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1

Trade-offs between Angular and Spatial Resolution in High Angular Resolution Diffusion Imaging  

E-print Network

Trade-offs between Angular and Spatial Resolution in High Angular Resolution Diffusion Imaging? HARDI is one of Q-space imaging techniques for resolving complex fiber geometries. Where fibers cross linearly registered to a high-resolution single subject template, the Colin27, using 9-parameter

Thompson, Paul

2

High angular resolution neutron interferometry.  

PubMed

The currently largest perfect-crystal neutron interferometer with six beam splitters and two interference loops offers novel applications in neutron interferometry. The two additional lamellas can be used for quantitative measurements of a phase shift due to crystal diffraction in the vicinity of a Bragg condition. The arising phase, referred to as "Laue phase," reveals an extreme angular sensitivity, which allows the detection of beam deflections of the order of 10(-6) s of arc. Furthermore, a precise measurement of the Laue phase at different reflections might constitute an interesting opportunity for the extraction of fundamental quantities like the neutron-electron scattering length, gravitational short-range interactions in the sub-micron range and the Debye Waller factor. For that purpose several harmonics can be utilized at the interferometer instrument ILL-S18. PMID:21731155

Zawisky, M; Springer, J; Lemmel, H

2011-04-01

3

Genetic Analysis of High Angular Resolution Diffusion Images (HARDI)  

E-print Network

Genetic Analysis of High Angular Resolution Diffusion Images (HARDI) Liang Zhan1 , Alex D. Leow2 adult twins (29 identical and 29 fraternal twin pairs) with high-angular resolution diffusion imaging of variations in fiber integrity and connectivity in large human populations. Keywords: High-Angular Resolution

Thompson, Paul

4

Photoelectron angular distributions beyond the dipole approximation  

SciTech Connect

This paper reports the measurement of nondipolar asymmetry parameters for the angular distributions of Ar 1s, Kr 2s, and Kr 2p photoemission within 2-3 keV above their respective thresholds. Pronounced asymmetries with respect to direction of photon propagation are present even at low electron kinetic energies. The energy dependence of the asymmetry is Z- and subshell-specific and causes the direction of preferred electron emission to change sign at least once in each case. Towards higher energies, the asymmetry increases and the photoelectron emission pattern is forward-skewed for all 3 cases. Measured asymmetry parameters are in good agreement with recent predictions from nonrelativistic calculations which include interference between electric-dipole and electric-quadrupole transition amplitudes in the photoabsorption process.

Kraessig, B.; Jung, M.; Gemmell, D.S.; Kanter, e.P.; LeBrun, T.; Southworth, S.H.; Young, L.

1996-08-01

5

Investigating the uncertainty in multi-fiber estimation in High Angular Resolution Diffusion Imaging  

E-print Network

-values. Keywords: High Angular Resolution Diffusion Imaging, Tensor Distribution Function, multi-fiberInvestigating the uncertainty in multi-fiber estimation in High Angular Resolution Diffusion between scanning time and angular precision in High Angular Resolution Diffusion Imaging (HARDI

Thompson, Paul

6

Analyzing Multi-Fiber Reconstruction in High Angular Resolution Diffusion Imaging using the Tensor Distribution Function  

E-print Network

Analyzing Multi-Fiber Reconstruction in High Angular Resolution Diffusion Imaging using the Tensor. Index Terms-- High Angular Resolution Diffusion Imaging, Tensor Distribution Function, multi-fiber protocols with higher angular and radial resolutions, such as the high- angular resolution diffusion imaging

Thompson, Paul

7

Optical Design of the Submillimeter High Angular Resolution Camera (SHARC)  

Microsoft Academic Search

The optical and mechanical design and performance of the Submillimeter High Angular Resolution Camera (SHARC) is described. The camera currently operates with a monolithic 24-pixel linear bolometer array in the 350 and 450 micron atmospheric windows at the Caltech Submillimeter Observatory (CSO). The design extends the techniques of geometric optics employed in optical and near-infrared cameras to submillimeter wavelengths. Using

T. R. Hunter; D. J. Benford; E. Serabyn

1996-01-01

8

Galactic nuclei and quasars at high angular resolution  

NASA Astrophysics Data System (ADS)

Astrophysics and cosmology progress expected from high angular resolution observations in the optical and ultraviolet ranges is discussed. Gravitational lenses, gas and star motions in active nuclei; physics of jets; determination of the mass of individual compact objects in the dark halos of galaxies, and estimation of the fraction of the mass of the Universe which is in baryonic form are mentioned.

Ulrich, M. H.

1987-08-01

9

Research on the Three Angular Resolution of Terrestrial Laser Scanning  

NASA Astrophysics Data System (ADS)

Terrestrial laser scanning technology has been applied more and more widely in the field of Surveying and mapping. Although requirements of the accuracy for different laser scanner survey may differ considerably, spatial resolution is an important aspect, which can be divided into range and angular components. The latter is a focus of this paper and is governed primarily by scanning interval, laser beam width and angle quantisation. An ultimate goal of this research is to derive the relationship and simplified formula between scanning interval and the angular quantisation when the EIFOV(Effective Instantaneous Field of View) is equal to the scanning interval; the relationship and simplified formula of scanning interval and the angular quantisation when the EIFOV is equal to the laser beam width, and the relationship and simplified formula of the theoretical minimum EIFOV and the angular quantisation. Firstly, this paper introduces the EIFOV model and the AMTF(Average Modulation Transfer Function) model. Secondly, the dimensionless AMTF and EIFOV generic model are proposed. Thirdly, the above relathionships are deduced?which are ellipse or hyperbola, and the three simplified formulas are proposed. The simplified formulas have direct significance on the angular resolution's calculation and the scanning interval setting.

Yang, R.; Hua, X.; Liu, J.; Wu, H.

2012-07-01

10

Tensor Distribution Function in Multiple Shell High Angular Resolution Diffusion Imaging  

E-print Network

Tensor Distribution Function in Multiple Shell High Angular Resolution Diffusion Imaging Liang Zhan ODF plot, while high b shell data has partial information loss in the fiber crossing region, Wedeen VJ. High angular resolution diffusion imaging re

Thompson, Paul

11

Computing White Matter Fiber Orientations in High Angular Resolution Diffusion-Weighted MRI  

E-print Network

Computing White Matter Fiber Orientations in High Angular Resolution Diffusion-Weighted MRI Ning is characterized by Gaussian diffusion process. High angular resolution diffusion imaging (HARDI) adds are recovered in separate steps. Keywords: high angular resolution diffusion imaging (HARDI), apparent diffusion

Zhang, Jun

12

ATLAS-BASED FIBER CLUSTERING FOR MULTI-SUBJECT ANALYSIS OF HIGH ANGULAR RESOLUTION DIFFUSION  

E-print Network

ATLAS-BASED FIBER CLUSTERING FOR MULTI-SUBJECT ANALYSIS OF HIGH ANGULAR RESOLUTION DIFFUSION and connectivity in high angular resolution diffusion images (HARDI), compute population-based statistics from measured from high angular resolution diffusion images (HARDI) · Tractography recovers geometry

Thompson, Paul

13

High-energy resolution, high-angular acceptance crystal monochromator  

SciTech Connect

The design principles, construction and characterization of a 4- bounce dispersive crystal monochromator is discussed. This monochromator is designed to reduce the bandpass of synchrotron radiation to 10--50 meV level, without sacrificing angular acceptance. This is achieved by combining an asymmetrically-cut, low order reflection with a symmetrically-cut, high order reflection in a nested configuration. This monochromator is being used as a beam conditioner for nuclear resonant scattering of synchrotron radiation to produce x-rays with [mu]eV[minus]neV resolution in the hard x-ray regime.

Toellner, T.S.; Mooney, T.; Alp, E.E. (Argonne National Lab., IL (United States)); Shastri, S. (Cornell Univ., Ithaca, NY (United States). Dept. of Applied Physics)

1992-06-01

14

High-energy resolution, high-angular acceptance crystal monochromator  

SciTech Connect

The design principles, construction and characterization of a 4- bounce dispersive crystal monochromator is discussed. This monochromator is designed to reduce the bandpass of synchrotron radiation to 10--50 meV level, without sacrificing angular acceptance. This is achieved by combining an asymmetrically-cut, low order reflection with a symmetrically-cut, high order reflection in a nested configuration. This monochromator is being used as a beam conditioner for nuclear resonant scattering of synchrotron radiation to produce x-rays with {mu}eV{minus}neV resolution in the hard x-ray regime.

Toellner, T.S.; Mooney, T.; Alp, E.E. [Argonne National Lab., IL (United States); Shastri, S. [Cornell Univ., Ithaca, NY (United States). Dept. of Applied Physics

1992-06-01

15

Optical Design of the Submillimeter High Angular Resolution Camera (SHARC)  

NASA Astrophysics Data System (ADS)

The optical and mechanical design and performance of the Submillimeter High Angular Resolution Camera (SHARC) is described. The camera currently operates with a monolithic 24-pixel linear bolometer array in the 350 and 450 micron atmospheric windows at the Caltech Submillimeter Observatory (CSO). The design extends the techniques of geometric optics employed in optical and near-infrared cameras to submillimeter wavelengths. Using an off-axis ellipsoidal mirror and cold stops, excellent imaging (Strehl ratio > 0.95) is achieved across a 2' by 2' focal plane field even with secondary throws of up to 4'. The camera's symmetric mechanical assembly provides fixed, machined alignment of the optical elements. We demonstrate the imaging capabilities of the system with 350 micron observations of a point source at the telescope. The optical design can easily accommodate future planned upgrades to two-dimensional bolometer arrays. (SECTION: Astronomical Instrumentation)

Hunter, T. R.; Benford, D. J.; Serabyn, E.

1996-11-01

16

HOW DOES ANGULAR RESOLUTION AFFECT DIFFUSION IMAGING MEASURES?  

PubMed Central

A key question in diffusion imaging is how many diffusion-weighted images suffice to provide adequate signal-to-noise ratio (SNR) for studies of fiber integrity. Motion, physiological effects, and scan duration all affect the achievable SNR in real brain images, making theoretical studies and simulations only partially useful. We therefore scanned 50 healthy adults with 105-gradient high-angular resolution diffusion imaging (HARDI) at 4 Tesla. From gradient image subsets of varying size (6?N?94) that optimized a spherical angular distribution energy, we created SNR plots (versus gradient numbers) for seven common diffusion anisotropy indices: fractional and relative anisotropy (FA, RA), mean diffusivity (MD), volume ratio (VR), geodesic anisotropy (GA), its hyperbolic tangent (tGA), and generalized fractional anisotropy (GFA). SNR, defined in a region of interest in the corpus callosum, was near-maximal with 58, 66 and 62 gradients for MD, FA and RA in respectively, and with about 55 gradients for GA and tGA. For VR and GFA, SNR increased rapidly with more gradients. SNR was optimized when the ratio of diffusion-sensitized to non-sensitized images was 9.13 for GA and tGA, 10.57 for FA, 9.17 for RA, and 26 for MD and VR. In orientation density functions modeling the HARDI signal as a continuous mixture of tensors, the diffusion profile reconstruction accuracy rose rapidly with additional gradients. These plots may help in making trade-off decisions when designing diffusion imaging protocols. PMID:19819339

Zhan, Liang; Leow, Alex D.; Jahanshad, Neda; Chiang, Ming-Chang; Barysheva, Marina; Lee, Agatha D.; Toga, Arthur W.; McMahon, Katie L.; de Zubicaray, Greig I.; Wright, Margaret J.; Thompson, Paul M.

2011-01-01

17

Visualization tools for high angular resolution diffusion imaging.  

PubMed

There is a major effort in medical imaging to develop algorithms to extract information from DTI and HARDI, which provide detailed information on brain integrity and connectivity. As the images have recently advanced to provide extraordinarily high angular resolution and spatial detail, including an entire manifold of information at each point in the 3D images, there has been no readily available means to view the results. This impedes developments in HARDI research, which need some method to check the plausibility and validity of image processing operations on HARDI data or to appreciate data features or invariants that might serve as a basis for new directions in image segmentation, registration, and statistics. We present a set of tools to provide interactive display of HARDI data, including both a local rendering application and an off-screen renderer that works with a web-based viewer. Visualizations are presented after registration and averaging of HARDI data from 90 human subjects, revealing important details for which there would be no direct way to appreciate using conventional display of scalar images. PMID:18982618

Shattuck, David W; Chiang, Ming-Chang; Barysheva, Marina; McMahon, Katie L; de Zubicaray, Greig I; Meredith, Matthew; Wright, Margaret J; Toga, Arthur W; Thompson, Paul M

2008-01-01

18

"Halo" type sources from microwave observations with high angular resolution  

NASA Astrophysics Data System (ADS)

The results of a study of the fine structure of an image of a microwave radiation source, which is usually located in the solar atmosphere above active regions, are presented. The source is equal to the whole active region in size (2-5 arcmin); it is conventionally called a "halo". Observations of two active regions of different morphological types (NOAA 7123, 1992 and NOAA 11142, 2011) with a high angular resolution (2-5 arcsec) were used. According to these observations, the majority (>50%) of the halo consists of diffused optically transparent thermal plasma. A brighter underlying region shines through it; in the case of NOAA 7123, this region looks like a two-ribbon structure along the magnetic field neutral line with a radiation depression along the H? filament. In the case of NOAA 11142, the halo brightening regions are associated with regions of cluster of small sunspots and pores. The conclusion is drawn that the brighter component of the halo is due to the cyclotron radiation of coronal plasma in a relatively weak magnetic field (600-800 Gs).

Peterova, N. G.; Opeikina, L. V.; Topchilo, N. A.

2014-12-01

19

Instrument for Achieving High Angular Resolution on the Infrared Telescope  

NASA Technical Reports Server (NTRS)

Aberrations in stellar images caused by the atmosphere sets a significant limit on angular resolution in ground based astronomy. The largest of these aberrations is the image motion or wavefront tilt. Since the image motion is random it causes a blurring of the image, and this causes a blurring of the image from 0.3 arcseconds to about 0.7 arcseconds. The purpose of the tip-tilt project was to devise a system for the NASA Infrared Telescope Facility that would measure the image movement and correct it by rapidly tilting a mirror in two axes (tip and tilt). The system would involve building a CCD sensor package to measure the image motion, a new top end for the telescope to hold the tip-tilt mirror, a control system, and software. The system was designed to correct images for the facility camera, NSFCAM, and for the facility spectrometer, SPEX. Both of these instruments are equipped with a cold beamsplitter to feed the sensor package.

Hall, Donald N. B.

1998-01-01

20

High Angular Resolution Diffusion Imaging Reveals Intravoxel White Matter Fiber Heterogeneity  

E-print Network

High Angular Resolution Diffusion Imaging Reveals Intravoxel White Matter Fiber Heterogeneity David fibers (10). Using high angular resolution, high b-value diffusion gradient sampling, we were able1* Magnetic resonance (MR) diffusion tensor imaging (DTI) can resolve the white matter fiber

Duncan, James S.

21

Theoretical Models relating Angular and Spatial Resolution Trade-offs in HARDI  

E-print Network

of Radiology, Mayo Clinic, Rochester, MN, USA Introduction: High angular resolution diffusion imaging (HARDI-50% of the brain's voxels where fibers mix [1]. HARDI collects more gradient images than DTMRI, so if scan time to reduce patient discomfort, higher angular resolution can make white matter fiber-tracking more accurate

Thompson, Paul

22

Analysis of Fiber Reconstruction Accuracy in High Angular Resolution Diffusion Images (HARDI)  

E-print Network

Analysis of Fiber Reconstruction Accuracy in High Angular Resolution Diffusion Images (HARDI) L Institute of Medical Research, Brisbane, Australia Introduction: High angular resolution diffusion imaging-ball imaging, DOT, PAS) which restrict all component fibers in a voxel to have the same anisotropy profile

Thompson, Paul

23

How Many Gradients are Sufficient in High-Angular Resolution Diffusion Imaging (HARDI)?  

E-print Network

How Many Gradients are Sufficient in High-Angular Resolution Diffusion Imaging (HARDI)? Liang Zhan1, Brisbane, Australia Introduction: High-angular resolution diffusion imaging (HARDI) is a powerful extension to the set of diffusion images, and maps of fiber integrity such as fractional or relative anisotropy (FA, RA

Thompson, Paul

24

Validating the Tensor Distribution Function for Fiber Reconstruction in HARDI (High-Angular Resolution Diffusion Imaging)  

E-print Network

matter configurations. High-angular resolution diffusion imaging (HARDI) addresses this problemValidating the Tensor Distribution Function for Fiber Reconstruction in HARDI (High-Angular Resolution Diffusion Imaging) L. Zhan1 , A.D.Leow1 , S.Zhu2 , M.C. Chiang1 , M. Barysheva1 , A.W. Toga1 , K

Thompson, Paul

25

Characterization of Anisotropy in High Angular Resolution Diffusion-Weighted MRI  

E-print Network

Characterization of Anisotropy in High Angular Resolution Diffusion-Weighted MRI Lawrence R. Frank brain data collected with a stimulated echo spiral high angular resolution diffusion- weighted (HARD is the presence of multiple fiber direc- tions within a single imaging voxel. Because the single fiber diffusion

Duncan, James S.

26

Registration of Spherical Functions from High Angular Resolution Diffusion Imaging using the Heat Kernel  

E-print Network

Registration of Spherical Functions from High Angular Resolution Diffusion Imaging using the Heat, Tempe, AZ, USA Abstract. High angular resolution diffusion imaging (HARDI) is a powerful variant, these functions are used to map fiber trajectories (tractography) and fiber integrity. To average and compare

Wang, Yalin

27

Cepheids at high angular resolution: circumstellar envelope and pulsation  

NASA Astrophysics Data System (ADS)

In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out a statistical study of the speckle noise and inspect a possible asymmetry. Secondly, I analysed VISIR data to study the spectral energy distribution of a sample of Cepheids. These diffraction-limited images enabled me to carry out an accurate photometry in the N band and to detect an IR excess linked to the presence of a circumstellar component. On the other hand, applying a Fourier analysis I showed that some components are resolved. I then explored the K' band with the recombination instrument FLUOR for some bright Cepheids. Thanks to new set of data of Y Oph, I improved the study of its circumstellar envelope, using a ring-like model for the CSE. For two other Cepheids, U Vul and S Sge, I applied the interferometric Baade-Wesselink method in order to estimate their distance.

Gallenne, Alexandre

2011-12-01

28

ATLAS-BASED FIBER CLUSTERING FOR MULTI-SUBJECT ANALYSIS OF HIGH ANGULAR RESOLUTION DIFFUSION IMAGING TRACTOGRAPHY  

E-print Network

ATLAS-BASED FIBER CLUSTERING FOR MULTI-SUBJECT ANALYSIS OF HIGH ANGULAR RESOLUTION DIFFUSION, USA ABSTRACT High angular resolution diffusion imaging (HARDI) allows in vivo analysis of the white and connectivity in the living brain may be measured using high angular resolution diffusion imaging (HARDI), which

Thompson, Paul

29

Analyzing Multi-Fiber Reconstruction in High Angular Resolution Diffusion Imaging Using the Tensor Distribution Function  

Microsoft Academic Search

High-angular resolution diffusion imaging (HARDI) can reconstruct fiber pathways in the brain with extraordinary detail, identifying anatomical features and connections not seen with conventional MRI. HARDI overcomes several limitations of standard diffusion tensor imaging, which fails to model diffusion correctly in regions where fibers cross or mix. As HARDI can accurately resolve sharp signal peaks in angular space where fibers

Liang Zhan; Alex D. Leow; Siwei Zhu; Ming-Chang Chiang; Marina Barysheva; Arthur W. Toga; Katie McMahon; Greig I. de Zubicaray; Margaret J. Wright; Paul M. Thompson

2009-01-01

30

SMA OBSERVATIONS OF CLASS 0 PROTOSTARS: A HIGH ANGULAR RESOLUTION SURVEY OF PROTOSTELLAR BINARY SYSTEMS  

SciTech Connect

We present high angular resolution 1.3 mm and 850 {mu}m dust continuum data obtained with the Submillimeter Array toward 33 Class 0 protostars in nearby clouds (distance < 500 pc), which represents so far the largest survey toward protostellar binary/multiple systems. The median angular resolution in the survey is 2.''5, while the median linear resolution is approximately 600 AU. Compact dust continuum emission is observed from all sources in the sample. Twenty-one sources in the sample show signatures of binarity/multiplicity, with separations ranging from 50 AU to 5000 AU. The numbers of singles, binaries, triples, and quadruples in the sample are 12, 14, 5, and 2, respectively. The derived multiplicity frequency (MF) and companion star fraction (CSF) for Class 0 protostars are 0.64 {+-} 0.08 and 0.91 {+-} 0.05, respectively, with no correction for completeness. The derived MF and CSF in this survey are approximately two times higher than the values found in the binary surveys toward Class I young stellar objects, and approximately three (for MF) and four (for CSF) times larger than the values found among main-sequence stars, with a similar range of separations. Furthermore, the observed fraction of high-order multiple systems to binary systems in Class 0 protostars (0.50 {+-} 0.09) is also larger than the fractions found in Class I young stellar objects (0.31 {+-} 0.07) and main-sequence stars ({<=}0.2). These results suggest that binary properties evolve as protostars evolve, as predicted by numerical simulations. The distribution of separations for Class 0 protostellar binary/multiple systems shows a general trend in which CSF increases with decreasing companion separation. We find that 67% {+-} 8% of the protobinary systems have circumstellar mass ratios below 0.5, implying that unequal-mass systems are preferred in the process of binary star formation. We suggest an empirical sequential fragmentation picture for binary star formation, based on this work and existing lower resolution single-dish observations.

Chen Xuepeng [Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008 (China); Arce, Hector G.; Dunham, Michael M. [Department of Astronomy, Yale University, Box 208101, New Haven, CT 06520-8101 (United States); Zhang Qizhou; Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Launhardt, Ralf; Henning, Thomas [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Jorgensen, Jes K. [Niels Bohr Institute and Centre for Star and Planet Formation, Copenhagen University, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark); Lee, Chin-Fei [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan (China); Foster, Jonathan B. [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States); Pineda, Jaime E., E-mail: xpchen@pmo.ac.cn, E-mail: xuepeng.chen@yale.edu [ESO, Karl Schwarzschild Str. 2, D-85748 Garching bei Munchen (Germany)

2013-05-10

31

SMA Observations of Class 0 Protostars: A High Angular Resolution Survey of Protostellar Binary Systems  

NASA Astrophysics Data System (ADS)

We present high angular resolution 1.3 mm and 850 ?m dust continuum data obtained with the Submillimeter Array toward 33 Class 0 protostars in nearby clouds (distance < 500 pc), which represents so far the largest survey toward protostellar binary/multiple systems. The median angular resolution in the survey is 2.''5, while the median linear resolution is approximately 600 AU. Compact dust continuum emission is observed from all sources in the sample. Twenty-one sources in the sample show signatures of binarity/multiplicity, with separations ranging from 50 AU to 5000 AU. The numbers of singles, binaries, triples, and quadruples in the sample are 12, 14, 5, and 2, respectively. The derived multiplicity frequency (MF) and companion star fraction (CSF) for Class 0 protostars are 0.64 ± 0.08 and 0.91 ± 0.05, respectively, with no correction for completeness. The derived MF and CSF in this survey are approximately two times higher than the values found in the binary surveys toward Class I young stellar objects, and approximately three (for MF) and four (for CSF) times larger than the values found among main-sequence stars, with a similar range of separations. Furthermore, the observed fraction of high-order multiple systems to binary systems in Class 0 protostars (0.50 ± 0.09) is also larger than the fractions found in Class I young stellar objects (0.31 ± 0.07) and main-sequence stars (<=0.2). These results suggest that binary properties evolve as protostars evolve, as predicted by numerical simulations. The distribution of separations for Class 0 protostellar binary/multiple systems shows a general trend in which CSF increases with decreasing companion separation. We find that 67% ± 8% of the protobinary systems have circumstellar mass ratios below 0.5, implying that unequal-mass systems are preferred in the process of binary star formation. We suggest an empirical sequential fragmentation picture for binary star formation, based on this work and existing lower resolution single-dish observations.

Chen, Xuepeng; Arce, Héctor G.; Zhang, Qizhou; Bourke, Tyler L.; Launhardt, Ralf; Jørgensen, Jes K.; Lee, Chin-Fei; Foster, Jonathan B.; Dunham, Michael M.; Pineda, Jaime E.; Henning, Thomas

2013-05-01

32

SEX DIFFERENCES IN THE HUMAN CONNECTOME: 4-TESLA HIGH ANGULAR RESOLUTION DIFFUSION IMAGING (HARDI)  

E-print Network

SEX DIFFERENCES IN THE HUMAN CONNECTOME: 4-TESLA HIGH ANGULAR RESOLUTION DIFFUSION IMAGING (HARDI diffusion imaging at 4 Tesla, we scanned 234 young adult twins and siblings (mean age: 23.4 ± 2.0 SD years

Thompson, Paul

33

MAPPING GENET IC INFLUENCES ON BRAIN FIBER ARCHITECTURE WITH HIGH ANGULAR RESOLUTION DIFFUSION IMAGING (HARDI)  

E-print Network

MAPPING GENET IC INFLUENCES ON BRAIN FIBER ARCHITECTURE WITH HIGH ANGULAR RESOLUTION DIFFUSION resolution diffusion imaging (HARDI) reveals more information on water diffusion and fiber connectivity than effects on brain fiber complexity. We analyzed HARDI brain imaging data from 90 young adult twins using

Thompson, Paul

34

High energy resolution, high angular acceptance crystal monochromator  

DOEpatents

A 4-bounce dispersive crystal monochromator reduces the bandpass of synchrotron radiation to a 10-50 meV range without sacrificing angular acceptance. The monochromator includes the combination of an asymmetrical channel-cut single crystal of lower order reflection and a symmetrical channel-cut single crystal of higher order reflection in a nested geometric configuration. In the disclosed embodiment, a highly asymmetrically cut ({alpha}=20) outer silicon crystal (4 2 2) with low order reflection is combined with a symmetrically cut inner silicon crystal (10 6 4) with high order reflection to condition a hard x-ray component (5--30 keV) of synchrotron radiation down to the {micro}eV-neV level. Each of the crystals is coupled to the combination of a positioning inchworm and angle encoder via a respective rotation stage for accurate relative positioning of the crystals and precise energy tuning of the monochromator. 7 figs.

Alp, E.E.; Mooney, T.M.; Toellner, T.

1996-06-04

35

High angular resolution 30 microns observations of the Galactic Center  

Microsoft Academic Search

We have mapped the central 2 min (5 pc) of the Galaxy with 4 sec resolution at 30 microns, using the MSFC bolometer array on the NASA Infrared Telescope Facility at Mauna Kea. Complementary maps at 10 and 20 microns covering the same region were obtained contemporaneously with the same instrumentation. The maps encompass both the central cavity at the

Charles M. Telesco; Jacqueline A. Davidson; Michael W. Werner

1995-01-01

36

Geometrical expression for the angular resolution of a network of gravitational-wave detectors  

SciTech Connect

We report for the first time general geometrical expressions for the angular resolution of an arbitrary network of interferometric gravitational-wave (GW) detectors when the arrival time of a GW is unknown. We show explicitly elements that decide the angular resolution of a GW detector network. In particular, we show the dependence of the angular resolution on areas formed by projections of pairs of detectors and how they are weighted by sensitivities of individual detectors. Numerical simulations are used to demonstrate the capabilities of the current GW detector network. We confirm that the angular resolution is poor along the plane formed by current LIGO-Virgo detectors. A factor of a few to more than ten fold improvement of the angular resolution can be achieved if the proposed new GW detectors LCGT or AIGO are added to the network. We also discuss the implications of our results for the design of a GW detector network, optimal localization methods for a given network, and electromagnetic follow-up observations.

Wen Linqing; Chen Yanbei [International Center for Radio Astronomy Research, School of Physics, University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia 6009 (Australia); Division of Physics, Mathematics, and Astronomy, Caltech, Pasadena, California 91125 (United States)

2010-04-15

37

HOW DO SPATIAL AND ANGULAR RESOLUTION AFFECT BRAIN CONNECTIVITY MAPS FROM DIFFUSION MRI?  

PubMed Central

Diffusion tensor imaging (DTI) is sensitive to the directionally- constrained flow of water, which diffuses preferentially along axons. Tractography programs may be used to infer matrices of connectivity (anatomical networks) between pairs of brain regions. Little is known about how these computed connectivity measures depend on the scans’ spatial and angular resolutions. To determine this, we scanned 8 young adults with DTI at 2.5 and 3 mm resolutions, and an additional subject at 4 resolutions between 2–4 mm. We computed 70×70 connectivity matrices, using whole-brain tractography to measure fiber density between all pairs of 70 cortical and subcortical regions. Spatial and angular resolution affected the computed connectivity for narrower tracts (internal capsule and cerebellum), but also for the corticospinal tract. Data resolution affected the apparent role of some key structures in cortical anatomic networks. Care is needed when comparing network data across studies, and interpreting apparent disagreements among findings. PMID:22903027

Zhan, Liang; Franc, Daniel; Patel, Vishal; Jahanshad, Neda; Jin, Yan; Mueller, Bryon A.; Bernstein, Matt A.; Borowski, Bret J.; Jack, Clifford R.; Toga, Arthur W.; Lim, Kelvin O.; Thompson, Paul M.

2012-01-01

38

High angular resolution 30 microns observations of the Galactic Center  

NASA Technical Reports Server (NTRS)

We have mapped the central 2 min (5 pc) of the Galaxy with 4 sec resolution at 30 microns, using the MSFC bolometer array on the NASA Infrared Telescope Facility at Mauna Kea. Complementary maps at 10 and 20 microns covering the same region were obtained contemporaneously with the same instrumentation. The maps encompass both the central cavity at the very center of the Galaxy and the disk of gas and dust which surrounds it. Our data show thermal emissions from dust particles within the cavity and - for the first time at this resolution - within the disk itself. The emission peaks at the position of IRS1 at all three wavelengths, and the 20/30 micron brightness ratio falls uniformly from this peak toward the outer regions of the source. The 30 micron emission correlates well with the HCN emission in the southwest portion of the circumnuclear disk and with the (O I) emission in the north. No feature is apparent at the position of SgrA at any of the three wavelengths. The circumnuclear disk was discovered from the KAO and has been extensively studied in both continuum and line emission in numerous subsequent flights. The poster will attempt to show how these latest ground-based observations intersect and build upon these airborne investigations.

Telesco, Charles M.; Davidson, Jacqueline A.; Werner, Michael W.

1995-01-01

39

Angular resolution study of a combined gamma-neutron coded aperture imager for standoff detection  

NASA Astrophysics Data System (ADS)

Nuclear threat source observables at standoff distances of tens of meters from mCi class sources include both gamma-rays and neutrons. This work uses simulations to investigate the effects of the angular resolution of a mobile gamma-ray and neutron coded aperture imaging system upon orphan source detection significance and specificity. The design requires maintaining high sensitivity and specificity while keeping the system size as compact as possible to reduce weight, footprint, and cost. A mixture of inorganic and organic scintillators was considered in the detector plane for high sensitivity to both gamma-rays and fast neutrons. For gamma-rays (100 to 2500 keV) and fission spectrum neutrons, angular resolutions of 1-9° and radiation angles of incidence appropriate for mobile search were evaluated. Detection significance for gamma-rays considers those events that contribute to the photopeak of the image pixel corresponding the orphan source location. For detection of fission spectrum neutrons, energy depositions above a set pulse shape discrimination threshold were tallied. The results show that the expected detection significance for the system at an angular resolution of 1° is significantly lower compared to its detection significance an angular resolution of ˜3-4°. An angular resolution of ˜3-4° is recommended both for better detection significance and improved false alarm rate, considering that finer angular resolution does not result in improved background rejection when the coded aperture method is used. Instead, over-pixelating the search space may result in an unacceptably high false alarm rate.

Ayaz-Maierhafer, Birsen; Hayward, Jason P.; Ziock, Klaus P.; Blackston, Matthew A.; Fabris, Lorenzo

2013-06-01

40

A measurement of the angular resolution of air showers using the muonic component at ground level  

SciTech Connect

The angular resolution of cosmic ray air showers is found to be 13.4 mr using single tracks and as good as 2 to 4 mr from all of the tracks for selected events by using the muonic component of air showers and a fine grained calorimeter. The sample of events was 8776 events triggered by an air shower array in which 3 to 76 muons were reconstructed. There was very little dependence of the single track angular resolution on either the number of muons or the shower angle.

Goodman, M.C.; Ellsworth, G.B.; Bofill, J.; Bogert, D.; Freudenreich, H.; Goodman, J.A.; Busza, W.; Eldridge, T.; Abolins, M.; Gupta, S.C.

1987-01-01

41

Angular resolution in underground detectors and a status report of the Soudan II nucleon decay detector  

SciTech Connect

This paper is a status report of the Soudan II honeycomb drift chamber project. It reports on the physics goals, present progress and future schedule of our experiment. It also includes a discussion of the angular resolution of cosmic ray muons which can be achieved in underground detectors, and in particular how to calibrate the resolution using the moon's shadow in cosmic rays. This last point has relevance in trying to understand the angular distributions in the reported observations of underground muons from Cygnus X-3. 12 refs., 9 figs.

Ambats, I.; Ayres, D.; Barrett, W.; Barron, K.; Dawson, J.; Fields, T.; Goodman, M.C.; Lopez, F.; May, E.; Price, L.

1987-01-01

42

HARDI: A high angular resolution deployable interferometer for space  

NASA Technical Reports Server (NTRS)

We describe here a proposed orbiting interferometer covering the UV, visible, and near-IR spectral ranges. With a 6-m baseline and a collecting area equivalent to about a 1.4 m diameter full aperture, this instrument will offer significant improvements in resolution over the Hubble Space Telescope, and complement the new generation of ground-based interferometers with much better limiting magnitude and spectral coverage. On the other hand, it has been designed as a considerably less ambitious project (one launch) than other current proposals. We believe that this concept is feasible given current technological capabilities, yet would serve to prove the concepts necessary for the much larger systems that must eventually be flown. The interferometer is of the Fizeau type. It therefore has a much larger field (for guiding) better UV throughout (only 4 surfaces) than phased arrays. Optimize aperture configurations and ideas for the cophasing and coalignment system are presented. The interferometer would be placed in a geosynchronous or sunsynchronous orbit to minimize thermal and mechanical disturbances and to maximize observing efficiency.

Bely, Pierre Y.; Burrows, Christopher; Roddier, Francois; Weigelt, Gerd

1992-01-01

43

2p-2h excitations in neutrino scattering: angular distribution and frozen approximation  

E-print Network

We study the phase-space dependence of 2p-2h excitations in neutrino scattering using the relativistic Fermi gas model. We follow a similar approach to other authors, but focusing in the phase-space properties, comparing with the non-relativistic model. A careful mathematical analysis of the angular distribution function for the outgoing nucleons is performed. Our goals are to optimize the CPU time of the 7D integral to compute the hadron tensor in neutrino scattering, and to conciliate the different relativistic and non relativistic models by describing general properties independently of the two-body current. For some emission angles the angular distribution becomes infinite in the Lab system, and we derive a method to integrate analytically around the divergence. Our results show that the frozen approximation, obtained by neglecting the momenta of the two initial nucleons inside the integral of the hadron tensor, reproduces fairly the exact response functions for constant current matrix elements.

I. Ruiz Simo; C. Albertus; J. E. Amaro; M. B. Barbaro; J. A. Caballero; T. W. Donnelly

2015-01-28

44

High-Angular-Resolution Microbeam X-Ray Diffraction with CCD Detector  

SciTech Connect

We have introduced a CCD-type two-dimensional X-ray detector for a microbeam X-ray diffraction system using synchrotron radiation, so that we can measure local reciprocal space maps (RSM) of samples rapidly. A local RSM of a strain-relaxed SiGe 004 grown on a Si (001) substrate was measured in higher-angular-resolution and faster than a conventional way. The measurement was achieved in 1 h 40 min. with the 2theta resolution of 80 murad and the spatial resolution of 1.4(h)x0.5(v) {mu}m{sup 2}. The introduction of the CCD enabled us to measure RSMs at many points in a sample, that is, the distribution of strain fields and lattice tilts can be revealed in high-angular- and high-spatial-resolution.

Imai, Yasuhiko; Kimura, Shigeru; Sakaia, Akira [Japan Synchrotron Radiation Research Institute, SPring-8, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Sakata, Osami [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 670-8531 (Japan)

2010-04-06

45

High-Angular-Resolution Microbeam X-Ray Diffraction with CCD Detector  

NASA Astrophysics Data System (ADS)

We have introduced a CCD-type two-dimensional X-ray detector for a microbeam X-ray diffraction system using synchrotron radiation, so that we can measure local reciprocal space maps (RSM) of samples rapidly. A local RSM of a strain-relaxed SiGe 004 grown on a Si (001) substrate was measured in higher-angular-resolution and faster than a conventional way. The measurement was achieved in 1 h 40 min. with the 2? resolution of 80 ?rad and the spatial resolution of 1.4(h)×0.5(v) ?m2. The introduction of the CCD enabled us to measure RSMs at many points in a sample, that is, the distribution of strain fields and lattice tilts can be revealed in high-angular- and high-spatial-resolution.

Imai, Yasuhiko; Kimura, Shigeru; Sakata, Osami; Sakaia, Akira

2010-04-01

46

Anatomy of a Photodissociation Region: High angular resolution images of molecular emission in the Orion Bar  

NASA Technical Reports Server (NTRS)

We present observations of the molecular component of the Orion Bar, a prototypical Photodissociation Region (PDR) illuminated by the Trapezium cluster. The high angular resolution (6 sec-10 sec) that we have achieved by combining single-dish and interferometric observations has allowed us to examine in detail the spatial and kinematic morphology of this region and to estimate the physical characteristics of the molecular gas it contains. Our observations indicate that this PDR can be essentially described as a homogeneously distributed slab of moderately dense material (approximately 5 x 10(exp 4)/cu cm), in which are embedded a small number of dense (greater than 10(exp 6)/cu cm) clumps. The latter play little or no role in determining the thickness and kinetic temperature structure of this PDR. This observational picture is largely supported by PDR model calculations for this region, which we describe in detail in this work. We also find our model predictions of the intensities of a variety of atomic and molecular lines to be in good general agreement with a number of previous observations.

Tauber, Jan A.; Tielens, A. G. G. M.; Meixner, Margaret; Foldsmith, Paul F.

1994-01-01

47

An angular momentum approximation for molecular collisions in the presence of intense laser radiation  

NASA Technical Reports Server (NTRS)

An approximation to a previously presented rigorous description of molecular (atom-atom) collisions occurring in the presence of intense radiation is investigated. This rigorous description explicitly considers the angular momentum transferred between the molecule and the radiation field in the absorption or emission of a photon, but involves a complicated system of close-coupled equations which must be solved independently for each projection M of the initial, total molecular angular momentum. (This is a direct consequence of the lack of rotational invariance in the molecule-field problem). These equations are solved for a model system which mimics the collision of a halogen with a rare gas atom. Empirical observations made in the course of performing these calculations lead to the development of an approximation which avoids the repeated calculations for each initial M. This orientational average approximation greatly reduces the effort required to describe the system, and for the model calculation, yields accurate results for field intensities as high as 10 GW/sq cm.

