or magnetic compass cues as the primary calibration reference. Both the geomagnetic field and polarized light cues present at sunrise and sunset have been shown to play a role in compass cue integration, and evidence suggests that polarized light cues at sunrise and sunset may provide the primary calibration reference for the other compass systems. We tested whether migratory garden warblers recalibrated their compasses when they were exposed to the natural celestial cues at sunset in a shifted magnetic field, which are conditions that have been shown to be necessary for the use of a compass reference based on polarized light cues. We released the birds on the same evening under a starry sky and followed them by radio tracking. We found no evidence of compass recalibration, even though the birds had a full view of polarized light cues near the horizon at sunset during the cue-conflict exposure. Based on a meta-analysis of the available literature, we propose an extended unifying theory on compass cue hierarchy used by migratory birds to calibrate the different compasses. According to this scheme, birds recalibrate their magnetic compass by sunrise/sunset polarized light cues, provided they have access to the vertically aligned band of maximum polarization near the horizon and a view of landmarks. Once the stars appear in the sky, the birds then recalibrate the star compass with respect of the recalibrated magnetic compass. If sunrise and sunset information can be viewed from the same location, the birds average the information to get a true geographic reference. If polarized light information is not available near the horizon at sunrise or sunset, the birds temporarily transfer the previously calibrated magnetic compass information to the available celestial compasses. We conclude that the type of cue-conflict manipulation and the availability of stars can explain the discrepancies between studies.

A New View on an Old Debate: Type of Cue-Conflict Manipulation and Availability of Stars Can Explain the Discrepancies between Cue-Calibration Experiments with Migratory Songbirds

PubMed Central

Sjöberg, Sissel; Muheim, Rachel

2016-01-01

Migratory birds use multiple compass systems for orientation, including a magnetic, star and sun/polarized light compass. To keep these compasses in register, birds have to regularly update them with respect to a common reference. However, cue-conflict studies have revealed contradictory results on the compass hierarchy, favoring either celestial or magnetic compass cues as the primary calibration reference. Both the geomagnetic field and polarized light cues present at sunrise and sunset have been shown to play a role in compass cue integration, and evidence suggests that polarized light cues at sunrise and sunset may provide the primary calibration reference for the other compass systems. We tested whether migratory garden warblers recalibrated their compasses when they were exposed to the natural celestial cues at sunset in a shifted magnetic field, which are conditions that have been shown to be necessary for the use of a compass reference based on polarized light cues. We released the birds on the same evening under a starry sky and followed them by radio tracking. We found no evidence of compass recalibration, even though the birds had a full view of polarized light cues near the horizon at sunset during the cue-conflict exposure. Based on a meta-analysis of the available literature, we propose an extended unifying theory on compass cue hierarchy used by migratory birds to calibrate the different compasses. According to this scheme, birds recalibrate their magnetic compass by sunrise/sunset polarized light cues, provided they have access to the vertically aligned band of maximum polarization near the horizon and a view of landmarks. Once the stars appear in the sky, the birds then recalibrate the star compass with respect of the recalibrated magnetic compass. If sunrise and sunset information can be viewed from the same location, the birds average the information to get a true geographic reference. If polarized light information is not available near the horizon at sunrise or sunset, the birds temporarily transfer the previously calibrated magnetic compass information to the available celestial compasses. We conclude that the type of cue-conflict manipulation and the availability of stars can explain the discrepancies between studies. PMID:26941631

Can invertebrates see the e-vector of polarization as a separate modality of light?

PubMed

Labhart, Thomas

2016-12-15

The visual world is rich in linearly polarized light stimuli, which are hidden from the human eye. But many invertebrate species make use of polarized light as a source of valuable visual information. However, exploiting light polarization does not necessarily imply that the electric (e)-vector orientation of polarized light can be perceived as a separate modality of light. In this Review, I address the question of whether invertebrates can detect specific e-vector orientations in a manner similar to that of humans perceiving spectral stimuli as specific hues. To analyze e-vector orientation, the signals of at least three polarization-sensitive sensors (analyzer channels) with different e-vector tuning axes must be compared. The object-based, imaging polarization vision systems of cephalopods and crustaceans, as well as the water-surface detectors of flying backswimmers, use just two analyzer channels. Although this excludes the perception of specific e-vector orientations, a two-channel system does provide a coarse, categoric analysis of polarized light stimuli, comparable to the limited color sense of dichromatic, 'color-blind' humans. The celestial compass of insects employs three or more analyzer channels. However, that compass is multimodal, i.e. e-vector information merges with directional information from other celestial cues, such as the solar azimuth and the spectral gradient in the sky, masking e-vector information. It seems that invertebrate organisms take no interest in the polarization details of visual stimuli, but polarization vision grants more practical benefits, such as improved object detection and visual communication for cephalopods and crustaceans, compass readings to traveling insects, or the alert 'water below!' to water-seeking bugs. © 2016. Published by The Company of Biologists Ltd.

Can invertebrates see the e-vector of polarization as a separate modality of light?

PubMed Central

2016-01-01

ABSTRACT The visual world is rich in linearly polarized light stimuli, which are hidden from the human eye. But many invertebrate species make use of polarized light as a source of valuable visual information. However, exploiting light polarization does not necessarily imply that the electric (e)-vector orientation of polarized light can be perceived as a separate modality of light. In this Review, I address the question of whether invertebrates can detect specific e-vector orientations in a manner similar to that of humans perceiving spectral stimuli as specific hues. To analyze e-vector orientation, the signals of at least three polarization-sensitive sensors (analyzer channels) with different e-vector tuning axes must be compared. The object-based, imaging polarization vision systems of cephalopods and crustaceans, as well as the water-surface detectors of flying backswimmers, use just two analyzer channels. Although this excludes the perception of specific e-vector orientations, a two-channel system does provide a coarse, categoric analysis of polarized light stimuli, comparable to the limited color sense of dichromatic, ‘color-blind’ humans. The celestial compass of insects employs three or more analyzer channels. However, that compass is multimodal, i.e. e-vector information merges with directional information from other celestial cues, such as the solar azimuth and the spectral gradient in the sky, masking e-vector information. It seems that invertebrate organisms take no interest in the polarization details of visual stimuli, but polarization vision grants more practical benefits, such as improved object detection and visual communication for cephalopods and crustaceans, compass readings to traveling insects, or the alert ‘water below!’ to water-seeking bugs. PMID:27974532

Position determination systems. [using orbital antenna scan of celestial bodies

NASA Technical Reports Server (NTRS)

Shores, P. W. (Inventor)

1976-01-01

A system for an orbital antenna, operated at a synchronous altitude, to scan an area of a celestial body is disclosed. The antenna means comprises modules which are operated by a steering signal in a repetitive function for providing a scanning beam over the area. The scanning covers the entire area in a pattern and the azimuth of the scanning beam is transmitted to a control station on the celestial body simultaneous with signals from an activated ground beacon on the celestial body. The azimuth of the control station relative to the antenna is known and the location of the ground beacon is readily determined from the azimuth determinations.

Reviving a neglected celestial underwater polarization compass for aquatic animals.

PubMed

Waterman, Talbot H

2006-02-01

Substantial in situ measurements on clear days in a variety of marine environments at depths in the water down to 200 m have demonstrated the ubiquitous daytime presence of sun-related e-vector (=plane of polarization) patterns. In most lines of sight the e-vectors tilt from horizontal towards the sun at angles equal to the apparent underwater refracted zenith angle of the sun. A maximum tilt-angle of approximately 48.5 degrees , is reached in horizontal lines of sight at 90 degrees to the sun's bearing (the plane of incidence). This tilt limit is set by Snell's window, when the sun is on the horizon. The biological literature since the 1980s has been pervaded with assumptions that daytime aquatic e-vectors are mainly horizontal. This review attempts to set the record straight concerning the potential use of underwater e-vectors as a visual compass and to reopen the field to productive research on aquatic animals' orientation and navigation.

Opportunities of Teaching Archaeoastronomy in Thailand

ERIC Educational Resources Information Center

Anantasook, Sakanan; Yuenyong, Chokchai; Coll, Richard K.

2015-01-01

Ancient cultures around the world systematically observed the sky and noticed the motions of celestial objects including the stars, Moon, Sun, and planets. Many structural symbolic patterns were built to perceive, visualize and understand the celestial phenomena. They have used this knowledge, archaeoastronomy, to survive, and as bases for…

Neural mechanisms in insect navigation: polarization compass and odometer.

PubMed

Labhart, Thomas; Meyer, Eric P

2002-12-01

Insect navigation relies on path integration, a procedure by which information about compass bearings pursued and distances travelled are combined to calculate position. Three neural levels of the polarization compass, which uses the polarization of skylight as a reference, have been analyzed in orthopteran insects. A group of dorsally directed, highly specialized ommatidia serve as polarization sensors. Polarization-opponent neurons in the optic lobe condition the polarization signal by removing unreliable and irrelevant components of the celestial stimulus. Neurons found in the central complex of the brain possibly represent elements of the compass output. The odometer for measuring travelling distances in honeybees relies on optic flow experienced during flight, whereas desert ants most probably use proprioreceptive cues.

Polarization of the zodiacal light - First results from Skylab

NASA Technical Reports Server (NTRS)

Sparrow, J. G.; Weinberg, J. L.; Hahn, R. C.

1976-01-01

A brief description is given of the Skylab ten color photoelectric photometer and the programs of measurements made during Skylab missions SL-2 and SL-3. Results obtained on the polarized brightness of zodiacal light at five points on the antisolar hemisphere are discussed and compared with other published data for the north celestial pole, south ecliptic pole, at elongation 90 degrees on the ecliptic, and at two places near the north galactic pole.

Data catalog series for space science and applications flight missions. Volume 1A: Brief descriptions of planetary and heliocentric spacecraft and investigations

NASA Technical Reports Server (NTRS)

Cameron, W. S. (Editor); Vostreys, R. W. (Editor)

1982-01-01

Planetary and heliocentric spacecraft, including planetary flybys and probes, are described. Imaging, particles and fields, ultraviolet, infrared, radio science and celestial mechanics, atmospheres, surface chemistry, biology, and polarization are discussed.

Investigation on navigation patterns of inertial/celestial integrated systems

NASA Astrophysics Data System (ADS)

Luo, Dacheng; Liu, Yan; Liu, Zhiguo; Jiao, Wei; Wang, Qiuyan

2014-11-01

It is known that Strapdown Inertial Navigation System (SINS), Global Navigation Satellite System (GNSS) and Celestial Navigation System (CNS) can complement each other's advantages. The SINS/CNS integrated system, which has the characteristics of strong autonomy, high accuracy and good anti-jamming, is widely used in military and civilian applications. Similar to SINS/GNSS integrated system, the SINS/CNS integrated system can also be divided into three kinds according to the difference of integrating depth, i.e., loosely coupled pattern, tightly coupled pattern and deeply coupled pattern. In this paper, the principle and characteristics of each pattern of SINS/CNS system are analyzed. Based on the comparison of these patterns, a novel deeply coupled SINS/CNS integrated navigation scheme is proposed. The innovation of this scheme is that a new star pattern matching method aided by SINS information is put forward. Thus the complementary features of these two subsystems are reflected.

A distinct layer of the medulla integrates sky compass signals in the brain of an insect.

PubMed

el Jundi, Basil; Pfeiffer, Keram; Homberg, Uwe

2011-01-01

Mass migration of desert locusts is a common phenomenon in North Africa and the Middle East but how these insects navigate is still poorly understood. Laboratory studies suggest that locusts are able to exploit the sky polarization pattern as a navigational cue. Like other insects locusts detect polarized light through a specialized dorsal rim area (DRA) of the eye. Polarization signals are transmitted through the optic lobe to the anterior optic tubercle (AOTu) and, finally, to the central complex in the brain. Whereas neurons of the AOTu integrate sky polarization and chromatic cues in a daytime dependent manner, the central complex holds a topographic representation of azimuthal directions suggesting a role as an internal sky compass. To understand further the integration of sky compass cues we studied polarization-sensitive (POL) neurons in the medulla that may be intercalated between DRA photoreceptors and AOTu neurons. Five types of POL-neuron were characterized and four of these in multiple recordings. All neurons had wide arborizations in medulla layer 4 and most, additionally, in the dorsal rim area of the medulla and in the accessory medulla, the presumed circadian clock. The neurons showed type-specific orientational tuning to zenithal polarized light and azimuth tuning to unpolarized green and UV light spots. In contrast to neurons of the AOTu, we found no evidence for color opponency and daytime dependent adjustment of sky compass signals. Therefore, medulla layer 4 is a distinct stage in the integration of sky compass signals that precedes the time-compensated integration of celestial cues in the AOTu.

A Distinct Layer of the Medulla Integrates Sky Compass Signals in the Brain of an Insect

PubMed Central

el Jundi, Basil; Pfeiffer, Keram; Homberg, Uwe

2011-01-01

Mass migration of desert locusts is a common phenomenon in North Africa and the Middle East but how these insects navigate is still poorly understood. Laboratory studies suggest that locusts are able to exploit the sky polarization pattern as a navigational cue. Like other insects locusts detect polarized light through a specialized dorsal rim area (DRA) of the eye. Polarization signals are transmitted through the optic lobe to the anterior optic tubercle (AOTu) and, finally, to the central complex in the brain. Whereas neurons of the AOTu integrate sky polarization and chromatic cues in a daytime dependent manner, the central complex holds a topographic representation of azimuthal directions suggesting a role as an internal sky compass. To understand further the integration of sky compass cues we studied polarization-sensitive (POL) neurons in the medulla that may be intercalated between DRA photoreceptors and AOTu neurons. Five types of POL-neuron were characterized and four of these in multiple recordings. All neurons had wide arborizations in medulla layer 4 and most, additionally, in the dorsal rim area of the medulla and in the accessory medulla, the presumed circadian clock. The neurons showed type-specific orientational tuning to zenithal polarized light and azimuth tuning to unpolarized green and UV light spots. In contrast to neurons of the AOTu, we found no evidence for color opponency and daytime dependent adjustment of sky compass signals. Therefore, medulla layer 4 is a distinct stage in the integration of sky compass signals that precedes the time-compensated integration of celestial cues in the AOTu. PMID:22114712

Children Learning to Explain Daily Celestial Motion: Understanding Astronomy across Moving Frames of Reference

ERIC Educational Resources Information Center

Plummer, Julia D.; Wasko, Kyle D.; Slagle, Cynthia

2011-01-01

This study investigated elementary students' explanations for the daily patterns of apparent motion of the Sun, Moon, and stars. Third-grade students were chosen for this study because this age level is at the lower end of when many US standards documents suggest students should learn to use the Earth's rotation to explain daily celestial motion.…

Students' development of astronomy concepts across time

NASA Astrophysics Data System (ADS)

Plummer, Julia Diane

2006-02-01

The National Science Education Standards (NRC, 1996) recommend that students understand the apparent patterns of motion of the sun, moon and stars visible by the end of early elementary school. However, little information exists on students' knowledge of apparent celestial motion or instruction in this area. The goals of this dissertation were to describe children's knowledge of apparent celestial motion across elementary and middle school, explore early elementary students' ability to learn these topics through planetarium instruction, and begin the development of a learning progression for these concepts, First, third, and eighth grade students (N=60) were interviewed using a planetarium-like setting that allowed the students to demonstrate their ideas both verbally and with their own motions on an artificial sky. Analysis of these interviews suggests that students are not making the types of observations of the sky necessary to learn apparent celestial motion and any instruction they may have received has not helped them reach an accurate understanding of most topics. Most students at each grade level could not accurately describe the patterns of motion. Though the older students were more accurate in most of their descriptions than the younger students, in several areas the eighth grade students showed no improvement over the third grade students. The use of kinesthetic learning techniques in a planetarium program was also explored as a method to improve understanding of celestial motion. Pre- and post-interviews were conducted with participants from seven classes of first and second grade students (N=63). Students showed significant improvement in all areas of apparent celestial motion covered by the planetarium program and surpassed the middle school students' understanding of these concepts in most areas. This suggests that students in early elementary school are capable of learning the accurate description of apparent celestial motion. The results demonstrate the value of both kinesthetic learning techniques and the rich visual environment of the planetarium for improved understanding of celestial motion. Based on the results of these studies, I developed a learning progression describing how children may progress through successively more complex ways of understanding apparent celestial motion across elementary grades.

Wavelength dependence of position angle in polarization standards

NASA Astrophysics Data System (ADS)

Dolan, J. F.; Tapia, S.

1986-08-01

Eleven of the 15 stars on Serkowski's (1974) list of "Standard Stars with Large Interstellar Polarization" were investigated to determine whether the orientation of the plane of their linear polarization showed any dependence on wavelength. Nine of the eleven stars exhibited a statistically significant wavelength dependence of position angle when measured with an accuracy of ≡0°.1 standard deviation. For the majority of these stars, the effect is caused primarily by intrinsic polarization. The calibration of polarimeter position angles in a celestial coordinate frame must evidently be done at the 0°.1 level of accuracy by using only carefully selected standard stars or by using other astronomical or laboratory methods.

Wavelength dependence of position angle in polarization standards. [of stellar systems

NASA Technical Reports Server (NTRS)

Dolan, J. F.; Tapia, S.

1986-01-01

Eleven of the 15 stars on Serkowski's (1974) list of 'Standard Stars with Large Interstellar Polarization' were investigated to determine whether the orientation of the plane of their linear polarization showed any dependence on wavelength. Nine of the eleven stars exhibited a statistically significant wavelength dependence of position angle when measured with an accuracy of about 0.1 deg standard deviation. For the majority of these stars, the effect is caused primarily by intrinsic polarization. The calibration of polarimeter position angles in a celestial coordinate frame must evidently be done at the 0.1 deg level of accuracy by using only carefully selected standard stars or by using other astronomical or laboratory methods.

Flying Drosophila orient to sky polarization.

PubMed

Weir, Peter T; Dickinson, Michael H

2012-01-10

Insects maintain a constant bearing across a wide range of spatial scales. Monarch butterflies and locusts traverse continents [1, 2], and foraging bees and ants travel hundreds of meters to return to their nests [1, 3, 4], whereas many other insects fly straight for only a few centimeters before changing direction. Despite this variation in spatial scale, the brain region thought to underlie long-distance navigation is remarkably conserved [5, 6], suggesting that the use of a celestial compass is a general and perhaps ancient capability of insects. Laboratory studies of Drosophila have identified a local search mode in which short, straight segments are interspersed with rapid turns [7, 8]. However, this flight mode is inconsistent with measured gene flow between geographically separated populations [9-11], and individual Drosophila can travel 10 km across desert terrain in a single night [9, 12, 13]-a feat that would be impossible without prolonged periods of straight flight. To directly examine orientation behavior under outdoor conditions, we built a portable flight arena in which a fly viewed the natural sky through a liquid crystal device that could experimentally rotate the polarization angle. Our findings indicate that Drosophila actively orient using the sky's natural polarization pattern. Copyright © 2012 Elsevier Ltd. All rights reserved.

Planck intermediate results. XLIV. Structure of the Galactic magnetic field from dust polarization maps of the southern Galactic cap

NASA Astrophysics Data System (ADS)

Planck Collaboration; Aghanim, N.; Alves, M. I. R.; Arzoumanian, D.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Basak, S.; Benabed, K.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Bucher, M.; Burigana, C.; Calabrese, E.; Cardoso, J.-F.; Chiang, H. C.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Di Valentino, E.; Dickinson, C.; Diego, J. M.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Dusini, S.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Fantaye, Y.; Ferrière, K.; Finelli, F.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frolov, A.; Galeotta, S.; Galli, S.; Ganga, K.; Génova-Santos, R. T.; Gerbino, M.; Ghosh, T.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Guillet, V.; Hansen, F. K.; Helou, G.; Henrot-Versillé, S.; Herranz, D.; Hivon, E.; Huang, Z.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Krachmalnicoff, N.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Langer, M.; Lasenby, A.; Lattanzi, M.; Le Jeune, M.; Levrier, F.; Liguori, M.; Lilje, P. B.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Matarrese, S.; Mauri, N.; McEwen, J. D.; Melchiorri, A.; Mennella, A.; Migliaccio, M.; Miville-Deschênes, M.-A.; Molinari, D.; Moneti, A.; Montier, L.; Morgante, G.; Moss, A.; Naselsky, P.; Natoli, P.; Neveu, J.; Nørgaard-Nielsen, H. U.; Oppermann, N.; Oxborrow, C. A.; Pagano, L.; Paoletti, D.; Partridge, B.; Perdereau, O.; Perotto, L.; Pettorino, V.; Piacentini, F.; Plaszczynski, S.; Polenta, G.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rossetti, M.; Roudier, G.; Ruiz-Granados, B.; Salvati, L.; Sandri, M.; Savelainen, M.; Scott, D.; Sirignano, C.; Soler, J. D.; Suur-Uski, A.-S.; Tauber, J. A.; Tavagnacco, D.; Tenti, M.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Trombetti, T.; Valiviita, J.; Vansyngel, F.; Van Tent, F.; Vielva, P.; Villa, F.; Wandelt, B. D.; Wehus, I. K.; Zacchei, A.; Zonca, A.

2016-12-01

Using data from the Planck satellite, we study the statistical properties of interstellar dust polarization at high Galactic latitudes around the south pole (b < -60°). Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a modelling framework of the polarized dust foreground for use in cosmic microwave background (CMB) component-separation procedures. We examine the Stokes I, Q, and U maps at 353 GHz, and particularly the statistical distribution of the polarization fraction (p) and angle (ψ), in order to characterize the ordered and turbulent components of the Galactic magnetic field (GMF) in the solar neighbourhood. The Q and U maps show patterns at large angular scales, which we relate to the mean orientation of the GMF towards Galactic coordinates (l0,b0) = (70° ± 5°,24° ± 5°). The histogram of the observed p values shows a wide dispersion up to 25%. The histogram of ψ has a standard deviation of 12° about the regular pattern expected from the ordered GMF. We build a phenomenological model that connects the distributions of p and ψ to a statistical description of the turbulent component of the GMF, assuming a uniform effective polarization fraction (p0) of dust emission. To compute the Stokes parameters, we approximate the integration along the line of sight (LOS) as a sum over a set of N independent polarization layers, in each of which the turbulent component of the GMF is obtained from Gaussian realizations of a power-law power spectrum. We are able to reproduce the observed p and ψ distributions using a p0 value of 26%, a ratio of 0.9 between the strengths of the turbulent and mean components of the GMF, and a small value of N. The mean value of p (inferred from the fit of the large-scale patterns in the Stokes maps) is 12 ± 1%. We relate the polarization layers to the density structure and to the correlation length of the GMF along the LOS. We emphasize the simplicity of our model (involving only a few parameters), which can be easily computed on the celestial sphere to produce simulated maps of dust polarization. Our work is an important step towards a model that can be used to assess the accuracy of component-separation methods in present and future CMB experiments designed to search the B mode CMB polarization from primordial gravity waves.

Planck intermediate results: XLIV. Structure of the Galactic magnetic field from dust polarization maps of the southern Galactic cap

DOE PAGES

Aghanim, N.; Alves, M. I. R.; Arzoumanian, D.; ...

2016-12-12

Using data from the Planck satellite, we study in this paper the statistical properties of interstellar dust polarization at high Galactic latitudes around the south pole (b < -60°). Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a modelling framework of the polarized dust foreground for use in cosmic microwave background (CMB) component-separation procedures. We examine the Stokes I, Q, and U maps at 353 GHz, and particularly the statistical distribution of the polarization fraction (p) and angle (ψ), in order to characterize the ordered and turbulent components of the Galactic magneticmore » field (GMF) in the solar neighbourhood. The Q and U maps show patterns at large angular scales, which we relate to the mean orientation of the GMF towards Galactic coordinates (l 0,b 0) = (70° ± 5°,24° ± 5°). The histogram of the observed p values shows a wide dispersion up to 25%. The histogram of ψ has a standard deviation of 12° about the regular pattern expected from the ordered GMF. We build a phenomenological model that connects the distributions of p and ψ to a statistical description of the turbulent component of the GMF, assuming a uniform effective polarization fraction (p 0) of dust emission. To compute the Stokes parameters, we approximate the integration along the line of sight (LOS) as a sum over a set of N independent polarization layers, in each of which the turbulent component of the GMF is obtained from Gaussian realizations of a power-law power spectrum. We are able to reproduce the observed p and ψ distributions using a p 0 value of 26%, a ratio of 0.9 between the strengths of the turbulent and mean components of the GMF, and a small value of N. The mean value of p (inferred from the fit of the large-scale patterns in the Stokes maps) is 12 ± 1%. We relate the polarization layers to the density structure and to the correlation length of the GMF along the LOS. We emphasize the simplicity of our model (involving only a few parameters), which can be easily computed on the celestial sphere to produce simulated maps of dust polarization. Finally, our work is an important step towards a model that can be used to assess the accuracy of component-separation methods in present and future CMB experiments designed to search the B mode CMB polarization from primordial gravity waves.« less

Planck intermediate results: XLIV. Structure of the Galactic magnetic field from dust polarization maps of the southern Galactic cap

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

Aghanim, N.; Alves, M. I. R.; Arzoumanian, D.

Using data from the Planck satellite, we study in this paper the statistical properties of interstellar dust polarization at high Galactic latitudes around the south pole (b < -60°). Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a modelling framework of the polarized dust foreground for use in cosmic microwave background (CMB) component-separation procedures. We examine the Stokes I, Q, and U maps at 353 GHz, and particularly the statistical distribution of the polarization fraction (p) and angle (ψ), in order to characterize the ordered and turbulent components of the Galactic magneticmore » field (GMF) in the solar neighbourhood. The Q and U maps show patterns at large angular scales, which we relate to the mean orientation of the GMF towards Galactic coordinates (l 0,b 0) = (70° ± 5°,24° ± 5°). The histogram of the observed p values shows a wide dispersion up to 25%. The histogram of ψ has a standard deviation of 12° about the regular pattern expected from the ordered GMF. We build a phenomenological model that connects the distributions of p and ψ to a statistical description of the turbulent component of the GMF, assuming a uniform effective polarization fraction (p 0) of dust emission. To compute the Stokes parameters, we approximate the integration along the line of sight (LOS) as a sum over a set of N independent polarization layers, in each of which the turbulent component of the GMF is obtained from Gaussian realizations of a power-law power spectrum. We are able to reproduce the observed p and ψ distributions using a p 0 value of 26%, a ratio of 0.9 between the strengths of the turbulent and mean components of the GMF, and a small value of N. The mean value of p (inferred from the fit of the large-scale patterns in the Stokes maps) is 12 ± 1%. We relate the polarization layers to the density structure and to the correlation length of the GMF along the LOS. We emphasize the simplicity of our model (involving only a few parameters), which can be easily computed on the celestial sphere to produce simulated maps of dust polarization. Finally, our work is an important step towards a model that can be used to assess the accuracy of component-separation methods in present and future CMB experiments designed to search the B mode CMB polarization from primordial gravity waves.« less

Low-frequency polarization measurements of the diffuse radio emission of the galaxy

NASA Astrophysics Data System (ADS)

Vinyaikin, E. N.; Paseka, A. M.

2015-07-01

Polarization measurements of diffuse Galactic radio emission at 151.5, 198, 217, 237, and 290 MHz have been carried out in the direction of the North Celestial Pole, North Galactic Pole, one region of the North Polar Spur, minimum radio brightness of the Northern sky ( l = 190°, b = 50°), and in the direction l = 147°, b = 9° in the so-called FAN region with enhanced polarization. The results obtained testify to the presence of low spatial frequencies in the angular distribution of the Stokes parameters Q and U of the diffuse Galactic synchrotron emission that are not detectable in interferometric observations. The spectra of the brightness temperature of the polarized component, rotation measures, and intrinsic polarization position angles of the radio emission in the studied regions are presented.

The development of the imaging polarimeter's polarizer on the basis of the polarizing film

NASA Astrophysics Data System (ADS)

Vidmachenko, A. P.; Ivanov, Yu. S.; Syniavskyi, I. I.

2015-07-01

Work has begun on the developing of the scientific equipment "Spectrometer polarimeter", which is planned as one of five devices that form part of the Russian-Ukrainian space experiment "Planetary Monitoring". The devices are designed to form images of celestial objects in the focal plane of a planetary telescope (PT-600) and to register spectral and polarimetric information on gas and aerosol composition of the atmospheres of planets and physics and chemical properties of the surface layers of atmosphereless astronomical bodies. A model of a polarizer based on the use of polarizing films has been designed. This model can be used in the spectrometer-polarimeter. The results of the investigation of the polarizer in the spectral range 420-850 nm are given.

A novel autonomous real-time position method based on polarized light and geomagnetic field.

PubMed

Wang, Yinlong; Chu, Jinkui; Zhang, Ran; Wang, Lu; Wang, Zhiwen

2015-04-08

Many animals exploit polarized light in order to calibrate their magnetic compasses for navigation. For example, some birds are equipped with biological magnetic and celestial compasses enabling them to migrate between the Western and Eastern Hemispheres. The Vikings' ability to derive true direction from polarized light is also widely accepted. However, their amazing navigational capabilities are still not completely clear. Inspired by birds' and Vikings' ancient navigational skills. Here we present a combined real-time position method based on the use of polarized light and geomagnetic field. The new method works independently of any artificial signal source with no accumulation of errors and can obtain the position and the orientation directly. The novel device simply consists of two polarized light sensors, a 3-axis compass and a computer. The field experiments demonstrate device performance.

A novel autonomous real-time position method based on polarized light and geomagnetic field

PubMed Central

Wang, Yinlong; Chu, Jinkui; Zhang, Ran; Wang, Lu; Wang, Zhiwen

2015-01-01

Many animals exploit polarized light in order to calibrate their magnetic compasses for navigation. For example, some birds are equipped with biological magnetic and celestial compasses enabling them to migrate between the Western and Eastern Hemispheres. The Vikings' ability to derive true direction from polarized light is also widely accepted. However, their amazing navigational capabilities are still not completely clear. Inspired by birds' and Vikings' ancient navigational skills. Here we present a combined real-time position method based on the use of polarized light and geomagnetic field. The new method works independently of any artificial signal source with no accumulation of errors and can obtain the position and the orientation directly. The novel device simply consists of two polarized light sensors, a 3-axis compass and a computer. The field experiments demonstrate device performance. PMID:25851793

A novel autonomous real-time position method based on polarized light and geomagnetic field

NASA Astrophysics Data System (ADS)

Wang, Yinlong; Chu, Jinkui; Zhang, Ran; Wang, Lu; Wang, Zhiwen

2015-04-01

Many animals exploit polarized light in order to calibrate their magnetic compasses for navigation. For example, some birds are equipped with biological magnetic and celestial compasses enabling them to migrate between the Western and Eastern Hemispheres. The Vikings' ability to derive true direction from polarized light is also widely accepted. However, their amazing navigational capabilities are still not completely clear. Inspired by birds' and Vikings' ancient navigational skills. Here we present a combined real-time position method based on the use of polarized light and geomagnetic field. The new method works independently of any artificial signal source with no accumulation of errors and can obtain the position and the orientation directly. The novel device simply consists of two polarized light sensors, a 3-axis compass and a computer. The field experiments demonstrate device performance.

Migration along orthodromic sun compass routes by arctic birds.

PubMed

Alerstam, T; Gudmundsson, G A; Green, M; Hedenstrom, A

2001-01-12

Flight directions of birds migrating at high geographic and magnetic latitudes can be used to test bird orientation by celestial or geomagnetic compass systems under polar conditions. Migration patterns of arctic shorebirds, revealed by tracking radar studies during an icebreaker expedition along the Northwest Passage in 1999, support predicted sun compass trajectories but cannot be reconciled with orientation along either geographic or magnetic loxodromes (rhumb lines). Sun compass routes are similar to orthodromes (great circle routes) at high latitudes, showing changing geographic courses as the birds traverse longitudes and their internal clock gets out of phase with local time. These routes bring the shorebirds from high arctic Canada to the east coast of North America, from which they make transoceanic flights to South America. The observations are also consistent with a migration link between Siberia and the Beaufort Sea region by way of sun compass routes across the Arctic Ocean.

Scientific Verification of Faraday Rotation Modulators: Detection of Diffuse Polarized Galactic Emission

NASA Technical Reports Server (NTRS)

Moyerman, S.; Bierman, E.; Ade, P. A. R.; Aiken, R.; Barkats, D.; Bischoff, C.; Bock, J. J.; Chiang, H. C.; Dowell, C. D.; Duband, L.;

Concise CIO based precession-nutation formulations

NASA Astrophysics Data System (ADS)

Capitaine, N.; Wallace, P. T.

2008-01-01

Context: The IAU 2000/2006 precession-nutation models have precision goals measured in microarcseconds. To reach this level of performance has required series containing terms at over 1300 frequencies and involving several thousand amplitude coefficients. There are many astronomical applications for which such precision is not required and the associated heavy computations are wasteful. This justifies developing smaller models that achieve adequate precision with greatly reduced computing costs. Aims: We discuss strategies for developing simplified IAU 2000/2006 precession-nutation procedures that offer a range of compromises between accuracy and computing costs. Methods: The chain of transformations linking celestial and terrestrial coordinates comprises frame bias, precession-nutation, Earth rotation and polar motion. We address the bias and precession-nutation (NPB) portion of the chain, linking the Geocentric Celestial Reference System (GCRS) with the Celestial Intermediate Reference System (CIRS), the latter based on the Celestial Intermediate Pole (CIP) and Celestial Intermediate Origin (CIO). Starting from direct series that deliver the CIP coordinates X,Y and (via the quantity s + XY/2) the CIO locator s, we look at the opportunities for simplification. Results: The biggest reductions come from truncating the series, but some additional gains can be made in the areas of the matrix formulation, the expressions for the nutation arguments and by subsuming long period effects into the bias quantities. Three example models are demonstrated that approximate the IAU 2000/2006 CIP to accuracies of 1 mas, 16 mas and 0.4 arcsec throughout 1995-2050 but with computation costs reduced by 1, 2 and 3 orders of magnitude compared with the full model. Appendices A to G are only available in electronic form at http://www.aanda.org

Use of Reference Frames for Interplanetary Navigation at JPL

NASA Technical Reports Server (NTRS)

Heflin, Michael; Jacobs, Chris; Sovers, Ojars; Moore, Angelyn; Owen, Sue

2010-01-01

Navigation of interplanetary spacecraft is typically based on range, Doppler, and differential interferometric measurements made by ground-based telescopes. Acquisition and interpretation of these observations requires accurate knowledge of the terrestrial reference frame and its orientation with respect to the celestial frame. Work is underway at JPL to reprocess historical VLBI and GPS data to improve realizations of the terrestrial and celestial frames. Improvements include minimal constraint alignment, improved tropospheric modeling, better orbit determination, and corrections for antenna phase center patterns.

Modulation of cosmic microwave background polarization with a warm rapidly rotating half-wave plate on the Atacama B-Mode Search instrument.

PubMed

Kusaka, A; Essinger-Hileman, T; Appel, J W; Gallardo, P; Irwin, K D; Jarosik, N; Nolta, M R; Page, L A; Parker, L P; Raghunathan, S; Sievers, J L; Simon, S M; Staggs, S T; Visnjic, K

2014-02-01

We evaluate the modulation of cosmic microwave background polarization using a rapidly rotating, half-wave plate (HWP) on the Atacama B-Mode Search. After demodulating the time-ordered-data (TOD), we find a significant reduction of atmospheric fluctuations. The demodulated TOD is stable on time scales of 500-1000 s, corresponding to frequencies of 1-2 mHz. This facilitates recovery of cosmological information at large angular scales, which are typically available only from balloon-borne or satellite experiments. This technique also achieves a sensitive measurement of celestial polarization without differencing the TOD of paired detectors sensitive to two orthogonal linear polarizations. This is the first demonstration of the ability to remove atmospheric contamination at these levels from a ground-based platform using a rapidly rotating HWP.

The Atacama Cosmology Telescope: Two-season spectrum and parameters

NASA Astrophysics Data System (ADS)

Hlozek, Renée; Louis, Thibaut; Grace, Emily; Hasselfield, Matthew; Lungu, Marius; Maurin, Loic; Atacama Cosmology Telescope

2017-01-01

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope polarimeter (ACTPol) over 548 deg^2 of sky on the celestial Equator, from nighttime data collected during 2013-14 using two kilo-detector arrays at 146 GHz. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP satellite data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the ΛCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature power spectrum, including the baryon density and the acoustic peak position angle, and the derived Hubble constant. Adding the new data to Planck temperature data tightens the limits on damping tail parameters, which we present here.

Mariner Mars 1971 project. Volume 2: Preliminary science results

NASA Technical Reports Server (NTRS)

1972-01-01

Data from six Mariner Mars experiments are presented. Television reconnaissance of Mars and its satellites yielded information on atmospheric phenomena, surface features of the South Polar region, geology, and satellite astronomy. Other experiments involved infrared spectroscopy and radiometry; ultraviolet spectrometry; S band occultation for observing the atmosphere, ionosphere, and topography of Mars; and the use of celestial mechanics, to determine the gravity field pole direction of the planet.

Aquarius Whole Range Calibration: Celestial Sky, Ocean, and Land Targets

NASA Technical Reports Server (NTRS)

Dinnat, Emmanuel P.; Le Vine, David M.; Bindlish, Rajat; Piepmeier, Jeffrey R.; Brown, Shannon T.

2014-01-01

Aquarius is a spaceborne instrument that uses L-band radiometers to monitor sea surface salinity globally. Other applications of its data over land and the cryosphere are being developed. Combining its measurements with existing and upcoming L-band sensors will allow for long term studies. For that purpose, the radiometers calibration is critical. Aquarius measurements are currently calibrated over the oceans. They have been found too cold at the low end (celestial sky) of the brightness temperature scale, and too warm at the warm end (land and ice). We assess the impact of the antenna pattern model on the biases and propose a correction. We re-calibrate Aquarius measurements using the corrected antenna pattern and measurements over the Sky and oceans. The performances of the new calibration are evaluated using measurements over well instrument land sites.

Johannes Kepler and the Supernova of 1604

NASA Astrophysics Data System (ADS)

Boner, P. J.

2006-08-01

The brilliant luminary that first appeared in October 1604 was considered by many contemporaries to be a new star of unrivalled magnitude. Shining forth near the historic conjunction of Mars, Jupiter and Saturn, the new star held important implications for several areas of interest, notably astrology, astronomy, chronology and theology. Addressing all of these areas in his comprehensive book, De stella nova (1606), Johannes Kepler (1571-1630) studied the new star extensively under the aegis of Holy Roman Emperor Rudolf II (1552-1612) in Prague. The focus of the following presentation is Kepler's theory of the new star's origins in the celestial ether. Describing the heavens poetically as a fertile expanse of "liquid fields", Kepler suggested that the new star sprung from the celestial ether much like the numerous living beings in the sublunary realm which were spontaneously generated from the Earth. As evidence for his claim, Kepler pointed to the conspicuous mathematical patterns similarly observed in earthly and celestial entities. Kepler's efficient cause for this explanation, known as the animate faculty, accounted for both the generation and form of new phenomena in the celestial and terrestrial realms. The new star of 1604 proved to be no exception.

The depth of the honeybee's backup sun-compass systems.

PubMed

Dovey, Katelyn M; Kemfort, Jordan R; Towne, William F

2013-06-01

Honeybees have at least three compass mechanisms: a magnetic compass; a celestial or sun compass, based on the daily rotation of the sun and sun-linked skylight patterns; and a backup celestial compass based on a memory of the sun's movements over time in relation to the landscape. The interactions of these compass systems have yet to be fully elucidated, but the celestial compass is primary in most contexts, the magnetic compass is a backup in certain contexts, and the bees' memory of the sun's course in relation to the landscape is a backup system for cloudy days. Here we ask whether bees have any further compass systems, for example a memory of the sun's movements over time in relation to the magnetic field. To test this, we challenged bees to locate the sun when their known celestial compass systems were unavailable, that is, under overcast skies in unfamiliar landscapes. We measured the bees' knowledge of the sun's location by observing their waggle dances, by which foragers indicate the directions toward food sources in relation to the sun's compass bearing. We found that bees have no celestial compass systems beyond those already known: under overcast skies in unfamiliar landscapes, bees attempt to use their landscape-based backup system to locate the sun, matching the landscapes or skylines at the test sites with those at their natal sites as best they can, even if the matches are poor and yield weak or inconsistent orientation.

Empirical corroboration of an earlier theoretical resolution to the UV paradox of insect polarized skylight orientation.

PubMed

Wang, Xin; Gao, Jun; Fan, Zhiguo

2014-02-01

It is surprising that many insect species use only the ultraviolet (UV) component of the polarized skylight for orientation and navigation purposes, while both the intensity and the degree of polarization of light from the clear sky are lower in the UV than at longer (blue, green, red) wavelengths. Why have these insects chosen the UV part of the polarized skylight? This strange phenomenon is called the "UV-sky-pol paradox". Although earlier several speculations tried to resolve this paradox, they did this without any quantitative data. A theoretical and computational model has convincingly explained why it is advantageous for certain animals to detect celestial polarization in the UV. We performed a sky-polarimetric approach and built a polarized skylight sensor that models the processing of polarization signals by insect photoreceptors. Using this model sensor, we carried out measurements under clear and cloudy sky conditions. Our results showed that light from the cloudy sky has maximal degree of polarization in the UV. Furthermore, under both clear and cloudy skies the angle of polarization of skylight can be detected with a higher accuracy. By this, we corroborated empirically the soundness of the earlier computational resolution of the UV-sky-pol paradox.

Empirical corroboration of an earlier theoretical resolution to the UV paradox of insect polarized skylight orientation

NASA Astrophysics Data System (ADS)

Wang, Xin; Gao, Jun; Fan, Zhiguo

2014-02-01

It is surprising that many insect species use only the ultraviolet (UV) component of the polarized skylight for orientation and navigation purposes, while both the intensity and the degree of polarization of light from the clear sky are lower in the UV than at longer (blue, green, red) wavelengths. Why have these insects chosen the UV part of the polarized skylight? This strange phenomenon is called the "UV-sky-pol paradox". Although earlier several speculations tried to resolve this paradox, they did this without any quantitative data. A theoretical and computational model has convincingly explained why it is advantageous for certain animals to detect celestial polarization in the UV. We performed a sky-polarimetric approach and built a polarized skylight sensor that models the processing of polarization signals by insect photoreceptors. Using this model sensor, we carried out measurements under clear and cloudy sky conditions. Our results showed that light from the cloudy sky has maximal degree of polarization in the UV. Furthermore, under both clear and cloudy skies the angle of polarization of skylight can be detected with a higher accuracy. By this, we corroborated empirically the soundness of the earlier computational resolution of the UV-sky-pol paradox.

Seven-year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Planets and Celestial Calibration Sources

NASA Astrophysics Data System (ADS)

Weiland, J. L.; Odegard, N.; Hill, R. S.; Wollack, E.; Hinshaw, G.; Greason, M. R.; Jarosik, N.; Page, L.; Bennett, C. L.; Dunkley, J.; Gold, B.; Halpern, M.; Kogut, A.; Komatsu, E.; Larson, D.; Limon, M.; Meyer, S. S.; Nolta, M. R.; Smith, K. M.; Spergel, D. N.; Tucker, G. S.; Wright, E. L.

2011-02-01

We present WMAP seven-year observations of bright sources which are often used as calibrators at microwave frequencies. Ten objects are studied in five frequency bands (23-94 GHz): the outer planets (Mars, Jupiter, Saturn, Uranus, and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg A, 3C274, and 3C58). The seven-year analysis of Jupiter provides temperatures which are within 1σ of the previously published WMAP five-year values, with slightly tighter constraints on variability with orbital phase (0.2% ± 0.4%), and limits (but no detections) on linear polarization. Observed temperatures for both Mars and Saturn vary significantly with viewing geometry. Scaling factors are provided which, when multiplied by the Wright Mars thermal model predictions at 350 μm, reproduce WMAP seasonally averaged observations of Mars within ~2%. An empirical model is described which fits brightness variations of Saturn due to geometrical effects and can be used to predict the WMAP observations to within 3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated. Uncertainties in Uranus temperatures are 3%-4% in the 41, 61, and 94 GHz bands; the smallest uncertainty for Neptune is 8% for the 94 GHz band. Intriguingly, the spectrum of Uranus appears to show a dip at ~30 GHz of unidentified origin, although the feature is not of high statistical significance. Flux densities for the five selected fixed celestial sources are derived from the seven-year WMAP sky maps and are tabulated for Stokes I, Q, and U, along with polarization fraction and position angle. Fractional uncertainties for the Stokes I fluxes are typically 1% to 3%. Source variability over the seven-year baseline is also estimated. Significant secular decrease is seen for Cas A and Tau A: our results are consistent with a frequency-independent decrease of about 0.53% per year for Cas A and 0.22% per year for Tau A. We present WMAP polarization data with uncertainties of a few percent for Tau A. Where appropriate, WMAP results are compared against previous findings in the literature. With an absolute calibration uncertainty of 0.2%, WMAP data are a valuable asset for calibration work. WMAP is the result of a partnership between Princeton University and NASA's Goddard Space Flight Center. Scientific guidance is provided by the WMAP Science Team.

SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: PLANETS AND CELESTIAL CALIBRATION SOURCES

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

Weiland, J. L.; Odegard, N.; Hill, R. S.

2011-02-01

We present WMAP seven-year observations of bright sources which are often used as calibrators at microwave frequencies. Ten objects are studied in five frequency bands (23-94 GHz): the outer planets (Mars, Jupiter, Saturn, Uranus, and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg A, 3C274, and 3C58). The seven-year analysis of Jupiter provides temperatures which are within 1{sigma} of the previously published WMAP five-year values, with slightly tighter constraints on variability with orbital phase (0.2% {+-} 0.4%), and limits (but no detections) on linear polarization. Observed temperatures for both Mars and Saturn vary significantly with viewing geometry.more » Scaling factors are provided which, when multiplied by the Wright Mars thermal model predictions at 350 {mu}m, reproduce WMAP seasonally averaged observations of Mars within {approx}2%. An empirical model is described which fits brightness variations of Saturn due to geometrical effects and can be used to predict the WMAP observations to within 3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated. Uncertainties in Uranus temperatures are 3%-4% in the 41, 61, and 94 GHz bands; the smallest uncertainty for Neptune is 8% for the 94 GHz band. Intriguingly, the spectrum of Uranus appears to show a dip at {approx}30 GHz of unidentified origin, although the feature is not of high statistical significance. Flux densities for the five selected fixed celestial sources are derived from the seven-year WMAP sky maps and are tabulated for Stokes I, Q, and U, along with polarization fraction and position angle. Fractional uncertainties for the Stokes I fluxes are typically 1% to 3%. Source variability over the seven-year baseline is also estimated. Significant secular decrease is seen for Cas A and Tau A: our results are consistent with a frequency-independent decrease of about 0.53% per year for Cas A and 0.22% per year for Tau A. We present WMAP polarization data with uncertainties of a few percent for Tau A. Where appropriate, WMAP results are compared against previous findings in the literature. With an absolute calibration uncertainty of 0.2%, WMAP data are a valuable asset for calibration work.« less

The effect of ocean tides on the earth's rotation as predicted by the results of an ocean tide model

NASA Technical Reports Server (NTRS)

Gross, Richard S.

1993-01-01

The published ocean tidal angular momentum results of Seiler (1991) are used to predict the effects of the most important semidiurnal, diurnal, and long period ocean tides on the earth's rotation. The separate, as well as combined, effects of ocean tidal currents and sea level height changes on the length-of-day, UT1, and polar motion are computed. The predicted polar motion results reported here account for the presence of the free core nutation and are given in terms of the motion of the celestial ephemeris pole so that they can be compared directly to the results of observations. Outside the retrograde diurnal tidal band, the summed effect of the semidiurnal and diurnal ocean tides studied here predict peak-to-peak polar motion amplitudes as large as 2 mas. Within the retrograde diurnal tidal band, the resonant enhancement caused by the free core nutation leads to predicted polar motion amplitudes as large as 9 mas.

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

NASA Technical Reports Server (NTRS)

Louis, Thibaut; Grace, Emily; Hasselfield, Matthew; Lungu, Marius; Maurin, Loic; Addison, Graeme E.; Adem Peter A. R.; Aiola, Simone; Allison, Rupert; Amiri, Mandana;

The Atacama Cosmology Telescope: two-season ACTPol spectra and parameters

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

Louis, Thibaut; Grace, Emily; Aiola, Simone

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013–14 using two detector arrays at 149 GHz, from 548 deg{sup 2} of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008–10, in combination with planck and wmap data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the ΛCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters thanmore » the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. The new ACTPol data provide information on damping tail parameters. The joint uncertainty on the number of neutrino species and the primordial helium fraction is reduced by 20% when adding ACTPol to Planck temperature data alone.« less

The Atacama Cosmology Telescope: two-season ACTPol spectra and parameters

NASA Astrophysics Data System (ADS)

Louis, Thibaut; Grace, Emily; Hasselfield, Matthew; Lungu, Marius; Maurin, Loïc; Addison, Graeme E.; Ade, Peter A. R.; Aiola, Simone; Allison, Rupert; Amiri, Mandana; Angile, Elio; Battaglia, Nicholas; Beall, James A.; de Bernardis, Francesco; Bond, J. Richard; Britton, Joe; Calabrese, Erminia; Cho, Hsiao-mei; Choi, Steve K.; Coughlin, Kevin; Crichton, Devin; Crowley, Kevin; Datta, Rahul; Devlin, Mark J.; Dicker, Simon R.; Dunkley, Joanna; Dünner, Rolando; Ferraro, Simone; Fox, Anna E.; Gallardo, Patricio; Gralla, Megan; Halpern, Mark; Henderson, Shawn; Hill, J. Colin; Hilton, Gene C.; Hilton, Matt; Hincks, Adam D.; Hlozek, Renée; Ho, S. P. Patty; Huang, Zhiqi; Hubmayr, Johannes; Huffenberger, Kevin M.; Hughes, John P.; Infante, Leopoldo; Irwin, Kent; Muya Kasanda, Simon; Klein, Jeff; Koopman, Brian; Kosowsky, Arthur; Li, Dale; Madhavacheril, Mathew; Marriage, Tobias A.; McMahon, Jeff; Menanteau, Felipe; Moodley, Kavilan; Munson, Charles; Naess, Sigurd; Nati, Federico; Newburgh, Laura; Nibarger, John; Niemack, Michael D.; Nolta, Michael R.; Nuñez, Carolina; Page, Lyman A.; Pappas, Christine; Partridge, Bruce; Rojas, Felipe; Schaan, Emmanuel; Schmitt, Benjamin L.; Sehgal, Neelima; Sherwin, Blake D.; Sievers, Jon; Simon, Sara; Spergel, David N.; Staggs, Suzanne T.; Switzer, Eric R.; Thornton, Robert; Trac, Hy; Treu, Jesse; Tucker, Carole; Van Engelen, Alexander; Ward, Jonathan T.; Wollack, Edward J.

2017-06-01

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg2 of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with planck and wmap data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the ΛCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. The new ACTPol data provide information on damping tail parameters. The joint uncertainty on the number of neutrino species and the primordial helium fraction is reduced by 20% when adding ACTPol to Planck temperature data alone.

Skylab experiment SO73: Gegenschein/zodiacal light. [electrophotometry of surface brightness and polarization

NASA Technical Reports Server (NTRS)

Weinberg, J. L.

1976-01-01

A 10 color photoelectric polarimeter was used to measure the surface brightness and polarization associated with zodiacal light, background starlight, and spacecraft corona during each of the Skylab missions. Fixed position and sky scanning observations were obtained during Skylab missions SL-2 and SL-3 at 10 wavelenghts between 4000A and 8200A. Initial results from the fixed-position data are presented on the spacecraft corona and on the polarized brightness of the zodiacal light. Included among the fixed position regions that were observed are the north celestial pole, south ecliptic pole, two regions near the north galactic pole, and 90 deg from the sun in the ecliptic. The polarized brightness of the zodiacal light was found to have the color of the sun at each of these positions. Because previous observations found the total brightness to have the color of the sun from the near ultraviolet out to 2.4 micrometers, the degree of polarization of the zodiacal light is independent of wavelength from 4000A to 8200A.

Polyarnye siyaniya sistemy avroral'nogo ovala kak kosmoloficheskij obraz drevnej mifologii %t The northern light of the auroral oval system as a cosmological concept of the archaic mythology

NASA Astrophysics Data System (ADS)

Alekseeva, L. M.

Since archaic epochs people attentively observe the sky. They used to associate the sky phenomena with gods, heroes, spirits, etc. People interpreted the regularities in the motion of celestial objects in terms of their mythological model of the Universe. These observations and interpretations were first steps of the archaeoastronomy. Many remarkable features are inherent in the patterns of northern lights of the auroral oval system. Their manifestations are fairly regular. Did the ancients observe and some how classify these northern light phenomena? If yes, with which mythological personages were they associated? When were studies of the polar lights initiated? The present work is an attempt to answer these questions. We shall see that the ancient people assumed the spirit-world to be situated on the North. If so, it should manifest itself in spectacular polar aurorae. The specifically northern mythic cosmology formed the basis for Slavic fairy tales (theme of the Serpent and Serpent Fighter) and folk-beliefs. Other inhabitants of snowy latitudes should also manifest similar views. Studying the mythological reflections of typical auroral phenomena, it is possible to trace up long-standing ideological trends from the late glaciation epoch to the present time. Our results can help geophysicists in studying paleoauroral phenomena.

Chinese Armillary Spheres

NASA Astrophysics Data System (ADS)

Sun, Xiaochun

The armillary sphere was perhaps the most important type of astronomical instrument in ancient China. It was first invented by Luoxia Hong in the first century BC. After Han times, the structure of the armillary sphere became increasingly sophisticated by including more and more rings representing various celestial movements as recognized by the Chinese astronomers. By the eighth century, the Chinese armillary sphere consisted of three concentric sets of rings revolving on the south-north polar axis. The relative position of the rings could be adjusted to reflect the precession of the equinoxes and the regression of the Moon's nodes along the ecliptic. To counterbalance the defect caused by too many rings, Guo Shoujing from the late thirteenth century constructed the Simplified Instruments which reorganized the rings of the armillary sphere into separate instruments for measuring equatorial coordinates and horizontal coordinates. The armillary sphere was still preserved because it was a good illustration of celestial movements. A fifteenth-century replica of Guo Shoujing's armillary sphere still exists today.

Cosmic microwave background polarimetry with ABS and ACT: Instrumental design, characterization, and analysis

NASA Astrophysics Data System (ADS)

Simon, Sara Michelle

The LCDM model of the universe is supported by an abundance of astronomical observations, but it does not confirm a period of inflation in the early universe or explain the nature of dark energy and dark matter. The polarization of the cosmic microwave background (CMB) may hold the key to addressing these profound questions. If a period of inflation occurred in the early universe, it could have left a detectable odd-parity pattern called B-modes in the polarization of the CMB on large angular scales. Additionally, the CMB can be used to probe the structure of the universe on small angular scales through lensing and the detection of galaxy clusters and their motions via the Sunyaev-Zel'dovich effect, which can improve our understanding of neutrinos, dark matter, and dark energy. The Atacama B-mode Search (ABS) instrument was a cryogenic crossed-Dragone telescope located at an elevation of 5190m in the Atacama Desert in Chile that observed from February 2012 until October 2014. ABS searched on degree-angular scales for inflationary B-modes in the CMB and pioneered the use of a rapidly-rotating half-wave plate (HWP), which modulates the polarization of incoming light to permit the measurement of celestial polarization on large angular scales that would otherwise be obscured by 1/f noise from the atmosphere. Located next to ABS in the Atacama is the Atacama Cosmology Telescope (ACT), which is an off-axis Gregorian telescope. Its large 6m primary mirror facilitates measurements of the CMB on small angular scales. HWPs are baselined for use with the upgraded polarization-sensitive camera for ACT, called Advanced ACTPol, to extend observations of the polarized CMB to larger angular scales while also retaining sensitivity to small angular scales. The B-mode signal is extremely faint, and measuring it poses an instrumental challenge that requires the development of new technologies and well-characterized instruments. I will discuss the use of novel instrumentation and methods on the ABS telescope and Advanced ACTPol, the characterization of the ABS instrument, and the first two seasons of ABS data, including an overview of the data selection process.

Seeing the Solar System through Two Perspectives. Part 1 of a Series Focusing on Learning Progressions

ERIC Educational Resources Information Center

Thornburgh, Bill R.; Tretter, Tom R.; Duckwall, Mark

2015-01-01

Space has fascinated and intrigued humans of all ages since time immemorial, and continues to do so today. The natural curiosity is engaged when looking up into the sky, notice patterns among celestial objects such as the Sun, Moon, and stars, and wonder. Scientific understanding of those patterns has progressed immensely over the span of human…

Archaeoastronomy and Calendar Cities

NASA Astrophysics Data System (ADS)

Campion, Nicholas

2016-02-01

The use of astronomy for collective purposes, both religious and political, is apparent in the earliest astronomical records, from the evidence for Palaeolithic lunar calendars to megalithic monuments and Mesopotamian celestial-omen reports. This paper will consider the application of the heavens to the organisation of the ‘Cosmic State’, the human polity modelled on the assumption of a close relationship between society on the one hand and planetary and stellar patterns on the other. I will also examine the foundation of Baghdad within the tradition of celestial town planning and argue that the city may be seen as a ‘talisman’, designed to connect heaven to Earth and ensure peace, stability and political success by harmonising time and space.

Polarimetric Study of Jupiter's Atmosphere

NASA Astrophysics Data System (ADS)

Yanamandra-Fisher, P. A.; McLean, W.; Wesley, A.; Miles, P.; Masding, P.

2017-12-01

Jupiter's atmosphere displays polarization, attributed to changes in the clouds/thermal filed that can be brought about by endogenic dynamical processes such merger of vortices; global, planetary scale upheavals, and external factors such as celestial collisions (such as D/Shoemaker-Levy 9 impact with Jupiter in 1994, etc.). Although the range of phase angles available from Earth for Jupiter is restricted to a narrow range, limb polarization measurements provide constraints on the polarimetric properties. Jupiter is known to exhibit a strong polar limb polarization and a low equatorial limb polarization due to the presence of haze particles and Rayleigh scattering at the poles. In contrast, at the equator, the concentration of particulates in the high atmosphere might change, changing the polarimetric signature and aurorae at both poles. The polarimetric maps, in conjunction with thermal maps and albedo maps, can provide constraints on modeling efforts to understand the nature of the aerosols/hazes in Jovian atmosphere. With Jupiter experiencing morphological changes at many latitudes, we have initiated a polarimetric observing campaign of Jupiter, in conjunction with The PACA Project and preliminary results will be discussed. Some of our observations are acquired by a team of professional/amateur planetary imagers astronomers.

IRIS-S - Extending geodetic very long baseline interferometry observations to the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Carter, W. E.; Robertson, D. S.; Nothnagel, A.; Nicolson, G. D.; Schuh, H.

1988-12-01

High-accuracy geodetic very long baseline interferometry measurements between the African, Eurasian, and North American plates have been analyzed to determine the terrestrial coordinates of the Hartebeesthoek observatory to better than 10 cm, to determine the celestial coordinates of eight Southern Hemisphere radio sources with milliarc second (mas) accuracy, and to derive quasi-independent polar motion, UTI, and nutation time series. Comparison of the earth orientation time series with ongoing International Radio Interferometric Surveying project values shows agreement at about the 1 mas of arc level in polar motion and nutation and 0.1 ms of time in UTI. Given the independence of the observing sessions and the unlikeliness of common systematic error sources, this level of agreement serves to bound the total errors in both measurement series.

Method for deploying multiple spacecraft

NASA Technical Reports Server (NTRS)

Sharer, Peter J. (Inventor)

2007-01-01

A method for deploying multiple spacecraft is disclosed. The method can be used in a situation where a first celestial body is being orbited by a second celestial body. The spacecraft are loaded onto a single spaceship that contains the multiple spacecraft and the spacecraft is launched from the second celestial body towards a third celestial body. The spacecraft are separated from each other while in route to the third celestial body. Each of the spacecraft is then subjected to the gravitational field of the third celestial body and each of the spacecraft assumes a different, independent orbit about the first celestial body. In those situations where the spacecraft are launched from Earth, the Sun can act as the first celestial body, the Earth can act as the second celestial body and the Moon can act as the third celestial body.

Determination of the lunar orbital and rotational parameters and of the ecliptic reference system orientation from LLR measurements and IERS data

NASA Astrophysics Data System (ADS)

Chapront, J.; Chapront-Touzé, M.; Francou, G.

1999-03-01

An analysis of Lunar Laser Ranging (LLR) observations from January 1972 till March 1998 is performed using the lunar theory ELP 2000-96 and the completed Moons' theory of the lunar libration. The LLR station coordinates, polar motion and Universal Time are provided by the International Earth Rotation Service (IERS). In Solution 1 the precession-nutation transformation is given by recent analytical theories, while in Solution 2 it is derived from the IERS daily corrections. Orbital and free libration parameters of the Moon, and coordinates of the reflectors are obtained in both cases. The position of the inertial mean ecliptic of J2000.0 with respect to the equator of the mean Celestial Ephemeris Pole (CEP) of J2000.0 (in Solution 1) and to the International Celestial Reference System (ICRS), the IERS celestial reference system, (in Solution 2) are fit. The position of the mean CEP equator of J2000.0 and of several dynamical reference planes and origins, with respect to ICRS, are derived from these fits (Fig. 1). The leading results are the following: 0farcs057 60+/- 0farcs000 20 (in the equator) for the separation of the origin of right ascensions in ICRS from the ascending node of the inertial mean ecliptic of J2000.0 on the reference plane of ICRS, -0farcs0460 +/- 0farcs0008 (in the ecliptic) for the separation of the latter point from the inertial dynamical mean equinox of J2000.0, -0farcs015 19+/- 0farcs000 35 (in the equator) for the separation of the inertial dynamical mean equinox of J2000.0 from the J2000.0 right ascension origin derived from IERS polar motion and Universal Time and from precise theories of precession-nutation, and 23degr26 arcmin21 farcs405 22+/- 0farcs000 07 for the inertial obliquity of J2000.0. A correction of -0farcs3437 +/- 0farcs0040 /cy to the IAU 1976 value of the precession constant is also obtained (the errors quoted are formal errors).

Spatial memory and navigation by honeybees on the scale of the foraging range

PubMed

Dyer

1996-01-01

Honeybees and other nesting animals face the problem of finding their way between their nest and distant feeding sites. Many studies have shown that insects can learn foraging routes in reference to both landmarks and celestial cues, but it is a major puzzle how spatial information obtained from these environmental features is encoded in memory. This paper reviews recent progress by my colleagues and me towards understanding three specific aspects of this problem in honeybees: (1) how bees learn the spatial relationships among widely separated locations in a familiar terrain; (2) how bees learn the pattern of movement of the sun over the day; and (3) whether, and if so how, bees learn the relationships between celestial cues and landmarks.

Nonuniformity of the Earth's rotation and the motion of the poles

NASA Technical Reports Server (NTRS)

Sidorenkov, N. S.

1983-01-01

The study of the nonuniformity of the Earth's rotation and the motion of the poles has great practical and theoretical significance. This study makes it possible to determine the coordinates of celestial and terrestrial objects, and to gain information in many domains of earth science. This paper reviews studies of rotation nonuniformity and polar motion, giving attention to astronomical data; the nature of periodic oscillations of the Earth's rotation; the nature of long-period variations of the Earth's rotation rate; and the use of Earth-rotation data in hydrometeorology.

XIPE, the X-ray imaging polarimetry explorer: Opening a new window in the X-ray sky

NASA Astrophysics Data System (ADS)

Soffitta, Paolo; XIPE Collaboration

2017-11-01

XIPE, the X-ray Imaging Polarimetry Explorer, is a candidate ESA fourth medium size mission, now in competitive phase A, aimed at time-spectrally-spatially-resolved X-ray polarimetry of a large number of celestial sources as a breakthrough in high energy astrophysics and fundamental physics. Its payload consists of three X-ray optics with a total effective area larger than one XMM mirror but with a low mass and of three Gas Pixel Detectors at their focus. The focal length is 4 m and the whole satellite fits within the fairing of the Vega launcher without the need of an extendable bench. XIPE will be an observatory with 75% of the time devoted to a competitive guest observer program. Its consortium across Europe comprises Italy, Germany, Spain, United Kingdom, Switzerland, Poland, Sweden Until today, thanks to a dedicated experiment that dates back to the '70, only the Crab Nebula showed a non-zero polarization with large significance [1] in X-rays. XIPE, with its innovative detector, promises to make significative measurements on hundreds of celestial sources.

Vienna VLBI and Satellite Software (VieVS) for Geodesy and Astrometry

NASA Astrophysics Data System (ADS)

Böhm, Johannes; Böhm, Sigrid; Boisits, Janina; Girdiuk, Anastasiia; Gruber, Jakob; Hellerschmied, Andreas; Krásná, Hana; Landskron, Daniel; Madzak, Matthias; Mayer, David; McCallum, Jamie; McCallum, Lucia; Schartner, Matthias; Teke, Kamil

2018-04-01

The Vienna VLBI and Satellite Software (VieVS) is state-of-the-art Very Long Baseline Interferometry (VLBI) analysis software for geodesy and astrometry. VieVS has been developed at Technische Universität Wien (TU Wien) since 2008, where it is used for research purposes and for teaching space geodetic techniques. In the past decade, it has been successfully applied on Very Long Baseline Interferometry (VLBI) observations for the determination of celestial and terrestrial reference frames as well as for the estimation of celestial pole offsets, universal Time (UT1-UTC), and polar motion based on least-squares adjustment. Furthermore, VieVS is equipped with tools for scheduling and simulating VLBI observations to extragalactic radio sources as well as to satellites and spacecraft, features which proved to be very useful for a variety of applications. VieVS is now available as version 3.0 and we do provide the software to all interested persons and institutions. A wiki with more information about VieVS is available at http://vievswiki.geo.tuwien.ac.at/.

Data acquisition system and ground calibration of polarized gamma-ray observer (PoGOLite)

NASA Astrophysics Data System (ADS)

Takahashi, Hiromitsu; Chauvin, Maxime; Fukazawa, Yasushi; Jackson, Miranda; Kamae, Tuneyoshi; Kawano, Takafumi; Kiss, Mozsi; Kole, Merlin; Mikhalev, Victor; Mizuno, Tsunefumi; Moretti, Elena; Pearce, Mark; Rydström, Stefan

2014-07-01

The Polarized Gamma-ray Observer, PoGOLite, is a balloon experiment with the capability of detecting 10% polarization from a 200 mCrab celestial object between the energy-range 25-80 keV in one 6 hour flight. Polarization measurements in soft gamma-rays are expected to provide a powerful probe into high-energy emission mechanisms in/around neutron stars, black holes, supernova remnants, active-galactic nuclei etc. The "pathfinder" flight was performed in July 2013 for 14 days from Sweden to Russia. The polarization is measured using Compton scattering and photoelectric absorption in an array of 61 well-type phoswich detector cells (PDCs) for the pathfinder instrument. The PDCs are surrounded by 30 BGO crystals which form a side anti-coincidence shield (SAS) and passive polyethylene neutron shield. There is a neutron detector consisting of LiCaAlF6 (LiCAF) scintillator covered with BGOs to measure the background contribution of atmospheric neutrons. The data acquisition system treats 92 PMT signals from 61 PDCs + 30 SASs + 1 neutron detector, and it is developed based on SpaceWire spacecraft communication network. Most of the signal processing is done by digital circuits in Field Programmable Gate Arrays (FPGAs). This enables the reduction of the mass, the space and the power consumption. The performance was calibrated before the launch.

Celestial mechanics - Methods of the theory of motion of 'artificial' celestial bodies

NASA Astrophysics Data System (ADS)

Duboshin, G. N.

This book is concerned with the translational motion of 'artificial' celestial bodies. The difference between natural celestial bodies, which are ordinarily considered by celestial mechanics, and 'artificial' celestial bodies is discussed, taking into account hypothetical celestial bodies introduced in connection with mathematical developments and problems, invisible celestial bodies whose existence can be assumed on the basis of some plausible hypothesis, and man-made satellites of the earth. The book consists of two parts. The first part presents introductory material, and examines a number of general mathematical questions to provide a basis for the studies conducted in the second part. Subjects considered in the first part are related to basic problems, integration methods, and perturbation theory. In the second part, attention is given to the motion of artificial celestial bodies in the gravitational field of the basic planet, external perturbations regarding the motion of these bodies, the motion of the bodies in the earth-moon system, and periodic solutions.

Walking Drosophila align with the e-vector of linearly polarized light through directed modulation of angular acceleration

PubMed Central

Velez, Mariel M.; Wernet, Mathias F.; Clark, Damon A.

2014-01-01

Understanding the mechanisms that link sensory stimuli to animal behavior is a central challenge in neuroscience. The quantitative description of behavioral responses to defined stimuli has led to a rich understanding of different behavioral strategies in many species. One important navigational cue perceived by many vertebrates and insects is the e-vector orientation of linearly polarized light. Drosophila manifests an innate orientation response to this cue (‘polarotaxis’), aligning its body axis with the e-vector field. We have established a population-based behavioral paradigm for the genetic dissection of neural circuits guiding polarotaxis to both celestial as well as reflected polarized stimuli. However, the behavioral mechanisms by which flies align with a linearly polarized stimulus remain unknown. Here, we present a detailed quantitative description of Drosophila polarotaxis, systematically measuring behavioral parameters that are modulated by the stimulus. We show that angular acceleration is modulated during alignment, and this single parameter may be sufficient for alignment. Furthermore, using monocular deprivation, we show that each eye is necessary for modulating turns in the ipsilateral direction. This analysis lays the foundation for understanding how neural circuits guide these important visual behaviors. PMID:24810784

Review on the Celestial Sphere Positioning of FITS Format Image Based on WCS and Research on General Visualization

NASA Astrophysics Data System (ADS)

Song, W. M.; Fan, D. W.; Su, L. Y.; Cui, C. Z.

2017-11-01

Calculating the coordinate parameters recorded in the form of key/value pairs in FITS (Flexible Image Transport System) header is the key to determine FITS images' position in the celestial system. As a result, it has great significance in researching the general process of calculating the coordinate parameters. By combining CCD related parameters of astronomical telescope (such as field, focal length, and celestial coordinates in optical axis, etc.), astronomical images recognition algorithm, and WCS (World Coordinate System) theory, the parameters can be calculated effectively. CCD parameters determine the scope of star catalogue, so that they can be used to build a reference star catalogue by the corresponding celestial region of astronomical images; Star pattern recognition completes the matching between the astronomical image and reference star catalogue, and obtains a table with a certain number of stars between CCD plane coordinates and their celestial coordinates for comparison; According to different projection of the sphere to the plane, WCS can build different transfer functions between these two coordinates, and the astronomical position of image pixels can be determined by the table's data we have worked before. FITS images are used to carry out scientific data transmission and analyze as a kind of mainstream data format, but only to be viewed, edited, and analyzed in the professional astronomy software. It decides the limitation of popular science education in astronomy. The realization of a general image visualization method is significant. FITS is converted to PNG or JPEG images firstly. The coordinate parameters in the FITS header are converted to metadata in the form of AVM (Astronomy Visualization Metadata), and then the metadata is added to the PNG or JPEG header. This method can meet amateur astronomers' general needs of viewing and analyzing astronomical images in the non-astronomical software platform. The overall design flow is realized through the java program and tested by SExtractor, WorldWide Telescope, picture viewer, and other software.

Stars and Seasons in Southern Africa

NASA Astrophysics Data System (ADS)

Snedegar, K. V.

Although the indigenous people of Southern Africa traditionally viewed the sky as a place quite apart from the Earth, they believed celestial phenomena to be natural signs united with those of the Earth in a harmonious synchronicity. There is no substantial evidence that the precolonial Africans imagined a casual relationship between celestial bodies and the seasonal patterns of life on Earth. They did, however, recognize a coincidental relationship. The traditional African cosmos, then, worked as a noetic principle unifying the observed motions of celestial bodies, the sequence of seasons, and the behavior of plants and animals. Such a cosmos, with local peculiarities, was widely understood in Southern Africa before the end of the last century. By the early 20th century European colonial paradigms had largely obliterated this African worldview. This paper will offer a partial reconstruction. Pre-colonial South African people viewed time as a sequence of discrete natural events; through annual repetition these events served as a guide for proper human action. The South Africans analyzed the passage of time in terms of the motions of celestial bodies, the maturation of beneficial plants, and the mating patterns of animals. The rightful course of human life was seen to fit within the seasonal context of these natural phenomena. The visibility of conspicuous stars and asterisms marked significant times of year. For instance, the Lovedu people greeted the dawn rising of Canopus with joy: "The boy has come out." The star was a signal for rainmaking and boys' initiation ceremonies to proceed. The Venda constellation Thutlwa, the giraffes, comprises α and β Crucis and α and β Centauri. In October Thutlwa skims the trees of the evening horizon. The Venda Thutlwa literally means 'rising above the trees,' an allusion to the majestic vegetarian creatures and the stars advising the people to be done with their spring planting. This paper will describe stellar associations with other creatures: wild dogs, warthogs, wildebeests, swallows, cuckoos and cicadas. In each case the visibility of a star will synchronize with a behavior of the associated species. Together, stars and species informed man of the order and unity of an African cosmos — a worldview that must have been as satisfying as it was beautiful.

Short Large-Amplitude Magnetic Structures (SLAMS) at Venus

NASA Technical Reports Server (NTRS)

Collinson, G. A.; Wilson, L. B.; Sibeck, D. G.; Shane, N.; Zhang, T. L.; Moore, T. E.; Coates, A. J.; Barabash, S.

2012-01-01

We present the first observation of magnetic fluctuations consistent with Short Large-Amplitude Magnetic Structures (SLAMS) in the foreshock of the planet Venus. Three monolithic magnetic field spikes were observed by the Venus Express on the 11th of April 2009. The structures were approx.1.5->11s in duration, had magnetic compression ratios between approx.3->6, and exhibited elliptical polarization. These characteristics are consistent with the SLAMS observed at Earth, Jupiter, and Comet Giacobini-Zinner, and thus we hypothesize that it is possible SLAMS may be found at any celestial body with a foreshock.

Research in Space Physics at the University of Iowa. [spaceborne experiments and instruments

NASA Technical Reports Server (NTRS)

Vanallen, J. A.

1981-01-01

Currently active projects conducted to extend knowledge of the energetic particles and the electric, magnetic, and electromagnetic fields associated with Earth, other celestial bodies, and the interplanetary medium are summarized. These include investigations and/or instruments for Hawkeye 1; Pioneers 10 and 11; Voyagers 1 and 2; ISEE; IMP 8; Dynamics Explorer; Galileo; Spacelab and Orbital flight test missions; VLBI; and the International Solar Polar mission. Experiments and instruments proposed for the future international comet mission, the origin of plasmas in the Earth's environment mission, and the NASA active magnetospheric particle tracer experiment are mentioned.

Identifying the stars on Johann Bayer's Chart of the South Polar Sky

NASA Astrophysics Data System (ADS)

Ridpath, I.

2014-04-01

The first chart of the stars in the region around the south celestial pole was published in 1603 by Johann Bayer (1572-1625) as part of his monumental star atlas called Uranometria. This south polar chart depicted 12 entirely new constellations that had been created only a few years earlier from stars observed during the first Dutch expedition to the East Indies in 1595-97. Bayer's chart plotted 121 stars in the 12 newly invented constellations. Five more stars formed a southern extension of the existing constellation Eridanus, while another twelve stars were left 'unformed', i.e. unattached to any constellation. Whereas Bayer famously applied Greek or Roman letters to the stars in the 48 Ptolemaic constellations, he left the stars in the newly invented constellations unlabelled. This paper attempts to identify the stars plotted on Bayer's chart. It also discusses the source of Bayer's data and the origin of the 12 new southern constellations.

On the trail of Vikings with polarized skylight: experimental study of the atmospheric optical prerequisites allowing polarimetric navigation by Viking seafarers.

PubMed

Horváth, Gábor; Barta, András; Pomozi, István; Suhai, Bence; Hegedüs, Ramón; Akesson, Susanne; Meyer-Rochow, Benno; Wehner, Rüdiger

2011-03-12

Between AD 900 and AD 1200 Vikings, being able to navigate skillfully across the open sea, were the dominant seafarers of the North Atlantic. When the Sun was shining, geographical north could be determined with a special sundial. However, how the Vikings could have navigated in cloudy or foggy situations, when the Sun's disc was unusable, is still not fully known. A hypothesis was formulated in 1967, which suggested that under foggy or cloudy conditions, Vikings might have been able to determine the azimuth direction of the Sun with the help of skylight polarization, just like some insects. This hypothesis has been widely accepted and is regularly cited by researchers, even though an experimental basis, so far, has not been forthcoming. According to this theory, the Vikings could have determined the direction of the skylight polarization with the help of an enigmatic birefringent crystal, functioning as a linearly polarizing filter. Such a crystal is referred to as 'sunstone' in one of the Viking's sagas, but its exact nature is unknown. Although accepted by many, the hypothesis of polarimetric navigation by Vikings also has numerous sceptics. In this paper, we summarize the results of our own celestial polarization measurements and psychophysical laboratory experiments, in which we studied the atmospheric optical prerequisites of possible sky-polarimetric navigation in Tunisia, Finland, Hungary and the high Arctic.

On the trail of Vikings with polarized skylight: experimental study of the atmospheric optical prerequisites allowing polarimetric navigation by Viking seafarers

PubMed Central

Horváth, Gábor; Barta, András; Pomozi, István; Suhai, Bence; Hegedüs, Ramón; Åkesson, Susanne; Meyer-Rochow, Benno; Wehner, Rüdiger

2011-01-01

Between AD 900 and AD 1200 Vikings, being able to navigate skillfully across the open sea, were the dominant seafarers of the North Atlantic. When the Sun was shining, geographical north could be determined with a special sundial. However, how the Vikings could have navigated in cloudy or foggy situations, when the Sun's disc was unusable, is still not fully known. A hypothesis was formulated in 1967, which suggested that under foggy or cloudy conditions, Vikings might have been able to determine the azimuth direction of the Sun with the help of skylight polarization, just like some insects. This hypothesis has been widely accepted and is regularly cited by researchers, even though an experimental basis, so far, has not been forthcoming. According to this theory, the Vikings could have determined the direction of the skylight polarization with the help of an enigmatic birefringent crystal, functioning as a linearly polarizing filter. Such a crystal is referred to as ‘sunstone’ in one of the Viking's sagas, but its exact nature is unknown. Although accepted by many, the hypothesis of polarimetric navigation by Vikings also has numerous sceptics. In this paper, we summarize the results of our own celestial polarization measurements and psychophysical laboratory experiments, in which we studied the atmospheric optical prerequisites of possible sky-polarimetric navigation in Tunisia, Finland, Hungary and the high Arctic. PMID:21282181

Observation of Celestial Phenomena in Ancient China

NASA Astrophysics Data System (ADS)

Sun, Xiaochun

Because of the need for calendar-making and portent astrology, the Chinese were diligent and meticulous observers of celestial phenomena. China has maintained the longest continuous historical records of celestial phenomena in the world. Extraordinary or abnormal celestial events were particularly noted because of their astrological significance. The historical records cover various types of celestial phenomena, which include solar and lunar eclipses, sunspots, "guest stars" (novae or supernovae as we understand today), comets and meteors, and all kinds of planetary phenomena. These records provide valuable historical data for astronomical studies today.

On testing of the photometer-polarimeter UVP layout using a telescope on Earth's surface

NASA Astrophysics Data System (ADS)

Nevodovskyi, P. V.; Vidmachenko, A. P.; Morozhenko, O. V.; Zbrutskyi, O.; Ivakhiv, O. V.

2016-08-01

One of the causes of climate change (changing of concentration of stratospheric ozone) - is variations due to aerosol optical thickness in the upper layers of Earth's atmosphere. To solve the problem is necessary to make a space experiment to receive polarization observational data. Their analysis will: determine the value of the real part of the refractive index, the size of the stratospheric aerosol, optical thickness of the stratospheric aerosol layer, investigate aerosol's layer horizontal structure and its changes over time. Main Astronomical Observatory of NAS of Ukraine jointly with the National Technical University of Ukraine "KPI" and National University "Lviv Polytechnic" for a long time working on the design of polarimeter to study the stratospheric layer of the Earth from board of artificial satellites. During this time accumulated a great experience in such work, and created a layout of compact board ultraviolet polarimeter UFP [1-4]. For testing of ground variant of layout of UFP, it is installed on the telescope AZT-2 of the Main Astronomical Observatory NAS of Ukraine (Kyiv). Using it we plan to investigate the possibility of determining the degree of polarization of the twilight glow of Earth's atmosphere, and implementation of this technique in the development of space experiment on investigation of the stratospheric aerosol from space. For this purpose we develop a special set of equipment that will adapt the layout for working of UFP with telescope AZT-2, and carry out the above mentioned work (see. in [5-7]). References. 1. P. Nevodovskyi, O. Morozhenko, A. Vidmachenko, O. Ivakhiv, M. Geraimchuk, O. Zbrutskyi. Tiny Ultraviolet Polarimeter for Earth Stratosphere from Space Investigation // Proceedings of 8th IEEE International Conference on Intelligent Data Acquisition and Advanced Computing Systems: Technology and Applications (IDAACS'2015). 24-26 September 2015, Proceedings. Warsaw, Poland. Vol.81, p. 28-32. 2. Nevodovsksiy P. V., Morozhenko A. V. Studies of stratospheric ozone layer from near-earth orbit utilizing ultraviolet polarimeter // Acta Astronautica. 2009, vol. 64, no 1, p. 54-58. 3. Nevodovskij P. V. Kvantakons and optimization of their parameters for astronomical observations Kinematika i Fizika Nebesnykh Tel. 2001, vol. 17, no. 3, p. 279-288. 4. A. P. Vid'machenko, P. V. Nevodovsky. A cooled photomultiplier with an InGaAs photocathode developed for the spectropolarimetry observations // Kinematika i Fizika Nebesnykh Tel. 2000. Suppl. 3, p. 283-285. 5. Morozhenko A. V., Vidmachenko A. P., Nevodovskiy P. V., Kostogryz N. M. On the efficiency of polarization measurements while studying aerosols in the terrestrial atmosphere // Kinematics and Physics of Celestial Bodies. 2014, vol. 30, no. 1, p. 11-21. 6. A.V. Morozhenko, A.P. Vidmachenko, P.V. Nevodovskyi. Aerosol in the upper layer of earth's atmosphere // Kinematics and Physics of Celestial Bodies. 2013, vol. 29, no. 5, p. 243-246. 7. Morozhenko A.V. Polarimetry of twilight sky and stratospheric aerosol // Kinematics and Physics of Celestial Bodies. 2010, vol. 26, no. 1, p. 36-38.

Protection of celestial environments and the law of outer space

NASA Astrophysics Data System (ADS)

Tennen, Leslie; Race, Margaret

The law of outer space expressly addresses the matter of preservation and protection of natural celestial environments from harmful contamination and disruption by mankind in the explo-ration and use of outer space, including the moon and other celestial bodies. The Outer Space Treaty, however, does not prohibit all human impact to an extraterrestrial environment, but rather permits a wide range of activities that could have significant environmental ramifications. This legal regime may be in conflict with the interests of preserving celestial environments for scientific research, especially when considered in relation to activities conducted for commercial purposes. Nevertheless, the Moon Agreement provides a mechanism by which special protective measures can be implemented to protect particular areas of the moon and other celestial bodies for scientific investigation. This paper examines the current status of the law of outer space vis-a-vis the protection and preservation of natural celestial environments. Particular emphasis is placed on the policies on which the legal obligations are based, together with consideration of the non-appropriation principle, and the commercial use of lunar and other celestial resources and areas. In addition, the concepts of international scientific preserves, special regions, keep out zones, and planetary parks are compared and evaluated as potential means to limit the disturbance to celestial environments caused by the activities of mankind.

Satellite Ephemeris Correction via Remote Site Observation for Star Tracker Navigation Performance Improvement

DTIC Science & Technology

2016-03-01

squared RMS root mean squared GCRF Geocentric Celestial Reference Frame xi List of Figures Figure Page 1 Geometry of single observation...RA and DEC in the celestial sphere. The Geocentric Celestial Reference Frame (GCRF) is the standard geocentric frame that measures the RA east in the...Figure 2. Right ascension (α) and declination (δ) in the celestial sphere[6] 7 made between geocentric and topocentric angles. Geocentric is referred to

Microarsecond models for the celestial motions of the CIP and CEO

NASA Astrophysics Data System (ADS)

Capitaine, N.

2004-09-01

The Celestial intermediate pole (CIP) and Celestial ephemeris (orintermediate) origin (CEO/CIO) have been adopted by the IAU (c.f. IAU2000 Resolution B1.8) as the celestial pole and origin, respectively,to be used for realizing the intermediate celestial system between theInternational Terrestrial System (ITRS) and Geocentric CelestialReference System (GCRS). Resolution B1.8 has also recommended that theInternational Earth Rotation and Reference Systems Service (IERS)continue to provide users with data and algorithms for the conventionaltransformation. The IAU 2000 Resolutions have been implemented in theIERS 2003 Conventions including Tables and routines that provide thecelestial motions of the CIP and the CEO with a theoretical accuracy ofone microarcsecond after one century using either the classical or thenew transformation. This paper reports on the method used for achievingthis accuracy in the positions of the CIP and CIO and on the differencebetween this rigorous procedure and the pre-2003 classical one.

The status of the QUIJOTE multi-frequency instrument

NASA Astrophysics Data System (ADS)

Hoyland, R. J.; Aguiar-González, M.; Aja, B.; Ariño, J.; Artal, E.; Barreiro, R. B.; Blackhurst, E. J.; Cagigas, J.; Cano de Diego, J. L.; Casas, F. J.; Davis, R. J.; Dickinson, C.; Arriaga, B. E.; Fernandez-Cobos, R.; de la Fuente, L.; Génova-Santos, R.; Gómez, A.; Gomez, C.; Gómez-Reñasco, F.; Grainge, K.; Harper, S.; Herran, D.; Herreros, J. M.; Herrera, G. A.; Hobson, M. P.; Lasenby, A. N.; Lopez-Caniego, M.; López-Caraballo, C.; Maffei, B.; Martinez-Gonzalez, E.; McCulloch, M.; Melhuish, S.; Mediavilla, A.; Murga, G.; Ortiz, D.; Piccirillo, L.; Pisano, G.; Rebolo-López, R.; Rubiño-Martin, J. A.; Ruiz, J. Luis; Sanchez de la Rosa, V.; Sanquirce, R.; Vega-Moreno, A.; Vielva, P.; Viera-Curbelo, T.; Villa, E.; Vizcargüenaga, A.; Watson, R. A.

2012-09-01

The QUIJOTE-CMB project has been described in previous publications. Here we present the current status of the QUIJOTE multi-frequency instrument (MFI) with five separate polarimeters (providing 5 independent sky pixels): two which operate at 10-14 GHz, two which operate at 16-20 GHz, and a central polarimeter at 30 GHz. The optical arrangement includes 5 conical corrugated feedhorns staring into a dual reflector crossed-draconian system, which provides optimal cross-polarization properties (designed to be < -35 dB) and symmetric beams. Each horn feeds a novel cryogenic on-axis rotating polar modulator which can rotate at a speed of up to 1 Hz. The science driver for this first instrument is the characterization of the galactic emission. The polarimeters use the polar modulator to derive linear polar parameters Q, U and I and switch out various systematics. The detection system provides optimum sensitivity through 2 correlated and 2 total power channels. The system is calibrated using bright polarized celestial sources and through a secondary calibration source and antenna. The acquisition system, telescope control and housekeeping are all linked through a real-time gigabit Ethernet network. All communication, power and helium gas are passed through a central rotary joint. The time stamp is synchronized to a GPS time signal. The acquisition software is based on PLCs written in Beckhoffs TwinCat and ethercat. The user interface is written in LABVIEW. The status of the QUIJOTE MFI will be presented including pre-commissioning results and laboratory testing.

The terrestrial gravitational wave environment from known sources

NASA Technical Reports Server (NTRS)

Webbink, Ronald F.

1993-01-01

The objective of this project was to produce a gravitational wave spectral line list of all known binary stars producing expected strain amplitudes at Earth in excess of h = 10 (exp -21), or gravitational wave fluxes in excess of F = 10 (exp -12) erg cm(exp -2) s(exp -1). These strain and flux limits lie above the anticipated detection thresholds for space-borne laser interferometers capable of detecting gravitational radiation in the 10 micron Hz to 1 Hz frequency range. The source list was intended to provide frequency (including each harmonic), amplitude and phase (for each polarization and harmonic), and celestial coordinates for each system, lacking only the orientation of the principal polarization axis with respect to the pole of the coordinate system, and the sign of the source phase and frequency (or, equivalently, of the sense of rotation of the strain tensor with time) from providing a complete source description. Such a spectral line list would lay essential groundwork for high-sensitivity, low-frequency searches for gravitational radiation.

Smoothing and Predicting Celestial Pole Offsets using a Kalman Filter and Smoother

NASA Astrophysics Data System (ADS)

Nastula, J.; Chin, T. M.; Gross, R. S.; Winska, M.; Winska, J.

2017-12-01

Since the early days of interplanetary spaceflight, accounting for changes in the Earth's rotation is recognized to be critical for accurate navigation. In the 1960s, tracking anomalies during the Ranger VII and VIII lunar missions were traced to errors in the Earth orientation parameters. As a result, Earth orientation calibration methods were improved to support the Mariner IV and V planetary missions. Today, accurate Earth orientation parameters are used to track and navigate every interplanetary spaceflight mission. The interplanetary spacecraft tracking and navigation teams at JPL require the UT1 and polar motion parameters, and these Earth orientation parameters are estimated by the use of a Kalman filter to combine past measurements of these parameters and predict their future evolution. A model was then used to provide the nutation/precession components of the Earth's orientation separately. As a result, variations caused by the free core nutation were not taken into account. But for the highest accuracy, these variations must be considered. So JPL recently developed an approach based upon the use of a Kalman filter and smoother to provide smoothed and predicted celestial pole offsets (CPOs) to the interplanetary spacecraft tracking and navigation teams. The approach used at JPL to do this and an evaluation of the accuracy of the predicted CPOs will be given here.

Lunar Laser Ranging: Glorious Past And A Bright Future

NASA Astrophysics Data System (ADS)

Shelus, Peter J.

Lunar Laser Ranging (LLR), a part of the NASA Apollo program, has beenon-going for more than 30 years. It provides the grist for a multi-disciplinarydata analysis mill. Results exist for solid Earth sciences, geodesy and geodynamics,solar system ephemerides, terrestrial and celestial reference frames, lunar physics,general relativity and gravitational theory. Combined with other data, it treatsprecession of the Earth''s spin axis, lunar induced nutation, polar motion/Earthrotation, Earth orbit obliquity to the ecliptic, intersection of the celestial equatorwith the ecliptic, luni-solar solid body tides, lunar tidal deceleration, lunar physicaland free librations, structure of the moon and energy dissipation in the lunar interior.LLR provides input to lunar surface cartography and surveying, Earth station and lunar retroreflector location and motion, mass of the Earth-moon system, lunar and terrestrial gravity harmonics and Love numbers, relativistic geodesic precession, and the equivalence principle of general relativity. With the passive nature of the reflectors and steady improvement in observing equipment and data analysis, LLR continues to provide state-of-the-art results. Gains are steady as the data-base expands. After more than 30 years, LLR remains the only active Apollo experiment. It is important to recognize examples of efficient and cost effective progress of research. LLR is just such an example.

Pattern and polarization measurements of integrated-circuit spiral antennas at 10-μm wavelength

NASA Astrophysics Data System (ADS)

MacDonald, Michael E.; Grossman, Erich N.

1996-12-01

Radiation patterns are presented for planar equiangular spiral antennas at wavelengths of approximately 10 micrometers . These antennas are fabricated using integrated-circuit processes on silicon substrates and are coupled through dielectric lenses. Patterns are presented over a full 2D scan for orthogonal linear polarizations, and for left- circular (LCP) and right-circular (RCP) polarizations. The antennas respond preferentially to left-circularly polarized radiation, as expected for the left-handed sense of the spiral arms. Cross-polarization ratios as large as 10 dB in circular polarization are obtained, corresponding to an axial ratio of 1.2. No difference in response between horizontally and vertically polarized radiation is observed, as expected for circularly polarized antennas. Directivities as large as 14 dB in left-circular polarization have been obtained. The cross-polarized directivity is considerably lower than the co-polarized directivity. All patterns are approximately circularly symmetric about the (theta) equals 0 axis. The cross-polarization ratio and pattern symmetry strongly depend on the alignment of the antenna and detector response is antenna coupled, even at radiation wavelength of the same order of magnitude as the resolution limit of the optical lithography used to define the antenna geometry.

Pseudo-polar drive patterns for brain electrical impedance tomography.

PubMed

Shi, Xuetao; Dong, Xiuzhen; Shuai, Wanjun; You, Fusheng; Fu, Feng; Liu, Ruigang

2006-11-01

Brain electrical impedance tomography (EIT) is a difficult task as brain tissues are enclosed by the skull of high resistance and cerebrospinal fluid (CSF) of low resistance, which makes internal resistivity information more difficult to extract. In order to seek a single source drive pattern that is more suitable for brain EIT, we built a more realistic experimental setting that simulates a head with the resistivity of the scalp, skull, CSF and brain, and compared the performance of adjacent, cross, polar and pseudo-polar drive patterns in terms of the boundary voltage dynamic range, independent measurement number, total boundary voltage changes and anti-noise performance based on it. The results demonstrate that the pseudo-polar drive pattern is optimal in all the aspects except for the dynamic range. The polar and cross drive patterns come next, and the adjacent drive pattern is the worst. Therefore, the pseudo-polar drive pattern should be chosen for brain EIT.

Earth: Physico-mathematical Meaning of "primary" and "secondary" Oceans Conception

NASA Astrophysics Data System (ADS)

Kochemasov, G.

Geologists term the Pacific ocean "primary" and Atlantic and Indian oceans "sec- ondary" meaning that the first is larger, deeper, older (?) and plays more fundamental role in the Earth's tectonics. The wave planetology as hierarchically higher than geol- ogy (Earth is only one of planets and of many celestial bodies), states that all celestial bodies are dichotomic ( "Pacific" as a tectonic feature is found in any celestial body) and sectoral (i.g., the Arctic-Antarctic symptom is also in any body) (Theorems 1, 2 [1]). The tectonic dichotomy and sectoring are related to the first and second harmon- ica (wave1 and wave2) of warping standing waves appearing in any body just because they move in non-circular (elliptic, parabolic) orbits and hence inertia forces tend to distort original shapes. This disfiguring of a rotating body is not just a superficial fea- ture, it involves fundamental changes in the entire vertical section above and below surface rises and falls (Theorem 4 [1]). Here acts the law of angular momentum equi- libration. Thus, under the Pacific basin hollow -the deepest hollow produced by wave1 - mantle is denser than under the Atlantic and Indian oceanic basins - basins produced by wave2. We know it because squeezed out of mantle tholeiites in the mid-oceanic ridges are Fe-richer in Pacific than in other oceans. The "primary" ocean is thus a fundamental or "wave1" or 2pR-structure. The "secondary" oceans are "wave2" or pR-structures. pR-structures represented by continents, secondary oceans and basins and the "superswell" (Darwin rise) in the Pacific, i.e. by most important terrestrial lithospheric tectonic blocks, are distributed on the Earth's surface not randomly. As must be expected of the standing wave interference picture, the pR-structure pattern shows regular grouping around certain centres. There are 6 centres - vertices of an oc- tahedron occurring at equator (1, 2), tropics (3, 4) and polar circles (5, 6). They are: 1. New Guinea, 2. Equatorial Atlantic, 3. Easter Isl., 4. the Pamirs-Hindukush, 5. Bering Strait, 6. Bouvet Isl. There is expected antipodality between 1-2, 3-4, 5-6. The vertices of the structural octahedron combine around them sectors by a similar algorithm: there always converge two opposite differently uplifted sectors separated by two differently 1 subsided sectors. I.g., around the Pamirs-Hindukush there are two uplifted sectors: African (++) Asian (+), and two separating them subsided ones: Eurasian (-) Indo- ceanic (- -). The cosmically oriented structural octahedron and other regularities show that the wave induced structurization is a real predominant factor in planetology. Ref. [1] Kochemasov G.G.(1999) Geophys.Res.Abstr., v.1, 3, 700. 2

Prehistory of Zodiac Dating: Three Strata of Upper Paleolithic Constellations

NASA Astrophysics Data System (ADS)

Gurshtein, Alex A.

A pattern of archaic proto-constellations is extracted from Aratus' "The Phaenomena" didactic poem list according to a size criterion elaborated earlier, and their symbolism is analyzed. As a result of this approach three celestial symbolical strata are discovered to be probably a reflection of the symbols for the Lower, the Middle and the Upper Worlds; the Under-World creatures have a water character, the Middle World ones are mostly anthropomorphic and flying beings are for the Upper World. The strata excerpted from Aratus' sky seems to be in agreement with the well-known Babylonian division into three god pathways for Ea (Enki), Anu and Enlil. There is a possibility of dating the pattern discovered because of precession's strong influence as far back as 16 thousand years, the result being supported by the comparison of different star group mean sizes. The archaic constellation pattern under consideration is a reasonable background of symbolical meanings for the first Zodiacal generation quartet (7.5 thousand years old) examined by the author previously. The enormous size of the Argo constellation (Ship of Argo and his Argonauts) as well as the large sizes of other southern constellations are explained as due to the existence of an accumulation zone near the South celestial pole. Some extra correlations between the reconstruction proposed and cultural data available are discussed. The paper is the second part of the investigation "On the Origin of the Zodiacal constellations" published in Vistas in Astronomy, vol.36, pp.171-190, 1993.

Design of a device for sky light polarization measurements.

PubMed

Wang, Yujie; Hu, Xiaoping; Lian, Junxiang; Zhang, Lilian; Xian, Zhiwen; Ma, Tao

2014-08-14

Sky polarization patterns can be used both as indicators of atmospheric turbidity and as a sun compass for navigation. The objective of this study is to improve the precision of sky light polarization measurements by optimal design of the device used. The central part of the system is composed of a Charge Coupled Device (CCD) camera; a fish-eye lens and a linear polarizer. Algorithms for estimating parameters of the polarized light based on three images are derived and the optimal alignments of the polarizer are analyzed. The least-squares estimation is introduced for sky light polarization pattern measurement. The polarization patterns of sky light are obtained using the designed system and they follow almost the same patterns of the single-scattering Rayleigh model. Deviations of polarization angles between observation and the theory are analyzed. The largest deviations occur near the sun and anti-sun directions. Ninety percent of the deviations are less than 5° and 40% percent of them are less than 1°. The deviations decrease evidently as the degree of polarization increases. It also shows that the polarization pattern of the cloudy sky is almost identical as in the blue sky.

Design of a Device for Sky Light Polarization Measurements

PubMed Central

Wang, Yujie; Hu, Xiaoping; Lian, Junxiang; Zhang, Lilian; Xian, Zhiwen; Ma, Tao

2014-01-01

Sky polarization patterns can be used both as indicators of atmospheric turbidity and as a sun compass for navigation. The objective of this study is to improve the precision of sky light polarization measurements by optimal design of the device used. The central part of the system is composed of a Charge Coupled Device (CCD) camera; a fish-eye lens and a linear polarizer. Algorithms for estimating parameters of the polarized light based on three images are derived and the optimal alignments of the polarizer are analyzed. The least-squares estimation is introduced for sky light polarization pattern measurement. The polarization patterns of sky light are obtained using the designed system and they follow almost the same patterns of the single-scattering Rayleigh model. Deviations of polarization angles between observation and the theory are analyzed. The largest deviations occur near the sun and anti-sun directions. Ninety percent of the deviations are less than 5° and 40% percent of them are less than 1°. The deviations decrease evidently as the degree of polarization increases. It also shows that the polarization pattern of the cloudy sky is almost identical as in the blue sky. PMID:25196003

Accuracy of sun localization in the second step of sky-polarimetric Viking navigation for north determination: a planetarium experiment.

PubMed

Farkas, Alexandra; Száz, Dénes; Egri, Ádám; Blahó, Miklós; Barta, András; Nehéz, Dóra; Bernáth, Balázs; Horváth, Gábor

2014-07-01

It is a widely discussed hypothesis that Viking seafarers might have been able to locate the position of the occluded sun by means of dichroic or birefringent crystals, the mysterious sunstones, with which they could analyze skylight polarization. Although the atmospheric optical prerequisites and certain aspects of the efficiency of this sky-polarimetric Viking navigation have been investigated, the accuracy of the main steps of this method has not been quantitatively examined. To fill in this gap, we present here the results of a planetarium experiment in which we measured the azimuth and elevation errors of localization of the invisible sun. In the planetarium sun localization was performed in two selected celestial points on the basis of the alignments of two small sections of two celestial great circles passing through the sun. In the second step of sky-polarimetric Viking navigation the navigator needed to determine the intersection of two such celestial circles. We found that the position of the sun (solar elevation θ(S), solar azimuth φ(S)) was estimated with an average error of +0.6°≤Δθ≤+8.8° and -3.9°≤Δφ≤+2.0°. We also calculated the compass direction error when the estimated sun position is used for orienting with a Viking sun-compass. The northern direction (ω(North)) was determined with an error of -3.34°≤Δω(North)≤+6.29°. The inaccuracy of the second step of this navigation method was high (Δω(North)=-16.3°) when the solar elevation was 5°≤θ(S)≤25°, and the two selected celestial points were far from the sun (at angular distances 95°≤γ(1), γ(2)≤115°) and each other (125°≤δ≤145°). Considering only this second step, the sky-polarimetric navigation could be more accurate in the mid-summer period (June and July), when in the daytime the sun is high above the horizon for long periods. In the spring (and autumn) equinoctial period, alternative methods (using a twilight board, for example) might be more appropriate. Since Viking navigators surely also committed further errors in the first and third steps, the orientation errors presented here underestimate the net error of the whole sky-polarimetric navigation.

Frontiers in Relativistic Celestial Mechanics, Vol. 2, Applications and Experiments

NASA Astrophysics Data System (ADS)

Kopeikin, Sergei

2014-08-01

Relativistic celestial mechanics - investigating the motion celestial bodies under the influence of general relativity - is a major tool of modern experimental gravitational physics. With a wide range of prominent authors from the field, this two-volume series consists of reviews on a multitude of advanced topics in the area of relativistic celestial mechanics - starting from more classical topics such as the regime of asymptotically-flat spacetime, light propagation and celestial ephemerides, but also including its role in cosmology and alternative theories of gravity as well as modern experiments in this area. This second volume of a two-volume series covers applications of the theory as well as experimental verifications. From tools to determine light travel times in curved space-time to laser ranging between earth and moon and between satellites, and impacts on the definition of time scales and clock comparison techniques, a variety of effects is discussed. On the occasion of his 80-th birthday, these two volumes honor V. A. Brumberg - one of the pioneers in modern relativistic celestial mechanics. Contributions include: J. Simon, A. Fienga: Victor Brumberg and the French school of analytical celestial mechanics T. Fukushima: Elliptic functions and elliptic integrals for celestial mechanics and dynamical astronomy P. Teyssandier: New tools for determining the light travel time in static, spherically symmetric spacetimes beyond the order G2 J. Müller, L. Biskupek, F. Hofmann and E. Mai: Lunar laser ranging and relativity N. Wex: Testing relativistic celestial mechanics with radio pulsars I. Ciufolini et al.: Dragging of inertial frames, fundamental physics, and satellite laser ranging G. Petit, P. Wolf, P. Delva: Atomic time, clocks, and clock comparisons in relativistic spacetime: a review

Imaging polarimetry of forest canopies: how the azimuth direction of the sun, occluded by vegetation, can be assessed from the polarization pattern of the sunlit foliage

NASA Astrophysics Data System (ADS)

Hegedüs, Ramón; Barta, András; Bernáth, Balázs; Benno Meyer-Rochow, Victor; Horváth, Gábor

2007-08-01

Radiance, color, and polarization of the light in forests combine to create complex optical patterns. Earlier sporadic polarimetric studies in forests were limited by the narrow fields of view of the polarimeters used in such studies. Since polarization patterns in the entire upper hemisphere of the visual environment of forests could be important for forest-inhabiting animals that make use of linearly polarized light for orientation, we measured 180° field-of-view polarization distributions in Finnish forests. From a hot air balloon we also measured the polarization patterns of Hungarian grasslands lit by the rising sun. We found that the pattern of the angle of polarization α of sunlit grasslands and sunlit tree canopies was qualitatively the same as that of the sky. We show here that contrary to an earlier assumption, the α-pattern characteristic of the sky always remains visible underneath overhead vegetation, independently of the solar elevation and the sky conditions (clear or partly cloudy with visible sun's disc), provided the foliage is sunlit and not only when large patches of the clear sky are visible through the vegetation. Since the mirror symmetry axis of the α-pattern of the sunlit foliage is the solar-antisolar meridian, the azimuth direction of the sun, occluded by vegetation, can be assessed in forests from this polarization pattern. Possible consequences of this robust polarization feature of the optical environment in forests are briefly discussed with regard to polarization-based animal navigation.

Research on the error model of airborne celestial/inertial integrated navigation system

NASA Astrophysics Data System (ADS)

Zheng, Xiaoqiang; Deng, Xiaoguo; Yang, Xiaoxu; Dong, Qiang

2015-02-01

Celestial navigation subsystem of airborne celestial/inertial integrated navigation system periodically correct the positioning error and heading drift of the inertial navigation system, by which the inertial navigation system can greatly improve the accuracy of long-endurance navigation. Thus the navigation accuracy of airborne celestial navigation subsystem directly decides the accuracy of the integrated navigation system if it works for long time. By building the mathematical model of the airborne celestial navigation system based on the inertial navigation system, using the method of linear coordinate transformation, we establish the error transfer equation for the positioning algorithm of airborne celestial system. Based on these we built the positioning error model of the celestial navigation. And then, based on the positioning error model we analyze and simulate the positioning error which are caused by the error of the star tracking platform with the MATLAB software. Finally, the positioning error model is verified by the information of the star obtained from the optical measurement device in range and the device whose location are known. The analysis and simulation results show that the level accuracy and north accuracy of tracking platform are important factors that limit airborne celestial navigation systems to improve the positioning accuracy, and the positioning error have an approximate linear relationship with the level error and north error of tracking platform. The error of the verification results are in 1000m, which shows that the model is correct.

Snapping shrimp sound production patterns on Caribbean coral reefs: relationships with celestial cycles and environmental variables

NASA Astrophysics Data System (ADS)

Lillis, Ashlee; Mooney, T. Aran

2018-06-01

The rich acoustic environment of coral reefs, including the sounds of a variety of fish and invertebrates, is a reflection of the structural complexity and biological diversity of these habitats. Emerging interest in applying passive acoustic monitoring and soundscape analysis to measure coral reef habitat characteristics and track ecological patterns is hindered by a poor understanding of the most common and abundant sound producers on reefs—the snapping shrimp. Here, we sought to address several basic biophysical drivers of reef sound by investigating acoustic activity patterns of snapping shrimp populations on two adjacent coral reefs using a detailed snap detection analysis routine to a high-resolution 2.5-month acoustic dataset from the US Virgin Islands. The reefs exhibited strong diel and lunar periodicity in snap rates and clear spatial differences in snapping levels. Snap rates peaked at dawn and dusk and were higher overall during daytime versus nighttime, a seldom-reported pattern in earlier descriptions of diel snapping shrimp acoustic activity. Small differences between the sites in snap rate rhythms were detected and illustrate how analyses of specific soundscape elements might reveal subtle between-reef variation. Snap rates were highly correlated with environmental variables, including water temperature and light, and were found to be sensitive to changes in oceanographic forcing. This study further establishes snapping shrimp as key players in the coral reef chorus and provides evidence that their acoustic output reflects a combination of environmental conditions, celestial influences, and spatial habitat variation. Effective application of passive acoustic monitoring in coral reef habitats using snap rates or snapping-influenced acoustic metrics will require a mechanistic understanding of the underlying spatial and temporal variation in snapping shrimp sound production across multiple scales.

Autonomous celestial navigation based on Earth ultraviolet radiance and fast gradient statistic feature extraction

NASA Astrophysics Data System (ADS)

Lu, Shan; Zhang, Hanmo

2016-01-01

To meet the requirement of autonomous orbit determination, this paper proposes a fast curve fitting method based on earth ultraviolet features to obtain accurate earth vector direction, in order to achieve the high precision autonomous navigation. Firstly, combining the stable characters of earth ultraviolet radiance and the use of transmission model software of atmospheric radiation, the paper simulates earth ultraviolet radiation model on different time and chooses the proper observation band. Then the fast improved edge extracting method combined Sobel operator and local binary pattern (LBP) is utilized, which can both eliminate noises efficiently and extract earth ultraviolet limb features accurately. And earth's centroid locations on simulated images are estimated via the least square fitting method using part of the limb edges. Taken advantage of the estimated earth vector direction and earth distance, Extended Kalman Filter (EKF) is applied to realize the autonomous navigation finally. Experiment results indicate the proposed method can achieve a sub-pixel earth centroid location estimation and extremely enhance autonomous celestial navigation precision.

Determination of Galactic Aberration from VLBI Measurements and Its Effect on VLBI Reference Frames and Earth Orientation Parameters.

NASA Astrophysics Data System (ADS)

MacMillan, D. S.

2014-12-01

Galactic aberration is due to the motion of the solar system barycenter around the galactic center. It results in a systematic pattern of apparent proper motion of radio sources observed by VLBI. This effect is not currently included in VLBI analysis. Estimates of the size of this effect indicate that it is important that this secular aberration drift be accounted for in order to maintain an accurate celestial reference frame and allow astrometry at the several microarcsecond level. Future geodetic observing systems are being designed to be capable of producing a future terrestrial reference frame with an accuracy of 1 mm and stability of 0.1 mm/year. We evaluate the effect galactic aberration on attaining these reference frame goals. This presentation will discuss 1) the estimation of galactic aberration from VLBI data and 2) the effect of aberration on the Terrestrial and Celestial Reference Frames and the Earth Orientation Parameters that connect these frames.

Relation between the celestial reference system and the terrestrial reference system of a rigid earth

NASA Astrophysics Data System (ADS)

Aoki, Shinko

The equations of motion for a rigid earth under the influence of the sun and moon are solved analytically up to the second-order perturbation, and the results are used to elucidate the relationship between the celestial and terrestrial reference systems. The derivations are given in detail, and consideration is given to celestial-ephemeris and instantaneous-rotation poles, wobble, the departure point as the origin of the local inertial system, the precession-nutation matrix, and techniques for improving the celestial reference system.

Combining sky and earth: desert ants (Melophorus bagoti) show weighted integration of celestial and terrestrial cues.

PubMed

Legge, Eric L G; Wystrach, Antoine; Spetch, Marcia L; Cheng, Ken

2014-12-01

Insects typically use celestial sources of directional information for path integration, and terrestrial panoramic information for view-based navigation. Here we set celestial and terrestrial sources of directional information in conflict for homing desert ants (Melophorus bagoti). In the first experiment, ants learned to navigate out of a round experimental arena with a distinctive artificial panorama. On crucial tests, we rotated the arena to create a conflict between the artificial panorama and celestial information. In a second experiment, ants at a feeder in their natural visually-cluttered habitat were displaced prior to their homing journey so that the dictates of path integration (feeder to nest direction) based on a celestial compass conflicted with the dictates of view-based navigation (release point to nest direction) based on the natural terrestrial panorama. In both experiments, ants generally headed in a direction intermediate to the dictates of celestial and terrestrial information. In the second experiment, the ants put more weight on the terrestrial cues when they provided better directional information. We conclude that desert ants weight and integrate the dictates of celestial and terrestrial information in determining their initial heading, even when the two directional cues are highly discrepant. © 2014. Published by The Company of Biologists Ltd.

Celestial Pattern Recognition Allowing Autonomous Earth-Surface or Deep-Space Positioning.

DTIC Science & Technology

1983-12-01

viii :% -7 .2 I. INTRODUCTION AND BACKGROUND Background of the Project This research project is conceptual and opportunistic. It is conceptual in that...alternative approaches and the usefulness of a device in different navigation regimes. Both the research and this report have tried to follow these...Packard, Potter, and Viglione (Ref 2; 7; 15; 17; 23) have published papers (most of these 20 years ago) suggesting that some form of star

Monstar polarization singularities with elliptically-symmetric q-plates.

PubMed

Cvarch, Ben A; Khajavi, Behzad; Jones, Joshua A; Piccirillo, Bruno; Marrucci, Lorenzo; Galvez, Enrique J

2017-06-26

Space-variant polarization patterns present in the transverse mode of optical beams highlight disclination patterns of polarization about a singularity, often a C-point. These patterns are important for understanding rotational dislocations and for characterizing complex polarization patterns. Liquid-crystal devices known as q-plates have been used to produce two of the three types of disclination patterns in optical beams: lemons and stars. Here we report the production of the third type of disclination, which is asymmetric, known as the monstar. We do so with elliptically-symmetric q-plates. We present theory and measurements, and find excellent agreement between the two.

[Galaxy/quasar classification based on nearest neighbor method].

PubMed

Li, Xiang-Ru; Lu, Yu; Zhou, Jian-Ming; Wang, Yong-Jun

2011-09-01

With the wide application of high-quality CCD in celestial spectrum imagery and the implementation of many large sky survey programs (e. g., Sloan Digital Sky Survey (SDSS), Two-degree-Field Galaxy Redshift Survey (2dF), Spectroscopic Survey Telescope (SST), Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) program and Large Synoptic Survey Telescope (LSST) program, etc.), celestial observational data are coming into the world like torrential rain. Therefore, to utilize them effectively and fully, research on automated processing methods for celestial data is imperative. In the present work, we investigated how to recognizing galaxies and quasars from spectra based on nearest neighbor method. Galaxies and quasars are extragalactic objects, they are far away from earth, and their spectra are usually contaminated by various noise. Therefore, it is a typical problem to recognize these two types of spectra in automatic spectra classification. Furthermore, the utilized method, nearest neighbor, is one of the most typical, classic, mature algorithms in pattern recognition and data mining, and often is used as a benchmark in developing novel algorithm. For applicability in practice, it is shown that the recognition ratio of nearest neighbor method (NN) is comparable to the best results reported in the literature based on more complicated methods, and the superiority of NN is that this method does not need to be trained, which is useful in incremental learning and parallel computation in mass spectral data processing. In conclusion, the results in this work are helpful for studying galaxies and quasars spectra classification.

Psychophysical study of the visual sun location in pictures of cloudy and twilight skies inspired by Viking navigation.

PubMed

Barta, András; Horváth, Gábor; Meyer-Rochow, Victor Benno

2005-06-01

In the late 1960s it was hypothesized that Vikings had been able to navigate the open seas, even when the sun was occluded by clouds or below the sea horizon, by using the angle of polarization of skylight. To detect the direction of skylight polarization, they were thought to have made use of birefringent crystals, called "sun-stones," and a large part of the scientific community still firmly believe that Vikings were capable of polarimetric navigation. However, there are some critics who treat the usefulness of skylight polarization for orientation under partly cloudy or twilight conditions with extreme skepticism. One of their counterarguments has been the assumption that solar positions or solar azimuth directions could be estimated quite accurately by the naked eye, even if the sun was behind clouds or below the sea horizon. Thus under partly cloudy or twilight conditions there might have been no serious need for a polarimetric method to determine the position of the sun. The aim of our study was to test quantitatively the validity of this qualitative counterargument. In our psychophysical laboratory experiments, test subjects were confronted with numerous 180 degrees field-of-view color photographs of partly cloudy skies with the sun occluded by clouds or of twilight skies with the sun below the horizon. The task of the subjects was to guess the position or the azimuth direction of the invisible sun with the naked eye. We calculated means and standard deviations of the estimated solar positions and azimuth angles to characterize the accuracy of the visual sun location. Our data do not support the common belief that the invisible sun can be located quite accurately from the celestial brightness and/or color patterns under cloudy or twilight conditions. Although our results underestimate the accuracy of visual sun location by experienced Viking navigators, the mentioned counterargument cannot be taken seriously as a valid criticism of the theory of the alleged polarimetric Viking navigation. Our results, however, do not bear on the polarimetric theory itself.

Psychophysical study of the visual sun location in pictures of cloudy and twilight skies inspired by Viking navigation

NASA Astrophysics Data System (ADS)

Barta, András; Horváth, Gábor; Benno Meyer-Rochow, Victor

2005-06-01

In the late 1960s it was hypothesized that Vikings had been able to navigate the open seas, even when the sun was occluded by clouds or below the sea horizon, by using the angle of polarization of skylight. To detect the direction of skylight polarization, they were thought to have made use of birefringent crystals, called "sunstones," and a large part of the scientific community still firmly believe that Vikings were capable of polarimetric navigation. However, there are some critics who treat the usefulness of skylight polarization for orientation under partly cloudy or twilight conditions with extreme skepticism. One of their counterarguments has been the assumption that solar positions or solar azimuth directions could be estimated quite accurately by the naked eye, even if the sun was behind clouds or below the sea horizon. Thus under partly cloudy or twilight conditions there might have been no serious need for a polarimetric method to determine the position of the sun. The aim of our study was to test quantitatively the validity of this qualitative counterargument. In our psychophysical laboratory experiments, test subjects were confronted with numerous 180° field-of-view color photographs of partly cloudy skies with the sun occluded by clouds or of twilight skies with the sun below the horizon. The task of the subjects was to guess the position or the azimuth direction of the invisible sun with the naked eye. We calculated means and standard deviations of the estimated solar positions and azimuth angles to characterize the accuracy of the visual sun location. Our data do not support the common belief that the invisible sun can be located quite accurately from the celestial brightness and/or color patterns under cloudy or twilight conditions. Although our results underestimate the accuracy of visual sun location by experienced Viking navigators, the mentioned counterargument cannot be taken seriously as a valid criticism of the theory of the alleged polarimetric Viking navigation. Our results, however, do not bear on the polarimetric theory itself.