Devries, P. L.; George, T. F.

1979-01-01

48

High Angular Resolution Imaging of Solar Radio Bursts from the Lunar Surface  

NASA Astrophysics Data System (ADS)

Locating low frequency radio observatories on the lunar surface has a number of advantages, including positional stability and a very low ionospheric radio cutoff. Here, we describe the Radio Observatory on the Lunar Surface for Solar studies (ROLSS), a concept for a low frequency, radio imaging interferometric array designed to study particle acceleration in the corona and inner heliosphere. ROLSS would be deployed during an early lunar sortie or by a robotic rover as part of an unmanned landing. The preferred site is on the lunar near side to simplify the data downlink to Earth. The prime science mission is to image type II and type III solar radio bursts with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Secondary science goals include constraining the density of the lunar ionosphere by measuring the low radio frequency cutoff of the solar radio emissions or background galactic radio emission, measuring the flux, particle mass, and arrival direction of interplanetary and interstellar dust, and constraining the low energy electron population in astrophysical sources. Furthermore, ROLSS serves a pathfinder function for larger lunar radio arrays. Key design requirements on ROLSS include the operational frequency and angular resolution. The electron densities in the solar corona and inner heliosphere are such that the relevant emission occurs below 10 MHz, essentially unobservable from Earth's surface due to the terrestrial ionospheric cutoff. Resolving the potential sites of particle acceleration requires an instrument with an angular resolution of at least 2 deg at 10 MHz, equivalent to a linear array size of approximately one kilometer. The major components of the ROLSS array are 3 antenna arms, each of 500 m length, arranged in a Y formation, with a central electronics package (CEP) at their intersection. Each antenna arm is a linear strip of polyimide film (e.g., Kapton) on which 16 single polarization dipole antennas are located by depositing a conductor (e.g., silver). The arms also contain transmission lines for carrying the radio signals from the science antennas to the CEP. Operations would consist of data acquisition during the lunar day, with data downlinks to Earth one or more times every 24 hours. This work is supported in part by the NASA Lunar Science Institute via Cooperative Agreement NNA09DB30A with the LUNAR team.

MacDowall, R. J.; Lazio, J.; Bale, S.; Burns, J. O.; Farrell, W. M.; Gopalswamy, N.; Jones, D. L.; Kasper, J. C.; Weiler, K.

2011-12-01

49

High Angular Resolution Imaging of Solar Radio Bursts from the Lunar Surface  

NASA Technical Reports Server (NTRS)

Locating low frequency radio observatories on the lunar surface has a number of advantages, including positional stability and a very low ionospheric radio cutoff. Here, we describe the Radio Observatory on the lunar Surface for Solar studies (ROLSS), a concept for a low frequency, radio imaging interferometric array designed to study particle acceleration in the corona and inner heliosphere. ROLSS would be deployed during an early lunar sortie or by a robotic rover as part of an unmanned landing. The preferred site is on the lunar near side to simplify the data downlink to Earth. The prime science mission is to image type II and type III solar radio bursts with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Secondary science goals include constraining the density of the lunar ionosphere by measuring the low radio frequency cutoff of the solar radio emissions or background galactic radio emission, measuring the flux, particle mass, and arrival direction of interplanetary and interstellar dust, and constraining the low energy electron population in astrophysical sources. Furthermore, ROLSS serves a pathfinder function for larger lunar radio arrays. Key design requirements on ROLSS include the operational frequency and angular resolution. The electron densities in the solar corona and inner heliosphere are such that the relevant emission occurs below 10 M Hz, essentially unobservable from Earth's surface due to the terrestrial ionospheric cutoff. Resolving the potential sites of particle acceleration requires an instrument with an angular resolution of at least 2 deg at 10 MHz, equivalent to a linear array size of approximately one kilometer. The major components of the ROLSS array are 3 antenna arms, each of 500 m length, arranged in a Y formation, with a central electronics package (CEP) at their intersection. Each antenna arm is a linear strip of polyimide film (e.g., Kapton(TradeMark)) on which 16 single polarization dipole antennas are located by depositing a conductor (e.g., silver). The arms also contain transmission lines for carrying the radio signals from the science antennas to the CEP. Operations would consist of data acquisition during the lunar day, with data downlinks to Earth one or more times every 24 hours.

MacDowall, Robert J.; Lazio, Joseph; Bale, Stuart; Burns, Jack O.; Farrell, William M.; Gopalswamy, Nat; Jones, Dayton L.; Kasper, Justin Christophe; Weiler, Kurt

2012-01-01

50

Evolution of the angular momentum of protogalaxies from tidal torques: Zel'dovich approximation  

NASA Astrophysics Data System (ADS)

The growth of the angular momentum L of protogalaxies induced by tidal torques is reconsidered. We adopt White's formalism and study the evolution of L in Lagrangian coordinates; the motion of the fluid elements is described by the Zel'dovich approximation. We obtain a general expression for the ensemble expectation value of the square of L in terms of the first and second invariant of the inertia tensor of the Lagrangian volume Lambda enclosing the collapsing mass of the proto-object. We then specialize the formalism to the particular case in which Lambda is centred on a peak of the smoothed Gaussian density field and approximated by an isodensity ellipsoid. The result is the appropriate analytical estimate for the rms angular momentum of peaks to be compared against simulations that make use of the Hoffman-Ribak algorithm to set up a constrained density field that contains a peak with given shape. Extending the work of Heavens & Peacock, we calculate the joint probability distribution function for several spin parameters and peak mass M using the distribution of peak shapes, for different initial power spectra. The probability distribution for the rms final angular momentum ^1/2 on the scales corresponding to common bright galaxies, M~=10^11M_, is centred on a value of ~=10^67 kg m^2 s^-1, for any cosmologically relevant power spectrum, in line with previous theoretical and observational estimates for L_f. Other astrophysical consequences are discussed. In particular, we find that typical values ^1/2~=0.1 of the dimensionless spin parameter for peaks smoothed on galactic scales and of height nu~1, usually associated with late-type galaxies, may be recovered in the framework of the Gaussian peak formalism. This partially relaxes the importance attributed to dissipative processes in generating such high values of centrifugal support for spiral galaxies. In addition, the values of the specific angular momentum versus mass - as deduced from observations of rotational velocities and photometric radii of spiral galaxies - are well fitted by our theoretical isoprobability contours. In contrast, the observed lower values for the specific angular momentum for ellipticals of the same mass cannot be accounted for within our linear-regime investigation, highlighting the importance of strongly non-linear phenomena to explain the spin of such objects.

Catelan, Paolo; Theuns, Tom

1996-09-01

51

An angularly refineable phase space finite element method with approximate sweeping procedure  

SciTech Connect

An angularly refineable phase space finite element method is proposed to solve the neutron transport equation. The method combines the advantages of two recently published schemes. The angular domain is discretized into small patches and patch-wise discontinuous angular basis functions are restricted to these patches, i.e. there is no overlap between basis functions corresponding to different patches. This approach yields block diagonal Jacobians with small block size and retains the possibility for S{sub n}-like approximate sweeping of the spatially discontinuous elements in order to provide efficient preconditioners for the solution procedure. On the other hand, the preservation of the full FEM framework (as opposed to collocation into a high-order S{sub n} scheme) retains the possibility of the Galerkin interpolated connection between phase space elements at arbitrary levels of discretization. Since the basis vectors are not orthonormal, a generalization of the Riemann procedure is introduced to separate the incoming and outgoing contributions in case of unstructured meshes. However, due to the properties of the angular discretization, the Riemann procedure can be avoided at a large fraction of the faces and this fraction rapidly increases as the level of refinement increases, contributing to the computational efficiency. In this paper the properties of the discretization scheme are studied with uniform refinement using an iterative solver based on the S{sub 2} sweep order of the spatial elements. The fourth order convergence of the scalar flux is shown as anticipated from earlier schemes and the rapidly decreasing fraction of required Riemann faces is illustrated. (authors)

Kophazi, J.; Lathouwers, D. [Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, NL-2629 JB Delft (Netherlands)

2013-07-01

52

Development of a high angular resolution diffusion imaging human brain template.  

PubMed

Brain diffusion templates contain rich information about the microstructure of the brain, and are used as references in spatial normalization or in the development of brain atlases. The accuracy of diffusion templates constructed based on the diffusion tensor (DT) model is limited in regions with complex neuronal micro-architecture. High angular resolution diffusion imaging (HARDI) overcomes limitations of the DT model and is capable of resolving intravoxel heterogeneity. However, when HARDI is combined with multiple-shot sequences to minimize image artifacts, the scan time becomes inappropriate for human brain imaging. In this work, an artifact-free HARDI template of the human brain was developed from low angular resolution multiple-shot diffusion data. The resulting HARDI template was produced in ICBM-152 space based on Turboprop diffusion data, was shown to resolve complex neuronal micro-architecture in regions with intravoxel heterogeneity, and contained fiber orientation information consistent with known human brain anatomy. PMID:24440528

Varentsova, Anna; Zhang, Shengwei; Arfanakis, Konstantinos

2014-05-01

53

Finsler Geometry on Higher Order Tensor Fields and Applications to High Angular Resolution Diffusion Imaging  

Microsoft Academic Search

We study three dimensional volumes of higher order tensors, using Finsler geometry. The application considered here is in\\u000a medical image analysis, specifically High Angular Resolution Diffusion Imaging (HARDI) [1] of the brain. We want to find robust\\u000a ways to reveal the architecture of the neural fibers in brain white matter. In Diffusion Tensor Imaging (DTI), the diffusion\\u000a of water is

Laura Astola; Luc Florack

2009-01-01

54

Finsler Streamline Tracking with Single Tensor Orientation Distribution Function for High Angular Resolution Diffusion Imaging  

Microsoft Academic Search

We introduce a new framework based on Riemann-Finsler geometry for the analysis of 3D images with spherical codomain, more\\u000a precisely, for which each voxel contains a set of directional measurements represented as samples on the unit sphere (antipodal\\u000a points identified). The application we consider here is in medical imaging, notably in High Angular Resolution Diffusion Imaging\\u000a (HARDI), but the methods

Laura Astola; Andrei Jalba; Evgeniya Balmashnova; Luc Florack

2011-01-01

55

Finsler Geometry on Higher Order Tensor Fields and Applications to High Angular Resolution Diffusion Imaging  

Microsoft Academic Search

We study 3D-multidirectional images, using Finsler geometry. The application considered here is in medical image analysis,\\u000a specifically in High Angular Resolution Diffusion Imaging (HARDI) (Tuch et al. in Magn. Reson. Med. 48(6):1358–1372, 2004) of the brain. The goal is to reveal the architecture of the neural fibers in brain white matter. To the variety of existing\\u000a techniques, we wish to add

Laura Astola; Luc Florack

2011-01-01

56

A New Tensorial Framework for Single-Shell High Angular Resolution Diffusion Imaging  

Microsoft Academic Search

Single-shell high angular resolution diffusion imaging data (HARDI) may be decomposed into a sum of eigenpolynomials of the\\u000a Laplace-Beltrami operator on the unit sphere. The resulting representation combines the strengths hitherto offered by higher\\u000a order tensor decomposition in a tensorial framework and spherical harmonic expansion in an analytical framework, but removes\\u000a some of the conceptual weaknesses of either. In particular

Luc Florack; Evguenia Balmashnova; Laura Astola; Ellen J. L. Brunenberg

2010-01-01

57

Next Generation X-ray Optics: High Angular Resolution, Light Weight, and Low Production Cost  

NASA Astrophysics Data System (ADS)

Every conceivable future x-ray astronomical mission would require x-ray optics. These optics must meet the three-fold requirements of angular resolution, effective area, and cost.In this poster we will present the rationale, technical approach, and status of an x-ray optics technology development program that has been underway at Goddard Space Flight Center and Marshall Space Flight Center.

Zhang, William

2014-08-01

58

Preliminary Design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS)  

NASA Astrophysics Data System (ADS)

The Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) is an integral field spectrograph (IFS) being built at Princeton University for the Subaru telescope. It is designed to disperse a 1.75x1.75 arcsecond field of view onto a Teledyne H2RG detector. The instrument will be located behind the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, which will provide a coronagraphic image with adequate strehl to achieve high detection contrast levels down to angular separations of 80 milliarcseconds in H band. CHARIS is designed specifically to image and spectrally characterize exoplanets and disks under two observation modes; The low resolution, R15 mode, will disperse Y+J+H+K (0.9-2.5 microns) bands across the detector and the high resolution, R80, mode will allow us to take detailed spectra of the target in Y, J, H, or K band. Since we seek very close companions, we cannot rely on angular differential imaging to detect the planet in the presence of residual quasi-static speckles. CHARIS is thus being designed to interface directly with SCExAO to modulate and correct such speckles to detect companions up to five orders of magnitude dimmer than the parent star. The IFS is based on a lenslet design with pinholes to mitigate diffractive crosstalk between spectra. We present the preliminary design of the instrument and detail design tradeoffs and challenges associated with such a spectrograph. First light is expected to be by the end of 2015.

Groff, Tyler D.; Peters, M.; Kasdin, N. J.; McElwain, M. W.; Galvin, M.; Carr, M.; Knapp, G. R.; Janson, M.; Brandt, T.; Lupton, R.; Gunn, J. E.; Guyon, O.; Martinache, F.; Hayashi, M.; Takato, N.

2013-01-01

59

Method for improving the angular resolution of a neutron scatter camera  

DOEpatents

An instrument that will directly image the fast fission neutrons from a special nuclear material source wherein the neutron detection efficiency is increased has been described. Instead of the previous technique that uses a time-of-flight (TOF) between 2 widely spaced fixed planes of neutron detectors to measure scatter neutron kinetic energy, we now use the recoil proton energy deposited in the second of the 2 scatter planes which can now be repositioned either much closer together or further apart. However, by doubling the separation distance between the 2 planes from 20 cm to a distance of 40 cm we improved the angular resolution of the detector from about 12.degree. to about 10.degree.. A further doubling of the separation distance to 80 cm provided an addition improvement in angular resolution of the detector to about 6.degree. without adding additional detectors or ancillary electronics. The distance between planes also may be dynamically changed using a suitable common technique such as a gear- or motor-drive to toggle between the various positions. The angular resolution of this new configuration, therefore, is increased at the expanse of detection sensitivity. However, the diminished sensitivity may be acceptable for those applications where the detector is able to interrogate a particular site for an extended period.

Mascarenhas, Nicholas; Marleau, Peter; Gerling, Mark; Cooper, Robert Lee; Mrowka, Stanley; Brennan, James S.

2012-12-25

60

M. Heydari-Malayeri, C. Reyle and R. Samadi (eds) B[E] STARS AT THE HIGHEST ANGULAR RESOLUTION  

E-print Network

with the FEROS instrument, high angular resolution imaging with the adaptive optics camera NACO, to the highest variability typical of a young stellar object. It shows one of the most extreme infrared excess of all B

Boyer, Edmond

61

High Angular Resolution and Lightweight X-Ray Optics for Astronomical Missions  

NASA Technical Reports Server (NTRS)

X-ray optics with both high angular resolution and lightweight is essential for further progress in x-ray astronomy. High angular resolution is important in avoiding source confusion and reducing background to enable the observation of the most distant objects of the early Universe. It is also important in enabling the use of gratings to achieve high spectral resolution to study, among other things, the myriad plasmas that exist in planetary, stellar, galactic environments, as well as interplanetary, inter-stellar, and inter-galactic media. Lightweight is important for further increase in effective photon collection area, because x-ray observations must take place on space platforms and the amount of mass that can be launched into space has always been very limited and is expected to continue to be very limited. This paper describes an x-ray optics development program and reports on its status that meets these two requirements. The objective of this program is to enable Explorer type missions in the near term and to enable flagship missions in the long term.

Zhang, W. W.; Biskach, M. P.; Blake, P. N.; Chan, K. W.; Evans, T. C.; Hong, M.; Jones, W. D.; Jones, W. D.; Kolos, L. D.; Mazzarella, J. M.; McClelland, R. S.; ODell, S. L.; Saha, T. T.; Sharpe, M. V.

2011-01-01

62

Next Generation X-ray Optics: High Angular Resolution, Light Weight, and Low Production Cost  

NASA Astrophysics Data System (ADS)

X-ray telescopes are essential to the future of x-ray astronomy. In this talk I will describe a comprehensive program to advance the technology for x-ray telescopes well beyond the state of the art represented by the dour missions currently in operations: Chandra, XMM-Newton, Suzaku, and NuSTAR. This program will address the three key issues in making an x-ray telescope: (1) angular resolution, (2) effective area per unit mass, and (3) cost per unit effective area. The objectives of this technology program are (1) in the near term, to enable Explorer-class x-ray missions and an IXO-type mission, and (2) in the long term, to enable a flagship x-ray mission with sub-arcsecond angular resolution and multi-square-meter effective area, at an affordable cost. We pursue two approaches concurrently, emphasizing the first approach in the near term (2-5 years) and the second in the long term (4-10 years). The first approach is precision slumping of borosilicate glass sheets. By design and choice at the outset, this technique makes lightweight and low-cost mirrors. The development program will continue to improve angular resolution, to enable the production of 5-arcsecond x-ray telescopes, to support Explorer-class missions and one or more missions to supersede the original IXO mission. The second approach is precision polishing and light-weighting of single-crystal silicon mirrors. This approach benefits from two recent commercial developments: (1) the inexpensive and abundant availability of large blocks of monocrystalline silicon, and (2) revolutionary advances in deterministic, precision polishing of mirrors. By design and choice at the outset, this technique is capable of producing lightweight mirrors with sub-arcsecond angular resolution. The development program will increase the efficiency and reduce the cost of the polishing and the light-weighting processes, to enable the production of lightweight sub-arcsecond x-ray telescopes. Concurrent with the fabrication of lightweight mirror segments is the continued development and perfection of alignment and integration techniques, for incorporating individual mirror segments into a precision mirror assembly.

Zhang, William; NGXO

2014-01-01

63

X-ray Interferometry with Transmissive Beam Combiners for Ultra-High Angular Resolution Astronomy  

NASA Technical Reports Server (NTRS)

Abstract Interferometry provides one of the possible routes to ultra-high angular resolution for X-ray and gamma-ray astronomy. Sub-micro-arc-second angular resolution, necessary to achieve objectives such as imaging the regions around the event horizon of a super-massive black hole at the center of an active galaxy, can be achieved if beams from parts of the incoming wavefront separated by 100s of meters can be stably and accurately brought together at small angles. One way of achieving this is by using grazing incidence mirrors. We here investigate an alternative approach in which the beams are recombined by optical elements working in transmission. It is shown that the use of diffractive elements is a particularly attractive option. We report experimental results from a simple 2-beam interferometer using a low-cost commercially available profiled film as the diffractive elements. A rotationally symmetric filled (or mostly filled) aperture variant of such an interferometer, equivalent to an X-ray axicon, is shown to offer a much wider bandpass than either a Phase Fresnel Lens (PFL) or a PFL with a refractive lens in an achromatic pair. Simulations of an example system are presented.

Skinner, G. K.; Krismanic, John F.

2009-01-01

64

High angular resolution 7 mm images toward the UC HII region W3(OH)  

NASA Astrophysics Data System (ADS)

Context. Recent high angular resolution radio observations of the ultracompact H ii region W3(OH) confirm the presence of an extremely compact (0.''05), time-variable source near its center. Aims: We use new, sensitive high angular resolution observations of radio continuum and recombination lines to study the compact source in W3(OH) and the ultracompact H ii region itself. Methods: We reduced and analyzed extensive Jansky Very Large Array observations of W3(OH) in the continuum at 41.0 GHz and in the H54? and He54? lines. Results: Our images confirm there is the compact source and show that it is connected by a linear filament to the brightest part of W3(OH). We discuss several possible explanations for this structure and propose future observations that may clarify its nature. Appendices are available in electronic form at http://www.aanda.orgReduced VLA FITS cubes are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/L5

Dzib, S. A.; Rodríguez, L. F.; Medina, S.-N. X.; Loinard, L.; Masqué, J. M.; Kurtz, S.; Qiu, K.

2014-07-01

65

Optimal Short-Time Acquisition Schemes in High Angular Resolution Diffusion-Weighted Imaging  

PubMed Central

This work investigates the possibilities of applying high-angular-resolution-diffusion-imaging- (HARDI-) based methods in a clinical setting by investigating the performance of non-Gaussian diffusion probability density function (PDF) estimation for a range of b-values and diffusion gradient direction tables. It does so at realistic SNR levels achievable in limited time on a high-performance 3T system for the whole human brain in vivo. We use both computational simulations and in vivo brain scans to quantify the angular resolution of two selected reconstruction methods: Q-ball imaging and the diffusion orientation transform. We propose a new analytical solution to the ODF derived from the DOT. Both techniques are analytical decomposition approaches that require identical acquisition and modest postprocessing times and, given the proposed modifications of the DOT, can be analyzed in a similar fashion. We find that an optimal HARDI protocol given a stringent time constraint (<10?min) combines a moderate b-value (around 2000?s/mm2) with a relatively low number of acquired directions (>48). Our findings generalize to other methods and additional improvements in MR acquisition techniques. PMID:23554808

Pr?kovska, V.; Achterberg, H. C.; Bastiani, M.; Pullens, P.; Balmashnova, E.; ter Haar Romeny, B. M.; Vilanova, A.; Roebroeck, A.

2013-01-01

66

High Angular Resolution Ammonia Observations of the Disk around the Massive Protostar Cep A HW2  

NASA Astrophysics Data System (ADS)

We present new VLA observations of the ammonia (3,3) and (4,4) inversion transitions with ˜0.8" angular resolution toward the massive protostar Cep A HW2. This source is one of the nearest and best studied disk-jet systems associated with a high mass protostar. We propose that the emission previously attributed to a nearby source may be actually the bluer side of the disk. In this way, we manage to separate the emission into a disk structure and a hot core. With our high angular resolution observations we are able to see the disk rotation and infer a reliable value for the central mass. From the ammonia (4,4) to (3,3) transition ratio, we show that the main heating source of the disk is spatially coincident with the position of the central protostar. In the case of the hot core, we find signs of external heating associated with the wide-angle water maser outflow powered by HW2 (Torrelles et al. 2011).

Macías, Enrique; Gómez, José F.; Osorio, Mayra; Anglada, Guillem; Torrelles, José M.; D'Alessio, Paola

2013-07-01

67

Approximate solution of the Duffin-Kemmer-Petiau equation for a vector Yukawa potential with arbitrary total angular momenta  

E-print Network

The usual approximation scheme is used to study the solution of the Duffin-Kemmer-Petiau (DKP) equation for a vector Yukawa potential in the framework of the parametric Nikiforov-Uvarov (NU) method. The approximate energy eigenvalue equation and the corresponding wave function spinor components are calculated for arbitrary total angular momentum in closed form. Further, the approximate energy equation and wave function spinor components are also given for case. A set of parameter values is used to obtain the numerical values for the energy states with various values of quantum levels

Hamzavi, Majid

2012-01-01

68

Acquisition of angular momentum by tidal torques in expanding, spherical-symmetric density perturbations - an analysis of different approximations. II  

NASA Astrophysics Data System (ADS)

This paper analyzes different approximations of the evolution of expanding spherical-symmetric density perturbations which gain angular momentum by tidal torques. The evolution of expanding spherical-symmetric density perturbations is improved and extended, with regard to both initial configuration and evolution, mainly in the context of an Einstein-de Sitter universe. Qualitative estimates are made of the angular momentum and of the spin parameter for different masses and peak heights. It is shown that, to obtain close agreement with a median value of spin parameter of about 0.05 found by several authors, an underestimate by a factor of at least 4 of the rate of acquisition of angular momentum has to be assumed.

Caimmi, R.

1990-11-01

69

Acquisition of angular momentum by tidal torques in expanding, spherical-symmetric density perturbations - an analysis of different approximations  

NASA Astrophysics Data System (ADS)

The evolution of expanding, spherical-symmetric density perturbations is reviewed, mainly in the context of an Einstein-de Sitter universe, according to an exact theory and to a first-order and zeroth-order approximation. Then, following Ryden and Gunn (1987) and Ryden (1988), we model inhomogeneities as central peaks surrounded by secondary perturbations, and review and extend (according to a number of different approximations) the analytic expressions of the rms torque acting on a thin spherical mass shell, and of the angular momentum thus acquired. In particular, two extreme physical situations have been analysed: (i) the core of density perturbations, or more generally homogeneous density perturbations; and (ii) the envelope of density perturbations, or more generally density perturbations with halos reduced to the Hubble flow. Though in early times the torque grows in proportion to t2/3 and the angular momentum in proportion to t5/3, different approximations lead to different results even before density perturbations decouple strongly from the Hubble flow. An interpretation of the results is consistent with a suggestion by Peebles (1969), that physical processes leading to the torques under consideration are switched off during the above-mentioned strong decoupling. After this epoch, a given approximation might have mathematical features which are not in contradiction with the physical meaning of the problem, but no physical meaning in itself; from a physical point of view, any approximation should be smoothed, or truncated. Additional support to this conclusion comes from a qualitative estimate of the angular momentum, and then of the spin parameter, related to the whole density perturbations under a number of simplifying assumptions; accordingly, the acquisition of angular momentum appears to end at late rather than at early stages of strong decouling. The related values of the spin parameter are ? greater-than or equivalent to 0.02, which is consistent with ? greater-than or equivalent to 0.05 found by both Barnes and Efstathiou (1987) using numerical computations based on N-body simulations, and Heavens and Peacock (1988) using analytical approximations. The results are also in agreement with current estimations of the Milky Way angular momentum.

Caimmi, R.

1989-10-01

70

Conceptual Design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) for the Subaru Telescope  

NASA Technical Reports Server (NTRS)

Recent developments in high-contrast imaging techniques now make possible both imaging and spectroscopy of planets around nearby stars. We present the conceptual design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), a lenslet-based, cryogenic integral field spectrograph (IFS) for imaging exoplanets on the Subaru telescope. The IFS will provide spectral information for 140 x 140 spatial elements over a 1.75 arcsecs x 1.75 arcsecs field of view (FOV). CHARIS will operate in the near infrared (lambda = 0.9 - 2.5 micron) and provide a spectral resolution of R = 14, 33, and 65 in three separate observing modes. Taking advantage of the adaptive optics systems and advanced coronagraphs (AO188 and SCExAO) on the Subaru telescope, CHARIS will provide sufficient contrast to obtain spectra of young self-luminous Jupiter-mass exoplanets. CHARIS is in the early design phases and is projected to have first light by the end of 2015. We report here on the current conceptual design of CHARIS and the design challenges.

Peters, Mary Anne; Groff, Tyler; Kasdin, N. Jeremy; McElwain, Michael W.; Galvin, Michael; Carr, Michael A.; Lupton, Robert; Gunn, James E.; Knapp, Gillian; Gong, Qian; Carlotti, Alexis; Brandt, Timothy; Janson, Markus; Guyon, Olivier; Martinache, Frantz; Hayashi, Masahiko; Takato, Naruhisa

2012-01-01

71

PREFACE: Astronomy at High Angular Resolution 2011: The central kiloparsec in galactic nuclei  

NASA Astrophysics Data System (ADS)

We are pleased to present the proceedings from the Astronomy at High Angular Resolution 2011: The central kiloparsec in galactic nuclei conference. The conference took place in the Physikzentrum of the Deutsche Physikalische Gesellschaft (DPG), Bad Honnef, Germany, from 28 August to 2 September 2011. It was the second conference of this kind, following the Astronomy at High Angular Resolution conference held in Bad Honnef, three years earlier in 2008. The main objective of the conference was to frame the discussion of the broad range of physical processes that occur in the central 100pc of galactic nuclei. In most cases, this domain is difficult to probe through observations. This is mainly because of the lack of angular resolution, the brightness of the central engine and possible obscurations through dust and gas, which play together in the central regions of host galaxies of galactic nuclei within a broad range of activity. The presence of large amounts of molecular and atomic (both neutral and ionized) gas, dust and central engines with outflows and jets implies that the conditions for star formation in these regions are very special, and probably different from those in the disks of host galaxies. Numerous presentations covering a broad range of topics, both theoretical and experimental, those related to research on Active Galactic Nuclei and on a wide range of observed wavelengths were submitted to the Scientific Organizing Committee. Presentations have been grouped into six sessions: The nuclei of active galaxies The Galactic Center The immediate environment of Super Massive Black Holes The physics of nuclear jets and the interaction of the interstellar medium The central 100pc of the nuclear environment Star formation in that region The editors thank all participants of the AHAR 2011 conference for their enthusiasm and their numerous and vivid contributions to this conference. We would especially like to thank John Hugh Seiradakis from the Aristotle University of Thessaloniki in Greece for giving the dinner talk on the most astounding ancient Antikythera mechanism. We would also like to thank Victor Gomer and the staff of the Physikzentrum of the Deutsche Physikalische Gesellschaft in Bad Honnef where the conference took place. Last but not least we would like to thank all unnamed helpers, without whom the organisation of this conference would not have been possible. Financial support for this conference was granted by the Deutsche Forschungsgemeinschaft (DFG) Sonderforschungsbereich project number SFB 956. We also acknowledge support from the European Community Framework Programme 7, Advanced Radio Astronomy in Europe, grant agreement no. 227290. Christof Iserlohe, Vladimir Karas, Melanie Krips, Andreas Eckart, Silke Britzen and Sebastian Fischer The Editors Conference photograph Conference Group Photo, 1 September 2011 The PDF also contains additional photographs from the conference and the Contents of the Proceedings.

Iserlohe, Christof; Karas, Vladimir; Krips, Melanie; Eckart, Andreas; Britzen, Silke; Fischer, Sebastian

2012-07-01

72

Measurement method for roll angular displacement with a high resolution by using diffraction gratings and a heterodyne interferometer  

SciTech Connect

The roll angle measurement is difficult to be achieved directly using a typical commercial interferometer due to its low sensitivity in axial direction, where the axial direction is orthogonal to the plane of the roll angular displacement. A roll angle measurement method combined diffraction gratings with a laser heterodyne interferometer is discussed in this paper. The diffraction grating placed in the plane of a roll angular displacement and the interferometer arranged in the plane's orthogonal direction, constitute the measurement pattern for the roll angle with high resolution. The roll angular displacement, considered as the linear, can be tested precisely when the corresponding angle is very small. Using the proposed method, the angle roll measurement obtains the high resolution of 0.002{sup ?}. Experiment has proved its feasibility and practicability.

Tang, Shanzhi, E-mail: shanzhit@gmail.com [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China) [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049 (China); Wang, Zhao [School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049 (China)] [School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049 (China); Gao, Jianmin; Guo, Junjie [State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an 710054 (China)] [State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an 710054 (China)

2014-04-15

73

The Multiplicity of Massive Stars: a High Angular Resolution Survey With the Guidance Sensor  

NASA Astrophysics Data System (ADS)

We present the results of an all-sky survey made with the Fine Guidance Sensor on the Hubble Space Telescope to search for angularly resolved binary systems among massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and luminous blue variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to the detection of companions with an angular separation between 0.?01 and 1.?0 and brighter than \\vartriangle m=5. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations, field stars, and runaway stars. These results confirm the high multiplicity fraction, especially among massive stars in clusters and associations. We show that the period distribution is approximately flat in increments of log P. We identify a number of systems of potential interest for long-term orbital determinations, and we note the importance of some of these companions for the interpretation of the radial velocities and light curves of close binaries that have third companions. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 11212, 11901, 11943, and 11944.

Aldoretta, E. J.; Caballero-Nieves, S. M.; Gies, D. R.; Nelan, E. P.; Wallace, D. J.; Hartkopf, W. I.; Henry, T. J.; Jao, W.-C.; Maíz Apellániz, J.; Mason, B. D.; Moffat, A. F. J.; Norris, R. P.; Richardson, N. D.; Williams, S. J.

2015-01-01

74

The Potential of High Angular Resolution and Contrast FUV Imagery for Studies of Star and Planetary System Formation  

Microsoft Academic Search

High contrast and high angular resolution imagery has opened new viewpoints on the formation and early evolution of planetary systems, revealing features of protoplanetary and young planetary systems which would go undetected in the integrated measures of the systems. Much of the power of such studies has resulted from pan-chromatic data, but the majority of studies to date have been

C. A. Grady; A. Brown; B. Woodgate; J. Hornbeck; G. Williger; G. Herczeg; J. Brown; S. Brittain; J. Wisniewski; M. Perrin; K. Hamaguchi; T. Henning; I. Kamp; R. Petre; G. Schneider; M. Sitko; F. Walter; D. Apai; T. Ayres

2011-01-01

75

Eulerian ZMP resolution based bipedal walking: Discussions on the intrinsic angular momentum rate change about center of mass  

Microsoft Academic Search

This paper is aimed at implementing Eulerian ZMP Resolution method to bipedal walking pattern generation. The main strategy in this method is to ensure the dynamic balance by generating feasible ZMP-based CoM trajectories. For this purpose, we employ ZMP equations in spherical coordinates, so that the intrinsic angular momentum rate change about center of mass is included explicitly in a

Barkan Ugurlu; Atsuo Kawamura

2010-01-01

76

Development of insula connectivity between ages 12 and 30 revealed by high angular resolution diffusion imaging.  

PubMed

The insula, hidden deep within the Sylvian fissures, has proven difficult to study from a connectivity perspective. Most of our current information on the anatomical connectivity of the insula comes from studies of nonhuman primates and post mortem human dissections. To date, only two neuroimaging studies have successfully examined the connectivity of the insula. Here we examine how the connectivity of the insula develops between ages 12 and 30, in 307 young adolescent and adult subjects scanned with 4-Tesla high angular resolution diffusion imaging (HARDI). The density of fiber connections between the insula and the frontal and parietal cortex decreased with age, but the connection density between the insula and the temporal cortex generally increased with age. This trajectory is in line with well-known patterns of cortical development in these regions. In addition, males and females showed different developmental trajectories for the connection between the left insula and the left precentral gyrus. The insula plays many different roles, some of them affected in neuropsychiatric disorders; this information on the insula's connectivity may help efforts to elucidate mechanisms of brain disorders in which it is implicated. PMID:23836455

Dennis, Emily L; Jahanshad, Neda; McMahon, Katie L; de Zubicaray, Greig I; Martin, Nicholas G; Hickie, Ian B; Toga, Arthur W; Wright, Margaret J; Thompson, Paul M

2014-04-01

77

Segmentation of high angular resolution diffusion MRI using sparse riemannian manifold clustering.  

PubMed

We address the problem of segmenting high angular resolution diffusion imaging (HARDI) data into multiple regions (or fiber tracts) with distinct diffusion properties. We use the orientation distribution function (ODF) to model diffusion and cast the ODF segmentation problem as a clustering problem in the space of ODFs. Our approach integrates tools from sparse representation theory and Riemannian geometry into a graph theoretic segmentation framework. By exploiting the Riemannian properties of the space of ODFs, we learn a sparse representation for each ODF and infer the segmentation by applying spectral clustering to a similarity matrix built from these representations. In cases where regions with similar (resp. distinct) diffusion properties belong to different (resp. same) fiber tracts, we obtain the segmentation by incorporating spatial and user-specified pairwise relationships into the formulation. Experiments on synthetic data evaluate the sensitivity of our method to image noise and to the concentration parameters, and show its superior performance compared to alternative methods when analyzing complex fiber configurations. Experiments on phantom and real data demonstrate the accuracy of the proposed method in segmenting simulated fibers and white matter fiber tracts of clinical importance. PMID:24108748

Çetingül, H Ertan; Wright, Margaret J; Thompson, Paul M; Vidal, René

2014-02-01

78

Simple Fourier optics formalism for high-angular-resolution systems and nulling interferometry.  

PubMed

Reviewed are various designs of advanced, multiaperture optical systems dedicated to high-angular-resolution imaging or to the detection of exoplanets by nulling interferometry. A simple Fourier optics formalism applicable to both imaging arrays and nulling interferometers is presented, allowing their basic theoretical relationships to be derived as convolution or cross-correlation products suitable for fast and accurate computation. Several unusual designs, such as a "superresolving telescope" utilizing a mosaicking observation procedure or a free-flying, axially recombined interferometer are examined, and their performance in terms of imaging and nulling capacity are assessed. In all considered cases, it is found that the limiting parameter is the diameter of the individual telescopes. A final section devoted to nulling interferometry shows an apparent superiority of axial versus multiaxial recombining schemes. The entire study is valid only in the framework of first-order geometrical optics and scalar diffraction theory. Furthermore, it is assumed that all entrance subapertures are optically conjugated with their associated exit pupils. PMID:20208933

Hénault, François

2010-03-01

79

High angular resolution diffusion imaging with stimulated echoes: compensation and correction in experiment design and analysis  

PubMed Central

Stimulated echo acquisition mode (STEAM) diffusion MRI can be advantageous over pulsed-gradient spin-echo (PGSE) for diffusion times that are long compared with T2. It therefore has potential for biomedical diffusion imaging applications at 7T and above where T2 is short. However, gradient pulses other than the diffusion gradients in the STEAM sequence contribute much greater diffusion weighting than in PGSE and lead to a disrupted experimental design. Here, we introduce a simple compensation to the STEAM acquisition that avoids the orientational bias and disrupted experiment design that these gradient pulses can otherwise produce. The compensation is simple to implement by adjusting the gradient vectors in the diffusion pulses of the STEAM sequence, so that the net effective gradient vector including contributions from diffusion and other gradient pulses is as the experiment intends. High angular resolution diffusion imaging (HARDI) data were acquired with and without the proposed compensation. The data were processed to derive standard diffusion tensor imaging (DTI) maps, which highlight the need for the compensation. Ignoring the other gradient pulses, a bias in DTI parameters from STEAM acquisition is found, due both to confounds in the analysis and the experiment design. Retrospectively correcting the analysis with a calculation of the full B matrix can partly correct for these confounds, but an acquisition that is compensated as proposed is needed to remove the effect entirely. PMID:24890716

Lundell, Henrik; Alexander, Daniel C; Dyrby, Tim B

2014-01-01

80

Acquisition of angular momentum by tidal torques in expanding, spherical-symmetric density perturbations: an analysis of different approximations. 3  

NASA Astrophysics Data System (ADS)

The evolution of expanding, spherical-symmetric density perturbations is improved and extended to all kinds of high-density (Omega0 greater than or approximately = 0.1) Friedmann universes made of dust only, according to an exact theory and to a first-order and zeroth-order approximation. Then inhomogeneities are modeled as central peaks surrounded by secondary perturbations, and the effects of spin growth on the expansion are investigated, concerning the expression of the rms torque acting on a thin spherical mass shell and the angular momentum thus acquired. Though in early times the angular momentum grows in proportion to t5/3, all the approximations used to lead to a gain of spin in proportion to t from a given time on, at least during the linear stages of evolution; in all cases, the torque attains a maximum value and then decreases later. The comparison of the results with those related to excluding the effects of spin growth on the expansion, discloses that considerable differences in both radius and torque, and to a lesser extent in angular momentum, occur at a given time for any approximation. The angular momentum of the whole density perturbation is calculated for different masses and peak heights, at the beginning of strong decoupling from the Hubble flow (bar-delta = 1). A dissipation by a factor 4-6 (consistent with the result of numerical simulations) has to occur during nonlinear evolution, if typical values of the spin parameter in the range 0.05-0.07 are wanted. Then the transition from linear to nonlinear regime appears to be the physical mechanism which makes spin growth turn off. In addition, more dissipation has to occur for lower masses and vice versa, in order to pass from J proportional to M5/3 found using a mass-peak height correlation by Ryden and Gunn (1987) to J proportional to M7/4 deduced for spiral galaxies by, e.g. Brosche (1977) and Fall (1983).