The research of the coupled orbital-attitude controlled motion of celestial body in the neighborhood of the collinear libration point L1

NASA Astrophysics Data System (ADS)

Shmyrov, A.; Shmyrov, V.; Shymanchuk, D.

2017-10-01

This article considers the motion of a celestial body within the restricted three-body problem of the Sun-Earth system. The equations of controlled coupled attitude-orbit motion in the neighborhood of collinear libration point L1 are investigated. The translational orbital motion of a celestial body is described using Hill's equations of circular restricted three-body problem of the Sun-Earth system. Rotational orbital motion is described using Euler's dynamic equations and quaternion kinematic equation. We investigate the problem of stability of celestial body rotational orbital motion in relative equilibrium positions and stabilization of celestial body rotational orbital motion with proposed control laws in the neighborhood of collinear libration point L1. To study stabilization problem, Lyapunov function is constructed in the form of the sum of the kinetic energy and special "kinematic function" of the Rodriguez-Hamiltonian parameters. Numerical modeling of the controlled rotational motion of a celestial body at libration point L1 is carried out. The numerical characteristics of the control parameters and rotational motion are given.

Imaging skeletal muscle with linearly polarized light

NASA Astrophysics Data System (ADS)

Li, X.; Ranasinghesagara, J.; Yao, G.

2008-04-01

We developed a polarization sensitive imaging system that can acquire reflectance images in turbid samples using incident light of different polarization states. Using this system, we studied polarization imaging on bovine sternomandibularis muscle strips using light of two orthogonal linearly polarized states. We found the obtained polarization sensitive reflectance images had interesting patterns depending on the polarization states. In addition, we computed four elements of the Mueller matrix from the acquired images. As a comparison, we also obtained polarization images of a 20% Intralipid"R" solution and compared the results with those from muscle samples. We found that the polarization imaging patterns from Intralipid solution can be described with a model based on single-scattering approximation. However, the polarization images in muscle had distinct patterns and can not be explained by this simple model. These results implied that the unique structural properties of skeletal muscle play important roles in modulating the propagation of polarized light.

Celestial bodies macroscopic movement is due to the radiation

NASA Astrophysics Data System (ADS)

Yongquan, Han

2016-03-01

The star is radiate, also as the planet. In fact, all the real objects are radiate, but the strength of the radiation is different. Radiation will reduce the quality of the object, but time is not long enough to reduce the mass of the subject, so it is difficult for us to observe. Due to the large object lifecycle, to study the changing rule of the object, we must consider the radiation on the quality of the celestial bodies, and the outer space radiate particles' motion, also consider objects interact with objects of radiation. The reason Celestial bodies moves is that the radiation of those Celestial bodies Interact with each other, Celestial bodies macroscopic movement is due to the radiation. The earth's rotation and revolution is a measure of the survive ability. Author: hanyongquan TEL: 15611860790

Modelling of celestial backgrounds

NASA Astrophysics Data System (ADS)

Hickman, Duncan L.; Smith, Moira I.; Lim, Jae-Wan; Jeon, Yun-Ho

2018-05-01

For applications where a sensor's image includes the celestial background, stars and Solar System Bodies compromise the ability of the sensor system to correctly classify a target. Such false targets are particularly significant for the detection of weak target signatures which only have a small relative angular motion. The detection of celestial features is well established in the visible spectral band. However, given the increasing sensitivity and low noise afforded by emergent infrared focal plane array technology together with larger and more efficient optics, the signatures of celestial features can also impact performance at infrared wavelengths. A methodology has been developed which allows the rapid generation of celestial signatures in any required spectral band using star data from star catalogues and other open-source information. Within this paper, the radiometric calculations are presented to determine the irradiance values of stars and planets in any spectral band.

Space-variant polarization patterns of non-collinear Poincaré superpositions

NASA Astrophysics Data System (ADS)

Galvez, E. J.; Beach, K.; Zeosky, J. J.; Khajavi, B.

2015-03-01

We present analysis and measurements of the polarization patterns produced by non-collinear superpositions of Laguerre-Gauss spatial modes in orthogonal polarization states, which are known as Poincaré modes. Our findings agree with predictions (I. Freund Opt. Lett. 35, 148-150 (2010)), that superpositions containing a C-point lead to a rotation of the polarization ellipse in 3-dimensions. Here we do imaging polarimetry of superpositions of first- and zero-order spatial modes at relative beam angles of 0-4 arcmin. We find Poincaré-type polarization patterns showing fringes in polarization orientation, but which preserve the polarization-singularity index for all three cases of C-points: lemons, stars and monstars.

Parallels between Global Transcriptional Programs of Polarizing Caco-2 Intestinal Epithelial Cells In Vitro and Gene Expression Programs in Normal Colon and Colon Cancer

PubMed Central

Sääf, Annika M.; Halbleib, Jennifer M.; Chen, Xin; Yuen, Siu Tsan; Leung, Suet Yi

2007-01-01

Posttranslational mechanisms are implicated in the development of epithelial cell polarity, but little is known about the patterns of gene expression and transcriptional regulation during this process. We characterized temporal patterns of gene expression during cell–cell adhesion-initiated polarization of cultured human Caco-2 cells, which develop structural and functional polarity resembling enterocytes in vivo. A distinctive switch in gene expression patterns occurred upon formation of cell–cell contacts. Comparison to gene expression patterns in normal human colon and colon tumors revealed that the pattern in proliferating, nonpolarized Caco-2 cells paralleled patterns seen in human colon cancer in vivo, including expression of genes involved in cell proliferation. The pattern switched in polarized Caco-2 cells to one more closely resembling that in normal colon tissue, indicating that regulation of transcription underlying Caco-2 cell polarization is similar to that during enterocyte differentiation in vivo. Surprisingly, the temporal program of gene expression in polarizing Caco-2 cells involved changes in signaling pathways (e.g., Wnt, Hh, BMP, FGF) in patterns similar to those during migration and differentiation of intestinal epithelial cells in vivo, despite the absence of morphogen gradients and interactions with stromal cells characteristic of enterocyte differentiation in situ. The full data set is available at http://microarray-pubs.stanford.edu/CACO2. PMID:17699589

Spatial water maze learning using celestial cues by the meadow vole, Microtus pennsylvanicus.

PubMed

Kavaliers, M; Galea, L A

1994-03-31

The Morris water maze is widely used to evaluate to evaluate the spatial learning ability of rodents under laboratory settings. The present study demonstrates that reproductive male meadow voles, Microtus pennsylvanicus, are able to acquire and retain a spatial water maze task using celestial cues. Voles were able to acquire a modified outdoor Morris water maze task over 4 trials per day, whereby they had to learn and remember the location of a submerged hidden platform, using the position of the sun and associated celestial cues. Their proficiency on this task was related to the availability of the celestial cues, with voles displaying significantly poorer spatial navigation on overcast than clear days and when the testing time (and position of the sun and associated celestial cues) was shifted from morning to afternoon. These findings with meadow voles support the ecological relevance of the water maze task.

Design of all-weather celestial navigation system

NASA Astrophysics Data System (ADS)

Sun, Hongchi; Mu, Rongjun; Du, Huajun; Wu, Peng

2018-03-01

In order to realize autonomous navigation in the atmosphere, an all-weather celestial navigation system is designed. The research of celestial navigation system include discrimination method of comentropy and the adaptive navigation algorithm based on the P value. The discrimination method of comentropy is studied to realize the independent switching of two celestial navigation modes, starlight and radio. Finally, an adaptive filtering algorithm based on P value is proposed, which can greatly improve the disturbance rejection capability of the system. The experimental results show that the accuracy of the three axis attitude is better than 10″, and it can work all weather. In perturbation environment, the position accuracy of the integrated navigation system can be increased 20% comparing with the traditional method. It basically meets the requirements of the all-weather celestial navigation system, and it has the ability of stability, reliability, high accuracy and strong anti-interference.

The ontogenetic development of orientation capabilities

NASA Technical Reports Server (NTRS)

Emlen, S. T.

1972-01-01

The effects of celestial references on the navigation ability of birds are discussed. Tests were conducted in a planetarium with indigo buntings to determine the amount of stellar pattern which could be removed before disorientation occurred. It was determined that young birds have a predisposition to respond to the apparent rotational motion of the night sky. It was concluded that the peak in responsiveness to rotational information is presented during the first summer of life, prior to the first migration season.

Arabidopsis AIP1-2 restricted by WER-mediated patterning modulates planar polarity

PubMed Central

Kiefer, Christian S.; Claes, Andrea R.; Nzayisenga, Jean-Claude; Pietra, Stefano; Stanislas, Thomas; Hüser, Anke; Ikeda, Yoshihisa; Grebe, Markus

2015-01-01

The coordination of cell polarity within the plane of the tissue layer (planar polarity) is crucial for the development of diverse multicellular organisms. Small Rac/Rho-family GTPases and the actin cytoskeleton contribute to planar polarity formation at sites of polarity establishment in animals and plants. Yet, upstream pathways coordinating planar polarity differ strikingly between kingdoms. In the root of Arabidopsis thaliana, a concentration gradient of the phytohormone auxin coordinates polar recruitment of Rho-of-plant (ROP) to sites of polar epidermal hair initiation. However, little is known about cytoskeletal components and interactions that contribute to this planar polarity or about their relation to the patterning machinery. Here, we show that ACTIN7 (ACT7) represents a main actin isoform required for planar polarity of root hair positioning, interacting with the negative modulator ACTIN-INTERACTING PROTEIN1-2 (AIP1-2). ACT7, AIP1-2 and their genetic interaction are required for coordinated planar polarity of ROP downstream of ethylene signalling. Strikingly, AIP1-2 displays hair cell file-enriched expression, restricted by WEREWOLF (WER)-dependent patterning and modified by ethylene and auxin action. Hence, our findings reveal AIP1-2, expressed under control of the WER-dependent patterning machinery and the ethylene signalling pathway, as a modulator of actin-mediated planar polarity. PMID:25428588

Moving in Dim Light: Behavioral and Visual Adaptations in Nocturnal Ants.

PubMed

Narendra, Ajay; Kamhi, J Frances; Ogawa, Yuri

2017-11-01

Visual navigation is a benchmark information processing task that can be used to identify the consequence of being active in dim-light environments. Visual navigational information that animals use during the day includes celestial cues such as the sun or the pattern of polarized skylight and terrestrial cues such as the entire panorama, canopy pattern, or significant salient features in the landscape. At night, some of these navigational cues are either unavailable or are significantly dimmer or less conspicuous than during the day. Even under these circumstances, animals navigate between locations of importance. Ants are a tractable system for studying navigation during day and night because the fine scale movement of individual animals can be recorded in high spatial and temporal detail. Ant species range from being strictly diurnal, crepuscular, and nocturnal. In addition, a number of species have the ability to change from a day- to a night-active lifestyle owing to environmental demands. Ants also offer an opportunity to identify the evolution of sensory structures for discrete temporal niches not only between species but also within a single species. Their unique caste system with an exclusive pedestrian mode of locomotion in workers and an exclusive life on the wing in males allows us to disentangle sensory adaptations that cater for different lifestyles. In this article, we review the visual navigational abilities of nocturnal ants and identify the optical and physiological adaptations they have evolved for being efficient visual navigators in dim-light. © The Author 2017. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.

Principles of Celestial Navigation: An Online Resource for Introducing Practical Astronomy to the Public

NASA Astrophysics Data System (ADS)

Urban, Sean E.

2015-08-01

Astronomy is often called a "gateway" science because it inspires appreciation and awe among children and non-scientists. Applied astronomy, with practical, real-world applications, can entice even the most utilitarian people to take notice and learn about the subject. Traditional celestial navigation is an astronomy topic that captures the attention of the public. The U.S. Naval Observatory has led the development of a publicly available online celestial navigation educational module titled, "Principles of Celestial Navigation". It can be used world-wide to introduce people to astronomy. This poster describes some of the aspects of this teaching module.

Celestial Object Imaging Model and Parameter Optimization for an Optical Navigation Sensor Based on the Well Capacity Adjusting Scheme.

PubMed

Wang, Hao; Jiang, Jie; Zhang, Guangjun

2017-04-21

The simultaneous extraction of optical navigation measurements from a target celestial body and star images is essential for autonomous optical navigation. Generally, a single optical navigation sensor cannot simultaneously image the target celestial body and stars well-exposed because their irradiance difference is generally large. Multi-sensor integration or complex image processing algorithms are commonly utilized to solve the said problem. This study analyzes and demonstrates the feasibility of simultaneously imaging the target celestial body and stars well-exposed within a single exposure through a single field of view (FOV) optical navigation sensor using the well capacity adjusting (WCA) scheme. First, the irradiance characteristics of the celestial body are analyzed. Then, the celestial body edge model and star spot imaging model are established when the WCA scheme is applied. Furthermore, the effect of exposure parameters on the accuracy of star centroiding and edge extraction is analyzed using the proposed model. Optimal exposure parameters are also derived by conducting Monte Carlo simulation to obtain the best performance of the navigation sensor. Finally, laboratorial and night sky experiments are performed to validate the correctness of the proposed model and optimal exposure parameters.

Celestial Object Imaging Model and Parameter Optimization for an Optical Navigation Sensor Based on the Well Capacity Adjusting Scheme

PubMed Central

Wang, Hao; Jiang, Jie; Zhang, Guangjun

2017-01-01

The simultaneous extraction of optical navigation measurements from a target celestial body and star images is essential for autonomous optical navigation. Generally, a single optical navigation sensor cannot simultaneously image the target celestial body and stars well-exposed because their irradiance difference is generally large. Multi-sensor integration or complex image processing algorithms are commonly utilized to solve the said problem. This study analyzes and demonstrates the feasibility of simultaneously imaging the target celestial body and stars well-exposed within a single exposure through a single field of view (FOV) optical navigation sensor using the well capacity adjusting (WCA) scheme. First, the irradiance characteristics of the celestial body are analyzed. Then, the celestial body edge model and star spot imaging model are established when the WCA scheme is applied. Furthermore, the effect of exposure parameters on the accuracy of star centroiding and edge extraction is analyzed using the proposed model. Optimal exposure parameters are also derived by conducting Monte Carlo simulation to obtain the best performance of the navigation sensor. Finally, laboratorial and night sky experiments are performed to validate the correctness of the proposed model and optimal exposure parameters. PMID:28430132

The Celestial Basis of Civilization

NASA Astrophysics Data System (ADS)

Masse, W. B.

Scholars have long puzzled over the reasons for the ubiquity of celestial images in the residue of the world's earliest civilizations: in art, myth, religious cosmology, iconography, cosmogony, eschatological beliefs, and as portents for the conduct of royal and chiefly power. The general consensus is that these images represented a need by early societies to use the fixed celestial heavens in order to regulate ritual and agricultural cycles, and to satisfy a psychological need by people to relate themselves to their surrounding Universe. Such explanations are facile and miss an important aspect of the celestial heavens. The fixed celestial heavens served as the back-drop for a large number of often spectacular temporary naked-eye visible celestial events which animated the night and sometimes the daytime sky, and which created an 'otherworld' for virtually all cultural groups. In this paper I present a model derived from the detailed analysis of Hawaiian oral traditions and culture history in relation to historic astronomical records of temporary celestial events, and then apply this model to cultural traditions from Mesoamerica and other geographic regions in order to demonstrate that novae, supernovae, variable stars, comets, great meteor showers, aurorae, solar and lunar eclipses, and impacting Solar System debris, together played a critical role in the artistic, intellectual, and political development of early civilizations. These data not only provide important insights into the development of civilization, but also provide important details and longitudinal records of astronomical events and phenomena which are otherwise not readily available for scientific scrutiny.

Simultaneous calibrations of Voyager celestial and inertial attitude control systems in flight

NASA Technical Reports Server (NTRS)

Jahanshahi, M. H.

1982-01-01

A mathematical description of the data reduction technique used to simultaneously calibrate the Voyager celestial and inertial attitude control subsystems is given. It is shown that knowledge of the spacecraft limit cycle motion, as measured by the celestial and the inertial sensors, is adequate to result in the estimates of a selected number of errors which adversely affect the spacecraft attitude knowledge.

Arabidopsis AIP1-2 restricted by WER-mediated patterning modulates planar polarity.

PubMed

Kiefer, Christian S; Claes, Andrea R; Nzayisenga, Jean-Claude; Pietra, Stefano; Stanislas, Thomas; Hüser, Anke; Ikeda, Yoshihisa; Grebe, Markus

2015-01-01

The coordination of cell polarity within the plane of the tissue layer (planar polarity) is crucial for the development of diverse multicellular organisms. Small Rac/Rho-family GTPases and the actin cytoskeleton contribute to planar polarity formation at sites of polarity establishment in animals and plants. Yet, upstream pathways coordinating planar polarity differ strikingly between kingdoms. In the root of Arabidopsis thaliana, a concentration gradient of the phytohormone auxin coordinates polar recruitment of Rho-of-plant (ROP) to sites of polar epidermal hair initiation. However, little is known about cytoskeletal components and interactions that contribute to this planar polarity or about their relation to the patterning machinery. Here, we show that ACTIN7 (ACT7) represents a main actin isoform required for planar polarity of root hair positioning, interacting with the negative modulator ACTIN-INTERACTING PROTEIN1-2 (AIP1-2). ACT7, AIP1-2 and their genetic interaction are required for coordinated planar polarity of ROP downstream of ethylene signalling. Strikingly, AIP1-2 displays hair cell file-enriched expression, restricted by WEREWOLF (WER)-dependent patterning and modified by ethylene and auxin action. Hence, our findings reveal AIP1-2, expressed under control of the WER-dependent patterning machinery and the ethylene signalling pathway, as a modulator of actin-mediated planar polarity. © 2015. Published by The Company of Biologists Ltd.

The polarization patterns of skylight reflected off wave water surface.

PubMed

Zhou, Guanhua; Xu, Wujian; Niu, Chunyue; Zhao, Huijie

2013-12-30

In this paper we propose a model to understand the polarization patterns of skylight when reflected off the surface of waves. The semi-empirical Rayleigh model is used to analyze the polarization of scattered skylight; the Harrison and Coombes model is used to analyze light radiance distribution; and the Cox-Munk model and Mueller matrix are used to analyze reflections from wave surface. First, we calculate the polarization patterns and intensity distribution of light reflected off wave surface. Then we investigate their relationship with incident radiation, solar zenith angle, wind speed and wind direction. Our results show that the polarization patterns of reflected skylight from waves and flat water are different, while skylight reflected on both kinds of water is generally highly polarized at the Brewster angle and the polarization direction is approximately parallel to the water's surface. The backward-reflecting Brewster zone has a relatively low reflectance and a high DOP in all observing directions. This can be used to optimally diminish the reflected skylight and avoid sunglint in ocean optics measurements.

Counter-rotational cell flows drive morphological and cell fate asymmetries in mammalian hair follicles.

PubMed

Cetera, Maureen; Leybova, Liliya; Joyce, Bradley; Devenport, Danelle

2018-05-01

Organ morphogenesis is a complex process coordinated by cell specification, epithelial-mesenchymal interactions and tissue polarity. A striking example is the pattern of regularly spaced, globally aligned mammalian hair follicles, which emerges through epidermal-dermal signaling and planar polarized morphogenesis. Here, using live-imaging, we discover that developing hair follicles polarize through dramatic cell rearrangements organized in a counter-rotational pattern of cell flows. Upon hair placode induction, Shh signaling specifies a radial pattern of progenitor fates that, together with planar cell polarity, induce counter-rotational rearrangements through myosin and ROCK-dependent polarized neighbour exchanges. Importantly, these cell rearrangements also establish cell fate asymmetry by repositioning radial progenitors along the anterior-posterior axis. These movements concurrently displace associated mesenchymal cells, which then signal asymmetrically to maintain polarized cell fates. Our results demonstrate how spatial patterning and tissue polarity generate an unexpected collective cell behaviour that in turn, establishes both morphological and cell fate asymmetry.

Lunar orientation in a beetle.

PubMed

Dacke, Marie; Byrne, Marcus J; Scholtz, Clarke H; Warrant, Eric J

2004-02-22

Many animals use the sun's polarization pattern to orientate, but the dung beetle Scarabaeus zambesianus is the only animal so far known to orientate using the million times dimmer polarization pattern of the moonlit sky. We demonstrate the relative roles of the moon and the nocturnal polarized-light pattern for orientation. We find that artificially changing the position of the moon, or hiding the moon's disc from the beetle's field of view, generally did not influence its orientation performance. We thus conclude that the moon does not serve as the primary cue for orientation. The effective cue is the polarization pattern formed around the moon, which is more reliable for orientation. Polarization sensitivity ratios in two photoreceptors in the dorsal eye were found to be 7.7 and 12.9, similar to values recorded in diurnal navigators. These results agree with earlier results suggesting that the detection and analysis of polarized skylight is similar in diurnal and nocturnal insects.

"Bridging the Gap" through Australian Cultural Astronomy

NASA Astrophysics Data System (ADS)

Hamacher, Duane W.; Norris, Ray P.

2011-01-01

For more than 50,000 years, Indigenous Australians have incorporated celestial events into their oral traditions and used the motions of celestial bodies for navigation, time-keeping, food economics, and social structure. In this paper, we explore the ways in which Aboriginal people made careful observations of the sky, measurements of celestial bodies, and incorporated astronomical events into complex oral traditions by searching for written records of time-keeping using celestial bodies, the use of rising and setting stars as indicators of special events, recorded observations of variable stars, the solar cycle, and lunar phases (including ocean tides and eclipses) in oral tradition, as well as astronomical measurements of the equinox, solstice, and cardinal points.

Polarization of Hazes and Aurorae on Jupiter

NASA Astrophysics Data System (ADS)

Yanamandra-Fisher, Padma A.; McLean, Will; PACA_Jupiter

2017-10-01

Our solar system planets show a large variety of atmospheric polarization properties, from the thick, highly polarizing haze on Titan and the poles of Jupiter, Rayleigh scattering by molecules on Uranus and Neptune, to clouds in the equatorial region of Jupiter or on Venus. Changes in the clouds/thermal filed can be brought about by endogenic dynamical processes such merger of vortices; global, planetary scale upheavals, and external factors such as celestial collisions (such as D/Shoemaker-Levy 9 impact with Jupiter in 1994, etc.). Although the range of phase angles available from Earth for outer planets is restricted to a narrow range, limb polarization measurements provide constraints on the polarimetric properties. For example, at the equator, much of the observed reflected radiation is due to the presence of clouds and therefore, low polarization. Polar asymmetry exists between the two poles, while the planetary disk is unpolarized. Jupiter is known to exhibit a strong polar limb polarization and a low equatorial limb polarization due to the presence of haze particles and Rayleigh scattering at the poles. In contrast, at the equator, the concentration of particulates in the high atmosphere might change, changing the polarimetric signature and aurorae at both poles. The polarimetric maps, in conjunction with thermal maps and albedo maps, can provide constraints on modeling efforts to understand the nature of the aerosols/hazes in Jovian atmosphere. With Jupiter experiencing morphological changes at many latitudes, we have initiated a polarimetric observing campaign of Jupiter, in conjunction with The PACA Project. With NASA/Juno mission in a 53-day orbit around Jupiter, and recent outbreaks in the atmosphere, changes in the polarimetric signature will provide insight to the changes occurring in the atmosphere. Some of our observations are acquired by a team of professional/amateur planetary imagers astronomers based in the U.K., Australia and Europe. France. Details/results of these studies will be presented to optimize the observing strategy of planetary atmospheres and their role in the atmospheric retrievals and the next stage of polarimetric exploration of Jupiter.

Polarization leakage in epoch of reionization windows - III. Wide-field effects of narrow-field arrays

NASA Astrophysics Data System (ADS)

Asad, K. M. B.; Koopmans, L. V. E.; Jelić, V.; de Bruyn, A. G.; Pandey, V. N.; Gehlot, B. K.

2018-05-01

Leakage of polarized Galactic diffuse emission into total intensity can potentially mimic the 21-cm signal coming from the epoch of reionization (EoR), as both of them might have fluctuating spectral structure. Although we are sensitive to the EoR signal only in small fields of view, chromatic side-lobes from further away can contaminate the inner region. Here, we explore the effects of leakage into the `EoR window' of the cylindrically averaged power spectra (PS) within wide fields of view using both observation and simulation of the 3C196 and North Celestial Pole (NCP) fields, two observing fields of the LOFAR-EoR project. We present the polarization PS of two one-night observations of the two fields and find that the NCP field has higher fluctuations along frequency, and consequently exhibits more power at high-k∥ that could potentially leak to Stokes I. Subsequently, we simulate LOFAR observations of Galactic diffuse polarized emission based on a model to assess what fraction of polarized power leaks into Stokes I because of the primary beam. We find that the rms fractional leakage over the instrumental k-space is 0.35 {per cent} in the 3C196 field and 0.27 {per cent} in the NCP field, and it does not change significantly within the diameters of 15°, 9°, and 4°. Based on the observed PS and simulated fractional leakage, we show that a similar level of leakage into Stokes I is expected in the 3C196 and NCP fields, and the leakage can be considered to be a bias in the PS.

Magnetic information affects the stellar orientation of young bird migrants

NASA Astrophysics Data System (ADS)

Weindler, Peter; Wiltschko, Roswitha; Wiltschko, Wolfgang

1996-09-01

WHEN young birds leave on their first migration, they are guided by innate information about their direction of migration. It is generally assumed that this direction is represented twice, namely with respect to celestial rotation and with respect to the Earth's magnetic field1,2. The interactions between the two cue systems have been analysed by exposing hand-raised young birds during the premigratory period to cue-conflict situations, in which celestial rotation and the magnetic field provided different information. Celestial rotation altered the course with respect to the magnetic field3-7, whereas conflicting magnetic information did not seem to affect the course with respect to the stars8,9. Celestial information thus seemed to dominate over magnetic information. Here we report that the interaction between the two cue systems is far more complex than this. Celestial rotation alone seems to provide only a tendency to move away from its centre (towards geographical south), which is then modified by information from the magnetic field to establish the distinctive, population-specific migratory direction.

The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry

NASA Astrophysics Data System (ADS)

Fey, A. L.; Gordon, D.; Jacobs, C. S.; Ma, C.; Gaume, R. A.; Arias, E. F.; Bianco, G.; Boboltz, D. A.; Böckmann, S.; Bolotin, S.; Charlot, P.; Collioud, A.; Engelhardt, G.; Gipson, J.; Gontier, A.-M.; Heinkelmann, R.; Kurdubov, S.; Lambert, S.; Lytvyn, S.; MacMillan, D. S.; Malkin, Z.; Nothnagel, A.; Ojha, R.; Skurikhina, E.; Sokolova, J.; Souchay, J.; Sovers, O. J.; Tesmer, V.; Titov, O.; Wang, G.; Zharov, V.

2015-08-01

We present the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths using nearly 30 years of Very Long Baseline Interferometry observations. ICRF2 contains precise positions of 3414 compact radio astronomical objects and has a positional noise floor of ∼40 μas and a directional stability of the frame axes of ∼10 μas. A set of 295 new “defining” sources was selected on the basis of positional stability and the lack of extensive intrinsic source structure. The positional stability of these 295 defining sources and their more uniform sky distribution eliminates the two greatest weaknesses of the first realization of the International Celestial Reference Frame (ICRF1). Alignment of ICRF2 with the International Celestial Reference System was made using 138 positionally stable sources common to both ICRF2 and ICRF1. The resulting ICRF2 was adopted by the International Astronomical Union as the new fundamental celestial reference frame, replacing ICRF1 as of 2010 January 1.

Generation of dynamo waves by spatially separated sources in the Earth and other celestial bodies

NASA Astrophysics Data System (ADS)

Popova, E.

2017-12-01

The amplitude and the spatial configuration of the planetary and stellar magnetic field can changing over the years. Celestial bodies can have cyclic, chaotic or unchanging in time magnetic activity which is connected with a dynamo mechanism. This mechanism is based on the consideration of the joint influence of the alpha-effect and differential rotation. Dynamo sources can be located at different depths (active layers) of the celestial body and can have different intensities. Application of this concept allows us to get different forms of solutions and some of which can include wave propagating inside the celestial body. We analytically showed that in the case of spatially separated sources of magnetic field each source generates a wave whose frequency depends on the physical parameters of its source. We estimated parameters of sources required for the generation nondecaying waves. We discus structure of such sources and matter motion (including meridional circulation) in the liquid outer core of the Earth and active layers of other celestial bodies.

Historic halo displays as weather indicator: Criteria and examples

NASA Astrophysics Data System (ADS)

Neuhäuser, Dagmar L.; Neuhäuser, Ralph

2016-04-01

There are numerous celestial signs reported in historic records, many of them refer to atmospheric ("sub-lunar") phenomena, such as ice halos and aurorae. In an interdisciplinary collaboration between astrophysics and cultural astronomy, we noticed that celestial observations including meteorological phenomena are often misinterpreted, mostly due to missing genuine criteria: especially ice crystal halos were recorded frequently in past centuries for religious reasons, but are mistaken nowadays often for other phenomena like aurorae. Ice halo displays yield clear information on humidity and temperature in certain atmospheric layers, and thereby indicate certain weather patterns. Ancient so-called rain makers used halo observations for weather forecast; e.g., a connection between certain halo displays and rain a few day later is statistically significant. Ice halos exist around sun and moon and are reported for both (they can stay for several days): many near, middle, and far eastern records from day- and night-time include such observations with high frequency. (Partly based on publications on halos by D.L. Neuhäuser & R. Neuhäuser, available at http://www.astro.uni-jena.de/index.php/terra-astronomy.html)

Feature in Antenna Pattern for Pointing and Orientation Determination

NASA Technical Reports Server (NTRS)

Rochblatt, David (Inventor)

2016-01-01

Systems and methods for antenna pointing are disclosed. A transmit antenna system having an adjustable boresight transmits a signal exhibiting a far-field pattern including a feature (e.g. a V-Notch) in a polarization of the signal disposed at a fixed position off a beam peak of the far-field pattern of the signal. A receive antenna system scans across the far-field pattern of the signal in the polarization to locate the feature and determine a pointing error of the adjustable boresight therefrom. The system may be applied to a cross-polarization of the signal where a co-polarization of the signal is simultaneously used for telecommunication.

Patterns and properties of polarized light in air and water

PubMed Central

Cronin, Thomas W.; Marshall, Justin

2011-01-01

Natural sources of light are at best weakly polarized, but polarization of light is common in natural scenes in the atmosphere, on the surface of the Earth, and underwater. We review the current state of knowledge concerning how polarization and polarization patterns are formed in nature, emphasizing linearly polarized light. Scattering of sunlight or moonlight in the sky often forms a strongly polarized, stable and predictable pattern used by many animals for orientation and navigation throughout the day, at twilight, and on moonlit nights. By contrast, polarization of light in water, while visible in most directions of view, is generally much weaker. In air, the surfaces of natural objects often reflect partially polarized light, but such reflections are rarer underwater, and multiple-path scattering degrades such polarization within metres. Because polarization in both air and water is produced by scattering, visibility through such media can be enhanced using straightforward polarization-based methods of image recovery, and some living visual systems may use similar methods to improve vision in haze or underwater. Although circularly polarized light is rare in nature, it is produced by the surfaces of some animals, where it may be used in specialized systems of communication. PMID:21282165

Effects of wildfire smoke on atmospheric polarization

NASA Astrophysics Data System (ADS)

Shaw, Joseph A.; Pust, Nathan J.; Forbes, Elizabeth

2014-05-01

A continuously operating all-sky polarization imager recorded the skylight polarization pattern as conditions transitioned from clear and clean to extremely smoky. This transition included a period when a local wildfire plume filled part of the sky with smoke, creating a highly asymmetric distribution of aerosols. Multiple scattering in the smoke plume strongly reduced the degree of polarization in the smoky region of the sky. Once the smoke plume spread out to cover the entire local sky, the degree of polarization was strongly reduced everywhere. However, this example differed from previously observed smoke events because, even though the usual skylight polarization pattern generally persisted throughout the event, this time the smoke-covered sky exhibited a spatially asymmetric profile along the band of maximum polarization. This pattern of reduced polarization toward the horizon is hypothesized to be a result of an optically thick but physically thin smoke layer. The skylight polarization observations are supplemented with optical depth measurements and aerosol size distribution retrievals from a solar radiometer.

Junction size dependence of ferroelectric properties in e-beam patterned BaTiO{sub 3} ferroelectric tunnel junctions

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

Singh, A. V.; Gupta, A.; Althammer, M.

We investigate the switching characteristics in BaTiO{sub 3}-based ferroelectric tunnel junctions patterned in a capacitive geometry with circular Ru top electrode with diameters ranging from ∼430 to 2300 nm. Two different patterning schemes, viz., lift-off and ion-milling, have been employed to examine the variations in the ferroelectric polarization, switching, and tunnel electro-resistance resulting from differences in the pattering processes. The values of polarization switching field are measured and compared for junctions of different diameter in the samples fabricated using both patterning schemes. We do not find any specific dependence of polarization switching bias on the size of junctions in both samplemore » stacks. The junctions in the ion-milled sample show up to three orders of resistance change by polarization switching and the polarization retention is found to improve with increasing junction diameter. However, similar switching is absent in the lift-off sample, highlighting the effect of patterning scheme on the polarization retention.« less

Establishing a celestial VLBI reference frame. 1: Searching for VLBI sources

NASA Technical Reports Server (NTRS)

Preston, R. A.; Morabito, D. D.; Williams, J. G.; Slade, M. A.; Harris, A. W.; Finley, S. G.; Skjerve, L. J.; Tanida, L.; Spitzmesser, D. J.; Johnson, B.

1978-01-01

The Deep Space Network is currently engaged in establishing a new high-accuracy VLBI celestial reference frame. The present status of the task of finding suitable celestial radio sources for constructing this reference frame is discussed. To date, 564 VLBI sources were detected, with 166 of these lying within 10 deg of the ecliptic plane. The variation of the sky distribution of these sources with source strength is examined.

A Native Intelligence Metric for Artificial Systems

DTIC Science & Technology

2002-08-01

an example to help clarify the GCEA. Say we are S and we stumble upon Stonehenge . We don’t wonder whether humans carried the stones (some...stones S encounters that may be exhibiting alignment with celestial bodies at certain seasonal times. S determines that the designer of Stonehenge had...matching of the stones with particular celestial events. The various celestial events and our prehistoric Stonehenge designer’s awareness of these events

Chimera proteins with affinity for membranes and microtubule tips polarize in the membrane of fission yeast cells.

PubMed

Recouvreux, Pierre; Sokolowski, Thomas R; Grammoustianou, Aristea; ten Wolde, Pieter Rein; Dogterom, Marileen

2016-02-16

Cell polarity refers to a functional spatial organization of proteins that is crucial for the control of essential cellular processes such as growth and division. To establish polarity, cells rely on elaborate regulation networks that control the distribution of proteins at the cell membrane. In fission yeast cells, a microtubule-dependent network has been identified that polarizes the distribution of signaling proteins that restricts growth to cell ends and targets the cytokinetic machinery to the middle of the cell. Although many molecular components have been shown to play a role in this network, it remains unknown which molecular functionalities are minimally required to establish a polarized protein distribution in this system. Here we show that a membrane-binding protein fragment, which distributes homogeneously in wild-type fission yeast cells, can be made to concentrate at cell ends by attaching it to a cytoplasmic microtubule end-binding protein. This concentration results in a polarized pattern of chimera proteins with a spatial extension that is very reminiscent of natural polarity patterns in fission yeast. However, chimera levels fluctuate in response to microtubule dynamics, and disruption of microtubules leads to disappearance of the pattern. Numerical simulations confirm that the combined functionality of membrane anchoring and microtubule tip affinity is in principle sufficient to create polarized patterns. Our chimera protein may thus represent a simple molecular functionality that is able to polarize the membrane, onto which additional layers of molecular complexity may be built to provide the temporal robustness that is typical of natural polarity patterns.

Polarization Properties of A Broadband Multi-Moded Concentrator

NASA Technical Reports Server (NTRS)

Kogut, Alan; Fixsen, Dale J.; Hill, Robert S.

2015-01-01

We present the design and performance of a non-imaging concentrator for use in broad-band polarimetry at millimeter through submillimeter wavelengths. A rectangular geometry preserves the input polarization state as the concentrator couples f/2 incident optics to a 2pi sr detector. Measurements of the co-polar and cross-polar beams in both the few-mode and highly over-moded limits agree with a simple model based on mode truncation. The measured co-polar beam pattern is nearly independent of frequency in both linear polarizations. The cross-polar beam pattern is dominated by a uniform term corresponding to polarization efficiency 94%. After correcting for efficiency, the remaining cross-polar response is -18 dB.

Saturnian north polar region: a triangle inside the hexagon?

NASA Astrophysics Data System (ADS)

Kochemasov, Gennady G.

2010-05-01

The famous and "mysterious" stable hexagon structure around the North Pole of Saturn was earlier interpreted as projections of faces of a structural tetrahedron [1]. This "hidden" simplest Plato's polyhedron is a result of an interference of four fundamental (wave 1) warping waves having in any rotating celestial body four directions: orthogonal and diagonal. Origin of the warping waves in any celestial body is due to their movements in elliptical keplerian orbits with periodically changing accelerations. The structural tetrahedron is an intrinsic geometric feature marking the celestial bodies ubiquitous tectonic dichotomy as in a tetrahedron always there is an opposition of a face (expansion) and a vertex (contraction). In the saturnian case the tetrahedron shows a face at the north and a vertex at the south. Morphologically this is manifested by the hexagon and opposing it in the south a vertex. Blue and pink hues of the northern and southern hemispheres also underline the tectonic dichotomy. These geometric expressions are enforced by a subtle dark equilateral triangle appearing in the image PIA11682 also around the north pole and inside the hexagon (the triangle side is about 15000 km long). One angle of the triangle is clearly visible, another one just shows itself and the third one is barely distinguished. The sides of the triangle are not strait lines but slightly broken amidst lines what makes the triangle appear a bit hexagonal (spherical) and the angle is a bit bigger than 60 degrees of a classical equilateral triangle (~70 degrees). The central part of the triangle is not imaged (a black hole in the PIA11682). This image also confirms that the wide northern polar region is also densely "peppered" with bright cloudy more or less isometric spots on average 400 to 800 km across as in other latitudinal belts of Saturn [2, 3, 4]. Earlier they were observed in IR wavelengths, now they show themselves in visible wavelengths. Their origin and size were interpreted as interference wave features of modulated atmospheric inertia-gravity waves [2, 3]. It seems, as it was mentioned before, that the "leopard' spots in the north are slightly larger than those in the south [3, 4]. This observation confirms the north-south dichotomy of Saturn with expanding northern hemisphere. Finally, very distinctive wave features of this giant gas planet (often geometrically regular) are probably due to its comparatively high eccentricity exciting important warping waves in its body. References: [1] Kochemasov G.G. (2007a) Dichotomous Saturn in infrared images: huge northern hexagon against smaller southern hurricane // ERSC Abctracts, Vol. 2, EPSC2007-A-00015, 2007. [2] Kochemasov G.G. (2007b) Calculating size of the Saturn's "leopard skin" spots // Lunar and Planetary Science Conference XXXVIII, Abstract #1040, CD-ROM. [3] Kochemasov G.G (2007c) Saturn's infrared spots at the southern and northern polar regions and calculation of their sizes by a wave modulation procedure // ERSC Abstracts, Vol. 2, EPSC2007-A-00017, 2007. [4] Kochemasov G.G. (2008) Systematic not random "peppering" saturnian surface by the IR round clouds: wave features with predictable size // European Geosciences Union General Assembly, 2008, Vienna, Austria, 13-18 April 2008, Abstracts, EGU2008-A-01274, CD-ROM.

Divergence in Patterns of Leaf Growth Polarity Is Associated with the Expression Divergence of miR396

PubMed Central

2015-01-01

Lateral appendages often show allometric growth with a specific growth polarity along the proximo-distal axis. Studies on leaf growth in model plants have identified a basipetal growth direction with the highest growth rate at the proximal end and progressively lower rates toward the distal end. Although the molecular mechanisms governing such a growth pattern have been studied recently, variation in leaf growth polarity and, therefore, its evolutionary origin remain unknown. By surveying 75 eudicot species, here we report that leaf growth polarity is divergent. Leaf growth in the proximo-distal axis is polar, with more growth arising from either the proximal or the distal end; dispersed with no apparent polarity; or bidirectional, with more growth contributed by the central region and less growth at either end. We further demonstrate that the expression gradient of the miR396-GROWTH-REGULATING FACTOR module strongly correlates with the polarity of leaf growth. Altering the endogenous pattern of miR396 expression in transgenic Arabidopsis thaliana leaves only partially modified the spatial pattern of cell expansion, suggesting that the diverse growth polarities might have evolved via concerted changes in multiple gene regulatory networks. PMID:26410303

A Polarimetric Approach for Constraining the Dynamic Foreground Spectrum for Cosmological Global 21 cm Measurements

NASA Astrophysics Data System (ADS)

Nhan, Bang D.; Bradley, Richard F.; Burns, Jack O.

2017-02-01

The cosmological global (sky-averaged) 21 cm signal is a powerful tool to probe the evolution of the intergalactic medium in high-redshift universe (z≤slant 6). One of the biggest observational challenges is to remove the foreground spectrum which is at least four orders of magnitude brighter than the cosmological 21 cm emission. Conventional global 21 cm experiments rely on the spectral smoothness of the foreground synchrotron emission to separate it from the unique 21 cm spectral structures in a single total-power spectrum. However, frequency-dependent instrumental and observational effects are known to corrupt such smoothness and complicate the foreground subtraction. We introduce a polarimetric approach to measure the projection-induced polarization of the anisotropic foreground onto a stationary dual-polarized antenna. Due to Earth rotation, when pointing the antenna at a celestial pole, the revolving foreground will modulate this polarization with a unique frequency-dependent sinusoidal signature as a function of time. In our simulations, by harmonic decomposing this dynamic polarization, our technique produces two separate spectra in parallel from the same observation: (I) a total sky power consisting both the foreground and the 21 cm background and (II) a model-independent measurement of the foreground spectrum at a harmonic consistent to twice the sky rotation rate. In the absence of any instrumental effects, by scaling and subtracting the latter from the former, we recover the injected global 21 cm model within the assumed uncertainty. We further discuss several limiting factors and potential remedies for future implementation.

Radiance and polarization in the diffusion region with an arbitrary scattering phase matrix

NASA Astrophysics Data System (ADS)

Sun, Bingqiang; Kattawar, George W.; Yang, Ping

2016-11-01

Radiance and polarization patterns in an optically deep region, the so-called diffusion region or asymptotic region, of a homogeneous atmosphere or ocean, depend mainly on the scattering phase matrix and the single-scattering albedo of the medium. The radiance and polarization properties in the diffusion region for an arbitrary scattering phase matrix can be obtained in terms of a series of the generalized spherical functions. The number of terms is closely related to the single-scattering albedo of the medium. If the medium is conservative, the radiance is isotropic in conjunction with no polarization. If the single-scattering albedo is close to 1, several terms are sufficient to obtain the patterns, in which the degree of polarization feature is less than 1%. If the medium is highly absorptive, more expansion terms are required to obtain the diffusion patterns. The examples of simulated radiance and polarization patterns for Rayleigh scattering, Henyey-Greenstein-Rayleigh scattering, and haze L and cloud C1 scattering, defined by Deirmendjian, are calculated.

Astrometry for Astrophysics

NASA Astrophysics Data System (ADS)

van Altena, William F.

Part I. Astrometry in the Twenty-First Century: 1. Opportunities and challenges for astrometry in the twenty-first century M. Perryman; 2. Astrometric satellites L. Lindegren; 3. Ground-based opportunities for astrometry N. Zacharias; Part II. Relativistic Foundations of Astrometry and Celestial Mechanics: 4. Vectors in astrometry, an introduction L. Lindegren; 5. Relativistic principles of astrometry and celestial mechanics S. Klioner; 6. Celestial mechanics of the N-body problem S. Klioner; 7. Celestial coordinate systems and positions N. Capitaine and M. Stavinschi; 8. Fundamental algorithms for celestial coordinates and positions P. Wallace; Part III. Observing through the Atmosphere: 9. The Earth's atmosphere: refraction, turbulence, delays and limitations to astrometic precision W. van Altena and E. Fomalont; 10. Astrometry with ground-based diffraction-limited imaging A. Ghez; 11. Optical interferometry A. Glindermann; 12. Radio interferometry E. Fomalont; Part VI. From Detected Photons to the Celestial Sphere: 13. Geometrical optics and astrometry D. Schroeder; 14. CCD imaging detectors S. Howell; 15. Using CCDs in the time-delayed integration mode D. Rabinowitz; 16. Statistical astronomy A. Brown; 17. Analyzing poorly-sampled images: HST imaging astrometry J. Anderson; 18. Image deconvolution J. Nuñez; 19. From measures to celestial coordinates Z. H. Tang and W. van Altena; 20. Astrometric catalogs: concepts, history and necessity C. López; 21. Trigonometric parallaxes F. Benedict and B. McArthur; Part V. Applications of Astrometry to Topics in Astrophysics: 22. Galactic structure astrometry R. Méndez; 23. Binary and multiple stars E. Horch; 24. Binaries: HST, Hipparcos and Gaia D. Pourbaix; 25. Star clusters I. Platais; 26. Solar System astrometry F. Mignard; 27. Extrasolar planets A. Sozzetti; 28. Astrometric measurement and cosmology R. Easther; Appendices; Index.

Astrometry for Astrophysics

NASA Astrophysics Data System (ADS)

van Altena, William F.

2012-11-01

Part I. Astrometry in the Twenty-First Century: 1. Opportunities and challenges for astrometry in the twenty-first century M. Perryman; 2. Astrometric satellites L. Lindegren; 3. Ground-based opportunities for astrometry N. Zacharias; Part II. Relativistic Foundations of Astrometry and Celestial Mechanics: 4. Vectors in astrometry, an introduction L. Lindegren; 5. Relativistic principles of astrometry and celestial mechanics S. Klioner; 6. Celestial mechanics of the N-body problem S. Klioner; 7. Celestial coordinate systems and positions N. Capitaine and M. Stavinschi; 8. Fundamental algorithms for celestial coordinates and positions P. Wallace; Part III. Observing through the Atmosphere: 9. The Earth's atmosphere: refraction, turbulence, delays and limitations to astrometic precision W. van Altena and E. Fomalont; 10. Astrometry with ground-based diffraction-limited imaging A. Ghez; 11. Optical interferometry A. Glindermann; 12. Radio interferometry E. Fomalont; Part VI. From Detected Photons to the Celestial Sphere: 13. Geometrical optics and astrometry D. Schroeder; 14. CCD imaging detectors S. Howell; 15. Using CCDs in the time-delayed integration mode D. Rabinowitz; 16. StaStatistical astronomy A. Brown; 17. Analyzing poorly-sampled images: HST imaging astrometry J. Anderson; 18. Image deconvolution J. Nuñez; 19. From measures to celestial coordinates Z. H. Tang and W. van Altena; 20. Astrometric catalogs: concepts , history and necessity C. Löpez; 21. Trigonometric parallaxes F. Benedict and B. McArthur; Part V. Applications of Astrometry to Topics in Astrophysics: 22. Galactic structure astrometry R. Méndez; 23. Binary and multiple stars E. Horch; 24. Binaries: HST, Hipparcos and Gaia D. Pourbaix; 25. Star clusters I. Platais; 26. Solar System astrometry F. Mignard; 27. Extrasolar planets A. Sozzetti; 28. Astrometric measurement and cosmology R. Easther; Appendices; Index.

Free polar motion of a triaxial and elastic body in Hamiltonian formalism: Application to the Earth and Mars

NASA Astrophysics Data System (ADS)

Folgueira, M.; Souchay, J.

2005-03-01

The purpose of this paper is to show how to solve in Hamiltonian formalism the equations of the polar motion of any arbitrarily shaped elastic celestial body, i.e. the motion of its rotation axis (or angular momentum) with respect to its figure axis. With this aim, we deduce from canonical equations related to the rotational Hamiltonian of the body, the analytical solution for its free polar motion which depends both on the elasticity and on its moments of inertia. In particular, we study the influence of the phase angle δ, responsible for the dissipation, on the damping of the polar motion. In order to validate our analytical equations, we show that, to first order, they are in complete agreement with those obtained from the classical Liouville equations. Then we adapt our calculations to the real data obtained from the polar motion of the Earth (polhody). For that purpose, we characterize precisely the differences in radius J-χ and in angle l-θ between the polar coordinates (χ,θ) and (J,l) representing respectively the motion of the axis of rotation of the Earth and the motion of its angular momentum axis, with respect to an Earth-fixed reference frame, after showing the influence of the choice of the origin on these coordinates, and on the determination of the Chandler period as well. Then we show that the phase lag δ responsible for the damping for the selected time interval, between Feb. 1982 and Apr. 1990, might be of the order of δ ≈ 6 °, according to a numerical integration starting from our analytical equations. Moreover, we emphasize the presence in our calculations for both χ and θ, of an oscillation with a period TChandler/2, due to the triaxial shape of our planet, and generally not taken into account. In a last step, we apply our analytical formulation to the polar motion of Mars, thus showing the high dependence of its damping on the poorly known value of its Love number k. Moreover we emphasize the large oscillations of Mars' polar motion due to the triaxiality of this planet.

14 CFR 63.55 - Experience requirements.

Code of Federal Regulations, 2013 CFR

2013-01-01

... satisfactory flight navigation including celestial and radio navigation and dead reckoning. A pilot who has... exclusively for practicing long-range navigation methods, with emphasis on celestial navigation and dead...

14 CFR 63.55 - Experience requirements.

Code of Federal Regulations, 2010 CFR

2010-01-01

... satisfactory flight navigation including celestial and radio navigation and dead reckoning. A pilot who has... exclusively for practicing long-range navigation methods, with emphasis on celestial navigation and dead...

14 CFR 63.55 - Experience requirements.

Code of Federal Regulations, 2011 CFR

2011-01-01

... satisfactory flight navigation including celestial and radio navigation and dead reckoning. A pilot who has... exclusively for practicing long-range navigation methods, with emphasis on celestial navigation and dead...

14 CFR 63.55 - Experience requirements.

Code of Federal Regulations, 2014 CFR

2014-01-01

... satisfactory flight navigation including celestial and radio navigation and dead reckoning. A pilot who has... exclusively for practicing long-range navigation methods, with emphasis on celestial navigation and dead...

14 CFR 63.55 - Experience requirements.

Code of Federal Regulations, 2012 CFR

2012-01-01

... satisfactory flight navigation including celestial and radio navigation and dead reckoning. A pilot who has... exclusively for practicing long-range navigation methods, with emphasis on celestial navigation and dead...

Solar oscillation time delay measurement assisted celestial navigation method

NASA Astrophysics Data System (ADS)

Ning, Xiaolin; Gui, Mingzhen; Zhang, Jie; Fang, Jiancheng; Liu, Gang

2017-05-01

Solar oscillation, which causes the sunlight intensity and spectrum frequency change, has been studied in great detail, both observationally and theoretically. In this paper, owing to the existence of solar oscillation, the time delay between the sunlight coming from the Sun directly and the sunlight reflected by the other celestial body such as the satellite of planet or asteroid can be obtained with two optical power meters. Because the solar oscillation time delay is determined by the relative positions of the spacecraft, reflective celestial body and the Sun, it can be adopted as the navigation measurement to estimate the spacecraft's position. The navigation accuracy of single solar oscillation time delay navigation system depends on the time delay measurement accuracy, and is influenced by the distance between spacecraft and reflective celestial body. In this paper, we combine it with the star angle measurement and propose a solar oscillation time delay measurement assisted celestial navigation method for deep space exploration. Since the measurement model of time delay is an implicit function, the Implicit Unscented Kalman Filter (IUKF) is applied. Simulations demonstrate the effectiveness and superiority of this method.

The significance of the Sun, Moon and celestial bodies to societies in the Carpathian basin during the Bronze Age

NASA Astrophysics Data System (ADS)

Pásztor, Emília

2011-06-01

Celestial events often exerted a great or even decisive influence on the life of ancient communities. They may provide some of the foundations on which an understanding of the deeper meaning of mythologies, religious systems and even folk tales can be based. These influences are reflected and may be detected in the archaeological material as well. There is good evidence that celestial (especially solar and perhaps lunar) phenomena played a particularly important rôle in the worldview of prehistoric Europe. To reveal the social and ideational significance of concepts relating to the celestial bodies in the prehistory of the Carpathian Basin, complex investigations on orientations of houses and graves, prestige archaeological finds and iconography have been accomplished. The results indicate ideological and/or social changes, which developed into a likely organized ideological system in large part of Central Europe including the Carpathian Basin by the Late Bronze Age. It might also be the first period in prehistory when people became really interested in celestial phenomena.

Constraining foreground spectrum with the projection-induced polarization for the cosmological global 21-cm experiments

NASA Astrophysics Data System (ADS)

Nhan, Bang D.; Bradley, Richard F.; Burns, Professor O.

2018-01-01

Detecting the cosmological global (sky-averaged) 21-cm spectrum as a function of observed frequency will provide a powerful tool to study the thermal history of intergalactic medium (IGM) in the high-redshift Universe (~ 400 million years after the Big Bang). The biggest challenge in conventional ground-based total-power global 21-cm experiments is the removal of the Galactic and extragalactic synchrotron foreground (~ 1e4-1e5 K) to uncover the weak cosmological signal (~ 10-100 mK). The foreground is further corrupted by the frequency-dependent instrumental systematics. We have developed a new polarimetry-based observational approach that aims to measure the foreground emission by modulating it as a function of time through its circumpolar motion. Due to geometry, the projection of the anisotropic foreground sources onto the dual-polarized antenna induces a net foreground polarization, which is distinct from the much weaker intrinsic polarization of synchrotron sources. Instead of pointing the radio antenna at the zenith as in the conventional experiments, we point the antenna at the North Celestial Pole (NCP) and measure the projection-induced polarization modulated by the foreground's circumpolar diurnal periodicity. This temporal signature allows us to separate the dynamic foreground spectrum from the static cosmological background. In this presentation, we describe the design, construction, and initial results from the "Cosmic Twilight Polarimeter'' (CTP) as a proof-of-concept implementation of this technique. The instrument consists of a dual-polarized broadband antenna (60-120 MHz) with a two-stage thermally stabilized front-end electronics, tilted toward the NCP. The instrument is currently being evaluated at a site near Charlottesville, VA. Ultimately, the instrument will be relocated to an RFI-quiet site closer to the Geographic North Pole (GNP) to mitigate sky obstruction due to the horizon at a lower latitude.

Vector navigation in desert ants, Cataglyphis fortis: celestial compass cues are essential for the proper use of distance information.

PubMed

Sommer, Stefan; Wehner, Rüdiger

2005-10-01

Foraging desert ants navigate primarily by path integration. They continually update homing direction and distance by employing a celestial compass and an odometer. Here we address the question of whether information about travel distance is correctly used in the absence of directional information. By using linear channels that were partly covered to exclude celestial compass cues, we were able to test the distance component of the path-integration process while suppressing the directional information. Our results suggest that the path integrator cannot process the distance information accumulated by the odometer while ants are deprived of celestial compass information. Hence, during path integration directional cues are a prerequisite for the proper use of travel-distance information by ants.

Terrestrial passage theory of the moon illusion.

PubMed

Reed, C F

1984-12-01

Theories of the celestial, or moon, illusion have neglected geometric characteristics of movement along and above the surface of the earth. The illusion occurs because the characteristics of terrestrial passage are attributed to celestial passage. In terrestrial passage, the visual angle subtended by an object changes discriminably as an essentially invariant function of elevation above the horizon. In celestial passage, by contrast, change in visual angle is indiscriminable at all elevations. If a terrestrial object gains altitude, its angular subtense fails to follow the expansion projected for an orbital course: Angular diminution or constancy is equivalent to distancing. On the basis of terrestrial projections, a similar failure of celestial objects in successive elevations is also equivalent to distancing. The illusion occurs because of retinal image constancy, not--as traditionally stated--despite it.

Characterization of highly scattering media by measurement of diffusely backscattered polarized light

DOEpatents

Hielscher, Andreas H.; Mourant, Judith R.; Bigio, Irving J.

2000-01-01

An apparatus and method for recording spatially dependent intensity patterns of polarized light that is diffusely backscattered from highly scattering media are described. These intensity patterns can be used to differentiate different turbid media, such as polystyrene-sphere and biological-cell suspensions. Polarized light from a He-Ne laser (.lambda.=543 nm) is focused onto the surface of the scattering medium, and a surface area of approximately 4.times.4 cm centered on the light input point is imaged through polarization analysis optics onto a CCD camera. A variety of intensity patterns may be observed by varying the polarization state of the incident laser light and changing the analyzer configuration to detect different polarization components of the backscattered light. Experimental results for polystyrene-sphere and Intralipid suspensions demonstrate that the radial and azimuthal variations of the observed pattern depend on the concentration, size, and anisotropy factor, g, of the particles constituting the scattering medium. Measurements performed on biological cell suspensions show that intensity patterns can be used to differentiate between suspensions of cancerous and non-cancerous cells. Introduction of the Mueller-matrix for diffusely backscattered light, permits the selection of a subset of measurements which comprehensively describes the optical properties of backscattering media.

Polarized luminescence of nc-Si-SiO x nanostructures on silicon substrates with patterned surface

NASA Astrophysics Data System (ADS)

Michailovska, Katerina; Mynko, Viktor; Indutnyi, Ivan; Shepeliavyi, Petro

2018-05-01

Polarization characteristics and spectra of photoluminescence (PL) of nc-Si-SiO x structures formed on the patterned and plane c-Si substrates are studied. The interference lithography with vacuum chalcogenide photoresist and anisotropic wet etching are used to form a periodic relief (diffraction grating) on the surface of the substrates. The studied nc-Si-SiO x structures were produced by oblique-angle deposition of Si monoxide in vacuum and the subsequent high-temperature annealing. The linear polarization memory (PM) effect in PL of studied structure on plane substrate is manifested only after the treatment of the structures in HF and is explained by the presence of elongated Si nanoparticles in the SiO x nanocolumns. But the PL output from the nc-Si-SiO x structure on the patterned substrate depends on how this radiation is polarized with respect to the grating grooves and is much less dependent on the polarization of the exciting light. The measured reflection spectra of nc-Si-SiO x structure on the patterned c-Si substrate confirmed the influence of pattern on the extraction of polarized PL.

Osculating Keplerian Elements for Highly Non-Keplerian Orbits

DTIC Science & Technology

2017-03-27

1.52133 2 McInnes, C. R., “The Existence and Stability of Families of Displacement Two-Body Orbits”, Celestial Mechanics and Dynamical Astronomy , Vol...j.actaastro.2011.08.012 5 Xu, M. and Xu, S., “Nonlinear dynamical analysis for displaced orbits above a planet”, Celestial Mechanics and Dynamical Astronomy ...Celestial Mechanics and Dynamical Astronomy , Vol. 110, No. 3, 2011, pp. 199-215. doi: 10.1007/s10569-011-9351-5 7 Macdonald, M., McKay, R. J., Vasile, M

The Celestial Vault: The Magic of Astrology

NASA Astrophysics Data System (ADS)

McGaha, J.

2004-11-01

Astrology is a "Geocentric System" that supports the "Astrological Principle". This principle, that human beings and their actions are influenced by the positions of celestial objects, is not objectively supported. The "planetary gods" found in the heavens provided order to help explain the chaotic events in life on earth. Is this why many people think their horoscopes are correct, with the "stars" taking credit? Do "celestial movements" foretell the future? What is the evidence for Astrology? The historical, psychological and physical foundations of astrology will be discussed.

The Hands of the Pleiades: The Celestial Clock in the Classical Arabic Poetry of Dhū al-Rumma

NASA Astrophysics Data System (ADS)

Adams, W. B.

2011-06-01

In the desert poetry of Dhū al-Rumma (d. 117 AH/735 CE), astronomical phenomena sometimes function as familiar celestial timepieces that indicate the poetic timeframe literally and accurately. The literary, lexical, floral and astronomical analyses of a selection from this poetry illustrate the role of the Pleiades star cluster as a celestial clock and illuminate the utility of naked-eye astronomy in interpreting Arabic poetry of the early Islamic period.

Polarization pattern of vector vortex beams generated by q-plates with different topological charges.

PubMed

Cardano, Filippo; Karimi, Ebrahim; Slussarenko, Sergei; Marrucci, Lorenzo; de Lisio, Corrado; Santamato, Enrico

2012-04-01

We describe the polarization topology of the vector beams emerging from a patterned birefringent liquid crystal plate with a topological charge q at its center (q-plate). The polarization topological structures for different q-plates and different input polarization states have been studied experimentally by measuring the Stokes parameters point-by-point in the beam transverse plane. Furthermore, we used a tuned q=1/2-plate to generate cylindrical vector beams with radial or azimuthal polarizations, with the possibility of switching dynamically between these two cases by simply changing the linear polarization of the input beam.

Divergence in Patterns of Leaf Growth Polarity Is Associated with the Expression Divergence of miR396.

PubMed

Das Gupta, Mainak; Nath, Utpal

2015-10-01

Lateral appendages often show allometric growth with a specific growth polarity along the proximo-distal axis. Studies on leaf growth in model plants have identified a basipetal growth direction with the highest growth rate at the proximal end and progressively lower rates toward the distal end. Although the molecular mechanisms governing such a growth pattern have been studied recently, variation in leaf growth polarity and, therefore, its evolutionary origin remain unknown. By surveying 75 eudicot species, here we report that leaf growth polarity is divergent. Leaf growth in the proximo-distal axis is polar, with more growth arising from either the proximal or the distal end; dispersed with no apparent polarity; or bidirectional, with more growth contributed by the central region and less growth at either end. We further demonstrate that the expression gradient of the miR396-GROWTH-REGULATING FACTOR module strongly correlates with the polarity of leaf growth. Altering the endogenous pattern of miR396 expression in transgenic Arabidopsis thaliana leaves only partially modified the spatial pattern of cell expansion, suggesting that the diverse growth polarities might have evolved via concerted changes in multiple gene regulatory networks. © 2015 American Society of Plant Biologists. All rights reserved.

Focusing of concentric piecewise vector Bessel-Gaussian beam

NASA Astrophysics Data System (ADS)

Li, Jinsong; Fang, Ying; Zhou, Shenghua; Ye, Youxiang

2010-12-01

The focusing properties of a concentric piecewise vector Bessel-Gaussian beam are investigated in this paper. The beam consists of three portions: the center circular portion and outer annular portion are radially polarized, while the inner annular portion is generalized polarized with tunable polarized angle. Numerical simulations show that the evolution of focal pattern is altered considerably with different Bessel parameters in the Bessel term of the vector Bessel-Gaussian beam. The polarized angle also affects the focal pattern remarkably. Some interesting focal patterns may appear, such as two-peak, dark hollow focus; ring focus; spherical shell focus; cylindrical shell focus; and multi-ring-peak focus, and transverse focal switch occurs with increasing polarized angle of the inner annular portion, which may be used in optical manipulation.

Real-time polarization imaging algorithm for camera-based polarization navigation sensors.

PubMed

Lu, Hao; Zhao, Kaichun; You, Zheng; Huang, Kaoli

2017-04-10

Biologically inspired polarization navigation is a promising approach due to its autonomous nature, high precision, and robustness. Many researchers have built point source-based and camera-based polarization navigation prototypes in recent years. Camera-based prototypes can benefit from their high spatial resolution but incur a heavy computation load. The pattern recognition algorithm in most polarization imaging algorithms involves several nonlinear calculations that impose a significant computation burden. In this paper, the polarization imaging and pattern recognition algorithms are optimized through reduction to several linear calculations by exploiting the orthogonality of the Stokes parameters without affecting precision according to the features of the solar meridian and the patterns of the polarized skylight. The algorithm contains a pattern recognition algorithm with a Hough transform as well as orientation measurement algorithms. The algorithm was loaded and run on a digital signal processing system to test its computational complexity. The test showed that the running time decreased to several tens of milliseconds from several thousand milliseconds. Through simulations and experiments, it was found that the algorithm can measure orientation without reducing precision. It can hence satisfy the practical demands of low computational load and high precision for use in embedded systems.

Study of the polarimetric performance of a Si/CdTe semiconductor Compton camera for the Hitomi satellite

NASA Astrophysics Data System (ADS)

Katsuta, Junichiro; Edahiro, Ikumi; Watanabe, Shin; Odaka, Hirokazu; Uchida, Yusuke; Uchida, Nagomi; Mizuno, Tsunefumi; Fukazawa, Yasushi; Hayashi, Katsuhiro; Habata, Sho; Ichinohe, Yuto; Kitaguchi, Takao; Ohno, Masanori; Ohta, Masayuki; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shin'ichiro; Tajima, Hiroyasu; Yuasa, Takayuki; Itou, Masayoshi; SGD Team

2016-12-01

Gamma-ray polarization offers a unique probe into the geometry of the γ-ray emission process in celestial objects. The Soft Gamma-ray Detector (SGD) onboard the X-ray observatory Hitomi is a Si/CdTe Compton camera and is expected to be an excellent polarimeter, as well as a highly sensitive spectrometer due to its good angular coverage and resolution for Compton scattering. A beam test of the final-prototype for the SGD Compton camera was conducted to demonstrate its polarimetric capability and to verify and calibrate the Monte Carlo simulation of the instrument. The modulation factor of the SGD prototype camera, evaluated for the inner and outer parts of the CdTe sensors as absorbers, was measured to be 0.649-0.701 (inner part) and 0.637-0.653 (outer part) at 122.2 keV and 0.610-0.651 (inner part) and 0.564-0.592 (outer part) at 194.5 keV at varying polarization angles with respect to the detector. This indicates that the relative systematic uncertainty of the modulation factor is as small as ∼ 3 % .

132. STANDARD NAVAL AIR STATIONS CELESTIAL NAVIGATION, ELEVATIONS AND SECTIONS, ...

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

132. STANDARD NAVAL AIR STATIONS CELESTIAL NAVIGATION, ELEVATIONS AND SECTIONS, BUDOCKS, OCTOBER 14, 1943. QP ACC 9689. - Quonset Point Naval Air Station, Roger Williams Way, North Kingstown, Washington County, RI

Celestial Seasonings: Astronomy and Rock Art in the American Southwest

NASA Astrophysics Data System (ADS)

Krupp, E. C.

1994-12-01

Astronomical interpretations of prehistoric rock art have played a significant part in the development of modern archaeoastronomy since 1975, when interest was renewed in the possibility that the Crab supernova explosion of 1054 A.D. was represented in rock art of the American Southwest. (This hypothesis was actually first formulated in 1955.) In the last two decades, a variety of astronomical functions for rock art have been proposed and investigated. These include representation of specific historical celestial events, symbolic representation of elements of celestial myths, star maps, markers for astronomical observing stations markers for celestially tempered shrines, images intended to invoke and exploit cosmo-magical power, seasonally significant light-and-shadow displays. Examples of astronomical connotations in prehistoric rock art from the Southwest and California illustrate the necessity of understanding the culture in any attempt to understand its astronomy.

Spatial and polarization entanglement of lasing patterns and related dynamic behaviors in laser-diode-pumped solid-state lasers.

PubMed

Otsuka, K; Chu, S-C; Lin, C-C; Tokunaga, K; Ohtomo, T

2009-11-23

To provide the underlying physical mechanism for formations of spatial- and polarization-entangled lasing patterns (namely, SPEPs), we performed experiments using a c-cut Nd:GdVO(4) microchip laser with off-axis laser-diode pumping. This extends recent work on entangled lasing pattern generation from an isotropic laser, where such a pattern was explained only in terms of generalized coherent states (GCSs) formed by mathematical manipulation. Here, we show that polarization-resolved transverse patterns can be well explained by the transverse mode-locking of distinct orthogonal linearly polarized Ince-Gauss (IG) mode pairs rather than GCSs. Dynamic properties of SPEPs were experimentally examined in both free-running and modulated conditions to identify long-term correlations of IG mode pairs over time. The complete chaos synchronization among IG mode pairs subjected to external perturbation is also demonstrated.

Applications of polarization speckle in skin cancer detection and monitoring

NASA Astrophysics Data System (ADS)

Lee, Tim K.; Tchvialeva, Lioudmila; Phillips, Jamie; Louie, Daniel C.; Zhao, Jianhua; Wang, Wei; Lui, Harvey; Kalia, Sunil

2018-01-01

Polarization speckle is a rapidly developed field. Unlike laser speckle, polarization speckle consists of stochastic interference patterns with spatially random polarizations, amplitudes and phases. We have been working in this exciting research field, developing techniques to generate polarization patterns from skin. We hypothesize that polarization speckle patterns could be used in biomedical applications, especially, for detecting and monitoring skin cancers, the most common neoplasmas for white populations around the world. This paper describes our effort in developing two polarization speckle devices. One of them captures the Stokes parameters So and S1 simultaneously, and another one captures all four Stokes parameters So, S1, S2, and S3 in one-shot, within milliseconds. Hence these two devices could be used in medical clinics and assessed skin conditions in-vivo. In order to validate our hypothesis, we conducted a series of three clinical studies. These are early pilot studies, and the results suggest that the devices have potential to detect and monitor skin cancers.

Generation of isolated asymmetric umbilics in light's polarization

NASA Astrophysics Data System (ADS)

Galvez, Enrique J.; Rojec, Brett L.; Kumar, Vijay; Viswanathan, Nirmal K.

2014-03-01

Polarization-singularity C points, a form of line singularities, are the vectorial counterparts of the optical vortices of spatial modes and fundamental optical features of polarization-spatial modes. Their generation in tailored beams has been limited to so-called "lemon" and "star" C points that contain symmetric dislocations in state-of-polarization patterns. In this Rapid Communication we present the theory and laboratory measurements of two complementary methods to generate isolated asymmetric C points in tailored beams, of which symmetric lemon and star patterns are limiting cases; and we report on the generation of so-called "monstar" patterns, an asymmetric C point with characteristics of both lemons and stars.

Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes.

PubMed

Egri, Adám; Blahó, Miklós; Kriska, György; Farkas, Róbert; Gyurkovszky, Mónika; Akesson, Susanne; Horváth, Gábor

2012-03-01

The characteristic striped appearance of zebras has provoked much speculation about its function and why the pattern has evolved, but experimental evidence is scarce. Here, we demonstrate that a zebra-striped horse model attracts far fewer horseflies (tabanids) than either homogeneous black, brown, grey or white equivalents. Such biting flies are prevalent across Africa and have considerable fitness impact on potential mammalian hosts. Besides brightness, one of the likely mechanisms underlying this protection is the polarization of reflected light from the host animal. We show that the attractiveness of striped patterns to tabanids is also reduced if only polarization modulations (parallel stripes with alternating orthogonal directions of polarization) occur in horizontal or vertical homogeneous grey surfaces. Tabanids have been shown to respond strongly to linearly polarized light, and we demonstrate here that the light and dark stripes of a zebra's coat reflect very different polarizations of light in a way that disrupts the attractiveness to tabanids. We show that the attractiveness to tabanids decreases with decreasing stripe width, and that stripes below a certain size are effective in not attracting tabanids. Further, we demonstrate that the stripe widths of zebra coats fall in a range where the striped pattern is most disruptive to tabanids. The striped coat patterns of several other large mammals may also function in reducing exposure to tabanids by similar mechanisms of differential brightness and polarization of reflected light. This work provides an experimentally supported explanation for the underlying mechanism leading to the selective advantage of a black-and-white striped coat pattern.

Vortex circulation and polarity patterns in closely packed cap arrays

DOE PAGES

Streubel, Robert; Kronast, Florian; Reiche, Christopher F.; ...

2016-01-25

For this work, we studied curvature-driven modifications to the magnetostatic coupling of vortex circulation and polarity in soft-magnetic closely packed cap arrays. A phase diagram for the magnetic remanent/transition states at room temperature as a function of diameter and thickness was assembled. For specimens with vortex remanent state (40 nm-thick Permalloy on 330 nm spherical nanoparticles), both vortex circulation and polarity were visualized. Intercap coupling upon vortex nucleation leads to the formation of vortex circulation patterns in closely packed arrays. The remanent circulation pattern can be tailored choosing the direction of the applied magnetic field with respect to the symmetrymore » axis of the hexagonal array. An even and random distribution of vortex polarity indicates the absence of any circulation-polarity coupling.« less

Ectopic KNOX Expression Affects Plant Development by Altering Tissue Cell Polarity and Identity[OPEN

PubMed Central

Rebocho, Alexandra B.

2016-01-01

Plant development involves two polarity types: tissue cell (asymmetries within cells are coordinated across tissues) and regional (identities vary spatially across tissues) polarity. Both appear altered in the barley (Hordeum vulgare) Hooded mutant, in which ectopic expression of the KNOTTED1-like Homeobox (KNOX) gene, BKn3, causes inverted polarity of differentiated hairs and ectopic flowers, in addition to wing-shaped outgrowths. These lemma-specific effects allow the spatiotemporal analysis of events following ectopic BKn3 expression, determining the relationship between KNOXs, polarity, and shape. We show that tissue cell polarity, based on localization of the auxin transporter SISTER OF PINFORMED1 (SoPIN1), dynamically reorients as ectopic BKn3 expression increases. Concurrently, ectopic expression of the auxin importer LIKE AUX1 and boundary gene NO APICAL MERISTEM is activated. The polarity of hairs reflects SoPIN1 patterns, suggesting that tissue cell polarity underpins oriented cell differentiation. Wing cell files reveal an anisotropic growth pattern, and computational modeling shows how polarity guiding growth can account for this pattern and wing emergence. The inverted ectopic flower orientation does not correlate with SoPIN1, suggesting that this form of regional polarity is not controlled by tissue cell polarity. Overall, the results suggest that KNOXs trigger different morphogenetic effects through interplay between tissue cell polarity, identity, and growth. PMID:27553356

Polarization mode control of long-wavelength VCSELs by intracavity patterning

DOE PAGES

Long, Christopher Michael; Mickovic, Zlatko; Dwir, Benjamin; ...

2016-04-26

Polarization mode control is enhanced in wafer-fused vertical-cavity surface-emitting lasers emitting at 1310 nm wavelength by etching two symmetrically arranged arcs above the gain structure within the laser cavity. The intracavity patterning introduces birefringence and dichroism, which discriminates between the two polarization states of the fundamental transverse modes. We find that the cavity modifications define the polarization angle at threshold with respect to the crystal axes, and increase the gain anisotropy and birefringence on average, leading to an increase in the polarization switching current. As a result, experimental measurements are explained using the spin-flip model of VCSEL polarization dynamics.

OPTICAL SPECTRA OF CANDIDATE SOUTHERN HEMISPHERE INTERNATIONAL CELESTIAL REFERENCE FRAME (ICRF) RADIO SOURCES

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

Titov, O.; Jauncey, D. L.; Johnston, H. M.

2011-11-15

We present the results of spectroscopic observations of the optical counterparts of 47 southern radio sources from the candidate International Celestial Reference Catalogue as part of a very long baseline interferometry (VLBI) program to strengthen the celestial reference frame, especially in the south. We made the observations with the 3.58 m European Southern Observatory New Technology Telescope. We obtained redshifts for 30 quasars and one radio galaxy, with a further seven objects being probable BL Lac objects with featureless spectra. Of the remainder, four were clear misidentifications with Galactic stars and five had low signal-to-noise spectra and could not bemore » classified. These results, in combination with new VLBI data of the radio sources with redshifts more than 2, add significantly to the existing data needed to refine the distribution of source proper motions over the celestial sphere.« less

A consistent time frame for Chaucer's Canterbury Pilgrimage

NASA Astrophysics Data System (ADS)

Kummerer, K. R.

2001-08-01

A consistent time frame for the pilgrimage that Geoffrey Chaucer describes in The Canterbury Tales can be established if the seven celestial assertions related to the journey mentioned in the text can be reconciled with each other and the date of April 18 that is also mentioned. Past attempts to establish such a consistency for all seven celestial assertions have not been successful. The analysis herein, however, indicates that in The Canterbury Tales Chaucer accurately describes the celestial conditions he observed in the April sky above the London(Canterbury region of England in the latter half of the fourteenth century. All seven celestial assertions are in agreement with each other and consistent with the April 18 date. The actual words of Chaucer indicate that the Canterbury journey began during the 'seson' he defines in the General Prologue and ends under the light of the full Moon on the night of April 18, 1391.

Dynamical configurations of celestial systems comprised of multiple irregular bodies

NASA Astrophysics Data System (ADS)

Jiang, Yu; Zhang, Yun; Baoyin, Hexi; Li, Junfeng

2016-09-01

This manuscript considers the main features of the nonlinear dynamics of multiple irregular celestial body systems. The gravitational potential, static electric potential, and magnetic potential are considered. Based on the three established potentials, we show that three conservative values exist for this system, including a Jacobi integral. The equilibrium conditions for the system are derived and their stability analyzed. The equilibrium conditions of a celestial system comprised of n irregular bodies are reduced to 12n - 9 equations. The dynamical results are applied to simulate the motion of multiple-asteroid systems. The simulation is useful for the study of the stability of multiple irregular celestial body systems and for the design of spacecraft orbits to triple-asteroid systems discovered in the solar system. The dynamical configurations of the five triple-asteroid systems 45 Eugenia, 87 Sylvia, 93 Minerva, 216 Kleopatra, and 136617 1994CC, and the six-body system 134340 Pluto are calculated and analyzed.

The Future of Past Skies: Historical Celestial Cartography at the Adler Planetarium

NASA Astrophysics Data System (ADS)

Raposo, Pedro M. P.

2018-01-01

The Adler Planetarium is home to a world-class collection of scientific instruments, rare books and works on paper. Since 2014, Adler staff has been digitizing a wide selection of items relating to celestial cartography, including: more than 236 rare books and atlases; 97 works on paper; globes and other artifacts, amounting to 58 objects; and approximately 3,750 Carte du Ciel prints. This work has been carried out under the auspices of the Celestial Cartography Digitization Project (CCDP), which is sponsored by the National Endowment for the Humanities. This poster presentation will include: 1) an update on the project; 2) a description of related resources and tools available to the research community; 3) examples of how the Adler Planetarium is integrating the history of celestial cartography with its public programs; 4) an overview of a prospective citizen science project involving the identification of constellations in historical atlases and charts.

Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera

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

Komura, S.; Takada, A.; Mizumura, Y.

2017-04-10

X-ray and gamma-ray polarimetry is a promising tool to study the geometry and the magnetic configuration of various celestial objects, such as binary black holes or gamma-ray bursts (GRBs). However, statistically significant polarizations have been detected in few of the brightest objects. Even though future polarimeters using X-ray telescopes are expected to observe weak persistent sources, there are no effective approaches to survey transient and serendipitous sources with a wide field of view (FoV). Here we present an electron-tracking Compton camera (ETCC) as a highly sensitive gamma-ray imaging polarimeter. The ETCC provides powerful background rejection and a high modulation factormore » over an FoV of up to 2 π sr thanks to its excellent imaging based on a well-defined point-spread function. Importantly, we demonstrated for the first time the stability of the modulation factor under realistic conditions of off-axis incidence and huge backgrounds using the SPring-8 polarized X-ray beam. The measured modulation factor of the ETCC was 0.65 ± 0.01 at 150 keV for an off-axis incidence with an oblique angle of 30° and was not degraded compared to the 0.58 ± 0.02 at 130 keV for on-axis incidence. These measured results are consistent with the simulation results. Consequently, we found that the satellite-ETCC proposed in Tanimori et al. would provide all-sky surveys of weak persistent sources of 13 mCrab with 10% polarization for a 10{sup 7} s exposure and over 20 GRBs down to a 6 × 10{sup −6} erg cm{sup −2} fluence and 10% polarization during a one-year observation.« less

Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera

NASA Astrophysics Data System (ADS)

Komura, S.; Takada, A.; Mizumura, Y.; Miyamoto, S.; Takemura, T.; Kishimoto, T.; Kubo, H.; Kurosawa, S.; Matsuoka, Y.; Miuchi, K.; Mizumoto, T.; Nakamasu, Y.; Nakamura, K.; Oda, M.; Parker, J. D.; Sawano, T.; Sonoda, S.; Tanimori, T.; Tomono, D.; Yoshikawa, K.

2017-04-01

X-ray and gamma-ray polarimetry is a promising tool to study the geometry and the magnetic configuration of various celestial objects, such as binary black holes or gamma-ray bursts (GRBs). However, statistically significant polarizations have been detected in few of the brightest objects. Even though future polarimeters using X-ray telescopes are expected to observe weak persistent sources, there are no effective approaches to survey transient and serendipitous sources with a wide field of view (FoV). Here we present an electron-tracking Compton camera (ETCC) as a highly sensitive gamma-ray imaging polarimeter. The ETCC provides powerful background rejection and a high modulation factor over an FoV of up to 2π sr thanks to its excellent imaging based on a well-defined point-spread function. Importantly, we demonstrated for the first time the stability of the modulation factor under realistic conditions of off-axis incidence and huge backgrounds using the SPring-8 polarized X-ray beam. The measured modulation factor of the ETCC was 0.65 ± 0.01 at 150 keV for an off-axis incidence with an oblique angle of 30° and was not degraded compared to the 0.58 ± 0.02 at 130 keV for on-axis incidence. These measured results are consistent with the simulation results. Consequently, we found that the satellite-ETCC proposed in Tanimori et al. would provide all-sky surveys of weak persistent sources of 13 mCrab with 10% polarization for a 107 s exposure and over 20 GRBs down to a 6 × 10-6 erg cm-2 fluence and 10% polarization during a one-year observation.

Polarimetric analysis of a CdZnTe spectro-imager under multi-pixel irradiation conditions

NASA Astrophysics Data System (ADS)

Pinto, M.; da Silva, R. M. Curado; Maia, J. M.; Simões, N.; Marques, J.; Pereira, L.; Trindade, A. M. F.; Caroli, E.; Auricchio, N.; Stephen, J. B.; Gonçalves, P.

2016-12-01

So far, polarimetry in high-energy astrophysics has been insufficiently explored due to the complexity of the required detection, electronic and signal processing systems. However, its importance is today largely recognized by the astrophysical community, therefore the next generation of high-energy space instruments will certainly provide polarimetric observations, contemporaneously with spectroscopy and imaging. We have been participating in high-energy observatory proposals submitted to ESA Cosmic Vision calls, such as GRI (Gamma-Ray Imager), DUAL and ASTROGAM, where the main instrument was a spectro-imager with polarimetric capabilities. More recently, the H2020 AHEAD project was launched with the objective to promote more coherent and mature future high-energy space mission proposals. In this context of high-energy proposal development, we have tested a CdZnTe detection plane prototype polarimeter under a partially polarized gamma-ray beam generated from an aluminum target irradiated by a 22Na (511 keV) radioactive source. The polarized beam cross section was 1 cm2, allowing the irradiation of a wide multi-pixelated area where all the pixels operate simultaneously as a scatterer and as an absorber. The methods implemented to analyze such multi-pixel irradiation are similar to those required to analyze a spectro-imager polarimeter operating in space, since celestial source photons should irradiate its full pixilated area. Correction methods to mitigate systematic errors inherent to CdZnTe and to the experimental conditions were also implemented. The polarization level ( 40%) and the polarization angle (precision of ±5° up to ±9°) obtained under multi-pixel irradiation conditions are presented and compared with simulated data.

Celestial dynamics and astrometry in expanding universe

NASA Astrophysics Data System (ADS)

Kopeikin, Sergei

2012-08-01

Post - Newtonian theory of motion of celestial bodies and propagation of light was instrumental in conducting the critical experimental tests of general relativity and in building the astronomical ephemerides of celestial bodies in the solar system with an unparalleled precision. The cornerstone of the theory is the postulate that the solar system is gravitationally isolated from the rest of the universe and the background spacetime is asymptotically flat. The present talk abolishes this postulate and lays down the principles of celestial dynamics of particles and light moving in gravitational field of a localized astronomical system embedded to the expanding universe. We formulate the precise mathematical concept of the Newtonian limit of Einstein ’s field equations in the conformally - flat spacetime and analyse the geodesic equations of motion o f particles and light in this limit. We demonstrate that the equations of motion of particles and light can be reduced to their Newtonian counterparts by doing conformal transformations of time and space coordinates. However, the Newtonian equations for particles and light differ by terms of the first order in the Hubble constant. This leads to the important conclusion that the equations of motion used currently by Space Navigation Centres and Astronomical Observatories for calculating orbits of celestial bodies, are incomplete and missing some terms of cosmological origin. We explicitly identify the missing terms and demonstrate that they bring about a noticeable discrepancy between the observed and calculated astronomical ephemerides. We argue that a number of observed celestial anomalies in the solar system can be explained as caused by the Hubble expansion of the universe.

Contemplation and Calculation: The Universe Discovered.

ERIC Educational Resources Information Center

Solovyov, Yury

1992-01-01

Discusses how early notions about celestial mechanics were restructured, one by one, involving the following concepts: the celestial sphere and its rotation; the spherical earth; planetary motion; and models for the solar system initiated by Eudoxus, Hipparchus, Ptolemy, and Copernicus. (JJK)

Celestial Navigation

ERIC Educational Resources Information Center

Rosenkrantz, Kurt

2005-01-01

In the unit described in this article, students discover the main principles of navigation, build tools to observe celestial bodies, and apply their new skills to finding their position on Earth. Along the way students see how science, mathematics, technology, and history are intertwined.

Multicamera polarized vision for the orientation with the skylight polarization patterns

NASA Astrophysics Data System (ADS)

Fan, Chen; Hu, Xiaoping; He, Xiaofeng; Zhang, Lilian; Wang, Yujie

2018-04-01

A robust orientation algorithm based on the skylight polarization patterns for the urban ground vehicle is presented. We present the orientation model with the Rayleigh scattering and propose the robust orientation algorithm with the total least square. The proposed algorithm can utilize the whole sky area polarization patterns for realizing a more robust and accurate orientation. To enhance the algorithm's robustness in the urban environment, we develop a real-time method that uses the gradient of the degree of the polarization to remove the obstacles in the polarization image. In addition, our algorithm can solve the ambiguity problem of the polarized orientation without any other sensors. We also conduct a static rotating and a dynamic car experiments to evaluate the algorithm. The results demonstrate that our proposed algorithm can provide an accurate orientation estimation for the ground vehicle in the open and urban environments-the root-mean-square error in the static experiment is 0.28 deg and in the dynamic experiment is 0.81 deg. Finally, we discuss insights gained with respect to further work in optics and robotics.

The segment polarity network is a robust developmental module

NASA Astrophysics Data System (ADS)

von Dassow, George; Meir, Eli; Munro, Edwin M.; Odell, Garrett M.

2000-07-01

All insects possess homologous segments, but segment specification differs radically among insect orders. In Drosophila, maternal morphogens control the patterned activation of gap genes, which encode transcriptional regulators that shape the patterned expression of pair-rule genes. This patterning cascade takes place before cellularization. Pair-rule gene products subsequently `imprint' segment polarity genes with reiterated patterns, thus defining the primordial segments. This mechanism must be greatly modified in insect groups in which many segments emerge only after cellularization. In beetles and parasitic wasps, for instance, pair-rule homologues are expressed in patterns consistent with roles during segmentation, but these patterns emerge within cellular fields. In contrast, although in locusts pair-rule homologues may not control segmentation, some segment polarity genes and their interactions are conserved. Perhaps segmentation is modular, with each module autonomously expressing a characteristic intrinsic behaviour in response to transient stimuli. If so, evolution could rearrange inputs to modules without changing their intrinsic behaviours. Here we suggest, using computer simulations, that the Drosophila segment polarity genes constitute such a module, and that this module is resistant to variations in the kinetic constants that govern its behaviour.

Celestial Pole Offsets: Conversion From (dX, dY) to (d(psi), d(epsilon). Version 3

DTIC Science & Technology

2005-05-01

observed angular offset of the celestial pole from its modelled position, expressed in terms of changes in ecliptic longitude and obliquity . These...the mean obliquity of the ecliptic of date (≈ J2000.0). As the celestial pole precesses farther from the ICRS Z-axis, two effects must be accounted for...to only a few significant digits. With dX ′ and dY ′ in hand we compute dψ = dX ′/ sin ² d² = dY ′ (8) where ² is the mean obliquity of the ecliptic

On the Origin of Rotation of a Celestial Body

NASA Astrophysics Data System (ADS)

Vujičić, V. A.

1988-03-01

The differential equations of the self-rotation of a celestial body have been evaluated. From an integral of these equations a formula for angular velocity of the celestial body was obtained. This formula after being applied to the rotation of the Sun and of the Earth gives, respectively, the following angular velocity ranges: 0.588×10-6<ω<18, 187×10-6 and 0.7533×10-5<ω<12,4266×10-5. These are up to three times narrower than those previously obtained by Savić and Kašanin [1].

Re-calibration of the magnetic compass in hand-raised European robins (Erithacus rubecula)

PubMed Central

Alert, Bianca; Michalik, Andreas; Thiele, Nadine; Bottesch, Michael; Mouritsen, Henrik

2015-01-01

Migratory birds can use a variety of environmental cues for orientation. A primary calibration between the celestial and magnetic compasses seems to be fundamental prior to a bird’s first autumn migration. Releasing hand-raised or rescued young birds back into the wild might therefore be a problem because they might not have established a functional orientation system during their first calendar year. Here, we test whether hand-raised European robins that did not develop any functional compass before or during their first autumn migration could relearn to orient if they were exposed to natural celestial cues during the subsequent winter and spring. When tested in the geomagnetic field without access to celestial cues, these birds could orient in their species-specific spring migratory direction. In contrast, control birds that were deprived of any natural celestial cues throughout remained unable to orient. Our experiments suggest that European robins are still capable of establishing a functional orientation system after their first autumn. Although the external reference remains speculative, most likely, natural celestial cues enabled our birds to calibrate their magnetic compass. Our data suggest that avian compass systems are more flexible than previously believed and have implications for the release of hand-reared migratory birds. PMID:26388258

The astronomy of Andean myth: The history of a cosmology

NASA Astrophysics Data System (ADS)

Sullivan, William F.

It is shown that Andean myth, on one level, represents a technical language recording astronomical observations of precession and, at the same time, an historical record of simultaneous social and celestial transformations. Topographic and architectural terms of Andean myth are interpreted as a metaphor for the organization of and locations on the celestial sphere. Via ethoastronomical date, mythical animals are identified as stars and placed on the celestial sphere according to their topographical location. Tested in the planetarium, these arrays generate cluster of dates - 200 B.C. and 650 A.D. Analysis of the names of Wiraqocha and Manco Capac indicates they represent Saturn and Jupiter and that their mythical meeting represents their conjunction in 650 A.D. The astronomy of Andean myth is then used as an historical tool to examine how the Andean priest-astronomers recorded the simultaneous creation of the avllu and of this distinctive astronomical system about 200 B.C. The idea that the agricultural avllu, with its double descent system stressing the importance of paternity, represents a transformation of society from an earlier matrilineal/horticultural era is examined in light of the sexual imagery employed in myth. Wiraqocha's androgyny and the division of the celestial sphere into male (ecliptic) and female (celestial equator = earth) are interpreted as cosmological validations of the new social structure.

An evaluation of skylight polarization patterns for navigation.

PubMed

Ma, Tao; Hu, Xiaoping; Zhang, Lilian; Lian, Junxiang; He, Xiaofeng; Wang, Yujie; Xian, Zhiwen

2015-03-10

Skylight polarization provides a significant navigation cue for certain polarization-sensitive animals. However, the precision of the angle of polarization (AOP) of skylight for vehicle orientation is not clear. An evaluation of AOP must be performed before it is utilized. This paper reports an evaluation of AOP of skylight by measuring the skylight polarization patterns of clear and cloudy skies using a full-sky imaging polarimetry system. AOP measurements of skylight are compared with the pattern calculated by the single-scattering Rayleigh model and these differences are quantified. The relationship between the degree of polarization (DOP) and the deviation of AOP of skylight is thoroughly studied. Based on these, a solar meridian extracted method is presented. The results of experiments reveal that the DOP is a key parameter to indicate the accuracy of AOP measurements, and all the output solar meridian orientations extracted by our method in both clear and cloudy skies can achieve a high accuracy for vehicle orientation.

An Evaluation of Skylight Polarization Patterns for Navigation

PubMed Central

Ma, Tao; Hu, Xiaoping; Zhang, Lilian; Lian, Junxiang; He, Xiaofeng; Wang, Yujie; Xian, Zhiwen

2015-01-01

Skylight polarization provides a significant navigation cue for certain polarization-sensitive animals. However, the precision of the angle of polarization (AOP) of skylight for vehicle orientation is not clear. An evaluation of AOP must be performed before it is utilized. This paper reports an evaluation of AOP of skylight by measuring the skylight polarization patterns of clear and cloudy skies using a full-sky imaging polarimetry system. AOP measurements of skylight are compared with the pattern calculated by the single-scattering Rayleigh model and these differences are quantified. The relationship between the degree of polarization (DOP) and the deviation of AOP of skylight is thoroughly studied. Based on these, a solar meridian extracted method is presented. The results of experiments reveal that the DOP is a key parameter to indicate the accuracy of AOP measurements, and all the output solar meridian orientations extracted by our method in both clear and cloudy skies can achieve a high accuracy for vehicle orientation. PMID:25763652

Angular and Polarization Response of Multimode Sensors with Resistive-Grid Absorbers

NASA Technical Reports Server (NTRS)

Kusaka, Akito; Wollack, Edward J.; Stevenson, Thomas R.

2014-01-01

High sensitivity receiver systems with near ideal polarization sensitivity are highly desirable for development of millimeter and sub-millimeter radio astronomy. Multimoded bolometers provide a unique solution to achieve such sensitivity, for which hundreds of single-mode sensors would otherwise be required. The primary concern in employing such multimoded sensors for polarimetery is the control of the polarization systematics. In this paper, we examine the angular- and polarization- dependent absorption pattern of a thin resistive grid or membrane, which models an absorber used for a multimoded bolometer. The result shows that a freestanding thin resistive absorber with a surface resistivity of eta/2, where eta is the impedance of free space, attains a beam pattern with equal E- and H-plane responses, leading to zero cross polarization. For a resistive-grid absorber, the condition is met when a pair of grids is positioned orthogonal to each other and both have a resistivity of eta/2. When a reflective backshort termination is employed to improve absorption efficiency, the cross-polar level can be suppressed below -30 dB if acceptance angle of the sensor is limited to < or approx. 60deg. The small cross-polar systematics have even-parity patterns and do not contaminate the measurements of odd-parity polarization patterns, for which many of recent instruments for cosmic microwave background are designed. Underlying symmetry that suppresses these cross-polar systematics is discussed in detail. The estimates and formalism provided in this paper offer key tools in the design consideration of the instruments using the multimoded polarimeters.

Design and Calibration of a Novel Bio-Inspired Pixelated Polarized Light Compass.

PubMed

Han, Guoliang; Hu, Xiaoping; Lian, Junxiang; He, Xiaofeng; Zhang, Lilian; Wang, Yujie; Dong, Fengliang

2017-11-14

Animals, such as Savannah sparrows and North American monarch butterflies, are able to obtain compass information from skylight polarization patterns to help them navigate effectively and robustly. Inspired by excellent navigation ability of animals, this paper proposes a novel image-based polarized light compass, which has the advantages of having a small size and being light weight. Firstly, the polarized light compass, which is composed of a Charge Coupled Device (CCD) camera, a pixelated polarizer array and a wide-angle lens, is introduced. Secondly, the measurement method of a skylight polarization pattern and the orientation method based on a single scattering Rayleigh model are presented. Thirdly, the error model of the sensor, mainly including the response error of CCD pixels and the installation error of the pixelated polarizer, is established. A calibration method based on iterative least squares estimation is proposed. In the outdoor environment, the skylight polarization pattern can be measured in real time by our sensor. The orientation accuracy of the sensor increases with the decrease of the solar elevation angle, and the standard deviation of orientation error is 0 . 15 ∘ at sunset. Results of outdoor experiments show that the proposed polarization navigation sensor can be used for outdoor autonomous navigation.

Design and Calibration of a Novel Bio-Inspired Pixelated Polarized Light Compass

PubMed Central

Hu, Xiaoping; Lian, Junxiang; He, Xiaofeng; Zhang, Lilian; Wang, Yujie; Dong, Fengliang

2017-01-01

Animals, such as Savannah sparrows and North American monarch butterflies, are able to obtain compass information from skylight polarization patterns to help them navigate effectively and robustly. Inspired by excellent navigation ability of animals, this paper proposes a novel image-based polarized light compass, which has the advantages of having a small size and being light weight. Firstly, the polarized light compass, which is composed of a Charge Coupled Device (CCD) camera, a pixelated polarizer array and a wide-angle lens, is introduced. Secondly, the measurement method of a skylight polarization pattern and the orientation method based on a single scattering Rayleigh model are presented. Thirdly, the error model of the sensor, mainly including the response error of CCD pixels and the installation error of the pixelated polarizer, is established. A calibration method based on iterative least squares estimation is proposed. In the outdoor environment, the skylight polarization pattern can be measured in real time by our sensor. The orientation accuracy of the sensor increases with the decrease of the solar elevation angle, and the standard deviation of orientation error is 0.15∘ at sunset. Results of outdoor experiments show that the proposed polarization navigation sensor can be used for outdoor autonomous navigation. PMID:29135927

A recovery principle provides insight into auxin pattern control in the Arabidopsis root

PubMed Central

Moore, Simon; Liu, Junli; Zhang, Xiaoxian; Lindsey, Keith

2017-01-01

Regulated auxin patterning provides a key mechanism for controlling root growth and development. We have developed a data-driven mechanistic model using realistic root geometry and formulated a principle to theoretically investigate quantitative auxin pattern recovery following auxin transport perturbation. This principle reveals that auxin patterning is potentially controlled by multiple combinations of interlinked levels and localisation of influx and efflux carriers. We demonstrate that (1) when efflux carriers maintain polarity but change levels, maintaining the same auxin pattern requires non-uniform and polar distribution of influx carriers; (2) the emergence of the same auxin pattern, from different levels of influx carriers with the same nonpolar localisation, requires simultaneous modulation of efflux carrier level and polarity; and (3) multiple patterns of influx and efflux carriers for maintaining an auxin pattern do not have spatially proportional correlation. This reveals that auxin pattern formation requires coordination between influx and efflux carriers. We further show that the model makes various predictions that can be experimentally validated. PMID:28220889

Novel On-wafer Radiation Pattern Measurement Technique for MEMS Actuator Based Reconfigurable Patch Antennas

NASA Technical Reports Server (NTRS)

Simons, Rainee N.

2002-01-01

The paper presents a novel on-wafer, antenna far field pattern measurement technique for microelectromechanical systems (MEMS) based reconfigurable patch antennas. The measurement technique significantly reduces the time and the cost associated with the characterization of printed antennas, fabricated on a semiconductor wafer or dielectric substrate. To measure the radiation patterns, the RF probe station is modified to accommodate an open-ended rectangular waveguide as the rotating linearly polarized sampling antenna. The open-ended waveguide is attached through a coaxial rotary joint to a Plexiglas(Trademark) arm and is driven along an arc by a stepper motor. Thus, the spinning open-ended waveguide can sample the relative field intensity of the patch as a function of the angle from bore sight. The experimental results include the measured linearly polarized and circularly polarized radiation patterns for MEMS-based frequency reconfigurable rectangular and polarization reconfigurable nearly square patch antennas, respectively.

The International Celestial Reference Frame (ICRF) and the Relationship Between Frames

NASA Technical Reports Server (NTRS)

Ma, Chopo

2000-01-01

The International Celestial Reference Frame (ICRF), a catalog of VLBI source positions, is now the basis for astrometry and geodesy. Its construction and extension/maintenance will be discussed as well as the relationship of the ICRF, ITRF, and EOP/nutation.

Celestial mechanics with geometric algebra

NASA Technical Reports Server (NTRS)

Hestenes, D.

1983-01-01

Geometric algebra is introduced as a general tool for Celestial Mechanics. A general method for handling finite rotations and rotational kinematics is presented. The constants of Kepler motion are derived and manipulated in a new way. A new spinor formulation of perturbation theory is developed.

A CMB polarization primer

NASA Astrophysics Data System (ADS)

Hu, Wayne; White, Martin

1997-10-01

We present a pedagogical and phenomenological introduction to the study of cosmic microwave background (CMB) polarization to build intuition about the prospects and challenges facing its detection. Thomson scattering of temperature anisotropies on the last scattering surface generates a linear polarization pattern on the sky that can be simply read off from their quadrupole moments. These in turn correspond directly to the fundamental scalar (compressional), vector (vortical), and tensor (gravitational wave) modes of cosmological perturbations. We explain the origin and phenomenology of the geometric distinction between these patterns in terms of the so-called electric and magnetic parity modes, as well as their correlation with the temperature pattern. By its isolation of the last scattering surface and the various perturbation modes, the polarization provides unique information for the phenomenological reconstruction of the cosmological model. Finally we comment on the comparison of theory with experimental data and prospects for the future detection of CMB polarization.

Unusual polarization patterns in flat epitaxial ferroelectric nanoparticles

NASA Astrophysics Data System (ADS)

Naumov, Ivan; Bratkovsky, Alexandr

2009-03-01

We investigate the effects of a lattice misfit strain on a ground state and polarization patterns in flat perovskite nanoparticles (nanoislands of BaTiO3 and PbZr0.5Ti0.5O3) with the use of an ab-initio derived effective Hamiltonian. We show that the strain strongly controls the balance between the depolarizing field and the polarization anizotropy in determining the equilibrium polarization patterns. Compressive strain favors 180 ^0 stripe/tweed domains while a tensile strain leads to in-plane vortex formation, with the unusual intermediate phase (s) where both ordering motifs coexist [1]. The results may allow to explain contradictions in recent experimental data for ferroelectric nanoparticles. [1] Ivan Naumov and Alexander M. Bratkovsky, Phys. Rev. Lett. 101, 107601 (2008).

High-Isolation Low Cross-Polarization Phased-Array Antenna for MPAR Application

NASA Astrophysics Data System (ADS)

Saeidi-Manesh, Hadi; Karimkashi, Shaya; Zhang, Guifu; Doviak, Richard J.

2017-12-01

The design and analysis of 12 × 12-element planar array of a dual-polarized aperture-coupled microstrip patch antenna operating in the frequency band of 2.7 GHz to 3.0 GHz for multifunction applications are presented. High-isolation between horizontal and vertical polarization ports and low cross-polarization are achieved through an aperture-coupled feed. The reflection coefficient and the isolation of horizontal and vertical ports at different scan angles are examined. The array antenna is fabricated and its radiation patterns are measured in the far-field and near-field chambers. The embedded element pattern of designed element is measured in the near-field chamber and is used for calculating the array scanning radiation pattern.

A preliminary estimate of the EUVE cumulative distribution of exposure time on the unit sphere. [Extreme Ultra-Violet Explorer

NASA Technical Reports Server (NTRS)

Tang, C. C. H.

1984-01-01

A preliminary study of an all-sky coverage of the EUVE mission is given. Algorithms are provided to compute the exposure of the celestial sphere under the spinning telescopes, taking into account that during part of the exposure time the telescopes are blocked by the earth. The algorithms are used to give an estimate of exposure time at different ecliptic latitudes as a function of the angle of field of view of the telescope. Sample coverage patterns are also given for a 6-month mission.

Bifocal Fresnel Lens Based on the Polarization-Sensitive Metasurface

NASA Astrophysics Data System (ADS)

Markovich, Hen; Filonov, Dmitrii; Shishkin, Ivan; Ginzburg, Pavel

2018-05-01

Thin structured surfaces allow flexible control over propagation of electromagnetic waves. Focusing and polarization state analysis are among functions, required for effective manipulation of radiation. Here a polarization sensitive Fresnel zone plate lens is proposed and experimentally demonstrated for GHz spectral range. Two spatially separated focal spots for orthogonal polarizations are obtained by designing metasurface pattern, made of overlapping tightly packed cross and rod shaped antennas with a strong polarization selectivity. Optimized subwavelength pattern allows multiplexing two different lenses with low polarization crosstalk on the same substrate and provides a control over focal spots of the lens only by changing of the polarization state of the incident wave. More than a wavelength separation between the focal spots was demonstrated for a broad spectral range, covering half a decade in frequency. The proposed concept could be straightforwardly extended for THz and visible spectra, where polarization-sensitive elements utilize localized plasmon resonance phenomenon.

It All Depends on Your Attitude.

ERIC Educational Resources Information Center

Kastner, Bernice

1992-01-01

Presents six learning exercises that introduce students to the mathematics used to control and track spacecraft attitude. Describes the geocentric system used for Earthbound location and navigation, the celestial sphere, the spacecraft-based celestial system, time-dependent angles, observer-fixed coordinate axes, and spacecraft rotational axes.…

Students' Development of Astronomy Concepts across Time

NASA Astrophysics Data System (ADS)

Plummer, Julia

Students in Grades 1, 3, and 8 (N = 60) were interviewed while using a planetarium-like setting that allowed the students to demonstrate their ideas about apparent celestial motion both verbally and with their own motions. Though the older students were generally more accurate in many conceptual areas compared with the younger students, in several areas, the eighth-grade students showed no improvement over the third-grade students. The use of kinesthetic learning techniques in a planetarium program was also explored as a method to improve understanding of celestial motion. Pre- and postinterviews were conducted with participants from seven classes of first- and second-grade students (N = 63). Students showed significant improvement in all areas of apparent celestial motion covered by the planetarium program and surpassed the middle school students' understanding of these concepts in most areas. Based on the results of these studies, a learning progression was developed describing how children may progress through successively more complex ways of understanding apparent celestial motion across elementary grades.

The Contribution of Galactic Free-Free Emission to Anistropies in the Cosmic Microwave Background Found by the Saskatoon Experiment

NASA Astrophysics Data System (ADS)

Simonetti, John H.; Dennison, Brian; Topasna, Gregory A.

1996-02-01

We made a sensitive, wide-field H alpha image of the north celestial polar region. Using this image, we constrain the contribution of irregularities in interstellar free-free emission to the degree-scale anisotropies in the cosmic microwave background detected in recent observations at Saskatoon by the Princeton group. The analysis of the H alpha image mimics the Saskatoon data analysis: the resulting signal is the strength of irregularities sampled with the Saskatoon beam (i.e., degree-scale) along the 85 deg declination circle. We found no such irregularities that could be attributed to H alpha emission. The implied upper bound on the rms variation in free-free brightness temperature is less than 4.6 mu K at 27.5 GHz. The observed cosmic microwave background anisotropies are much larger. Therefore, the contribution of irregularities in interstellar free-free emission to the observed anisotropies is negligible.

Development of a high-precision selenodetic coordinate system for the physical surface of the Moon based on LED beacons on its surface

NASA Astrophysics Data System (ADS)

Shirenin, A. M.; Mazurova, E. M.; Bagrov, A. V.

2016-11-01

The paper presents a mathematical algorithm for processing an array of angular measurements of light beacons on images of the lunar surface onboard a polar artificial lunar satellite (PALS) during the Luna-Glob mission and coordinate-time referencing of the PALS for the development of reference selenocentric coordinate systems. The algorithm makes it possible to obtain angular positions of point light beacons located on the surface of the Moon in selenocentric celestial coordinates. The operation of measurement systems that determine the position and orientation of the PALS during its active existence have been numerically simulated. Recommendations have been made for the optimal use of different types of measurements, including ground radio trajectory measurements, navigational star sensors based on the onboard star catalog, gyroscopic orientation systems, and space videos of the lunar surface.

The astronomical data base and retrieval system at NASA

NASA Technical Reports Server (NTRS)

Mead, J. M.; Nagy, T. A.; Hill, R. S.; Warren, W. H., Jr.

1982-01-01

More than 250 machine-readable catalogs of stars and extended celestial objects are now available at the NASA/Goddard Space Flight Center (GSFC) as the result of over a decade of catalog acquisition, verification and documentation. Retrieval programs are described which permit the user to obtain from a remote terminal bibliographical listings for stars; to find all celestial objects from a given list that are within a defined angular separation from each object in another list; to plot celestial objects on overlays for sky survey plate areas; and to search selected catalogs for objects by criteria of position, identification number, magnitude or spectral type.

Background Oriented Schlieren Using Celestial Objects

NASA Technical Reports Server (NTRS)

Haering, Edward, A., Jr. (Inventor); Hill, Michael A (Inventor)

2017-01-01

The present invention is a system and method of visualizing fluid flow around an object, such as an aircraft or wind turbine, by aligning the object between an imaging system and a celestial object having a speckled background, taking images, and comparing those images to obtain fluid flow visualization.

Spottier targets are less attractive to tabanid flies: on the tabanid-repellency of spotty fur patterns.

PubMed

Blaho, Miklos; Egri, Adam; Bahidszki, Lea; Kriska, Gyorgy; Hegedus, Ramon; Akesson, Susanne; Horvath, Gabor

2012-01-01

During blood-sucking, female members of the family Tabanidae transmit pathogens of serious diseases and annoy their host animals so strongly that they cannot graze, thus the health of the hosts is drastically reduced. Consequently, a tabanid-resistant coat with appropriate brightness, colour and pattern is advantageous for the host. Spotty coats are widespread among mammals, especially in cattle (Bos primigenius). In field experiments we studied the influence of the size and number of spots on the attractiveness of test surfaces to tabanids that are attracted to linearly polarized light. We measured the reflection-polarization characteristics of living cattle, spotty cattle coats and the used test surfaces. We show here that the smaller and the more numerous the spots, the less attractive the target (host) is to tabanids. We demonstrate that the attractiveness of spotty patterns to tabanids is also reduced if the target exhibits spottiness only in the angle of polarization pattern, while being homogeneous grey with a constant high degree of polarization. Tabanid flies respond strongly to linearly polarized light, and we show that bright and dark parts of cattle coats reflect light with different degrees and angles of polarization that in combination with dark spots on a bright coat surface disrupt the attractiveness to tabanids. This could be one of the possible evolutionary benefits that explains why spotty coat patterns are so widespread in mammals, especially in ungulates, many species of which are tabanid hosts.

Spottier Targets Are Less Attractive to Tabanid Flies: On the Tabanid-Repellency of Spotty Fur Patterns

PubMed Central

Blaho, Miklos; Egri, Adam; Bahidszki, Lea; Kriska, Gyorgy; Hegedus, Ramon; Åkesson, Susanne; Horvath, Gabor

2012-01-01

During blood-sucking, female members of the family Tabanidae transmit pathogens of serious diseases and annoy their host animals so strongly that they cannot graze, thus the health of the hosts is drastically reduced. Consequently, a tabanid-resistant coat with appropriate brightness, colour and pattern is advantageous for the host. Spotty coats are widespread among mammals, especially in cattle (Bos primigenius). In field experiments we studied the influence of the size and number of spots on the attractiveness of test surfaces to tabanids that are attracted to linearly polarized light. We measured the reflection-polarization characteristics of living cattle, spotty cattle coats and the used test surfaces. We show here that the smaller and the more numerous the spots, the less attractive the target (host) is to tabanids. We demonstrate that the attractiveness of spotty patterns to tabanids is also reduced if the target exhibits spottiness only in the angle of polarization pattern, while being homogeneous grey with a constant high degree of polarization. Tabanid flies respond strongly to linearly polarized light, and we show that bright and dark parts of cattle coats reflect light with different degrees and angles of polarization that in combination with dark spots on a bright coat surface disrupt the attractiveness to tabanids. This could be one of the possible evolutionary benefits that explains why spotty coat patterns are so widespread in mammals, especially in ungulates, many species of which are tabanid hosts. PMID:22876282

Anti-parallel polarization switching in a triglycine sulfate organic ferroelectric insulator: The role of surface charges

NASA Astrophysics Data System (ADS)

Ma, He; Wu, Zhuangchun; Peng, Dongwen; Wang, Yaojin; Wang, Yiping; Yang, Ying; Yuan, Guoliang

2018-04-01

Four consecutive ferroelectric polarization switchings and an abnormal ring-like domain pattern can be introduced by a single tip bias of a piezoresponse force microscope in the (010) triglycine sulfate (TGS) crystal. The external electric field anti-parallel to the original polarization induces the first polarization switching; however, the surface charges of TGS can move toward the tip location and induce the second polarization switching once the tip bias is removed. The two switchings allow a ring-like pattern composed of the central domain with downward polarization and the outer domain with upward polarization. Once the two domains disappear gradually as a result of depolarization, the other two polarization switchings occur one by one at the TGS where the tip contacts. However, the backswitching phenomenon does not occur when the external electric field is parallel to the original polarization. These results can be explained according to the surface charges instead of the charges injected inside.

Polarity-inverted lateral overgrowth and selective wet-etching and regrowth (PILOSWER) of GaN.

PubMed

Jang, Dongsoo; Jue, Miyeon; Kim, Donghoi; Kim, Hwa Seob; Lee, Hyunkyu; Kim, Chinkyo

2018-03-07

On an SiO 2 -patterned c-plane sapphire substrate, GaN domains were grown with their polarity controlled in accordance with the pattern. While N-polar GaN was grown on hexagonally arranged circular openings, Ga-polar GaN was laterally overgrown on mask regions due to polarity inversion occurring at the boundary of the circular openings. After etching of N-polar GaN on the circular openings by H 3 PO 4 , this template was coated with 40-nm Si by sputtering and was slightly etched by KOH. After slight etching, a thin layer of Si left on the circular openings of sapphire,but not on GaN, was oxidized during thermal annealing and served as a dielectric mask during subsequent regrowth. Thus, the subsequent growth of GaN was made only on the existing Ga-polar GaN domains, not on the circular openings of the sapphire substrate. Transmission electron microscopy analysis revealed no sign of threading dislocations in this film. This approach may help fabricating an unholed and merged GaN film physically attached to but epitaxially separated from the SiO 2 -patterned sapphire.

Cosmic Microwave Background Polarization and Inflation

NASA Technical Reports Server (NTRS)

Chuss, David T.

2011-01-01

Measurements of the cosmic microwave background (CMB) offer a means to explore the universe at a very early epoch. Specifically, if the universe went through a brief period of exponential expansion called inflation as current data suggest, gravitational waves from this period would polarize the CMB in a specific pattern. At GSFC, we are currently working towards two experiments that work in concert to measure this polarization pattern in search of evidence for inflation. The Cosmology Large Angular Scale Surveyor (CLASS) will measure the polarization at frequencies between 40 and 150 GHz from the Atacama Desert in Chile. The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne experiment that will make similar measurements at frequencies between 200 and 600 GHz.

Inquiry and Astronomy: Preservice Teachers' Investigations of Celestial Motion

ERIC Educational Resources Information Center

Plummer, Julia D.; Zahm, Valerie M.; Rice, Rebecca

2010-01-01

This study investigated the impact of an open inquiry experience on elementary science methods students' understanding of celestial motion as well as the methods developed by students to answer their own research questions. Pre/post interviews and assessments were used to measure change in participants' understanding (N = 18). A qualitative…

Laplacean Ideology for Preliminary Orbit Determination and Moving Celestial Body Identification in Virtual Epoch

NASA Astrophysics Data System (ADS)

Bykov, O. P.

Any CCD frames with stars or galaxies or clusters and other images must be studied for a searching of moving celestial objects, namely asteroids, comets, artificial Earth satellites inside them. At Pulkovo Astronomical Observatory, new methods and software were elaborated to solve this problem.

The Mathematics of Go to Telescopes

ERIC Educational Resources Information Center

Teets, Donald

2007-01-01

This article presents the mathematics involved in finding and tracking celestial objects with an electronically controlled telescope. The essential idea in solving this problem is to choose several different coordinate systems that simplify the various motions of the earth and other celestial objects. These coordinate systems are then related by…

Solar system lithograph set for earth and space science

NASA Technical Reports Server (NTRS)

1995-01-01

A color lithographs of many of the celestial bodies within our solar system are contained in this educational set of materials. Printed on the back of each lithograph is information regarding the particular celestial body. A sheet with information listing NASA resources and electronic resources for education is included.

Global-scale tectonic patterns on Pluto

NASA Astrophysics Data System (ADS)

Matsuyama, I.; Keane, J. T.; Kamata, S.

2016-12-01

The New Horizons spacecraft revealed a global-scale tectonic pattern on the surface of Pluto which is presumably related to its formation and early evolution. Changes in the rotational and tidal potentials, expansion, and loading can generate stresses capable of producing global-scale tectonic patterns. The current alignment of Sputnik Planum with the tidal axis suggests a reorientation of Pluto relative to the rotation and tidal axes, or true polar wander. This reorientation can be driven by mass loading associated with Sputnik Planum. We developed a general theoretical formalism for the calculation of tectonic patterns due to a variety of process including true polar wander, loading, and expansion. The formalism is general enough to be applicable to non-axisymmetric loads. We illustrate that the observed global-scale tectonic pattern can be explained by stresses generated by true polar wander, Sputnik Planum loading, and expansion.

Pattern formation in a liquid-crystal light valve with feedback, including polarization, saturation, and internal threshold effects

NASA Astrophysics Data System (ADS)

Neubecker, R.; Oppo, G.-L.; Thuering, B.; Tschudi, T.

1995-07-01

The use of liquid-crystal light valves (LCLV's) as nonlinear elements in diffractive optical systems with feedback leads to the formation of a variety of optical patterns. The spectrum of possible spatial instabilities is shown to be even richer when the LCLV's capability for polarization modulation is utilized and internal threshold and saturation effects are considered. We derive a model for the feedback system based on a realistic description of the LCLV's internal function and coupling to a polarizer. Thresholds of pattern formation are compared to the common Kerr-type approximation and show transitions involving rolls, squares, hexagons, and tiled patterns. Numerical and experimental results confirm our theoretical predictions and unveil how patterns and their typical length scales can be easily controlled by changes of the parameters.

Polarity Control and Doping in Aluminum Gallium Nitride

DTIC Science & Technology

2013-06-01

cooled quartz tube and a radio frequency (RF-)induction heated SiC coated graphite susceptor. Growth temperatures of 500–1250°C can be attained. The...will be discussed in the following. Lateral polar structures used in Chapter 4 for second harmonic generation were patterned into microns-wide stripes ...lateral polar structures. The second step included the patterning of the AlN nucleation layer into periodic stripes or circles by lithography and

A plane-polar approach for far-field construction from near-field measurements. [of large space-craft antennas

NASA Technical Reports Server (NTRS)

Rahmat-Samii, Y.; Galindo-Israel, V.; Mittra, R.