Andriani, E.; Caimmi, R.

1994-09-01

81

Full angular Stokes vectors of light scattering from two-dimensional randomly rough surfaces by Kirchhoff approximation method  

NASA Astrophysics Data System (ADS)

Light scattering from rough surfaces remains an important area of interest as it has great potential in a wide variety of fields such as polarized imaging and target identification. Compared to existing simulative methods, the Kirchhoff approximation method offers a much higher calculation efficiency and easy polarization setting that is especially fit for polarized scattering research. In this paper, by studying full angular Stokes vectors via the Kirchhoff approximation from two-dimensional (2D) randomly rough surfaces with various materials, the difference between Stokes vectors of metals and dielectrics is discovered. Moreover, we have successfully explained the distinction between metals and dielectrics by the phase difference between the incident and scattered waves using theoretical analysis. We believe the research could provide an easy and robust criterion for distinguishing metals and dielectrics in various fields such as laser radar and remote sensing.

Yan, Keding; Wang, Shouyu; Jiang, Shu; Song, Yuanyuan; Xue, Liang; Yan, Zhengang; Li, Zhenhua

2014-10-01

82

PREFACE: The Universe under the Microscope: Astrophysics at High Angular Resolution  

NASA Astrophysics Data System (ADS)

High angular resolution techniques at infrared and centimeter to millimeter wavelengths have become of ever increasing importance for astrophysical research in the past decade. They have led to important breakthroughs, like the direct imaging of protoplanetary discs and of the first exoplanets, the measurement of stellar orbits around the black hole at the center of the Milky Way, or the detection of sub-parsec-scale jets in low luminosity AGN. With adaptive optics in a mature state, infrared/optical astronomy is pushing toward extreme adaptive optics, extremely large telescopes, and infrared/optical interferometry with large aperture telescopes. At longer wavelengths, large arrays start to conquer the sub-millimeter window, with the mid-term goal of global VLBI at sub-millimeter wavelengths. These new techniques will have enormous impact on the field because they will enable us to address issues such as directly measuring the properties of exoplanets, imaging the surfaces of stars, examining stellar dynamics in extremely dense cluster cores, disentangling the processes at the bottom of black hole accretion flows in the jet launching region, or testing general relativity in the strong gravity regime near the event horizon of supermassive black holes. The conference The Universe under the Microscope: Astrophysics at High Angular Resolution, held at the Physikzentrum of the Deutsche Physikalische Gesellschaft in Bad Honnef, Germany, on 12-25 April 2008, aimed at an interdisciplinary approach by bringing together astrophysicists from the three great branches of the field, instrumentation, observation, and theory, to discuss the current state of research and the possibilities offered by the next-generation instruments. Editors of the proceedings Rainer Schödel Instituto de Astrofísica de Andalucía -CSIC, Granada, Spain Andreas Eckart I. Physikalisches Institut der Universität zu Köln, Köln, Germany Susanne Pfalzner I. Physikalisches Institut der Universität zu Köln, Köln, Germany Eduardo Ros Max-Planck-Institut für extraterrestrische Physik, Bonn, Germany Scientific organizing committee Dennis Downes Institut de Radio Astronomie Millimétrique, France Wolfgang Duschl University of Kiel, Germany Andrea Ghez University of California, Los Angeles, USA Vladimir Karas Academy of Sciences, Czech Republic Andreas Eckart University of Cologne, Germany Sera Marko University of Amsterdam, The Netherlands Susanne Pfalzner University of Cologne, Germany Sebastian Rabien Max-Planck-Institute for Extraterrestrial Physics, Germany Daniel Rouan Observatoire de Paris-Meudon, France Eduardo Ros Max-Planck-Institute for Radio Astronomy, Germany Rainer Schödel Instituto de Astrofísica de Andalucía -CSIC, Spain Zhiqiang Shen Shanghai Astronomical Observatory, China Anton Zensus Max-Planck-Institute for Radio Astronomy, Germany Local organizing committee Sebastian Fischer University of Cologne, Germany Devaky Kunneriath University of Cologne, Germany Leo Meyer University of Cologne, Germany Koraljka Muzic University of Cologne, Germany Rainer Schödel University of Cologne, Germany/IAA -CSIC, Spain Christian Straubmeier University of Cologne, Germany Mohammad Zamaninasab University of Cologne, Germany

Schödel, Rainer

2009-01-01

83

Development of cerebellar connectivity in human fetal brains revealed by high angular resolution diffusion tractography.  

PubMed

High angular resolution diffusion imaging (HARDI) tractography has provided insights into major white matter pathways and cortical development in the human fetal cerebrum. Our objective in this study was to further apply HARDI tracography to the developing human cerebellum ranging from fetal to adult stages, to outline in broad strokes the 3-dimensional development of white matter and local gray matter organization in the cerebellum. We imaged intact fixed fetal cerebellum specimens at 17 gestational weeks (W), 21W, 31W, 36W, and 38W along with an adult cerebellum for comparison. At the earliest gestational age studied (17W), coherent pathways that formed the superior, middle, and inferior cerebellar peduncles were already detected, but pathways between deep cerebellar nuclei and the cortex were not observed until after 38W. At 36-38W, we identified emerging regional specification of the middle cerebellar peduncle. In the cerebellar cortex, we observed disappearance of radial organization in the sagittal orientation during the studied developmental stages similar to our previous observations in developing cerebral cortex. In contrast, in the axial orientation, cerebellar cortical pathways emerged first sparsely (31W) and then with increased prominence at 36-38W with pathways detected both in the radial and tangential directions to the cortical surface. The cerebellar vermis first contained only pathways tangential to the long axes of folia (17-21W), but pathways parallel to the long axes of folia emerged between 21 and 31W. Our results show the potential for HARDI tractography to image developing human cerebellar connectivity. PMID:24650603

Takahashi, Emi; Hayashi, Emiko; Schmahmann, Jeremy D; Grant, P Ellen

2014-08-01

84

The X-Ray Optics for the High Angular Resolution Imager (HARI)  

NASA Technical Reports Server (NTRS)

This slide presentation shows the basic parameters of the x-ray optics, the housing,a graph of the effective area vs energy, another graph showing the angular off-set vs HEW, and a series of graphs showing the detector offsets and tilts,

Weisskopf, M. C.

2010-01-01

85

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): High Angular Resolution Astronomy at Far-Infrared Wavelengths  

NASA Technical Reports Server (NTRS)

Astronomical studies at infrared wavelengths have dramatically improved our understanding of the universe, and observations with Spitzer, the upcoming Herschel mission. and SOFIA will continue to provide exciting new discoveries. The comparatively low spatial resolution of these missions, however. is insufficient to resolve the physical scales on which mid- to far-infrared emission arises, resulting in source and structure ambiguities that limit our ability to answer key science questions. Interferometry enables high angular resolution at these wavelengths. We have proposed a new high altitude balloon experiment, the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII). High altitude operation makes far-infrared (30- 300micron) observations possible, and BETTII's 8-meter baseline provides unprecedented angular resolution (-0.5 arcsec) in this band. BETTII will use a double- Fourier instrument to simultaneously obtain both spatial and spectral informatioT. he spatially resolved spectroscopy provided by BETTII will address key questions about the nature of disks in young cluster stars and active galactic nuclei and the envelopes of evolved stars. BETTII will also lay the groundwork for future space interferometers.

Rinehart, Stephen A.

2008-01-01

86

Associations of water and methanol masers at milli-arcsec angular resolution in two high-mass young stellar objects  

E-print Network

Most previous high-angular (water or methanol masers. While high-angular resolution observations have clarified that water masers originate from shocks associated with protostellar jets, different environments have been proposed in several sources to explain the origin of methanol masers. Tha aim of the paper is to investigate the nature of the methanol maser birthplace in SFRs and the association between the water and methanol maser emission in the same young stellar object. We have conducted phase-reference Very Long Baseline Interferometry (VLBI) observations of water and methanol masers toward two high-mass SFRs, Sh 2-255 IR and AFGL 5142. In Sh 2-255 IR water masers are aligned along a direction close to the orientation of the molecular outflow observed on angular scales of 1-10 arcsec, tracing possibly the disk-wind emerging from the disk atmosphere. In AFGL 5142 water masers trace expansion at the base of a protostellar jet, whilst methanol masers are more probably tracing infalling than outflowing gas. The results for AFGL 5142 suggest that water and methanol masers trace different kinematic structures in the circumstellar gas.

C. Goddi; L. Moscadelli; A. Sanna; R. Cesaroni; V. Minier

2006-10-16

87

Microbeam high angular resolution x-ray diffraction in InGaN/GaN selective-area-grown ridge structures  

E-print Network

­7 Adequate character- ization tools, such as synchrotron radiation based microbeam high-resolution xMicrobeam high angular resolution x-ray diffraction in InGaN/GaN selective-area-grown ridge A. Kazimirov, S. Cornaby, and D. H. Bilderback Cornell High Energy Synchrotron Source (CHESS

Sirenko, Andrei

88

A Survey of the polarized emission from the Galactic plane at 1420 MHz with arcminute angular resolution  

NASA Astrophysics Data System (ADS)

Context. Observations of polarized emission are a significant source of information on the magnetic field that pervades the interstellar medium of the Galaxy. Despite the acknowledged importance of magnetic fields in interstellar processes, our knowledge of field configurations on all scales is seriously limited. Aims: This paper describes an extensive survey of polarized Galactic emission at 1.4 GHz that provides data with arcminute resolution and complete coverage of all structures from the broadest angular scales to the resolution limit, giving information on the magneto-ionic medium over a wide range of interstellar environments. Methods: Data from the DRAO Synthesis Telescope, the Effelsberg 100-m Telescope, and the DRAO 26-m Telescope have been combined. Angular resolution is ~1' and the survey extends from ? = 66° to ? = 175° over a range -3° < b < 5° along the northern Galactic plane, with a high-latitude extension from ? = 101° to ? = 116° up to b = 17.5°. This is the first extensive polarization survey to present aperture-synthesis data combined with data from single antennas, and the techniques developed to achieve this combination are described. Results: The appearance of the extended polarized emission at 1.4 GHz is dominated by Faraday rotation along the propagation path, and the diffuse polarized sky bears little resemblance to the total-intensity sky. There is extensive depolarization, arising from vector averaging on long lines of sight, from H II regions, and from diffuse ionized gas seen in H? images. Preliminary interpretation is presented of selected polarization features on scales from parsecs (the planetary nebula Sh 2-216) to hundreds of parsecs (a superbubble GSH 166-01-17), to kiloparsecs (polarized emission in the direction of Cygnus X).

Landecker, T. L.; Reich, W.; Reid, R. I.; Reich, P.; Wolleben, M.; Kothes, R.; Uyan?ker, B.; Gray, A. D.; Del Rizzo, D.; Fürst, E.; Taylor, A. R.; Wielebinski, R.

2010-09-01

89

The Gamma-ray Large Area Space Telescope (GLAST): a Wide Field, High Angular Resolution Observatory for High Energy Astrophysics  

NASA Astrophysics Data System (ADS)

The Gamma-ray Large Area Space Telescope (GLAST) is a proposed next-generation high-energy gamma-ray telescope for studying emission from astrophysical sources in the 10 MeV to 300 GeV energy range. It has been se;ected by NASA for a Mission Concept Study. The primary scientific targets include active galactic nuclei, gamma-ray bursts, neutron stars, and diffuse galactic and extragalactic high-energy radiation. GLAST relies on the unambigious identification of incident gamma-rays by detection of the electron and positron that result from pair creation in a thin converter material. Measurement of the energy and direction of the electron-positron shower provides information about the energy and direction of the incident gamma-ray. The GLAST design utilizes modern solid-state particle detector technology and recently developed advanced space-qualified computers. In particular, position-sensitive silicon strip detectors, interleaved between thin converters, are used to track particles. Because of this technical approach, the telescope design can be easily optimized to a range of sizes. For example, accomodation of GLAST within a Delta II size launch system results in an instrument with capabilities well beyond those of the highly successful EGRET currently operating on the Compton Observatory; namely, a broader energy range, larger effective area, wider field of view, and single-photon angular resolution 2 to 5 times more precise than EGRET's resolution. GLAST will have a maximum effective area of 8000 cm(2) above 300 MeV, a field of view of 2.6 sr, and a single photon angular resolution (rms projected) of 0.3deg at 1 GeV, approaching 0.03deg above 20 GeV.

Wood, K.; Michelson, P.; GLAST Collaboration

1995-12-01

90

Thin fused silica optics for a high angular resolution and large collecting area X Ray telescope after Chandra  

NASA Astrophysics Data System (ADS)

The implementation of an X-ray mission with high imaging capabilities, similar to those achieved with Chandra (<1 arcsec Half Energy Width, HEW), but with a much larger throughput is very attractive, even if challenging. For such a mission the scientific opportunities, in particular for the study of the early Universe, would remain at the state of the art for the next decades. Initially the ESA-led XEUS mission was proposed, with an effective area of several m2 and an angular resolution better than 2 arcsec HEW. Unfortunately, this mission was not implemented, mainly due to the costs and the low level of technology readiness. Currently the most advanced proposal for such a mission is the SMART-X project, led by CfA together with other US institutes. This project is based on adjustable segments of thin foil mirrors with piezo-electric actuators, aiming to achieve an effective area >2 m2 at 1 keV and an angular resolution better than 1 arcsec HEW. Another attractive technology to realize an X-ray telescope with similar characteristics is being developed at NASA/Goddard. In this case the mirrors are based on Si substrates that are super-polished and figured starting from a bulky Si ingot, from which they are properly cut. Here we propose an alternative method based on precise direct grinding, figuring and polishing of thin (a few mm) glass shells with innovative deterministic polishing methods. This is followed by a final correction via ion figuring to obtain the desired accuracy. For this purpose, a temporary stiffening structure is used to support the shell from the polishing operations up to its integration in the telescope supporting structure. This paper deals with the technological process under development, the results achieved so far and some mission scenarios based on this kind of optics, aiming to achieve an effective area more than 10 times larger than Chandra and an angular resolution of 1 arcsec HEW on axis and of a few arcsec off-axis across a large field of view (1o in diameter).

Pareschi, Giovanni; Citterio, Oberto; Civitani, Marta M; Basso, Stefano; Campana, Sergio; Conconi, Paolo; Ghigo, Mauro; Mattaini, Enrico; Moretti, Alberto; Parodi, Giancarlo; Tagliaferri, Gianpiero

2014-08-01

91

Thin fused silica optics for a few arcsec angular resolution and large collecting area x-ray telescope  

NASA Astrophysics Data System (ADS)

The implementation of a X-ray mission with high imaging capabilities, similar to those achieved with Chandra (< 1 arcsec Half Energy Width, HEW), but with a much larger throughput is a very attractive perspective, even if challenging. For such a mission the scientific opportunities, in particular for the study of the early Universe, would remain at the state of the art for the next decades. At the beginning of the new millennium the XEUS mission has been proposed, with an effective area of several m2 and an angular resolution better than 2 arcsec HEW. Unfortunately, after the initial study, this mission was not implemented, mainly due to the costs and the low level of technology readiness. Currently the most advanced proposal for such a kind of mission is the SMART-X project, led by CfA and involving several other US Institutes. This project is based on adjustable segments of thin foil mirrors with piezo-electric actuators, aiming to achieve an effective area < 2 m2 at 1 keV and an angular resolution better than 1 arcsec HEW. Another attractive technology to realize an X-ray telescope with similar characteristics is being developed at NASA/Goddard. In this case the mirrors are based on Si substrates that are super-polished and figured starting from a bulky Si ingot, from which they are properly cut. Here we propose an alternative method based on precise direct grinding, figuring and polishing of thin (a few mm) glass shells with innovative deterministic polishing methods. This is followed by a final correction via ion figuring to obtain the desired accuracy in order to achieve the 1 arc sec HEW requirement. For this purpose, a temporary stiffening structure is used to support the shell from the polishing operations up to its integration in the telescope supporting structure. We will present the technological process under development, the results achieved so far and some mission scenarios based on this kind of optics, aiming to achieve an effective area more than 10 times larger than Chandra and an angular resolution of 1 arcsec HEW on axis and of a few arcsec off-axis across a large field of view (1 deg in diameter).

Citterio, O.; Civitani, M. M.; Pareschi, G.; Basso, S.; Campana, S.; Conconi, P.; Ghigo, M.; Mattaini, E.; Moretti, A.; Parodi, G.; Tagliaferri, G.

2013-09-01

92

Tiny twists in time; exploring angular resolution of in situ EBSD orientation microstructures in solar system zircon  

NASA Astrophysics Data System (ADS)

Kikuchi discovered electron diffraction in samples of calcite in the 1920's, and orientation of lattice planes by Electron Backscatter Diffraction (EBSD) is now routinely measured by automated camera systems at a spatial resolution of tens of nanometers using Field Emission Gun SEM. The current methodology is proving particularly powerful when measuring lattice orientation microstructure in U-Pb geochronology minerals such as zircon and baddeleyite that have experienced high temperature deformation or shock metamorphism. These are among the oldest preserved mineral phases in inner solar system materials, and we have been applying EBSD to rare samples of the Early Earth and grains from extraterrestrial environments such as the Moon and Mars. In these cases the EBSD orientation data are useful for identifying high diffusivity pathways that may have afforded isotopic and trace element disturbance, microstructural proxies for shock metamorphic pressures, as well as resolving glide plane systems in ductile zircon and shear twin mechanisms. Blanket estimates of angular resolution for automated EBSD misorientation measurements are often in the range of 0.5 degrees. In some cases strain giving rise to only a few degrees of lattice misorientation has facilitated 100% Pb-loss. In some cases, however, there is a spatial correlation between trace element or cathodoluminescence zoning in zircon and what appears to be low magnitudes misorientation close to the limits of resolution. Given the proven value of performing EBSD analysis on geochronology minerals, a more thorough exploration of the precision and accuracy of EBSD lattice misorientation measurements is warranted. In this talk the relative weighting of the factors that limit EBSD angular resolution will be investigated, focusing on U-Pb dating minerals such as zircon. These factors include; sample surface preparation, phase symmetry, pseudo-symmetry effects, degree of crystallinity, Kikuchi band contrast and indexing, solid solution effects on unit cell, dimension camera calibration and camera-sample distance, beam conditions and focussing, and general microscope operating conditions (e.g. high vacuum vs. variable pressure). An assessment of potential zircon EBSD reference materials and sample preparation protocols will be presented, along with case studies of zircon orientation microstructures from meteorites and terrestrial craters representative of different strain and thermal environments in the inner solar system.BSD lattice misorientation maps of a) crystal-plastically deformed and partly recrystallized zircon, after Rayner et al. (in prep.), and b) shock-metamorphosed lunar zircon (Darling et al., in prep.).

Moser, D. E.

2012-12-01

93

Next Generation Astronomical X-ray Optics: High Angular Resolution, Light Weight, and Low Production Cost  

NASA Technical Reports Server (NTRS)

X-ray astronomy depends on the availability of telescopes with high resolution and large photon collecting areas. Since x-ray observation can only be carried out above the atmosphere, these telescopes must be necessarily lightweight. Compounding the lightweight requirement is that an x-ray telescope consists of many nested concentric shells, which further require that x-ray mirrors must also be geometrically thin to achieve high packing efficiency. This double lightweight and geometrically thin requirement poses significant technical challenges in fabricating the mirrors and in integrating them into mirror assemblies. This paper reports on the approach, strategy and status of our x-ray optics development program whose objective is to meet these technical challenges at modest cost to enable future x-ray missions, including small Explorer missions in the near term, probe class missions in the medium term, and large flagship missions in the long term.

Zhang. W. W.; Biskach, M. P.; Blake, P. N.; Chan, K. W.; Gaskin, J. A.; Hong, M. L.; Jones, W. D.; Kolos, L. D.; Mazzarella, J. R.; McClelland, R. S.; O'Dell, S. L.; Saha, T. T.; Sharpe, M. V.

2012-01-01

94

High resolution angular sensor. [reducing ring laser gyro output quantization using phase locked loops  

NASA Technical Reports Server (NTRS)

Specifications for the pointing stabilization system of the large space telescope were used in an investigation of the feasibility of reducing ring laser gyro output quantization to the sub-arc-second level by the use of phase locked loops and associated electronics. Systems analysis procedures are discussed and a multioscillator laser gyro model is presented along with data on the oscillator noise. It is shown that a second order closed loop can meet the measurement noise requirements when the loop gain and time constant of the loop filter are appropriately chosen. The preliminary electrical design is discussed from the standpoint of circuit tradeoff considerations. Analog, digital, and hybrid designs are given and their applicability to the high resolution sensor is examined. the electrical design choice of a system configuration is detailed. The design and operation of the various modules is considered and system block diagrams are included. Phase 1 and 2 test results using the multioscillator laser gyro are included.

Gneses, M. I.; Berg, D. S.

1981-01-01

95

Probing region-specific microstructure of human cortical areas using high angular and spatial resolution diffusion MRI.  

PubMed

Regional heterogeneity in cortical cyto- and myeloarchitecture forms the structural basis of mapping of cortical areas in the human brain. In this study, we investigate the potential of diffusion MRI to probe the microstructure of cortical gray matter and its region-specific heterogeneity across cortical areas in the fixed human brain. High angular resolution diffusion imaging (HARDI) data at an isotropic resolution of 92-?m and 30 diffusion-encoding directions were acquired using a 3D diffusion-weighted gradient-and-spin-echo sequence, from prefrontal (Brodmann area 9), primary motor (area 4), primary somatosensory (area 3b), and primary visual (area 17) cortical specimens (n=3 each) from three human subjects. Further, the diffusion MR findings in these cortical areas were compared with histological silver impregnation of the same specimens, in order to investigate the underlying architectonic features that constitute the microstructural basis of diffusion-driven contrasts in cortical gray matter. Our data reveal distinct and region-specific diffusion MR contrasts across the studied areas, allowing delineation of intracortical bands of tangential fibers in specific layers-layer I, layer VI, and the inner and outer bands of Baillarger. The findings of this work demonstrate unique sensitivity of diffusion MRI to differentiate region-specific cortical microstructure in the human brain, and will be useful for myeloarchitectonic mapping of cortical areas as well as to achieve an understanding of the basis of diffusion NMR contrasts in cortical gray matter. PMID:25449747

Aggarwal, Manisha; Nauen, David W; Troncoso, Juan C; Mori, Susumu

2015-01-15

96

The use of the linear sampling method for obtaining super-resolution effects in Born approximation  

NASA Astrophysics Data System (ADS)

A two-step reconstruction scheme is introduced to solve fixed frequency inverse scattering problems in Born approximation conditions. The aim of the approach is to achieve super-resolution effects by constraining the inversion method to exploit some a priori knowledge on the scatterer. Therefore, the first step is to apply the linear sampling method to the far-field data in order to obtain an estimate of the support of the inhomogeneity. The second step is to apply the projected Landweber method to the linearized scattering equation in order to obtain super-resolution effects via out-of-band extrapolation. The effectiveness of the approach, which has a rather wide applicability power, is tested in the case of a two-dimensional problem for some scatterers of simple geometry.

Brignone, M.; Coyle, J.; Piana, M.

2007-06-01

97

SMA High Angular Resolution Imaging of the Lensed Quasar APM08279+5255  

E-print Network

We present Submillimeter Array observations of the z=3.91 gravitationally lensed broad absorption line quasar APM08279+5255 which spatially resolve the 1.0mm (0.2mm rest-frame) dust continuum emission. At 0.4" resolution, the emission is separated into two components, a stronger, extended one to the northeast (46+/-5mJy) and a weaker, compact one to the southwest (15+/-2mJy). We have carried out simulations of the gravitational lensing effect responsible for the two submm components in order to constrain the intrinsic size of the submm continuum emission. Using an elliptical lens potential, the best fit lensing model yields an intrinsic (projected) diameter of ~80pc, which is not as compact as the optical/near-infrared (NIR) emission and agrees with previous size estimates of the gas and dust emission in APM08279+5255. Based on our estimate, we favor a scenario in which the 0.2mm (rest-frame) emission originates from a warm dust component (T_d=150-220K) that is mainly heated by the AGN rather than by a starburst (SB). The flux is boosted by a factor of ~90 in our model, consistent with recent estimates for APM08279+5255.

M. Krips; A. B. Peck; K. Sakamoto; G. B. Petitpas; D. J. Wilner; S. Matsushita; D. Iono

2007-10-25

98

Probe diagnostics of electron distributions in plasma with spatial and angular resolution  

SciTech Connect

This paper discusses the spatial resolution that is required to study inhomogeneous, low-temperature plasmas and is based on a review of low-temperature plasma electron kinetics and methods for probe measurements of electron energy distribution functions (EEDFs). It is stated that EEDFs can be extracted from probe measurements by applying an appropriate probe theory. The Druyvesteyn formula is most commonly used for this extraction and has been used in numerous publications, but more general theory can be used for a wider range of gas pressures. It is demonstrated that the Druyvesteyn formula can be obtained from the general theory as a limiting case. This paper justifies the application of wall probes in plasma studies of an energetic part of EEDFs. This justification is made for an idealized probe. We briefly review the methods for studying anisotropic plasmas and their usefulness in plasma research. It is demonstrated that to determine anisotropic electron energy distribution functions, a planar, one-sided probe is most convenient.

Demidov, V. I.; Kudryavtsev, A. A. [St. Petersburg State University, St. Petersburg 199034, Russia and ITMO University, Kronverkskiy pr. 49, St. Petersburg 197101 (Russian Federation)

2014-09-15

99

Pulsar timing arrays as imaging gravitational wave telescopes: Angular resolution and source (de)confusion  

NASA Astrophysics Data System (ADS)

Pulsar timing arrays (PTAs) will be sensitive to a finite number of gravitational wave (GW) “point” sources (e.g. supermassive black hole binaries). N quiet pulsars with accurately known distances dpulsar can characterize up to 2N/7 distant chirping sources per frequency bin ?fgw=1/T and localize them with “diffraction-limited” precision ???(1/SNR)(?gw/dpulsar). Even if the pulsar distances are poorly known, a PTA with F GW frequency bins can still characterize up to (2N/7)(1-(1)/(2F)) sources per bin, and the quasisingular pattern of timing residuals in the vicinity of a GW source still allows the source to be localized quasitopologically within roughly the smallest quadrilateral of quiet pulsars that encircles it on the sky, down to a limiting resolution ???(1/SNR)?gw/dpulsar. PTAs may be unconfused, even at the lowest GW frequencies: in that case, standard analysis techniques designed to detect a stochastic GW background would be incomplete and suboptimal, whereas matched filtering could provide more information and sensitivity.

Boyle, Latham; Pen, Ue-Li

2012-12-01

100

High angular resolution imaging and infrared spectroscopy of CoRoT candidates  

NASA Astrophysics Data System (ADS)

Context. Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured. An important part of transit-search programmes is the removal of false-positives. In the case of the CoRoT space mission, the majority of the false-positives are removed by a detailed analysis of the light curves and by seeing-limited imaging in- and out-of-transit. However, the critical question is how many of the candidates that passed all these tests are false-positives. Such false-positives can be caused by eclipsing binaries, which are either related or unrelated to the targets. Aims: For our study we selected 25 CoRoT candidates that have already been screened against false-positives using detailed analysis of the light curves and seeing-limited imaging, which has transits that are between 0.7 and 0.05% deep. Our aim is to search for companion candidates that had not been recognized in previous observations. Methods: We observed 20 candidates with the adaptive optics imager NaCo and 18 with the high-resolution infrared spectrograph CRIRES. Results: We found previously unknown stars within 2'' of the targets in seven of the candidates. All of these are too faint and too close to the targets to have been previously detected with seeing-limited telescopes in the optical. Our study thus leads to the surprising results that if we remove all candidates excluded by the sophisticated analysis of the light-curve, as well as carrying out deep imaging with seeing-limited telescopes, still 28-35% of the remaining candidates are found to possess companions that are bright enough to be false-positives. Conclusions: Given that the companion candidates cluster around the targets and that the J - K colours are consistent with physical companions, we conclude that the companion candidates are more likely to be physical companions rather than unrelated field stars. Based on observations obtained at the European Southern Observatory at Paranal, Chile in programmes 282.C-5015A, 282.C-5015B, 282.C-5015C, 285.C-5045A, and 285.C-5045B, 086.C-0235A, 086.C-0235B, 088.C-0707A, 088.C-0707B, 090.C-0251A, 090.C-0251B, and 091.C-203(A).Appendices A and B are available in electronic form at http://www.aanda.org

Guenther, E. W.; Fridlund, M.; Alonso, R.; Carpano, S.; Deeg, H. J.; Deleuil, M.; Dreizler, S.; Endl, M.; Gandolfi, D.; Gillon, M.; Guillot, T.; Jehin, E.; Léger, A.; Moutou, C.; Nortmann, L.; Rouan, D.; Samuel, B.; Schneider, J.; Tingley, B.

2013-08-01

101

The 6Hankel asymptotic approximation for the uniform description of rainbows and glories in the angular scattering of state-to-state chemical reactions: derivation, properties and applications.  

PubMed

This paper considers the asymptotic (semiclassical) analysis of a forward glory and a rainbow in the differential cross section (DCS) of a state-to-state chemical reaction, whose scattering amplitude is given by a Legendre partial wave series (PWS). A recent paper by C. Xiahou, J. N. L. Connor and D. H. Zhang [Phys. Chem. Chem. Phys., 2011, 13, 12981] stated without proof a new asymptotic formula for the scattering amplitude, which is uniform for a glory and a rainbow in the DCS. The new formula was designated "6Hankel" because it involves six Hankel functions. This paper makes three contributions: (1) we provide a detailed derivation of the 6Hankel approximation. This is done by first generalizing a method described by G. F. Carrier [J. Fluid Mech., 1966, 24, 641] for the uniform asymptotic evaluation of an oscillating integral with two real coalescing stationary phase points, which results in the "2Hankel" approximation (it contains two Hankel functions). Application of the 2Hankel approximation to the PWS results in the 6Hankel approximation for the scattering amplitude. We also test the accuracy of the 2Hankel approximation when it is used to evaluate three oscillating integrals of the cuspoid type. (2) We investigate the properties of the 6Hankel approximation. In particular, it is shown that for angles close to the forward direction, the 6Hankel approximation reduces to the "semiclassical transitional approximation" for glory scattering derived earlier. For scattering close to the rainbow angle, the 6Hankel approximation reduces to the "transitional Airy approximation", also derived earlier. (3) Using a J-shifted Eckart parameterization for the scattering matrix, we investigate the accuracy of the 6Hankel approximation for a DCS. We also compare with angular scattering results from the "uniform Bessel", "uniform Airy" and other semiclassical approximations. PMID:24519014

Xiahou, Chengkui; Connor, J N L

2014-06-01

102

Evolution of deformation structures under varying loading conditions followed in-situ by high angular resolution 3DXRD.  

SciTech Connect

With high angular resolution three-dimensional X-ray diffraction, individual subgrains are traced in the bulk of a polycrystalline specimen and their dynamics is followed in situ during varying loading conditions. The intensity distribution of single Bragg reflections from an individual grain is analyzed in reciprocal space. It consists of sharp high-intensity peaks arising from subgrains superimposed on a cloud of lower intensity arising from dislocation walls. Individual subgrains can be distinguished by their unique combination of orientation and elastic strain. The responses of polycrystalline copper to different loading conditions are presented: during uninterrupted tensile deformation, formation of subgrains can be observed concurrently with broadening of the Bragg reflection shortly after onset of plastic deformation. With continued tensile deformation, the subgrain structure develops intermittently. When the traction is terminated, stress relaxation occurs and number, size and orientation of subgrains are found to be constant. The subgrain structure freezes and only a minor clean-up of the dislocation structure is observed. When changing the tensile direction after pre-deformation in tension, a systematic correlation between the degree of strain path change and the changes in the dislocation structure quantified by the volume fraction of the subgrains is established. For obtaining the subgrain volume fraction, a new fitting method has been developed for partitioning the contributions of subgrains and dislocation walls.

Pantleon, W.; Wejdemann, C.; Jakobsen, B.; Lienert, U.; Poulsen, H. F.; X-Ray Science Division; Risoe National Lab.; Technical Univ. of Denmark; Roskilde Univ.

2009-10-25

103

Stability of dislocation structures in copper towards stress relaxation investigated by high angular resolution 3D x-ray diffraction.  

SciTech Connect

300 {micro}m thick tensile specimen of OFHC copper is subjected to a tensile loading sequence and deformed to a maximal strain of 3.11%. Using the novel three-dimensional X-ray diffraction method High angular resolution 3DXRD', the evolution of the microstructure within a deeply embedded grain is characterized in-situ by the behavior of individual subgrains. The loading sequence consists of three continuous deformation stages with strain rates of 1.1 x 10{sup -6} s{sup -1} and 3 x 10{sup -2} s{sup -1}, in each case followed by a period of extended stress relaxation at fixed motor positions, as well as an unloading step. In contrast to the deformation stages, during each stress relaxation stage, number, size and orientation of subgrains are found to be constant, while a minor amount of clean-up of the microstructure is observed as narrowing of the radial X-ray diffraction line profile. The associated decrease in the width of the strain distribution indicates homogenization of the elastic strains present in the deformation structure. During reloading, the subgrain structure seemingly starts to develop further when the entire dislocation structure is deforming plastically. Upon unloading of the sample, the average backward strain of the subgrains increases.

Jakobsen, B.; Poulsen, H. F.; Lienert, U.; Bernier, J.; Gundlach, C.; Pantleon, W.; Riso National Lab.; Roskilde Univ.; LLNL; European Synchrotron Research Facility

2008-01-01

104

ATLAS-BASED FIBER CLUSTERING FOR MULTI-SUBJECT ANALYSIS OF HIGH ANGULAR RESOLUTION DIFFUSION IMAGING TRACTOGRAPHY  

PubMed Central

High angular resolution diffusion imaging (HARDI) allows in vivo analysis of the white matter structure and connectivity. Based on orientation distribution functions (ODFs) that represent the directionality of water diffusion at each point in the brain, tractography methods can recover major axonal pathways. This enables tract-based analysis of fiber integrity and connectivity. For multi-subject comparisons, fibers may be clustered into bundles that are consistently found across subjects. To do this, we scanned 20 young adults with HARDI at 4 T. From the reconstructed ODFs, we performed whole-brain tractography with a novel Hough transform method. We then used measures of agreement between the extracted 3D curves and a co-registered probabilistic DTI atlas to select key pathways. Using median filtering and a shortest path graph search, we derived the maximum density path to compactly represent each tract in the population. With this tract-based method, we performed tract-based analysis of fractional anisotropy, and assessed how the chosen tractography algorithm influenced the results. The resulting method may expedite population-based statistical analysis of HARDI and DTI. PMID:25404992

Prasad, Gautam; Jahanshad, Neda; Aganj, Iman; Lenglet, Christophe; Sapiro, Guillermo; Toga, Arthur W.; Thompson, Paul M.

2014-01-01

105

A new analytic approximation method for the non-zero angular momentum states of the Hulthén potential  

NASA Astrophysics Data System (ADS)

We propose a new approximation scheme to obtain analytic expressions for the bond-state energies and eigenfunctions for any arbitrary bound nl-state of the Hulthén potential. The predicted energies Enl are in excellent agreement with the perturbative results of Lai and Lin. The scope for an extension of the method to the continuum states is also discussed.

Dutt, Ranabir; Mukherji, Uma

1982-08-01

106

Deviations from the diffusion tensor model as revealed by contour plot visualization using high angular resolution diffusion-weighted imaging (HARDI)  

Microsoft Academic Search

The standard diffusion tensor model is limited in its ability to provide detailed information about multidirectional fiber\\u000a architecture in human white matter. Additional directional acquisition of diffusivity properties with high angular resolution\\u000a diffusion-weighted imaging (HARDI) acquisition schemes may deliver more information on areas with fiber crossings than standard\\u000a DTI. However, representation of the additional information and the rating and visualization

Jochen G. Hirsch; Stefanie M. Schwenk; Christina Rossmanith; Michael G. Hennerici; Achim Gass

2003-01-01

107

Angular Acceleration  

NSDL National Science Digital Library

The simulation of a rotating wheel below shows the relationship between angular position, angular velocity, and angular acceleration. Graphs of angular position and angular velocity as a function of time are shown.

Christian, Wolfgang; Belloni, Mario

2008-02-19

108

High resolution electron energy loss spectroscopy of spin waves in ultra-thin film - The return of the adiabatic approximation?  

NASA Astrophysics Data System (ADS)

The paper reports on recent considerable improvements in electron energy loss spectroscopy (EELS) of spin waves in ultra-thin films. Spin wave spectra with 4 meV resolution are shown. The high energy resolution enables the observation of standing modes in ultra-thin films in the wave vector range of 0.15 Å- 1 < q|| < 0.3 Å- 1. In this range, Landau damping is comparatively small and standing spin wave modes are well-defined Lorentzians for which the adiabatic approximation is well suited, an approximation which was rightly dismissed by Mills and collaborators for spin waves near the Brillouin zone boundary. With the help of published exchange coupling constants, the Heisenberg model, and a simple model for the spectral response function, experimental spectra for Co-films on Cu(100) as well as for Co films capped with further copper layers are successfully simulated. It is shown that, depending on the wave vector and film thickness, the most prominent contribution to the spin wave spectrum may come from the first standing mode, not from the so-called surface mode. In general, the peak position of a low-resolution spin wave spectrum does not correspond to a single mode. A discussion of spin waves based on the “dispersion” of the peak positions in low resolution spectra is therefore subject to errors.

Ibach, Harald

2014-12-01

109

R&D proposal to DRDC fast EM calorimeter with excellent photon angular resolution and energy resolution using scintillating noble liquids  

E-print Network

Recent test beam data have shown fast and large signals for LKr, mixed with >1% LXe. Excellent uniformity in LKr and LXe was achieved over a 37 cm long cell. CsI cathode works well inside LKr/LXe with O(1%) resolution at 5 MeV. Precision calibration in-situ has been demonstrated. Scintillating LKr/LXe detectors are sufficiently radiation hard for LHC environment. These new developments simplify the construction of prototype LKr calorimeter, to demonstrate the superior e/gamma energy resolution and the determination of photon direction using longitudinal and transverse segmentations, which are vital for the detection of the multi-photon states. The constant term in the energy resolution is small, the electronics noise is negligible due to the large signal size. The overall pion/electron suppression is expected to be better than 10-4.

Chen, M; Sumorok, K; Zhang, X; Gaudreau, M P J; Akimov, D Y; Bolozdynya, A I; Churakov, D; Chernyshov, V; Koutchenkov, A; Kovalenko, A; Kuzichev, V F; Lamkov, V A; Lebedenko, V; Gusev, L; Safronov, G A; Sheinkman, V A; Smirnov, G; Krasnokutsky, R N; Shuvalov, R S; Fedyakin, N N; Sushkov, V V; Akopyan, M V; Gougas, Andreas; Pevsner, A; CERN. Geneva. Detector Research and Development Committee

1993-01-01

110

A new UV and VUV beamline for angular resolved photoemission with high resolution and at low energy  

NASA Astrophysics Data System (ADS)

A new 5-m normal-incidence monochromator at the third generation synchrotron source BESSY II of the Helmholz-Zentrum Berlin (HZB) has been constructed with the emphasis on angle-resolved photoelectron spectroscopy with high-resolution and at low energy utilizing photons from 5 eV to 40 eV. Optical design and preliminary performance results of the beamline and the photoemission endstation are presented and match the design goals.

Janowitz, Christoph; Zandt, Thorsten; Dudy, Lenart; Manzke, Recardo; Reichardt, Gerd

2012-11-01

111

An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers  

NASA Technical Reports Server (NTRS)

The high-resolution laboratory millimeter- and submillimeter-wave spectra of C-12H(3)OH and C-13H(3)OH have been extended to include transitions involving significantly higher angular momentum quantum numbers than studied previously. For C-12H(3)OH, the data set now includes 549 A torsional substate transitions and 524 E torsional substate transitions through J is not greater than 24, exclusive of blends. For C-13H(3)OH the data set now includes 453 A torsional substate transitions and 440 E torsional substate transitions through J is not greater than 24, exclusive of blends. The extended internal axis method Hamiltonian has been used to analyze the transitions to experimental accuracy. The molecular constants determined by this approach have been used to predict accurately the frequencies of many transitions through J = 25 not measured in the laboratory.

Anderson, Todd; Herbst, Eric; De Lucia, Frank C.

1992-01-01

112

HIGH ANGULAR RESOLUTION RADIO OBSERVATIONS OF A CORONAL MASS EJECTION SOURCE REGION AT LOW FREQUENCIES DURING A SOLAR ECLIPSE  

SciTech Connect

We carried out radio observations of the solar corona in the frequency range 109-50 MHz during the annular eclipse of 2010 January 15 from the Gauribidanur Observatory, located about 100 km north of Bangalore in India. The radio emission in the above frequency range originates typically in the radial distance range Almost-Equal-To 1.2-1.5 R{sub Sun} in the 'undisturbed' solar atmosphere. Our analysis indicates that (1) the angular size of the smallest observable radio source (associated with a coronal mass ejection in the present case) is Almost-Equal-To 1' {+-} 0.'3, (2) the source size does not vary with radial distance, (3) the peak brightness temperature of the source corresponding to the above size at a typical frequency like 77 MHz is Almost-Equal-To 3 Multiplication-Sign 10{sup 9} K, and (4) the coronal magnetic field near the source region is Almost-Equal-To 70 mG.

Ramesh, R.; Kathiravan, C.; Barve, Indrajit V.; Rajalingam, M., E-mail: ramesh@iiap.res.in, E-mail: kathir@iiap.res.in, E-mail: indrajit@iiap.res.in, E-mail: rajalingam@iiap.res.in [Indian Institute of Astrophysics, Bangalore 560 034 (India)

2012-01-10

113

Comparison between a Radiative Wind Model for Be Stars and High Angular Resolution Data from the GI2T Interferometer  

NASA Astrophysics Data System (ADS)

I present theoretical line profiles and intensity maps from an axi-symmetric radiative wind model from a rapidly rotating Be star. The introduction of a viscosity parameter in the latitude-dependent hydrodynamic code enables us to consider the effects of the viscous force in the azimuthal component of momentum equations (Araújo et al. 1994). Both velocity field and density law derived from the hydrodynamic equations have been used for solving the statistical equilibrium equations. By adopting the Sobolev approximation, we could easily obtain a good estimate of both electronic density and hydrogen level populations throughout the envelope. The numerical calculation was performed for parameters characterisic of the Be star? Cassiopeiae.

Stee, Ph.

1995-02-01

114

Resolution of the 1D regularized Burgers equation using a spatial wavelet approximation  

NASA Technical Reports Server (NTRS)

The Burgers equation with a small viscosity term, initial and periodic boundary conditions is resolved using a spatial approximation constructed from an orthonormal basis of wavelets. The algorithm is directly derived from the notions of multiresolution analysis and tree algorithms. Before the numerical algorithm is described these notions are first recalled. The method uses extensively the localization properties of the wavelets in the physical and Fourier spaces. Moreover, the authors take advantage of the fact that the involved linear operators have constant coefficients. Finally, the algorithm can be considered as a time marching version of the tree algorithm. The most important point is that an adaptive version of the algorithm exists: it allows one to reduce in a significant way the number of degrees of freedom required for a good computation of the solution. Numerical results and description of the different elements of the algorithm are provided in combination with different mathematical comments on the method and some comparison with more classical numerical algorithms.

Liandrat, J.; Tchamitchian, PH.

1990-01-01

115

High mass resolution, high angular acceptance time-of-flight mass spectroscopy for planetary missions under the Planetary Instrument Definition and Development Program (PIDDP)  

NASA Technical Reports Server (NTRS)

This final report covers three years and several phases of work in which instrumentation for the Planetary Instrument Definition and Development Program (PIDDP) were successfully developed. There were two main thrusts to this research: (1) to develop and test methods for electrostatically scanning detector field-of-views, and (2) to improve the mass resolution of plasma mass spectrometers to M/delta M approximately 25, their field-of-view (FOV) to 360 degrees, and their E-range to cover approximately 1 eV to 50 keV. Prototypes of two different approaches to electrostatic scanning were built and tested. The Isochronous time-of-flight (TOF) and the linear electric field 3D TOF devices were examined.

Young, David T.

1991-01-01

116

Design and Fabrication of Two-Dimensional Semiconducting Bolometer Arrays for the High Resolution Airborne Wideband Camera (HAWC) and the Submillimeter High Angular Resolution Camera II (SHARC-II)  

NASA Technical Reports Server (NTRS)

The High resolution Airborne Wideband Camera (HAWC) and the Submillimeter High Angular Resolution Camera II (SHARC II) will use almost identical versions of an ion-implanted silicon bolometer array developed at the National Aeronautics and Space Administration's Goddard Space Flight Center (GSFC). The GSFC 'Pop-up' Detectors (PUD's) use a unique folding technique to enable a 12 x 32-element close-packed array of bolometers with a filling factor greater than 95 percent. A kinematic Kevlar(trademark) suspension system isolates the 200 mK bolometers from the helium bath temperature, and GSFC - developed silicon bridge chips make electrical connection to the bolometers, while maintaining thermal isolation. The JFET preamps operate at 120 K. Providing good thermal heat sinking for these, and keeping their conduction and radiation from reaching the nearby bolometers, is one of the principal design challenges encountered. Another interesting challenge is the preparation of the silicon bolometers. They are manufactured in 32-element, planar rows using Micro Electro Mechanical Systems (MEMS) semiconductor etching techniques, and then cut and folded onto a ceramic bar. Optical alignment using specialized jigs ensures their uniformity and correct placement. The rows are then stacked to create the 12 x 32-element array. Engineering results from the first light run of SHARC II at the Caltech Submillimeter Observatory (CSO) are presented.

Voellmer, George M.; Allen, Christine A.; Amato, Michael J.; Babu, Sachidananda R.; Bartels, Arlin E.; Benford, Dominic J.; Derro, Rebecca J.; Dowell, C. Darren; Harper, D. Al; Jhabvala, Murzy D.

2002-01-01

117

Design and Fabrication of Two-Dimensional Semiconducting Bolometer Arrays for the High Resolution Airborne Wideband Camera (HAWC) and the Submillimeter High Angular Resolution Camera II (SHARC-II)  

NASA Technical Reports Server (NTRS)

The High resolution Airborne Wideband Camera (HAWC) and the Submillimeter High Angular Resolution Camera II (SHARC 11) will use almost identical versions of an ion-implanted silicon bolometer array developed at the National Aeronautics and Space Administration's Goddard Space Flight Center (GSFC). The GSFC "Pop-Up" Detectors (PUD's) use a unique folding technique to enable a 12 x 32-element close-packed array of bolometers with a filling factor greater than 95 percent. A kinematic Kevlar(Registered Trademark) suspension system isolates the 200 mK bolometers from the helium bath temperature, and GSFC - developed silicon bridge chips make electrical connection to the bolometers, while maintaining thermal isolation. The JFET preamps operate at 120 K. Providing good thermal heat sinking for these, and keeping their conduction and radiation from reaching the nearby bolometers, is one of the principal design challenges encountered. Another interesting challenge is the preparation of the silicon bolometers. They are manufactured in 32-element, planar rows using Micro Electro Mechanical Systems (MEMS) semiconductor etching techniques, and then cut and folded onto a ceramic bar. Optical alignment using specialized jigs ensures their uniformity and correct placement. The rows are then stacked to create the 12 x 32-element array. Engineering results from the first light run of SHARC II at the CalTech Submillimeter Observatory (CSO) are presented.

Voellmer, George M.; Allen, Christine A.; Amato, Michael J.; Babu, Sachidananda R.; Bartels, Arlin E.; Benford, Dominic J.; Derro, Rebecca J.; Dowell, C. Darren; Harper, D. Al; Jhabvala, Murzy D.; Simpson, A. D. (Technical Monitor)

2002-01-01

118

Spinflation with angular potentials  

NASA Astrophysics Data System (ADS)

We investigate in detail the cosmological consequences of realistic angular dependent potentials in the brane inflation scenario. Embedding a warped throat into a compact Calabi-Yau space with all moduli stabilized breaks the no-scale structure and induces angular dependence in the potential of the probe D3-brane. We solve the equations of motion from the DBI action in the warped deformed conifold including linearized perturbations around the imaginary self-dual solution. Our numerical solutions show that angular dependence is a next to leading order correction to the dominant radial motion of the brane, however, just as angular motion typically increases the amount of inflation (spin-flation), having additional angular dependence also increases the amount of inflation. We also derive an analytic approximation for the number of e-foldings along the DBI trajectory in terms of the compactification parameters.

Gregory, Ruth; Kaviani, Dariush

2012-01-01

119

HIGH-ANGULAR RESOLUTION DUST POLARIZATION MEASUREMENTS: SHAPED B-FIELD LINES IN THE MASSIVE STAR-FORMING REGION ORION BN/KL  

SciTech Connect

We present observational results of the thermal dust continuum emission and its linear polarization in one of the nearest massive star-forming sites Orion BN/KL in Orion Molecular Cloud-1. The observations were carried out with the Submillimeter Array. With an angular resolution of 1'' ({approx}2 mpc; 480 AU), we have detected and resolved the densest cores near the BN/KL region. At a wavelength of {approx}870 {mu}m, the polarized dust emission can be used to trace the structure of the magnetic field in this star-forming core. The dust continuum appears to arise from a V-shaped region, with a cavity nearly coincident with the center of the explosive outflows observed on larger scales. The position angles (P.A.s) of the observed polarization vary significantly by a total of about 90{sup 0} but smoothly, i.e., curl-like, across the dust ridges. Such a polarization pattern can be explained with dust grains being magnetically aligned instead of mechanically with outflows, since the latter mechanism would cause the P.A.s to be parallel to the direction of the outflow, i.e., radial-like. The magnetic field projected in the plane of sky is therefore derived by rotating the P.A.s of the polarization by 90{sup 0}. We find an azimuthally symmetric structure in the overall magnetic field morphology, with the field directions pointing toward 2.''5 west to the center of the explosive outflows. We also find a preferred symmetry plane at a P.A. of 36{sup 0}, which is perpendicular to the mean magnetic field direction (120{sup 0}) of the 0.5 pc dust ridge. Two possible interpretations of the origin of the observed magnetic field structure are discussed.

Tang, Ya-Wen; Ho, Paul T. P.; Koch, Patrick M.; Rao, Ramprasad, E-mail: ywtang@asiaa.sinica.edu.t [Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan (China)

2010-07-10

120

Stellar diameters and temperatures - VI. High angular resolution measurements of the transiting exoplanet host stars HD 189733 and HD 209458 and implications for models of cool dwarfs  

NASA Astrophysics Data System (ADS)

We present direct radii measurements of the well-known transiting exoplanet host stars HD 189733 and HD 209458 using the CHARA Array interferometer. We find the limb-darkened angular diameters to be ?LD = 0.3848 ± 0.0055 and 0.2254 ± 0.0072 mas for HD 189733 and HD 209458, respectively. HD 189733 and HD 209458 are currently the only two transiting exoplanet systems where detection of the respective planetary companion's orbital motion from high-resolution spectroscopy has revealed absolute masses for both star and planet. We use our new measurements together with the orbital information from radial velocity and photometric time series data, Hipparcos distances, and newly measured bolometric fluxes to determine the stellar effective temperatures (Teff = 4875 ± 43, 6092 ± 103 K), stellar linear radii (R* = 0.805 ± 0.016, 1.203 ± 0.061 R?), mean stellar densities (?* = 1.62 ± 0.11, 0.58 ± 0.14 ??), planetary radii (Rp = 1.216 ± 0.024, 1.451 ± 0.074 RJup), and mean planetary densities (?p = 0.605 ± 0.029, 0.196 ± 0.033 ?Jup) for HD 189733b and HD 209458b, respectively. The stellar parameters for HD 209458, an F9 dwarf, are consistent with indirect estimates derived from spectroscopic and evolutionary modelling. However, we find that models are unable to reproduce the observational results for the K2 dwarf, HD 189733. We show that, for stellar evolutionary models to match the observed stellar properties of HD 189733, adjustments lowering the solar-calibrated mixing-length parameter to ?MLT =1.34 need to be employed.

Boyajian, Tabetha; von Braun, Kaspar; Feiden, Gregory A.; Huber, Daniel; Basu, Sarbani; Demarque, Pierre; Fischer, Debra A.; Schaefer, Gail; Mann, Andrew W.; White, Timothy R.; Maestro, Vicente; Brewer, John; Lamell, C. Brooke; Spada, Federico; López-Morales, Mercedes; Ireland, Michael; Farrington, Chris; van Belle, Gerard T.; Kane, Stephen R.; Jones, Jeremy; ten Brummelaar, Theo A.; Ciardi, David R.; McAlister, Harold A.; Ridgway, Stephen; Goldfinger, P. J.; Turner, Nils H.; Sturmann, Laszlo

2015-02-01

121

Angular Momentum  

ERIC Educational Resources Information Center

The gyroscope in a smartphone was employed in a physics laboratory setting to verify the conservation of angular momentum and the nonconservation of rotational kinetic energy. As is well-known, smartphones are ubiquitous on college campuses. These devices have a panoply of built-in sensors. This creates a unique opportunity for a new paradigm in…

Shakur, Asif; Sinatra, Taylor

2013-01-01

122

Angular momentum  

NASA Astrophysics Data System (ADS)

The gyroscope in a smartphone was employed in a physics laboratory setting to verify the conservation of angular momentum and the nonconservation of rotational kinetic energy. As is well-known, smartphones are ubiquitous on college campuses. These devices have a panoply of built-in sensors. This creates a unique opportunity for a new paradigm in the physics laboratory. Many traditional physics experiments can now be performed very conveniently in a pedagogically enlightening environment while simultaneously reducing the laboratory budget substantially by using student-owned smartphones.

Shakur, Asif; Sinatra, Taylor

2013-12-01

123

Angular Measure  

NSDL National Science Digital Library

Students will learn about the Transit of Venus through reading a NASA press release and viewing a NASA eClips video that describes several ways to observe transits. Then students will study angular measurement by learning about parallax and how astronomers use this geometric effect to determine the distance to Venus during a Transit of Venus. This activity is part of the Space Math multimedia modules that integrate NASA press releases, NASA archival video, and mathematics problems targeted at specific math standards commonly encountered in middle school textbooks. The modules cover specific math topics at multiple levels of difficulty with real-world data and use the 5E instructional sequence.

124

Efficient parallel algorithm of second-order Møller-Plesset perturbation theory with resolution-of-identity approximation (RI-MP2)  

NASA Astrophysics Data System (ADS)

An efficient parallel algorithm is developed for second-order Møller-Plesset perturbation theory with the resolution-of-identity approximation of two-electron repulsion integrals (RI-MP2) to perform MP2 energy calculations of large molecules on distributed memory processors. Benchmark calculations are carried out for taxol (C47H51NO14), valinomycin (C54H90N6O18), and two-layer nanographene sheets (C96H24)2, which show the high parallel efficiency of the developed algorithm.

Katouda, Michio; Nagase, Shigeru

125

Linear-scaling self-consistent field calculations based on divide-and-conquer method using resolution-of-identity approximation on graphical processing units.  

PubMed

Graphical processing units (GPUs) are emerging in computational chemistry to include Hartree-Fock (HF) methods and electron-correlation theories. However, ab initio calculations of large molecules face technical difficulties such as slow memory access between central processing unit and GPU and other shortfalls of GPU memory. The divide-and-conquer (DC) method, which is a linear-scaling scheme that divides a total system into several fragments, could avoid these bottlenecks by separately solving local equations in individual fragments. In addition, the resolution-of-the-identity (RI) approximation enables an effective reduction in computational cost with respect to the GPU memory. The present study implemented the DC-RI-HF code on GPUs using math libraries, which guarantee compatibility with future development of the GPU architecture. Numerical applications confirmed that the present code using GPUs significantly accelerated the HF calculations while maintaining accuracy. © 2014 Wiley Periodicals, Inc. PMID:25392975

Yoshikawa, Takeshi; Nakai, Hiromi

2015-01-30

126

Minimum uncertainty measurements of angle and angular momentum.  

PubMed

We present an accurate description of the conjugate pair angle-angular momentum in terms of the exponential of the angle instead of the angle itself, which leads to dispersion as a natural measure of resolution. Intelligent states minimizing the uncertainty product under the constraint of a given uncertainty in angle or in angular momentum turn out to be given by Mathieu wave functions. We discuss Gaussian approximations to these optimal states in terms of von Mises distributions. The theory is successfully applied to the spatial degrees of freedom of a photon and verified in an experiment that employs computer-controlled spatial light modulators at both the state preparation and the analyzing stages. PMID:17280283

Hradil, Z; Rehácek, J; Bouchal, Z; Celechovský, R; Sánchez-Soto, L L

2006-12-15

127

The oceanic contribution to the Earth's seasonal angular momentum budget  

NASA Technical Reports Server (NTRS)

Seasonal variations in the speed of the Earth's rotation manifest themselves as fluctuations in the length of the day (LOD) with an amplitude of about 1000 microseconds. We know from previous work that at least 95% of these variations can be accounted for in terms of angular momentum exchanged between the atmosphere and the solid Earth. Here we examine the respective contributions of the Antarctic Circumpolar Current (ACC) and the global oceans to the Earth's seasonal angular momentum budget, using in situ data from the Drake Passage and results from both the oceanic regional model (Fine Resolution Antarctic Model -- FRAM) of Webb et al. (1991) and the global ocanic model of Maier-Reimer et al. (1993) as analyzed by Brosche et al. (1990). The estimated annual contribution of the ACC (2-4 microsec) is much smaller than the total variation in the oceanic models or the existing LOD-AAM residual (both approximately 15-20 microsec). The estimated semi-annual ACC contribution (3-8 microsec) is offset by counter-current further north in both oceanic models, which exhibit larger semi-annual variations in planetary angular momentum. Further refinements in the Earth's seasonal angular momentum budget, therefore, will require the full (planetary plus relative) contribution of the global oceans in addition to that of the ACC.

Dickey, J. O.; Marcus, S. L.; Johns, C. M.; Hide, R.; Thompson, S. R.

1993-01-01

128

THEORIES FOR ANGULAR DISTRIBUTIONS IN LOW ENERGY NUCLEAR REACTIONS  

Microsoft Academic Search

A series of six lectures presented at the Lawrence Radiation Laboratory ; on angular distributions in nuclear reactions are given. Topics covered include ; a survey of reaction mechanisms, Born approximation for direct interaction ; theory, semiclassical approximation for direct interaction, distorted wave ; analysis and direct surface interactions, the general theory of angular ; correlation, and interpretation of inelastic

S. A. Moszkowski; J. Benveniste; E. H. eds. Schwarcz

1962-01-01

129

On the interpretation of photonuclear angular distributions  

Microsoft Academic Search

Photonucleon angular distributions are calculated in the j-j coupling scheme for single-particle excitations. The electromagnetic interaction of the nucleus with the photon beam is treated in electric dipole and quadrupole absorption approximations. The general results allow the extraction of information about the one-particle-one-hole transition strengths from the experimentally-measured angular distributions. The importance of the coherent interference terms in the electric

David E. Frederick

1967-01-01

130

X-Ray Photoelectron Diffraction Studies of Surface Structure: Use of High-Angular Resolution, R-Factor Analysis, and Holography, with Applications to Carbon Monoxide on IRON(001) and to Oxygen and Sulfur on the NICKEL(001) Surface.  

NASA Astrophysics Data System (ADS)

This dissertation discusses the use of x-ray photoelectron diffraction (XPD) for elucidating the surface structure of several different types of chemisorption systems. The determination of the tilt angle and orientation of the alpha_3-state of CO on Fe(001) is particularly interesting since it could be a precursor state to atomic dissociation. A series of combined polar and azimuthal XPD scans was able to quickly determine that the CO molecule was indeed tilted by making use of the very strong intra-molecular electron forward scattering that permitted pinpointing the polar tilt angle and azimuthal orientation by simply sighting down the direction of the most intense photoelectron diffraction intensity. The study of c(2 times 2)S on Ni(001) represents the first use of higher angular resolution ( _sp{~}{<}{ +/-}1^circ) XPD and R-factor comparisons of experiment to theory for a very well-defined adsorbate system. This overlayer consists of an atomic adsorbate that sits rather high above the surface plane at z = ~1.3 A, and it is thus a challenging problem for forward-scattering-dominated XPD to resolve. The additional diffraction fine structure that appears in both the experimental and theoretical data, along with an R-factor analysis, illustrate the usefulness of this new direction and its potential for applications to a wide variety of systems. We also consider the possibility of holographically analyzing such XPD data using Fourier transform methods. These results are found to be encouraging, even for the limited experimental data set available here; theoretical simulations also suggest interesting directions for future study. Lastly, the determination of the various surface structures that appear on a clean Ni(001) surface upon its exposure to oxygen is investigated via a combined XPD/low energy electron diffraction (LEED) study. We conclude from our XPD data that oxide nucleation occurs quite early in the c(2 times 2)O chemisorption region and that this effect may have influenced prior studies of this structure. We have also discussed for the first time a NiO(001) superlattice that grows on the surface at saturation oxygen coverages; this is seen in our LEED results.

Saiki, Richard Shoichi

131

High-resolution STEM imaging with a quadrant detector-Conditions for differential phase contrast microscopy in the weak phase object approximation.  

PubMed

Differential phase contrast is a contrast mechanism that can be utilized in the scanning transmission electron microscope (STEM) to determine the distribution of magnetic or electric fields. In practice, several different detector geometries can be used to obtain differential phase contrast. As recent high resolution differential phase contrast experiments with the STEM are focused on ring quadrant detectors, we evaluate the contrast transfer characteristics of different quadrant detector geometries, namely two ring quadrant detectors with different inner detector angles and a conventional quadrant detector, by calculating the corresponding phase gradient transfer functions. For an ideal microscope and a weak phase object, this can be done analytically. The calculated phase gradient transfer functions indicate that the barely illuminated ring quadrant detector setup used for imaging magnetic fields in the specimen reduces the resolution limit to about 2.5? for an aberration corrected STEM. Our results show that the resolution can be drastically improved by using a conventional quadrant detector instead. PMID:25461584

Majert, S; Kohl, H

2015-01-01

132

Angular shear plate  

Microsoft Academic Search

One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative

Mitchell C. Ruda; Alan W. Greynolds; Tilman W. Stuhlinger

2009-01-01

133

Angular Acceleration without Torque?  

ERIC Educational Resources Information Center

Hardly. Just as Robert Johns qualitatively describes angular acceleration by an internal force in his article "Acceleration Without Force?" here we will extend the discussion to consider angular acceleration by an internal torque. As we will see, this internal torque is due to an internal force acting at a distance from an instantaneous center.

Kaufman, Richard D.

2012-01-01

134

Extended Limber Approximation  

E-print Network

We develop a systematic derivation for the Limber approximation to the angular cross-power spectrum of two random fields, as a series expansion in 1/(\\ell+1/2). This extended Limber approximation can be used to test the accuracy of the Limber approximation and to improve the rate of convergence at large \\ell's. We show that the error in ordinary Limber approximation is O(1/\\ell^2). We also provide a simple expression for the second order correction to the Limber formula, which improves the accuracy to O(1/\\ell^4). This correction can be especially useful for narrow redshift bins, or samples with small redshift overlap, for which the zeroth order Limber formula has a large error. We also point out that using \\ell instead of (\\ell+1/2), as is often done in the literature, spoils the accuracy of the approximation to O(1/\\ell).

Marilena LoVerde; Niayesh Afshordi

2008-09-30

135

Extended Limber Approximation  

E-print Network

We develop a systematic derivation for the Limber approximation to the angular cross-power spectrum of two random fields, as a series expansion in 1/(\\ell+1/2). This extended Limber approximation can be used to test the accuracy of the Limber approximation and to improve the rate of convergence at large \\ell's. We show that the error in ordinary Limber approximation is O(1/\\ell^2). We also provide a simple expression for the second order correction to the Limber formula, which improves the accuracy to O(1/\\ell^4). This correction can be especially useful for narrow redshift bins, or samples with small redshift overlap, for which the zeroth order Limber formula has a large error. We also point out that using \\ell instead of (\\ell+1/2), as is often done in the literature, spoils the accuracy of the approximation to O(1/\\ell).

LoVerde, Marilena

2008-01-01

136

Extended Limber approximation  

SciTech Connect

We develop a systematic derivation for the Limber approximation to the angular cross-power spectrum of two random fields, as a series expansion in (l+1/2){sup -1}. This extended Limber approximation can be used to test the accuracy of the Limber approximation and to improve the rate of convergence at large l's. We show that the error in ordinary Limber approximation is O(l{sup -2}). We also provide a simple expression for the 2nd order correction to the Limber formula, which improves the accuracy to O(l{sup -4}). This correction can be especially useful for narrow redshift bins, or samples with small redshift overlap, for which the 0th order Limber formula has a large error. We also point out that using l instead of l+1/2, as is often done in the literature, spoils the accuracy of the approximation to O(l{sup -1})

LoVerde, Marilena [Institute for Strings, Cosmology and Astro-particle Physics (ISCAP), Department of Physics, Columbia University, New York, New York 10027 (United States); Afshordi, Niayesh [Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, ON, N2L 2Y5 (Canada)

2008-12-15

137

Improving the resolution of chopper spectrometers at pulsed neutron sources  

SciTech Connect

We examine the relationships between intensity and resolution in pulsed-source chopper spectrometers, including the effects of Soller collimation, narrower rotor slits and higher rotor speeds. The basis is a simplified description of a spectrometer, approximately optimizing the rotor pulse and lighthouse effects. the analysis includes a new treatment of the angular distribution transmitted through a system consisting of a coarse collimator and a Soller collimator. The results encourage the prospect for a reasonably easily accomplished, higher resolution, optional configuration of the pulsed source chopper spectrometers at IPNS. 6 refs., 5 figs.

Carpenter, J.M. (Argonne National Lab., IL (USA)); Mildner, D.F.R. (National Bureau of Standards, Washington, DC (USA). Center for Analytical Chemistry)

1990-01-01

138

Predicting Stellar Angular Sizes  

E-print Network

Our survey of long-baseline infrared and optical interferometry measurements is producing considerable numbers of directly determined stellar angular sizes. We use our sample of 124 high-precision (5\\%) angular stellar diameter values and correlate them with stellar magnitude values from the literature to produce empirical relations for main-sequence stars between observed apparent magnitudes, stellar colors, and angular sizes (surface brightness relations). We find a significant dependence on stellar metallicity for ($B-V$) colors. The scatter in the calculated relations is small ($\\sim$5\\%), which makes them a robust tool for the prediction of main-sequence stellar angular sizes based on photometry. We apply these relations via the calculation of the radius of the multiplanet host star GJ 667C.

von Braun, Kaspar; van Belle, Gerard T

2013-01-01

139

Optical Broadband Angular Selectivity  

E-print Network

Light selection based purely on the angle of propagation is a long-standing scientific challenge. In angularly selective systems, however, the transmission of light usually also depends on the light frequency. We tailored ...

Shen, Yichen

140

Metamaterial broadband angular selectivity  

E-print Network

We demonstrate how broadband angular selectivity can be achieved with stacks of one-dimensionally periodic photonic crystals, each consisting of alternating isotropic layers and effective anisotropic layers, where each ...

Shen, Yichen

141

Angular velocity discrimination  

NASA Technical Reports Server (NTRS)

Three experiments designed to investigate the ability of naive observers to discriminate rotational velocities of two simultaneously viewed objects are described. Rotations are constrained to occur about the x and y axes, resulting in linear two-dimensional image trajectories. The results indicate that observers can discriminate angular velocities with a competence near that for linear velocities. However, perceived angular rate is influenced by structural aspects of the stimuli.

Kaiser, Mary K.

1990-01-01

142

The Angular Momentum Dichotomy  

NASA Astrophysics Data System (ADS)

In the context of the formation of spiral galaxies the evolution and distribution of the angular momentum of dark matter halos have been discussed for more than 20 years, especially the idea that the specific angular momentum of the halo can be estimated from the specific angular momentum of its disk (e.g. Fall & Efstathiou (1980), Fall (1983) and Mo et al. (1998)). We use a new set of hydrodynamic cosmological simulations called Magneticum Pathfinder which allow us to split the galaxies into spheroidal and disk galaxies via the circularity parameter ?, as commonly used (e.g. Scannapieco et al. (2008)). Here, we focus on the dimensionless spin parameter ? = J |E|1/2 / (G M5/2) (Peebles 1969, 1971), which is a measure of the rotation of the total halo and can be fitted by a lognormal distribution, e.g. Mo et al. (1998). The spin parameter allows one to compare the relative angular momentum of halos across different masses and different times. Fig. 1 reveals a dichotomy in the distribution of ? at all redshifts when the galaxies are split into spheroids (dashed) and disk galaxies (dash-dotted). The disk galaxies preferentially live in halos with slightly larger spin parameter compared to spheroidal galaxies. Thus, we see that the ? of the whole halo reflects the morphology of its central galaxy. For more details and a larger study of the angular momentum properties of disk and spheroidal galaxies, see Teklu et al. (in prep.).

Teklu, Adelheid; Remus, Rhea-Silvia; Dolag, Klaus; Burkert, Andreas

2015-02-01

143

Angular momentum radio  

NASA Astrophysics Data System (ADS)

Wireless communication amounts to encoding information onto physical observables carried by electromagnetic (EM) fields, radiating them into surrounding space, and detecting them remotely by an appropriate sensor connected to an informationdecoding receiver. Each observable is second order in the fields and fulfills a conservation law. In present-day radio only the EM linear momentum observable is fully exploited. A fundamental physical limitation of this observable, which represents the translational degrees of freedom of the charges (typically an oscillating current along a linear antenna) and the fields, is that it is single-mode. This means that a linear-momentum radio communication link comprising one transmitting and one receiving antenna, known as a single-input-single-output (SISO) link, can provide only one transmission channel per frequency (and polarization). In contrast, angular momentum, which represents the rotational degrees of freedom, is multi-mode, allowing an angular-momentum SISO link to accommodate an arbitrary number of independent transmission channels on one and the same frequency (and polarization). We describe the physical properties of EM angular momentum and how they can be exploited, discuss real-world experiments, and outline how the capacity of angular momentum links may be further enhanced by employing multi-port techniques, i.e., the angular momentum counterpart of linear-momentum multiple-input-multiple-output (MIMO).

Thidé, B.; Tamburini, F.; Then, H.; Someda, C. G.; Mari, Elletra; Parisi, G.; Spinello, F.; Romanato, Fra

2014-02-01

144

Creating High-Harmonic Beams with Controlled Orbital Angular Momentum  

NASA Astrophysics Data System (ADS)

A beam with an angular-dependant phase ? =?? about the beam axis carries an orbital angular momentum of ?? per photon. Such beams are exploited to provide superresolution in microscopy. Creating extreme ultraviolet or soft-x-ray beams with controllable orbital angular momentum is a critical step towards extending superresolution to much higher spatial resolution. We show that orbital angular momentum is conserved during high-harmonic generation. Experimentally, we use a fundamental beam with |?|=1 and interferometrically determine that the harmonics each have orbital angular momentum equal to their harmonic number. Theoretically, we show how any small value of orbital angular momentum can be coupled to any harmonic in a controlled manner. Our results open a route to microscopy on the molecular, or even submolecular, scale.

Gariepy, Genevieve; Leach, Jonathan; Kim, Kyung Taec; Hammond, T. J.; Frumker, E.; Boyd, Robert W.; Corkum, P. B.

2014-10-01

145

Creating high-harmonic beams with controlled orbital angular momentum.  

PubMed

A beam with an angular-dependant phase ? = ?? about the beam axis carries an orbital angular momentum of ?? per photon. Such beams are exploited to provide superresolution in microscopy. Creating extreme ultraviolet or soft-x-ray beams with controllable orbital angular momentum is a critical step towards extending superresolution to much higher spatial resolution. We show that orbital angular momentum is conserved during high-harmonic generation. Experimentally, we use a fundamental beam with |?| = 1 and interferometrically determine that the harmonics each have orbital angular momentum equal to their harmonic number. Theoretically, we show how any small value of orbital angular momentum can be coupled to any harmonic in a controlled manner. Our results open a route to microscopy on the molecular, or even submolecular, scale. PMID:25375710

Gariepy, Genevieve; Leach, Jonathan; Kim, Kyung Taec; Hammond, T J; Frumker, E; Boyd, Robert W; Corkum, P B

2014-10-10

146

Metamaterial broadband angular selectivity  

NASA Astrophysics Data System (ADS)

We demonstrate how broadband angular selectivity can be achieved with stacks of one-dimensionally periodic photonic crystals, each consisting of alternating isotropic layers and effective anisotropic layers, where each effective anisotropic layer is constructed from a multilayered metamaterial. We show that by simply changing the structure of the metamaterials, the selective angle can be tuned to a broad range of angles; and, by increasing the number of stacks, the angular transmission window can be made as narrow as desired. As a proof of principle, we realize the idea experimentally in the microwave regime. The angular selectivity and tunability we report here can have various applications such as in directional control of electromagnetic emitters and detectors.

Shen, Yichen; Ye, Dexin; Wang, Li; Celanovic, Ivan; Ran, Lixin; Joannopoulos, John D.; Solja?i?, Marin

2014-09-01

147

Angular shear plate  

SciTech Connect

One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.

Ruda, Mitchell C. (Tucson, AZ); Greynolds, Alan W. (Tucson, AZ); Stuhlinger, Tilman W. (Tucson, AZ)

2009-07-14

148

The High Resolution Array (HiRA).  

NASA Astrophysics Data System (ADS)

A new High Resolution Array (HiRA) is being constructed for experiments with rare isotope beams at the NSCL. It consists of twenty independent strip detector telescopes, which offer considerable flexibility in experimental setup. Each telescope is composed of two silicon strip detectors, 4 CsI(Tl) detectors and the necessary electronics, which includes a custom designed ASIC for the silicon strip detector readout. The thicknesses of the silicon detectors were selected to optimize the energy resolution for light particle detection over a wide range of particle energies. One of the silicon strip detectors is double-sided; the charge collected in orthogonal strips on opposite sides of this detector provide an x and y coordinate for each event in the telescope. The 1.9mm pitch in these detectors allows an approximate angular resolution of +/- .1 deg at a distance of 60cm. The silicon detectors are followed by 4 CsI(Th) scintillation detectors for detection of more energetic particles. High angular accuracy is needed for many proposed experiments with the array. This will be achieved with a semi-automated alignment procedure that utilizes a laser based optical triangulation sensor and precision stepper motor driven rotational stages.

Nett, B.; van Goethem; Lynch; Wallace; de Souza; Caraley; Davin; Viola; Alfaro-Molina; Hudan; Ryder; Yanez; Elson; Engel; Sobatka; Moroni

2002-10-01

149

Gears: Determining Angular Velocity  

NSDL National Science Digital Library

Students work as engineers and learn to conduct controlled experiments by changing one experimental variable at a time to study its effect on the experiment outcome. Specifically, they conduct experiments to determine the angular velocity for a gear train with varying gear ratios and lengths. Student groups assemble LEGO® MINDSTORMS® NXT robots with variously sized gears in a gear train and then design programs using the NXT software to cause the motor to rotate all the gears in the gear train. They use the LEGO data logging program and light sensors to set up experiments. They run the program with the motor and the light sensor at the same time and analyze the resulting plot in order to determine the angular velocity using the provided physics-based equations. Finally, students manipulate the gear train with different gears and different lengths in order to analyze all these factors and figure out which manipulation has a higher angular velocity. They use the equations for circumference of a circle and angular velocity; and convert units between radians and degrees.

AMPS GK-12 Program,

150

Angular momentum conservation demonstration  

NSDL National Science Digital Library

A short article describing the fabrication and operation of a simple angular momentum conservation demonstration. The demonstration is based on a Lazy Susan, and cylindrical brass weights tied with a nylon string. The string can be pulled or released changing the radius or rotation of the weights.

Berg, Richard E.; Anders, Robert E.

2010-12-23

151

Semiclassical complex angular momentum theory and Pade reconstruction for resonances, rainbows, and reaction thresholds  

SciTech Connect

A semiclassical complex angular momentum theory, used to analyze atom-diatom reactive angular distributions, is applied to several well-known potential (one-particle) problems. Examples include resonance scattering, rainbow scattering, and the Eckart threshold model. Pade reconstruction of the corresponding matrix elements from the values at physical (integral) angular momenta and properties of the Pade approximants are discussed in detail.

Sokolovski, D. [School of Mathematics and Physics, Queen's University of Belfast, Belfast, BT7 1NN (United Kingdom); Msezane, A.Z. [Department of Physics and Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta, Georgia 30314 (United States)

2004-09-01

152

High-resolution electron microscopy analysis of structural defects in a (2/1, 5/3)-type approximant of a decagonal quasicrystal of an Al-Pd-Mn alloy  

SciTech Connect

Structural defects were analyzed by means of high-resolution electron microscopy (HREM) in a crystalline (2/1, 5/3)-type Fibonacci approximant of an Al-Pd-Mn alloy system. A kind of stacking fault is observed with a projected displacement vector R parallel to the [{minus}3 0 29] direction; its amplitude {vert_bar}R{vert_bar} = 2a sin 18 deg = 1.19 nm, and its habit plane lies in the (1 0 1) plane. Two kinds of domain boundaries have been found and the domains are related by a 180 deg rotation around the c-axis plus a displacement along the [3 0 {minus}29] or the [{minus}3 0 {minus}29] direction in a plane perpendicular to the b-axis. The domain boundary planes are the {l_brace}1 0 1{r_brace} planes.