1980-01-01

The planar configuration with a probe scanning a polar geometry is discussed with reference to its usefulness in the determination of a far field from near-field measurements. The accuracy of the method is verified numerically, using the concept of probe compensation as a vector deconvolution. Advantages of the Jacobi-Bessel series over the fast Fourier transforms for the plane-polar geometry are demonstrated. Finally, the far-field pattern of the Viking high gain antenna is constructed from the plane-polar near-field measured data and compared with the previously measured far-field pattern.

Anatomy and physiology of neurons with processes in the accessory medulla of the cockroach Leucophaea maderae.

PubMed

Loesel, R; Homberg, U

2001-10-15

The accessory medulla (AMe), a small neuropil in the insect optic lobe, has been proposed to serve a circadian pacemaker function analogous to the role of the suprachiasmatic nucleus in mammals. Building upon considerable knowledge of the circadian system of the cockroach Leucophaea maderae, we investigated the properties of AMe neurons in this insect with intracellular recordings combined with dye injections. Responses of neurons with processes in the AMe to visual stimuli, including stationary white light, moving objects, and polarized light were compared with the responses of adjacent medulla tangential neurons. Neurons with processes in the AMe and additional ramifications in the medulla strongly responded to stationary light stimuli and might, therefore, be part of photic entrainment pathways to the clock. Accessory medulla neurons lacking significant processes in the medulla but with projections to the midbrain or to the contralateral optic lobe, in contrast, responded weakly or not at all to light and, thus, seem to be part of the clock's output pathway. Two types of commissural neurons with tangential arborizations in both medullae were sensitive to polarized light, suggesting a role of these neurons in celestial navigation. Sidebranches in the AMae of one of the two cell types are discussed with respect to a possible involvement of the AMe in polarization vision. Finally, neurons responding to movement stimuli did not arborize in the AMe. The results show that the AMe receives photic input and support a role of this neuropil in circadian timekeeping functions. Copyright 2001 Wiley-Liss, Inc.

True polar wander on Europa from global-scale small-circle depressions.

PubMed

Schenk, Paul; Matsuyama, Isamu; Nimmo, Francis

2008-05-15

The tectonic patterns and stress history of Europa are exceedingly complex and many large-scale features remain unexplained. True polar wander, involving reorientation of Europa's floating outer ice shell about the tidal axis with Jupiter, has been proposed as a possible explanation for some of the features. This mechanism is possible if the icy shell is latitudinally variable in thickness and decoupled from the rocky interior. It would impose high stress levels on the shell, leading to predictable fracture patterns. No satisfactory match to global-scale features has hitherto been found for polar wander stress patterns. Here we describe broad arcuate troughs and depressions on Europa that do not fit other proposed stress mechanisms in their current position. Using imaging from three spacecraft, we have mapped two global-scale organized concentric antipodal sets of arcuate troughs up to hundreds of kilometres long and 300 m to approximately 1.5 km deep. An excellent match to these features is found with stresses caused by an episode of approximately 80 degrees true polar wander. These depressions also appear to be geographically related to other large-scale bright and dark lineaments, suggesting that many of Europa's tectonic patterns may also be related to true polar wander.

Did a Comet Deliver the Chelyabinsk Meteorite?

NASA Astrophysics Data System (ADS)

Gladysheva, O. G.

2017-09-01

An explosion of a celestial body occurred on the fifteenth of February, 2013, near Chelyabinsk (Russia). The explosive energy was determined as 500 kt of TNT, on the basis of which the mass of the bolide was estimated at 107 kg, and its diameter at 19 m [1]. Fragments of the meteorite, such as LL5/S4-WO type ordinary chondrite [2] with a total mass only of 2•103 kg, fell to the earth's surface [3]. Here, we will demonstrate that the deficit of the celestial body's mass can be explained by the arrival of the Chelyabinsk chondrite on Earth by a significantly more massive but fragile ice-bearing celestial body.

UBVRI PHOTOMETRIC STANDARD STARS AROUND THE CELESTIAL EQUATOR: UPDATES AND ADDITIONS

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

Landolt, Arlo U.

2009-05-15

New broadband UBVRI photoelectric observations on the Johnson-Kron-Cousins photometric system have been made of 202 stars around the sky, and centered at the celestial equator. These stars constitute both an update of and additions to a previously published list of equatorial photometric standard stars. The list is capable of providing, for both celestial hemispheres, an internally consistent homogeneous broadband standard photometric system around the sky. When these new measurements are included with those previously published by Landolt (1992), the entire list of standard stars in this paper encompasses the magnitude range 8.90 < V < 16.30, and the color indexmore » range -0.35 < (B - V) < +2.30.« less

AstroNavigation: Freely-available Online Instruction for Performing a Sight Reduction

NASA Astrophysics Data System (ADS)

Gessner Stewart, Susan; Grundstrom, Erika; Caudel, Dave

2015-08-01

A reliable method of obtaining your geographic location from observations of celestial bodies is globally available. This online learning module, developed through a collaboration between Vanderbilt University and the U.S. Naval Observatory, serves to address the need for freely-available comprehensive instruction in celestial navigation online. Specifically targeted are the steps of preforming a sight reduction to obtain a terrestrial position using this technique. Difficult concepts such as plotting on a navigational chart and the complexities of using navigation publications are facilitated through this online content delivery, rooted in effective course design principles. There is good potential in using celestial navigation as a tool for stimulating interest in astronomy given its resourcefulness and accessibility.

Sky light polarization detection with linear polarizer triplet in light field camera inspired by insect vision.

PubMed

Zhang, Wenjing; Cao, Yu; Zhang, Xuanzhe; Liu, Zejin

2015-10-20

Stable information of a sky light polarization pattern can be used for navigation with various advantages such as better performance of anti-interference, no "error cumulative effect," and so on. But the existing method of sky light polarization measurement is weak in real-time performance or with a complex system. Inspired by the navigational capability of a Cataglyphis with its compound eyes, we introduce a new approach to acquire the all-sky image under different polarization directions with one camera and without a rotating polarizer, so as to detect the polarization pattern across the full sky in a single snapshot. Our system is based on a handheld light field camera with a wide-angle lens and a triplet linear polarizer placed over its aperture stop. Experimental results agree with the theoretical predictions. Not only real-time detection but simple and costless architecture demonstrates the superiority of the approach proposed in this paper.

Polar lipid composition of a new halobacterium

NASA Technical Reports Server (NTRS)

Tindall, B. J.; Tomlinson, G. A.; Hochstein, L. I.

1987-01-01

Investigations of the polar lipid composition of a new aerobic, extremely halophilic aracheabacterium capable of nitrate reduction have shown that this organism contains two previously unknown phospholycolipids derived from diphytanyl glycerol diethers. Comparison of the lipid pattern from this new isolate with other known strains indicate that this organism is novel. On the basis of the unique polar lipid pattern it can be concluded that this organism represents a new taxon, at least at the species level.

Microstrip Antenna Generates Circularly Polarized Beam

NASA Technical Reports Server (NTRS)

Huang, J.

1986-01-01

Circular microstrip antenna excited with higher order transverse magnetic (TM) modes generates circularly polarized, conical radiation patterns. Found both theoretically and experimentally that peak direction of radiation pattern is varied within wide angular range by combination of mode selection and loading substrate with materials of different dielectric constants.

Determination of meteor flux distribution over the celestial sphere

NASA Technical Reports Server (NTRS)

Andreev, V. V.; Belkovich, O. I.; Filimonova, T. K.; Sidorov, V. V.

1992-01-01

A new method of determination of meteor flux density distribution over the celestial sphere is discussed. The flux density was derived from observations by radar together with measurements of angles of arrival of radio waves reflected from meteor trails. The role of small meteor showers over the sporadic background is shown.

A Study of Planetarium Effectiveness on Student Achievement, Perceptions and Retention.

ERIC Educational Resources Information Center

Ridky, Robert William

Reported is a study to determine the effect of planetarium instruction in terms of immediate attainment, attitude, and retention in the teaching of selected celestial motion and non-celestial motion concepts, when contrasted to or combined with the inquiry activities utilized by the nationally developed science curricula. Observations were made on…

The consistency of the current conventional celestial and terrestrial reference frames and the conventional EOP series

NASA Astrophysics Data System (ADS)

Heinkelmann, R.; Belda-Palazon, S.; Ferrándiz, J.; Schuh, H.

2015-08-01

For applications in Earth sciences, navigation, and astronomy the celestial (ICRF) and terrestrial (ITRF) reference frames as well as the orientation among them, the Earth orientation parameters (EOP), have to be consistent at the level of 1 mm and 0.1 mm/yr (GGOS recommendations). We assess the effect of unmodelled geophysical signals in the regularized coordinates and the sensitivity with respect to different a priori EOP and celestial reference frames. The EOP are determined using the same VLBI data but with station coordinates fixed on different TRFs. The conclusion is that within the time span of data incorporated into ITRF2008 (Altamimi, et al., 2011) the ITRF2008 and the IERS 08 C04 are consistent. This consistency involves that non-linear station motion such as unmodelled geophysical signals partly affect the IERS 08 C04 EOP. There are small but not negligible inconsistencies between the conventional celestial reference frame, ICRF2 (Fey, et al., 2009), the ITRF2008 and the conventional EOP that are quantified by comparing VTRF2008 (Böckmann, et al., 2010) and ITRF2008.

PolarHub: A Global Hub for Polar Data Discovery

NASA Astrophysics Data System (ADS)

Li, W.

2014-12-01

This paper reports the outcome of a NSF project in developing a large-scale web crawler PolarHub to discover automatically the distributed polar dataset in the format of OGC web services (OWS) in the cyberspace. PolarHub is a machine robot; its goal is to visit as many webpages as possible to find those containing information about polar OWS, extract this information and store it into the backend data repository. This is a very challenging task given huge data volume of webpages on the Web. Three unique features was introduced in PolarHub to make it distinctive from earlier crawler solutions: (1) a multi-task, multi-user, multi-thread support to the crawling tasks; (2) an extensive use of thread pool and Data Access Object (DAO) design patterns to separate persistent data storage and business logic to achieve high extendibility of the crawler tool; (3) a pattern-matching based customizable crawling algorithm to support discovery of multi-type geospatial web services; and (4) a universal and portable client-server communication mechanism combining a server-push and client pull strategies for enhanced asynchronous processing. A series of experiments were conducted to identify the impact of crawling parameters to the overall system performance. The geographical distribution pattern of all PolarHub identified services is also demonstrated. We expect this work to make a major contribution to the field of geospatial information retrieval and geospatial interoperability, to bridge the gap between data provider and data consumer, and to accelerate polar science by enhancing the accessibility and reusability of adequate polar data.

On the definition and use of the ecliptic in modern astronomy

NASA Astrophysics Data System (ADS)

Capitaine, N.; Soffel, M.

2015-08-01

The ecliptic was a fundamental reference plane for astronomy from antiquity to the realization and use of the FK5 reference system. The situation has changed considerably with the adoption of the International Celestial Reference system (ICRS) by the IAU in 1998 and the IAU resolutions on reference systems that were adopted from 2000 to 2009. First, the ICRS has the property of being independent of epoch, ecliptic or equator. Second, the IAU 2000 resolutions, which specified the systems of space-time coordinates within the framework of General Relativity, for the solar system (the Barycentric Celestial Reference System, BCRS) and the Earth (the Geocentric Celestial Reference System, GCRS), did not refer to any ecliptic and did not provide a definition of a GCRS ecliptic. These resolutions also provided the definition of the pole of the nominal rotation axis (the Celestial intermediate pole, CIP) and of new origins on the equator (the Celestial and Terrestrial intermediate origins, CIO and TIO), which do not require the use of an ecliptic. Moreover, the models and standards adopted by the IAU 2006 and IAU 2009 resolutions are largely referred to the ICRS, BCRS, GCRS as well as to the new pole and origins. Therefore, the ecliptic has lost much of its importance. We review the consequences of these changes and improvements in the definition and use of the ecliptic and we discuss whether the concept of an ecliptic is still needed for some specific use in modern astronomy.

Dynamics of Natural and Artificial Celestial Bodies

NASA Astrophysics Data System (ADS)

Pretka-Ziomek, Halina; Wnuk, Edwin; Seidelmann, P. Kenneth; Richardson, David.

2002-01-01

This volume contains papers presented at the US/European Celestial Mechanics Workshop organized by the Astronomical Observatory of Adam Mickiewicz University in Poznan, Poland and held in Poznan, from 3 to 7 July 2000. The purpose of the workshop was to identify future research in celestial mechanics and astrometry and encourage collaboration among scientists from eastern and western countries. Also an emphasis was placed on attracting young members of the fields from around the world and encouraging them to undertake new research efforts needed for advancements in those fields. There was a full program of invited and contributed presentations on selected subjects and each day ended with a discussion period on a general subject in celestial mechanics. The discussion topics and the leaders were: Resonances and Chaos -- A. Morbidelli; Artificial Satellite Orbits -- K.T. Alfriend; Near Earth Objects -- K. Muinonen; Small Solar System Bodies -- I. Williams; and Summary -- P.K. Seidelmann. The goal of the discussions was to identify what we did not know and how we might further our knowledge. It was felt, in addition, that Poznan, Poland, with a core of scientists covering a range of ages, would provide an example of how a research and educational group could be developed elsewhere. Also, Poznan is a central location convenient to eastern and western countries. Thus, the gathering of people and the papers presented are to be the bases for building the future of astrometry and celestial mechanics. Link: http://www.wkap.nl/prod/b/1-4020-0115-0

Gravitational mechanism of active life of the Earth, planets and satellites

NASA Astrophysics Data System (ADS)

Barkin, Yury

2010-05-01

From positions of geodynamic model of the forced gravitational swing, wobble and displacements of shells of a planet are studied and fundamental problems of geodynamics, geology, geophysics, planetary sciences are solved etc.: 1) The mechanism of cyclic variations of activity of natural processes in various time scales. 2) The power of endogenous activity of planetary natural processes on planets and satellites. 3) The phenomenon of polar inversion of natural processes on planets and satellites. 4) Spasmodic and catastrophic changes of activity of natural processes. 5) The phenomenon of twisting of hemispheres (latitude zones or belts) of celestial bodies. 6) Formation of the pear-shaped form of celestial bodies and the mechanism of its change. 7) The ordered planetary structures of geological formations. 8) The phenomena of bipolarity of celestial bodies and antipodality of geology formations. Mechanism. The fundamental feature of a structure of celestial bodies is their shell structure. The most investigated is the internal structure of the Earth. For the Moon and wide set of other bodies of solar system models of an internal structure have been constructed on the basis of the data of observations obtained at studying of their gravitational fields as a result of realization of the appropriate space missions. The basic components for the majority of celestial bodies are the core, the mantle and the crust. To other shells we concern atmospheres (for example, at Venus, Mars, the Titan etc.) and oceanic shells (the Titan, the Earth, Enceladus etc.). Shells are the complex (composite) formations. Planets and satellites are not spherical celestial bodies. The centers of mass of shells of the given planet (or the satellite) and their appropriate principal axes of inertia do not coincide. Accordingly, all their shells are characterized by the certain dynamic oblatenesses. Differences of dynamical oblatenesses results in various forced influences of external celestial bodies on shells of the given body. Dynamical oblatenesses of shells, thus, characterize the endogenous activity of a planet by external celestial bodies. Other important factor of endogenous activity of a planet is a eccentric position of the centers of mass of the shells (for example, of the core and the mantle). The eccentricity of the shells is inherited during geological evolution of a planet as system of shells (Barkin, 2002). Consequences of exitation of the Earth system. The new tides (Barkin, 2005) are caused by relative displacements of the core and mantle. These displacements are reflected in variations of many natural processes due to gravitational action of the core. The displacing core causes deformations of all layers of viscous-elastic mantle. In the given work from more general positions the mechanisms of excitation of a system of shells of the Earth under action of a gravitational attraction of the Sun, the Moon and planets, the phenomena of their relative swings, translational displacements and turns relatively from each other, and the wide list geodynamical consequences of the specified excitation of the Earth are studied. At once we shall emphasize, that the developed geodynamic model has allowed to carry out the important dynamic researches of displacements of shells of the Earth, their deformations and changes, and variations of its natural processes and for the first time to explain the nature of such fundamental phenomena and processes in geodynamics, geology and geophysics as: cyclicity of natural processes and its mechanism; power of processes in various time scales; unity of cyclic processes and universality of their frequency bases; synchronism of geodynamic, geophysical, biophysical and social events; inversion, contrast and opposite directed changes of activity of natural processes in opposite hemispheres of the Earth; step-by-step variations of natural processes, sawtooth course of activity of natural processes in various time scales; orderliness in an distribution of geological formations on the Earth, planets and satellites; existence of antipodal formations on planets and satellites; the phenomenon of twisting of hemispheres of bodies of solar system, twisting of layers and latitudinal zones of shells of celestial bodies including inner layers and shells, etc. All the specified phenomena from the resulted list to some extent are discussed in the given work and illustrated on the basis of modern researches in Earth's sciences and the researches executed by means of space missions. In a complex, the executed researches have shown universality of discussed mechanisms and their important role in dynamics and geoevolution of planets and satellites in other planetary systems, and also stars and pulsars with the systems of planets (Barkin, 2009). Cyclicity. The excitation on the part of external celestial bodies of the system core-mantle depends from relative positions of external celestial bodies, from particularities of their perturbed orbital motions and from rotary motion of the planet. The specified motions have a cyclic nature which is shown in various time scales. Hence, and excitation of shells and their layers will have also cyclic character and to be shown in various time scales. Hence, cyclic variations of all planetary natural processes in all the variety widely should be observed, as takes place in reality. The periods of variations are characterized by extremely wide range - from hours up to tens and hundreds millions years. If the core makes slow secular drift relatively to the mantle all layers and shells of the Earth test secular deformation, thermodynamic and other changes. The cavity of the core and its flows are changed slowly that results in secular variations of a magnetic field (Barkin, 2002, 2009). Inversion and asymmetry of cyclic and secular variations of natural processes. The essence of it rather wide distributed phenomena is, that activity of natural processes varies in an antiphase in opposite hemispheres of the Earth (first of all in northern and southern hemispheres). Told concerns to all geodynamic and geophysical processes, to variations of physical fields, to tectonic and geodetic reorganizations of layers of the Earth, to redistributions of atmospheric, oceanic and other fluid masses of the Earth. The certain asymmetry of displays of processes in northern and southern hemispheres on the other hand is marked. So secular trends of some processes are contrast in northern and southern hemispheres, i.e. velocities of secular changes are essentially different. All described phenomena are caused first of all by cyclic oscillations and secular drift of the core to the north (in present epoch). In longer time scales the similar phenomena of inversion, dissymmetry also have place and determine a nature and style of displacements of continents and lithospheric plates, planetary magmatic activity and plume tectonics as a whole, formation of mountains, elevations and depressions, systems of lineaments and cracks, regressions and transgressions of sea level (Barkin, 2002). Synchronous steps of activity of natural processes. 'For an explanation of observably step-by-step variations of geodynamic and geophysical processes the mechanism of sharp sporadic relative displacements of the core and the mantle and deformations of the mantle in the certain periods of time (the phenomenon of "galloping of the core') is offered.

Aquarius L-Band Radiometers Calibration Using Cold Sky Observations

NASA Technical Reports Server (NTRS)

Dinnat, Emmanuel P.; Le Vine, David M.; Piepmeier, Jeffrey R.; Brown, Shannon T.; Hong, Liang

2015-01-01

An important element in the calibration plan for the Aquarius radiometers is to look at the cold sky. This involves rotating the satellite 180 degrees from its nominal Earth viewing configuration to point the main beams at the celestial sky. At L-band, the cold sky provides a stable, well-characterized scene to be used as a calibration reference. This paper describes the cold sky calibration for Aquarius and how it is used as part of the absolute calibration. Cold sky observations helped establish the radiometer bias, by correcting for an error in the spillover lobe of the antenna pattern, and monitor the long-term radiometer drift.

Polarized Light Corridor Demonstrations.

ERIC Educational Resources Information Center

Davies, G. R.

1990-01-01

Eleven demonstrations of light polarization are presented. Each includes a brief description of the apparatus and the effect demonstrated. Illustrated are strain patterns, reflection, scattering, the Faraday Effect, interference, double refraction, the polarizing microscope, and optical activity. (CW)

Activity Patterns of Eurasian Lynx Are Modulated by Light Regime and Individual Traits over a Wide Latitudinal Range

PubMed Central

Heurich, Marco; Hilger, Anton; Küchenhoff, Helmut; Andrén, Henrik; Bufka, Luděk; Krofel, Miha; Mattisson, Jenny; Odden, John; Persson, Jens; Rauset, Geir R.; Schmidt, Krzysztof; Linnell, John D. C.

2014-01-01

The activity patterns of most terrestrial animals are regarded as being primarily influenced by light, although other factors, such as sexual cycle and climatic conditions, can modify the underlying patterns. However, most activity studies have been limited to a single study area, which in turn limit the variability of light conditions and other factors. Here we considered a range of variables that might potentially influence the activity of a large carnivore, the Eurasian lynx, in a network of studies conducted with identical methodology in different areas spanning latitudes from 49°7′N in central Europe to 70°00′N in northern Scandinavia. The variables considered both light conditions, ranging from a day with a complete day–night cycle to polar night and polar day, as well as individual traits of the animals. We analysed activity data of 38 individual free-ranging lynx equipped with GPS-collars with acceleration sensors, covering more than 11,000 lynx days. Mixed linear additive models revealed that the lynx activity level was not influenced by the daily daylight duration and the activity pattern was bimodal, even during polar night and polar day. The duration of the active phase of the activity cycle varied with the widening and narrowing of the photoperiod. Activity varied significantly with moonlight. Among adults, males were more active than females, and subadult lynx were more active than adults. In polar regions, the amplitude of the lynx daily activity pattern was low, likely as a result of the polycyclic activity pattern of their main prey, reindeer. At lower latitudes, the basic lynx activity pattern peaked during twilight, corresponding to the crepuscular activity pattern of the main prey, roe deer. Our results indicated that the basic activity of lynx is independent of light conditions, but is modified by both individual traits and the activity pattern of the locally most important prey. PMID:25517902

Polarization-induced interference within electromagnetically induced transparency for atoms of double-V linkage

NASA Astrophysics Data System (ADS)

Sun, Yuan; Liu, Chang; Chen, Ping-Xing; Liu, Liang

2018-02-01

People have been paying attention to the role of atoms' complex internal level structures in the research of electromagnetically induced transparency (EIT) for a long time, where the various degenerate Zeeman levels usually generate complex linkage patterns for the atomic transitions. It turns out, with special choices of the atomic states and the atomic transitions' linkage structure, clear signatures of quantum interference induced by the probe and coupling light's polarizations can emerge from a typical EIT phenomena. We propose to study a four-state system with double-V linkage pattern for the transitions and analyze the polarization-induced interference under the EIT condition. We show that such interference arises naturally under mild conditions on the optical field and atom manipulation techniques. Moreover, we construct a variation form of double-M linkage pattern where the polarization-induced interference enables polarization-dependent cross modulation between incident weak lights that can be effective even at the few-photon level. The theme is to gain more insight into the essential question: how can we build a nontrivial optical medium where incident lights experience polarization-dependent nonlinear optical interactions, valid for a wide range of incidence intensities down to the few-photon level?

Mariner 9 celestial mechanics experiment - A status report.

NASA Technical Reports Server (NTRS)

Lorell, J.; Shapiro, I. I.

1973-01-01

There are two basic efforts in the Mariner 9 celestial mechanics experiment: the determination of the gravity field of Mars and the performance of a very precise test of the theory of general relativity. In addition, there are a number of astrodynamic constants that are being determined. All the analyses are based on the Mariner 9 radio tracking data.

Relationships between log N-log S and celestial distribution of gamma-ray bursts

NASA Technical Reports Server (NTRS)

Nishimura, J.; Yamagami, T.

1985-01-01

The apparent conflict between log N-log S curve and isotropic celestial distribution of the gamma ray bursts is discussed. A possible selection effect due to the time profile of each burst is examined. It is shown that the contradiction is due to this selection effect of the gamma ray bursts.

Celestial Navigation for High School Students.

ERIC Educational Resources Information Center

Bell, Carroll Wilson

Reported is a study of a syllabus designed to teach students how to determine a position by celestial means. The syllabus was intended to augment existing curricula and be a topic for special interest groups and not designed as a semester-long course in itself. Each of the 14 lessons included was preceded by specific objectives written in…

Determination of the observation conditions of celestial bodies with the aid of the DISPO system

NASA Technical Reports Server (NTRS)

Kazakov, R. K.; Krivov, A. V.

1984-01-01

The interactive system for determining the observation conditions of celestial bodies is described. A system of programs was created containing a part of the DISPO Display Interative System of Orbit Planning. The system was used for calculating the observatiion characteristics of Halley's comet during its approach to Earth in 1985-86.

Preventing Commercial Colonialism and Retaining Sovereignty Over National Policy and Military Strategy in Space

DTIC Science & Technology

2018-04-09

29 National Interests in Space – Commercial or State-Driven Celestial Expansion? ....... 31 Celestial Market Opportunities – When Will Commercial...Space Markets Open? ...... 38 Implications of Commercial Space Operations ............................................................ 45 Chapter 5...Successful development of competitiveness involves seeking to dominate or control an existing or emergent market . The development of market domination into

Sensory bases of navigation.

PubMed

Gould, J L

1998-10-08

Navigating animals need to know both the bearing of their goal (the 'map' step), and how to determine that direction (the 'compass' step). Compasses are typically arranged in hierarchies, with magnetic backup as a last resort when celestial information is unavailable. Magnetic information is often essential to calibrating celestial cues, though, and repeated recalibration between celestial and magnetic compasses is important in many species. Most magnetic compasses are based on magnetite crystals, but others make use of induction or paramagnetic interactions between short-wavelength light and visual pigments. Though odors may be used in some cases, most if not all long-range maps probably depend on magnetite. Magnetitebased map senses are used to measure only latitude in some species, but provide the distance and direction of the goal in others.

Second-harmonic patterned polarization-analyzed reflection confocal microscope

NASA Astrophysics Data System (ADS)

Okoro, Chukwuemeka; Toussaint, Kimani C.

2017-08-01

We introduce the second-harmonic patterned polarization-analyzed reflection confocal (SPPARC) microscope-a multimodal imaging platform that integrates Mueller matrix polarimetry with reflection confocal and second-harmonic generation (SHG) microscopy. SPPARC microscopy provides label-free three-dimensional (3-D), SHG-patterned confocal images that lend themselves to spatially dependent, linear polarimetric analysis for extraction of rich polarization information based on the Mueller calculus. To demonstrate its capabilities, we use SPPARC microscopy to analyze both porcine tendon and ligament samples and find differences in both circular degree-of-polarization and depolarization parameters. Moreover, using the collagen-generated SHG signal as an endogenous counterstain, we show that the technique can be used to provide 3-D polarimetric information of the surrounding extrafibrillar matrix plus cells or EFMC region. The unique characteristics of SPPARC microscopy holds strong potential for it to more accurately and quantitatively describe microstructural changes in collagen-rich samples in three spatial dimensions.

Reflection of a polarized light cone

NASA Astrophysics Data System (ADS)

Brody, Jed; Weiss, Daniel; Berland, Keith

2013-01-01

We introduce a visually appealing experimental demonstration of Fresnel reflection. In this simple optical experiment, a polarized light beam travels through a high numerical-aperture microscope objective, reflects off a glass slide, and travels back through the same objective lens. The return beam is sampled with a polarizing beam splitter and produces a surprising geometric pattern on an observation screen. Understanding the origin of this pattern requires careful attention to geometry and an understanding of the Fresnel coefficients for S and P polarized light. We demonstrate that in addition to a relatively simple experimental implementation, the shape of the observed pattern can be computed both analytically and by using optical modeling software. The experience of working through complex mathematical computations and demonstrating their agreement with a surprising experimental observation makes this a highly educational experiment for undergraduate optics or advanced-lab courses. It also provides a straightforward yet non-trivial system for teaching students how to use optical modeling software.

Polarization-dependent thin-film wire-grid reflectarray for terahertz waves

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

Niu, Tiaoming; School of Information Science and Engineering, Lanzhou University, Lanzhou 730000; Upadhyay, Aditi

2015-07-20

A thin-film polarization-dependent reflectarray based on patterned metallic wire grids is realized at 1 THz. Unlike conventional reflectarrays with resonant elements and a solid metal ground, parallel narrow metal strips with uniform spacing are employed in this design to construct both the radiation elements and the ground plane. For each radiation element, a certain number of thin strips with an identical length are grouped to effectively form a patch resonator with equivalent performance. The ground plane is made of continuous metallic strips, similar to conventional wire-grid polarizers. The structure can deflect incident waves with the polarization parallel to the stripsmore » into a designed direction and transmit the orthogonal polarization component. Measured radiation patterns show reasonable deflection efficiency and high polarization discrimination. Utilizing this flexible device approach, similar reflectarray designs can be realized for conformal mounting onto surfaces of cylindrical or spherical devices for terahertz imaging and communications.« less

Investigating circular patterns in linear polarization observations of Venus

NASA Astrophysics Data System (ADS)

Mahapatra, Gourav; Stam, Daphne; Rossi, Loic; Rodenhuis, Michiel; Snik, Frans

2017-04-01

ESA's Venus Express mission has revealed our neighbouring planet to be a highly dynamic world, with ever-changing cloud properties and structures, wind speeds that increase in time, and variable concentrations of atmospheric trace gases such as SO2. The SPICAV-IR instrument on Venus Express has provided us with close-up linear polarization data of sunlight reflected by Venus's clouds and hazes, that allows a characterisation of their composition and particle sizes. Here, we analyse linear polarization data of the planet at a distance, obtained with the Extreme Polarimeter (ExPo) on the William Herschel Telescope on La Palma. These spatially resolved, high-accuracy polarization observations of Venus show faint circular patterns centered on the sub-solar point that are absent in the flux observations. So far, careful analyses have ruled out instrumental effects which leaves us to wonder about atmospheric properties as the cause of the circular patterns. Using numerical simulations of the flux and polarization of sunlight that is reflected by Venus, we have investigated the relation between the observed patterns and several atmospheric properties, such as variations in particle sizes, composition, density and altitude. We discuss the plausibility of the possible causes in the view of the current knowledge of the composition and dynamical processes in Venus's atmosphere.

Statistical Patterns of Ionospheric Convection Derived From Mid-latitude, High-Latitude, and Polar SuperDARN HF Radar Observations

NASA Astrophysics Data System (ADS)

Thomas, E. G.; Shepherd, S. G.

2018-04-01

Over the last decade, the Super Dual Auroral Radar Network (SuperDARN) has undergone a dramatic expansion in the Northern Hemisphere with the addition of more than a dozen radars offering improved coverage at mid-latitudes (50°-60° magnetic latitude) and in the polar cap (80°-90° magnetic latitude). In this study, we derive a statistical model of ionospheric convection (TS18) using line-of-sight velocity measurements from the complete network of mid-latitude, high-latitude, and polar radars for the years 2010-2016. These climatological patterns are organized by solar wind, interplanetary magnetic field (IMF), and dipole tilt angle conditions. We find that for weak solar wind driving conditions the TS18 model patterns are largely similar to the average patterns obtained using high-latitude radar data only. For stronger solar wind driving the inclusion of mid-latitude radar data at the equatorward extent of the ionospheric convection can increase the measured cross-polar cap potential (ΦPC) by as much as 40%. We also derive an alternative model organized by the Kp index to better characterize the statistical convection under a range of magnetic activity conditions. These Kp patterns exhibit similar IMF By dependencies as the TS18 model results and demonstrate a linear increase in ΦPC with increasing Kp for a given IMF orientation. Overall, the mid-latitude radars provide a better specification of the flows within the nightside Harang reversal region for moderate to strong solar wind driving or geomagnetic activity, while the polar radars improve the quality of velocity measurements in the deep polar cap under all conditions.

PBX/extradenticle is required to re-establish axial structures and polarity during planarian regeneration

PubMed Central

Blassberg, Robert A.; Felix, Daniel A.; Tejada-Romero, Belen; Aboobaker, A. Aziz

2013-01-01

Recent advances in a number of systems suggest many genes involved in orchestrating regeneration are redeployed from similar processes in development, with others being novel to the regeneration process in particular lineages. Of particular importance will be understanding the architecture of regenerative genetic regulatory networks and whether they are conserved across broad phylogenetic distances. Here, we describe the role of the conserved TALE class protein PBX/Extradenticle in planarians, a representative member of the Lophotrocozoa. PBX/Extradenticle proteins play central roles in both embryonic and post-embryonic developmental patterning in both vertebrates and insects, and we demonstrate a broad requirement during planarian regeneration. We observe that Smed-pbx has pleiotropic functions during regeneration, with a primary role in patterning the anterior-posterior (AP) axis and AP polarity. Smed-pbx is required for expression of polarity determinants notum and wnt1 and for correct patterning of the structures polarized along the AP axis, such as the brain, pharynx and gut. Overall, our data suggest that Smed-pbx functions as a central integrator of positional information to drive patterning of regeneration along the body axis. PMID:23318635

PBX/extradenticle is required to re-establish axial structures and polarity during planarian regeneration.

PubMed

Blassberg, Robert A; Felix, Daniel A; Tejada-Romero, Belen; Aboobaker, A Aziz

2013-02-01

Recent advances in a number of systems suggest many genes involved in orchestrating regeneration are redeployed from similar processes in development, with others being novel to the regeneration process in particular lineages. Of particular importance will be understanding the architecture of regenerative genetic regulatory networks and whether they are conserved across broad phylogenetic distances. Here, we describe the role of the conserved TALE class protein PBX/Extradenticle in planarians, a representative member of the Lophotrocozoa. PBX/Extradenticle proteins play central roles in both embryonic and post-embryonic developmental patterning in both vertebrates and insects, and we demonstrate a broad requirement during planarian regeneration. We observe that Smed-pbx has pleiotropic functions during regeneration, with a primary role in patterning the anterior-posterior (AP) axis and AP polarity. Smed-pbx is required for expression of polarity determinants notum and wnt1 and for correct patterning of the structures polarized along the AP axis, such as the brain, pharynx and gut. Overall, our data suggest that Smed-pbx functions as a central integrator of positional information to drive patterning of regeneration along the body axis.

DSP-Based dual-polarity mass spectrum pattern recognition for bio-detection

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

Riot, V; Coffee, K; Gard, E

2006-04-21

The Bio-Aerosol Mass Spectrometry (BAMS) instrument analyzes single aerosol particles using a dual-polarity time-of-flight mass spectrometer recording simultaneously spectra of thirty to a hundred thousand points on each polarity. We describe here a real-time pattern recognition algorithm developed at Lawrence Livermore National Laboratory that has been implemented on a nine Digital Signal Processor (DSP) system from Signatec Incorporated. The algorithm first preprocesses independently the raw time-of-flight data through an adaptive baseline removal routine. The next step consists of a polarity dependent calibration to a mass-to-charge representation, reducing the data to about five hundred to a thousand channels per polarity. Themore » last step is the identification step using a pattern recognition algorithm based on a library of known particle signatures including threat agents and background particles. The identification step includes integrating the two polarities for a final identification determination using a score-based rule tree. This algorithm, operating on multiple channels per-polarity and multiple polarities, is well suited for parallel real-time processing. It has been implemented on the PMP8A from Signatec Incorporated, which is a computer based board that can interface directly to the two one-Giga-Sample digitizers (PDA1000 from Signatec Incorporated) used to record the two polarities of time-of-flight data. By using optimized data separation, pipelining, and parallel processing across the nine DSPs it is possible to achieve a processing speed of up to a thousand particles per seconds, while maintaining the recognition rate observed on a non-real time implementation. This embedded system has allowed the BAMS technology to improve its throughput and therefore its sensitivity while maintaining a large dynamic range (number of channels and two polarities) thus maintaining the systems specificity for bio-detection.« less

Behavioural and physiological mechanisms of polarized light sensitivity in birds.

PubMed

Muheim, Rachel

2011-03-12

Polarized light (PL) sensitivity is relatively well studied in a large number of invertebrates and some fish species, but in most other vertebrate classes, including birds, the behavioural and physiological mechanism of PL sensitivity remains one of the big mysteries in sensory biology. Many organisms use the skylight polarization pattern as part of a sun compass for orientation, navigation and in spatial orientation tasks. In birds, the available evidence for an involvement of the skylight polarization pattern in sun-compass orientation is very weak. Instead, cue-conflict and cue-calibration experiments have shown that the skylight polarization pattern near the horizon at sunrise and sunset provides birds with a seasonally and latitudinally independent compass calibration reference. Despite convincing evidence that birds use PL cues for orientation, direct experimental evidence for PL sensitivity is still lacking. Avian double cones have been proposed as putative PL receptors, but detailed anatomical and physiological evidence will be needed to conclusively describe the avian PL receptor. Intriguing parallels between the functional and physiological properties of PL reception and light-dependent magnetoreception could point to a common receptor system.

Behavioural and physiological mechanisms of polarized light sensitivity in birds

PubMed Central

Muheim, Rachel

2011-01-01

Polarized light (PL) sensitivity is relatively well studied in a large number of invertebrates and some fish species, but in most other vertebrate classes, including birds, the behavioural and physiological mechanism of PL sensitivity remains one of the big mysteries in sensory biology. Many organisms use the skylight polarization pattern as part of a sun compass for orientation, navigation and in spatial orientation tasks. In birds, the available evidence for an involvement of the skylight polarization pattern in sun-compass orientation is very weak. Instead, cue-conflict and cue-calibration experiments have shown that the skylight polarization pattern near the horizon at sunrise and sunset provides birds with a seasonally and latitudinally independent compass calibration reference. Despite convincing evidence that birds use PL cues for orientation, direct experimental evidence for PL sensitivity is still lacking. Avian double cones have been proposed as putative PL receptors, but detailed anatomical and physiological evidence will be needed to conclusively describe the avian PL receptor. Intriguing parallels between the functional and physiological properties of PL reception and light-dependent magnetoreception could point to a common receptor system. PMID:21282180

Daple coordinates organ-wide and cell-intrinsic polarity to pattern inner-ear hair bundles

PubMed Central

Siletti, Kimberly; Hudspeth, A. J.

2017-01-01

The establishment of planar polarization by mammalian cells necessitates the integration of diverse signaling pathways. In the inner ear, at least two systems regulate the planar polarity of sensory hair bundles. The core planar cell polarity (PCP) proteins coordinate the orientations of hair cells across the epithelial plane. The cell-intrinsic patterning of hair bundles is implemented independently by the G protein complex classically known for orienting the mitotic spindle. Although the primary cilium also participates in each of these pathways, its role and the integration of the two systems are poorly understood. We show that Dishevelled-associating protein with a high frequency of leucine residues (Daple) interacts with PCP and cell-intrinsic signals. Regulated by the cell-intrinsic pathway, Daple is required to maintain the polarized distribution of the core PCP protein Dishevelled and to position the primary cilium at the abneural edge of the apical surface. Our results suggest that the primary cilium or an associated structure influences the domain of cell-intrinsic signals that shape the hair bundle. Daple is therefore essential to orient and pattern sensory hair bundles. PMID:29229865

Polarization models of filamentary molecular clouds.

NASA Astrophysics Data System (ADS)

Carlqvist, P.; Kristen, H.

1997-08-01

We study numerically the linear polarization and extinction of light from background stars in three types of models of elongated molecular clouds by following the development of the Stokes parameters. The clouds are assumed to be of cylindrical shape and penetrated by a helical magnetic field {vec}(B). In the first two models we study only the relative magnitude of the polarization assuming that the polarization is proportional to Bmu^, where primarily μ=2. Provided there is no background/foreground polarization present we find from the cylindrically symmetric Model I that the angle of polarization has a bimodal character with the polarization being either parallel with or perpendicular to the axis of the filament. For some magnetic-field geometries both angles may exist in one and the same filament. It is concluded that it is not a straightforward task to find the magnetic-field-line pattern from the polarization pattern. If a background/foreground polarization exists or, as in Model II, the filament is not cylindrically symmetric, the bimodal character of the angle of polarization is lost. By means of Model III we have, using semi-empirical methods based on the Davis-Greenstein mechanism, estimated the absolute degree of polarization in the filamentary molecular cloud L204. It is found that the polarization produced by the model is much less than the polarization observed. We therefore conclude that most of the polarization measured in the L204 cloud is not produced in the cloud itself but is constituted by a large-scale background/foreground polarization.

Ocelli contribute to the encoding of celestial compass information in the Australian desert ant Melophorus bagoti.

PubMed

Schwarz, Sebastian; Albert, Laurence; Wystrach, Antoine; Cheng, Ken

2011-03-15

Many animal species, including some social hymenoptera, use the visual system for navigation. Although the insect compound eyes have been well studied, less is known about the second visual system in some insects, the ocelli. Here we demonstrate navigational functions of the ocelli in the visually guided Australian desert ant Melophorus bagoti. These ants are known to rely on both visual landmark learning and path integration. We conducted experiments to reveal the role of ocelli in the perception and use of celestial compass information and landmark guidance. Ants with directional information from their path integration system were tested with covered compound eyes and open ocelli on an unfamiliar test field where only celestial compass cues were available for homing. These full-vector ants, using only their ocelli for visual information, oriented significantly towards the fictive nest on the test field, indicating the use of celestial compass information that is presumably based on polarised skylight, the sun's position or the colour gradient of the sky. Ants without any directional information from their path-integration system (zero-vector) were tested, also with covered compound eyes and open ocelli, on a familiar training field where they have to use the surrounding panorama to home. These ants failed to orient significantly in the homeward direction. Together, our results demonstrated that M. bagoti could perceive and process celestial compass information for directional orientation with their ocelli. In contrast, the ocelli do not seem to contribute to terrestrial landmark-based navigation in M. bagoti.

Same concept…Different terms

NASA Astrophysics Data System (ADS)

Heafner, Joe

2018-03-01

Most introductory physics courses begin with the concept of an object (usually a particle) having a precise position or location in space (I will not address spacetime here) relative to something else, the origin of a three-dimensional coordinate system perhaps. My experience has been that physics students are inherently at home with this concept. In astronomy, we often begin by thinking about the sky. For the purposes of this article, I will simply define it as that which we see when we look away from Earth's surface. It appears almost as a two-dimensional plane, perhaps even a curved surface. When we look at something in the sky, we really have no sense of distance. Indeed, when astronomers need the "position" of a star or planet in the sky, the quantity is two dimensional. Because the sky appears to wrap around Earth, celestial positions can be given entirely by angular quantities. Astronomers use right ascension and declination, respectively, as analogs of terrestrial longitude and latitude. Right ascension is the angular distance eastward around the celestial equator (the projection of Earth's equator onto the celestial sphere) from the vernal equinox (where the celestial equator and the ecliptic intersect such that the Sun is moving from the Southern Hemisphere to the Northern Hemisphere) to the object and declination is the object's angular distance north or south of the celestial equator. So to an astronomer, for the purposes of aiming a telescope, position refers to a two-dimensional quantity because in the sky there is no direct sense of depth or distance.

Celestial Treasury

NASA Astrophysics Data System (ADS)

Lachièze-Rey, Marc; Luminet, Jean-Pierre

2001-07-01

Throughout history, the mysterious dark skies have inspired our imaginations in countless ways, influencing our endeavors in science and philosophy, religion, literature, and art. Filled with 380 full-color illustrations, Celestial Treasury shows the influence of astronomical theories and the richness of illustrations in Western civilization through the ages. The authors explore the evolution of our understanding of astronomy and weave together ancient and modern theories in a fascinating narrative. They incorporate a wealth of detail from Greek verse, medieval manuscripts and Victorian poetry with contemporary spacecraft photographs and computer-generated star charts. Celestial Treasury is more than a beautiful book: it answers a variety of questions that have intrigued scientists and laymen for centuries. -- How did philosophers and scientists try to explain the order that governs celestial motion? -- How did geometers and artists measure and map the skies? -- How many different answers have been proposed for the most fundamental of all questions: When and how did Earth come about? -- Who inhabits the heavens--gods, angels or extraterrestrials? No other book recounts humankind's fascination with the heavens as compellingly as Celestial Treasury. Marc Lachièze-Rey is a director of research at the Centre National pour la Récherche Scientifique and astrophysicist at the Centre d'Etudes de Saclay. He is the author of The Cosmic Background Radiation (Cambridge, 1999), and and The Quest for Unity, (Oxford, 1999 ), as well as many books in French. Jean-Pierre Luminet is a research director of the Centre National pour la Rechérche Scientifique, based at the Paris-Meudon observatory. He is the author of Black Holes, (Cambridge 1992), as well as science documentaries for television.

OPTICAL SPECTRA OF CANDIDATE INTERNATIONAL CELESTIAL REFERENCE FRAME (ICRF) FLAT-SPECTRUM RADIO SOURCES

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

Titov, O.; Stanford, Laura M.; Johnston, Helen M.

2013-07-01

Continuing our program of spectroscopic observations of International Celestial Reference Frame (ICRF) sources, we present redshifts for 120 quasars and radio galaxies. Data were obtained with five telescopes: the 3.58 m European Southern Observatory New Technology Telescope, the two 8.2 m Gemini telescopes, the 2.5 m Nordic Optical Telescope (NOT), and the 6.0 m Big Azimuthal Telescope of the Special Astrophysical Observatory in Russia. The targets were selected from the International VLBI Service for Geodesy and Astrometry candidate International Celestial Reference Catalog which forms part of an observational very long baseline interferometry (VLBI) program to strengthen the celestial reference frame.more » We obtained spectra of the potential optical counterparts of more than 150 compact flat-spectrum radio sources, and measured redshifts of 120 emission-line objects, together with 19 BL Lac objects. These identifications add significantly to the precise radio-optical frame tie to be undertaken by Gaia, due to be launched in 2013, and to the existing data available for analyzing source proper motions over the celestial sphere. We show that the distribution of redshifts for ICRF sources is consistent with the much larger sample drawn from Faint Images of the Radio Sky at Twenty cm (FIRST) and Sloan Digital Sky Survey, implying that the ultra-compact VLBI sources are not distinguished from the overall radio-loud quasar population. In addition, we obtained NOT spectra for five radio sources from the FIRST and NRAO VLA Sky Survey catalogs, selected on the basis of their red colors, which yielded three quasars with z > 4.« less

Identifying polar bear resource selection patterns to inform offshore development in a dynamic and changing Arctic

USGS Publications Warehouse

Wilson, Ryan R.; Horne, Jon S.; Rode, Karyn D.; Regehr, Eric V.; Durner, George M.

2014-01-01

Although sea ice loss is the primary threat to polar bears (Ursus maritimus), little can be done to mitigate its effects without global efforts to reduce greenhouse gas emissions. Other factors, however, could exacerbate the impacts of sea ice loss on polar bears, such as exposure to increased industrial activity. The Arctic Ocean has enormous oil and gas potential, and its development is expected to increase in the coming decades. Estimates of polar bear resource selection will inform managers how bears use areas slated for oil development and to help guide conservation planning. We estimated temporally-varying resource selection patterns for non-denning adult female polar bears in the Chukchi Sea population (2008–2012) at two scales (i.e., home range and weekly steps) to identify factors predictive of polar bear use throughout the year, before any offshore development. From the best models at each scale, we estimated scale-integrated resource selection functions to predict polar bear space use across the population's range and determined when bears were most likely to use the region where offshore oil and gas development in the United States is slated to occur. Polar bears exhibited significant intra-annual variation in selection patterns at both scales but the strength and annual patterns of selection differed between scales for most variables. Bears were most likely to use the offshore oil and gas planning area during ice retreat and growth with the highest predicted use occurring in the southern portion of the planning area. The average proportion of predicted high-value habitat in the planning area was >15% of the total high-value habitat for the population during sea ice retreat and growth and reached a high of 50% during November 2010. Our results provide a baseline on which to judge future changes to non-denning adult female polar bear resource selection in the Chukchi Sea and help guide offshore development in the region. Lastly, our study provides a framework for assessing potential impacts of offshore oil and gas development to other polar bear populations around the Arctic.

Dark Energy Survey finds more celestial neighbors | News

Science.gov Websites

Energy Survey finds more celestial neighbors August 17, 2015 icon icon icon New dwarf galaxy candidates could mean our sky is more crowded than we thought The Dark Energy Survey has now mapped one-eighth of Survey Collaboration The Dark Energy Survey has now mapped one-eighth of the full sky (red shaded region

Galileo Spacecraft Scan Platform Celestial Pointing Cone Control Gain Redesign

NASA Technical Reports Server (NTRS)

In, C-H. C.; Hilbert, K. B.

1994-01-01

During September and October 1991, pictures of the Gaspra asteroid and neighboring stars were taken by the Galileo Optical Navigation (OPNAV) Team for the purpose of navigation the spacecraft for a successful Gaspra encounter. The star tracks in these pictures showed that the scan platform celestial pointing cone controller performed poorly in compensating for wobble-induced cone offsets.

The dynamical behaviour of our planetary system. Proceedings. 4th Alexander von Humboldt Colloquium on Celestial Mechanics, Ramsau (Austria), 17 - 23 Mar 1996.

NASA Astrophysics Data System (ADS)

Dvorak, R.; Henrard, J.

1996-03-01

The following topics were dealt with: celestial mechanics, dynamical astronomy, planetary systems, resonance scattering, Hamiltonian mechanics non-integrability, irregular periodic orbits, escape, dynamical system mapping, fast Fourier method, precession-nutation, Nekhoroshev theorem, asteroid dynamics, the Trojan problem, planet-crossing orbits, Kirkwood gaps, future research, human comprehension limitations.

241. BUILDINGS 455, 456, 509, 510 AND 457 (CELESTIAL NAVIGATION ...

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

241. BUILDINGS 455, 456, 509, 510 AND 457 (CELESTIAL NAVIGATION COMPLEX), 1942-43. BUREAU OF YARDS AND DOCKS STANDARD PLANS. VIEW NORTH ACROSS WASP ST. SHOWING THE 4 TRAINING SILOS FROM LEFT TO RIGHT: BUILDINGS 455, 456, 509, AND 510; AND, BESIDE THEM, BUILDING 457. - Quonset Point Naval Air Station, Roger Williams Way, North Kingstown, Washington County, RI

Celestial mechanics during the last two decades

NASA Technical Reports Server (NTRS)

Szebehely, V.

1978-01-01

The unprecedented progress in celestial mechanics (orbital mechanics, astrodynamics, space dynamics) is reviewed from 1957 to date. The engineering, astronomical and mathematical aspects are synthesized. The measuring and computational techniques developed parallel with the theoretical advances are outlined. Major unsolved problem areas are listed with proposed approaches for their solutions. Extrapolations and predictions of the progress for the future conclude the paper.

A celestial assisted INS initialization method for lunar explorers.

PubMed

Ning, Xiaolin; Wang, Longhua; Wu, Weiren; Fang, Jiancheng

2011-01-01

The second and third phases of the Chinese Lunar Exploration Program (CLEP) are planning to achieve Moon landing, surface exploration and automated sample return. In these missions, the inertial navigation system (INS) and celestial navigation system (CNS) are two indispensable autonomous navigation systems which can compensate for limitations in the ground based navigation system. The accurate initialization of the INS and the precise calibration of the CNS are needed in order to achieve high navigation accuracy. Neither the INS nor the CNS can solve the above problems using the ground controllers or by themselves on the lunar surface. However, since they are complementary to each other, these problems can be solved by combining them together. A new celestial assisted INS initialization method is presented, in which the initial position and attitude of the explorer as well as the inertial sensors' biases are estimated by aiding the INS with celestial measurements. Furthermore, the systematic error of the CNS is also corrected by the help of INS measurements. Simulations show that the maximum error in position is 300 m and in attitude 40″, which demonstrates this method is a promising and attractive scheme for explorers on the lunar surface.

A Celestial Assisted INS Initialization Method for Lunar Explorers

PubMed Central

Ning, Xiaolin; Wang, Longhua; Wu, Weiren; Fang, Jiancheng

2011-01-01

The second and third phases of the Chinese Lunar Exploration Program (CLEP) are planning to achieve Moon landing, surface exploration and automated sample return. In these missions, the inertial navigation system (INS) and celestial navigation system (CNS) are two indispensable autonomous navigation systems which can compensate for limitations in the ground based navigation system. The accurate initialization of the INS and the precise calibration of the CNS are needed in order to achieve high navigation accuracy. Neither the INS nor the CNS can solve the above problems using the ground controllers or by themselves on the lunar surface. However, since they are complementary to each other, these problems can be solved by combining them together. A new celestial assisted INS initialization method is presented, in which the initial position and attitude of the explorer as well as the inertial sensors’ biases are estimated by aiding the INS with celestial measurements. Furthermore, the systematic error of the CNS is also corrected by the help of INS measurements. Simulations show that the maximum error in position is 300 m and in attitude 40″, which demonstrates this method is a promising and attractive scheme for explorers on the lunar surface. PMID:22163998

The role of the sun in the celestial compass of dung beetles

PubMed Central

Dacke, M.; el Jundi, Basil; Smolka, Jochen; Byrne, Marcus; Baird, Emily

2014-01-01

Recent research has focused on the different types of compass cues available to ball-rolling beetles for orientation, but little is known about the relative precision of each of these cues and how they interact. In this study, we find that the absolute orientation error of the celestial compass of the day-active dung beetle Scarabaeus lamarcki doubles from 16° at solar elevations below 60° to an error of 29° at solar elevations above 75°. As ball-rolling dung beetles rely solely on celestial compass cues for their orientation, these insects experience a large decrease in orientation precision towards the middle of the day. We also find that in the compass system of dung beetles, the solar cues and the skylight cues are used together and share the control of orientation behaviour. Finally, we demonstrate that the relative influence of the azimuthal position of the sun for straight-line orientation decreases as the sun draws closer to the horizon. In conclusion, ball-rolling dung beetles possess a dynamic celestial compass system in which the orientation precision and the relative influence of the solar compass cues change over the course of the day. PMID:24395963

The role of the sun in the celestial compass of dung beetles.

PubMed

Dacke, M; el Jundi, Basil; Smolka, Jochen; Byrne, Marcus; Baird, Emily

2014-01-01

Recent research has focused on the different types of compass cues available to ball-rolling beetles for orientation, but little is known about the relative precision of each of these cues and how they interact. In this study, we find that the absolute orientation error of the celestial compass of the day-active dung beetle Scarabaeus lamarcki doubles from 16° at solar elevations below 60° to an error of 29° at solar elevations above 75°. As ball-rolling dung beetles rely solely on celestial compass cues for their orientation, these insects experience a large decrease in orientation precision towards the middle of the day. We also find that in the compass system of dung beetles, the solar cues and the skylight cues are used together and share the control of orientation behaviour. Finally, we demonstrate that the relative influence of the azimuthal position of the sun for straight-line orientation decreases as the sun draws closer to the horizon. In conclusion, ball-rolling dung beetles possess a dynamic celestial compass system in which the orientation precision and the relative influence of the solar compass cues change over the course of the day.

Mariner Mars 1971 attitude control subsystem

NASA Technical Reports Server (NTRS)

Edmunds, R. S.

1974-01-01

The Mariner Mars 1971 attitude control subsystem (ACS) is discussed. It is comprised of a sun sensor set, a Canopus tracker, an inertial reference unit, two cold gas reaction control assemblies, two rocket engine gimbal actuators, and an attitude control electronics unit. The subsystem has the following eight operating modes: (1) launch, (2) sun acquisition, (3) roll search, (4) celestial cruise, (5) all-axes inertial, (6) roll inertial, (7) commanded turn, and (8) thrust vector control. In the celestial cruise mode, the position control is held to plus or minus 0.25 deg. Commanded turn rates are plus or minus 0.18 deg/s. The attitude control logic in conjunction with command inputs from other spacecraft subsystems establishes the ACS operating mode. The logic utilizes Sun and Canopus acquisition signals generated within the ACS to perform automatic mode switching so that dependence of ground control is minimized when operating in the sun acquisition, roll search, and celestial cruise modes. The total ACS weight is 65.7 lb, and includes 5.4 lb of nitrogen gas. Total power requirements vary from 9 W for the celestial cruise mode to 54 W for the commanded turn mode.

Visual navigation in desert ants Cataglyphis fortis: are snapshots coupled to a celestial system of reference?

PubMed

Akesson, Susanne; Wehner, Rüdiger

2002-07-01

Central-place foraging insects such as desert ants of the genus Cataglyphis use both path integration and landmarks to navigate during foraging excursions. The use of landmark information and a celestial system of reference for nest location was investigated by training desert ants returning from an artificial feeder to find the nest at one of four alternative positions located asymmetrically inside a four-cylinder landmark array. The cylindrical landmarks were all of the same size and arranged in a square, with the nest located in the southeast corner. When released from the compass direction experienced during training (southeast), the ants searched most intensely at the fictive nest position. When instead released from any of the three alternative directions of approach (southwest, northwest or northeast), the same individuals instead searched at two of the four alternative positions by initiating their search at the position closest to the direction of approach when entering the landmark square and then returning to the position at which snapshot, current landmark image and celestial reference information were in register. The results show that, in the ants' visual snapshot memory, a memorized landmark scene can temporarily be decoupled from a memorized celestial system of reference.

Femtosecond laser-induced herringbone patterns

NASA Astrophysics Data System (ADS)

Garcell, Erik M.; Lam, Billy; Guo, Chunlei

2018-06-01

Femtosecond laser-induced herringbone patterns are formed on copper (Cu). These novel periodic structures are created following s-polarized, large incident angle, femtosecond laser pulses. Forming as slanted and axially symmetric laser-induced periodic surface structures along the side walls of ablated channels, the result is a series of v-shaped structures that resemble a herringbone pattern. Fluence mapping, incident angle studies, as well as polarization studies have been conducted and provide a clear understanding of this new structure.

Spatial and temporal variation in size of polar bear (Ursus maritimus) sexual organs and its use in pollution and climate change studies.

PubMed

Sonne, Christian; Dietz, Rune; Born, Erik W; Riget, Frank F; Leifsson, Pall S; Bechshøft, Thea Ø; Kirkegaard, Maja

2007-11-15

Sexual organs and their development are susceptible to atmospheric transported environmental xenoendocrine pollutants and climate change (food availability). We therefore investigated sexual organs from 55 male and 44 female East Greenland polar bears (Ursus maritimus) to obtain information about growth/size and sexual maturity. Then, the genitalia size was compared with those previously reported from Canadian and Svalbard polar bears. Growth models showed that East Greenland male polar bears reached sexual maturity around 7 years of age and females around 4 years of age. When comparing East Greenland and Svalbard polar bears, the size of baculum and uterus were significantly lower in the East Greenland polar bears (ANOVA: all p < 0.05). Based on previously published baculum mean values from Canadian polar bears, a similar baculum pattern was found for East Greenland vs. Canadian polar bears. It is speculated whether this could be a result of the general high variation in polar bear body size, temporal distribution patterns of anthropogenic long-range transported persistent organic pollutants or climate change (decreasing food availability). The present investigation represents conservation and background data for future spatial and temporal assessments of hunting, pollution and climate change scenarios.