Yu, D.P.; Ren, G.; Zhang, Z. [Chinese Academy of Sciences, Beijing (China). Beijing Lab. of Electron Microscopy

1996-10-01

153

Equal-channel angular extrusion of beryllium  

Microsoft Academic Search

The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P\\/M) source Be alloy. Extrusions\\u000a have been successfully completed on Ni-canned billets of Be at approximately 425?C. No cracking was observed in the billets,\\u000a and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed\\u000a for a singlepass extrusion, including evidence of

R. D. Field; K. T. Hartwig; C. T. Necker; J. F. Bingert; S. R. Agnew

2002-01-01

154

Approximate resolution of hard numbering problems  

SciTech Connect

We present a new method for estimating the number of solutions of constraint satisfaction problems. We use a stochastic forward checking algorithm for drawing a sample of paths from a search tree. With this sample, we compute two values related to the number of solutions of a CSP instance. First, an unbiased estimate, second, a lower bound with an arbitrary low error probability. We will describe applications to the Boolean Satisfiability problem and the Queens problem. We shall give some experimental results for these problems.

Bailleux, O.; Chabrier, J.J. [CRID Universite de Bourgogne, Dijon (France)

1996-12-31

155

Nuclear Level Density with Non-zero Angular Momentum  

NASA Astrophysics Data System (ADS)

The statistical properties of interacting fermions have been studied for various angular momentum with the inclusion of pairing interaction. The dependence of the critical temperature on angular momentum for several nuclei, have been studied. The yrast energy as a function of angular momentum for 28Si and 24Mg nuclei have been calculated up to 60.0 MeV of excitation energy. The computed limiting angular momenta are compared with the experimental results for 26Al produced by 12C+14N reaction. The relevant nuclear level densities for non-zero angular momentum have been computed for 44Ti and 136Ba nuclei. The results are compared with their corresponding values obtained from the approximate formulas.

A. N., Behkami; Gholami, M.; Kildir, M.; Soltani, M.

2006-09-01

156

Precompound nucleon angular distributions in the continuum  

SciTech Connect

Angular distributions for nucleon induced reactions (incident energies 14 to 90 MeV) leading to precompound nucleon emission in the continuum (emitted particle energies 9-70 MeV) are calculated based on nucleon-nucleon scattering kinematics for an incident nucleon on a Fermi gas. Analytic expressions due to Kikuchi and Kawai are used for the single scattering kernel. The geometry dependent hybrid model is used to generate the differential cross sections for first, second, etc. order scattering, these weightings being used to fold the single scattering kernel. Results are found to reproduce all experimental angular distributions quite well at angles in the 20/sup 0/ to 90/sup 0/ range. Ad-hoc modifications to approximate quantal effects and Coulomb deflections are explored, but the results do not seem to offer a consistent means of reproducing back angle yields, and give generally poorer results at very forward angles.

Blann, M.; Scobel, W.; Plechaty, E.

1985-08-01

157

A Discrimination Procedure between Muon and Electron in Superkamiokande Experiment Based on the Angular Distribution Function Method  

E-print Network

In the previous paper, we construct the angular distribution functions for muon and electron as well as their relative fluctuation functions to find suitable discrimination procedure between muon and electron in Superkamiokande experiment. In the present paper, we are able to discriminate muons from electrons in Fully Contained Events with a probability of error of less than several %. At the same time, our geometrical reconstruction procedure, considering only the ring-like structure of the Cherenkov image, gives an unsatisfactory resolution for 1GeV electron and muon, with a mean vertex position error, delta r, of 5-10 m and a mean directional error, delta theta, of about 6-20 degrees. In contrast, a geometrical reconstruction procedure utilizing the full image and using a detailed approximation of the event angular distribution works much better: for a 1 GeV electron, delta r is about 2 m and delta theta is about 3 degrees; for a 1GeV muon, delta r is about 3 m and delta theta is about 5 degrees. At 5 GeV, the corresponding values are about 1.4 m and about 2 degree for electron and are about 2.9m and about 4.3 degrees for muon. The numerical values depend on a single PMT contribution threshold. The values quoted above are the minima with respect to this threshold. Even the methodologically correct approach we have adopted, based on detailed simulations using closer approximations than those adopted in the SK analysis, cannot reproduce the accuracies for particle discrimination, momentum resolution, interaction vertex location, and angular resolution obtained by the SK simulations, suggesting the assumptions in these may be inadequate.

V. I. Galkin[1; A. M. Anokhina[1; E. Konishi[2; A. Misaki{3

2005-01-21

158

Supersensitive measurement of angular displacements using entangled photons  

SciTech Connect

We show that the use of path-entangled states of photons, having nonzero orbital angular momentum (OAM), increases the resolution and sensitivity of angular-displacement measurements performed using an interferometer. In the ideal case of maximally path-entangled states, the resolution of angular-displacement measurements increases by a factor of Nl, while the uncertainty in the measurement of angular displacements scales as 1/Nl, where N is the number of entangled photons, half of which carry, on average, an OAM of +l({h_bar}/2{pi}) per photon and the other half carry an OAM of -l({h_bar}/2{pi}) per photon. We analyze measurement schemes for two- and four-photon entangled states produced by parametric down-conversion and, by employing a 4x4 matrix formalism to study the propagation of entangled OAM modes, obtain explicit expressions for the resolution and sensitivity in these schemes. These results constitute an improvement over what could be obtained with N nonentangled photons carrying an orbital angular momentum of |l|({h_bar}/2{pi}) per photon.

Jha, Anand Kumar; Boyd, Robert W. [The Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Agarwal, Girish S. [Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078 (United States)

2011-05-15

159

Approximating pi  

NSDL National Science Digital Library

This web page features mathematical information about Archimedes' successful approach to finding an approximation to pi and an interactive manipulative that replicates the approach. The user can approximate pi as a number between the lengths of the perimeters of two polygons, one inscribed inside a circle and one circumscribed around the circle. The number of sides for the polygons may be increased to 96 with the value for pi always being between the two approximations. Similarities and differences between Archimedes' approach and the manipulative's approach are noted. The page is part of a NOVA web site that describes the discovery of the Archimedes palimpsest and examines the mathematical and philosophical meanings of infinity. Copyright 2005 Eisenhower National Clearinghouse

British Broadcasting Corporation (BBC)

2003-01-01

160

On spectral approximations in elliptical geometries using Mathieu functions  

NASA Astrophysics Data System (ADS)

We consider in this paper approximation properties and applications of Mathieu functions. A first set of optimal error estimates are derived for the approximation of periodic functions by using angular Mathieu functions. These approximation results are applied to study the Mathieu-Legendre approximation to the modified Helmholtz equation and Helmholtz equation. Illustrative numerical results consistent with the theoretical analysis are also presented.

Shen, Jie; Wang, Li-Lian

2009-06-01

161

Wissenschaftliches Approximation  

E-print Network

' am Digitalcomputer Archimedes und die Berechnung von = 3.14159 . . . Das leidige Integral Das Einleitung: `Alles ist Zahl' am Digitalcomputer Archimedes und die Berechnung von = 3.14159 . . . Das Approximation als SparmaÃ?nahme Anhang Ã?berblick Einleitung: `Alles ist Zahl' am Digitalcomputer Archimedes und

Auzinger, Winfried

162

The angular momentum of baryons and dark matter halos revisited  

Microsoft Academic Search

Recent theoretical studies have shown that galaxies at high redshift are fed by cold, dense gas filaments, suggesting angular momentum transport by gas differs from that by dark matter. Revisiting this issue using high-resolution cosmological hydrodynamics simulations with adaptive mesh refinement, we find that at the time of accretion, gas and dark matter do carry a similar amount of specific

Taysun Kimm; Julien Devriendt; Adrianne Slyz; Christophe Pichon; Susan A. Kassin; Yohan Dubois

2011-01-01

163

Intrinsic Angular Momentum of Light.  

ERIC Educational Resources Information Center

Derives a familiar torque-angular momentum theorem for the electromagnetic field, and includes the intrinsic torques exerted by the fields on the polarized medium. This inclusion leads to the expressions for the intrinsic angular momentum carried by the radiation traveling through a charge-free medium. (Author/MA)

Santarelli, Vincent

1979-01-01

164

Angular momentum in human walking  

Microsoft Academic Search

SUMMARY Angular momentum is a conserved physical quantity for isolated systems where no external moments act about a body?s center of mass (CM). However, in the case of legged locomotion, where the body interacts with the environment (ground reaction forces), there is no a priori reason for this relationship to hold. A key hypothesis in this paper is that angular

Hugh Herr; Marko Popovic

2008-01-01

165

The Angular Gyrus  

PubMed Central

There is considerable interest in the structural and functional properties of the angular gyrus (AG). Located in the posterior part of the inferior parietal lobule, the AG has been shown in numerous meta-analysis reviews to be consistently activated in a variety of tasks. This review discusses the involvement of the AG in semantic processing, word reading and comprehension, number processing, default mode network, memory retrieval, attention and spatial cognition, reasoning, and social cognition. This large functional neuroimaging literature depicts a major role for the AG in processing concepts rather than percepts when interfacing perception-to-recognition-to-action. More specifically, the AG emerges as a cross-modal hub where converging multisensory information is combined and integrated to comprehend and give sense to events, manipulate mental representations, solve familiar problems, and reorient attention to relevant information. In addition, this review discusses recent findings that point to the existence of multiple subdivisions in the AG. This spatial parcellation can serve as a framework for reporting AG activations with greater definition. This review also acknowledges that the role of the AG cannot comprehensibly be identified in isolation but needs to be understood in parallel with the influence from other regions. Several interesting questions that warrant further investigations are finally emphasized. PMID:22547530

2013-01-01

166

Sub-micron resolution selected area electron channeling patterns.  

PubMed

Collection of selected area channeling patterns (SACPs) on a high resolution FEG-SEM is essential to carry out quantitative electron channeling contrast imaging (ECCI) studies, as it facilitates accurate determination of the crystal plane normal with respect to the incident beam direction and thus allows control the electron channeling conditions. Unfortunately commercial SACP modes developed in the past were limited in spatial resolution and are often no longer offered. In this contribution we present a novel approach for collecting high resolution SACPs (HR-SACPs) developed on a Gemini column. This HR-SACP technique combines the first demonstrated sub-micron spatial resolution with high angular accuracy of about 0.1°, at a convenient working distance of 10mm. This innovative approach integrates the use of aperture alignment coils to rock the beam with a digitally calibrated beam shift procedure to ensure the rocking beam is maintained on a point of interest. Moreover a new methodology to accurately measure SACP spatial resolution is proposed. While column considerations limit the rocking angle to 4°, this range is adequate to index the HR-SACP in conjunction with the pattern simulated from the approximate orientation deduced by EBSD. This new technique facilitates Accurate ECCI (A-ECCI) studies from very fine grained and/or highly strained materials. It offers also new insights for developing HR-SACP modes on new generation high-resolution electron columns. PMID:25436927

Guyon, J; Mansour, H; Gey, N; Crimp, M A; Chalal, S; Maloufi, N

2015-02-01

167

Angular Size Test on the Expansion of the Universe  

Microsoft Academic Search

Assuming the standard cosmological model to be correct, the average linear size of the galaxies with the same luminosity is six times smaller at z = 3.2 than at z = 0; and their average angular size for a given luminosity is approximately proportional to z-1. Neither the hypothesis that galaxies which formed earlier have much higher densities nor their

Martín López-Corredoira

2010-01-01

168

Extending the Eikonal Approximation to Low Energy  

E-print Network

E-CDCC and DEA, two eikonal-based reaction models are compared to CDCC at low energy (e.g. 20AMeV) to study their behaviour in the regime at which the eikonal approximation is supposed to fail. We confirm that these models lack the Coulomb deflection of the projectile by the target. We show that a hybrid model, built on the CDCC framework at low angular momenta and the eikonal approximation at larger angular momenta gives a perfect agreement with CDCC. An empirical shift in impact parameter can also be used reliably to simulate this missing Coulomb deflection.

Pierre Capel; Tokuro Fukui; Kazuyuki Ogata

2014-11-21

169

Lightweight and High Angular Resolution X-Ray Optics  

NASA Technical Reports Server (NTRS)

The International X-ray Observatory (IXO) mission requires a lightweight and high throughput spectroscopic telescope. The fabrication, alignment, and integration of this mirror assembly require breakthroughs in many areas. In this paper we report on our recent progress in all these areas, including mirror fabrication, coating, metrology, alignment, mechanical characteristics, and their integration into mirror modules. In particular, we will also outline our plan for the next few of years, showing approaches that will progress toward reaching the 5' HPD requirement.

Zhang, William

2008-01-01

170

Lightweight and High Angular Resolution X-Ray Optics  

NASA Technical Reports Server (NTRS)

The International X-ray Observatory (IXO) mission requires a lightweight and high throughput spectroscopic telescope. The fabrication, alignment, and integration of this mirror assembly require breakthroughs in many areas. In this paper we report on our recent progress in all these areas, including mirror fabrication, coating, metrology, alignment, mechanical characteristics, and their integration into mirror modules. In particular, we will also outline our plan for the next few of years, showing approaches that will progress toward reaching the 5" HPD requirement.

Zhang, William W.

2009-01-01

171

High-angular resolution observations of the Pistol Star  

E-print Network

First results of near-IR adaptive optics (AO)-assisted imaging, interferometry, and spectroscopy of this Luminous Blue Variable (LBV) are presented. They suggest that the Pistol Star is at least double. If the association is physical, it would reinforce questions concerning the importance of multiplicity for the formation and evolution of extremely massive stars.

Martayan, Christophe; Bouquin, Jean-Baptiste Le; Merand, Antoine; Montagnier, Guillaume; Selman, Fernando; Girard, Julien; Fox, Andrew; Baade, Dietrich; Fremat, Yves; Lobel, Alex; Martins, Fabrice; Patru, Fabien; Rivinius, Thomas; Sana, Hugues; Stefl, Stan; Zorec, Jean; Semaan, Thierry

2010-01-01

172

"High Angular Resolution Observations of Protoplanetary Disks with Adaptive Optics"  

NASA Technical Reports Server (NTRS)

Significant results were obtained and published in the literature. The first optical detection of a circumbinary disk was reported in the ApJ at millimetric wavelengths. The size and inclination of this disk were found to be consistent with millimetric observations. Evidence was found for a cavity inside the disk as theory predicts from dust clearing by the stellar companion.

Roddier, Francois

1999-01-01

173

Photoelectron spectrometer for high-resolution angular resolved studies  

SciTech Connect

We report on a new electron spectrometer system designed for use on storage-ring light sources. The system features a large (76 cm dia. x 92 cm long) triply magnetically shielded vacuum chamber and two 10.2 cm mean radius hemispherical electron-energy analyzers. One of the analyzers is fixed and the other is rotatable through about 150/sup 0/. The chamber is pumped by a cryopump and a turbomolecular pump combination so as to enable experiments with a variety of gases under different conditions. The light detection includes both a direct beam monitor and polarization analyzer. The electron detection is accomplished with either a continuous-channel electron multiplier or with multichannel arrays used as area detectors.

Parr, A.C.; Southworth, S.H.; Dehmer, J.L.; Holland, D.M.P.

1982-01-01

174

Progress toward light weight high angular resolution multilayer coated optics  

SciTech Connect

We have been working on 3 separate projects that together will give us the ability to make 1 arc second, light weight Wolter I optics that work above 40 keV. The three separate tasks are: (a) plasma spraying of metal-coated micro-balloons; (b) coating of the inside of Wolter I mirrors, (c) actuator designs for improving figure quality. We give a progress report on our work on all three areas. In summary, for future space missions it will be desirable for them to be affordable by reducing mass, keeping the focal length manageable, and yet having high figure quality. The avenues we have described above are straight forward paths to achieving this goal, but a great deal of work needs to be done to take us from the concept stage to a functional system.

Ulmer, M.P.; Graham, M.E.; Vaynman, S.; Echt, J.; Farber, M.; Ehlert, S.; Varlese, S. (NWU); (Ball Aero. & Tech.)

2008-11-18

175

An Acousto-Optical Sensor with High Angular Resolution  

PubMed Central

The paper introduces a new laser interferometry-based sensor for diagnosis of random media by means of high accuracy angle measurements and describes the results of its development and testing. Theoretical calculations of the dependence of the range of the laser interferometer on laser beam parameters, device geometry, and atmospheric turbulence characteristics are reported. It is demonstrated that at moderate turbulence intensities corresponding to those observed most frequently in turbulent atmosphere at moderate latitudes and with low interference contrast values, the performance range of the laser interferometer-based device exceeds 5 km. PMID:22737034

Kaloshin, Gennady; Lukin, Igor

2012-01-01

176

Aldebaran's angular diameter: How well do we know it?  

NASA Astrophysics Data System (ADS)

The bright, well-known K5 giant Aldebaran, ? Tau, is probably the star with the largest number of direct angular diameter determinations, achieved over a long time by several authors using various techniques. In spite of this wealth of data, or perhaps as a direct result of it, there is not a very good agreement on a single angular diameter value. This is particularly unsettling if one considers that Aldebaran is also used as a primary calibrator for some angular resolution methods, notably for optical and infrared long baseline interferometry. Directly connected to Aldebaran's angular diameter and its uncertainties is its effective temperature, which also has been used for several empirical calibrations. Among the proposed explanations for the elusiveness of an accurate determination of the angular diameter of Aldebaran are the possibility of temporal variations as well as a possible dependence of the angular diameter on the wavelength. We present here a few, very accurate new determinations obtained by means of lunar occultations and long baseline interferometry. We derive an average value of 19.96±0.03 milliarcsec for the uniform disk diameter. The corresponding limb-darkened value is 20.58±0.03 milliarcsec, or 44.2±0.9 R?. We discuss this result, in connection with previous determinations and with possible problems that may affect such measurements. Based on observations collected at TIRGO (Gornergrat, Switzerland). TIRGO is operated by CNR - CAISMI Arcetri, Italy.

Richichi, A.; Roccatagliata, V.

2005-04-01

177

Angular correlations of galaxy distribution  

E-print Network

We study the angular correlations of various galaxy catalogs (CfA1, SSRS1, Perseus-Pisces, APM Bright Galaxies and Zwicky). We find that the angular correlation exponent is $\\gamma_a= 0.1 \\pm 0.1$ rather than $\\gamma_a=0.7$ as usually found by the standard correlation function $\\omega(\\theta)$. We identify the problem in the artificial decay of $\\omega(\\theta)$. Moreover we find that no characteristic angular scale is present in any of the analyzed catalogs. Finally we show that all the available data are consistent with each other and the angular distribution of galaxies is quite naturally compatible with a fractal structure with $D \\approx 2$.

M. Montuori; F. Sylos-Labini

1997-06-30

178

Transverse angular momentum of photons  

NASA Astrophysics Data System (ADS)

We develop the quantum theory of transverse angular momentum of light beams. The theory applies to paraxial and quasiparaxial photon beams in vacuum and reproduces the known results for classical beams when applied to coherent states of the field. Both the Poynting vector, alias the linear momentum, and the angular-momentum quantum operators of a light beam are calculated including contributions from first-order transverse derivatives. This permits a correct description of the energy flow in the beam and the natural emergence of both the spin and the angular momentum of the photons. We show that for collimated beams of light, orbital angular-momentum operators do not satisfy the standard commutation rules. Finally, we discuss the application of our theory to some concrete cases.

Aiello, Andrea; Marquardt, Christoph; Leuchs, Gerd

2010-05-01

179

Estimates of mass and angular momentum in the oort cloud.  

PubMed

Estimates can be made of unseen mass (in the form of cometary nuclei) at the heliocentric distances between 3 x 10(3) and 2 x 10(4) astronomical units(AU) under the assumptions (i) that the Oort cloud is a rarefied halo surrounding the core (dense, inner cometary cloud) and (ii) that the mass and albedo of comet Halley is typical for comets both in the core and the Oort cloud populations. The mass appears to be approximately 0.03 solar masses, with angular momentum of the order of 10(52) to 10(53) g-cm(2)/s. This mass is of the order of the total mass of the planetary system before the loss of volatiles. This leads to an estimate of a mass M(o) approximately 100 M( plus sign in circle) (where M( plus sign in circle) is the mass of Earth) concentrated in the Oort cloud (r > 2 x 10(4) AU) with an angular momentum that may exceed the present angular momentum of the whole planetary system by one order of magnitude. The present angular momentum of the Oort cloud appears to be of the same order as the total angular momentum of the planetary system before the loss of volatiles. PMID:17815893

Marochnik, L S; Mukhin, L M; Sagdeev, R Z

1988-10-28

180

An optimal estimator for the CMB-LSS angular power spectrum and its application to WMAP and NVSS data  

NASA Astrophysics Data System (ADS)

We use a quadratic maximum likelihood (QML) method to estimate the angular power spectrum of the cross-correlation between cosmic microwave background and large-scale structure maps as well as their individual auto-spectra. We describe our implementation of this method and demonstrate its accuracy on simulated maps. We apply this optimal estimator to Wilkinson Microwave Anisotropy Probe (WMAP) 7-yr and National Radio Astronomical Observatory (NRAO) Very Large Array Sky Survey (NVSS) data and explore the robustness of the angular power spectrum estimates obtained by the QML method. With the correction of the declination systematics in NVSS, we can safely use most of the information contained in this survey. We then make use of the angular power spectrum estimates obtained by the QML method to derive constraints on the dark energy critical density in a flat ? cold dark matter model by different likelihood prescriptions. When using just the cross-correlation between WMAP 7-yr and NVSS maps with 1°.8 resolution, the best-fitting model has a cosmological constant of approximately 70 per cent of the total energy density, disfavouring an Einstein-de sitter universe at more than 2? confidence level.

Schiavon, F.; Finelli, F.; Gruppuso, A.; Marcos-Caballero, A.; Vielva, P.; Crittenden, R. G.; Barreiro, R. B.; Martínez-González, E.

2012-12-01

181

A sparse sampling strategy for angular superresolution of real beam scanning radar  

NASA Astrophysics Data System (ADS)

This paper investigates techniques for angular superresolution using limited data of real beam scanning radar (RBSR). In order to improve the angular resolution of RBSR, many algorithms have been proposed. However, for most algorithms, large amounts of sampling data is necessary. The requirement of data increases the burden of the radar system. Fortunately, the sparse signal reconstruction techniques provide a new train of thought for us. It has been proved in array signal processing and image processing that the techniques only need limited sampling data to realize DOA estimation and image superresolution. This paper describes the sparse sampling model of RBSR as an underdetermined equation-solving problem, the received signals are sparsely recovered in target domain. Two algorithms, including smooth approximation algorithm and focal underdetermined system solver (FOCUSS), based on different optimization ideas, are adopted to solve the problem. Simulation results show that compressive sampling methods can recover the target domain accurately, especially under the condition of high signal-to-noise ratio (SNR).

Zhang, Yin; Wu, Junjie; Yang, Jianyu

2014-12-01

182

Angular Diameters of O- and B-type Stars  

NASA Astrophysics Data System (ADS)

We are observing a sample of 10 O-type stars and 60 B-type stars to determine angular diameters using the Center for High Angular Resolution Astronomy (CHARA) Array, the foremost optical long baseline interferometer in the world. Our goal is to establish accurate stellar parameters to test modern theories of stellar evolution that include rotation. We will combine our stellar angular diameter measurements with flux and line measurements from spectroscopy, projected rotational velocities, and distances to determine radius, effective temperature, luminosity, equatorial rotational velocity, and evolutionary mass. Knowing these properties will allow us to place the stars in a Hertzsprung-Russell diagram and obtain estimates for the age and evolutionary state.

Gordon, Kathryn; Gies, Douglas; Schaefer, Gail

2015-01-01

183

Variations in atmospheric angular momentum  

NASA Technical Reports Server (NTRS)

Twice-daily values of the atmosphere's angular momentum about the polar axis during the five years from 1976 through 1980 are presented in graphs and a table. The compilation is based on a global data set, incorporating 90 percent of the mass of the atmosphere. The relationship between changes in the angular momentum of the atmosphere and changes in the length of day is described, as are the main sources of error in the data. The variability in angular momentum is revealed in a preliminary fashion by means of a spectral decomposition. The data presented should stimulate comparisons with other measures of the length of day and so provide a basis for greater understanding of Earth-atmosphere interactions.

Rosen, R. D.; Salstein, D. A.

1981-01-01

184

Angular distribution of Auger electrons due to 3d-shell impact ionization of krypton  

NASA Technical Reports Server (NTRS)

Cross sections for electron impact ionization of krypton due to ejection of a 3d-shell electron have been calculated using screened hydrogenic and Hartree-Slater wavefunctions for the target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3d electrons, are widely different in the two approximations. The angular distribution due to the Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

Omidvar, K.

1977-01-01

185

Angular distribution of Auger electrons due to 3d-shell ionization of krypton  

NASA Technical Reports Server (NTRS)

Cross sections for electron impact ionization of krypton due to ejection of a 3rd shell electron have been calculated using screened hydrogenic and Hartree-Slater wave functions for target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3rd electrons, is widely different in the two approximations. The angular distribution due to Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

Omidvar, K.

1977-01-01

186

Angular momentum in QGP holography  

NASA Astrophysics Data System (ADS)

The quark chemical potential is one of the fundamental parameters describing the quark-gluon plasma produced by sufficiently energetic heavy-ion collisions. It is not large at the extremely high temperatures probed by the LHC, but it plays a key role in discussions of the beam energy scan programmes at the RHIC and other facilities. On the other hand, collisions at such energies typically (that is, in peripheral collisions) give rise to very high values of the angular momentum density. Here we explain that holographic estimates of the quark chemical potential of a rotating sample of plasma can be very considerably improved by taking the angular momentum into account.

McInnes, Brett

2014-10-01

187

RIS-M-2426 RESOLUTION IN DIFFRACTION  

E-print Network

RISÃ?-M-2426 RESOLUTION IN DIFFRACTION An Outline of the Method of Conjugate Diameters. Lecture-plane resolution of a diffraction apparatus is discussed in the Gaussian approximation. This approximation with the general problem of resolution in a diffraction experiment. The approach taken here builds on the method

188

Higher order treatment on temporal derivative of angular flux for time-dependent MOC  

SciTech Connect

A new kinetic analysis method, whose angular dependence of temporal derivative for angular flux is accurately treated within practical memory requirement, is proposed. The method of characteristics (MOC) is being widely used for reactor analysis thanks to the advances of numerical algorithms and computer hardware. However, the computational resources, i.e., the memory capacity, can be still a crucial problem for rigorous kinetic calculations using MOC. In the straightforward approach for kinetic calculation using MOC, the segment-averaged angular fluxes should be stored on the memory in order to explicitly calculate the temporal derivative of the angular flux, which would require huge memory. Thus, in the conventional kinetic calculation code using MOC, the temporal derivative of the angular flux has been approximated as angularly isotropic in order to reduce the memory requirement (isotropic assumption). However, the approximation error caused by the conventional isotropic assumption has not been thoroughly and quantitatively investigated so far and an accurate kinetic calculation method, which can quantitatively estimate the above approximation error within practical memory storage, has not been developed. The present study tries to address this issue with a newly developed approach. Effect of the approximate treatment for the temporal derivative of angular flux is evaluated through benchmark calculations. (authors)

Tsujita, K.; Endo, T.; Yamamoto, A. [Nagoya University, Department of Material, Physics and Energy Engineering, Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan); Kamiyama, Y.; Kirimura, K. [Mitsubishi Heavy Industries, Ltd., Wadasakicho1-1-1, Hyogo-ku, Kobe, 652-8585 (Japan)

2013-07-01

189

The Angular Momentum of Baryons and Dark Matter Halos Revisited  

NASA Technical Reports Server (NTRS)

Recent theoretical studies have shown that galaxies at high redshift are fed by cold, dense gas filaments, suggesting angular momentum transport by gas differs from that by dark matter. Revisiting this issue using high-resolution cosmological hydrodynamics simulations with adaptive-mesh refinement (AMR), we find that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum, but that it is systematically higher than that of the dark matter halo as a whole. At high redshift, freshly accreted gas rapidly streams into the central region of the halo, directly depositing this large amount of angular momentum within a sphere of radius r = 0.1R(sub vir). In contrast, dark matter particles pass through the central region unscathed, and a fraction of them ends up populating the outer regions of the halo (r/R(sub vir) > 0.1), redistributing angular momentum in the process. As a result, large-scale motions of the cosmic web have to be considered as the origin of gas angular momentum rather than its virialised dark matter halo host. This generic result holds for halos of all masses at all redshifts, as radiative cooling ensures that a significant fraction of baryons remain trapped at the centre of the halos. Despite this injection of angular momentum enriched gas, we predict an amount for stellar discs which is in fair agreement with observations at z=0. This arises because the total specific angular momentum of the baryons (gas and stars) remains close to that of dark matter halos. Indeed, our simulations indicate that any differential loss of angular momentum amplitude between the two components is minor even though dark matter halos continuously lose between half and two-thirds of their specific angular momentum modulus as they evolve. In light of our results, a substantial revision of the standard theory of disc formation seems to be required. We propose a new scenario where gas efficiently carries the angular momentum generated by large-scale structure motions deep inside dark matter halos, redistributing it only in the vicinity of the disc.

Kimm, Taysun; Devriendt, Julien; Slyz, Adrianne; Pichon, Christophe; Kassin, Susan A.; Dubois, Yohan

2011-01-01

190

Gamma-neutrino angular correlations in muon capture.  

NASA Technical Reports Server (NTRS)

Using a high-resolution Ge(Li) spectrometer, it proved possible to observe several Doppler-broadened gamma-ray transitions in Al-28 excited by muon capture in Si-28. Several of these transitions are shown to be suitable for analysis in terms of angular correlations between the neutrino and a deexcitation nuclear gamma-ray. The observed transitions are interpreted in terms of gamma-neutrino correlation coefficients which are functions of the weak-interaction coupling constants.

Miller, G. H.; Kane, F. R.; Martin, P.; Welsh, R. E.; Eckhause, M.

1972-01-01

191

Noncontact measurement of angular deflection  

NASA Technical Reports Server (NTRS)

Technique for measuring instantaneous angular deflection of object requires no physical contact. Technique utilizes two flat refractors, converging lens, and different photocell. Distinction of method is its combination of optical and electromechanical components into feedback system in which measurement error is made to approach zero. Application is foreseen in measurement of torsional strain.

Bryant, E. L.

1978-01-01

192

Angular size test on the expansion of the Universe  

Microsoft Academic Search

Assuming the standard cosmological model as correct, the average linear size\\u000aof galaxies with the same luminosity is six times smaller at z=3.2 than at z=0,\\u000aand their average angular size for a given luminosity is approximately\\u000aproportional to 1\\/z. Neither the hypothesis that galaxies which formed earlier\\u000ahave much higher densities nor their luminosity evolution, mergers ratio, or\\u000amassive

Martin Lopez-Corredoira

2010-01-01

193

Achromatic orbital angular momentum generator  

NASA Astrophysics Data System (ADS)

We describe a novel approach for generating light beams that carry orbital angular momentum (OAM) by means of total internal reflection in an isotropic medium. A continuous space-varying cylindrically symmetric reflector, in the form of two glued hollow axicons, is used to introduce a nonuniform rotation of polarization into a linearly polarized input beam. This device acts as a full spin-to-orbital angular momentum convertor. It functions by switching the helicity of the incoming beam?s polarization, and by conservation of total angular momentum thereby generates a well-defined value of OAM. Our device is broadband, since the phase shift due to total internal reflection is nearly independent of wavelength. We verify the broad-band behaviour by measuring the conversion efficiency of the device for three different wavelengths corresponding to the RGB colours, red, green and blue. An average conversion efficiency of 95% for these three different wavelengths is observed. This device may find applications in imaging from micro- to astronomical systems where a white vortex beam is needed.

Bouchard, Frédéric; Mand, Harjaspreet; Mirhosseini, Mohammad; Karimi, Ebrahim; Boyd, Robert W.

2014-12-01

194

Asteroid orbit fitting with radar and angular observations  

NASA Astrophysics Data System (ADS)

The asteroid orbit fitting problem using their radar and angular observations has been considered. The problem was solved in a standanrd way by means of minimization of weighted sum of squares of residuals. In the orbit fitting both kinds of radar observa-tions have been used: the observations of time delays and of Doppler frequency shifts. The weight for angular observations has been set the same for all of them and has been determined as inverse mean-square residual obtained in the orbit fitting using just angular observations. The weights of radar observations have been set as inverse squared errors of these observations published together with them in the Minor Planet Center electronical circulars (MPECs). For the orbit fitting some five asteroids have been taken from these circulars. The asteroids have been chosen fulfilling the requirement of more than six radar observations of them to be available. The asteroids are 1950 DA, 1999 RQ36, 2002 NY40, 2004 DC and 2005 EU2. Several orbit fittings for these aster-oids have been done: with just angular observations; with just radar observations; with both angular and radar observations. The obtained results are quite acceptable because in the last case the mean-square angular residuals are approximately equal to the same ones obtained in the fitting with just angular observations. As to radar observations mean-square residuals, the time delay residuals for three asteroids do not exceed 1 ?s, for two others ˜ 10 ?s and the Doppler shift residuals for three asteroids do not exceed 1 Hz, for two others ˜ 10 Hz. The motion equations included perturbations from 9 planets and the Moon using their ephemerides DE422. The numerical integration has been performed with Everhart 27-order method with variable step. All calculations have been exe-cuted to a 34-digit decimal precision (i.e. using 128-bit floating-point numbers). Further, the sizes of confidence ellipsoids of im-proved orbit parameters have been compared. It has been accepted that an indicator of ellipsoid size is a geometric mean of its six semi-axes. A comparison of sizes has shown that confidence ellipsoids obtained in orbit fitting with both angular and radar obser-vations are several times less than ellipsoids obtained with just angular observations.

Baturin, A. P.

2013-12-01

195

Dirac Equation with Coupling to 1\\/ r Singular Vector Potentials for all Angular Momenta  

Microsoft Academic Search

We consider the Dirac equation in 3+1 dimensions with spherical symmetry and coupling to 1\\/ r singular vector potential. An approximate analytic solution for all angular momenta is obtained. The approximation is made for the 1\\/ r orbital term in the Dirac equation itself not for the traditional and more singular 1\\/ r 2 term in the resulting second order

A. D. Alhaidari

2010-01-01

196

Space-angle approximations in the variational nodal method  

Microsoft Academic Search

The variational nodal method is formulated such that the angular and spatial approximations maybe examined separately. Spherical harmonic, simplified spherical harmonic, and discrete ordinate approximations are coupled to the primal hybrid finite element treatment of the spatial variables. Within this framework, two classes of spatial trial functions are presented: (1) orthogonal polynomials for the treatment of homogeneous nodes and (2)

E. E. Lewis; G. Palmiotti; T. Taiwo

1999-01-01

197

Spin Angular Momentum Imparted by Gravitational Waves  

E-print Network

Following the demonstration that gravitational waves impart linear momentum, it is argued that if they are polarized they should impart angular momentum to appropriately placed 'test rods' in their path. A general formula for this angular momentum is obtained and used to provide expressions for the angular momentum imparted by plane and cylindrical gravitational waves.

M Sharif

2007-01-23

198

The angular momentum of the Oort cloud  

Microsoft Academic Search

An evaluation is made of the work of Marochnik et al. (1988), which estimated that the angular momentum of the Oort cloud is 2-3 orders of magnitude greater than the planetary system's total angular momentum. It is noted that most of the angular momentum in the currently observed Oort cloud is the result of the effects of external perturbers over

P Weissman

1991-01-01

199

Low angular momentum flow model of Sgr A* activity  

E-print Network

Sgr A* is the closest massive black hole and can be observed with the highest angular resolution. Nevertheless, our current understanding of the accretion process in this source is very poor. The inflow is almost certainly of low radiative efficiency and it is accompanied by a strong outflow and the flow is strongly variable but the details of the dynamics are unknown. Even the amount of angular momentum in the flow is an open question. Here we argue that low angular momentum scenario is better suited to explain the flow variability. We present a new hybrid model which describes such a flow and consists of an outer spherically symmetric Bondi flow and an inner axially symmetric flow described through MHD simulations. The assumed angular momentum of the matter is low, i.e. the corresponding circularization radius in the equatorial plane of the flow is just above the innermost stable circular orbit in pseudo-Newtonian potential. We compare the radiation spectrum from such a flow to the broad band observational data for Sgr A*.

B. Czerny; M. Moscibrodzka

2008-08-21

200

Light scattering by large spheroids in the Physical Optics Approximation: numerical comparison with other approximate and exact results  

Microsoft Academic Search

Physical Optics Approximation is used to compute scattering efficiency factors forward- and back-scattering intensities, angular distributions of intensity and depolarization by large dielectric or absorbing spheroids. The results are compared with those obtained by exact theories or other approximate calculations. If the radius of curvature at any point of the illuminated part of the scatterer is greater than about a

J. C. Ravey; P. Mazeron

1983-01-01

201

Generalizing resolution  

NASA Astrophysics Data System (ADS)

Of those things that can be estimated well in an inverse problem, which is best to estimate? Backus-Gilbert resolution theory answers a version of this question for linear (or linearized) inverse problems in Hilbert spaces with additive zero-mean errors with known, finite covariance, and no constraints on the unknown other than the data. This paper generalizes resolution: it defines the resolution and Bayes resolution of an estimator, intrinsic minimax and Bayes resolution, and intrinsic minimax and Bayes design resolution. Intrinsic resolution is the smallest value of a penalty across parameters that can be estimated with controlled (minimax or Bayes) risk. Intrinsic minimax resolution includes Backus-Gilbert resolution and subtractive optimally localized averages (SOLA) as special cases. Intrinsic design resolution is the smallest value of a penalty among parameters that can be estimated with controlled (minimax or Bayes) risk using observations with controlled acquisition cost. Intrinsic resolution wraps the classical problem of choosing an optimal estimator of an abstract parameter inside the problem of choosing an optimal parameter to estimate. Intrinsic design resolution adds another layer: optimizing what to observe. Equivalently, it wraps a problem in information-based complexity inside the problem of choosing an optimal parameter. The definitions apply to inverse problems with constraints, to nonlinear inverse problems, to nonlinear and biased estimators and estimators with controlled computational cost, to general definitions of risk (not just the variance of unbiased estimators), to confidence set estimators as well as point estimators, and to abstract penalties not necessarily related to 'spread'. Simple examples are given, including a definition of the resolution of 'strict bounds' confidence intervals.

Stark, Philip B.

2008-06-01

202

Two-axis angular effector  

DOEpatents

A new class of coplanar two-axis angular effectors. These effectors combine a two-axis rotational joint analogous to a Cardan joint with linear actuators in a manner to produce a wider range of rotational motion about both axes defined by the joint. This new class of effectors also allows design of robotic manipulators having very high strength and efficiency. These effectors are particularly suited for remote operation in unknown surroundings, because of their extraordinary versatility. An immediate application is to the problems which arise in nuclear waste remediation.

Vaughn, Mark R. (Albuquerque, NM); Robinett, III, Rush D. (Tijeras, NM); Phelan, John R. (Albuquerque, NM); Van Zuiden, Don M. (Albuquerque, NM)

1997-01-21

203

Variable Distance Angular Symbology Reader  

NASA Technical Reports Server (NTRS)

A variable distance angular symbology, reader utilizes at least one light source to direct light through a beam splitter and onto a target. A target may be angled relative to the impinging light beam up to and maybe even greater than 45deg. A reflected beam from the target passes through the beam splitter and is preferably directed 90deg relative to the light source through a telecentric lens to a scanner which records an image of the target such as a direct part marking code.

Schramm, Harry F., Jr. (Inventor); Corder, Eric L. (Inventor)

2006-01-01

204

Is photon angular momentum important in molecular collision processes occurring in a laser field  

NASA Technical Reports Server (NTRS)

The importance of the rigorous treatment of photon angular momentum in molecular-collision processes occurring in the presence of intense radiation is investigated. An alternate approximate treatment, which essentially neglects the angular momentum coupling between the photon and the molecular degrees of freedom by averaging over the angular dependence of the interaction matrix elements, is presented and applied to a model calculation. The degeneracy-averaged results of this calculation compare remarkably well with the results of a rigorous calculation, from which we conclude (with reservation) that the explicit consideration of photoangular momentum coupling in molecular-collision problems is unnecessary.

Devries, P. L.; George, T. F.

1978-01-01

205

Resolution Matters  

NSDL National Science Digital Library

This is an activity about image resolution. Learners will recreate a solar image taken by the Solar Dynamics Observatory (SDO) using various sizes of building bricks, and discuss how their recreations relate to image resolution. Learners will also compare SDO images to solar images from older spacecraft to see how improved technology helps scientists learn more about the Sun.

206

High-resolution bottom-loss estimation using the ambient-noise vertical coherence function.  

PubMed

The seabed reflection loss (shortly "bottom loss") is an important quantity for predicting transmission loss in the ocean. A recent passive technique for estimating the bottom loss as a function of frequency and grazing angle exploits marine ambient noise (originating at the surface from breaking waves, wind, and rain) as an acoustic source. Conventional beamforming of the noise field at a vertical line array of hydrophones is a fundamental step in this technique, and the beamformer resolution in grazing angle affects the quality of the estimated bottom loss. Implementation of this technique with short arrays can be hindered by their inherently poor angular resolution. This paper presents a derivation of the bottom reflection coefficient from the ambient-noise spatial coherence function, and a technique based on this derivation for obtaining higher angular resolution bottom-loss estimates. The technique, which exploits the (approximate) spatial stationarity of the ambient-noise spatial coherence function, is demonstrated on both simulated and experimental data. PMID:25618076

Muzi, Lanfranco; Siderius, Martin; Quijano, Jorge E; Dosso, Stan E

2015-01-01

207

Measurement of polarization with the Degree Angular Scale Interferometer.  

PubMed

Measurements of the cosmic microwave background (CMB) radiation can reveal with remarkable precision the conditions of the Universe when it was approximately 400,000 years old. The three most fundamental properties of the CMB are its frequency spectrum (which determines the temperature), and the fluctuations in both the temperature and polarization across a range of angular scales. The frequency spectrum has been well determined, and considerable progress has been made in measuring the power spectrum of the temperature fluctuations. But despite many efforts to measure the polarization, detection of this property of the CMB has hitherto been beyond the reach of even the most sensitive observations. Here we describe the Degree Angular Scale Interferometer (DASI), an array of radio telescopes, which for the past two years has conducted polarization-sensitive observations of the CMB from the Amundsen-Scott South Pole research station. PMID:12490940

Leitch, E M; Kovac, J M; Pryke, C; Carlstrom, J E; Halverson, N W; Holzapfel, W L; Dragovan, M; Reddall, B; Sandberg, E S

208

Interpolation and Approximation Theory.  

ERIC Educational Resources Information Center

Introduced are the basic ideas of interpolation and approximation theory through a combination of theory and exercises written for extramural education at the university level. Topics treated are spline methods, Lagrange interpolation, trigonometric approximation, Fourier series, and polynomial approximation. (MDH)

Kaijser, Sten

1991-01-01

209

High-Resolution X-Ray Telescopes  

NASA Technical Reports Server (NTRS)

Fundamental needs for future x-ray telescopes: a) Sharp images => excellent angular resolution. b) High throughput => large aperture areas. Generation-X optics technical challenges: a) High resolution => precision mirrors & alignment. b) Large apertures => lots of lightweight mirrors. Innovation needed for technical readiness: a) 4 top-level error terms contribute to image size. b) There are approaches to controlling those errors. Innovation needed for manufacturing readiness. Programmatic issues are comparably challenging.

ODell, Stephen L.; Brissenden, Roger J.; Davis, William; Elsner, Ronald F.; Elvis, Martin; Freeman, Mark; Gaetz, Terry; Gorenstein, Paul; Gubarev, Mikhail V.

2010-01-01

210

Variations in atmospheric angular momentum and the length of day  

NASA Technical Reports Server (NTRS)

Six years of twice daily global analyses were used to create and study a lengthy time series of high temporal resolution angular momentum values. Changes in these atmospheric values were compared to independently determined charges in the rotation rate of the solid Earth. Finally, the atmospheric data was examined in more detail to determine the time and space scales on which variations in momentum occur within the atmosphere and which regions are contributing most to the changes found in the global integral. The data and techniques used to derive the time series of momentum values are described.

Rosen, R. D.; Salstein, D. A.

1982-01-01

211

Relativistic Statistical Mechanics with Angular Momentum  

E-print Network

The equilibrium distribution function of a relativistic ideal gas has been derived to include the effect of angular momentum. The result agrees with the one obtained from kinetic theory, and consistent with relativistic thermodynamics. The role of angular momentum becomes transparent in this derivation, and the equilibrium distribution can be generalized to accommodate the effect of intrinsic angular momentum. The results here is for a flat spacetime, however, same approach can be applied to static curved spacetimes.

Tadas K Nakamura

2011-12-01

212

Asymptotic Diffusion-Limit Accuracy of Sn Angular Differencing Schemes  

SciTech Connect

In a previous paper, Morel and Montry used a Galerkin-based diffusion analysis to define a particular weighted diamond angular discretization for S{sub n}n calculations in curvilinear geometries. The weighting factors were chosen to ensure that the Galerkin diffusion approximation was preserved, which eliminated the discrete-ordinates flux dip. It was also shown that the step and diamond angular differencing schemes, which both suffer from the flux dip, do not preserve the diffusion approximation in the Galerkin sense. In this paper we re-derive the Morel and Montry weighted diamond scheme using a formal asymptotic diffusion-limit analysis. The asymptotic analysis yields more information than the Galerkin analysis and demonstrates that the step and diamond schemes do in fact formally preserve the diffusion limit to leading order, while the Morel and Montry weighted diamond scheme preserves it to first order, which is required for full consistency in this limit. Nonetheless, the fact that the step and diamond differencing schemes preserve the diffusion limit to leading order suggests that the flux dip should disappear as the diffusion limit is approached for these schemes. Computational results are presented that confirm this conjecture. We further conjecture that preserving the Galerkin diffusion approximation is equivalent to preserving the asymptotic diffusion limit to first order.

Bailey, T S; Morel, J E; Chang, J H

2009-11-05

213

Berkeley High-Resolution Ball  

SciTech Connect

Criteria for a high-resolution ..gamma..-ray system are discussed. Desirable properties are high resolution, good response function, and moderate solid angle so as to achieve not only double- but triple-coincidences with good statistics. The Berkeley High-Resolution Ball involved the first use of bismuth germanate (BGO) for anti-Compton shield for Ge detectors. The resulting compact shield permitted rather close packing of 21 detectors around a target. In addition, a small central BGO ball gives the total ..gamma..-ray energy and multiplicity, as well as the angular pattern of the ..gamma.. rays. The 21-detector array is nearly complete, and the central ball has been designed, but not yet constructed. First results taken with 9 detector modules are shown for the nucleus /sup 156/Er. The complex decay scheme indicates a transition from collective rotation (prolate shape) to single- particle states (possibly oblate) near spin 30 h, and has other interesting features.

Diamond, R.M.

1984-10-01

214

Theory of angular dispersive imaging hard x-ray spectrographs  

E-print Network

A spectrograph is an optical instrument that disperses photons of different energies into distinct directions and space locations, and images photon spectra on a position-sensitive detector. Spectrographs consist of collimating, angular dispersive, and focusing optical elements. Bragg reflecting crystals arranged in an asymmetric scattering geometry are used as the dispersing elements. A ray-transfer matrix technique is applied to propagate x-rays through the optical elements. Several optical designs of hard x-ray spectrographs are proposed and their performance is analyzed. Spectrographs with an energy resolution of 0.1 meV and a spectral window of imaging up to a few tens of meVs are shown to be feasible for inelastic x-ray scattering (IXS) spectroscopy applications. In another example, a spectrograph with a 1-meV spectral resolution and 85-meV spectral window of imaging is considered for Cu K-edge resonant IXS (RIXS).

Shvyd'ko, Yuri

2015-01-01

215

Angular sensitivity analysis of vegetation indices derived from CHRIS\\/PROBA data  

Microsoft Academic Search

View angle effects present in spectral vegetation indices can either be regarded as an added source of uncertainty for variable retrieval or as a source of additional information, enhancing the variable retrieval; however, the magnitude of these angular effects remains for most indices unknown or unquantified. We use the ESA-mission CHRIS-PROBA (Compact High Resolution Imaging Spectrometer onboard the Project for

J. Verrelst; M. E. Schaepman; B. Koetz; M. Kneubühler

2008-01-01

216

Angular-Rate Estimation Using Quaternion Measurements  

NASA Technical Reports Server (NTRS)

In most spacecraft (SC) there is a need to know the SC angular rate. Precise angular rate is required for attitude determination, and a coarse rate is needed for attitude control damping. Classically, angular rate information is obtained from gyro measurements. These days, there is a tendency to build smaller, lighter and cheaper SC, therefore the inclination now is to do away with gyros and use other means and methods to determine the angular rate. The latter is also needed even in gyro equipped satellites when performing high rate maneuvers whose angular-rate is out of range of the on board gyros or in case of gyro failure. There are several ways to obtain the angular rate in a gyro-less SC. When the attitude is known, one can differentiate the attitude in whatever parameters it is given and use the kinematics equation that connects the derivative of the attitude with the satellite angular-rate and compute the latter. Since SC usually utilize vector measurements for attitude determination, the differentiation of the attitude introduces a considerable noise component in the computed angular-rate vector.

Azor, Ruth; Bar-Itzhack, Y.; Deutschmann, Julie K.; Harman, Richard R.

1998-01-01

217

Jet angular momentum and quantum chromodynamics  

Microsoft Academic Search

We discuss several observable properties of hadronic final states in electron-positron annihilation that bear on the angular momentum content of jets. In particular we calculate in perturbative quantum chromodynamics the jet oblateness and the jet axis angular distribution as a function of jet invariant mass. We also consider QCD information on the PT correlation in opposite jets.

L. Clavelli

1980-01-01

218

Dijet angular distributions at D0  

SciTech Connect

Measurements of the dijet angular distributions are relatively insensitive to parton distribution functions and thus offer an excellent method of testing the LO and NLO predictions of perturbative QCD. The authors present measurements of the dijet angular distributions for {vert_bar}{eta}{vert_bar} < 3.0 in p{anti p} collisions at {radical}s = 1.8 TeV.

Fatyga, M.K. [Univ. of Rochester, NY (United States); D0 Collaboration

1996-09-01

219

The Angular Momentum-Energy Space  

E-print Network

In this paper we shall define and study the angular momentum-energy space for the classical problem of plane-motions of a particle situated in a potential field of a central force. We shall present the angular momentum-energy space for some important cases.

Dan Comanescu

2007-02-09

220

Angular Dependences of Prism Liquid Crystal Polarizer  

Microsoft Academic Search

The angular dependences of extinction ratio and polarization plane orientation for prism liquid crystal polarizers have been measured fix 632. 8nm vawelength in the limits of angular aperture. The planar and homeotropic orientations of nematic liquid crystal layer were used.

A. A. Karetnikov; A. P. Kavshik; Y. I. Rjumtsev

1997-01-01

221

Quartz angular rate sensor for automotive control  

Microsoft Academic Search

A new quartz angular rate sensor has been developed for automotive controls. The principle of the sensor is detection of the Coriolis force with a vibrator An H shape vibrator supported with a stein at the center was used The vibrator supported at the center was good for the isolation of a small motion detecting angular rate from an extremely

Y. Nonomura; M. Fujiyoshi; Y. Omura; K. Tsukada; M. Okuwa; T. Morikawa; N. Sugitani; S. Satou; N. Kurata; S. Matsushige

2001-01-01

222

Angular momentum in the global atmospheric circulation  

Microsoft Academic Search

Angular momentum is a variable of central importance to the dynamics of the atmosphere both regionally and globally. Moreover, the angular momentum equations yield a precise description of the dynamic interaction of the atmosphere with the oceans and the solid Earth via various torques as exerted by friction, pressure against the mountains and the nonspherical shape of the Earth, and

Joseph Egger; Klaus Weickmann; Klaus-Peter Hoinka

2007-01-01

223

The angular momentum of the Oort cloud  

NASA Technical Reports Server (NTRS)

An evaluation is made of the work of Marochnik et al. (1988), which estimated that the angular momentum of the Oort cloud is 2-3 orders of magnitude greater than the planetary system's total angular momentum. It is noted that most of the angular momentum in the currently observed Oort cloud is the result of the effects of external perturbers over the solar system's history, and it is demonstrated that the total current angular momentum is probably in the 6.0 x 10 to the 50th to 1.1 x 10 to the 51st g sq cm/sec range; original angular momentum was probably a factor of 5 below such values.

Weissman, Paul R.

1991-01-01

224

The angular momentum of the Oort cloud  

SciTech Connect

An evaluation is made of the work of Marochnik et al. (1988), which estimated that the angular momentum of the Oort cloud is 2-3 orders of magnitude greater than the planetary system's total angular momentum. It is noted that most of the angular momentum in the currently observed Oort cloud is the result of the effects of external perturbers over the solar system's history, and it is demonstrated that the total current angular momentum is probably in the 6.0 x 10 to the 50th to 1.1 x 10 to the 51st g sq cm/sec range; original angular momentum was probably a factor of 5 below such values. 21 refs.

Weissman, P.R. (JPL, Pasadena, CA (USA))

1991-01-01

225

Quark angular momentum in a spectator model  

E-print Network

We investigate the quark angular momentum in a model with the nucleon being a quark and a spectator. Both scalar and axial-vector spectators are included. We perform the calculations in the light-cone formalism where the parton concept is well defined. We calculate the quark helicity and canonical orbital angular momentum. Then we calculate the gravitational form factors which are often related to the kinetic angular momentums, and find that even in a no gauge field model we cannot identify the canonical angular momentums with half the sum of gravitational form factors. In addition, we examine the model relation between the orbital angular momentum and pretzelosity, and find it is violated in the axial-vector case.

Liu, Tianbo

2015-01-01

226

A high resolution scintillating fiber gamma-ray telescope  

Microsoft Academic Search

Scintillating fibers coupled to position sensitive photomultipliers have good angular precision and good energy resolution in detecting gamma-rays. Scintillating fibers stacked up into scintillating fiber planes U, V and W that are rotated by 60° angle relative to each other and coupled to position sensitive photomultipliers can be used as high resolution imaging gamma-ray detectors. With this arrangement the Compton

M. Atac; D. B. Cline; E. J. Fenyves; R. C. Chaney; H. Hammack

1989-01-01

227

Measuring angular diameters of extended sources  

NASA Astrophysics Data System (ADS)

When measuring diameters of partially resolved sources like planetary nebulae, Hii regions or galaxies, often a technique called Gaussian deconvolution is used. This technique yields a Gaussian diameter, which subsequently has to be multiplied by a conversion factor to obtain the true angular diameter of the source. This conversion factor is a function of the FWHM of the beam or point spread function, and also depends on the intrinsic surface brightness distribution of the source. In this paper, conversion factors are presented for a number of simple geometries: a circular constant surface brightness disc and a spherical constant emissivity shell, using a range of values for the inner radius. Also, more realistic geometries are studied, based on a spherically symmetric photoionization model of a planetary nebula. This enables a study of optical depth effects, a comparison between images in various emission lines, and the use of power-law density distributions. It is found that the conversion factor depends quite critically on the intrinsic surface brightness distribution, which is usually unknown. The uncertainty is particularly large if extended regions of low surface brightness are present in the nebula. In such cases the use of Gaussian or second-moment deconvolution is not recommended. As an alternative, a new algorithm is presented which allows the determination of the intrinsic FWHM of the source using only the observed surface brightness distribution and the FWHM of the beam. Hence no assumptions concerning the intrinsic surface brightness distribution are needed. Tests show that this implicit deconvolution method works well in realistic conditions, even when the signal-to-noise ratio is low, provided that the beamsize is less than roughly 2/3 of the observed FWHM and the beam profile can be approximated by a Gaussian. A code implementing this algorithm is available.

van Hoof, P. A. M.

2000-05-01

228

DIOPHANTINE APPROXIMATION HOMEWORK II  

E-print Network

| y0 (the condition that y > y0 is new). To get this, the proof of Theorem 2) A star has n planets, all whose orbits are circular and lie in the same plane. Each planet has a constant angular velocity with which it traverses its orbit. Prove that the planets are in almost the same

Evertse, Jan-Hendrik

229

Cascade gamma-gamma tomography and angular correlation measurements  

NASA Astrophysics Data System (ADS)

Cascade gamma-ray tomography depends on the measurement of two or more gamma-rays emitted from a radionuclide in coincidence. In using suitable detectors of appropriate timing resolution it may also be possible to obtain information about the 'chemical environment' of the radionuclide i.e. the binding site in the material to which it is attached by carrying out, simultaneously, time differential perturbed angular correlation (TDPAC) measurements. A dual block bismuth germanate (BGO) detector system, designed for use in positron emission tomography (PET) has been employed to perform cascade gamma-ray tomography with a point 60Co source (1173 and 1332 keV). It is shown that despite the poor energy resolution of the coincidence system, the point source can be imaged with a multi-hole collimator, on one or both detectors, with a resolution (full width at half maximum) of 3.8 and 2.4 +/- 0.2 mm respectively, at the expense of significantly reduced sensitivity. Practical constraints limit usefulness of the system which new scintillation systems, with respect to time and energy resolution, should overcome.

Spyrou, Nicholas M.; Mesbahi, M. Esmail; Mallion, Stephen N.

2000-04-01

230

On Approximate Calculations.  

ERIC Educational Resources Information Center

The ability to undertake approximate calculations and to get a rough feel for data is an important skill which should not be overlooked. Presents some ideas for teaching and assessing approximate calculation. Contains 13 references. (Author/ASK)

Jolliffe, Flavia

1999-01-01

231

Approximate flavor symmetries  

SciTech Connect

We discuss the idea of approximate flavor symmetries. Relations between approximate flavor symmetries and natural flavor conservation and democracy models is explored. Implications for neutrino physics are also discussed.

Rasin, A.

1994-04-01

232

Approximation through Multicommodity Flow  

Microsoft Academic Search

The first approximate max-flow-min-cut theorem for general multicommodity flow is proved. It is used to obtain approximation algorithms for minimum deletion of clauses of a 2-CNF?formula, via minimization problems, and other problems. Also presented are approximation algorithms for chordalization of a graph and for register sufficiency that are based on undirected and directed node separators

Philip N. Klein; Ajit Agrawal; R. Ravi; Satish Rao

1990-01-01

233

Dirac Equation with Coupling to 1\\/ r Singular Vector Potentials for all Angular Momenta  

Microsoft Academic Search

We consider the Dirac equation in 3+1 dimensions with spherical symmetry and coupling to 1\\/r singular vector potential. An approximate analytic solution for all angular momenta is obtained. The approximation is made\\u000a for the 1\\/r orbital term in the Dirac equation itself not for the traditional and more singular 1\\/r\\u000a 2 term in the resulting second order differential equation. Consequently,

A. D. Alhaidari

2010-01-01

234

The transverse angular momentum sum rule  

E-print Network

We explain the origin of the controversy about the existence of a transverse angular momentum sum rule, and show that it stems from utilizing an incorrect result in the literature, concerning the expression for the expectation values of the angular momentum operators. We demonstrate a new, short and direct way of obtaining correct expressions for these expectation values, from which a perfectly good transverse angular momentum sum rule can be deduced. We also introduce a new classification of sum rules into primary and secondary types. In the former all terms occurring in the sum rule can be measured experimentally; in the latter some terms cannot be measured experimentally.

Elliot Leader

2008-06-30

235

Circus Physics: Conservation of Angular Momentum  

NSDL National Science Digital Library

This video-based resource examines conservation of angular momentum through the motion of an acrobat doing aerial flips. It explores how a tucked position decreases the acrobat's moment of inertia, resulting in increased rotational velocity. To slow his rotation, he extends his legs. Through the acrobat's motion, the video illustrates how angular momentum is conserved for a body in flight. Supplementary materials help students integrate concepts to perform calculations relating to angular momentum and moment of inertia. This resource was developed in conjunction with the PBS series Circus. See Related Materials for a link to the full set of 8 Circus Physics video-based lessons.

2013-11-19

236

Angular momentum decomposition from a QED example  

NASA Astrophysics Data System (ADS)

We investigate the angular momentum decomposition with a quantum electrodynamics example to clarify the proton spin decomposition debates. We adopt the light-front formalism where the parton model is well defined. We prove that the sum of fermion and boson angular momenta is equal to half the sum of the two gravitational form factors A (0 ) and B (0 ) , as is well known. However, the suggestion to make a separation of the above relation into the fermion and boson pieces, as a way to measure the orbital angular momentum of fermions or bosons, respectively, is not justified from our explicit calculation.

Liu, Tianbo; Ma, Bo-Qiang

2015-01-01

237

Angular momentum in the Local Group  

SciTech Connect

We briefly review models for the Local Group and the acquisition of its angular momentum. We describe early attempts to understand the origin of the spin of the galaxies discussing the hypothesis that the Local Group has little angular momentum. Finally we show that using Peebles` least action principle there should be a rather large amount of orbital angular momentum compared to the magnitude of the spin of its galaxies. Therefore the Local Group cannot be thought as tidally isolated. Using Peebles` trajectories we give a possible set of trajectories for Local Group galaxies which would predict their spin.

Dunn, A. [Cambridge Univ. (United Kingdom). Inst. of Astronomy; Laflamme, R. [Los Alamos National Lab., NM (United States)

1994-04-01

238

Modeling texture evolution in equal channel angular extrusion using crystal plasticity finite element models  

Microsoft Academic Search

A new approach to modeling crystallographic texture evolution in Equal Channel Angular Extrusion (ECAE) is presented in this paper. The proposed approach utilizes an elastic–viscoplastic single crystal constitutive model implemented in a finite element framework. A representative volume element of the polycrystal is subjected to boundary conditions that simulate the approximate deformation history experienced by different regions of the sample

Surya R. Kalidindi; Brendan R. Donohue; Saiyi Li

2009-01-01

239

Numerical calculation of near field scalar diffraction using angular spectrum of plane waves theory and FFT  

Microsoft Academic Search

t is a known fact that near field diffraction or Fresnel diffraction calculations are difficult to perform exactly. It is in general necessary to make some approximations in order to obtain a more suitable form. In this work, a numerical implementation based on angular spectrum theory for near field diffraction is presented. The method uses Fast Fourier Transforms (FFT) and

Adrian Carbajal-Dominguez; J. Bernal; Jesus E. Gomez Correa; Gabriel Martinez Niconoff

2010-01-01

240

A polarization-sensitive light field imager for multi-channel angular spectroscopy of light scattering in biological tissues  

PubMed Central

Background Angular spectroscopy of light scattering can be used for quantitative analysis of cellular and subcellular properties, and thus promises a noninvasive methodology for in vivo assessment cellular integrity to complement in vitro histological examination. Spatial information is essential for accurate identification of localized abnormalities. However, conventional angular spectroscopy systems only provide single-channel measurement, which suffers from poor spatial resolution or requires time-consuming scanning over extended area. The purpose of this study was to develop a multi-channel angular spectroscopy for light field imaging in biological tissues. Materials and methods A microlens array (MLA) (8×8) based light field imager for 64-channel angular spectroscopy was developed. A pair of crossed polarizers was employed for polarization-sensitive recording to enable quantitative measurement at high signal specificity and sensitivity. The polarization-sensitive light field imager enables rapid measurement of multiple sampling volumes simultaneously at 18 ?m spatial-resolution and 3° angular-resolution. Comparative light field imaging and electrophysiological examination of freshly isolated and physiologically deteriorated lobster leg nerves have been conducted. Results Two-dimensional (2D) polarization-sensitive scattering patterns of the fresh nerves were highly elliptical, while they gradually lost the ellipticity and became rotationally symmetric (i.e., circular) as the nerves physiologically deteriorated due to repeated electrical stimulations. Characterized parameters, i.e., the ellipticity and the scattering intensity, rendered spatially various characteristics such as different values and deteriorating rates. Conclusions The polarization-sensitive light field imager is able to provide multi-channel angular spectroscopy of light scattering with both spatial and angular resolutions. The light scattering properties of nerves are highly dependent on the orientation of nerves and their physiological status. Further development of polarization-sensitive multi-channel angular spectroscopy may promise a methodology for rapid and reliable identification of localized abnormalities in biological tissues.

Lu, Rongwen; Zhang, Qiuxiang; Zhi, Yanan

2015-01-01

241

Approximation for the Rayleigh Resolution of a Circular Aperture  

ERIC Educational Resources Information Center

Rayleigh's criterion states that a pair of point sources are barely resolved by an optical instrument when the central maximum of the diffraction pattern due to one source coincides with the first minimum of the pattern of the other source. As derived in standard introductory physics textbooks, the first minimum for a rectangular slit of width "a"…

Mungan, Carl E.

2009-01-01

242

The physics of angular momentum radio  

E-print Network

Wireless communications, radio astronomy and other radio science applications are mainly implemented with techniques built on top of the electromagnetic linear momentum (Poynting vector) physical layer. As a supplement and/or alternative to this conventional approach, techniques rooted in the electromagnetic angular momentum physical layer have been advocated, and promising results from proof-of-concept radio communication experiments using angular momentum were recently published. This sparingly exploited physical observable describes the rotational (spinning and orbiting) physical properties of the electromagnetic fields and the rotational dynamics of the pertinent charge and current densities. In order to facilitate the exploitation of angular momentum techniques in real-world implementations, we present a systematic, comprehensive theoretical review of the fundamental physical properties of electromagnetic angular momentum observable. Starting from an overview that puts it into its physical context among ...

Thidé, B; Then, H; Someda, C G; Ravanelli, R A

2014-01-01

243

Detection of the Angular Correlation of Faint X-ray Sources  

E-print Network

We have analyzed a set of deep ROSAT observations with a total sky coverage of 40 square degrees to search for clustering of faint X-ray sources. Using the resulting catalog of discrete X-ray sources, we detect, for the first time in X-rays, a positive correlation on angular scales of 0.5'-10'. When corrected for a bias due to limited spatial resolution which amplifies the correlation, the observed angular correlation function agrees well with that expected from the spatial correlation of optically selected quasars, provided that they comprise an appreciable fraction (>= ~50%) of detected X-ray sources.

A. Vikhlinin; W. Forman

1995-10-06

244

Motionless system to measure relative angular emission intensity of decaying or modulated light emitting diodes.  

PubMed

In this paper, a measurement system is presented which enables fast and accurate determination of the relative angular emission intensity of light emitting devices, taking into account their specific features such as low light output, narrow spectral distribution, high spatial luminous intensity ratios, and small dimensions. Application of logarithmic sensors allows for fast measurement of relative emission by simple analog circuitry, while locating 18 of them on a fixed ring around the emitter allows a motionless measurement system. As a result, the proposed system can determine the relative angular emission in less than 100 ms with a resolution of 5° for symmetric emitters. PMID:25362367

Radziwon, M; Hernandez-Sosa, G; Lackner, C; Sitter, H; Simbrunner, C

2014-10-01

245

Angular performance measure for tighter uncertainty relations  

SciTech Connect

The uncertainty principle places a fundamental limit on the accuracy with which we can measure conjugate quantities. However, the fluctuations of these variables can be assessed in terms of different estimators. We propose an angular performance that allows for tighter uncertainty relations for angle and angular momentum. The differences with previous bounds can be significant for particular states and indeed may be amenable to experimental measurement with the present technology.

Hradil, Z.; Rehacek, J. [Department of Optics, Palacky University, 17. listopadu 50, 772 00 Olomouc (Czech Republic); Klimov, A. B. [Departamento de Fisica, Universidad de Guadalajara, 44420 Guadalajara, Jalisco (Mexico); Rigas, I.; Sanchez-Soto, L. L. [Departamento de Optica, Facultad de Fisica, Universidad Complutense, E-28040 Madrid (Spain)

2010-01-15

246

Partial angular coherence and the angular Schmidt spectrum of entangled two-photon fields  

SciTech Connect

We study partially coherent fields that have a coherent-mode representation in the orbital-angular-momentum-mode basis. For such fields, we introduce the concepts of the angular coherence function and the coherence angle. Such fields are naturally produced by the process of parametric down-conversion--a second-order nonlinear optical process in which a pump photon breaks up into two entangled photons, known as the signal and idler photons. We show that the angular coherence functions of the signal and idler fields are directly related to the angular Schmidt (spiral) spectrum of the down-converted two-photon field and thus that the angular Schmidt spectrum can be measured directly by measuring the angular coherence function of either the signal or the idler field, without requiring coincidence detection.

Jha, Anand Kumar; Boyd, Robert W. [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Agarwal, Girish S. [Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078 (United States)

2011-12-15

247

Goal-based angular adaptivity applied to a wavelet-based discretisation of the neutral particle transport equation  

NASA Astrophysics Data System (ADS)

A method for applying goal-based adaptive methods to the angular resolution of the neutral particle transport equation is presented. The methods are applied to an octahedral wavelet discretisation of the spherical angular domain which allows for anisotropic resolution. The angular resolution is adapted across both the spatial and energy dimensions. The spatial domain is discretised using an inner-element sub-grid scale finite element method. The goal-based adaptive methods optimise the angular discretisation to minimise the error in a specific functional of the solution. The goal-based error estimators require the solution of an adjoint system to determine the importance to the specified functional. The error estimators and the novel methods to calculate them are described. Several examples are presented to demonstrate the effectiveness of the methods. It is shown that the methods can significantly reduce the number of unknowns and computational time required to obtain a given error. The novelty of the work is the use of goal-based adaptive methods to obtain anisotropic resolution in the angular domain for solving the transport equation.

Goffin, Mark A.; Buchan, Andrew G.; Dargaville, Steven; Pain, Christopher C.; Smith, Paul N.; Smedley-Stevenson, Richard P.

2015-01-01

248

Surfaces: Representation and approximation  

NASA Technical Reports Server (NTRS)

Schemes for the representation and approximation of surfaces, based on Coon's and triangular patches and blending are discussed. The necessary criteria/characteristics for resulting spaces are outlined.

Barnhill, R. E.

1982-01-01

249

DISTRIBUTION OF ACCRETING GAS AND ANGULAR MOMENTUM ONTO CIRCUMPLANETARY DISKS  

SciTech Connect

We investigate gas accretion flow onto a circumplanetary disk from a protoplanetary disk in detail by using high-resolution three-dimensional nested-grid hydrodynamic simulations, in order to provide a basis of formation processes of satellites around giant planets. Based on detailed analyses of gas accretion flow, we find that most of gas accretion onto circumplanetary disks occurs nearly vertically toward the disk surface from high altitude, which generates a shock surface at several scale heights of the circumplanetary disk. The gas that has passed through the shock surface moves inward because its specific angular momentum is smaller than that of the local Keplerian rotation, while gas near the midplane in the protoplanetary disk cannot accrete to the circumplanetary disk. Gas near the midplane within the planet's Hill sphere spirals outward and escapes from the Hill sphere through the two Lagrangian points L{sub 1} and L{sub 2}. We also analyze fluxes of accreting mass and angular momentum in detail and find that the distributions of the fluxes onto the disk surface are well described by power-law functions and that a large fraction of gas accretion occurs at the outer region of the disk, i.e., at about 0.1 times the Hill radius. The nature of power-law functions indicates that, other than the outer edge, there is no specific radius where gas accretion is concentrated. These source functions of mass and angular momentum in the circumplanetary disk would provide us with useful constraints on the structure and evolution of the circumplanetary disk, which is important for satellite formation.

Tanigawa, Takayuki; Ohtsuki, Keiji [Center for Planetary Science, Kobe University, Kobe (Japan); Machida, Masahiro N., E-mail: tanigawa@cps-jp.org [Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, Fukuoka (Japan)

2012-03-01

250

Annihilation of angular momentum bias during thrusting and spinning-up maneuvers  

NASA Technical Reports Server (NTRS)

During spinning-up and thrusting maneuvers of rockets and spacecraft, undesired transverse torques (from error sources such as thruster misalignment, center-of-mass offset and thruster mismatch) perturb the angular momentum vector from its original orientation. In this paper a maneuver scheme is presented which virtually annihilates the angular momentum vector bias, even though the magnitude and direction of the perturbing body-fixed torques are unknown. In the analysis it is assumed that the torques are small and constant and that the spacecraft or rocket can be approximated by a rigid body, which may be asymmetric. Typical maneuvers of the Galileo spacecraft are simulated to demonstrate the technique.

Longuski, J. M.; Kia, T.; Breckenridge, W. G.

1989-01-01

251

Approximate spatial reasoning  

NASA Technical Reports Server (NTRS)

A model for approximate spatial reasoning using fuzzy logic to represent the uncertainty in the environment is presented. Algorithms are developed which can be used to reason about spatial information expressed in the form of approximate linguistic descriptions similar to the kind of spatial information processed by humans. Particular attention is given to static spatial reasoning.

Dutta, Soumitra

1988-01-01

252

Approximation theory for matrices  

NASA Astrophysics Data System (ADS)

We review the theory of optimal polynomial and rational Chebyshev approximations, and Zolotarev's formula for the sign function over the range ? < ? z? < 1. We explain how rational approximations can be applied to large sparse matrices efficiently by making use of partial fraction expansions and multi-shift Krylov space solvers.

Kennedy, A. D.

2004-02-01

253

Digital Angular Position Sensor Using Wavelength Division Multiplexing  

NASA Astrophysics Data System (ADS)

Future aircraft will use fly-by-light control systems with fiber-linked optical sensors for such measurands as temperature, pressure, and linear and angular position. We describe a digital optical sensor which was developed to transmit the angular position of such slowly rotating parts as a throttle or fuel flow control valve on an aircraft. The sensor employs a reflective code plate with ten channels providing a resolution of 0.35 degrees. Two light-emitting diodes with overlapping spectra are used as light sources. A single micro-optic multiplexer-demultiplexer composed of a GRIN rod lens and a miniature grating is used to disperse the spectrum and recombine the spectral components from each channel after reflection by the code plate. We discuss the results of preliminary environmental tests of this unit. We have operated the sensor for brief periods of time between -60°C and +125°C without adverse effects. Preliminary vibration tests indicate that the unit will work properly at the maximum vibration levels expected in a jet-engine environment. Use of a reference track on the code plate in conjunction with an automatic gain control in the electronic circuit compensates for large changes in transmitted light intensity.

Fritsch, Klaus; Beheim, Glenn; Sotomayor, Jorge L.

1990-02-01

254

Partial CMB maps: bias removal and optimal binning of the angular power spectrum  

NASA Astrophysics Data System (ADS)

We present a semi-analytical method to investigate the systematic effects and statistical uncertainties of the calculated angular power spectrum when incomplete spherical maps are used. The computed power spectrum suffers in particular a loss of angular frequency resolution, which can be written as ? l ~ ?/?max, where ?max is the effective maximum extent of the partial spherical maps. We propose a correction algorithm to reduce systematic effects on the estimated Cl, as obtained from the partial map projection on the spherical harmonic Yml basis. We have derived near-optimal bands and weighting functions in l-space for the power spectrum calculation using small maps, and a correction algorithm for partially masked spherical maps that contain information on the angular correlations on all scales.

Ansari, R.; Magneville, C.

2010-07-01

255

Stellar Mixing. IV. The angular momentum problem  

NASA Astrophysics Data System (ADS)

We present a formalism that provides the Reynolds stresses needed to solve the angular momentum equation. The traditional Reynolds stress model assumes that the only contribution comes from shear (a down-gradient flux), but this leads to an extraction of angular momentum from the interior that is far too small compared to what is required to explain the helio seismological data. An illustrative solution of the new Reynolds stress equations shows that the presence of vorticity in a stably stratified regime, such as the one in the radiative zone, contributes a new term to the angular momentum equation that has an up-gradient flux like the one provided by the IGW model (internal gravity waves). The time scale entailed by such a term may be of the same order of 107 yrs produced by the IGW model. It would be instructive to solve the new angular momentum equation together with the formalism developed in Paper III to study not only the solar angular momentum distribution vs. helio data, but also the evolution of elements such as 7Li and 4He. These results would allow a more quantitative assessment of the overall model. The complete model yields Reynolds stresses that include differential rotation, unstable/stable stratification, double diffusion, radiative losses (arbitrary Peclet number), and meridional currents. This work is dedicated to Aura Sofia Canuto.

Canuto, V. M.

2011-04-01

256

Ultrafast angular momentum transfer in multisublattice ferrimagnets.  

PubMed

Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co0.8Gd0.2 and Co0.74Tb0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time-resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange-coupled sublattices while the total angular momentum stays constant. In Co0.74Tb0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by ~150?fs. PMID:24614016

Bergeard, N; López-Flores, V; Halté, V; Hehn, M; Stamm, C; Pontius, N; Beaurepaire, E; Boeglin, C

2014-01-01

257

The High Resolution Array HiRA  

NASA Astrophysics Data System (ADS)

A large solid angle, segmented, position sensitive, high-resolution array is being constructed for nuclear structure, astrophysics and reaction studies with radioactive ion beams. The array consists of 20 Silicon-Silicon-CsI(Tl) telescopes, each composed of a 65 um thick strip detector (DE1), a 1.5 mm thick silicon strip detector (DE2) and a 4 cm thick CsI(Tl) scintillator read out by a PIN diode (E). It will cover an laboratory angular range from 5 to 28 deg with angular resolution +- 0.16 deg. In this talk, details of the design and of the science that can be studied with the new array will be discussed. This work was supported by the National Science Foundation under Grant No. PHY-99-77707.

van Goethem, Marc-Jan; Caraley, A.; Charity, R. J.; Desouza, R. T.; Hosmer, P.; Lynch, William; Moroni, A.; Sobotka, L. G.; Verde, G.; Viola, V. E.; Wallace, M.