FREQUENCY DEPENDENCE OF POLARIZATION OF ZEBRA PATTERN IN TYPE-IV SOLAR RADIO BURSTS

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

Kaneda, Kazutaka; Misawa, H.; Tsuchiya, F.

2015-08-01

We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZPs. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50%–70% right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50–70 ms relative to the right-handed component over the entiremore » frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double-plasma-resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.« less

[The celestial phenomena in A. Dürer's engraving Melancholia I].

PubMed

Weitzel, Hans

2009-01-01

The celestial body of Dürer's engraving Melencolia I is connected with his painting of a meteor, the Raveningham-painting; it is shown that the origin of this painting owns to the impact of the meteor of Ensisheim in 1492. Until now the celestial body, the balance, and the magic square are nearly consistently interpreted as the planet Saturn, the zodiac sign Libra, and the planet Jupiter, and the melancholy woman is subject to these heavenly bodies. Consequently, neoplatonic astrology has been the main focus of the engraving; including the rainbow, the engraving has also been interpreted biblically. The present paper, however, places emphasis on problems of the geometry as the reason of melancholy. Any astronomical meaning of the configuration of the numbers of the magic square is discarded.

Heavenly Networks. Celestial Maps and Globes in Circulation between Artisans, Mathematicians, and Noblemen in Renaissance Europe.

PubMed

Gessner, Samuel

2015-01-01

The aim of this paper is to examine the iconography on a set of star charts by Albrecht Dürer (1515), and celestial globes by Caspar Vopel (1536) and Christoph Schissler (1575). The iconography on these instruments is conditioned by strong traditions which include not only the imagery on globes and planispheres (star charts), but also ancient literature about the constellations. Where this iconography departs from those traditions, the change had to do with humanism in the sixteenth century. This "humanistic" dimension is interwoven with other concerns that involve both "social" and "technical" motivations. The interplay of these three dimensions illustrates how the iconography on celestial charts and globes expresses some features of the shared knowledge and shared culture between artisans, mathematicians, and nobles in Renaissance Europe.

Measurement of the azimuthal dependence of cross-polarized lidar returns and its relation to optical depth.

PubMed

Roy, Nathalie; Roy, Gilles; Bissonnette, Luc R; Simard, Jean-Robert

2004-05-01

We measure with a gated intensified CCD camera the cross-polarized backscattered light from a linearly polarized laser beam penetrating a cloud made of spherical particles. In accordance with previously published results we observe a clear azimuthal pattern in the recorded images. We show that the pattern is symmetrical, that it originates from second-order scattering, and that higher-order scattering causes blurring that increases with optical depth. We also find that the contrast in the symmetrical features can be related to measurement of the optical depth. Moreover, when the blurring contributions are identified and subtracted, the resulting pattern provides a pure second-order scattering measurement that can be used for retrieval of droplet size.

How to find home backwards? Navigation during rearward homing of Cataglyphis fortis desert ants.

PubMed

Pfeffer, Sarah E; Wittlinger, Matthias

2016-07-15

Cataglyphis ants are renowned for their impressive navigation skills, which have been studied in numerous experiments during forward locomotion. However, the ants' navigational performance during backward homing when dragging large food loads has not been investigated until now. During backward locomotion, the odometer has to deal with unsteady motion and irregularities in inter-leg coordination. The legs' sensory feedback during backward walking is not just a simple reversal of the forward stepping movements: compared with forward homing, ants are facing towards the opposite direction during backward dragging. Hence, the compass system has to cope with a flipped celestial view (in terms of the polarization pattern and the position of the sun) and an inverted retinotopic image of the visual panorama and landmark environment. The same is true for wind and olfactory cues. In this study we analyze for the first time backward-homing ants and evaluate their navigational performance in channel and open field experiments. Backward-homing Cataglyphis fortis desert ants show remarkable similarities in the performance of homing compared with forward-walking ants. Despite the numerous challenges emerging for the navigational system during backward walking, we show that ants perform quite well in our experiments. Direction and distance gauging was comparable to that of the forward-walking control groups. Interestingly, we found that backward-homing ants often put down the food item and performed foodless search loops around the left food item. These search loops were mainly centred around the drop-off position (and not around the nest position), and increased in length the closer the ants came to their fictive nest site. © 2016. Published by The Company of Biologists Ltd.

Testing avian compass calibration: comparative experiments with diurnal and nocturnal passerine migrants in South Sweden

PubMed Central

Åkesson, Susanne; Odin, Catharina; Hegedüs, Ramón; Ilieva, Mihaela; Sjöholm, Christoffer; Farkas, Alexandra; Horváth, Gábor

2015-01-01

ABSTRACT Cue-conflict experiments were performed to study the compass calibration of one predominantly diurnal migrant, the dunnock (Prunella modularis), and two species of nocturnal passerine migrants, the sedge warbler (Acrocephalus schoenobaenus), and the European robin (Erithacus rubecula) during autumn migration in South Sweden. The birds' orientation was recorded in circular cages under natural clear and simulated overcast skies in the local geomagnetic field, and thereafter the birds were exposed to a cue-conflict situation where the horizontal component of the magnetic field (mN) was shifted +90° or −90° at two occasions, one session starting shortly after sunrise and the other ca. 90 min before sunset and lasting for 60 min. The patterns of the degree and angle of skylight polarization were measured by full-sky imaging polarimetry during the cue-conflict exposures and orientation tests. All species showed orientation both under clear and overcast skies that correlated with the expected migratory orientation towards southwest to south. For the European robin the orientation under clear skies was significantly different from that recorded under overcast skies, showing a tendency that the orientation under clear skies was influenced by the position of the Sun at sunset resulting in more westerly orientation. This sun attraction was not observed for the sedge warbler and the dunnock, both orientating south. All species showed similar orientation after the cue-conflict as compared to the preferred orientation recorded before the cue-conflict, with the clearest results in the European robin and thus, the results did not support recalibration of the celestial nor the magnetic compasses as a result of the cue-conflict exposure. PMID:25505150

Electric field driven mesoscale phase transition in polarized colloids

NASA Astrophysics Data System (ADS)

Khusid, Boris; Elele, Ezinwa; Lei, Qian

2016-11-01

A mesoscale phase transition in a polarized suspension was reported by Kumar, Khusid, Acrivos, PRL95, 2005 and Agarwal, Yethiraj, PRL102, 2009. Following the application of a strong AC field, particles aggregated head-to-tail into chains that bridged the interelectrode gap and then formed a cellular pattern, in which large particle-free domains were enclosed by particle-rich thin walls. Cellular structures were not observed in numerous simulations of field induced phase transitions in a polarized suspension. A requirement for matching the particle and fluid densities to avoid particle settling limits terrestrial experiments to negatively polarized particles. We present data on the phase diagram and kinetics of the phase transition in a neutrally buoyant, negatively polarized suspension subjected to a combination of AC and DC. Surprisingly, a weak DC component drastically speeds up the formation of a cellular pattern but does not affect its key characteristic. However, the application of a strong DC field destroys the cellular pattern, but it restores as the DC field strength is reduced. We also discuss the design of experiments to study phase transitions in a suspension of positively polarized, non-buoyancy-matched particles in the International Space Station. Supported by NASA's Physical Science Research Program, NNX13AQ53G.

Vector nature of multi-soliton patterns in a passively mode-locked figure-eight fiber laser.

PubMed

Ning, Qiu-Yi; Liu, Hao; Zheng, Xu-Wu; Yu, Wei; Luo, Ai-Ping; Huang, Xu-Guang; Luo, Zhi-Chao; Xu, Wen-Cheng; Xu, Shan-Hui; Yang, Zhong-Min

2014-05-19

The vector nature of multi-soliton dynamic patterns was investigated in a passively mode-locked figure-eight fiber laser based on the nonlinear amplifying loop mirror (NALM). By properly adjusting the cavity parameters such as the pump power level and intra-cavity polarization controllers (PCs), in addition to the fundamental vector soliton, various vector multi-soliton regimes were observed, such as the random static distribution of vector multiple solitons, vector soliton cluster, vector soliton flow, and the state of vector multiple solitons occupying the whole cavity. Both the polarization-locked vector solitons (PLVSs) and the polarization-rotating vector solitons (PRVSs) were observed for fundamental soliton and each type of multi-soliton patterns. The obtained results further reveal the fundamental physics of multi-soliton patterns and demonstrate that the figure-eight fiber lasers are indeed a good platform for investigating the vector nature of different soliton types.

Novel High-Activity Organic Piezoelectric Materials - From Single-Molecule Response to Energy Harvesting Films

DTIC Science & Technology

2015-08-24

microcontact printing techniques to deposit and pattern intrinsically polar self - assembled monolayers (SAMs) on smooth template-stripped gold films...and large piezoresponse. Stamp Stamp Gold Gold 10 μm 10 μ m 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 nm Fig. 7. Patterned self - assembled monolayers of...SAM. Importantly, deposition and patterning of thiol self - assembled monolayers on gold surfaces is facile, creating in intrinsically polar film for

Polarization Control of Morphological Pattern Orientation During Light-Mediated Synthesis of Nanostructured Se–Te Films

DOE PAGES

Carim, Azhar I.; Batara, Nicolas A.; Premkumar, Anjali; ...

2015-11-23

The template-free growth of well ordered, highly anisotropic lamellar structures has been demonstrated during the photoelectrodeposition of Se–Te films, wherein the orientation of the pattern can be directed by orienting the linear polarization of the incident light. This control mechanism was investigated further herein by examining the morphologies of films grown photoelectrochemically using light from two simultaneous sources that had mutually different linear polarizations. Photoelectrochemical growth with light from two nonorthogonally polarized same-wavelength sources generated lamellar morphologies in which the long axes of the lamellae were oriented parallel to the intensity-weighted average polarization orientation. Simulations of light scattering at themore » solution–film interface were consistent with this observation. Computer modeling of these growths using combined full-wave electromagnetic and Monte Carlo growth simulations successfully reproduced the experimental morphologies and quantitatively agreed with the pattern orientations observed experimentally by considering only the fundamental light-material interactions during growth. Deposition with light from two orthogonally polarized same-wavelength as well as different-wavelength sources produced structures that consisted of two intersecting sets of orthogonally oriented lamellae in which the relative heights of the two sets could be varied by adjusting the relative source intensities. Simulations of light absorption were performed in analogous, idealized intersecting lamellar structures and revealed that the lamellae preferentially absorbed light polarized with the electric field vector along their long axes. In conclusion, these data sets cumulatively indicate that anisotropic light scattering and light absorption generated by the light polarization produces the anisotropic morphology and that the resultant morphology is a function of all illumination inputs despite differing polarizations.« less

Building a Learning Progression for Celestial Motion: An Exploration of Students' Reasoning about the Seasons

ERIC Educational Resources Information Center

Plummer, Julia D.; Maynard, L.

2014-01-01

We present the development of a construct map addressing the reason for the seasons, as a subset of a larger learning progression on celestial motion. Five classes of 8th grade students (N?=?38) participated in a 10-day curriculum on the seasons. We revised a hypothetical seasons construct map using a Rasch model analysis of students'…

High-Resolution Structural Monitoring of Ionospheric Absorption Events

DTIC Science & Technology

2013-07-01

ionospheric plasma conductivity 5 . This results in enhanced absorption of the cosmic high frequency (HF; typically 10 – 60 MHz) radio background ...7 riometry. Incorporation of an outrigger site, to enable treatment of the unknown structure of the celestial background and the effects of...riometry. Incorporation of an outrigger site, to enable treatment of the unknown structure of the celestial background and the effects of confusion

Kinetic attractor phase diagrams of active nematic suspensions: the dilute regime.

PubMed

Forest, M Gregory; Wang, Qi; Zhou, Ruhai

2015-08-28

Large-scale simulations by the authors of the kinetic-hydrodynamic equations for active polar nematics revealed a variety of spatio-temporal attractors, including steady and unsteady, banded (1d) and cellular (2d) spatial patterns. These particle scale activation-induced attractors arise at dilute nanorod volume fractions where the passive equilibrium phase is isotropic, whereas all previous model simulations have focused on the semi-dilute, nematic equilibrium regime and mostly on low-moment orientation tensor and polarity vector models. Here we extend our previous results to complete attractor phase diagrams for active nematics, with and without an explicit polar potential, to map out novel spatial and dynamic transitions, and to identify some new attractors, over the parameter space of dilute nanorod volume fraction and nanorod activation strength. The particle-scale activation parameter corresponds experimentally to a tunable force dipole strength (so-called pushers with propulsion from the rod tail) generated by active rod macromolecules, e.g., catalysis with the solvent phase, ATP-induced propulsion, or light-activated propulsion. The simulations allow 2d spatial variations in all flow and orientational variables and full spherical orientational degrees of freedom; the attractors correspond to numerical integration of a coupled system of 125 nonlinear PDEs in 2d plus time. The phase diagrams with and without the polar interaction potential are remarkably similar, implying that polar interactions among the rodlike particles are not essential to long-range spatial and temporal correlations in flow, polarity, and nematic order. As a general rule, above a threshold, low volume fractions induce 1d banded patterns, whereas higher yet still dilute volume fractions yield 2d patterns. Again as a general rule, varying activation strength at fixed volume fraction induces novel dynamic transitions. First, stationary patterns saturate the instability of the isotropic state, consisting of discrete 1d banded or 2d cellular patterns depending on nanorod volume fraction. Increasing activation strength further induces a sequence of attractor bifurcations, including oscillations superimposed on the 1d and 2d stationary patterns, a uniform translational motion of 1d and 2d oscillating patterns, and periodic switching between 1d and 2d patterns. These results imply that active macromolecular suspensions are capable of long-range spatial and dynamic organization at isotropic equilibrium concentrations, provided particle-scale activation is sufficiently strong.

Celestial and terrestrial tele-ophthalmology: a health monitoring helmet for astronaut/cosmonaut and general public use

NASA Astrophysics Data System (ADS)

Ansari, Rafat R.; Rovati, Luigi; Sebag, Jerry

2001-06-01

A goggles-like head-mounted device equipped with several non-invasive techniques for quantitative medical evaluation of the eye, skin, and brain is envisioned for monitoring the health of astronauts and cosmonauts during long-term space travel and exploration. Real-time non-invasive evaluation of the different structures within these organs will provide indices of the health of these organs, as well as the entire body. The techniques such as dynamic light scattering (for the early detection of cataracts to evaluate effects of cosmic radiation), corneal autofluorescence (to assess extracellular matrix biology (e.g., diabetes), optical polarization (of aqueous fluid to evaluate serum chemistry), laser Doppler velocimetry (of retinal, optic nerve, and choroidal blood flow to assess ocular as well as central nervous system blood flow), reflectometry/oximetry (for oxygen metabolism), optical coherence tomography (for retinal microstructure), and possibility scanning laser technology for intraocular imaging and scanning will be integrated into this compact device.

PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA

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

Wang Lingzhi; Macri, Lucas M.; Krisciunas, Kevin

Dome A on the Antarctic plateau is likely one of the best observing sites on Earth thanks to the excellent atmospheric conditions present at the site during the long polar winter night. We present high-cadence time-series aperture photometry of 10,000 stars with i < 14.5 mag located in a 23 deg{sup 2} region centered on the south celestial pole. The photometry was obtained with one of the CSTAR telescopes during 128 days of the 2008 Antarctic winter. We used this photometric data set to derive site statistics for Dome A and to search for variable stars. Thanks to the nearlymore » uninterrupted synoptic coverage, we found six times as many variables as previous surveys with similar magnitude limits. We detected 157 variable stars, of which 55% were unclassified, 27% were likely binaries, and 17% were likely pulsating stars. The latter category includes {delta} Scuti, {gamma} Doradus, and RR Lyrae variables. One variable may be a transiting exoplanet.« less

CPO Prediction: Accuracy Assessment and Impact on UT1 Intensive Results

NASA Technical Reports Server (NTRS)

Malkin, Zinovy

2010-01-01

The UT1 Intensive results heavily depend on the celestial pole offset (CPO) model used during data processing. Since accurate CPO values are available with a delay of two to four weeks, CPO predictions are necessarily applied to the UT1 Intensive data analysis, and errors in the predictions can influence the operational UT1 accuracy. In this paper we assess the real accuracy of CPO prediction using the actual IERS and PUL predictions made in 2007-2009. Also, results of operational processing were analyzed to investigate the actual impact of EOP prediction errors on the rapid UT1 results. It was found that the impact of CPO prediction errors is at a level of several microseconds, whereas the impact of the inaccuracy in the polar motion prediction may be about one order of magnitude larger for ultra-rapid UT1 results. The situation can be amended if the IERS Rapid solution will be updated more frequently.

Optics of short-pitch deformed-helix ferroelectric liquid crystals: Symmetries, exceptional points, and polarization-resolved angular patterns

NASA Astrophysics Data System (ADS)

Kiselev, Alexei D.; Chigrinov, Vladimir G.

2014-10-01

In order to explore electric-field-induced transformations of polarization singularities in the polarization-resolved angular (conoscopic) patterns emerging after deformed-helix ferroelectric liquid crystal (DHFLC) cells with subwavelength helix pitch, we combine the transfer matrix formalism with the results for the effective dielectric tensor of biaxial FLCs evaluated using an improved technique of averaging over distorted helical structures. Within the framework of the transfer matrix method, we deduce a number of symmetry relations and show that the symmetry axis of L lines (curves of linear polarization) is directed along the major in-plane optical axis which rotates under the action of the electric field. When the angle between this axis and the polarization plane of incident linearly polarized light is above its critical value, the C points (points of circular polarization) appear in the form of symmetrically arranged chains of densely packed star-monstar pairs. We also emphasize the role of phase singularities of a different kind and discuss the enhanced electro-optic response of DHFLCs near the exceptional point where the condition of zero-field isotropy is fulfilled.

On the evolution of developmental mechanisms: Divergent polarities in leaf growth as a case study.

PubMed

Gupta, Mainak Das; Nath, Utpal

2016-01-01

Most model plants used to study leaf growth share a common developmental mechanism, namely basipetal growth polarity, wherein the distal end differentiates first with progressively more proliferative cells toward the base. Therefore, this base-to-tip growth pattern has served as a paradigm to explain leaf growth and also formed the basis for several computational models. However, our recent report in The Plant Cell on the investigation of leaf growth in 75 eudicot species covering a wide range of eudicot families showed that leaves grow with divergent polarities in the proximo-distal axis or without any obvious polarity. This divergence in growth polarity is linked to the expression divergence of a conserved microRNA-transcription factor module. This study raises several questions on the evolutionary origin of leaf growth pattern, such as 'when and why in evolution did the divergent growth polarities arise?' and 'what were the molecular changes that led to this divergence?'. Here, we discuss a few of these questions in some detail.

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

Streubel, Robert; Kronast, Florian; Reiche, Christopher F.

For this work, we studied curvature-driven modifications to the magnetostatic coupling of vortex circulation and polarity in soft-magnetic closely packed cap arrays. A phase diagram for the magnetic remanent/transition states at room temperature as a function of diameter and thickness was assembled. For specimens with vortex remanent state (40 nm-thick Permalloy on 330 nm spherical nanoparticles), both vortex circulation and polarity were visualized. Intercap coupling upon vortex nucleation leads to the formation of vortex circulation patterns in closely packed arrays. The remanent circulation pattern can be tailored choosing the direction of the applied magnetic field with respect to the symmetrymore » axis of the hexagonal array. An even and random distribution of vortex polarity indicates the absence of any circulation-polarity coupling.« less

Femtosecond laser-induced surface structures on carbon fibers.

PubMed

Sajzew, Roman; Schröder, Jan; Kunz, Clemens; Engel, Sebastian; Müller, Frank A; Gräf, Stephan

2015-12-15

The influence of different polarization states during the generation of periodic nanostructures on the surface of carbon fibers was investigated using a femtosecond laser with a pulse duration τ=300  fs, a wavelength λ=1025  nm, and a peak fluence F=4  J/cm². It was shown that linear polarization results in a well-aligned periodic pattern with different orders of magnitude concerning their period and an alignment parallel and perpendicular to fiber direction, respectively. For circular polarization, both types of uniform laser-induced periodic surface structures (LIPSS) patterns appear simultaneously with different dominance in dependence on the position at the fiber surface. Their orientation was explained by the polarization-dependent absorptivity and the geometrical anisotropy of the carbon fibers.

The General History of Astronomy

NASA Astrophysics Data System (ADS)

Taton, René; Wilson, Curtis; Hoskin, editor Michael, , General

2009-09-01

Part V. Early Phases in the Reception of Newton's Theory: 14. The vortex theory in competition with Newtonian celestial dynamics Eric J. Aiton; 15. The shape of the Earth Seymour L. Chapin; 16. Clairaut and the motion of the lunar apse: The inverse-square law undergoes a test Craig B. Waff; 17. The precession of the equinoxes from Newton to d'Alembert and Euler Curtis Wilson; 18. The solar tables of Lacaille and the lunar tables of Mayer Eric G. Forbes and Curtis Wilson; 19. Predicting the mid-eighteenth-century return of Halley's Comet Craig B. Waff; Part VI. Celestial Mechanics During the Eighteenth Century: 20. The problem of perturbation analytically treated: Euler, Clairaut, d'Alembert Curtis Wilson; 21. The work of Lagrange in celestial mechanics Curtis Wilson; 22. Laplace Bruno Morando; Part VII. Observational Astronomy and the Application of Theory in the Late Eighteenth and Early Nineteenth Century: 23. Measuring solar parallax: The Venus transits of 1761 and 1769 and their nineteenth-century sequels Albert Van Helden; 24. The discovery of Uranus, the Titius-Bode and the asteroids Michael Hoskin; 25. Eighteenth-and nineteenth century developments in the theory and practice of orbit determination Brian G. Marsden; 26. The introduction of statistical reasoning into astronomy: from Newton to Poincaré Oscar Sheynin; 27. Astronomy and the theory of errors: from the method of averages to the method of least squares F. Schmeidler; Part VIII. The Development of Theory During the Nineteenth Century: 28. The golden age of celestial mechanics Bruno Morando; Part IX. The Application of Celestial Mechanics to the Solar System to the End of the Nineteenth Century: 29. Three centuries of lunar and planetary ephemerides and tables Bruno Morando; 30. Satellite ephemerides to 1900 Yoshihide Kozai; Illustrations; Combined index for Parts 2A and 2B.

Camera characterization for all-sky polarization measurements during the 2017 solar eclipse

NASA Astrophysics Data System (ADS)

Hashimoto, Taiga; Dahl, Laura M.; Laurie, Seth A.; Shaw, Joseph A.

2017-08-01

A solar eclipse provides a rare opportunity to observe skylight polarization during conditions that are fundamentally different than what we see every day. On 21 August 2017 we will measure the skylight polarization during a total solar eclipse in Rexburg, Idaho, USA. Previous research has shown that during totality the sky polarization pattern is altered significantly to become nominally symmetric about the zenith. However, there are still questions remaining about the details of how surface reflectance near the eclipse observation site and optical properties of aerosols in the atmosphere influence the totality sky polarization pattern. We will study how skylight polarization in a solar eclipse changes through each phase and how surface and atmospheric features affect the measured polarization signatures. To accomplish this, fully characterizing the cameras and fisheye lenses is critical. This paper reports measurements that include finding the camera sensitivity and its relationship to the required short exposure times, measuring the camera's spectral response function, mapping the angles of each camera pixel with the fisheye lens, and taking test measurements during daytime and twilight conditions. The daytime polarimetric images were compared to images from an existing all-sky polarization imager and a polarimetric radiative transfer model.

In Vitro Polarization of Colonoids to Create an Intestinal Stem Cell Compartment

PubMed Central

Attayek, Peter J.; Ahmad, Asad A.; Wang, Yuli; Williamson, Ian; Sims, Christopher E.; Magness, Scott T.; Allbritton, Nancy L.

2016-01-01

The polarity of proliferative and differentiated cellular compartments of colonic crypts is believed to be specified by gradients of key mitogens and morphogens. Indirect evidence demonstrates a tight correlation between Wnt- pathway activity and the basal-luminal patterning; however, to date there has been no direct experimental manipulation demonstrating that a chemical gradient of signaling factors can produce similar patterning under controlled conditions. In the current work, colonic organoids (colonoids) derived from cultured, multicellular organoid fragments or single stem cells were exposed in culture to steep linear gradients of two Wnt-signaling ligands, Wnt-3a and R-spondin1. The use of a genetically engineered Sox9-Sox9EGFP:CAGDsRED reporter gene mouse model and EdU-based labeling enabled crypt patterning to be quantified in the developing colonoids. Colonoids derived from multicellular fragments cultured for 5 days under a Wnt-3a or a combined Wnt-3a and R-spondin1 gradient were highly polarized with proliferative cells localizing to the region of the higher morphogen concentration. In a Wnt-3a gradient, Sox9EGFP polarization was 7.3 times greater than that of colonoids cultured in the absence of a gradient; and the extent of EdU polarization was 2.2 times greater than that in the absence of a gradient. Under a Wnt-3a/R-spondin1 gradient, Sox9EGFP polarization was 8.2 times greater than that of colonoids cultured in the absence of a gradient while the extent of EdU polarization was 10 times greater than that in the absence of a gradient. Colonoids derived from single stem cells cultured in Wnt-3a/R-spondin1 gradients were most highly polarized demonstrated by a Sox9EGFP polarization 20 times that of colonoids grown in the absence of a gradient. This data provides direct evidence that a linear gradient of Wnt signaling factors applied to colonic stem cells is sufficient to direct patterning of the colonoid unit in culture. PMID:27100890

The Importance of Primary Martian Surface and Airfall Dust Sample Return for Toxicological Hazard Evaluations for Human Exploration

NASA Technical Reports Server (NTRS)

Harrington, A. D.; McCubbin, F. M.

2018-01-01

Manned missions to the Moon highlight a major hazard for future human exploration of the Moon and beyond: surface dust. Not only did the dust cause mechanical and structural integrity issues with the suits, the dust 'storm' generated upon reentrance into the crew cabin caused "lunar hay fever" and "almost blindness" . It was further reported that the allergic response to the dust worsened with each exposure. Due to the prevalence of these high exposures, the Human Research Roadmap developed by NASA identifies the Risk of Adverse Health and Performance Effects of Celestial Dust Exposure as an area of concern. Extended human exploration will further increase the probability of inadvertent and repeated exposures to celestial dusts. Going forward, hazard assessments of celestial dusts will be determined through sample return efforts prior to astronaut deployment.

JPL VLBI Analysis Center IVS Annual Report for 2004

NASA Technical Reports Server (NTRS)

Jacobs, Chris

2005-01-01

This report describes the activities of the JPL VLBI analysis center for the year 2004. We continue to be celestial reference frame, terrestrial reference frame, earth orientation, and spacecraft navigation work using the VLBI technique. There are several areas of our work that are undergoing active development. In 2004 we demonstrated 1 mm level troposphere calibration on an intercontinental baseline. We detected our first X/Ka (8.4/32 GHz) VLBI fringes. We began to deploy Mark 5 recorders and to interface the Mark 5 units to our software correlator. We also have actively participated in the international VLBI community through our involvement in six papers at the February IVS meeting and by collaborating on a number of projects such as densifying the S/X celestial frame creating celestial frames at K (24 GHz) and Q-bands ($# GHz)>

Defect-Induced Hedgehog Polarization States in Multiferroics

NASA Astrophysics Data System (ADS)

Li, Linze; Cheng, Xiaoxing; Jokisaari, Jacob R.; Gao, Peng; Britson, Jason; Adamo, Carolina; Heikes, Colin; Schlom, Darrell G.; Chen, Long-Qing; Pan, Xiaoqing

2018-03-01

Continuous developments in nanotechnology require new approaches to materials synthesis that can produce novel functional structures. Here, we show that nanoscale defects, such as nonstoichiometric nanoregions (NSNRs), can act as nano-building blocks for creating complex electrical polarization structures in the prototypical multiferroic BiFeO3 . An array of charged NSNRs are produced in BiFeO3 thin films by tuning the substrate temperature during film growth. Atomic-scale scanning transmission electron microscopy imaging reveals exotic polarization rotation patterns around these NSNRs. These polarization patterns resemble hedgehog or vortex topologies and can cause local changes in lattice symmetries leading to mixed-phase structures resembling the morphotropic phase boundary with high piezoelectricity. Phase-field simulations indicate that the observed polarization configurations are mainly induced by charged states at the NSNRs. Engineering defects thus may provide a new route for developing ferroelectric- or multiferroic-based nanodevices.

Defect-Induced Hedgehog Polarization States in Multiferroics.

PubMed

Li, Linze; Cheng, Xiaoxing; Jokisaari, Jacob R; Gao, Peng; Britson, Jason; Adamo, Carolina; Heikes, Colin; Schlom, Darrell G; Chen, Long-Qing; Pan, Xiaoqing

2018-03-30

Continuous developments in nanotechnology require new approaches to materials synthesis that can produce novel functional structures. Here, we show that nanoscale defects, such as nonstoichiometric nanoregions (NSNRs), can act as nano-building blocks for creating complex electrical polarization structures in the prototypical multiferroic BiFeO_{3}. An array of charged NSNRs are produced in BiFeO_{3} thin films by tuning the substrate temperature during film growth. Atomic-scale scanning transmission electron microscopy imaging reveals exotic polarization rotation patterns around these NSNRs. These polarization patterns resemble hedgehog or vortex topologies and can cause local changes in lattice symmetries leading to mixed-phase structures resembling the morphotropic phase boundary with high piezoelectricity. Phase-field simulations indicate that the observed polarization configurations are mainly induced by charged states at the NSNRs. Engineering defects thus may provide a new route for developing ferroelectric- or multiferroic-based nanodevices.

Generation and dynamics of optical beams with polarization singularities.

PubMed

Cardano, Filippo; Karimi, Ebrahim; Marrucci, Lorenzo; de Lisio, Corrado; Santamato, Enrico

2013-04-08

We present a convenient method to generate vector beams of light having polarization singularities on their axis, via partial spin-to-orbital angular momentum conversion in a suitably patterned liquid crystal cell. The resulting polarization patterns exhibit a C-point on the beam axis and an L-line loop around it, and may have different geometrical structures such as "lemon", "star", and "spiral". Our generation method allows us to control the radius of L-line loop around the central C-point. Moreover, we investigate the free-air propagation of these fields across a Rayleigh range.

Status of the GroundBIRD Telescope

NASA Astrophysics Data System (ADS)

Choi, J.; Génova-Santos, R.; Hattori, M.; Hazumi, M.; Ishitsuka, H.; Kanno, F.; Karatsu, K.; Kiuchi, K.; Koyano, R.; Kutsuma, H.; Lee, K.; Mima, S.; Minowa, M.; Nagai, M.; Nagasaki, T.; Naruse, M.; Oguri, S.; Okada, T.; Otani, C.; Rebolo, R.; Rubiño-Martín, J.; Sekimoto, Y.; Suzuki, J.; Taino, T.; Tajima, O.; Tomita, N.; Uchida, T.; Won, E.; Yoshida, M.

2018-01-01

Our understanding of physics at very early Universe, as early as 10-35 s after the Big Bang, relies on the scenario known as the inflationary cosmology. Inflation predicts a particular polarization pattern in the cosmic microwave background, known as the B-mode yet the strength of such polarization pattern is extremely weak. To search for the B-mode of the polarization in the cosmic microwave background, we are constructing an off-axis rotating telescope to mitigate systematic effects as well as to maximize the sky coverage of the observation. We will discuss the present status of the GroundBIRD telescope.

Tree-level gluon amplitudes on the celestial sphere

NASA Astrophysics Data System (ADS)

Schreiber, Anders Ø.; Volovich, Anastasia; Zlotnikov, Michael

2018-06-01

Pasterski, Shao and Strominger have recently proposed that massless scattering amplitudes can be mapped to correlators on the celestial sphere at infinity via a Mellin transform. We apply this prescription to arbitrary n-point tree-level gluon amplitudes. The Mellin transforms of MHV amplitudes are given by generalized hypergeometric functions on the Grassmannian Gr (4 , n), while generic non-MHV amplitudes are given by more complicated Gelfand A-hypergeometric functions.

Measuring Angular Rate of Celestial Objects Using the Space Surveillance Telescope

DTIC Science & Technology

2015-03-01

is not subject to copyright protection in the United States. AFIT-ENG-MS-15-M-019 MEASURING ANGULAR RATE OF CELESTIAL OBJECTS USING THE SPACE ...Hypothesis Test MHTOR Multi-Hypothesis Test with Outlier Removal NEAs Near Earth Asteroids NASA National Aeronautics and Space Administration OTF...capabilities to warfighters, protecting them from collision with space debris, meteors and microsatellites has become a top priority [19]. In general, EO

Astronomy, Divination, and Politics in the Neo-Assyrian Empire

NASA Astrophysics Data System (ADS)

Verderame, Lorenzo

Celestial divination had an important role in the complex political and military machine of the Neo-Assyrian empire. Thousand of cuneiform documents dealing with celestial divination have come to light from the excavated archives of this period, as the Assurbanipal's library. Among them letters and reports enlight the relation of the king with his experts (ummânu), who performed divination and apotropaic rituals for his protection.

The Moon Illusion

NASA Astrophysics Data System (ADS)

Rees, W. G.

1986-06-01

The Moon illusion, or celestial illusion, is the illusion that the Moon near the horizon is larger than the Moon near the zenith, usually by a factor of about 2 in the diameter. The illusion has been known for over 2,000 years, and many explanations have been advanced for it. Four modern theories are discussed in this paper, and new data are presented which tend to confirm the common 'flattened celestial vault' hypothesis.

Obliquity of the Ecliptic

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

The angle between the planes of the ecliptic and the equator. On the celestial sphere, the angle at which the ecliptic intersects the celestial equator. The current (year 2000) value of the obliquity of ecliptic, which is denoted by the symbol ɛ, is 23° 26' 21''. Its value varies by ±9'' over a period of 18.6 years as a consequence of a phenomenon called nutation. Over a much longer period (abou...

Correlation analysis of 1 to 30 MeV celestial gamma rays

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

Long, J.L.

1984-01-01

This paper outlines the development of a method of producing celestial sky maps from the data generated by the University of California, Riverside's double Compton scatter gamma ray telescope. The method makes use of a correlation between the telescope's data and theoretical calculated response functions. The results of applying this technique to northern hemisphere data obtained from a 1978 balloon flight from Palestine, Texas are included.

Validation of Aquarius Measurements Using Radiative Transfer Models at L-Band

NASA Technical Reports Server (NTRS)

Dinnat, E.; LeVine, David M.; Abraham, S.; DeMattheis, P.; Utku, C.

2012-01-01

Aquarius/SAC-D was launched in June 2011 by NASA and CONAE (Argentine space agency). Aquarius includes three L-band (1.4 GHz) radiometers dedicated to measuring sea surface salinity. We report detailed comparisons of Aquarius measurements with radiative transfer model predictions. These comparisons were used as part ofthe initial assessment of Aquarius data. In particular, they were used successfully to estimate the radiometer calibration bias and stability. Further comparisons are being performed to assess the performance of models in the retrieval algorithm for correcting the effect of sources of geophysical "noise" (e.g. the galactic background, atmospheric attenuation and reflected signal from the Sun). Such corrections are critical in bringing the error in retrieved salinity down to the required 0.2 practical salinity unit (psu) on monthly global maps at 150 km by 150 km resolution. The forward models making up the Aquarius simulator have been very useful for preparatory studies in the years leading to Aquarius' launch. The simulator includes various components to compute effects ofthe following processes on the measured signal: 1) emission from Earth surfaces (ocean, land, ice), 2) atmospheric emission and absorption, 3) emission from the Sun, Moon and celestial Sky (directly through the antenna sidelobes or after reflection/scattering at the Earth surface), 4) Faraday rotation, and 5) convolution of the scene by the antenna gain patterns. Since the Aquarius radiometers tum-on in late July 2011, the simulator has been used to perform a first order validation of the data. This included checking the order of magnitude ofthe signal over ocean, land and ice surfaces, checking the relative amplitude of signal at different polarizations, and checking the variation with incidence angle. The comparisons were also used to assess calibration bias and monitor instruments calibration drift. The simulator is also being used in the salinity retrieval. For example, initial assessments of the salinity retrieved from Aquarius data showed degradation in accuracy at locations where glint from the galactic sky background was important. This was traced to an inaccurate correction for the Sky glint. We present comparisons of the simulator prediction to the Aquarius data in order to assess the performances of the models of various physical processes impacting the measurements, such as the effect of sea surface roughness, the impact of the celestial Sky and the Sun emission scattered at the rough ocean surface. We discuss what components of the simulator appear reliable and which ones need improvements. Improved knowledge on the radiative transfer models at L-band will not only lead to better salinity retrieved from Aquarius data, it will also allow be beneficial for SMOS or the upcoming SMAP mission.

Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic.

PubMed

Peacock, Elizabeth; Sonsthagen, Sarah A; Obbard, Martyn E; Boltunov, Andrei; Regehr, Eric V; Ovsyanikov, Nikita; Aars, Jon; Atkinson, Stephen N; Sage, George K; Hope, Andrew G; Zeyl, Eve; Bachmann, Lutz; Ehrich, Dorothee; Scribner, Kim T; Amstrup, Steven C; Belikov, Stanislav; Born, Erik W; Derocher, Andrew E; Stirling, Ian; Taylor, Mitchell K; Wiig, Øystein; Paetkau, David; Talbot, Sandra L

2015-01-01

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1-3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.

Implications of the Circumpolar Genetic Structure of Polar Bears for Their Conservation in a Rapidly Warming Arctic

PubMed Central

Peacock, Elizabeth; Sonsthagen, Sarah A.; Obbard, Martyn E.; Boltunov, Andrei; Regehr, Eric V.; Ovsyanikov, Nikita; Aars, Jon; Atkinson, Stephen N.; Sage, George K.; Hope, Andrew G.; Zeyl, Eve; Bachmann, Lutz; Ehrich, Dorothee; Scribner, Kim T.; Amstrup, Steven C.; Belikov, Stanislav; Born, Erik W.; Derocher, Andrew E.; Stirling, Ian; Taylor, Mitchell K.; Wiig, Øystein; Paetkau, David; Talbot, Sandra L.

2015-01-01

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat. PMID:25562525

Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic

USGS Publications Warehouse

Peacock, Elizabeth; Sonsthagen, Sarah A.; Obbard, Martyn E.; Boltunov, Andrei N.; Regehr, Eric V.; Ovsyanikov, Nikita; Aars, Jon; Atkinson, Stephen N.; Sage, George K.; Hope, Andrew G.; Zeyl, Eve; Bachmann, Lutz; Ehrich, Dorothee; Scribner, Kim T.; Amstrup, Steven C.; Belikov, Stanislav; Born, Erik W.; Derocher, Andrew E.; Stirling, Ian; Taylor, Mitchell K.; Wiig, Øystein; Paetkau, David; Talbot, Sandra L.

2015-01-01

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.

Polarimetric Imaging System for Automatic Target Detection and Recognition

DTIC Science & Technology

2000-03-01

technique shown in Figure 4(b) can also be used to integrate polarizer arrays with other types of imaging sensors, such as LWIR cameras and uncooled...vertical stripe pattern in this φ image is caused by nonuniformities in the particular polarizer array used. 2. CIRCULAR POLARIZATION IMAGING USING

Planar Cell Polarity Pathway – Coordinating morphogenetic cell behaviors with embryonic polarity

PubMed Central

Gray, Ryan S.; Roszko, Isabelle; Solnica-Krezel, Lilianna

2011-01-01

Planar cell polarization entails establishment of cellular asymmetries within the tissue plane. An evolutionarily conserved Planar Cell Polarity (PCP) signaling system employs intra- and intercellular feedback interactions between its core components, including Frizzled, Van Gogh, Flamingo, Prickle and Dishevelled, to establish their characteristic asymmetric intracellular distributions and coordinate planar polarity of cell populations. By translating global patterning information into asymmetries of cell membranes and intracellular organelles, PCP signaling coordinates morphogenetic behaviors of individual cells and cell populations with the embryonic polarity. In vertebrates, by polarizing cilia in the node/Kupffer’s vesicle, PCP signaling links the anteroposterior to left-right embryonic polarity. PMID:21763613

Population substructure and space use of Foxe Basin polar bears.

PubMed

Sahanatien, Vicki; Peacock, Elizabeth; Derocher, Andrew E

2015-07-01

Climate change has been identified as a major driver of habitat change, particularly for sea ice-dependent species such as the polar bear (Ursus maritimus). Population structure and space use of polar bears have been challenging to quantify because of their circumpolar distribution and tendency to range over large areas. Knowledge of movement patterns, home range, and habitat is needed for conservation and management. This is the first study to examine the spatial ecology of polar bears in the Foxe Basin management unit of Nunavut, Canada. Foxe Basin is in the mid-Arctic, part of the seasonal sea ice ecoregion and it is being negatively affected by climate change. Our objectives were to examine intrapopulation spatial structure, to determine movement patterns, and to consider how polar bear movements may respond to changing sea ice habitat conditions. Hierarchical and fuzzy cluster analyses were used to assess intrapopulation spatial structure of geographic position system satellite-collared female polar bears. Seasonal and annual movement metrics (home range, movement rates, time on ice) and home-range fidelity (static and dynamic overlap) were compared to examine the influence of regional sea ice on movements. The polar bears were distributed in three spatial clusters, and there were differences in the movement metrics between clusters that may reflect sea ice habitat conditions. Within the clusters, bears moved independently of each other. Annual and seasonal home-range fidelity was observed, and the bears used two movement patterns: on-ice range residency and annual migration. We predict that home-range fidelity may decline as the spatial and temporal predictability of sea ice changes. These new findings also provide baseline information for managing and monitoring this polar bear population.

Tunable ultra-broadband polarization filter based on three-core resonance of the fluid-infiltrated and gold-coated photonic crystal fiber

NASA Astrophysics Data System (ADS)

Liu, Yingchao; Chen, Hailiang; Ma, Mingjian; Zhang, Wenxun; Wang, Yujun; Li, Shuguang

2018-03-01

We propose a tunable ultra-broadband polarization filter based on three-core resonance of the fluid-infiltrated and gold-coated high birefringent photonic crystal fiber (HB-PCF). Gold film was applied to the inner walls of two cladding air holes and surface plasmon polaritons were generated on its surface. The two gold-coated cladding air holes acted as two defective cores. As the phase matching condition was satisfied, light transmitted in the fiber core and coupled to the two defective cores. The three-core PCF supported three super modes in two orthogonal polarization directions. The coupling characteristics among these modes were investigated using the finite-element method. We found that the coupling wavelengths and strength between these guided modes can be tuned by altering the structural parameters of the designed HB-PCF, such as the size of the voids, thickness of the gold-films and liquid infilling pattern. Under the optimized structural parameters, a tunable broadband polarization filter was realized. For one liquid infilling pattern, we obtained a broadband polarization filter which filtered out the light in y-polarization direction at the wavelength of 1550 nm. For another liquid infilling pattern, we filtered out light in the x-polarization direction at the wavelength of 1310 nm. Our studies on the designed HB-PCF made contributions to the further devising of tunable broadband polarization filters, which are extensively used in telecommunication and sensor systems. Project supported by the National Natural Science Foundation of China (Grant Nos. 61505175 and 61475134) and the Natural Science Foundation of Hebei Province (Grant Nos. F2017203110 and F2017203193).

Independent Manipulation of Topological Charges and Polarization Patterns of Optical Vortices

PubMed Central

Yang, Ching-Han; Chen, Yuan-Di; Wu, Shing-Trong; Fuh, Andy Ying-Guey

2016-01-01

We present a simple and flexible method to generate various vectorial vortex beams (VVBs) with a Pancharatnam phase based on the scheme of double reflections from a single liquid crystal spatial light modulator (SLM). In this configuration, VVBs are constructed by the superposition of two orthogonally polarized orbital angular momentum (OAM) eigenstates. To verify the optical properties of the generated beams, Stokes polarimetry is developed to measure the states of polarization (SOP) over the transverse plane, while a Shack–Hartmann wavefront sensor is used to measure the OAM charge of beams. It is shown that both the simulated and the experimental results are in good qualitative agreement. In addition, polarization patterns and OAM charges of generated beams can be controlled independently using the proposed method. PMID:27526858

Interface-mediated ferroelectric patterning and Mn valency in nano-structured PbTiO{sub 3}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3}

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

Krug, Ingo P.; Institut für Optik and Atomare Physik; Helmholtzzentrum für Materialien und Energie

2016-09-07

We employed a multitechnique approach using piezo-force response microscopy and photoemission microscopy to investigate a self-organizing polarization domain pattern in PbTiO{sub 3}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (PTO/LSMO) nanostructures. The polarization is correlated with the nanostructure morphology as well as with the thickness and Mn valence of the LSMO template layer. On the LSMO dots, the PTO is upwards polarized, whereas outside the nanodots, the polarization appears both strain and interface roughness dependent. The results suggest that the electronic structure and strain of the PTO/LSMO interface contribute to determining the internal bias of the ferroelectric layer.

Very-Long-Chain Fatty Acids Are Involved in Polar Auxin Transport and Developmental Patterning in Arabidopsis[W

PubMed Central

Roudier, François; Gissot, Lionel; Beaudoin, Frédéric; Haslam, Richard; Michaelson, Louise; Marion, Jessica; Molino, Diana; Lima, Amparo; Bach, Liên; Morin, Halima; Tellier, Frédérique; Palauqui, Jean-Christophe; Bellec, Yannick; Renne, Charlotte; Miquel, Martine; DaCosta, Marco; Vignard, Julien; Rochat, Christine; Markham, Jonathan E.; Moreau, Patrick; Napier, Johnathan; Faure, Jean-Denis

2010-01-01

Very-long-chain fatty acids (VLCFAs) are essential for many aspects of plant development and necessary for the synthesis of seed storage triacylglycerols, epicuticular waxes, and sphingolipids. Identification of the acetyl-CoA carboxylase PASTICCINO3 and the 3-hydroxy acyl-CoA dehydratase PASTICCINO2 revealed that VLCFAs are important for cell proliferation and tissue patterning. Here, we show that the immunophilin PASTICCINO1 (PAS1) is also required for VLCFA synthesis. Impairment of PAS1 function results in reduction of VLCFA levels that particularly affects the composition of sphingolipids, known to be important for cell polarity in animals. Moreover, PAS1 associates with several enzymes of the VLCFA elongase complex in the endoplasmic reticulum. The pas1 mutants are deficient in lateral root formation and are characterized by an abnormal patterning of the embryo apex, which leads to defective cotyledon organogenesis. Our data indicate that in both tissues, defective organogenesis is associated with the mistargeting of the auxin efflux carrier PIN FORMED1 in specific cells, resulting in local alteration of polar auxin distribution. Furthermore, we show that exogenous VLCFAs rescue lateral root organogenesis and polar auxin distribution, indicating their direct involvement in these processes. Based on these data, we propose that PAS1 acts as a molecular scaffold for the fatty acid elongase complex in the endoplasmic reticulum and that the resulting VLCFAs are required for polar auxin transport and tissue patterning during plant development. PMID:20145257

Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics.

PubMed

Cherry, Seth G; Derocher, Andrew E; Thiemann, Gregory W; Lunn, Nicholas J

2013-07-01

Understanding how seasonal environmental conditions affect the timing and distribution of synchronized animal movement patterns is a central issue in animal ecology. Migration, a behavioural adaptation to seasonal environmental fluctuations, is a fundamental part of the life history of numerous species. However, global climate change can alter the spatiotemporal distribution of resources and thus affect the seasonal movement patterns of migratory animals. We examined sea ice dynamics relative to migration patterns and seasonal geographical fidelity of an Arctic marine predator, the polar bear (Ursus maritimus). Polar bear movement patterns were quantified using satellite-linked telemetry data collected from collars deployed between 1991-1997 and 2004-2009. We showed that specific sea ice characteristics can predict the timing of seasonal polar bear migration on and off terrestrial refugia. In addition, fidelity to specific onshore regions during the ice-free period was predicted by the spatial pattern of sea ice break-up but not by the timing of break-up. The timing of migration showed a trend towards earlier arrival of polar bears on shore and later departure from land, which has been driven by climate-induced declines in the availability of sea ice. Changes to the timing of migration have resulted in polar bears spending progressively longer periods of time on land without access to sea ice and their marine mammal prey. The links between increased atmospheric temperatures, sea ice dynamics, and the migratory behaviour of an ice-dependent species emphasizes the importance of quantifying and monitoring relationships between migratory wildlife and environmental cues that may be altered by climate change. © 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.

Bio-inspired polarized skylight navigation: a review

NASA Astrophysics Data System (ADS)

Zhang, Xi; Wan, Yongqin; Li, Lijing

2015-12-01

The idea of using skylight polarization in navigation is learned from animals such as desert ants and honeybees. Various research groups have been working on the development of novel navigation systems inspired by polarized skylight. The research of background in polarized skylight navigation is introduced, and basic principle of the insects navigation is expatiated. Then, the research progress status at home and abroad in skylight polarization pattern, three bio-inspired polarized skylight navigation sensors and polarized skylight navigation are reviewed. Finally, the research focuses in the field of polarized skylight navigation are analyzed. At the same time, the trend of development and prospect in the future are predicted. It is believed that the review is helpful to people understand polarized skylight navigation and polarized skylight navigation sensors.

Killer rocks and the celestial police - The search for near-earth asteroids

NASA Technical Reports Server (NTRS)

Yeomans, Donald K.

1991-01-01

The discovery of asteroids near the earth as the result of search programs is detailed with attention given to methods for locating, tracking, and identifying asteroids. The concept of 'prediscovery' is discussed in which new asteroids are tracked backward in time through previous celestial observational data. The need for more comprehensive programs is identified in order to locate objects that present a clear danger of colliding with the earth.

Pattern formation in mass conserving reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Brauns, Fridtjof; Halatek, Jacob; Frey, Erwin

We present a rigorous theoretical framework able to generalize and unify pattern formation for quantitative mass conserving reaction-diffusion models. Mass redistribution controls chemical equilibria locally. Separation of diffusive mass redistribution on the level of conserved species provides a general mathematical procedure to decompose complex reaction-diffusion systems into effectively independent functional units, and to reveal the general underlying bifurcation scenarios. We apply this framework to Min protein pattern formation and identify the mechanistic roles of both involved protein species. MinD generates polarity through phase separation, whereas MinE takes the role of a control variable regulating the existence of MinD phases. Hence, polarization and not oscillations is the generic core dynamics of Min proteins in vivo. This establishes an intrinsic mechanistic link between the Min system and a broad class of intracellular pattern forming systems based on bistability and phase separation (wave-pinning). Oscillations are facilitated by MinE redistribution and can be understood mechanistically as relaxation oscillations of the polarization direction.

General-relativistic celestial mechanics. 4: Theory of satellite motion

NASA Astrophysics Data System (ADS)

Damour, T.; Soffel, M.; Xu, C.

1993-09-01

The basic equations needed for developing a complete relativistic theory of artificial Earth satellites are explicitly written down. These equations are given both in a local, geocentric frame and in the global, barycentric one. They are derived within our recently introduced general-relativistic celestial mechanics framework. Our approach is more satisfactory than previous ones, especially with regard to its consistency, completeness, and flexibility. In particular, the problem of representing the relativistic gravitational effects associated with the quadrupole and higher multipole moments of the moving Earth, which caused difficulties in several other approaches, is easily dealth with in our approach, thanks to the use of previously developed tools: definition of relativistic multipole moments and transformation theory between reference frames. With this last paper in a series, we hope to indicate the way of using our formalism in specific problems in applied celestial mechanics and astrometry.

Polynomial equations for science orbits around Europa

NASA Astrophysics Data System (ADS)

Cinelli, Marco; Circi, Christian; Ortore, Emiliano

2015-07-01

In this paper, the design of science orbits for the observation of a celestial body has been carried out using polynomial equations. The effects related to the main zonal harmonics of the celestial body and the perturbation deriving from the presence of a third celestial body have been taken into account. The third body describes a circular and equatorial orbit with respect to the primary body and, for its disturbing potential, an expansion in Legendre polynomials up to the second order has been considered. These polynomial equations allow the determination of science orbits around Jupiter's satellite Europa, where the third body gravitational attraction represents one of the main forces influencing the motion of an orbiting probe. Thus, the retrieved relationships have been applied to this moon and periodic sun-synchronous and multi-sun-synchronous orbits have been determined. Finally, numerical simulations have been carried out to validate the analytical results.

Almanac services for celestial navigation

NASA Astrophysics Data System (ADS)

Nelmes, S.; Whittaker, J.

2015-08-01

Celestial navigation remains a vitally important back up to Global Navigation Satellite Systems (GNSS) and relies on the use of almanac services. HM Nautical Almanac Office (HMNAO) provides a number of these services. The printed book, The Nautical Almanac, produced yearly and now available as an electronic publication, is continuously being improved, making use of the latest ideas and ephemerides to provide the user with their required data. HMNAO also produces NavPac, a software package that assists the user in calculating their position as well as providing additional navigational and astronomical tools. A new version of NavPac will be released in 2015 that will improve the user experience. The development of applications for mobile devices is also being considered. HMNAO continues to combine the latest improvements and theories of astrometry with the creation of books and software that best meet the needs of celestial navigation users.

Infrared radiation scene generation of stars and planets in celestial background

NASA Astrophysics Data System (ADS)

Guo, Feng; Hong, Yaohui; Xu, Xiaojian

2014-10-01

An infrared (IR) radiation generation model of stars and planets in celestial background is proposed in this paper. Cohen's spectral template1 is modified for high spectral resolution and accuracy. Based on the improved spectral template for stars and the blackbody assumption for planets, an IR radiation model is developed which is able to generate the celestial IR background for stars and planets appearing in sensor's field of view (FOV) for specified observing date and time, location, viewpoint and spectral band over 1.2μm ~ 35μm. In the current model, the initial locations of stars are calculated based on midcourse space experiment (MSX) IR astronomical catalogue (MSX-IRAC) 2 , while the initial locations of planets are calculated using secular variations of the planetary orbits (VSOP) theory. Simulation results show that the new IR radiation model has higher resolution and accuracy than common model.

Archaic artifacts resembling celestial spheres

NASA Astrophysics Data System (ADS)

Dimitrakoudis, S.; Papaspyrou, P.; Petoussis, V.; Moussas, X.

We present several bronze artifacts from the Archaic Age in Greece (750-480 BC) that resemble celestial spheres or forms of other astronomical significance. They are studied in the context of the Dark Age transition from Mycenaean Age astronomical themes to the philosophical and practical revival of astronomy in the Classical Age with its plethora of astronomical devices. These artifacts, mostly votive in nature are spherical in shape and appear in a variety of forms their most striking characteristic being the depiction of meridians and/or an equator. Most of those artifacts come from Thessaly, and more specifically from the temple of Itonia Athena at Philia, a religious center of pan-Hellenic significance. Celestial spheres, similar in form to the small artifacts presented in this study, could be used to measure latitudes, or estimate the time at a known place, and were thus very useful in navigation.

Patterned light flash evoked short latency activity in the visual system of visually normal and in amblyopic subjects.

PubMed

Sjöström, A; Abrahamsson, M

1994-04-01

In a previous experimental study on anaesthetized cat it was shown that a short latency (35-40 ms) cortical potential changed polarity due to the presence or absence of a pattern in the flash stimulus. The results suggested one pathway of neuronal activation in the cortex to a pattern that was within the level of resolution and another to patterns that were not. It was implied that a similar difference in impulse transmission to pattern and non-pattern stimuli may be recorded in humans. The present paper describes recordings of the short-latency visual evoked response to varying light flash checkerboard pattern stimuli of high intensity in visually normal and amblyopic children and adults. When stimulating the normal eye a visual evoked response potential with a peak latency between 35 to 40 ms showed a polarity change to patterned compared to non-patterned stimulation. The visual evoked response resolution limit could be correlated to a visual acuity of 0.5 and below. In amblyopic eyes the shift in polarity was recorded at the acuity limit level. The latency of the pattern depending potential was increased in patients with amblyopia compared to normal, but not directly related to amblyopic degree. It is concluded that the short latency, visual evoked response that mainly represents the retino-geniculo-cortical activation may be used to estimate visual resolution below 0.5 in acuity level.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducing the Photospheric Magnetic Field Evolution During the Rise of Cycle 24 with Flux Transport by Supergranules

NASA Technical Reports Server (NTRS)

Hathaway, David H.; Upton, Lisa

2012-01-01

We simulate the transport of magnetic flux in the Sun s photosphere by an evolving pattern of cellular horizontal flows (supergranules). Characteristics of the simulated flow pattern match observed characteristics including the velocity power spectrum, cell lifetimes, and cell pattern motion in longitude and latitude. Simulations using an average, and north-south symmetric, meridional motion of the cellular pattern produce polar magnetic fields that are too weak in the North and too strong in the South. Simulations using cellular patterns with meridional motions that evolve with the observed changes in strength and north-south asymmetry will be analyzed to see if they reproduce the polar field evolution observed during the rise of Cycle 24.

Ultrafast Microscopy of Spin-Momentum-Locked Surface Plasmon Polaritons.

PubMed

Dai, Yanan; Dąbrowski, Maciej; Apkarian, Vartkess A; Petek, Hrvoje

2018-06-26

Using two-photon photoemission electron microscopy (2P-PEEM) we image the polarization dependence of coupling and propagation of surface plasmon polaritons (SPPs) launched from edges of a triangular, micrometer size, single-crystalline Ag crystal by linearly or circularly polarized light. 2P-PEEM records interferences between the optical excitation field and SPPs it creates with nanofemto space-time resolution. Both the linearly and circularly polarized femtosecond light pulses excite spatially asymmetric 2PP yield distributions, which are imaged. We attribute the asymmetry for linearly polarized light to the relative alignments of the laser polarization and triangle edges, which affect the efficiency of excitation of the longitudinal component of the SPP field. For circular polarization, the asymmetry is caused by matching of the spin angular momenta (SAM) of light and the transverse SAM of SPPs. Moreover, we show that the interference patterns recorded in the 2P-PEEM images are cast by phase shifts and amplitudes for coupling of light into the longitudinal and transverse components of SPP fields. While the interference patterns depend on the excitation polarization, nanofemto movies show that the phase and group velocities of SPPs are independent of SAM of light in time-reversal invariant media. Simulations of the wave interference reproduce the polarization and spin-dependent coupling of optical pulses into SPPs.

Transcriptional Modulation of Genes Encoding Structural Characteristics of Differentiating Enterocytes During Development of a Polarized Epithelium In Vitro

PubMed Central

Halbleib, Jennifer M.; Sääf, Annika M.

2007-01-01

Although there is considerable evidence implicating posttranslational mechanisms in the development of epithelial cell polarity, little is known about the patterns of gene expression and transcriptional regulation during this process. We characterized the temporal program of gene expression during cell–cell adhesion–initiated polarization of human Caco-2 cells in tissue culture, which develop structural and functional polarity similar to that of enterocytes in vivo. A distinctive switch in gene expression patterns occurred upon formation of cell–cell contacts between neighboring cells. Expression of genes involved in cell proliferation was down-regulated concomitant with induction of genes necessary for functional specialization of polarized epithelial cells. Transcriptional up-regulation of these latter genes correlated with formation of important structural and functional features in enterocyte differentiation and establishment of structural and functional cell polarity; components of the apical microvilli were induced as the brush border formed during polarization; as barrier function was established, expression of tight junction transmembrane proteins peaked; transcripts encoding components of the apical, but not the basal-lateral trafficking machinery were increased during polarization. Coordinated expression of genes encoding components of functional cell structures were often observed indicating temporal control of expression and assembly of multiprotein complexes. PMID:17699590

Airborne antenna polarization study for the microwave landing system

NASA Technical Reports Server (NTRS)

Gilreath, M. C.