2000-10-01

258

ThreeThree--Jet Angular CorrelationsJet Angular Correlations inin epep CollisionsCollisions  

E-print Network

ThreeThree--Jet Angular CorrelationsJet Angular Correlations inin epep CollisionsCollisions Stephen the ZEUS Collaboration #12;Tests of QCD at HERATests of QCD at HERA Jet cross sections vs fixed-order QCD groups QCD Color Factors #12;Color Factors in 4Color Factors in 4--Jet Events at LEPJet Events at LEP 4

259

Variation in Angular Velocity and Angular Acceleration of a Particle in Rectilinear Motion  

ERIC Educational Resources Information Center

We discuss the angular velocity ([image omitted]) and angular acceleration ([image omitted]) associated with a particle in rectilinear motion with constant acceleration. The discussion was motivated by an observation that students and even teachers have difficulty in ascribing rotational motion concepts to a particle when the trajectory is a…

Mashood, K. K.; Singh, V. A.

2012-01-01

260

Approximations to toroidal harmonics  

SciTech Connect

Toroidal harmonics P/sub n-1/2/ (cosh ) and Q/sub n-1/2/ (cosh ) are useful in solutions to Maxwell's equations in toroidal coordinates. In order to speed their computation, a set of approximations has been developed that is valid over the range 0 < < infinity. The functional form used for these approximations is dictated by their behavior as 0 and as infinity, and is similar to that used by Hastings in his approximations to the elliptic integrals K and E. This report lists approximations of several mathematical forms with varying numbers of terms; approximations to the above Legendre functions are given for n = 0 through 6. Coefficients of each expansion have been adjusted to distribute the relative error in equi-amplitude peaks over some range, typically .05 < < 5, and in the best cases these peaks are less than 10 . The simple method used to determine the approximations is described. Relative error curves are also presented, obtained by comparing approximations to the more accurate values computed by direct summation of the hypergeometric series.

Pribyl, P.A.

1985-10-01

261

Pumping angular momentum by driven chaotic scattering  

E-print Network

Chaotic scattering with an internal degree of freedom and the possibility to generate directed transport of angular momentum is studied in a specific model, a magnetic dipole moving in a periodically modulated magnetic field confined to a compact region in space. We show that this system is an irregular scatterer in large parts of its parameter space. If in addition all spatio-temporal symmetries are broken, directed transport of mass as well as angular momentum occurs. The sensitive parameter dependence of the corresponding currents includes frequent sign reversals. Zeros of either quantity entail the exclusive occurrence of the other and thus give rise in particular to angular-momentum separation without mass transport as a classical analogue of spin-polarized currents.

T. Dittrich; F. L. Dubeibe

2008-04-29

262

Linear Approximation SAR Azimuth Processing Study  

NASA Technical Reports Server (NTRS)

A segmented linear approximation of the quadratic phase function that is used to focus the synthetic antenna of a SAR was studied. Ideal focusing, using a quadratic varying phase focusing function during the time radar target histories are gathered, requires a large number of complex multiplications. These can be largely eliminated by using linear approximation techniques. The result is a reduced processor size and chip count relative to ideally focussed processing and a correspondingly increased feasibility for spaceworthy implementation. A preliminary design and sizing for a spaceworthy linear approximation SAR azimuth processor meeting requirements similar to those of the SEASAT-A SAR was developed. The study resulted in a design with approximately 1500 IC's, 1.2 cubic feet of volume, and 350 watts of power for a single look, 4000 range cell azimuth processor with 25 meters resolution.

Lindquist, R. B.; Masnaghetti, R. K.; Belland, E.; Hance, H. V.; Weis, W. G.

1979-01-01

263

Cosmic microwave background bispectrum on small angular scales  

E-print Network

This article investigates the non-linear evolution of cosmological perturbations on sub-Hubble scales in order to evaluate the unavoidable deviations from Gaussianity that arise from the non-linear dynamics. It shows that the dominant contribution to modes coupling in the cosmic microwave background temperature anisotropies on small angular scales is driven by the sub-Hubble non-linear evolution of the dark matter component. The perturbation equations, involving in particular the first moments of the Boltzmann equation for the photons, are integrated up to second order in perturbations. An analytical analysis of the solutions gives a physical understanding of the result as well as an estimation of its order of magnitude. This allows to quantify the expected deviation from Gaussianity of the cosmic microwave background temperature anisotropy and, in particular, to compute its bispectrum on small angular scales. Restricting to equilateral configurations, we show that the non-linear evolution accounts for a contribution that would be equivalent to a constant primordial non-Gaussianity of order fNL~25 on scales ranging approximately from l~1000 to l~3000.

Cyril Pitrou; Jean-Philippe Uzan; Francis Bernardeau

2008-09-18

264

ANGULAR MOMENTUM TRANSPORT IN CONVECTIVELY UNSTABLE SHEAR FLOWS  

SciTech Connect

Angular momentum transport due to hydrodynamic turbulent convection is studied using local three-dimensional numerical simulations employing the shearing box approximation. We determine the turbulent viscosity from non-rotating runs over a range of values of the shear parameter and use a simple analytical model in order to extract the non-diffusive contribution ({Lambda}-effect) to the stress in runs where rotation is included. Our results suggest that the turbulent viscosity is on the order of the mixing length estimate and weakly affected by rotation. The {Lambda}-effect is non-zero and a factor of 2-4 smaller than the turbulent viscosity in the slow rotation regime. We demonstrate that for Keplerian shear, the angular momentum transport can change sign and be outward when the rotation period is greater than the turnover time, i.e., when the Coriolis number is below unity. This result seems to be relatively independent of the value of the Rayleigh number.

Kaepylae, Petri J.; Korpi, Maarit J.; Snellman, Jan E. [Department of Physics, Division of Geophysics and Astronomy, FI-00014 University of Helsinki (Finland); Brandenburg, Axel [NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden); Narayan, Ramesh [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)

2010-08-10

265

Angular-momentum-dependent orbital-free density functional theory.  

PubMed

Orbital-free (OF) density functional theory (DFT) directly solves for the electron density rather than the wave function of many electron systems, greatly simplifying and enabling large scale first principles simulations. However, the required approximate noninteracting kinetic energy density functionals and local electron-ion pseudopotentials severely restrict the general applicability of conventional OFDFT. Here, we present a new generation of OFDFT called angular-momentum-dependent (AMD)-OFDFT to harness the accuracy of Kohn-Sham DFT and the simplicity of OFDFT. The angular momenta of electrons are explicitly introduced within atom-centered spheres so that the important ionic core region can be accurately described. In addition to conventional OF total energy functionals, we introduce a crucial nonlocal energy term with a set of AMD energies to correct errors due to the kinetic energy density functional and the local pseudopotential. We find that our AMD-OFDFT formalism offers substantial improvements over conventional OFDFT, as we show for various properties of the transition metal titanium. PMID:23971595

Ke, Youqi; Libisch, Florian; Xia, Junchao; Wang, Lin-Wang; Carter, Emily A

2013-08-01

266

Orbital angular momentum in the nucleons  

E-print Network

In the last decade, it has been realized that the orbital angular momentum of partons inside the nucleon plays a major role. It contributes significantly to nucleon properties and is at the origin of many asymmetries observed in spin physics. It is therefore of paramount importance to determine this quantity if we want to understand the nucleon internal structure and experimental observables. This triggered numerous discussions and controversies about the proper definition of orbital angular momentum and its extraction from experimental data. We summarize the present situation and discuss recent developments in this field.

Cédric Lorcé

2014-06-26

267

Probing Angular Correlations in Sequential Double Ionization  

SciTech Connect

We study electron correlation in sequential double ionization of noble gas atoms and HCl in intense, femtosecond laser pulses. We measure the photoelectron angular distributions of Ne{sup +} relative to the first electron in a pump-probe experiment with 8 fs, 800 nm, circularly polarized laser pulses at a peak intensity of a few 10{sup 15} W/cm{sup 2}. Using a linear-linear pump-probe setup, we further study He, Ar, and HCl. We find a clear angular correlation between the two ionization steps in the sequential double ionization intensity regime.

Fleischer, A. [Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario, K1A 0R6 (Canada); Department of Physics and Solid State Institute, Technion, Haifa 32000 (Israel); Woerner, H. J. [Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario, K1A 0R6 (Canada); ETH Zuerich, Wolfgang-Pauli-Strasse 10, 8093 Zuerich (Switzerland); Arissian, L. [Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario, K1A 0R6 (Canada); Texas A and M University, College Station, Texas 77843 (United States); Liu, L. R. [Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario, K1A 0R6 (Canada); University of Toronto, 40 St. George Street, Toronto, Ontario M5S 2E4 (Canada); Meckel, M.; Rippert, A.; Doerner, R. [Institut fuer Kernphysik, Goethe Universitaet, Max-von-Laue Strasse 1, D-60438 Frankfurt (Germany); Villeneuve, D. M.; Corkum, P. B.; Staudte, A. [Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario, K1A 0R6 (Canada)

2011-09-09

268

Angular distribution of emission from hyperbolic metamaterials  

NASA Astrophysics Data System (ADS)

We have studied angular distribution of emission of dye molecules deposited on lamellar metal/dielectric and Si/Ag nanowire based metamaterials with hyperbolic dispersion. In agreement with the theoretical prediction, the emission pattern of dye on top of lamellar metamaterial is similar to that on top of metal. At the same time, the effective medium model predicts the emission patterns of the nanowire array and the dye film deposited on glass to be nearly identical to each other. This is not the case of our experiment. We tentatively explain the nearly Lambertian (~cos?) angular distribution of emission of the nanowire based sample by a surface roughness.

Gu, Lei; Livenere, J. E.; Zhu, G.; Tumkur, T. U.; Hu, H.; Cortes, C. L.; Jacob, Z.; Prokes, S. M.; Noginov, M. A.

2014-12-01

269

Angular distribution of emission from hyperbolic metamaterials  

PubMed Central

We have studied angular distribution of emission of dye molecules deposited on lamellar metal/dielectric and Si/Ag nanowire based metamaterials with hyperbolic dispersion. In agreement with the theoretical prediction, the emission pattern of dye on top of lamellar metamaterial is similar to that on top of metal. At the same time, the effective medium model predicts the emission patterns of the nanowire array and the dye film deposited on glass to be nearly identical to each other. This is not the case of our experiment. We tentatively explain the nearly Lambertian (?cos?) angular distribution of emission of the nanowire based sample by a surface roughness. PMID:25476126

Gu, Lei; Livenere, J. E.; Zhu, G.; Tumkur, T. U.; Hu, H.; Cortes, C. L.; Jacob, Z.; Prokes, S. M.; Noginov, M. A.

2014-01-01

270

Angular distribution of emission from hyperbolic metamaterials.  

PubMed

We have studied angular distribution of emission of dye molecules deposited on lamellar metal/dielectric and Si/Ag nanowire based metamaterials with hyperbolic dispersion. In agreement with the theoretical prediction, the emission pattern of dye on top of lamellar metamaterial is similar to that on top of metal. At the same time, the effective medium model predicts the emission patterns of the nanowire array and the dye film deposited on glass to be nearly identical to each other. This is not the case of our experiment. We tentatively explain the nearly Lambertian (?cos?) angular distribution of emission of the nanowire based sample by a surface roughness. PMID:25476126

Gu, Lei; Livenere, J E; Zhu, G; Tumkur, T U; Hu, H; Cortes, C L; Jacob, Z; Prokes, S M; Noginov, M A

2014-01-01

271

Evaluation of the table Mountain Ronchi telescope for angular tracking  

NASA Technical Reports Server (NTRS)

The performance of the University of California at San Diego (UCSD) Table Mountain telescope was evaluated to determine the potential of such an instrument for optical angular tracking. This telescope uses a Ronchi ruling to measure differential positions of stars at the meridian. The Ronchi technique is summarized and the operational features of the Table Mountain instrument are described. Results from an analytic model, simulations, and actual data are presented that characterize the telescope's current performance. For a star pair of visual magnitude 7, the differential uncertainty of a 5-min observation is about 50 nrad (10 marcsec), and tropospheric fluctuations are the dominant error source. At magnitude 11, the current differential uncertainty is approximately 800 nrad (approximately 170 marcsec). This magnitude is equivalent to that of a 2-W laser with a 0.4-m aperture transmitting to Earth from a spacecraft at Saturn. Photoelectron noise is the dominant error source for stars of visual magnitude 8.5 and fainter. If the photoelectron noise is reduced, ultimately tropospheric fluctuations will be the limiting source of error at an average level of 35 nrad (7 marcsec) for stars approximately 0.25 deg apart. Three near-term strategies are proposed for improving the performance of the telescope to the 10-nrad level: improving the efficiency of the optics, masking background starlight, and averaging tropospheric fluctuations over multiple observations.

Lanyi, G.; Purcell, G.; Treuhaft, R.; Buffington, A.

1992-01-01

272

Freehand spatial-angular compounding of photoacoustic images  

NASA Astrophysics Data System (ADS)

Photoacoustic (PA) imaging is an emerging medical imaging modality that relies on the absorption of optical energy and the subsequent emission of acoustic waves that are detected with a conventional ultrasound probe. PA images are susceptible to background noise artifacts that reduce the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). We investigated spatial-angular compounding of PA images to enhance these image qualities. Spatial-angular compounding was implemented by averaging multiple PA images acquired as an ultrasound probe was rotated about the elevational axis with the laser beam and PA target fixed in the same location. An external tracking system was used to provide the position and orientation (i.e. pose) information of each PA image. Based on this pose information, frames in similar elevational planes were filtered from the acquired image data and compounded using one of two methods. One method registered overlapping signals between frames prior to compounding (using the pose information), while the second method omitted this spatial registration step. These two methods were applied to pre-beamformed RF, beamformed RF, and envelope-detected data, resulting in six different compounding pipelines. Compounded PA images with similar lateral resolution to a single reference image had factors of 1.1 - 1.6, 2.0 - 11.1, and 2.0 - 11.1 improvements in contrast, CNR, and SNR, respectively, when compared to the reference image. These improvements depended on the amount of relative motion between the reference image and the images that were compounded. The inclusion of spatial registration prior to compounding preserved lateral resolution and signal location when the relative rotations about the elevation axis were 3.5° or less for images that were within an elevational distance of 2.5 mm from the reference image, particularly when the method was applied to the enveloped-detected data. Results indicate that spatial-angular compounding has the potential to improve image quality for a variety of photoacoustic imaging applications.

Kang, Hyun-Jae; Lediju Bell, Muyinatu A.; Guo, Xiaoyu; Taylor, Russell H.; Boctor, Emad M.

2014-03-01

273

Fourier Series Approximation  

NSDL National Science Digital Library

This site includes a Java applet that displays Fourier series approximations and corresponding magnitude and phase spectra of a periodic continuous-time signal. Select from provided signals, or draw a signal with the mouse.

2012-08-14

274

Tsunami Travel Time Approximation  

NSDL National Science Digital Library

Eric Grosfils, Pomona College Summary Students are asked to calculate approximate tsunami travel times across the Pacific basin. The assignment builds off of a lab introducing students to Spatial Analyst, and ...

Grosfils, Eric

275

Excited bands of [sup 168]Yb in an angular momentum projected theory  

SciTech Connect

The angular momentum projected Tamm-Dancoff approximation is applied to describe eight excited rotational bands of the nucleus [sup 168]Yb up to very high angular momenta. The good agreement with the experimental data allows us to assign parity and angular momentum to some bands which previously had uncertain assignment. Beside the energy levels, we describe moments of inertia, gyromagnetic factors, and [ital B]([ital E]2) transition probabilities along the yrast band. The pairing properties of this nucleus at high spins are discussed in the frame of a symmetry violating wave function. We do not find it necessary to invoke a phase transition to obtain a good agreement with the experimental data at very high spins.

Sun, Y.; Egido, J.L. (Departamento de Fisica Teorica C-XI, Universidad Autonoma de Madrid, E-28049 Madrid (Spain))

1994-10-01

276

SUB-M-RAD ANGULAR STABILITY MEASUREMENTS BY USE OF LONG TRACE PROFILER BASED SYSTEMS.  

SciTech Connect

High accuracy angle measurement at the sub-{mu}rad level requires extremely high instrument stability. In order to reach sub-{mu}rad stability (0.1 arc second or less) over long time periods, it is necessary to maintain the test object and almost all of the optical components in the measuring instrument in very steady positions. However, mechanical force relaxation, thermal expansion, and asymmetric structures produce angular and linear displacements in the system resulting in angular measurement error. A Long-Trace-Profiler (LTP)-based stable equipment is used to test precision angular stability with sub-{mu}rad resolution. Long term stability over 15 hours has been measured on different kind of mechanical structures. Temperature monitoring during the tests is extremely important. Some test results showing the effects of thermal variations are presented, which indicate that temperature stability on the order of 0.1 C is absolutely necessary for repeatable sub-{mu}rad measurements. The optical method, using optics with an even number of reflecting surfaces (for example, a right angle prism, pentaprism, or rhomboid prism) to reduce the influence of existing angular displacement, is introduced and the comparison measurement is presented. An optical fiber transfer line is able to reduce the laser angular shift from about 10 {mu}rad to a level of 0.3 {mu}rad rms. Careful system configuration, design and operation are very important for the sub-{mu}rad angle stability.

QIAN,S.

1999-07-23

277

Angular distribution of atoms ejected by laser ablation of different metals  

SciTech Connect

Angular distributions of 13 different metals ejected by laser ablation using fourth harmonics (wavelength=266 nm) of neodymium doped yttrium aluminum garnet laser and a fluence close to near-threshold value (2.3 J/cm{sup 2}) have been investigated with a high angular resolution. The angular distribution which is characterized by the exponent n of cos{sup n} theta distribution showed very broad range of values between 3 and 24 for different metals. A simple relation that the exponent n is proportional to the square root of particle atomic weight as reported previously has not been observed. Instead, a general trend has been found that the metals with higher sublimation energy such as Ta and Zr show narrower angular distribution than those with lower sublimation energy such as Sn and In. While the sublimation energy of metals has a great influence on the angular distribution of ejected atoms, a simple consideration suggests that their thermal conductivity and specific heat have little effect on it.

Konomi, I.; Motohiro, T. [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku-ku, Nagoya 468-8511 (Japan); Toyota Central Research and Development Laboratories, Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Asaoka, T. [Toyota Central Research and Development Laboratories, Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan)

2009-07-01

278

Approximation and invariant measures  

Microsoft Academic Search

We prove certain approximation theorems for the class of invertible, measurable, and non-singular transformations of the unit interval. The main results concern the approximation of such transformations by those having no a-finite invariant measure absolutely continuous with respect to Lebesgue measure. We are indebted to A. ION~SCTJ TULC~A for making available to us a preprint of her paper [6] which

R. V. Chacon; N. Friedman

1965-01-01

279

Diophantine Approximations on Fractals  

Microsoft Academic Search

We exploit dynamical properties of diagonal actions to derive results in Diophantine approximations. In particular, we prove\\u000a that the continued fraction expansion of almost any point on the middle third Cantor set (with respect to the natural measure)\\u000a contains all finite patterns (hence is well approximable). Similarly, we show that for a variety of fractals in [0, 1]2, possessing some

Manfred Einsiedler; Lior Fishman; Uri Shapira

2011-01-01

280

Approximating Markov chains.  

PubMed

A common framework of finite state approximating Markov chains is developed for discrete time deterministic and stochastic processes. Two types of approximating chains are introduced: (i) those based on stationary conditional probabilities (time averaging) and (ii) transient, based on the percentage of the Lebesgue measure of the image of cells intersecting any given cell. For general dynamical systems, stationary measures for both approximating chains converge weakly to stationary measures for the true process as partition width converges to 0. From governing equations, transient chains and resultant approximations of all n-time unit probabilities can be computed analytically, despite typically singular true-process stationary measures (no density function). Transition probabilities between cells account explicitly for correlation between successive time increments. For dynamical systems defined by uniformly convergent maps on a compact set (e.g., logistic, Henon maps), there also is weak continuity with a control parameter. Thus all moments are continuous with parameter change, across bifurcations and chaotic regimes. Approximate entropy is seen as the information-theoretic rate of entropy for approximating Markov chains and is suggested as a parameter for turbulence; a discontinuity in the Kolmogorov-Sinai entropy implies that in the physical world, some measure of coarse graining in a mixing parameter is required. PMID:11607293

Pincus, S M

1992-05-15

281

Approximate kernel competitive learning.  

PubMed

Kernel competitive learning has been successfully used to achieve robust clustering. However, kernel competitive learning (KCL) is not scalable for large scale data processing, because (1) it has to calculate and store the full kernel matrix that is too large to be calculated and kept in the memory and (2) it cannot be computed in parallel. In this paper we develop a framework of approximate kernel competitive learning for processing large scale dataset. The proposed framework consists of two parts. First, it derives an approximate kernel competitive learning (AKCL), which learns kernel competitive learning in a subspace via sampling. We provide solid theoretical analysis on why the proposed approximation modelling would work for kernel competitive learning, and furthermore, we show that the computational complexity of AKCL is largely reduced. Second, we propose a pseudo-parallelled approximate kernel competitive learning (PAKCL) based on a set-based kernel competitive learning strategy, which overcomes the obstacle of using parallel programming in kernel competitive learning and significantly accelerates the approximate kernel competitive learning for large scale clustering. The empirical evaluation on publicly available datasets shows that the proposed AKCL and PAKCL can perform comparably as KCL, with a large reduction on computational cost. Also, the proposed methods achieve more effective clustering performance in terms of clustering precision against related approximate clustering approaches. PMID:25528318

Wu, Jian-Sheng; Zheng, Wei-Shi; Lai, Jian-Huang

2015-03-01

282

Canopus Angular Diameter Revisited by the AMBER Instrument of the VLT Interferometer  

Microsoft Academic Search

We used the VLTI\\/AMBER instrument to obtain interferometric data on the F0I star Canopus (visibilities and closure phases in the H and K bands with spectral resolution of 35). The adopted baselines (100 m) and the high quality of the VLTI\\/AMBER observations allowed us to measure fringe visibilities up to the third visibility lobe of Canopus.The angular diameter has been

P. Bendjoya; A. Domiciano de Souza; F. Vakili; F. Millour; R. Petrov

2009-01-01

283

A New Automatic System for Angular Measurement and Calibration in Radiometric Instruments  

PubMed Central

This paper puts forward the design, construction and testing of a new automatic system for angular-response measurement and calibration in radiometric instruments. Its main characteristics include precision, speed, resolution, noise immunity, easy programming and operation. The developed system calculates the cosine error of the radiometer under test by means of a virtual instrument, from the measures it takes and through a mathematical procedure, thus allowing correcting the radiometer with the aim of preventing cosine error in its measurements. PMID:22319320

Marquez, Jose Manuel Andujar; Bohórquez, Miguel Ángel Martínez; Garcia, Jonathan Medina; Nieto, Francisco Jose Aguilar

2010-01-01

284

A Multiwire Proportional Chamber for Precision Studies of Neutron Beta Decay Angular Correlations  

E-print Network

A new multiwire proportional chamber (MWPC) was designed and constructed for precision studies of neutron beta decay angular correlations. Its design has several novel features, including the use of low pressure neopentane as the MWPC gas and an entrance window made of thin Mylar sheet reinforced with Kevlar fibers. In the initial off-line performance tests, the gas gain of neopentane and the position resolution were studied.

Ito, T M; Filippone, B W; Martin, J W; Plaster, B; Rybka, G; Yuan, J; 10.1016/j.nima.2006.11.026

2008-01-01

285

A Multiwire Proportional Chamber for Precision Studies of Neutron Beta Decay Angular Correlations  

E-print Network

A new multiwire proportional chamber (MWPC) was designed and constructed for precision studies of neutron beta decay angular correlations. Its design has several novel features, including the use of low pressure neopentane as the MWPC gas and an entrance window made of thin Mylar sheet reinforced with Kevlar fibers. In the initial off-line performance tests, the gas gain of neopentane and the position resolution were studied.

T. M. Ito; R. Carr; B. W. Filippone; J. W. Martin; B. Plaster; G. Rybka; J. Yuan

2007-02-10

286

An adiabatic approximation for grain alignment theory  

NASA Astrophysics Data System (ADS)

The alignment of interstellar dust grains is described by the joint distribution function for certain `internal' and `external' variables, where the former describe the orientation of the axes of a grain with respect to its angular momentum, J, and the latter describe the orientation of J relative to the interstellar magnetic field. I show how the large disparity between the dynamical time-scales of the internal and external variables - which is typically 2-3 orders of magnitude - can be exploited to simplify calculations of the required distribution greatly. The method is based on an `adiabatic approximation' which closely resembles the Born-Oppenheimer approximation in quantum mechanics. The adiabatic approximation prescribes an analytic distribution function for the `fast' dynamical variables and a simplified Fokker-Planck equation for the `slow' variables which can be solved straightforwardly using various techniques. These solutions are accurate to O(epsilon), where epsilon is the ratio of the fast and slow dynamical time-scales. As a simple illustration of the method, I derive an analytic solution for the joint distribution established when Barnett relaxation acts in concert with gas damping. The statistics of the analytic solution agree with the results of laborious numerical calculations which do not exploit the adiabatic approximation.

Roberge, W. G.

1997-10-01

287

An Adiabatic Approximation for Grain Alignment Theory  

NASA Astrophysics Data System (ADS)

The alignment of interstellar dust grains is described by the joint distribution function for certain ``internal'' and ``external'' variables, where the former describe the orientation of a grain's axes with respect to its angular momentum, J, and the latter describe the orientation of J relative to the interstellar magnetic field. I show how the large disparity between the dynamical timescales of the internal and external variables--- which is typically 2--3 orders of magnitude--- can be exploited to greatly simplify calculations of the required distribution. The method is based on an ``adiabatic approximation'' which closely resembles the Born-Oppenheimer approximation in quantum mechanics. The adiabatic approximation prescribes an analytic distribution function for the ``fast'' dynamical variables and a simplified Fokker-Planck equation for the ``slow'' variables which can be solved straightforwardly using various techniques. These solutions are accurate to cal {O}(epsilon ), where epsilon is the ratio of the fast and slow dynamical timescales. As a simple illustration of the method, I derive an analytic solution for the joint distribution established when Barnett relaxation acts in concert with gas damping. The statistics of the analytic solution agree with the results of laborious numerical calculations which do not exploit the adiabatic approximation.

Roberge, W. G.

1997-12-01

288

TE10 resonant iris with angular alignment  

E-print Network

TE10 resonant iris with angular alignment TE101 mode cavities TM110 mode cavities TE01 (TE10) resonant iris 1a 1b Fig. 1: Filter configurations utilizing cavity and iris resonances. Resonant irises and resonant irises. Two different configurations, which allow precise control of the direct couplings between

Bornemann, Jens

289

Angular distribution of turbulence in wave space  

NASA Technical Reports Server (NTRS)

An alternative to the one-point closure model for turbulence, the large eddy simulation (LES), together with its more exact relative, direct numerical simulation (DNS) are discussed. These methods are beginning to serve as partial substitutes for turbulence experiments. The eddy damped quasi-normal Markovian (EDQNM) theory is reviewed. Angular distribution of the converted data was examined in relationship to EDQNM.

Coleman, G.; Ferziger, J. H.; Bertoglio, J. P.

1987-01-01

290

Thermally Activated Seizure of Angular Contact Bearings  

Microsoft Academic Search

Equations have been developed relating friction-power to bearing element temperatures for the particular case of prelubricated or lightly lubricated ball bearings. An expression is derived for the change in relative dimensions of an angular contact bearing, as determined by the temperature gradient across the bearing. A second expression is found for the accommodation of the bearing to expansion, this accommodation

R. A. Burton; H. E. Staph

1967-01-01

291

SCUFFING BEHAVIOUR IN ANGULAR CONTACT BALLBEARINGS  

Microsoft Academic Search

An experimental study has been performed both on the specimens and original test rig to estimate scuffing limits in angular contact ball bearings. From the scuffing approaches, it can be detached the idea that, any scuffing mechanism considered, there is an energetically unbalance in the rolling contact. Therefore we consider an energetically criterion the most adequate to estimate scuffing limits.

Carmen Bujoreanu; Daniel Nelias

292

Heteromodal conceptual processing in the angular gyrus  

PubMed Central

Concepts bind together the features commonly associated with objects and events to form networks in long-term semantic memory. These conceptual networks are the basis of human knowledge and underlie perception, imagination, and the ability to communicate about experiences and the contents of the environment. Although it is often assumed that this distributed semantic information is integrated in higher-level heteromodal association cortices, open questions remain about the role and anatomic basis of heteromodal representations in semantic memory. Here we used combined neuroimaging evidence from functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) to characterize the cortical networks underlying concept representation. Using a lexical decision task, we examined the processing of concepts in four semantic categories that varied on their sensory-motor feature associations (sight, sound, manipulation, and abstract). We found that the angular gyrus was activated across all categories regardless of their modality-specific feature associations, consistent with a heteromodal account for the angular gyrus. Exploratory analyses suggested that categories with weighted sensory-motor features additionally recruited modality-specific association cortices. Furthermore, DTI tractography identified white matter tracts connecting these regions of modality-specific functional activation with the angular gyrus. These findings are consistent with a distributed semantic network that includes a heteromodal, integrative component in the angular gyrus in combination with sensory-motor feature representations in modality-specific association cortices. PMID:23333416

Bonner, Michael F.; Peelle, Jonathan E.; Cook, Philip A.; Grossman, Murray

2013-01-01

293

An angular momentum bound at null infinity  

E-print Network

We prove an inequality relating the trace of the extrinsic curvature, the total angular momentum, the centre of mass, and the Trautman-Bondi mass for a class of gravitational initial data sets with constant mean curvature extending to null infinity. As an application we obtain non-existence results for the asymptotic Dirichlet problem for CMC hypersurfaces in stationary space-times.

Piotr T. Chru?ciel; Paul Tod

2007-06-27

294

Optical angular momentum: Multipole transitions and photonics  

SciTech Connect

The premise that multipolar decay should produce photons uniquely imprinted with a measurably corresponding angular momentum is shown in general to be untrue. To assume a one-to-one correlation between the transition multipoles involved in source decay and detector excitation is to impose a generally unsupportable one-to-one correlation between the multipolar form of emission transition and a multipolar character for the detected field. It is specifically proven impossible to determine without ambiguity, by use of any conventional detector, and for any photon emitted through the nondipolar decay of an atomic excited state, a unique multipolar character for the transition associated with its generation. Consistent with the angular quantum uncertainty principle, removal of a detector from the immediate vicinity of the source produces a decreasing angular uncertainty in photon propagation direction, reflected in an increasing range of integer values for the measured angular momentum. In such a context it follows that when the decay of an electronic excited state occurs by an electric quadrupolar transition, for example, any assumption that the radiation so produced is conveyed in the form of 'quadrupole photons' is experimentally unverifiable. The results of the general proof based on irreducible tensor analysis invite experimental verification, and they signify certain limitations on quantum optical data transmission.

Andrews, David L. [Nanostructures and Photomolecular Systems, School of Chemistry, University of East Anglia, Norwich NR4 7TJ (United Kingdom)

2010-03-15

295

Texture evolution during equal channel angular extrusion  

Microsoft Academic Search

It is shown that equal channel angular extrusion (ECAE) is an effective technique to control texture of metals and alloys. Two processing parameters, the route and number of passes, exert an important influence on texture evolution. Routes define orientations allowing the creation of numerous new components. Before four passes, depending on route and initial texture strength, all types of texture

S Ferrasse; V. M Segal; S. R Kalidindi; F Alford

2004-01-01

296

?-Neutrino Angular Correlations in Muon Capture  

NASA Astrophysics Data System (ADS)

Doppler-broadened ?-ray transitions have been observed for the first time in the reaction ?-+(Z,A)-->(Z-1,A)+??, which are suitable for analysis in terms of angular correlations between the neutrino and a de-excitation nuclear ?-ray. The observed transitions are interpreted in terms of ?-? correlation coefficients which are functions of the weak-interaction coupling constants.

Miller, G. H.; Eckhause, M.; Kane, F. R.; Martin, P.; Welsh, R. E.

1972-10-01

297

Spacecraft Angular State Estimation After Sensor Failure  

NASA Technical Reports Server (NTRS)

This work describes two algorithms for computing the angular rate and attitude in case of a gyro failure in a spacecraft (SC) with a special mission profile. The source of the problem is presented, two algorithms are suggested, an observability study is carried out, and the efficiency of the algorithms is demonstrated.

Bauer, Frank (Technical Monitor); BarItzhack, Itzhack Y.; Harman, Richard R.

2002-01-01

298

Adaptive Encoding Strongly Improves Function Approximation with CMAC  

Microsoft Academic Search

The Cerebellar Model Arithmetic Computer (CMAC) (Albus 1981) is well known as a good function approximator with local generalization abilities. Depending on the smoothness of the function to be approximated, the resolution as the smallest distinguishable part of the input domain plays a crucial role. If the binary quantizing functions in CMAC are dropped in favor of more general, continuous-valued

Martin Eldracher; Alexander Staller; René Pompl

1997-01-01

299

THE ANGULAR DISTRIBUTION OF Ly{alpha} RESONANT PHOTONS EMERGING FROM AN OPTICALLY THICK MEDIUM  

SciTech Connect

We investigate the angular distribution of Ly{alpha} photons scattering or emerging from an optically thick medium. Since the evolution of specific intensity I in frequency space and angular space are coupled with each other, we first develop the WENO numerical solver to find the time-dependent solutions of the integro-differential equation of I in frequency and angular space simultaneously. We first show that the solutions with the Eddington approximation, which assume that I is linearly dependent on the angular variable {mu}, yield similar frequency profiles of the photon flux as those without the Eddington approximation. However, the solutions of the {mu} distribution evolution are significantly different from those given by the Eddington approximation. First, the angular distribution of I is found to be substantially dependent on the frequency of the photons. For photons with the resonant frequency {nu}{sub 0}, I contains only a linear term of {mu}. For photons with frequencies at the double peaks of the flux, the {mu}-distribution is highly anisotropic; most photons are emitted radially forward. Moreover, either at {nu}{sub 0} or at the double peaks, the {mu} distributions actually are independent of the initial {mu} distribution of photons of the source. This is because the photons with frequencies either at {nu}{sub 0} or the double peaks undergo the process of forgetting their initial conditions due to resonant scattering. We also show that the optically thick medium is a collimator of photons at the double peaks. Photons from the double peaks form a forward beam with a very small opening angle.

Yang Yang; Shu Chiwang [Division of Applied Mathematics, Brown University, Providence, RI 02912 (United States); Roy, Ishani [Imaging Sciences and Biomedical Engineering Division, St Thomas Hospital, Kings College London, SE1 7EH (United Kingdom); Fang Lizhi [Department of Physics, University of Arizona, Tucson, AZ 85721 (United States)

2013-07-20

300

Mechanical and biomechanical analysis of a linear piston design for angular-velocity-based orthotic control.  

PubMed

A linear piston hydraulic angular-velocity-based control knee joint was designed for people with knee-extensor weakness to engage knee-flexion resistance when knee-flexion angular velocity reaches a preset threshold, such as during a stumble, but to otherwise allow free knee motion. During mechanical testing at the lowest angular-velocity threshold, the device engaged within 2 degrees knee flexion and resisted moment loads of over 150 Nm. The device completed 400,000 loading cycles without mechanical failure or wear that would affect function. Gait patterns of nondisabled participants were similar to normal at walking speeds that produced below-threshold knee angular velocities. Fast walking speeds, employed purposely to attain the angular-velocity threshold and cause knee-flexion resistance, reduced maximum knee flexion by approximately 25 degrees but did not lead to unsafe gait patterns in foot ground clearance during swing. In knee collapse tests, the device successfully engaged knee-flexion resistance and stopped knee flexion with peak knee moments of up to 235.6 Nm. The outcomes from this study support the potential for the linear piston hydraulic knee joint in knee and knee-ankle-foot orthoses for people with lower-limb weakness. PMID:23516082

Lemaire, Edward D; Samadi, Reza; Goudreau, Louis; Kofman, Jonathan

2013-01-01

301

Model validation of turbulence effects on orbital angular momentum of single photons for optical communication  

NASA Astrophysics Data System (ADS)

The orbital angular momentum of photons in paraxial beams offers the possibility of arbitrary base-N digits for freespace laser communications. Atmospheric turbulence can cause the orbital angular momentum of photons in a propagating beam to scatter from its original azimuthal mode. The probability of obtaining correct or incorrect measurement of the transmitted orbital angular momentum state after propagation through atmospheric turbulence is calculated from the rotational field correlation (second order field moment). A previously published model of the rotational field correlation for Laguerre-Gaussian beams is limited to the weak turbulence regime and assumes that the turbulence effects can be considered a pure phase perturbation. This model is validated by calculating the same quantity with the extended Huygens-Fresnel integral, valid in all regimes of turbulence. To obtain closed form expressions, a quadratic structure function approximation was applied. The probability of receiving the transmitted orbital angular momentum state was calculated and compared to the existing model. The results indicate that the quadratic structure function approximation leads to a slight overprediction of the probability in the weak turbulence regime. For finite transmitter apertures, the previously published model, with a spherical wave structure function, rather than the plane wave structure function used in the original work, is believed to be the most accurate model in the weak turbulence regime.

Strömqvist Vetelino, Frida E.; Morgan, Ricky J.

2010-04-01

302

A high-resolution optical see-through head-mounted display with eyetracking capability.  

PubMed

A head-mounted display system with fully-integrated eyetracking capability offers multi-fold benefits, not only to fundamental scientific research but also to emerging applications of such technology. A key limitation of the state-of-the-art eyetracked head-mounted display (ET-HMD) technology is the lack of compactness and portability. In this paper, we present an innovative design of a high resolution optical see-through ET-HMD system based on freeform optical technology. A prototype system is demonstrated, which offers a goggle-like compact form factor, non-obstructive see-through field of view and true high-definition image resolution for the virtual display. The see-through view, via the combination of a freeform prism and corrector, achieved better than 0.5 arc minute of angular resolution for the central region of approximately 40-degrees to ensure minimal impacts on the see-through vision of an HMD user. PMID:24514672

Hua, Hong; Hu, Xinda; Gao, Chunyu

2013-12-16

303

Covariant approximation averaging  

E-print Network

We present a new class of statistical error reduction techniques for Monte-Carlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as all-mode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in $N_f=2+1$ lattice QCD using domain-wall fermions. This comparison indicates that AMA significantly reduces statistical errors in Monte-Carlo calculations over conventional methods for the same cost.