1976-01-01

The feasibility of the microwave landing system (MLS) airborne antenna pattern coverage requirements are investigated for a large commercial aircraft using a single omnidirectional antenna. Omnidirectional antennas having vertical and horizontal polarizations were evaluated at several different station locations on a one-eleventh scale model Boeing 737 aircraft. The results obtained during this experimental program are presented which include principal plane antenna patterns and complete volumetric coverage plots.

Quadrupole radiation from terahertz dipole antennas.

PubMed

Rudd, J V; Johnson, J L; Mittleman, D M

2000-10-15

We report what is to our knowledge the first detailed investigation of the polarization state of radiation from lens-coupled terahertz dipole antennas. The radiation exhibits a weak but measurable component that is polarized orthogonally to the orientation of the emitter dipole. The angular radiation pattern of this cross-polarized emission reveals that it is quadrupolar, rather than dipolar, in nature. One can understand this result by taking into account the photocurrent flowing in the strip lines that feed the dipole antenna. A Fresnel-Kirchhoff scalar diffraction calculation is used for calculating the frequency-dependent angular distribution of the radiation pattern, providing satisfactory agreement with the measurements.

Wave-vector and polarization dependence of conical refraction.

PubMed

Turpin, A; Loiko, Yu V; Kalkandjiev, T K; Tomizawa, H; Mompart, J

2013-02-25

We experimentally address the wave-vector and polarization dependence of the internal conical refraction phenomenon by demonstrating that an input light beam of elliptical transverse profile refracts into two beams after passing along one of the optic axes of a biaxial crystal, i.e. it exhibits double refraction instead of refracting conically. Such double refraction is investigated by the independent rotation of a linear polarizer and a cylindrical lens. Expressions to describe the position and the intensity pattern of the refracted beams are presented and applied to predict the intensity pattern for an axicon beam propagating along the optic axis of a biaxial crystal.

Transfer Printing Method to Obtain Polarized Light Emission in Organic Light-Emitting Device

NASA Astrophysics Data System (ADS)

Noh, Hee Yeon; Park, Chang-sub; Park, Ji-Sub; Kang, Shin-Won; Kim, Hak-Rin

2012-06-01

We demonstrate a transfer printing method to obtain polarized light emission in organic light-emitting devices (OLEDs). On a rubbed self-assembled monolayer (SAM), a spin-coated liquid crystalline light-emissive polymer is aligned along the rubbing direction because of the anisotropic interfacial intermolecular interaction. Owing to the low surface energy of the SAM surface, the light-emissive layer was easily transferred to a patterned poly(dimethylsiloxane) (PDMS) stamp surface without degrading the ordering. Finally, a polarized light-emissive OLED device was prepared by transferring the patterned light-emissive layer to the charge transport layer of the OLED structure.

Design of a polarization-independent, wide-angle, broadband visible absorber

NASA Astrophysics Data System (ADS)

Jia, Xiuli; Wang, Xiaoou

2018-01-01

Many optical systems benefit from elements that can absorb a broad range of wavelengths over a wide range of angles, independent of polarization. In this paper, we present a polarization-independent, wide-angle, broadband absorber in the visible regime that exploits strong symmetric and asymmetric resonance modes of electromagnetic dipoles. It makes use of a bilayer cross-pattern structure which is simple, having five layers that include two stacks of metal ribbon in cross-patterns, two dielectric spacers and a metal reflecting layer. Simulations show that the design exhibits a significantly enhanced absorption property when compared to a device with a bilayer metal film structure or any other complex structure of cross-patterns that have no intersection angle. The maximum absorption efficiency of the device is 100% at resonances, and its absorption characteristics can be maintained over a wide range of angles of incidence - up to ± 60° - regardless of the incident polarization. This strategy can, in principle, be applied to other material systems and could be useful in diverse applications, including thermal emitters, photovoltaics and photodetectors.

Discovery of the surface polarity gradient on iridescent Morpho butterfly scales reveals a mechanism of their selective vapor response

PubMed Central

Potyrailo, Radislav A.; Starkey, Timothy A.; Vukusic, Peter; Ghiradella, Helen; Vasudev, Milana; Bunning, Timothy; Naik, Rajesh R.; Tang, Zhexiong; Larsen, Michael; Deng, Tao; Zhong, Sheng; Palacios, Manuel; Grande, James C.; Zorn, Gilad; Goddard, Gregory; Zalubovsky, Sergey

2013-01-01

For almost a century, the iridescence of tropical Morpho butterfly scales has been known to originate from 3D vertical ridge structures of stacked periodic layers of cuticle separated by air gaps. Here we describe a biological pattern of surface functionality that we have found in these photonic structures. This pattern is a gradient of surface polarity of the ridge structures that runs from their polar tops to their less-polar bottoms. This finding shows a biological pattern design that could stimulate numerous technological applications ranging from photonic security tags to self-cleaning surfaces, gas separators, protective clothing, sensors, and many others. As an important first step, this biomaterial property and our knowledge of its basis has allowed us to unveil a general mechanism of selective vapor response observed in the photonic Morpho nanostructures. This mechanism of selective vapor response brings a multivariable perspective for sensing, where selectivity is achieved within a single chemically graded nanostructured sensing unit, rather than from an array of separate sensors. PMID:24019497

Surface Structuring with Polarization-Singular Femtosecond Laser Beams Generated by a q-plate

PubMed Central

Nivas, Jijil JJ; Cardano, Filippo; Song, Zhenming; Rubano, Andrea; Fittipaldi, Rosalba; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2017-01-01

In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.) have been used to generate complex, regular surface patterns on different materials. Here we present an experimental investigation on direct femtosecond laser surface structuring based on a larger class of vector beams generated by means of a q-plate with topological charge q = +1/2. In fact, voltage tuning of q-plate optical retardation allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane. These beams can be thought of as a controlled coherent superposition of a Gaussian beam with uniform polarization and a vortex beam with a radial or azimuthal state of polarization. The use of this family of ultrashort laser beams in surface structuring leads to a further extension of the achievable surface patterns. The comparison of theoretical predictions of the vector beam characteristics at the focal plane and the generated surface patterns is used to rationalize the dependence of the surface structures on the local state of the laser beam, thus offering an effective way to either design unconventional surface structures or diagnose complex ultrashort laser beams. PMID:28169342

Surface Structuring with Polarization-Singular Femtosecond Laser Beams Generated by a q-plate.

PubMed

Nivas, Jijil Jj; Cardano, Filippo; Song, Zhenming; Rubano, Andrea; Fittipaldi, Rosalba; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2017-02-07

In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.) have been used to generate complex, regular surface patterns on different materials. Here we present an experimental investigation on direct femtosecond laser surface structuring based on a larger class of vector beams generated by means of a q-plate with topological charge q = +1/2. In fact, voltage tuning of q-plate optical retardation allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane. These beams can be thought of as a controlled coherent superposition of a Gaussian beam with uniform polarization and a vortex beam with a radial or azimuthal state of polarization. The use of this family of ultrashort laser beams in surface structuring leads to a further extension of the achievable surface patterns. The comparison of theoretical predictions of the vector beam characteristics at the focal plane and the generated surface patterns is used to rationalize the dependence of the surface structures on the local state of the laser beam, thus offering an effective way to either design unconventional surface structures or diagnose complex ultrashort laser beams.

Surface Structuring with Polarization-Singular Femtosecond Laser Beams Generated by a q-plate

NASA Astrophysics Data System (ADS)

Nivas, Jijil Jj; Cardano, Filippo; Song, Zhenming; Rubano, Andrea; Fittipaldi, Rosalba; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2017-02-01

In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.) have been used to generate complex, regular surface patterns on different materials. Here we present an experimental investigation on direct femtosecond laser surface structuring based on a larger class of vector beams generated by means of a q-plate with topological charge q = +1/2. In fact, voltage tuning of q-plate optical retardation allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane. These beams can be thought of as a controlled coherent superposition of a Gaussian beam with uniform polarization and a vortex beam with a radial or azimuthal state of polarization. The use of this family of ultrashort laser beams in surface structuring leads to a further extension of the achievable surface patterns. The comparison of theoretical predictions of the vector beam characteristics at the focal plane and the generated surface patterns is used to rationalize the dependence of the surface structures on the local state of the laser beam, thus offering an effective way to either design unconventional surface structures or diagnose complex ultrashort laser beams.

Ortho-Babinet polarization-interrogating filter: an interferometric approach to polarization measurement.

PubMed

Van Delden, Jay S

2003-07-15

A novel, interferometric, polarization-interrogating filter assembly and method for the simultaneous measurement of all four Stokes parameters across a partially polarized irradiance image in a no-moving-parts, instantaneous, highly sensitive manner is described. In the reported embodiment of the filter, two spatially varying linear retarders and a linear polarizer comprise an ortho-Babinet, polarization-interrogating (OBPI) filter. The OBPI filter uniquely encodes the incident ensemble of electromagnetic wave fronts comprising a partially polarized irradiance image in a controlled, deterministic, spatially varying manner to map the complete state of polarization across the image to local variations in a superposed interference pattern. Experimental interferograms are reported along with a numerical simulation of the method.

Unusual polarity-dependent patterns in a bent-core nematic liquid crystal under low-frequency ac field.

PubMed

Xiang, Ying; Zhou, Meng-jie; Xu, Ming-Ya; Salamon, Péter; Éber, Nándor; Buka, Ágnes

2015-04-01

Electric-field-induced patterns of diverse morphology have been observed over a wide frequency range in a recently synthesized bent-core nematic (BCN) liquid crystal. At low frequencies (up to ∼25 Hz), the BCN exhibited unusual polarity-dependent patterns. When the amplitude of the ac field was enhanced, these two time-asymmetrical patterns turned into time-symmetrical prewavylike stripes. At ac frequencies in the middle-frequency range (∼50-3000 Hz), zigzag patterns were detected whose obliqueness varied with the frequency. Finally, if the frequency was increased above 3 kHz, the zigzag pattern was replaced by another, prewavylike pattern, whose threshold voltage depended on the frequency; however, the wave vector did not. For a more complete characterization, material parameters such as elastic constants, dielectric permittivities, and the anisotropy of the diamagnetic susceptibility were also determined.

Nonlinear Uncertainty Propagation of Satellite State Error for Tracking and Conjunction Risk Assessment

DTIC Science & Technology

2017-12-18

Determination on Orbital Element Representations,” Celestial Mechanics and Dynamical Astronomy , Vol. 118, pp.165-195, 2014. [8] R. Weisman, M. Jah...Nonlinear Filtering,” Celestial Mechanics and Dynamical Astronomy , Vol. 118, pp.129-164, 2014. [10] R. Weisman, M. Majji, K. Alfriend, “Analytic...Conference on Mathematics and Astronomy : A Joint Long Journey, American Institute of Physics, 10.1063/1.3506064, Madrid, Spain, 2009. [33] X.L. Xu, Y.Q

Surface Photometry of Celestial Sources from a Space Vehicle: Introduction and Observational Procedures*

PubMed Central

Roach, Franklin E.; Carroll, Benjamin; Aller, Lawrence H.; Smith, Leroi

1972-01-01

Diffuse celestial sources of relatively low surface brightness such as the Milky Way, zodiacal light, and gegenschein (or contre lumière) can be studied most reliably from above the earth's atmosphere with equipment flown in artificial satellites. We review the techniques used and some of the difficulties encountered in day-time observations from satellites by the use of a special photometer and polarimeter flown in the orbiting skylab observatory, OSO-6. PMID:16591970

Pulmonary Inflammatory Responses to Acute Meteorite Dust Exposures - Implications for Human Space Exploration

NASA Technical Reports Server (NTRS)

Harrington, A. D.; McCubbin, F. M.; Vander Kaaden, K. E.; Kaur, J.; Smirnov, A.; Galdanes, K.; Schoonen, M. A. A.; Chen, L. C.; Tsirka, S. E.; Gordon, T.

2018-01-01

New initiatives to send humans to Mars within the next few decades are illustrative of the resurgence of interest in space travel. However, as with all exploration, there are risks. The Human Research Roadmap developed by NASA identifies the Risk of Adverse Health and Performance Effects of Celestial Dust Exposure as an area of concern. Extended human exploration will further increase the probability of inadvertent and repeated exposures to celestial dusts.

Analysis of spatial pseudodepolarizers in imaging systems

NASA Technical Reports Server (NTRS)

Mcguire, James P., Jr.; Chipman, Russell A.

1990-01-01

The objective of a number of optical instruments is to measure the intensity accurately without bias as to the incident polarization state. One method to overcome polarization bias in optical systems is the insertion of a spatial pseudodepolarizer. Both the degree of depolarization and image degradation (from the polarization aberrations of the pseudodepolarizer) are analyzed for two depolarizer designs: (1) the Cornu pseudodepolarizer, effective for linearly polarized light, and (2) the dual Babinet compensator pseudodepolarizer, effective for all incident polarization states. The image analysis uses a matrix formalism to describe the polarization dependence of the diffraction patterns and optical transfer function.

Bio-Inspired Polarized Skylight-Based Navigation Sensors: A Review

PubMed Central

Karman, Salmah B.; Diah, S. Zaleha M.; Gebeshuber, Ille C.

2012-01-01

Animal senses cover a broad range of signal types and signal bandwidths and have inspired various sensors and bioinstrumentation devices for biological and medical applications. Insects, such as desert ants and honeybees, for example, utilize polarized skylight pattern-based information in their navigation activities. They reliably return to their nests and hives from places many kilometers away. The insect navigation system involves the dorsal rim area in their compound eyes and the corresponding polarization sensitive neurons in the brain. The dorsal rim area is equipped with photoreceptors, which have orthogonally arranged small hair-like structures termed microvilli. These are the specialized sensors for the detection of polarized skylight patterns (e-vector orientation). Various research groups have been working on the development of novel navigation systems inspired by polarized skylight-based navigation in animals. Their major contributions are critically reviewed. One focus of current research activities is on imitating the integration path mechanism in desert ants. The potential for simple, high performance miniaturized bioinstrumentation that can assist people in navigation will be explored. PMID:23202158

Bio-inspired polarized skylight-based navigation sensors: a review.

PubMed

Karman, Salmah B; Diah, S Zaleha M; Gebeshuber, Ille C

2012-10-24

Animal senses cover a broad range of signal types and signal bandwidths and have inspired various sensors and bioinstrumentation devices for biological and medical applications. Insects, such as desert ants and honeybees, for example, utilize polarized skylight pattern-based information in their navigation activities. They reliably return to their nests and hives from places many kilometers away. The insect navigation system involves the dorsal rim area in their compound eyes and the corresponding polarization sensitive neurons in the brain. The dorsal rim area is equipped with photoreceptors, which have orthogonally arranged small hair-like structures termed microvilli. These are the specialized sensors for the detection of polarized skylight patterns (e-vector orientation). Various research groups have been working on the development of novel navigation systems inspired by polarized skylight-based navigation in animals. Their major contributions are critically reviewed. One focus of current research activities is on imitating the integration path mechanism in desert ants. The potential for simple, high performance miniaturized bioinstrumentation that can assist people in navigation will be explored.

Formation of polarity convergences underlying shoot outgrowths

PubMed Central

Abley, Katie; Sauret-Güeto, Susanna; Marée, Athanasius FM; Coen, Enrico

2016-01-01

The development of outgrowths from plant shoots depends on formation of epidermal sites of cell polarity convergence with high intracellular auxin at their centre. A parsimonious model for generation of convergence sites is that cell polarity for the auxin transporter PIN1 orients up auxin gradients, as this spontaneously generates convergent alignments. Here we test predictions of this and other models for the patterns of auxin biosynthesis and import. Live imaging of outgrowths from kanadi1 kanadi2 Arabidopsis mutant leaves shows that they arise by formation of PIN1 convergence sites within a proximodistal polarity field. PIN1 polarities are oriented away from regions of high auxin biosynthesis enzyme expression, and towards regions of high auxin importer expression. Both expression patterns are required for normal outgrowth emergence, and may form part of a common module underlying shoot outgrowths. These findings are more consistent with models that spontaneously generate tandem rather than convergent alignments. DOI: http://dx.doi.org/10.7554/eLife.18165.001 PMID:27478985

Mastery in Goal Scoring, T-Pattern Detection, and Polar Coordinate Analysis of Motor Skills Used by Lionel Messi and Cristiano Ronaldo

PubMed Central

Castañer, Marta; Barreira, Daniel; Camerino, Oleguer; Anguera, M. Teresa; Fernandes, Tiago; Hileno, Raúl

2017-01-01

Research in soccer has traditionally given more weight to players' technical and tactical skills, but few studies have analyzed the motor skills that underpin specific motor actions. The objective of this study was to investigate the style of play of the world's top soccer players, Cristiano Ronaldo and Lionel Messi, and how they use their motor skills in attacking actions that result in a goal. We used and improved the easy-to-use observation instrument (OSMOS-soccer player) with 9 criteria, each one expanded to build 50 categories. Associations between these categories were investigated by T-pattern detection and polar coordinate analysis. T-pattern analysis detects temporal structures of complex behavioral sequences composed of simpler or directly distinguishable events within specified observation periods (time point series). Polar coordinate analysis involves the application of a complex procedure to provide a vector map of interrelated behaviors obtained from prospective and retrospective sequential analysis. The T-patterns showed that for both players the combined criteria were mainly between the different aspects of motor skills, namely the use of lower limbs, contact with the ball using the outside of the foot, locomotion, body orientation with respect to the opponent goal line, and the criteria of technical actions and the right midfield. Polar coordinate analysis detected significant associations between the same criteria included in the T-patterns as well as the criteria of turning the body, numerical equality with no pressure, and relative numerical superiority. PMID:28553245

Mastery in Goal Scoring, T-Pattern Detection, and Polar Coordinate Analysis of Motor Skills Used by Lionel Messi and Cristiano Ronaldo.

PubMed

Castañer, Marta; Barreira, Daniel; Camerino, Oleguer; Anguera, M Teresa; Fernandes, Tiago; Hileno, Raúl

2017-01-01

Research in soccer has traditionally given more weight to players' technical and tactical skills, but few studies have analyzed the motor skills that underpin specific motor actions. The objective of this study was to investigate the style of play of the world's top soccer players, Cristiano Ronaldo and Lionel Messi, and how they use their motor skills in attacking actions that result in a goal. We used and improved the easy-to-use observation instrument (OSMOS-soccer player) with 9 criteria, each one expanded to build 50 categories. Associations between these categories were investigated by T-pattern detection and polar coordinate analysis. T-pattern analysis detects temporal structures of complex behavioral sequences composed of simpler or directly distinguishable events within specified observation periods (time point series). Polar coordinate analysis involves the application of a complex procedure to provide a vector map of interrelated behaviors obtained from prospective and retrospective sequential analysis. The T-patterns showed that for both players the combined criteria were mainly between the different aspects of motor skills, namely the use of lower limbs, contact with the ball using the outside of the foot, locomotion, body orientation with respect to the opponent goal line, and the criteria of technical actions and the right midfield. Polar coordinate analysis detected significant associations between the same criteria included in the T-patterns as well as the criteria of turning the body, numerical equality with no pressure, and relative numerical superiority.

Linearly Polarized Single-Frequency Oscillations of Laser-Diode-Pumped Microchip Ceramic Nd:YAG Lasers with Forced Ince-Gaussian Mode Operations

NASA Astrophysics Data System (ADS)

Otsuka, Kenju; Nemoto, Kana; Kamikariya, Koji; Miyasaka, Yoshihiko; Chu, Shu-Chun

2007-09-01

Detailed oscillation spectra and polarization properties have been examined in laser-diode-pumped (LD-pumped) microchip ceramic (i.e., polycrystalline) Nd:YAG lasers and the inherent segregation of lasing patterns into local modes possessing different polarization states was observed. Single-frequency linearly-polarized stable oscillations were realized by forcing the laser to Ince-Gaussian mode operations by adjusting azimuthal cavity symmetry.

Anisotropic properties of periodically polarity-inverted zinc oxide structures

NASA Astrophysics Data System (ADS)

Park, J. S.; Minegishi, T.; Lee, J. W.; Hong, S. K.; Song, J. H.; Lee, J. Y.; Yoon, E.; Yao, T.

2010-06-01

We report on the anisotropic structural properties of periodically polarity-inverted (PPI) ZnO structures grown on patterned templates. The etching and growth rates along ⟨112¯0⟩ direction of ZnO structures are higher than those of ⟨101¯0⟩ direction of ZnO films. From the strain evaluation by Raman spectroscopy, compressive strains are observed in all PPI ZnO samples with different stripe pattern size and the smaller pattern size is more effective to residual stress relaxation. The detailed structures at transition region show relationship with the anisotropic crystal quality.

Polarization control in flexible interference lithography for nano-patterning of different photonic structures with optimized contrast.

PubMed

He, Jianfang; Fang, Xiaohui; Lin, Yuanhai; Zhang, Xinping

2015-05-04

Half-wave plates were introduced into an interference-lithography scheme consisting of three fibers that were arranged into a rectangular triangle. Such a flexible and compact geometry allows convenient tuning of the polarizations of both the UV laser source and each branch arm. This not only enables optimization of the contrast of the produced photonic structures with expected square lattices, but also multiplies the nano-patterning functions of a fixed design of fiber-based interference lithography. The patterns of the photonic structures can be thus tuned simply by rotating a half-wave plate.

Self-organizing periodicity in development: organ positioning in plants.

PubMed

Bhatia, Neha; Heisler, Marcus G

2018-02-08

Periodic patterns during development often occur spontaneously through a process of self-organization. While reaction-diffusion mechanisms are often invoked, other types of mechanisms that involve cell-cell interactions and mechanical buckling have also been identified. Phyllotaxis, or the positioning of plant organs, has emerged as an excellent model system to study the self-organization of periodic patterns. At the macro scale, the regular spacing of organs on the growing plant shoot gives rise to the typical spiral and whorled arrangements of plant organs found in nature. In turn, this spacing relies on complex patterns of cell polarity that involve feedback between a signaling molecule - the plant hormone auxin - and its polar, cell-to-cell transport. Here, we review recent progress in understanding phyllotaxis and plant cell polarity and highlight the development of new tools that can help address the remaining gaps in our understanding. © 2018. Published by The Company of Biologists Ltd.

Risk of Adverse Health and Performance Effects of Celestial Dust Exposure

NASA Technical Reports Server (NTRS)

Scully, Robert R.; Meyers, Valerie E.

2015-01-01

Crew members can be directly exposed to celestial dust in several ways. After crew members perform extravehicular activities (EVAs), they may introduce into the habitat dust that will have collected on spacesuits and boots. Cleaning of the suits between EVAs and changing of the Environmental Control Life Support System filters are other operations that could result in direct exposure to celestial dusts. In addition, if the spacesuits used in exploration missions abrade the skin, as current EVA suits have, then contact with these wounds would provide a source of exposure. Further, if celestial dusts gain access to a suit's interior, as was the case during the Apollo missions, the dust could serve as an additional source of abrasions or enhance suit-induced injuries. When a crew leaves the surface of a celestial body and returns to microgravity, the dust that is introduced into the return vehicle will "float," thus increasing the opportunity for ocular and respiratory injury. Because the features of the respirable fraction of lunar dusts indicate they could be toxic to humans, NASA conducted several studies utilizing lunar dust simulants and authentic lunar dust to determine the unique properties of lunar dust that affect physiology, assess the dermal and ocular irritancy of the dust, and establish a permissible exposure limit for episodic exposure to airborne lunar dust during missions that would involve no more than 6 months stay on the lunar surface. Studies, with authentic lunar soils from both highland (Apollo 16) and mare (Apollo17) regions demonstrated that the lunar soil is highly abrasive to a high fidelity model of human skin. Studies of lunar dust returned during the Apollo 14 mission from an area of the moon in which the soils were comprised of mineral constituents from both major geological regions (highlands and mares regions) demonstrated only minimal ocular irritancy, and pulmonary toxicity that was less than the highly toxic terrestrial crystalline silica (Permissible Exposure Limit [PEL] 0.05 mg/m3) but more toxic than the nuisance dust titanium dioxide (TiO2 [PEL 5.0 mg/m3]). A PEL for episodic exposure to airborne lunar dust during a six-month stay on the lunar surface was established, in consultation with an independent, extramural panel of expert pulmonary toxicologists, at 0.3 mg/m3. The PEL provided for lunar dust is limited to the conditions and exposure specified therefore additional research remains to be accomplished with lunar dust to further address the issues of activation, address other areas of more unique lunar geology (Glotch et al., 2010; Greenhagen et al., 2010), examine potential toxicological effects of inhaled or ingested dust upon other organ systems, such cardiovascular, nervous systems, and examine effects of acute exposure to massive doses of dust such as may occur during off-nominal situations. Work to support the establishment of PELs for Martian dust and dusts of asteroids remains to be accomplished. The literature that describes health effects of exposure to toxic terrestrial dusts provides substantial basis for concern that prolonged exposure to respirable celestial dust could be detrimental to human health. Celestial bodies where a substantial portion of the dust is in the respirable range or where the dusts have large reactive surface areas or contain transition metals or volatile organics, represent greater risks of adverse effects from exposure to the dust. It is possible that in addition to adverse effects to the respiratory system, inhalation and ingestion of celestial dusts could pose risks to other systems

Celestial ephemerides in an expanding universe

NASA Astrophysics Data System (ADS)

Kopeikin, Sergei M.

2012-09-01

The post-Newtonian theory of motion of celestial bodies and propagation of light was instrumental in conducting the critical experimental tests of general relativity and in building the astronomical ephemerides of celestial bodies in the Solar System with unparalleled precision. The cornerstone of the theory is the postulate that the Solar System is gravitationally isolated from the rest of the Universe and the background spacetime is asymptotically flat. The present article extends this theoretical concept and formulates the principles of celestial dynamics of particles and light moving in the gravitational field of a localized astronomical system embedded to the expanding Friedmann-Lemaître-Robertson-Walker universe. We formulate the precise mathematical concept of the Newtonian limit of Einstein’s field equations in the conformally flat Friedmann-Lemaître-Robertson-Walker spacetime and analyze the geodesic motion of massive particles and light in this limit. We prove that by doing conformal spacetime transformations, one can reduce the equations of motion of particles and light to the classical form of the Newtonian theory. However, the time arguments in the equations of motion of particles and light differ from each other in terms being proportional to the Hubble constant H. This leads to the important conclusion that the equations of light propagation used currently by space navigation centers for fitting range and Doppler-tracking observations of celestial bodies are missing some terms of the cosmological origin that are proportional to the Hubble constant H. We also analyze the effect of the cosmological expansion on motion of electrons in atoms. We prove that the Hubble expansion does not affect the atomic frequencies and hence does not affect the atomic time scale used in the creation of astronomical ephemerides. We derive the cosmological correction to the light travel time equation and argue that its measurement opens an exciting opportunity to determine the local value of the Hubble constant H in the Solar System independently of cosmological observations.

Ferroelectric Domain Studies of Patterned (001) BiFeO 3 by Angle-Resolved Piezoresponse Force Microscopy

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

Kim, Bumsoo; Barrows, Frank P.; Sharma, Yogesh

We have studied the ferroelectric domains in (001) BiFeO 3 (BFO) films patterned into mesas with various aspect ratios, using angle-resolved piezoresponse force microscope (AR-PFM), which can image the in-plane polarization component with an angular resolution of 30 degrees. We observed not only stable polarization variants, but also meta-stable polarization variants, which can reduce the charge accumulated at domain boundaries. We considered the number of neighboring domains that are in contact, in order to analyze the complexity of the ferroelectric domain structure. Comparison of the ferroelectric domains from the patterned and unpatterned regions showed that the elastic relaxation induced bymore » removal of the film surrounding the mesas led to a reduction of the average number of neighboring domains, indicative of a decrease in domain complexity. Finally, we also found that the rectangular BFO patterns with high aspect ratio had a simpler domain configuration and enhanced piezoelectric characteristics than square-shaped mesas. Manipulation of the ferroelectric domains by controlling the aspect ratio of the patterned BFO thin film mesas can be useful for nanoelectronic applications.« less

Ferroelectric Domain Studies of Patterned (001) BiFeO 3 by Angle-Resolved Piezoresponse Force Microscopy

DOE PAGES

Kim, Bumsoo; Barrows, Frank P.; Sharma, Yogesh; ...

2018-01-09

We have studied the ferroelectric domains in (001) BiFeO 3 (BFO) films patterned into mesas with various aspect ratios, using angle-resolved piezoresponse force microscope (AR-PFM), which can image the in-plane polarization component with an angular resolution of 30 degrees. We observed not only stable polarization variants, but also meta-stable polarization variants, which can reduce the charge accumulated at domain boundaries. We considered the number of neighboring domains that are in contact, in order to analyze the complexity of the ferroelectric domain structure. Comparison of the ferroelectric domains from the patterned and unpatterned regions showed that the elastic relaxation induced bymore » removal of the film surrounding the mesas led to a reduction of the average number of neighboring domains, indicative of a decrease in domain complexity. Finally, we also found that the rectangular BFO patterns with high aspect ratio had a simpler domain configuration and enhanced piezoelectric characteristics than square-shaped mesas. Manipulation of the ferroelectric domains by controlling the aspect ratio of the patterned BFO thin film mesas can be useful for nanoelectronic applications.« less

Patterning highly ordered arrays of complex nanofeatures through EUV directed polarity switching of non chemically amplified photoresist

PubMed Central

Ghosh, Subrata; Satyanarayana, V. S. V.; Pramanick, Bulti; Sharma, Satinder K.; Pradeep, Chullikkattil P.; Morales-Reyes, Israel; Batina, Nikola; Gonsalves, Kenneth E.

2016-01-01

Given the importance of complex nanofeatures in the filed of micro-/nanoelectronics particularly in the area of high-density magnetic recording, photonic crystals, information storage, micro-lens arrays, tissue engineering and catalysis, the present work demonstrates the development of new methodology for patterning complex nanofeatures using a recently developed non-chemically amplified photoresist (n-CARs) poly(4-(methacryloyloxy)phenyl)dimethylsulfoniumtriflate) (polyMAPDST) with the help of extreme ultraviolet lithography (EUVL) as patterning tool. The photosensitivity of polyMAPDST is mainly due to the presence of radiation sensitive trifluoromethanesulfonate unit (triflate group) which undergoes photodegradation upon exposure with EUV photons, and thus brings in polarity change in the polymer structure. Integration of such radiation sensitive unit into polymer network avoids the need of chemical amplification which is otherwise needed for polarity switching in the case of chemically amplified photoresists (CARs). Indeed, we successfully patterned highly ordered wide-raging dense nanofeatures that include nanodots, nanowaves, nanoboats, star-elbow etc. All these developed nanopatterns have been well characterized by FESEM and AFM techniques. Finally, the potential of polyMAPDST has been established by successful transfer of patterns into silicon substrate through adaptation of compatible etch recipes. PMID:26975782

Effect of high-latitude ionospheric convection on Sun-aligned polar caps

NASA Technical Reports Server (NTRS)

Sojka, J. J.; Zhu, L.; Crain, D. J.; Schunk, R. W.

1994-01-01

A coupled magnetospheric-ionospheric (M-I) magnetohydrodynamic (MHD) model has been used to simulate the formation of Sun-aligned polar cap arcs for a variety of interplanetary magnetic field (IMF) dependent polar cap convection fields. The formation process involves launching an Alfven shear wave from the magnetosphere to the ionosphere where the ionospheric conductance can react self-consistently to changes in the upward currents. We assume that the initial Alfven shear wave is the result of solar wind-magnetosphere interactions. The simulations show how the E region density is affected by the changes in the electron precipitation that are associated with the upward currents. These changes in conductance lead to both a modified Alfven wave reflection at the ionosphere and the generation of secondary Alfven waves in the ionosphere. The ensuing bouncing of the Alfven waves between the ionosphere and magnetosphere is followed until an asymptotic solution is obtained. At the magnetosphere the Alfven waves reflect at a fixed boundary. The coupled M-I Sun-aligned polar cap arc model of Zhu et al.(1993a) is used to carry out the simulations. This study focuses on the dependence of the polar cap arc formation on the background (global) convection pattern. Since the polar cap arcs occur for northward and strong B(sub y) IMF conditions, a variety of background convection patterns can exist when the arcs are present. The study shows that polar cap arcs can be formed for all these convection patterns; however, the arc features are dramatically different for the different patterns. For weak sunward convection a relatively confined single pair of current sheets is associated with the imposed Alfven shear wave structure. However, when the electric field exceeds a threshold, the arc structure intensifies, and the conductance increases as does the local Joule heating rate. These increases are faster than a linear dependence on the background electric field strength. Furthermore, above the threshold, the single current sheet pair splits into multiple current sheet pairs. For the fixed initial ionospheric and magnetospheric conditions used in this study, the separation distance between the current pairs was found to be almost independent of the background electric field strength. For either three-cell or distorted two-cell background convection patterns the arc formation favored the positive B(sub y) case in the northern hemisphere.

Photo electron emission microscopy of polarity-patterned materials

NASA Astrophysics Data System (ADS)

Yang, W.-C.; Rodriguez, B. J.; Gruverman, A.; Nemanich, R. J.

2005-04-01

This study presents variable photon energy photo electron emission microscopy (PEEM) of polarity-patterned epitaxial GaN films, and ferroelectric LiNbO3 (LNO) single crystals and PbZrTiO3 (PZT) thin films. The photo electrons were excited with spontaneous emission from the tunable UV free electron laser (FEL) at Duke University. We report PEEM observation of polarity contrast and measurement of the photothreshold of each polar region of the materials. For a cleaned GaN film with laterally patterned Ga- and N-face polarities, we found a higher photoelectric yield from the N-face regions compared with the Ga-face regions. Through the photon energy dependent contrast in the PEEM images of the surfaces, we can deduce that the threshold of the N-face region is less than ~4.9 eV while that of the Ga-face regions is greater than 6.3 eV. In both LNO and PZT, bright emission was detected from the negatively poled domains, indicating that the emission threshold of the negative domain is lower than that of the positive domain. For LNO, the measured photothreshold was ~4.6 eV at the negative domain and ~6.2 eV at the positive domain, while for PZT, the threshold of the negative domain was less than 4.3 eV. Moreover, PEEM observation of the PZT surface at elevated temperatures displayed that the domain contrast disappeared near the Curie temperature of ~300 °C. The PEEM polarity contrast of the polar materials is discussed in terms of internal screening from free carriers and defects and the external screening due to adsorbed ions.

Celestial Software Scratches More Than the Surface

NASA Technical Reports Server (NTRS)

2005-01-01

While NASA is preparing to send humans back to the Moon by 2020 and then eventually to Mars, the average person can explore the landscapes of these celestial bodies much sooner, without the risk and training, and without even leaving the comfort of home. Geological data and imagery collected from NASA missions are enabling anybody with computer access to virtually follow the footsteps of Apollo astronauts who walked on the Moon or trace the tracks of the exploration rovers currently on Mars.

Proceedings of the Symposium on Military Space Communications and Operations Held at USAF Academy, Colorado on 2-4 August 1983

DTIC Science & Technology

1983-08-04

IS CURRERTLY OFF; TRANSMITSTHE COM TO TURHE AN N; WAITS FO Procedures are valuable because they provide hCGMDTOTR PROPTION AN POCSSI OELAS...legal and Other Celestial Bodies ,!/ was a regime which has been created by brilliant accomplishment of the world international treaties. These legal...difficulty posed by some controversial provisions in the Agreement Governing the Activities of States on the Moon and Other Celestial Bodies and the

Investigating dust trapping in transition disks with millimeter-wave polarization

NASA Astrophysics Data System (ADS)

Pohl, A.; Kataoka, A.; Pinilla, P.; Dullemond, C. P.; Henning, Th.; Birnstiel, T.

2016-08-01

Context. Spatially resolved polarized (sub-)mm emission has been observed for example in the protoplanetary disk around HL Tau. Magnetically aligned grains are commonly interpreted as the source of polarization. However, self-scattering by large dust grains with a high enough albedo is another polarization mechanism, which is becoming a compelling method independent of the spectral index to constrain the dust grain size in protoplanetary disks. Aims: We study the dust polarization at mm wavelengths in the dust trapping scenario proposed for transition disks, when a giant planet opens a gap in the disk. We investigate the characteristic polarization patterns and their dependence on disk inclination, dust size evolution, planet position, and observing wavelength. Methods: We combine two-dimensional hydrodynamical simulations of planet-disk interactions with self-consistent dust growth models. These size-dependent dust density distributions are used for follow-up three-dimensional radiative transfer calculations to predict the polarization degree at ALMA bands due to scattered thermal emission. Results: Dust self-scattering has been proven to be a viable mechanism for producing polarized mm-wave radiation. We find that the polarization pattern of a disk with a planetary gap after 1 Myr of dust evolution shows a distinctive three-ring structure. Two narrow inner rings are located at the planet gap edges. A third wider ring of polarization is situated in the outer disk beyond 100 au. For increasing observing wavelengths, all three rings change their position slightly, where the innermost and outermost rings move inward. This distance is detectable when comparing the results at ALMA bands 3, 6, and 7. Within the highest polarized intensity regions the polarization vectors are oriented in the azimuthal direction. For an inclined disk there is an interplay between polarization originating from a flux gradient and inclination-induced quadrupole polarization. For intermediate inclined transition disks, the polarization degree is as high as ~2% at λ = 3.1 mm (band 3), which is well above the detection limit of future ALMA observations.

Martian City Map

NASA Technical Reports Server (NTRS)

2004-01-01

30 May 2004 Seasonal frost can enhance the view from orbit of polar polygonal patterns on the surface of Mars. Sometimes these patterns look something like a city map, or the view from above a city lit-up at night. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example from the south polar region near 80.7oS, 70.6oW. Polar polygons on Mars are generally believed, though not proven, to be the result of freeze/thaw cycles of ice occurring within the upper few meters (several yards) of the martian subsurface. The image shown here covers an area about 3 km (1.9 mi) across; sunlight illuminates the scene from the upper left.

Generation of continuously rotating polarization by combining cross-polarizations and its application in surface structuring.

PubMed

Lam, Billy; Zhang, Jihua; Guo, Chunlei

2017-08-01

In this study, we develop a simple but highly effective technique that generates a continuously varying polarization within a laser beam. This is achieved by having orthogonal linear polarizations on each side of the beam. By simply focusing such a laser beam, we can attain a gradually and continuously changing polarization within the entire Rayleigh range due to diffraction. To demonstrate this polarization distribution, we apply this laser beam onto a metal surface and create a continuously rotating laser induced periodic surface structure pattern. This technique provides a very effective way to produce complex surface structures that may potentially find applications, such as polarization modulators and metasurfaces.

An efficient technique for determining apparent temperature distributions from antenna temperature measurements

NASA Technical Reports Server (NTRS)

Claassen, J. P.; Fung, A. K.

1973-01-01

A method by which the apparent microwave temperature characteristic of a flat scene is estimated from dual polarized measurements is derived and interpreted. Approximate linear relationships between antenna and apparent temperatures are established by weighting emission components in spherical bands under the assumption that the surface is isotropic. The weighting factors are formed by integrating the antenna pattern functions over these bands. The vector aspect of the formulation is retained to account for the difference between the definition of the antenna polarizations and the polarizations of the emitted fields. The method is largely applicable to the measurement of smooth temperature distributions by an antenna having good spatial resolution of the distributions and is considered efficient for inverting large volumes of measurements. Sample cases are presented and the implications of these cases on remote radiometer observations are discussed. It is shown that cross-coupling occurs between the polarizations of the emitted fields and the polarizations of the antenna. For this reason and because practical antennas have cross-polarized patterns associated with them, it is necessary to conduct measurements at both horizontal and vertical polarizations to realize the inversion. It is also made evident that thorough inversions require that the apparent temperatures be sampled at a sufficient number of points between nadir and zenith.

Ionospheric convection driven by NBZ currents

NASA Technical Reports Server (NTRS)

Rasmussen, C. E.; Schunk, R. W.

1987-01-01

Computer simulations of Birkeland currents and electric fields in the polar ionosphere during periods of northward IMF were conducted. When the IMF z component is northward, an additional current system, called the NBZ current system, is present in the polar cap. These simulations show the effect of the addition of NBZ currents on ionospheric convection, particularly in the polar cap. When the total current in the NBZ system is roughly 25 to 50 percent of the net region 1 and 2 currents, convection in the central portion of the polar cap reverses direction and turns sunward. This creates a pattern of four-cell convection with two small cells located in the polar cap, rotating in an opposite direction from the larger cells. When the Birkeland currents are fixed (constant current source), the electric field is reduced in regions of relatively high conductivity, which affects the pattern of ionospheric convection. Day-night asymmetries in conductivity change convection in such a way that the two polar-cap cells are located within the large dusk cell. When ionospheric convection is fixed (constant voltage source), Birkeland currents are increased in regions of relatively high conductivity. Ionospheric currents, which flow horizontally to close the Birkeland currents, are changed appreciably by the NBZ current system. The principal effect is an increase in ionospheric current in the polar cap.

Is there a universal answering strategy for rejecting negative propositions? Typological evidence on the use of prosody and gesture

PubMed Central

González-Fuente, Santiago; Tubau, Susagna; Espinal, M. Teresa; Prieto, Pilar

2015-01-01

Previous research has proposed that languages diverge with respect to how their speakers confirm and contradict negative questions. Taking into account the classification between truth-based and polarity-based languages, this paper is mainly concerned with the expression of REJECT (a semantic operation that signals a contradiction move with respect to the common ground, along Krifka's lines) in two languages belonging to two typologically distinct answering systems, namely Catalan (polarity-based) and Russian (a mixed system using polarity-based, truth-based, and echoic strategies). This investigation has two goals. First, to assess empirically the relevance of prosodic and gestural patterns in the interpretation of confirming and rejecting responses to negative polar questions. Second, to test the claim that in fact speakers resort to strikingly similar universal strategies at the time of expressing rejecting answers to discourse accessible negative assertions and negative polar questions, namely the use of linguistic units that encode REJECT in combination with ASSERT. The results of our investigation support the existence of a universal answering system for rejecting negative polar questions that integrates lexical and syntactic strategies with prosodic and gestural patterns, and instantiate the REJECT and ASSERT operators. We will also discuss the implications these results have for the truth-based vs. polarity-based taxonomy. PMID:26217255

On-chip polarimetry for high-throughput screening of nanoliter and smaller sample volumes

NASA Technical Reports Server (NTRS)

Bachmann, Brian O. (Inventor); Bornhop, Darryl J. (Inventor); Dotson, Stephen (Inventor)

2012-01-01

A polarimetry technique for measuring optical activity that is particularly suited for high throughput screening employs a chip or substrate (22) having one or more microfluidic channels (26) formed therein. A polarized laser beam (14) is directed onto optically active samples that are disposed in the channels. The incident laser beam interacts with the optically active molecules in the sample, which slightly alter the polarization of the laser beam as it passes multiple times through the sample. Interference fringe patterns (28) are generated by the interaction of the laser beam with the sample and the channel walls. A photodetector (34) is positioned to receive the interference fringe patterns and generate an output signal that is input to a computer or other analyzer (38) for analyzing the signal and determining the rotation of plane polarized light by optically active material in the channel from polarization rotation calculations.

Spatiotemporal polarization modulation microscopy with a microretarder array

NASA Astrophysics Data System (ADS)

Ding, Changqin; Ulcickas, James R. W.; Simpson, Garth J.

2018-02-01

A patterned microretarder array positioned in the rear conjugate plane of a microscope enables rapid polarizationdependent nonlinear optical microscopy. The pattern introduced to the array results in periodic modulation of the polarization-state of the incident light as a function of position within the field of view with no moving parts or active control. Introduction of a single stationary optical element and a fixed polarizer into the beam of a nonlinear optical microscope enabled nonlinear optical tensor recovery, which informs on local structure and orientation. Excellent agreement was observed between the measured and predicted second harmonic generation (SHG) of z-cut quartz, selected as a test system with well-established nonlinear optical properties. Subsequent studies of spatially varying samples further support the general applicability of this relatively simple strategy for detailed polarization analysis in both conventional and nonlinear optical imaging of structurally diverse samples.

Idealized model of polar cap currents, fields, and auroras

NASA Technical Reports Server (NTRS)

Cornwall, J. M.

1985-01-01

During periods of northward Bz, the electric field applied to the magnetosphere is generally opposite to that occurring during southward Bz and complicated patterns of convection result, showing some features reversed in comparison with the southward Bz case. A study is conducted of a simple generalization of early work on idealized convection models, which allows for coexistence of sunward convection over the central polar cap and antisunward convection elsewhere in the cap. The present model, valid for By approximately 0, has a four-cell convection pattern and is based on the combination of ionospheric current conservation with a relation between parallel auroral currents and parallel potential drops. Global magnetospheric issues involving, e.g., reconnection are not considered. The central result of this paper is an expression giving the parallel potential drop for polar cap auroras (with By approximately 0) in terms of the polar cap convection field profile.

On the breakup of tectonic plates by polar wandering

NASA Technical Reports Server (NTRS)

Liu, H. S.

1973-01-01

The observed boundary system of the major tectonic plates on the surface of the earth lends fresh support to the hypothesis of polar wandering. A dynamic model of the outer shell of the earth under the influence of polar shift is developed. The analysis falls into two parts: (1) deriving equations for stresses caused by polar shifting; and (2) deducing the pattern according to which the fracture of the shell can be expected. For stress analysis, the theory of plates and shells is the dominant feature of this model. In order to determine the fracture pattern, the existence of a mathematical theorem of plasticity is recalled: it says that the plastic flow begins to occur when a function in terms of the differences of the three principal stresses surpasses a certain critical value. By introducing the figures for the geophysical constants, this model generates stresses which could produce an initial break in the lithosphere.

The electron-spin--nuclear-spin interaction studied by polarized neutron scattering.

PubMed

Stuhrmann, Heinrich B

2007-11-01

Dynamic nuclear spin polarization (DNP) is mediated by the dipolar interaction of paramagnetic centres with nuclear spins. This process is most likely to occur near paramagnetic centres at an angle close to 45 degrees with respect to the direction of the external magnetic field. The resulting distribution of polarized nuclear spins leads to an anisotropy of the polarized neutron scattering pattern, even with randomly oriented radical molecules. The corresponding cross section of polarized coherent neutron scattering in terms of a multipole expansion is derived for radical molecules in solution. An application using data of time-resolved polarized neutron scattering from an organic chromium(V) molecule is tested.

Reproducing the Photospheric Magnetic Field Evolution during the Rise of Cycle 24 with Flux Transport by Supergranules

NASA Technical Reports Server (NTRS)

Hathaway, David; Upton, Lisa

2012-01-01

We simulate the transport of magnetic flux in the Sun s photosphere by an evolving pattern of cellular horizontal flows (supergranules). Characteristics of the simulated flow pattern can match observed characteristics including the velocity power spectrum, cell lifetimes, and cell motions in longitude and latitude. Simulations using an average, and north-south symmetric, meridional motion of the cellular pattern produce polar magnetic fields that are too weak in the North and too strong in the South. Simulations using cellular patterns with meridional motions that evolve with the observed changes in strength and north-south asymmetry will be analyzed to see if they reproduce the polar field evolution observed during the rise of Cycle 24.

Invariant polar bear habitat selection during a period of sea ice loss

USGS Publications Warehouse

Wilson, Ryan R.; Regehr, Eric V.; Rode, Karyn D.; St Martin, Michelle

2016-01-01

Climate change is expected to alter many species' habitat. A species' ability to adjust to these changes is partially determined by their ability to adjust habitat selection preferences to new environmental conditions. Sea ice loss has forced polar bears (Ursus maritimus) to spend longer periods annually over less productive waters, which may be a primary driver of population declines. A negative population response to greater time spent over less productive water implies, however, that prey are not also shifting their space use in response to sea ice loss. We show that polar bear habitat selection in the Chukchi Sea has not changed between periods before and after significant sea ice loss, leading to a 75% reduction of highly selected habitat in summer. Summer was the only period with loss of highly selected habitat, supporting the contention that summer will be a critical period for polar bears as sea ice loss continues. Our results indicate that bears are either unable to shift selection patterns to reflect new prey use patterns or that there has not been a shift towards polar basin waters becoming more productive for prey. Continued sea ice loss is likely to further reduce habitat with population-level consequences for polar bears.

Dual polarized receiving steering antenna array for measurement of ultrawideband pulse polarization structure

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

Balzovsky, E. V.; Buyanov, Yu. I.; Koshelev, V. I., E-mail: koshelev@lhfe.hcei.tsc.ru

To measure simultaneously two orthogonal components of the electromagnetic field of nano- and subnano-second duration, an antenna array has been developed. The antenna elements of the array are the crossed dipoles of dimension 5 × 5 cm. The arms of the dipoles are connected to the active four-pole devices to compensate the frequency response variations of a short dipole in the frequency band ranging from 0.4 to 4 GHz. The dipoles have superimposed phase centers allowing measuring the polarization structure of the field in different directions. The developed antenna array is the linear one containing four elements. The pattern maximummore » position is controlled by means of the switched ultrawideband true time delay lines. Discrete steering in seven directions in the range from −40° to +40° has been realized. The error at setting the pattern maximum position is less than 4°. The isolation of the polarization exceeds 29 dB in the direction orthogonal to the array axis and in the whole steering range it exceeds 23 dB. Measurement results of the polarization structure of radiated and scattered pulses with different polarization are presented as well.« less

Expected Improvements in VLBI Measurements of the Earth's Orientation

NASA Technical Reports Server (NTRS)

Ma, Chopo

2003-01-01

Measurements of the Earth s orientation since the 1970s using space geodetic techniques have provided a continually expanding and improving data set for studies of the Earth s structure and the distribution of mass and angular momentum. The accuracy of current one-day measurements is better than 100 microarcsec for the motion of the pole with respect to the celestial and terrestrial reference frames and better than 3 microsec for the rotation around the pole. VLBI uniquely provides the three Earth orientation parameters (nutation and UTI) that relate the Earth to the extragalactic celestial reference frame. The accuracy and resolution of the VLBI Earth orientation time series can be expected to improve substantially in the near future because of refinements in the realization of the celestial reference frame, improved modeling of the troposphere and non-linear station motions, larger observing networks, optimized scheduling, deployment of disk-based Mark V recorders, full use of Mark IV capabilities, and e-VLBI. More radical future technical developments will be discussed.

Water in the trail of the Chelyabinsk bolide

NASA Astrophysics Data System (ADS)

Gladysheva, O. G.

2017-09-01

At 03:20 UTC on February 15, 2013 a very bright bolide entered Earth's atmosphere. Fragments of the meteorite fell to the earth's surface. Examination of these fragments revealed that several of them were located directly on the surface of the celestial body [1], while the majority lay at a depth of less than 2.5 m from the surface [2, 3]. The stone meteorite's durability, >15 MPa, corresponded to <1% of the initial mass, while the rest of the object possessed a low durability of 1 MPa [4]. Moreover, Fe3+ hydroxyls were discovered in meteorite samples, the formation of which required water [5]. The glow at the head of the bolide trail, lasting 8 seconds after the flight of the object, and the development of the cloud trail indicate that the celestial body carried water. The Chinese weather satellite Feng-Yun 2D discovered ice debris (water) in the bolide trail [6]. Here, we will demonstrate that the Chelyabinsk chondrite was delivered to the Earth by an ice-bearing celestial body.

Optimization design about gimbal structure of high-precision autonomous celestial navigation tracking mirror system

NASA Astrophysics Data System (ADS)

Huang, Wei; Yang, Xiao-xu; Han, Jun-feng; Wei, Yu; Zhang, Jing; Xie, Mei-lin; Yue, Peng

2016-01-01

High precision tracking platform of celestial navigation with control mirror servo structure form, to solve the disadvantages of big volume and rotational inertia, slow response speed, and so on. It improved the stability and tracking accuracy of platform. Due to optical sensor and mirror are installed on the middle-gimbal, stiffness and resonant frequency requirement for high. Based on the application of finite element modality analysis theory, doing Research on dynamic characteristics of the middle-gimbal, and ANSYS was used for the finite element dynamic emulator analysis. According to the result of the computer to find out the weak links of the structure, and Put forward improvement suggestions and reanalysis. The lowest resonant frequency of optimization middle-gimbal avoid the bandwidth of the platform servo mechanism, and much higher than the disturbance frequency of carrier aircraft, and reduces mechanical resonance of the framework. Reaching provides a theoretical basis for the whole machine structure optimization design of high-precision of autonomous Celestial navigation tracking mirror system.

Synergies in Astrometry: Predicting Navigational Error of Visual Binary Stars

NASA Astrophysics Data System (ADS)

Gessner Stewart, Susan

2015-08-01

Celestial navigation can employ a number of bright stars which are in binary systems. Often these are unresolved, appearing as a single, center-of-light object. A number of these systems are, however, in wide systems which could introduce a margin of error in the navigation solution if not handled properly. To illustrate the importance of good orbital solutions for binary systems - as well as good astrometry in general - the relationship between the center-of-light versus individual catalog position of celestial bodies and the error in terrestrial position derived via celestial navigation is demonstrated. From the list of navigational binary stars, fourteen such binary systems with at least 3.0 arcseconds apparent separation are explored. Maximum navigational error is estimated under the assumption that the bright star in the pair is observed at maximum separation, but the center-of-light is employed in the navigational solution. The relationships between navigational error and separation, orbital periods, and observers' latitude are discussed.

Planetary cores, their energy flux relationship, and its implications

NASA Astrophysics Data System (ADS)

Johnson, Fred M.

2018-02-01

Integrated surface heat flux data from each planet in our solar system plus over 50 stars, including our Sun, was plotted against each object's known mass to generate a continuous exponential curve at an R-squared value of 0.99. The unexpected yet undeniable implication of this study is that all planets and celestial objects have a similar mode of energy production. It is widely accepted that proton-proton reactions require hydrogen gas at temperatures of about 15 million degrees, neither of which can plausibly exist inside a terrestrial planet. Hence, this paper proposes a nuclear fission mechanism for all luminous celestial objects, and uses this mechanism to further suggest a developmental narrative for all celestial bodies, including our Sun. This narrative was deduced from an exponential curve drawn adjacent to the first and passing through the Earth's solid core (as a known prototype). This trend line was used to predict the core masses for each planet as a function of its luminosity.

Two odometers in honeybees?

PubMed

Dacke, M; Srinivasan, M V

2008-10-01

Although several studies have examined how honeybees gauge and report the distance and direction of a food source to their nestmates, relatively little is known about how this information is combined to obtain a representation of the position of the food source. In this study we manipulate the amount of celestial compass information available to the bee during flight, and analyse the encoding of spatial information in the waggle dance as well as in the navigation of the foraging bee. We find that the waggle dance encodes information about the total distance flown to the food source, even when celestial compass cues are available only for a part of the journey. This stands in contrast to how a bee gauges distance flown when it navigates back to a food source that it already knows. When bees were trained to find a feeder placed at a fixed distance in a tunnel in which celestial cues were partially occluded and then tested in a tunnel that was fully open to the sky, they searched for the feeder at a distance that corresponds closely to the distance that was flown under the open sky during the training. Thus, when navigating back to a food source, information about distance travelled is disregarded when there is no concurrent input from the celestial compass. We suggest that bees may possess two different odometers - a 'community' odometer that is used to provide information to nestmates via the dance, and a 'personal' odometer that is used by an experienced individual to return to a previously visited source.

Line patterning of anisotropic spin chains by polarized laser for application in micro-thermal management

NASA Astrophysics Data System (ADS)

Terakado, Nobuaki; Takahashi, Ryosuke; Takahashi, Yoshihiro; Fujiwara, Takumi

2017-05-01

The control of heat flow has become increasingly important in energy saving and harvesting. Among various thermal management materials, spinon thermal conductivity materials are promising for heat flow control at microscales because they exhibit high, anisotropic thermal conductivity resulting from spin chains. However, there has been only little development of the materials for controlling heat flow. Here, we present the line patterning of the spin chain structure on a SrCuO2 nanocrystalline film by laser scanning. When the polarization direction of laser light was orthogonal to the scanning direction, we found that the spin-chain structure anisotropically grew on the patterned line.

Measuring polarization dependent dispersion of non-polarizing beam splitter cubes with spectrally resolved white light interferometry

NASA Astrophysics Data System (ADS)

Csonti, K.; Hanyecz, V.; Mészáros, G.; Kovács, A. P.

2017-06-01

In this work we have measured the group-delay dispersion of an empty Michelson interferometer for s- and p-polarized light beams applying two different non-polarizing beam splitter cubes. The interference pattern appearing at the output of the interferometer was resolved with two different spectrometers. It was found that the group-delay dispersion of the empty interferometer depended on the polarization directions in case of both beam splitter cubes. The results were checked by inserting a glass plate in the sample arm of the interferometer and similar difference was obtained for the two polarization directions. These results show that to reach high precision, linearly polarized white light beam should be used and the residual dispersion of the empty interferometer should be measured at both polarization directions.

Coding and decoding in a point-to-point communication using the polarization of the light beam.

PubMed

Kavehvash, Z; Massoumian, F

2008-05-10

A new technique for coding and decoding of optical signals through the use of polarization is described. In this technique the concept of coding is translated to polarization. In other words, coding is done in such a way that each code represents a unique polarization. This is done by implementing a binary pattern on a spatial light modulator in such a way that the reflected light has the required polarization. Decoding is done by the detection of the received beam's polarization. By linking the concept of coding to polarization we can use each of these concepts in measuring the other one, attaining some gains. In this paper the construction of a simple point-to-point communication where coding and decoding is done through polarization will be discussed.

Hipparchus' coordinate system

NASA Astrophysics Data System (ADS)

Duke, Dennis W.

2002-07-01

In his "Histoire de l'Astronomie Ancienne" Delambre concludes unequivocally that Hipparchus knew and used a definite system of celestial spherical coordinates, namely the right ascension and declination system that we use today. The basis of Delambre's conclusion was disarmingly simple: he pointed out that in the "Commentary to Aratus" Hipparchus actually quotes the positions of numerous stars directly in right ascension and declination (or more often its complement, polar distance). Nearly two centuries later, in his "A History of Ancient Mathematical Astronomy", Neugebauer not only completely ignores Delambre's conclusion on this issue, but goes further to propose his own, as we shall see quite fanciful, theory that begins "From the Commentary to Aratus, it is quite obvious that at Hipparchus' time a definite system of spherical coordinates for stellar positions did not yet exist." and concludes "...nowhere in Greek astronomy before the catalogue of stars in the Almagest is it attested that orthogonal spherical coordinates are used to determine stellar positions." Today it is clear that Neugebauer's theory is conventionally accepted. It is the purpose of this paper to offer fresh arguments that Delambre was correct.

Analysis of the Effect of UTI-UTC to High Precision Orbit

NASA Astrophysics Data System (ADS)

Shin, Dongseok; Kwak, Sunghee; Kim, Tag-Gon

1999-12-01

As the spatial resolution of remote sensing satellites becomes higher, very accurate determination of the position of a LEO (Low Earth Orbit) satellite is demanding more than ever. Non-symmetric Earth gravity is the major perturbation force to LEO satellites. Since the orbit propagation is performed in the celestial frame while Earth gravity is defined in the terrestrial frame, it is required to convert the coordinates of the satellite from one to the other accurately. Unless the coordinate conversion between the two frames is performed accurately the orbit propagation calculates incorrect Earth gravitational force at a specific time instant, and hence, causes errors in orbit prediction. The coordinate conversion between the two frames involves precession, nutation, Earth rotation and polar motion. Among these factors, unpredictability and uncertainty of Earth rotation, called UTI-UTC, is the largest error source. In this paper, the effect of UTI-UTC on the accuracy of the LEO propagation is introduced, tested and analzed. Considering the maximum unpredictability of UTI-UTC, 0.9 seconds, the meaningful order of non-spherical Earth harmonic functions is derived.

High-precision source location of the 1978 November 19 gamma-ray burst

NASA Technical Reports Server (NTRS)

Cline, T. L.; Desai, U. D.; Teegarden, B. J.; Pizzichini, G.; Evans, W. D.; Klebesadel, R. W.; Laros, J. G.; Barat, C.; Hurley, K.; Niel, M.

1981-01-01

The celestial source location of the November 19, 1978, intense gamma ray burst has been determined from data obtained with the interplanetary gamma-ray sensor network by means of long-baseline wave front timing instruments. Each of the instruments was designed for studying events with observable spectra of approximately greater than 100 keV, and each provides accurate event profile timing in the several millisecond range. The data analysis includes the following: the triangulated region is centered at (gamma, delta) 1950 = (1h16m32s, -28 deg 53 arcmin), at -84 deg galactic latitude, where the star density is very low and the obscuration negligible. The gamma-ray burst source region, consistent with that of a highly polarized radio source described by Hjellming and Ewald (1981), may assist in the source modeling and may facilitate the understanding of the source process. A marginally identifiable X-ray source was also found by an Einstein Observatory investigation. It is concluded that the burst contains redshifted positron annihilation and nuclear first-excited iron lines, which is consistent with a neutron star origin.

Polarization manipulation in single refractive prism based holography lithography

NASA Astrophysics Data System (ADS)

Xiong, Wenjie; Xu, Yi; Xiao, Yujian; Lv, Xiaoxu; Wu, Lijun

2015-01-01

We propose theoretically and demonstrate experimentally a simple but effective strategy for polarization manipulation in single refractive prism based holographic lithography. By tuning the polarization of a single laser beam, we can obtain the pill shape interference pattern with a high-contrast where a complex optical setup and multiple polarizers are needed in the conventional holography lithography. Fabrication of pill shape two-dimensional polymer photonic crystals using one beam and one shoot holography lithography is shown as an example to support our theoretical results. This integrated polarization manipulation technique can release the crucial stability restrictions imposed on the multiple beams holography lithography.

Mapping 180° polar domains using electron backscatter diffraction and dynamical scattering simulations

DOE PAGES

Burch, Matthew J.; Fancher, Chris M.; Patala, Srikanth; ...

2016-11-18

A novel technique, which directly and nondestructively maps polar domains using electron backscatter diffraction (EBSD) is described and demonstrated. Through dynamical diffraction simulations and quantitative comparison to experimental EBSD patterns, the absolute orientation of a non-centrosymmetric crystal can be determined. With this information, the polar domains of a material can be mapped. The technique is demonstrated by mapping the non-ferroelastic, or 180°, ferroelectric domains in periodically poled LiNbO 3 single crystals. Furthermore, the authors demonstrate the possibility of mapping polarity using this technique in other polar materials system.

Progress in Insect-Inspired Optical Navigation Sensors

NASA Technical Reports Server (NTRS)

Thakoor, Sarita; Chahl, Javaan; Zometzer, Steve

2005-01-01

Progress has been made in continuing efforts to develop optical flight-control and navigation sensors for miniature robotic aircraft. The designs of these sensors are inspired by the designs and functions of the vision systems and brains of insects. Two types of sensors of particular interest are polarization compasses and ocellar horizon sensors. The basic principle of polarization compasses was described (but without using the term "polarization compass") in "Insect-Inspired Flight Control for Small Flying Robots" (NPO-30545), NASA Tech Briefs, Vol. 29, No. 1 (January 2005), page 61. To recapitulate: Bees use sky polarization patterns in ultraviolet (UV) light, caused by Rayleigh scattering of sunlight by atmospheric gas molecules, as direction references relative to the apparent position of the Sun. A robotic direction-finding technique based on this concept would be more robust in comparison with a technique based on the direction to the visible Sun because the UV polarization pattern is distributed across the entire sky and, hence, is redundant and can be extrapolated from a small region of clear sky in an elsewhere cloudy sky that hides the Sun.

IMF B(y) and day-night conductivity effects in the expanding polar cap convection model

NASA Technical Reports Server (NTRS)

Moses, J. J.; Gorney, D. J.; Siscoe, G. L.; Crooker, N. U.

1987-01-01

During southward B(z) periods the open field line region in the ionosphere (polar cap) expands due to increased dayside merging. Ionospheric plasma flow patterns result which can be classified by the sign of the interplanetary magnetic field (IMF) B(y) component. In this paper, a time-dependent ionospheric convection model is constructed to simulate these flows. The model consists of a spiral boundary with a gap in it. The sign of the IMF B(y) component determines the geometry of the gap. A potential is applied across the gap and distributed around the boundary. A flow results which enters the polar cap through the gap and uniformly pushes the boundary outward. Results of the model show that B(y) effects are greatest near the gap and virtually unnoticeable on the nightside of the polar cap. Adding a day-night ionospheric conductivity gradient concentrates the polar cap electric field toward dawn. The resulting flow curvature gives a sunward component that is independent of B(y). These patterns are shown to be consistent with published observations.

False lock performance in polarity-type Costas receivers in the presence of periodic data patterns

NASA Technical Reports Server (NTRS)

Wang, James June-Ming; Lai, Dennis Teng-Tsun; Heng, Veronica Siang-Gek; Godfrey, Robert D.

1987-01-01

The authors address the false-lock performance of receivers which use polarity-type Costas loops for the carrier recovery of unbalanced quadrature phase-shift keyed (QPSK), asynchronous QPSK or binary PSK (BPSK) signals in the presence of periodic data patterns. The potential false-lock frequencies are first identified. Expressions for both true-lock and false-lock components are also derived, thereby allowing numerical evaluation of various key parameters for cases of practical interest.

Controllable light diffraction in woodpile photonic crystals filled with liquid crystal

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

Ho, Chih-Hua; Zeng, Hao; Wiersma, Diederik S.

2015-01-12

An approach to switching between different patterns of light beams transmitted through the woodpile photonic crystals filled with liquid crystals is proposed. The phase transition between the nematic and isotropic liquid crystal states leads to an observable variation of the spatial pattern transmitted through the photonic structure. The transmission profiles in the nematic phase also show polarization sensibility due to refractive index dependence on the field polarization. The experimental results are consistent with a numerical calculation by Finite Difference Time Domain method.

Broadband Venetian-Blind Polarizer With Dual Vanes

NASA Technical Reports Server (NTRS)

Conroy, Bruce L.; Hoppe, Daniel J.

1995-01-01

Improved venetian-blind polarizer features optimized tandem, two-layer vane configuration reducing undesired reflections and deformation of radiation pattern below those of prior single-layer vane configuration. Consists of number of thin, parallel metal strips placed in path of propagating radio-frequency beam. Offers simple way to convert polarization from linear to circular or from circular to linear. Particularly useful for beam-wave-guide applications.

Broadband Venetian Blind polarizer with dual vanes

NASA Technical Reports Server (NTRS)

Conroy, Bruce L.; Hoppe, Daniel J.; Imbriale, William A.

1993-01-01

During development of a Venetian Blind polarizer, high reflections and substantial pattern deformation were noted. Analysis showed that when the polarizer was illuminated slightly off axis, a degenerate mode was excited. This mode is resonant at the design center frequency, and was the cause of the problems. A design developed using dual vanes has been shown to be free of the problem. It also has greater bandwidth.

Computationally designed and experimentally confirmed diastereoselective rhodium-catalyzed Pauson-Khand reaction at room temperature.

PubMed

Baik, Mu-Hyun; Mazumder, Shivnath; Ricci, Paolo; Sawyer, James R; Song, Ye-Geun; Wang, Huijun; Evans, P Andrew

2011-05-25

The computational analysis of the rhodium-catalyzed Pauson-Khand reaction indicates that the key transition state is highly charge-polarized, wherein different diastereoisomers have distinctively different charge polarization patterns. Experimental studies demonstrate that chloro-enynes provide the optimal σ-electron-withdrawing group to promote polarization and thereby reduce the activation barrier to provide a highly diastereoselective reaction at room temperature.

Pressure-induced switching in ferroelectrics: Phase-field modeling, electrochemistry, flexoelectric effect, and bulk vacancy dynamics

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

Cao, Ye; Morozovska, Anna; Kalinin, Sergei V.

Pressure-induced polarization switching in ferroelectric thin films has emerged as a powerful method for domain patterning, allowing us to create predefined domain patterns on free surfaces and under thin conductive top electrodes. However, the mechanisms for pressure-induced polarization switching in ferroelectrics remain highly controversial, with flexoelectricity, polarization rotation and suppression, and bulk and surface electrochemical processes all being potentially relevant. Here we classify possible pressure-induced switching mechanisms, perform elementary estimates, and study in depth using phase-field modeling. Finally, we show that magnitudes of these effects are remarkably close and give rise to complex switching diagrams as a function of pressuremore » and film thickness with nontrivial topology or switchable and nonswitchable regions.« less

Pressure-induced switching in ferroelectrics: Phase-field modeling, electrochemistry, flexoelectric effect, and bulk vacancy dynamics

DOE PAGES

Cao, Ye; Morozovska, Anna; Kalinin, Sergei V.

2017-11-01

Pressure-induced polarization switching in ferroelectric thin films has emerged as a powerful method for domain patterning, allowing us to create predefined domain patterns on free surfaces and under thin conductive top electrodes. However, the mechanisms for pressure-induced polarization switching in ferroelectrics remain highly controversial, with flexoelectricity, polarization rotation and suppression, and bulk and surface electrochemical processes all being potentially relevant. Here we classify possible pressure-induced switching mechanisms, perform elementary estimates, and study in depth using phase-field modeling. Finally, we show that magnitudes of these effects are remarkably close and give rise to complex switching diagrams as a function of pressuremore » and film thickness with nontrivial topology or switchable and nonswitchable regions.« less

The 20 GHz circularly polarized, high temperature superconducting microstrip antenna array

NASA Technical Reports Server (NTRS)

Morrow, Jarrett D.; Williams, Jeffery T.; Long, Stuart A.; Wolfe, John C.

1994-01-01

The primary goal was to design and characterize a four-element, 20 GHz, circularly polarized microstrip patch antenna fabricated from YBa2Cu3O(x) superconductor. The purpose is to support a high temperature superconductivity flight communications experiment between the space shuttle orbiter and the ACTS satellite. This study is intended to provide information into the design, construction, and feasibility of a circularly polarized superconducting 20 GHz downlink or cross-link antenna. We have demonstrated that significant gain improvements can be realized by using superconducting materials for large corporate fed array antennas. In addition, we have shown that when constructed from superconducting materials, the efficiency, and therefore the gain, of microstrip patches increases if the substrate is not so thick that the dominant loss mechanism for the patch is radiation into the surface waves of the conductor-backed substrate. We have considered two design configurations for a superconducting 20 GHz four-element circularly polarized microstrip antenna array. The first is the Huang array that uses properly oriented and phased linearly polarized microstrip patch elements to realize a circularly polarized pattern. The second is a gap-coupled array of circularly polarized elements. In this study we determined that although the Huang array operates well on low dielectric constant substrates, its performance becomes extremely sensitive to mismatches, interelement coupling, and design imperfections for substrates with high dielectric constants. For the gap-coupled microstrip array, we were able to fabricate and test circularly polarized elements and four-element arrays on LaAlO3 using sputtered copper films. These antennas were found to perform well, with relatively good circular polarization. In addition, we realized a four-element YBa2Cu3O(x) array of the same design and measured its pattern and gain relative to a room temperature copper array. The patterns were essentially the same as that for the copper array. The measured gain of the YBCO antenna was greater than that for the room temperature copper design at temperatures below 82K, reaching a value of 3.4 dB at the lowest temperatures.

Plasticity in Cell Division Patterns and Auxin Transport Dependency during in Vitro Embryogenesis in Brassica napus[C][W

PubMed Central

Soriano, Mercedes; Li, Hui; Jacquard, Cédric; Angenent, Gerco C.; Krochko, Joan; Offringa, Remko; Boutilier, Kim

2014-01-01

In Arabidopsis thaliana, zygotic embryo divisions are highly regular, but it is not clear how embryo patterning is established in species or culture systems with irregular cell divisions. We investigated this using the Brassica napus microspore embryogenesis system, where the male gametophyte is reprogrammed in vitro to form haploid embryos in the absence of exogenous growth regulators. Microspore embryos are formed via two pathways: a zygotic-like pathway, characterized by initial suspensor formation followed by embryo proper formation from the distal cell of the suspensor, and a pathway characterized by initially unorganized embryos lacking a suspensor. Using embryo fate and auxin markers, we show that the zygotic-like pathway requires polar auxin transport for embryo proper specification from the suspensor, while the suspensorless pathway is polar auxin transport independent and marked by an initial auxin maximum, suggesting early embryo proper establishment in the absence of a basal suspensor. Polarity establishment in this suspensorless pathway was triggered and guided by rupture of the pollen exine. Irregular division patterns did not affect cell fate establishment in either pathway. These results confirm the importance of the suspensor and suspensor-driven auxin transport in patterning, but also uncover a mechanism where cell patterning is less regular and independent of auxin transport. PMID:24951481

Development of X-ray spectroscopic polarimetry with bent Si crystals and CFRP substrate

NASA Astrophysics Data System (ADS)

Iizuka, Ryo; Izumiya, Takanori; Tsuboi, Yohko

2016-07-01

The light from celestial objects includes four important quantities; images, time variation, energy spectrum, and polarization. In the field of X-ray astronomy, the capabilities of the former three have remarkably developed. On the other hand, the progress for the polarimetry is considerably delayed because of technical difficulties. In order to make a breakthrough in the field of X-ray polarimetry, we have developed a new type of optics for X-ray polarimetry. The system is collecting Bragg crystal with large area and very high sensitivity for the polarization dedicated to Fe-K lines. We adopt the 400 re ection of Si(100) crystals with high sensitivity for the polarization around Fe-K lines (6 7 keV), and bent the crystals with the wide X-ray band and high S/N ratio. Furthermore, to install small area of CCD to non-focal plane, it also has the spectroscopic capability with the better resolution than that of general X-ray CCD. Our previous development was to bent Si crystals to the cylindrical shape of circle and parabola with the DLC deposition. However, for the better optics for the X-ray polarimetry, the shape should be the paraboloid of revolution to collect X-rays with high S/N ratio. We searched for the method to bent the Si crystals to the shape of the paraboloid of revolution. We devised the method to mold the crystal and the CFRP substrate simultaneously pushed to the sophisticated foundation with the paraboloid of revolution. We developed the prototype of about 8 inch in radius of one-quater size. The crystals was also bent in the circumferential direction. Therefore, the image capability examined with optical parallel beam is 0.6 degree. In this thesis, we discussed the new design for X-ray spectroscopic polarimetry, the evaluation of image capability.

Earth Rotation Parameter Solutions using BDS and GPS Data from MEGX Network

NASA Astrophysics Data System (ADS)

Xu, Tianhe; Yu, Sumei; Li, Jiajing; He, Kaifei

2014-05-01

Earth rotation parameters (ERPs) are necessary parameters to achieve mutual transformation of the celestial reference frame and earth-fix reference frame. They are very important for satellite precise orbit determination (POD), high-precision space navigation and positioning. In this paper, the determination of ERPs including polar motion (PM), polar motion rate (PMR) and length of day (LOD) are presented using BDS and GPS data of June 2013 from MEGX network based on least square (LS) estimation with constraint condition. BDS and GPS data of 16 co-location stations from MEGX network are the first time used to estimate the ERPs. The results show that the RMSs of x and y component errors of PM and PM rate are about 0.9 mas, 1.0 mas, 0.2 mas/d and 0.3 mas/d respectively using BDS data. The RMS of LOD is about 0.03 ms/d using BDS data. The RMSs of x and y component errors of PM and PM rate are about 0.2 mas, 0.2 mas/d respectively using GPS data. The RMS of LOD is about 0.02 ms/d using GPS data. The optimal relative weight is determined by using variance component estimation when combining BDS and GPS data. The accuracy improvements of adding BDS data is between 8% to 20% for PM and PM rate. There is no obvious improvement in LOD when BDS data is involved. System biases between BDS and GPS are also resolved per station. They are very stable from day to day with the average accuracy of about 20 cm. Keywords: Earth rotation parameter; International GNSS Service; polar motion; length of day; least square with constraint condition Acknowledgments: This work was supported by Natural Science Foundation of China (41174008) and the Foundation for the Author of National Excellent Doctoral Dissertation of China (2007B51) .

Bandwidth broadening of a graphene-based circular polarization converter by phase compensation.

PubMed

Gao, Xi; Yang, Wanli; Cao, Weiping; Chen, Ming; Jiang, Yannan; Yu, Xinhua; Li, Haiou

2017-10-02

We present a broadband tunable circular polarization converter composed of a single graphene sheet patterned with butterfly-shaped holes, a dielectric spacer, and a 7-layer graphene ground plane. It can convert a linearly polarized wave into a circularly polarized wave in reflection mode. The polarization converter can be dynamically tuned by varying the Fermi energy of the single graphene sheet. Furthermore, the 7-layer graphene acting as a ground plane can modulate the phase of its reflected wave by controlling the Femi energy, which provides constructive interference condition at the surface of the single graphene sheet in a broad bandwidth and therefore significantly broadens the tunable bandwidth of the proposed polarization converter.

On the asteroid hazard

NASA Astrophysics Data System (ADS)

Eneev, T. M.; Akhmetshin, R. Z.; Efimov, G. B.

2012-04-01

The concept of "space patrol" is considered, aimed at discovering and cataloging the majority of celestial bodies that constitute a menace for the Earth [1, 2]. The scheme of "optical barrier" formed by telescopes of the space patrol is analyzed, requirements to the observation system are formulated, and some schemes of sighting the optical barrier region are suggested (for reliable detection of the celestial bodies approaching the Earth and for determination of their orbits). A comparison is made of capabilities of electro-jet engines and traditional chemical engines for arrangement of patrol spacecraft constellation in the Earth's orbit.

On a celestial occurrence recorded in the hagiography of St. Vladimir

NASA Astrophysics Data System (ADS)

Banjević, Boris

2002-04-01

There were recorded a number of celestial occurrences in Serbian early history. Amongst them are a few appearances of comets. One except from Bible bearing on life of king David, relating to a phenomenon that might be interpreted as a comet, is in some way similar to the quotation from the hagiography of St. Vladimir. There is possibility that Halley's comet was observed at some time. This affects the chronology of the reign of St. Vladimir by about 11 years. This author thinks that it was in the summer 989 AD.

Comparison of Measured Galactic Background Radiation at L-Band with Model

NASA Technical Reports Server (NTRS)

LeVine, David M.; Abraham, Saji; Kerr, Yann H.; Wilson, William J.; Skou, Niels; Sobjaerg, Sten

2004-01-01

Radiation from the celestial sky in the spectral window at 1.413 GHz is strong and an accurate accounting of this background radiation is needed for calibration and retrieval algorithms. Modern radio astronomy measurements in this window have been converted into a brightness temperature map of the celestial sky at L-band suitable for such applications. This paper presents a comparison of the background predicted by this map with the measurements of several modern L-band remote sensing radiometer Keywords-Galactic background, microwave radiometry; remote sensing;

The Southern Hemisphere VLBI experiment

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

Preston, R.A.; Meier, D.L.; Louie, A.P.

1989-07-01

Six radio telescopes were operated as the first Southern Hemisphere VLBI array in April and May 1982. Observations were made at 2.3 and 8.4 GHz. This array provided VLBI modeling and hybrid imaging of celestial radio sources in the Southern Hemisphere, high-accuracy VLBI geodesy between Southern Hemisphere sites, and subarcsecond radio astrometry of celestial sources south of declination -45 deg. The goals and implementation of the array are discussed, the methods of modeling and hybrid image production are explained, and the VLBI structure of the sources that were observed is summarized. 36 refs.

General Methodology for Designing Spacecraft Trajectories

NASA Technical Reports Server (NTRS)

Condon, Gerald; Ocampo, Cesar; Mathur, Ravishankar; Morcos, Fady; Senent, Juan; Williams, Jacob; Davis, Elizabeth C.

2012-01-01

A methodology for designing spacecraft trajectories in any gravitational environment within the solar system has been developed. The methodology facilitates modeling and optimization for problems ranging from that of a single spacecraft orbiting a single celestial body to that of a mission involving multiple spacecraft and multiple propulsion systems operating in gravitational fields of multiple celestial bodies. The methodology consolidates almost all spacecraft trajectory design and optimization problems into a single conceptual framework requiring solution of either a system of nonlinear equations or a parameter-optimization problem with equality and/or inequality constraints.

Celestial Mechanics: from the bases of the past to the challenges of the future

NASA Astrophysics Data System (ADS)

de Melo, C. F.; Prado, A. F. B. A.; Macau, E. E. N.; Winter, O. C.; Gomes, V. M.

2015-10-01

This special issue of Journal of Physics: Conference Series brings a set of 31 papers presented in the Brazilian Colloquium on Orbital Dynamics (CBDO), held on December 1 - 5, 2014, in the city of Águas de Lindoia, Brazil. CBDO is a traditional and important scientific meeting in the areas of Theoretical and Applied Celestial Mechanics. The meeting takes place every two years, when researchers from South America and also guests from other continents present their works and discuss the paths trodden by the space sciences.

Impacts of four northern-hemisphere teleconnection patterns on atmospheric circulations over Eurasia and the Pacific

NASA Astrophysics Data System (ADS)

Gao, Tao; Yu, Jin-yi; Paek, Houk

2017-08-01

The impacts of four teleconnection patterns on atmospheric circulation components over Eurasia and the Pacific region, from low to high latitudes in the Northern Hemisphere (NH), were investigated comprehensively in this study. The patterns, as identified by the Climate Prediction Center (USA), were the East Atlantic (EA), East Atlantic/Western Russia (EAWR), Polar/Eurasia (POLEUR), and Scandinavian (SCAND) teleconnections. Results indicate that the EA pattern is closely related to the intensity of the subtropical high over different sectors of the NH in all seasons, especially boreal winter. The wave train associated with this pattern serves as an atmospheric bridge that transfers Atlantic influence into the low-latitude region of the Pacific. In addition, the amplitudes of the EAWR, SCAND, and POLEUR patterns were found to have considerable control on the "Vangengeim-Girs" circulation that forms over the Atlantic-Eurasian region in winter or spring. The EA and EAWR mainly affect the westerlies in winter and spring and the POLEUR and SCAND, respectively, in summer and winter. Strong westerlies confine the extension of the North Polar vortex, which generally results in a small weak vortex and a shallow East Asian trough located in a position further east than normal. Furthermore, the North Polar vortex presents significant connections with the patterns during winter and summer. Analyses in this work suggest that the teleconnection patterns in summer could be driven, at least partly, by the Atlantic Multidecadal Oscillation, which to some degree might transmit the influence of the Atlantic Ocean to Eurasia and the Pacific region.

Polarization speckle imaging as a potential technique for in vivo skin cancer detection.

PubMed

Tchvialeva, Lioudmila; Dhadwal, Gurbir; Lui, Harvey; Kalia, Sunil; Zeng, Haishan; McLean, David I; Lee, Tim K

2013-06-01

Skin cancer is the most common cancer in the Western world. In order to accurately detect the disease, especially malignant melanoma-the most fatal form of skin cancer-at an early stage when the prognosis is excellent, there is an urgent need to develop noninvasive early detection methods. We believe that polarization speckle patterns, defined as a spatial distribution of depolarization ratio of traditional speckle patterns, can be an important tool for skin cancer detection. To demonstrate our technique, we conduct a large in vivo clinical study of 214 skin lesions, and show that statistical moments of the polarization speckle pattern could differentiate different types of skin lesions, including three common types of skin cancers, malignant melanoma, squamous cell carcinoma, basal cell carcinoma, and two benign lesions, melanocytic nevus and seborrheic keratoses. In particular, the fourth order moment achieves better or similar sensitivity and specificity than many well-known and accepted optical techniques used to differentiate melanoma and seborrheic keratosis.

Selective area growth of N-polar GaN nanorods by plasma-assisted MBE on micro-cone-patterned c-sapphire substrates

NASA Astrophysics Data System (ADS)

Jmerik, V. N.; Kuznetsova, N. V.; Nechaev, D. V.; Shubina, T. V.; Kirilenko, D. A.; Troshkov, S. I.; Davydov, V. Yu.; Smirnov, A. N.; Ivanov, S. V.

2017-11-01

The site-controlled selective area growth of N-polar GaN nanorods (NR) was developed by plasma-assisted MBE (PA MBE) on micro-cone-patterned sapphire substrates (μ-CPSS) by using a two-stage growth process. A GaN nucleation layer grown by migration enhanced epitaxy provides the best selectivity for nucleation of NRs on the apexes of 3.5-μm-diameter cones, whereas the subsequent growth of 1-μm-high NRs with a constant diameter of about 100 nm proceeds by standard high-temperature PA MBE at nitrogen-rich conditions. These results are explained by anisotropy of the surface energy for GaN of different polarity and crystal orientation. The InGaN single quantum wells inserted in the GaN NRs grown on the μ-CPSS demonstrate photoluminescence at 510 nm with a spatially periodic variation of its intensity with a period of ∼6 μm equal to that of the substrate patterning profile.

Polarization speckle imaging as a potential technique for in vivo skin cancer detection

NASA Astrophysics Data System (ADS)

Tchvialeva, Lioudmila; Dhadwal, Gurbir; Lui, Harvey; Kalia, Sunil; Zeng, Haishan; McLean, David I.; Lee, Tim K.

2013-06-01

Skin cancer is the most common cancer in the Western world. In order to accurately detect the disease, especially malignant melanoma-the most fatal form of skin cancer-at an early stage when the prognosis is excellent, there is an urgent need to develop noninvasive early detection methods. We believe that polarization speckle patterns, defined as a spatial distribution of depolarization ratio of traditional speckle patterns, can be an important tool for skin cancer detection. To demonstrate our technique, we conduct a large in vivo clinical study of 214 skin lesions, and show that statistical moments of the polarization speckle pattern could differentiate different types of skin lesions, including three common types of skin cancers, malignant melanoma, squamous cell carcinoma, basal cell carcinoma, and two benign lesions, melanocytic nevus and seborrheic keratoses. In particular, the fourth order moment achieves better or similar sensitivity and specificity than many well-known and accepted optical techniques used to differentiate melanoma and seborrheic keratosis.

Using satellite telemetry to define spatial population structure in polar bears in the Norwegian and western Russian Arctic

USGS Publications Warehouse

Mauritzen, Mette; Derocher, Andrew E.; Wiig, Øystein; Belikov, Stanislav; Boltunov, Andrei N.; Garner, Gerald W.

2002-01-01

1. Animal populations, defined by geographical areas within a species’ distribution where population dynamics are largely regulated by births and deaths rather than by migration from surrounding areas, may be the correct unit for wildlife management. However, in heterogeneous landscapes varying habitat quality may yield subpopulations with distinct patterns in resource use and demography significant to the dynamics of populations.2. To define the spatial population structure of polar bears Ursus maritimus in the Norwegian and western Russian Arctic, and to assess the existence of a shared population between the two countries, we analysed satellite telemetry data obtained from 105 female polar bears over 12 years.3. Using both cluster analyses and home-range estimation methods, we identified five population units inhabiting areas with different sea-ice characteristics and prey availability.4. The continuous distribution of polar bear positions indicated that the different subpopulations formed one continuous polar bear population in the Norwegian and western Russian Arctic. Hence, Norway and Russia have a shared management responsibility.5. The spatial population structure identified will provide a guide for evaluating geographical patterns in polar bear ecology, the dynamics of polar bear–seal relationships and the effects of habitat alteration due to climate change. The work illustrates the importance of defining population borders and subpopulation structure in understanding the dynamics and management of larger animals.

VOLATILE POLAR METABOLITES IN EXHALED BREATH CONDENSATE (EBC): COLLECTION AND ANALYSIS

EPA Science Inventory

Environmental exposures, individual activities, and disease states can perturb normal metabolic processes and be expressed as a change in the patterns of polar volatile organic compounds (PVOCs) present in biological fluids. We explore the measurement of volatile endogenous bioma...

Polarization-resolved optical response of plasmonic particle-on-film nanocavities

NASA Astrophysics Data System (ADS)

Zhang, Q.; Li, G.-C.; Lo, T. W.; Lei, D. Y.

2018-02-01

Placing a metal nanoparticle atop a metal film forms a plasmonic particle-on-film nanocavity. Such a nanocavity supports strong plasmonic coupling that results in rich hybridized plasmon modes, rendering the cavity a versatile platform for exploiting a wide range of plasmon-enhanced spectroscopy applications. In this paper, we fully address the polarization-resolved, orientation-dependent far-field optical responses of plasmonic monomer- and dimer-on-film nanocavities by numerical simulations and experiments. With polarization-resolved dark-field spectroscopy, the distinct plasmon resonances of these nanocavities are clearly determined from their scattering spectra. Moreover, the radiation patterns of respective plasmon modes, which are often mixed together in common dark-field imaging, can be unambiguously resolved with our proposed quasi-multispectral imaging method. Explicitly, the radiation pattern of the monomer-on-film nanocavity gradually transitions from a solid spot in the green imaging channel to a doughnut ring in the red channel when tuning the excitation polarization from parallel to perpendicular to the sample surface. This observation holds true for the plasmonic dimer-on-film nanocavity with the dimer axis aligned in the incidence plane; when the dimer axis is normal to the incidence plane, the pattern transitions from a solid spot to a doughnut ring both in the red channel. These studies not only demonstrate a flexible polarization control over the optical responses of plasmonic particle-on-film nanostructures but also enrich the optical tool kit for far-field imaging and spectroscopy characterization of various plasmonic nanostructures.

An Instrument to Measure Polarized CMB Foregrounds at 10 and 15 GHz

NASA Astrophysics Data System (ADS)

O'Neill, Hugh

New CMB experiments are being proposed and built with the goal of eventually resolving the B-mode polarization pattern imprinted in the CMB from a stochastic background of gravitional waves left over from an inflationary epoch in the very early universe. It has been widely acknowledged that the ability to resolve the B-mode polarization pattern in the CMB will require a more sophisticated understanding of the obscuring galactic foreground emission than what currently exists. Of the various galactic foregrounds, synchrotron radiation is identified as both the most polarized, and the most complicated in terms of spectral and spatial variability. The COsmic Foreground Explorer (COFE), described in this dissertation, is a NASA funded balloon borne mission to map polarized galactic foreground emission in two frequency bands, one centered at 10 GHz and the other at 15 GHz. These frequency bands make COFE particularly sensitive to polarized synchrotron radiation, and the separation between these two frequency bands facilitates the discrimination of the synchrotron component from the CMB and other foreground sourced such as free-free emission and spinning dust. COFE was successfully launched in September of 2011, and acquired data during a 22 hour flight. COFE is currently being reconfigured to acquire additional data from a high altitude, ground based observatory.

Invariant polar bear habitat selection during a period of sea ice loss.

PubMed

Wilson, Ryan R; Regehr, Eric V; Rode, Karyn D; St Martin, Michelle

2016-08-17

Climate change is expected to alter many species' habitat. A species' ability to adjust to these changes is partially determined by their ability to adjust habitat selection preferences to new environmental conditions. Sea ice loss has forced polar bears (Ursus maritimus) to spend longer periods annually over less productive waters, which may be a primary driver of population declines. A negative population response to greater time spent over less productive water implies, however, that prey are not also shifting their space use in response to sea ice loss. We show that polar bear habitat selection in the Chukchi Sea has not changed between periods before and after significant sea ice loss, leading to a 75% reduction of highly selected habitat in summer. Summer was the only period with loss of highly selected habitat, supporting the contention that summer will be a critical period for polar bears as sea ice loss continues. Our results indicate that bears are either unable to shift selection patterns to reflect new prey use patterns or that there has not been a shift towards polar basin waters becoming more productive for prey. Continued sea ice loss is likely to further reduce habitat with population-level consequences for polar bears. © 2016 The Author(s).

Common and distinctive localization patterns of Crumbs polarity complex proteins in the mammalian eye.

PubMed

Kim, Jin Young; Song, Ji Yun; Karnam, Santi; Park, Jun Young; Lee, Jamie J H; Kim, Seonhee; Cho, Seo-Hee

2015-01-01

Crumbs polarity complex proteins are essential for cellular and tissue polarity, and for adhesion of epithelial cells. In epithelial tissues deletion of any of three core proteins disrupts localization of the other proteins, indicating structural and functional interdependence among core components. Despite previous studies of function and co-localization that illustrated the properties that these proteins share, it is not known whether an individual component of the complex plays a distinct role in a unique cellular and developmental context. In order to investigate this question, we primarily used confocal imaging to determine the expression and subcellular localization of the core Crumbs polarity complex proteins during ocular development. Here we show that in developing ocular tissues core Crumbs polarity complex proteins, Crb, Pals1 and Patj, generally appear in an overlapping pattern with some exceptions. All three core complex proteins localize to the apical junction of the retinal and lens epithelia. Pals1 is also localized in the Golgi of the retinal cells and Patj localizes to the nuclei of the apically located subset of progenitor cells. These findings suggest that core Crumbs polarity complex proteins exert common and independent functions depending on cellular context. Copyright © 2015 Elsevier B.V. All rights reserved.

Mitochondrial distribution and activity in human mature oocytes: gonadotropin-releasing hormone agonist versus antagonist for pituitary down-regulation.

PubMed

Dell'Aquila, Maria Elena; Ambruosi, Barbara; De Santis, Teresa; Cho, Yoon Sung

2009-01-01

To analyze the effects of GnRH agonists versus antagonists on mitochondrial distribution and activity in human mature oocytes. Randomized research experimental study. Academic basic research laboratory and hospital-based fertility center. Two hundred twenty-five supernumerary mature oocytes from 44 patients. Fluorescent staining and confocal laser scanning microscopy on oocytes after the use of either GnRH agonist (group A) or GnRH antagonist (group B). Oocyte mitochondrial distribution pattern and activity using MitoTracker Orange CMTM Ros. More oocytes showing polarized mitochondrial distribution pattern were found in group A than in group B (35% vs. 14%). In group B, hCG rather than GnRH agonist, for ovulation induction, resulted in more oocytes showing heterogeneous (57% vs. 14%), in particular polarized (24% vs. 0) mitochondrial distribution. In groups A and B, fluorescence intensity did not vary according to mitochondrial distribution pattern. However, fluorescence intensity was higher in oocytes with polarized and large granules configurations in group B compared to group A. The GnRH agonist and antagonist may have different effects on oocyte mitochondrial distribution pattern and activity. The GnRH antagonist may induce mitochondrial hyperactivity, which may be detrimental to the oocyte.

Effects of deterministic surface distortions on reflector antenna performance

NASA Technical Reports Server (NTRS)

Rahmat-Samii, Y.

1985-01-01

Systematic distortions of reflector antenna surfaces can cause antenna radiation patterns to be undesirably different from those of perfectly smooth reflector surfaces. In this paper, a simulation model for systematic distortions is described which permits an efficient computation of the effects of distortions in the reflector pattern. The model uses a vector diffraction physical optics analysis for the determination of both the co-polar and cross-polar fields. An interpolation scheme is also presented for the description of reflector surfaces which are prescribed by discrete points. Representative numerical results are presented for reflectors with sinusoidally and thermally distorted surfaces. Finally, comparisons are made between the measured and calculated patterns of a slowly-varying distorted offset parabolic reflector.

92 GHz dual-polarized integrated horn antennas

NASA Technical Reports Server (NTRS)

Ali-Ahmad, Walid Y.; Rebeiz, Gabriel M.

1991-01-01

A dual-polarized two-dimensional imaging array was designed for millimeter-wave applications. The dual-polarized design consists of two dipoles perpendicular to each other and suspended on the same membrane inside a pyramidal cavity etched in silicon. The dual-polarized antenna is fully monolithic with room available for processing electronics. The IF or video signals are taken out through a novel bias and feeding structure. The measured polarization isolation is better than 20 dB at 92 GHz, and the orthogonal channels show identical far-field patterns. The antenna is well suited for millimeter-wave polarimetric synthetic-aperture radars (SARs) and high-efficiency balanced-mixer receivers.

Reconsidering the advantages of the three-dimensional representation of the interferometric transform for imaging with non-coplanar baselines and wide fields of view

NASA Astrophysics Data System (ADS)

Smith, D. M. P.; Young, A.; Davidson, D. B.

2017-07-01

Radio telescopes with baselines that span thousands of kilometres and with fields of view that span tens of degrees have been recently deployed, such as the Low Frequency Array, and are currently being developed, such as the Square Kilometre Array. Additionally, there are proposals for space-based instruments with all-sky imaging capabilities, such as the Orbiting Low Frequency Array. Such telescopes produce observations with three-dimensional visibility distributions and curved image domains. In most work to date, the visibility distribution has been converted to a planar form to compute the brightness map using a two-dimensional Fourier transform. The celestial sphere is faceted in order to counter pixel distortion at wide angles, with each such facet requiring a unique planar form of the visibility distribution. Under the above conditions, the computational and storage complexities of this approach can become excessive. On the other hand, when using the direct Fourier transform approach, which maintains the three-dimensional shapes of the visibility distribution and celestial sphere, the non-coplanar visibility component requires no special attention. Furthermore, as the celestial samples are placed directly on the curved surface of the celestial sphere, pixel distortion at wide angles is avoided. In this paper, a number of examples illustrate that under these conditions (very long baselines and very wide fields of view) the costs of the direct Fourier transform may be comparable to (or even lower than) methods that utilise the two-dimensional fast Fourier transform.

Dynamics of a vertical flight in the stationary gravitational field of a celestial body: Post-newtonian corrections and gravitational redshift

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

Imshennik, V. S., E-mail: imshennik@itep.r

2010-04-15

The standard problem of a radial motion of test particles in the stationary gravitational field of a spherically symmetric celestial body is solved and is used to determine the time features of this motion. The problem is solved for the equations of motion of general relativity (GR), and the time features are obtained in the post-Newtonian approximation, with linear GR corrections proportional to r{sub g}/r and {beta}{sup 2} (in the solution being considered, they are of the same order of smallness) being taken rigorously into account. Total times obtained by integrating the time differentials along the trajectories of motion aremore » considered as the time features in question. It is shown that, for any parameters of the motion, the proper time (which corresponds to watches comoving with a test particle) exceeds the time of watches at rest (watches at the surface of the celestial body being considered). The mass and the radius of the celestial body, as well as the initial velocity of the test particle, serve as arbitrary parameters of the motion. The time difference indicated above implies a leading role of the gravitational redshift, which decreases somewhat because of the opposite effect of the Doppler shift. The results are estimated quantitatively for the important (from the experimental point of view) case of vertical flights of rockets starting from the Earth's surface. In this case, the GR corrections, albeit being extremely small (a few microseconds for several hours of the flight), aremeasurable with atomic (quantum) watches.« less

A New Precession Formula

NASA Astrophysics Data System (ADS)

Fukushima, Toshio

2003-07-01

We adapt J. G. Williams' expression of the precession and nutation using the 3-1-3-1 rotation to an arbitrary inertial frame of reference. The modified formulation avoids a singularity caused by finite pole offsets near the epoch. By adopting the planetary precession formula numerically determined from DE405 and by using a recent theory of the forced nutation of the nonrigid Earth by Shirai & Fukishima, we analyze the celestial pole offsets observed by VLBI for 1979-2000 and determine the best-fit polynomials of the lunisolar precession angles. We then translate the results into classical precession quantities and evaluate the difference due to the difference in the ecliptic definition. The combination of these formulae and the periodic part of the Shirai-Fukishima nutation theory serves as a good approximation of the precession-nutation matrix in the International Celestial Reference Frame. As a by-product, we determine the mean celestial pole offset at J2000.0 as X0=-(17.12+/-0.01) mas and Y0=-(5.06+/-0.02) mas. Also, we estimate the speed of general precession in longitude at J2000.0 as p=5028.7955"+/-0.0003" per Julian century, the mean obliquity at J2000.0 in the inertial sense as (ɛ0)I=84381.40621"+/-0.00001" and in the rotational sense as (ɛ0)R=84381.40955"+/-0.00001", and the dynamical flattening of Earth as Hd=(3.2737804+/-0.0000003)×10-3. Furthermore, we establish a fast way to compute the precession-nutation matrix and provide a best-fit polynomial of an angle to specify the mean Celestial Ephemeris Origin.

Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis.

PubMed

Rogers, A E; Cappallo, R J; Hinteregger, H F; Levine, J I; Nesman, E F; Webber, J C; Whitney, A R; Clark, T A; Ma, C; Ryan, J; Corey, B E; Counselman, C C; Herring, T A; Shapiro, I I; Knight, C A; Shaffer, D B; Vandenberg, N R; Lacasse, R; Mauzy, R; Rayhrer, B; Schupler, B R; Pigg, J C

1983-01-07

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.

High-pressure synthesis of predicted oxynitride perovskite: Yttrium Silicon Oxynitride (YSiO2N)

NASA Astrophysics Data System (ADS)

Ahart, Muhtar; Somayazulu, M.; Vadapoo, Rajasekarakumar; Cohen, R. E.

We synthesized the previously predicted polar oxynitride perovskite in a diamond anvil cell with laser heating. YSiO2N was predicted to have the polar P4mm structure with an effective spontaneous polarization of 130 μC/cm2. A mixture of Yttrium nitride (YN) and amorphous Silicon dioxide (SiO2) were loaded into a diamond anvil cell and laser heated at or above 1200 C at 12 GPa. The run products were investigated by x-ray diffraction, Raman spectroscopy, and second harmonic generation, for their phase and structural properties. The x-ray diffraction pattern (a = 3.235 Å, c = 4.485 Å) shows the phase formation of YSiO2N and matches with the diffraction pattern derived from the first-principle predicted lattice parameters. However, minor unknown peaks are on the diffraction pattern indicating of the co-existence of other unknown phases. Further study of Raman spectroscopy observes the theoretically predicted modes, and second harmonic generation shows strong non-linear optical signal, which confirms the polar properties of YSiO2N. This work is supported by ONR Grants N00014-12-1-1038 and N00014-14-1-0561, by the ERC Advanced Grant ToMCaT.

Procedure for measuring photon and vector meson circular polarization variation with respect to the reaction plane in relativistic heavy-ion collisions

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

Tang, A. H.; Wang, G.

The electromagnetic (EM) eld pattern created by spectators in relativistic heavy-ion collisions plants a seed of positive (negative) magnetic helicity in the hemisphere above (below) the reaction plane. Owing to the chiral anomaly, the magnetic helicity interacts with the fermionic helicity of the collision system, and causes photons emitted in upper- and lower-hemispheres to have different preferences in the circular polarization. Similar helicity separation for massive particles, due to the global vorticity, is also possible. In this paper, we lay down a procedure to measure the variation of the circular polarization w.r.t the reaction plane in relativistic heavy-ion collisions formore » massless photons, as well as similar polarization patterns for vector mesons decaying into two daughters. We propose to study the yield differentially and compare the yield between upper- and lower-hemispheres in order to identify and quantify such effects.« less

Procedure for measuring photon and vector meson circular polarization variation with respect to the reaction plane in relativistic heavy-ion collisions

DOE PAGES

Tang, A. H.; Wang, G.

2016-08-30

The electromagnetic (EM) eld pattern created by spectators in relativistic heavy-ion collisions plants a seed of positive (negative) magnetic helicity in the hemisphere above (below) the reaction plane. Owing to the chiral anomaly, the magnetic helicity interacts with the fermionic helicity of the collision system, and causes photons emitted in upper- and lower-hemispheres to have different preferences in the circular polarization. Similar helicity separation for massive particles, due to the global vorticity, is also possible. In this paper, we lay down a procedure to measure the variation of the circular polarization w.r.t the reaction plane in relativistic heavy-ion collisions formore » massless photons, as well as similar polarization patterns for vector mesons decaying into two daughters. We propose to study the yield differentially and compare the yield between upper- and lower-hemispheres in order to identify and quantify such effects.« less

The origin of the structure of large-scale magnetic fields in disc galaxies

NASA Astrophysics Data System (ADS)

Nixon, C. J.; Hands, T. O.; King, A. R.; Pringle, J. E.

2018-07-01

The large-scale magnetic fields observed in spiral disc galaxies are often thought to result from dynamo action in the disc plane. However, the increasing importance of Faraday depolarization along any line of sight towards the galactic plane suggests that the strongest polarization signal may come from well above (˜0.3-1 kpc) this plane, from the vicinity of the warm interstellar medium (WIM)/halo interface. We propose (see also Henriksen & Irwin 2016) that the observed spiral fields (polarization patterns) result from the action of vertical shear on an initially poloidal field. We show that this simple model accounts for the main observed properties of large-scale fields. We speculate as to how current models of optical spiral structure may generate the observed arm/interarm spiral polarization patterns.

A Long Journey of Mathematics and Astronomy in Romania

NASA Astrophysics Data System (ADS)

Stavinschi, Magda

2010-10-01

Bucharest Astronomical Observatory celebrated recently its centenary. Its founders were all mathematicians or, better said, astronomers specialized in celestial mechanics. Their first doctoral theses were defended at Sorbonne, in the second half of the 19th century, under the guidance of the greatest specialists of the time. After they returned home, they continued what they had begun in Paris, namely celestial mechanics. The instruments they ordered and the first programmes of astronomical observations had an increasingly closer relation to mathematics, as they referred to astrometry and especially to stellar catalogues. Naturally, there were also astrophysical concerns, timid ones in the beginning, and then ever larger, especially beginning with the International Geophysical Year. The evolution of world astronomy, as well as that of Romania, seems to be following but one direction: astrophysics. The truth is that astrometry and celestial mechanics continue to lie at the basis of all astrophysical researches, actually in an entirely new and modern form. The astrometry schools recently organized, the new astrometry textbooks, as well as the IAU working groups dedicated to modern astrometry prove that the long journey of mathematics and astronomy is not over yet.

Numerical analysis of seismic events distributions on the planetary scale and celestial bodies astrometrical parameters

NASA Astrophysics Data System (ADS)

Bulatova, Dr.

2012-04-01

Modern research in the domains of Earth sciences is developing from the descriptions of each individual natural phenomena to the systematic complex research in interdisciplinary areas. For studies of its kind in the form numerical analysis of three-dimensional (3D) systems, the author proposes space-time Technology (STT), based on a Ptolemaic geocentric system, consist of two modules, each with its own coordinate system: (1) - 3D model of a Earth, the coordinates of which provides databases of the Earth's events (here seismic), and (2) - a compact model of the relative motion of celestial bodies in space - time on Earth known as the "Method of a moving source" (MDS), which was developed in MDS (Bulatova, 1998-2000) for the 3D space. Module (2) was developed as a continuation of the geocentric Ptolemaic system of the world, built on the astronomical parameters heavenly bodies. Based on the aggregation data of Space and Earth Sciences, systematization, and cooperative analysis, this is an attempt to establish a cause-effect relationship between the position of celestial bodies (Moon, Sun) and Earth's seismic events.

Generation of cylindrically polarized vector vortex beams with digital micromirror device

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

Gong, Lei; Liu, Weiwei; Wang, Meng

We propose a novel technique to directly transform a linearly polarized Gaussian beam into vector-vortex beams with various spatial patterns. Full high-quality control of amplitude and phase is implemented via a Digital Micro-mirror Device (DMD) binary holography for generating Laguerre-Gaussian, Bessel-Gaussian, and helical Mathieu–Gaussian modes, while a radial polarization converter (S-waveplate) is employed to effectively convert the optical vortices into cylindrically polarized vortex beams. Additionally, the generated vector-vortex beams maintain their polarization symmetry after arbitrary polarization manipulation. Due to the high frame rates of DMD, rapid switching among a series of vector modes carrying different orbital angular momenta paves themore » way for optical microscopy, trapping, and communication.« less

Wide-bandgap III-Nitride based Second Harmonic Generation

DTIC Science & Technology

2014-10-02

fabrication process for a GaN LPS. Fig. 1: 3-step Fabrication process of a GaN based lateral polar structure. ( a ) Growth of a 20 nm AlN buffer layer...etching of the LT-AlN stripes. This results are shown in Fig. 2 ( a ) and (b). Fig. 2: AFM images of KOH ( a ) and RIE (b) patterned templates for lateral ...was varied between 0.6 - 1.0. FIG. 3: Growth process of AlGaN based Lateral Polar Structures. ( a ) RIE patterning. (b) Growth of HT- AlN. (c

A comparative study of corrugated horn design by evolutionary techniques

NASA Technical Reports Server (NTRS)

Hoorfar, A.

2003-01-01

Here an evolutionary programming algorithm is used to optimize the pattern of a corrugated circular horn subject to various constraints on return loss, antenna beamwidth, pattern circularity, and low cross polarization.

Fingering instabilities and pattern formation in a two-component dipolar Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Xi, Kui-Tian; Byrnes, Tim; Saito, Hiroki

2018-02-01

We study fingering instabilities and pattern formation at the interface of an oppositely polarized two-component Bose-Einstein condensate with strong dipole-dipole interactions in three dimensions. It is shown that the rotational symmetry is spontaneously broken by fingering instability when the dipole-dipole interactions are strengthened. Frog-shaped and mushroom-shaped patterns emerge during the dynamics due to the dipolar interactions. We also demonstrate the spontaneous density modulation and domain growth of a two-component dipolar BEC in the dynamics. Bogoliubov analyses in the two-dimensional approximation are performed, and the characteristic lengths of the domains are estimated analytically. Patterns resembling those in magnetic classical fluids are modulated when the number ratio of atoms, the trap ratio of the external potential, or tilted polarization with respect to the z direction is varied.

Perspectives and Open Problems in the Early Phases of Left-Right Patterning

PubMed Central

Vandenberg, Laura N.; Levin, Michael

2009-01-01

Summary Embryonic left-right (LR) patterning is a fascinating aspect of embryogenesis. The field currently faces important questions about the origin of LR asymmetry, the mechanisms by which consistent asymmetry is imposed on the scale of the whole embryo, and the degree of conservation of early phases of LR patterning among model systems. Recent progress on planar cell polarity and cellular asymmetry in a variety of tissues and species provides a new perspective on the early phases of LR patterning. Despite the huge diversity in body-plans over which consistent LR asymmetry is imposed, and the apparent divergence in molecular pathways that underlie laterality, the data reveal conservation of physiological modules among phyla and a basic scheme of cellular chirality amplified by a planar cell polarity-like pathway over large cell fields. PMID:19084609

Orthogonal vector algorithm to obtain the solar vector using the single-scattering Rayleigh model.

PubMed

Wang, Yinlong; Chu, Jinkui; Zhang, Ran; Shi, Chao

2018-02-01

Information obtained from a polarization pattern in the sky provides many animals like insects and birds with vital long-distance navigation cues. The solar vector can be derived from the polarization pattern using the single-scattering Rayleigh model. In this paper, an orthogonal vector algorithm, which utilizes the redundancy of the single-scattering Rayleigh model, is proposed. We use the intersection angles between the polarization vectors as the main criteria in our algorithm. The assumption that all polarization vectors can be considered coplanar is used to simplify the three-dimensional (3D) problem with respect to the polarization vectors in our simulation. The surface-normal vector of the plane, which is determined by the polarization vectors after translation, represents the solar vector. Unfortunately, the two-directionality of the polarization vectors makes the resulting solar vector ambiguous. One important result of this study is, however, that this apparent disadvantage has no effect on the complexity of the algorithm. Furthermore, two other universal least-squares algorithms were investigated and compared. A device was then constructed, which consists of five polarized-light sensors as well as a 3D attitude sensor. Both the simulation and experimental data indicate that the orthogonal vector algorithms, if used with a suitable threshold, perform equally well or better than the other two algorithms. Our experimental data reveal that if the intersection angles between the polarization vectors are close to 90°, the solar-vector angle deviations are small. The data also support the assumption of coplanarity. During the 51 min experiment, the mean of the measured solar-vector angle deviations was about 0.242°, as predicted by our theoretical model.

Model for the role of auxin polar transport in patterning of the leaf adaxial-abaxial axis.

PubMed

Shi, Jianmin; Dong, Jiaqiang; Xue, Jingshi; Wang, Hua; Yang, Zhongnan; Jiao, Yuling; Xu, Lin; Huang, Hai

2017-11-01

Leaf adaxial-abaxial polarity refers to the two leaf faces, which have different types of cells performing distinct biological functions. In 1951, Ian Sussex reported that when an incipient leaf primordium was surgically isolated by an incision across the vegetative shoot apical meristem (SAM), a radialized structure without an adaxial domain would form. This led to the proposal that a signal, now called the Sussex signal, is transported from the SAM to emerging primordia to direct leaf adaxial-abaxial patterning. It was recently proposed that instead of the Sussex signal, polar transport of the plant hormone auxin is critical in leaf polarity formation. However, how auxin polar transport functions in the process is unknown. Through live imaging, we established a profile of auxin polar transport in and around young leaf primordia. Here we show that auxin polar transport in lateral regions of an incipient primordium forms auxin convergence points. We demonstrated that blocking auxin polar transport in the lateral regions of the incipient primordium by incisions abolished the auxin convergence points and caused abaxialized leaves to form. The lateral incisions also blocked the formation of leaf middle domain and margins and disrupted expression of the middle domain/margin-associated marker gene WUSCHEL-RELATED HOMEOBOX 1 (SlWOX1). Based on these results we propose that the auxin convergence points are required for the formation of leaf middle domain and margins, and the functional middle domain and margins ensure leaf adaxial-abaxial polarity. How middle domain and margins function in the process is discussed. © 2017 The Authors The Plant Journal © 2017 John Wiley & Sons Ltd.

Probing Protoplanetary Disks: From Birth to Planets

NASA Astrophysics Data System (ADS)

Cox, Erin Guilfoil

2018-01-01

Disks are very important in the evolution of protostars and their subsequent planets. How early disks can form has implications for early planet formation. In the youngest protostars (i.e., Class 0 sources) magnetic fields can control disk growth. When the field is parallel to the collapsing core’s rotation axis, infalling material loses angular momentum and disks form in later stages. Sub-/millimeter polarization continuum observations of Class 0 sources at ~1000 au resolution support this idea. However, in the inner (~100 au), denser regions, it is unknown if the polarization only traces aligned dust grains. Recent theoretical studies have shown that self-scattering of thermal emission in the disk may contribute significantly to the polarization. Determining the scattering contribution in these sources is important to disentangle the magnetic field. At older times (the Class II phase), the disk structure can both act as a modulator and signpost of planet formation, if there is enough of a mass reservoir. In my dissertation talk, I will present results that bear on disk evolution at both young and late ages. I will present 8 mm polarization results of two Class 0 protostars (IRAS 4A and IC348 MMS) from the VLA at ~50 au resolution. The inferred magnetic field of IRAS 4A has a circular morphology, reminiscent of material being dragged into a rotating structure. I will show results from SOFIA polarization data of the area surrounding IRAS 4A at ~4000 au. I will also present ALMA 850 micron polarization data of ten protostars in the Perseus Molecular Cloud. Most of these sources show very ordered patterns and low (~0.5%) polarization in their inner regions, while having very disordered patterns and high polarization patterns in their extended emission that may suggest different mechanisms in the inner/outer regions. Finally, I will present results from our ALMA dust continuum survey of protoplanetary disks in Rho Ophiuchus; we measured both the sizes and fluxes of 49 pre main-sequence stellar systems and detected either gaps or cavities in ~6 of these sources. Combined, these results build upon how early protoplanetary disks can form around young protostars and thus how early planets can begin to form.

Flying Drosophilamelanogaster maintain arbitrary but stable headings relative to the angle of polarized light.

PubMed

Warren, Timothy L; Weir, Peter T; Dickinson, Michael H

2018-05-11

Animals must use external cues to maintain a straight course over long distances. In this study, we investigated how the fruit fly Drosophila melanogaster selects and maintains a flight heading relative to the axis of linearly polarized light, a visual cue produced by the atmospheric scattering of sunlight. To track flies' headings over extended periods, we used a flight simulator that coupled the angular velocity of dorsally presented polarized light to the stroke amplitude difference of the animals' wings. In the simulator, most flies actively maintained a stable heading relative to the axis of polarized light for the duration of 15 min flights. We found that individuals selected arbitrary, unpredictable headings relative to the polarization axis, which demonstrates that D . melanogaster can perform proportional navigation using a polarized light pattern. When flies flew in two consecutive bouts separated by a 5 min gap, the two flight headings were correlated, suggesting individuals retain a memory of their chosen heading. We found that adding a polarized light pattern to a light intensity gradient enhanced flies' orientation ability, suggesting D . melanogaster use a combination of cues to navigate. For both polarized light and intensity cues, flies' capacity to maintain a stable heading gradually increased over several minutes from the onset of flight. Our findings are consistent with a model in which each individual initially orients haphazardly but then settles on a heading which is maintained via a self-reinforcing process. This may be a general dispersal strategy for animals with no target destination. © 2018. Published by The Company of Biologists Ltd.

ALMA Dust Polarization Observations of Two Young Edge-on Protostellar Disks

NASA Astrophysics Data System (ADS)

Lee, Chin-Fei; Li, Zhi-Yun; Ching, Tao-Chung; Lai, Shih-Ping; Yang, Haifeng

2018-02-01

Polarized emission is detected in two young nearly edge-on protostellar disks in 343 GHz continuum at ∼50 au (∼0.″12) resolution with Atacama Large Millimeter/submillimeter Array. One disk is in HH 212 (Class 0) and the other in the HH 111 (early Class I) protostellar system. The polarization fraction is ∼1%. The disk in HH 212 has a radius of ∼60 au. The emission is mainly detected from the nearside of the disk. The polarization orientations are almost perpendicular to the disk major axis, consistent with either self-scattering or emission by grains aligned with a poloidal field around the outer edge of the disk because of the optical depth effect and temperature gradient; the presence of a poloidal field would facilitate the launching of a disk wind, for which there is already tentative evidence in the same source. The disk of HH 111 VLA 1 has a larger radius of ∼220 au and is thus more resolved. The polarization orientations are almost perpendicular to the disk major axis in the nearside, but more along the major axis in the farside, forming roughly half of an elliptical pattern there. It appears that toroidal and poloidal magnetic field may explain the polarization on the near and far sides of the disk, respectively. However, it is also possible that the polarization is due to self-scattering. In addition, alignment of dust grains by radiation flux may play a role in the farside. Our observations reveal a diversity of disk polarization patterns that should be taken into account in future modeling efforts.