Eigo Shintani; Rudy Arthur; Thomas Blum; Taku Izubuchi; Chulwoo Jung; Christoph Lehner

2014-02-02

304

Development of a high resolution scintillating fiber gamma ray telescope  

Microsoft Academic Search

The authors report on further development and testing of a Compton telescope composed of scintillating fibers and position-sensitive photomultipliers. Initial tests of the telescope showed a better than 1-mm (RMS) position resolution and a 17.5-mrad (RMS) angular resolution for 1.2-MeV photons from a collimated 60Co gamma source. This type of device can be used for constructing large-area telescopes for gamma-ray

M. Atac; R. Chaney; D. Chrisman; E. Fenyves; P. Antich

1991-01-01

305

Spin angular momentum transfer from TEM00 focused Gaussian beams to negative refractive index spherical particles  

PubMed Central

We investigate optical torques over absorbent negative refractive index spherical scatterers under the influence of linear and circularly polarized TEM00 focused Gaussian beams, in the framework of the generalized Lorenz-Mie theory with the integral localized approximation. The fundamental differences between optical torques due to spin angular momentum transfer in positive and negative refractive index optical trapping are outlined, revealing the effect of the Mie scattering coefficients in one of the most fundamental properties in optical trapping systems. PMID:21833372

Ambrosio, Leonardo A.; Hernández-Figueroa, Hugo E.

2011-01-01

306

Numerical calculation of near field scalar diffraction using angular spectrum of plane waves theory and FFT  

Microsoft Academic Search

t is a known fact that near field diffraction or Fresnel diffraction\\u000acalculations are difficult to perform exactly. It is in general necessary to\\u000amake some approximations in order to obtain a more suitable form. In this work,\\u000aa numerical implementation based on angular spectrum theory for near field\\u000adiffraction is presented. The method uses Fast Fourier Transforms (FFT) and

Adrian Carbajal-Dominguez; J. Bernal; Jesus E. Gomez Correa; Gabriel Martinez Niconoff

2010-01-01

307

Linear force and moment equations for an annular smooth shaft seal perturbed both angularly and laterally  

NASA Technical Reports Server (NTRS)

Coefficients are derived for equations expressing the lateral force and pitching moments associated with both planar translation and angular perturbations from a nominally centered rotating shaft with respect to a stationary seal. The coefficients for the lowest order and first derivative terms emerge as being significant and are of approximately the same order of magnitude as the fundamental coefficients derived by means of Black's equations. Second derivative, shear perturbation, and entrance coefficient variation effects are adjudged to be small.

Fenwick, J.; Dijulio, R.; Ek, M. C.; Ehrgott, R.

1982-01-01

308

Science/Mathematics Approximation  

E-print Network

: : : : : : 9 Lecture 2 11 2.1 Four MoreWays to Skin a Cat: Approximation Algorithms for Set Cover 11 2 : : : : : : : : : : : : : : : : : : : : : : : 46 6.1.1 A Dumb Randomized Algorithm for MAX CUT : : : : : : : : 46 6.1.2 MAX CUT in Dense Graphs : : : : : : : : : : : : : : : : : : : : : 60 7.1.3 Graph Coloring : : : : : : : : : : : : : : : : : : : : : : : : : : 62 Lecture 8 67 8

Sgall, Jiri

309

Extended Abstract Approximating Visibility  

E-print Network

for Figure 4 June 1, 2000, 21:3 #12;Franklin Approximating Visibility 7 Figure 6: Lake Champlain W Cell 2.2 Lake Champlain West The second test case was the £¥¤§¦¨£T©U£¥¤§¦A£ Lake Champlain West level-1 DEM from

Franklin, W. Randolph

310

Approximating Integrals Using Probability  

ERIC Educational Resources Information Center

As part of a discussion on Monte Carlo methods, which outlines how to use probability expectations to approximate the value of a definite integral. The purpose of this paper is to elaborate on this technique and then to show several examples using visual basic as a programming tool. It is an interesting method because it combines two branches of…

Maruszewski, Richard F., Jr.; Caudle, Kyle A.

2005-01-01

311

Living Expenses (includes approximately  

E-print Network

Students Fall 2014 - Spring 2015 Summer Estimated Expenses -- See Footnote #3 All figures cited are broad approximately $800 for fees) $43,700 $19,600 $55,200 $21,300 $20,900 3 SUMMER 2014-2015 ESTIMATES - Full ) Altoona, Berks, Erie, and Harrisburg 12-Month Estimated Expenses and Financial Guarantee for International

Yener, Aylin

312

Rough approximation quality revisited  

Microsoft Academic Search

In rough set theory, the approximation quality is the traditional measure to evaluate the clas- sification success of attributes in terms of a numerical evaluation of the dependency properties generated by these attributes. In this paper we re-interpret the classical in terms of MZ and PRE measures, and exhibit infinitely many possibilities to define -like measures which are meaning- ful

Gunther Gediga; Ivo Duntsch

2001-01-01

313

Nodal collocation approximation for the multidimensional PL equations applied to transport source problems  

SciTech Connect

PL equations are classical high order approximations to the transport equations which are based on the expansion of the angular dependence of the angular neutron flux and the nuclear cross sections in terms of spherical harmonics. A nodal collocation method is used to discretize the PL equations associated with a neutron source transport problem. The performance of the method is tested solving two 1D problems with analytical solution for the transport equation and a classical 2D problem. (authors)

Verdu, G. [Departamento de Ingenieria Quimica Y Nuclear, Universitat Politecnica de Valencia, Cami de Vera, 14, 46022. Valencia (Spain); Capilla, M.; Talavera, C. F.; Ginestar, D. [Dept. of Nuclear Engineering, Departamento de Matematica Aplicada, Universitat Politecnica de Valencia, Cami de Vera, 14, 46022. Valencia (Spain)

2012-07-01

314

Angular momentum dependent orbital-free density functional theory: Formulation and implementation  

NASA Astrophysics Data System (ADS)

Orbital-free density functional theory (OFDFT) directly solves for the ground-state electron density. It scales linearly with respect to system size, providing a promising tool for large-scale material simulations. Removal of the orbitals requires use of approximate noninteracting kinetic energy density functionals. If replacing ionic cores with pseudopotentials, removal of the orbitals also requires these pseudopotentials to be local. These are two severe challenges to the capabilities of conventional OFDFT. While main group elements are often well described within conventional OFDFT, transition metals remain intractable due to their localized d electrons. To advance the accuracy and general applicability of OFDFT, we have recently reported a general angular momentum dependent formulation as a next-generation OFDFT. In this formalism, we incorporate the angular momenta of electrons by devising a hybrid scheme based on a muffin tin geometry: inside spheres centered at the ionic cores, the electron density is expanded in a set of atom-centered basis functions combined with an onsite density matrix. The explicit treatment of the angular momenta of electrons provides an important basis for accurately describing the important ionic core region, which is not possible in conventional OFDFT. In addition to the conventional OFDFT total energy functional, we introduce a nonlocal energy term containing a set of angular momentum dependent energies to correct the errors due to the approximate kinetic energy density functional and local pseudopotentials. Our approach greatly increases the accuracy of OFDFT while largely preserving its numerical simplicity. Here, we provide details of the theoretical formulation and practical implementation, including the hybrid scheme, the derivation of the nonlocal energy term, the choice of basis functions, the direct minimization of the total energy, the procedure to determine the angular momentum dependent energies, the force formula with Pulay correction, and the solution to emerging numerical instability. To test the angular momentum dependent OFDFT formalism and its numerical implementations, we calculate a diverse set of properties of the transition metal Ti and compare with different levels of DFT approximation. The results suggest that angular momentum dependent OFDFT ultimately will extend the reliable reach of OFDFT to the rest of the periodic table.

Ke, Youqi; Libisch, Florian; Xia, Junchao; Carter, Emily A.

2014-04-01

315

Phenomenological determination of the orbital angular momentum.  

SciTech Connect

Measurements involving the gluon spin, {Delta}G(x, t) and the corresponding asymmetry, A(x,t) = {Delta}G(x,t)/G(x,t) play an important role in quantitative understanding of proton structure. We have modeled the asymmetry perturbatively and calculated model corrections to obtain information about non-perturbative spin-orbit effects. These models are consistent with existing COMPASS and HERMES data on the gluon asymmetry. The J{sub z} = 1/2 sum rule is used to generate values of orbital angular momentum at LO and NLO. For models consistent with data, the orbital angular momentum is small. Our studies specify accuracy that future measurements should achieve to constrain theoretical models for nucleon structure.

Ramsey, G. P.; High Energy Physics; Loyola Univ.

2009-01-01

316

Phenomenological Determination of the Orbital Angular Momentum  

SciTech Connect

Measurements involving the gluon spin, {delta}G(x, t) and the corresponding asymmetry, A(x,t) = {delta}G(x,t)/G(x,t) play an important role in quantitative understanding of proton structure. We have modeled the asymmetry perturbatively and calculated model corrections to obtain information about non-perturbative spin-orbit effects. These models are consistent with existing COMPASS and HERMES data on the gluon asymmetry. The J{sub z} = (1/2) sum rule is used to generate values of orbital angular momentum at LO and NLO. For models consistent with data, the orbital angular momentum is small. Our studies specify accuracy that future measurements should achieve to constrain theoretical models for nucleon structure.

Ramsey, Gordon P. [Physics Department, Loyola University, Chicago, IL 60626 (United States) and High Energy Physics Division, Argonne National Lab, Argonne, IL 60439 (United States)

2009-08-04

317

The quantum angular Calogero-Moser model  

NASA Astrophysics Data System (ADS)

The rational Calogero-Moser model of n one-dimensional quantum particles with inverse-square pairwise interactions (in a confining harmonic potential) is reduced along the radial coordinate of to the `angular Calogero-Moser model' on the sphere S n-1.We discuss the energy spectrum of this quantum system, its degeneracies and the eigenstates. The spectral flow with the coupling parameter yields isospectrality for integer increments. Decoupling the center of mass before effecting the spherical reduction produces a `relative angular Calogero-Moser model', which is analyzed in parallel. We generalize our considerations to the Calogero-Moser models associated with Coxeter groups. Finally, we attach spin degrees of freedom to our particles and extend the results to the spin-Calogero system.

Feigin, Mikhail; Lechtenfeld, Olaf; Polychronakos, Alexios P.

2013-07-01

318

Warped Galaxies From Misaligned Angular Momenta  

E-print Network

A galaxy disk embedded in a rotating halo experiences a dynamical friction force which causes it to warp when the angular momentum axes of the disk and halo are misaligned. Our fully self-consistent simulations of this process induce long-lived warps in the disk which mimic Briggs's rules of warp behavior. They also demonstrate that random motion within the disk adds significantly to its stiffness. Moreover, warps generated in this way have no winding problem and are more pronounced in the extended \\h1 disk. As emphasized by Binney and his co-workers, angular momentum misalignments, which are expected in hierarchical models of galaxy formation, can account for the high fraction of warped galaxies. Our simulations exemplify the role of misaligned spins in warp formation even when the halo density is not significantly flattened.

Victor P. Debattista; J. A. Sellwood

1999-01-12

319

Angular Momentum Transport in Thin Accretion Disks and Intermittent Accretion  

NASA Astrophysics Data System (ADS)

The modes, which can transport angular momentum outward in thin accretion disks, under the least restrictive conditions, are shown to be of the singular type when the ideal MHD approximation is adopted. Thus, a similarity with the theory of the modes, which produce magnetic reconnection in current carrying plasmas, is established. The combined effects of finite plasma temperature, of plasma compressibility, of the gradient of the rotation frequency and of small but not negligible transport coefficients (i.e., violation of the ideal MHD approximation), are shown(B. Coppi and P.S. Coppi, MIT(RLE) Report PTP 97/08, Cambridge, MA, to be published in Ann. Physics (2001)) to be needed for the onset of these non axisymmetric modes when both the vertical and the toroidal component of the magnetic field are of the same magnitudes. The ballooning mode form of the ideal MHD axisymmetric instability, which can fit in a thin disk, is derived ^1 and demonstrated to be difficult to excite. Thus, accretion is envisioned as an intrinsically intermittent process, similar to that of the so-called sawtooth oscillations in magnetically confined plasmas characterized by a preheating phase followed by an infall of matter. Supported in part by the US Department of Energy.

Coppi, P. S.; Coppi, B.

2001-04-01

320

Measurement of angular distributions and  

Microsoft Academic Search

.   Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the meson over a range in the virtual photon negative four-momentum squared GeV and the photon-nucleon invariant mass range GeV. The experiment was performed with the Hermes spectrometer, using a longitudinally polarized positron beam and a He gas target internal to the HERA e storage ring.

P. Galumian; F. Garibaldi; G. Gavrilov; P. Geiger; V. Gharibyan; A. Golendukhin; G. Graw; O. Grebeniouk; C. Grosshauser; A. Gute; V. Gyurjyan; W. Haeberli; D. Hasch; R. Henderson; R. Hertenberger; Y. Holler; H. Ihssen; M. Iodice; A. Izotov; A. Jgoun; C. Jones; R. Kaiser; E. Kinney; M. Kirsch; A. Kisselev; P. Kitching; M. Kolstein; H. Kolster; W. Korsch; V. Kozlov; B. Krause; G. Kyle; W. Lachnit; W. Lorenzon; A. Lung; A. Mateos; K. McIlhany; F. Meissner; F. Menden; D. Mercer; A. Metz; N. Meyners; O. Mikloukho; R. Milner; V. Mitsyn; R. Mozzetti; V. Muccifora; A. Nagaitsev; Y. Naryshkin; F. Neunreither; M. Nupieri; P. Oelwein; H. Ogami; R. Openshaw; J. Ouyang; M. Pitt; S. Potashov; G. Rakness; R. Redwine; R. Ristinen

2000-01-01

321

Angular momentum quantization from Planck's energy quantization  

E-print Network

We present in this work a pedagogical way of quantizing the atomic orbit for the hydrogen's atom model proposed by Bohr without using his hypothesis of angular momentum quantization. In contrast to the usual treatment for the orbital quantization, we show that using energy conservation, correspondence principle and Plank's energy quantization Bohr's hypothesis can be deduced from and is a consequence of the Planck's energy quantization.

Sales, J H O; Bonafe, D S

2007-01-01

322

Modern Physics Problem: Angular Wave Functions  

NSDL National Science Digital Library

The two Physlets show a density plot of the Hydrogenic wavefunction and the solution to the angular, that is, polar, equation. The word "density" refers to a method for plotting 3-D information on a two dimensional screen. Here it has nothing to do with the probability density in quantum mechanics. The polar solutions used here are the unnormalized associated Legendre polynomials, Plm(q,f). Note that the x and z coordinates range from -1 to +1.

Christian, Wolfgang; Belloni, Mario

2007-03-03

323

High Angular Momentum Rydberg Wave Packets  

NASA Astrophysics Data System (ADS)

High angular momentum Rydberg wave packets are studied. Application of carefully tailored electric fields to low angular momentum, high- n (n ˜ 300) Rydberg atoms creates coherent superpositions of Stark states with near extreme values of angular momentum, ?. Wave packet components orbit the parent nucleus at rates that depend on their energy, leading to periods of localization and delocalization as the components come into and go out of phase with each other. Monitoring survival probability signals in the presence of position dependent probing leads to observation of characteristic oscillations based on the composition of the wave packet. The discrete nature of electron energy levels is observed through the measurement of quantum revivals in the wave packet localization signal. Time-domain spectroscopy of these signals allows determination of both the population and phase of individual superposition components. Precise manipulation of wave packets is achieved through further application of pulsed electric fields. Decoherence effects due to background gas collisions and electrical noise are also detailed. Quantized classical trajectory Monte-Carlo simulations are introduced and agree remarkably well with experimental results.

Wyker, Brendan

2011-12-01

324

Angular Momentum Transport in Circumplanetary Disks  

NASA Astrophysics Data System (ADS)

The Galilean satellites likely formed in a late-stage accretion disk that persisted around Jupiter after it was fully formed. The structure of this disk is highly dependent on its ability to transport angular momentum. Uncertainty in the level of angular momentum transport has led to competing theories of circumplanetary disk structure. Despite success in other astrophysical contexts, recent studies indicate that the conditions were not suitable for magnetorotational instabilities to develop in circumplanetary disks. However, it has been suggested that baroclinic instabilities can generate turbulence and provide the necessary transport of angular momentum. We present a 1+1D numerical model of the circumplanetary accretion disk that surrounded Jupiter during the epoch of regular satellite formation. An analysis of the radial entropy gradient in this model indicates that baroclinic instabilities can not only develop but persist throughout the majority of the disk. Furthermore, we find evidence for a two-component, gas-starved disk which may help to reconcile the differences in current competing theories of circumplanetary disk structure.

Mitchell, Tyler R.

2014-11-01

325

Physics from Angular Projection of Rectangular Grids  

E-print Network

In this paper, we present a mathematical model for the angular projection of a rectangular arrangement of points in a grid. This simple, yet interesting problem, has both a scholarly value and applications for data extraction techniques to study the physics of various systems. Our work can interest undergraduate students to understand subtle points in the angular projection of a grid and describes various quantities of interest in the projection with completeness and sufficient rigour. We show that for certain angular ranges, the projection has non-distinctness, and calculate the details of such angles, and correspondingly, the number of distinct points and the total projected length. We focus on interesting trends obtained for the projected length of the grid elements and present a simple application of the model to determine the geometry of an unknown grid whose spatial extensions are known, using measurement of the grid projection at two angles only. Towards the end, our model is shown to have potential applications in various branches of physical sciences including crystallography, astrophysics and bulk properties of materials.

Ashmeet Singh

2014-12-08

326

Round and angular kyphosis in paediatric patients.  

PubMed

Structural kyphosis is a posterior convex deformity of the spine that may appear in childhood then worsen with growth, most notably during the pubertal growth spurt. The abnormal curvature may be smooth, defining round kyphosis, or may display a sharp angular pattern. Angular kyphosis is the more severe of the two forms. The main causes of round kyphosis are postural kyphosis and Scheuermann's disease. The spontaneous outcome is favourable, and round kyphosis is well tolerated in adulthood. The treatment relies on orthopaedic methods in the overwhelming majority of cases. Surgery is reserved for severe rigid kyphosis in older children and for kyphosis responsible for refractory pain or neurological deficits. Surgical treatment carries a non-negligible risk of neurological, gastrointestinal, mechanical, and septic complications, which should be explained clearly to the family. Advances in contemporary posterior instrumentation have considerably limited the indications for anterior approaches. Many conditions may cause angular kyphosis, whose greater severity is related to a greater potential for progression and neurological impairment. Clinical investigations are in order to identify the cause and to plan the surgical strategy. Early surgery may be indicated, via a combined anterior and posterior approach. Anterior strut grafting, anterior or posterior osteotomies, or even vertebral column resections may be necessary to correct a major deformity. PMID:23287399

Miladi, L

2013-02-01

327

Approximate spacetime symmetries and conservation laws  

E-print Network

A notion of geometric symmetry is introduced that generalizes the classical concepts of Killing fields and other affine collineations. There is a sense in which flows under these new vector fields minimize deformations of the connection near a specified observer. Any exact affine collineations that may exist are special cases. The remaining vector fields can all be interpreted as analogs of Poincare and other well-known symmetries near timelike worldlines. Approximate conservation laws generated by these objects are discussed for both geodesics and extended matter distributions. One example is a generalized Komar integral that may be taken to define the linear and angular momenta of a spacetime volume as seen by a particular observer. This is evaluated explicitly for a gravitational plane wave spacetime.

Abraham I Harte

2008-05-28

328

Angular Propagation Descriptions Relevant for Base Station Adaptive Antenna Operations  

Microsoft Academic Search

This paper presents basic short-term angular domain propagation descriptions relevant for beam-oriented SDMA operations, i.e. for spatially based algorithms, contrary to temporally based. A distinction is made between angular variant and invariant situations, i.e. whether the antenna system radiation pattern remains unchanged or not when sweeping over the angular domain. For the angular invariant case, multibeam diversity relations are explained,

Patrick C. F. Eggers

1999-01-01

329

Angular Propagation Descriptions Relevant for Base Station Adaptive Antenna Operations  

Microsoft Academic Search

This paper presents basic short-term angular domain propagation descriptions relevant for beam- oriented SDMA operations, i.e. for spatially based algorithms, contrary to temporally based. A distinction is made between angular variant and invariant situations, i.e. whether the antenna system radiation pattern remains unchanged or not when sweeping over the angular domain. For the angular invariant case, multibeam diversity relations are

PATRICK C. F. EGGERS

1999-01-01

330

Orbital angular momentum exchange in parametric down conversion  

NASA Astrophysics Data System (ADS)

Orbital angular momentum exchange, both in cavity free stimulated parametric down conversion and in an optical parametric oscillator, is studied. In both cases, the conditions for parametric amplification are discussed in terms of the orbital angular momentum exchange between the interacting fields. It is shown that in cavity free parametric down conversion, parametric amplification is conditioned to conserve orbital angular momentum. However, for parametric oscillation, cavity and anisotropy effects play a crucial role in the orbital angular momentum exchange between the interacting fields.

Huguenin, J. A. O.; Martinelli, M.; Caetano, D. P.; Coutinho Dos Santos, B.; Almeida, M. P.; Souto Ribeiro, P. H.; Nussenzveig, P.; Khoury, A. Z.

2006-05-01

331

Photoelectron Angular Distributions of Pyridinide: A Benchmark Application of the Mixed s-p Model to a Truly Polyatomic Anion  

E-print Network

Photoelectron Angular Distributions of Pyridinide: A Benchmark Application of the Mixed s-p Model application to a truly polyatomic system. The mixed s-p model describes the initial state of the anion. The results confirm the predictive power of the mixed s-p model and suggest that despite its approximate

Sanov, Andrei

332

Orbital angular momentum exchange in parametric down conversion  

Microsoft Academic Search

Orbital angular momentum exchange, both in cavity free stimulated parametric down conversion and in an optical parametric oscillator, is studied. In both cases, the conditions for parametric amplification are discussed in terms of the orbital angular momentum exchange between the interacting fields. It is shown that in cavity free parametric down conversion, parametric amplification is conditioned to conserve orbital angular

J. A. O. HUGUENINy; M. Martinelli; D. P. Caetano; B. Coutinho dos santos; M. P. Almeida; P. H. Souto Ribeiro; P. Nussenzveig; A. Z. Khoury

2006-01-01

333

Angular Momentum Regulation during Human Walking: Biomechanics and Control  

Microsoft Academic Search

Motivated by biomechanical studies on human walking, we present a control strategy for biologically realistic walking based on the principle of spin angular momentum regulation. Using a morphologically realistic human model and kinematic gait data, we compute the total spin angular momentum at a self-selected walking speed for one human test subject. We find that dimensionless spin angular momentum remains

Marko Popovic; Andreas Hofmann; Hugh Herr

2004-01-01

334

Two-dimensional code acquisition in time and angular domains  

Microsoft Academic Search

The extension of conventional delay-domain code acquisition to the angular domain is explored. The uncertainty region is partitioned into a number of delay and angular cells. In single-path channels where the interference is modeled as temporarily and spatially white, there exists an optimum number of angular cells minimizing the mean acquisition time. Mean acquisition times up to three times shorter

Marcos D. Katz; Jari H. J. Iinatti; Savo Glisic

2001-01-01

335

Calculation of the dielectric and Kerr constant angular correlation parameters  

Microsoft Academic Search

The angular correlation parameters GL involved in the dielectric and Kerr constants are written as averages over the angular pair correlation function. A perturbation theory for these parameters is developed, based on the expansion of Gubbins and Gray for the angular pair correlation function. Numerical calculations are presented showing the influence of polar and quadrupolar forces on these parameters.

C. G. Gray; K. E. Gubbins

1975-01-01

336

Angularly-resolved elastic light scattering of micro-particles  

NASA Astrophysics Data System (ADS)

From microbiology to astrophysics, the scientific community has long embraced elastic light scattering from small particles as a diagnostic tool. Elastic light scattering has an extremely large scattering cross-section, allowing for single particle interrogation. This is critical in applications where trace amounts of suspect particles are to be detected in a diverse background of natural aerosols. By angularly-resolving the elastically scattered light, features can be detected in these patterns that are sensitive to a particle's morphology (shape, size, internal structure, and composition). An apparatus to collect LA TAOS (Large-Angle Two-dimensional Angular Optical Scattering) patterns from single particles in-situ and in real-time was designed and constructed. The setup utilizes a cross-beam trigger system to minimize the effects of the aberration coma stemming from the main collection optic, an ellipsoidal mirror. LA TAOS patterns of ambient aerosols were collected and analyzed. Approximately 15% of the ambient aerosol had a sphere-like shape. The refractive index of these spheres was estimated by curve-fitting to Lorenz-Mie theory. In addition, the island features prevalent in the LA TAOS pattern were analyzed. Metrics generated from these were used to get partial discrimination between clusters of Bacillus subtilis spores (a simulant for anthrax) and aerosol particles found in the ambient atmosphere. A novel experimental setup for collecting simultaneously LA TAOS patterns at two wavelengths in the mid-infrared was also implemented. With this setup, the relative strength of single-particle absorption could be discerned at the two illuminating wavelengths.

Aptowicz, Kevin B.

337

Measuring the angular momentum distribution in core-collapse supernova progenitors with gravitational waves  

NASA Astrophysics Data System (ADS)

The late collapse, core bounce, and the early postbounce phase of rotating core collapse leads to a characteristic gravitational wave (GW) signal. The precise shape of the signal is governed by the interplay of gravity, rotation, nuclear equation of state (EOS), and electron capture during collapse. We explore the detailed dependence of the signal on total angular momentum and its distribution in the progenitor core by means of a large set of axisymmetric general-relativistic hydrodynamics core-collapse simulations, in which we systematically vary the initial angular momentum distribution in the core. Our simulations include a microphysical finite-temperature EOS, an approximate electron capture treatment during collapse, and a neutrino leakage scheme for the postbounce evolution. Our results show that the total angular momentum of the inner core at bounce and the inner core's ratio of rotational kinetic energy to gravitational energy T/|W| are both robust parameters characterizing the GW signal. We find that the precise distribution of angular momentum is relevant only for very rapidly rotating cores with T/|W|?8% at bounce. We construct a numerical template bank from our baseline set of simulations, and carry out additional simulations to generate trial waveforms for injection into simulated Advanced LIGO noise at a fiducial galactic distance of 10 kpc. Using matched filtering, we show that for an optimally oriented source and Gaussian noise, Advanced LIGO could measure the total angular momentum to within ±20%, for rapidly rotating cores. For most waveforms, the nearest known degree of precollapse differential rotation is correctly inferred by both our matched filtering analysis and an alternative Bayesian model selection approach. We test our results for robustness against systematic uncertainties by injecting waveforms from simulations utilizing a different EOS and variations in the electron fraction in the inner core. The results of these tests show that these uncertainties significantly reduce the accuracy with which the total angular momentum and its precollapse distribution can be inferred from observations.

Abdikamalov, Ernazar; Gossan, Sarah; DeMaio, Alexandra M.; Ott, Christian D.

2014-08-01

338

Optical imaging through non-transparent small aquatic creatures with angular-domain imaging  

NASA Astrophysics Data System (ADS)

When imaging through small aquatic creatures, scattered photons produce problems in image quality and resolution. Angular Domain Imaging (ADI) reduces scattered photons and improves the image quality and resolution. ADI is an imaging technique which utilizes the angular spectrum of photons to filter multiple-scattered photons and accept only photons with small angular deviation from their original trajectory. Advantages of the ADI technique are that it is insensitive to wavelength and the sources are not required to be high optical quality, coherent, or pulsed, as with OCT or time domain. Our target is to image a small species called Branchiostoma lanceolatum, a lancet that is 5-8cm long and 5mm thick, by using ADI to remove the scattering in order to image internal structures. A laser illuminates the lancelet in a water-filled container and a spatiofrequency filter removes the scattered photons before the imager. Experimentally, a coherent Nd:Yag second harmonic (533nm) laser creates images but also optical interference occuring within the internal structures of the lancelet. Conversely, an incoherent broad-band white light source eliminates the structural interference effect; however, the wavelength variation of the scattering coefficient combined with the limitation of the image sensor's dynamic range limit the ability to distinguish the internal structures in many areas. Thus, an IR diode laser (780nm) is used to lower the scattering coefficient as compared to conventional visible light source and to diminish the interference effects due to its shorter coherence length.

Cheng, Rongen L. K.; Tsui, Polly B. L.; Chiang, Gary; Chapman, Glenn H.

2011-03-01

339

APPROXIMATE - A Query Processor that Produces Monotonically Improving Approximate Answers  

Microsoft Academic Search

APPROXIMATE, a query processor that makes approximate answers available if part of the database is unavailable, or if there is not enough time to produce an exact answer, is described. The processor implements approximate query processing, and the accuracy of the approximate result produced improves monotonically with the amount of data retrieved to produce the result. The monotone query processing

Susan V. Vrbsky; Jane W.-S. Liu

1993-01-01

340

Coherent detection and ambiguity resolution for Frequency Diversity Separated Subarray Radar  

Microsoft Academic Search

Radar system using separated subarrays can improve both angular accuracy and resolution at a reduced cost as well as easier transportation. However, the inherent ambiguities due to the existence of grating lobes deteriorate the performance greatly. Frequency diversity technique can be adopted to reduce the ambiguities. In this paper we have investigated the coherent detection and ambiguity resolution performance of

Jiang Wei; Wang Ju; Wu Siliang; Wang Dajun

2008-01-01

341

Angular-momentum evolution in laser-plasma accelerators.  

PubMed

The transverse properties of an electron beam are characterized by two quantities, the emittance which indicates the electron beam extent in the phase space and the angular momentum which allows for nonplanar electron trajectories. Whereas the emittance of electron beams produced in a laser-plasma accelerator has been measured in several experiments, their angular momentum has been scarcely studied. It was demonstrated that electrons in a laser-plasma accelerator carry some angular momentum, but its origin was not established. Here we identify one source of angular-momentum growth and we present experimental results showing that the angular-momentum content evolves during the acceleration. PMID:24116787

Thaury, C; Guillaume, E; Corde, S; Lehe, R; Le Bouteiller, M; Ta Phuoc, K; Davoine, X; Rax, J M; Rousse, A; Malka, V

2013-09-27

342

Angular Momentum and Galaxy Formation Revisited  

NASA Astrophysics Data System (ADS)

Motivated by a new wave of kinematical tracers in the outer regions of early-type galaxies (ellipticals and lenticulars), we re-examine the role of angular momentum in galaxies of all types. We present new methods for quantifying the specific angular momentum j, focusing mainly on the more challenging case of early-type galaxies, in order to derive firm empirical relations between stellar j sstarf and mass M sstarf (thus extending earlier work by Fall). We carry out detailed analyses of eight galaxies with kinematical data extending as far out as 10 effective radii, and find that data at two effective radii are generally sufficient to estimate total j sstarf reliably. Our results contravene suggestions that ellipticals could harbor large reservoirs of hidden j sstarf in their outer regions owing to angular momentum transport in major mergers. We then carry out a comprehensive analysis of extended kinematic data from the literature for a sample of ~100 nearby bright galaxies of all types, placing them on a diagram of j sstarf versus M sstarf. The ellipticals and spirals form two parallel j sstarf-M sstarf tracks, with log-slopes of ~0.6, which for the spirals are closely related to the Tully-Fisher relation, but for the ellipticals derives from a remarkable conspiracy between masses, sizes, and rotation velocities. The ellipticals contain less angular momentum on average than spirals of equal mass, with the quantitative disparity depending on the adopted K-band stellar mass-to-light ratios of the galaxies: it is a factor of ~3-4 if mass-to-light ratio variations are neglected for simplicity, and ~7 if they are included. We decompose the spirals into disks and bulges and find that these subcomponents follow j sstarf-M sstarf trends similar to the overall ones for spirals and ellipticals. The lenticulars have an intermediate trend, and we propose that the morphological types of galaxies reflect disk and bulge subcomponents that follow separate, fundamental j sstarf-M sstarf scaling relations. This provides a physical motivation for characterizing galaxies most basically with two parameters: mass and bulge-to-disk ratio. Next, in an approach complementary to numerical simulations, we construct idealized models of angular momentum content in a cosmological context, using estimates of dark matter halo spin and mass from theoretical and empirical studies. We find that the width of the halo spin distribution cannot account for the differences between spiral and elliptical j sstarf, but that the observations are reproduced well if these galaxies simply retained different fractions of their initial j complement (~60% and ~10%, respectively). We consider various physical mechanisms for the simultaneous evolution of j sstarf and M sstarf (including outflows, stripping, collapse bias, and merging), emphasizing that the vector sum of all such processes must produce the observed j sstarf-M sstarf relations. We suggest that a combination of early collapse and multiple mergers (major or minor) may account naturally for the trend for ellipticals. More generally, the observed variations in angular momentum represent simple but fundamental constraints for any model of galaxy formation.

Romanowsky, Aaron J.; Fall, S. Michael

2012-12-01

343

Angular dependence of dissociative electron attachment topolyatomic molecules: application to the 2B1 metastable state of the H2Oand H2S anions  

SciTech Connect

The angular dependence of dissociative electron attachment (DEA) to polyatomic targets is formulated in the local complex potential model, under the assumption that the axial recoil approximation describes the dissociation dynamics. An additional approximation, which is found to be valid in the case of H2O but not in the case of H2S, makes it possible to describe the angular dependence of DEA solely from an analysis of the fixed-nuclei entrance amplitude, without carrying out nuclear dynamics calculations. For H2S, the final-vibrational-state-specific angular dependence of DEA is obtained by incorporating the variation of the angular dependence of the entrance amplitude with nuclear geometry into the nuclear dynamics. Scattering calculations using the complex Kohn method and, for H2S, full quantum calculations of the nuclear dynamics using the Multi-Configuration Time-Dependent Hartree method, are performed.

Haxton, Daniel J.; McCurdy, C. William; Rescigno, Thomas N.

2006-01-12

344

A gear rattle metric based on the wavelet multi-resolution analysis: Experimental investigation  

NASA Astrophysics Data System (ADS)

In the article an investigation about the feasibility of a wavelet analysis for gear rattle metric in transmission gears, due to tooth impacts under unloaded conditions, is conducted. The technique adopts the discrete wavelet transform (DWT), following the Multi-resolution analysis, to decompose an experimental signal of the relative angular motion of gears into an approximation and in some detail vectors. The described procedure, previously developed by the authors, permits the qualitative evaluation of the impacts occurring between the teeth by examining in particular the detail vectors coming out from the wavelet decomposition. The technique enables discriminating between the impacts occurring on the two different sides of tooth. This situation is typical of the double-sided gear rattle produced in the automotive gear boxes. This paper considers the influence of oil lubricant, inserted between the teeth, in reducing the impacts. Analysis is performed by comparing three different lubrication conditions, and some of the classical wavelet functions adopted in literature are tested as “mother” wavelet. Moreover, comparisons with a metric based on the harmonic analysis by means of the Fast Fourier Transform (FFT), often adopted in this field, are conducted to put in evidence the advantages of the Wavelet technique with reference to the influence of some fundamental operative parameters. The experimental signals of the relative angular rotation of gear are acquired by two high resolution incremental encoders on a specific test rig for lightly loaded gears. The results of the proposed method appear optimistic also in the detection of defects that could produce little variations in the dynamic behavior of unloaded gears.

Brancati, Renato; Rocca, Ernesto; Savino, Sergio

2015-01-01

345

Whole-body angular momentum during stair ascent and descent.  

PubMed

The generation of whole-body angular momentum is essential in many locomotor tasks and must be regulated in order to maintain dynamic balance. However, angular momentum has not been investigated during stair walking, which is an activity that presents a biomechanical challenge for balance-impaired populations. We investigated three-dimensional whole-body angular momentum during stair ascent and descent and compared it to level walking. Three-dimensional body-segment kinematic and ground reaction force (GRF) data were collected from 30 healthy subjects. Angular momentum was calculated using a 13-segment whole-body model. GRFs, external moment arms and net joint moments were used to interpret the angular momentum results. The range of frontal plane angular momentum was greater for stair ascent relative to level walking. In the transverse and sagittal planes, the range of angular momentum was smaller in stair ascent and descent relative to level walking. Significant differences were also found in the ground reaction forces, external moment arms and net joint moments. The sagittal plane angular momentum results suggest that individuals alter angular momentum to effectively counteract potential trips during stair ascent, and reduce the range of angular momentum to avoid falling forward during stair descent. Further, significant differences in joint moments suggest potential neuromuscular mechanisms that account for the differences in angular momentum between walking conditions. These results provide a baseline for comparison to impaired populations that have difficulty maintaining dynamic balance, particularly during stair ascent and descent. PMID:24636222

Silverman, Anne K; Neptune, Richard R; Sinitski, Emily H; Wilken, Jason M

2014-04-01

346

Time-dependent angularly averaged inverse transport  

E-print Network

This paper concerns the reconstruction of the absorption and scattering parameters in a time-dependent linear transport equation from knowledge of angularly averaged measurements performed at the boundary of a domain of interest. We show that the absorption coefficient and the spatial component of the scattering coefficient are uniquely determined by such measurements. We obtain stability results on the reconstruction of the absorption and scattering parameters with respect to the measured albedo operator. The stability results are obtained by a precise decomposition of the measurements into components with different singular behavior in the time domain.

Guillaume Bal; Alexandre Jollivet

2009-02-19

347

Angular size-redshift: Experiment and calculation  

NASA Astrophysics Data System (ADS)

In this paper the next attempt is made to clarify the nature of the Euclidean behavior of the boundary in the angular size-redshift cosmological test. It is shown experimentally that this can be explained by the selection determined by anisotropic morphology and anisotropic radiation of extended radio sources. A catalogue of extended radio sources with minimal flux densities of about 0.01 Jy at 1.4 GHz was compiled for conducting the test. Without the assumption of their size evolution, the agreement between the experiment and calculation was obtained both in the ?CDM model (? m = 0.27, ? v = 0.73) and the Friedman model (? = 0.1).

Amirkhanyan, V. R.

2014-10-01

348

Angular correlation studies in noble gases  

NASA Technical Reports Server (NTRS)

There has been a recent revival of interest in the measurement of angular correlation of annihilation photons from the decay of positrons and positronium in gases. This revival has been stimulated by the possibility offered by the technique to shed new light on the apparently low positronium formation fraction in the heavier noble gases and to provide information on positronium quenching processes in gases such as oxygen. There is also the potential for learning about positronium slowing down in gases. This review focuses on experimental noble gas work and considers what new information has been, and may be, gained from these studies.

Coleman, P. G.

1990-01-01

349

Magnetic Bearing With Radial and Angular Control  

NASA Technical Reports Server (NTRS)

Active magnetic bearing stably levitates rotor against radial (lateral) and axial motion and points rotor axis in controllable direction, yet allows rotor to turn freely about own axis. Rotor only moving part, and absence of mechanical contact between rotor and stator assures long life. Active magnetic bearing includes electromagnet coils tilting rotor clockwise or counterclockwise, or move it right or left. Feedback control system maintains rotor at equilibrium radial and angular positions in response to signals from position sensors. No active control needed to maintain equilibrium axial position. Adjustable magnetic bearing useful in high-speed rotating devices, robotic joints, and supports for optical elements.

Studer, P. A.

1987-01-01

350

EQUAL CHANNEL ANGULAR EXTRUSION (ECAE) OF BERYLLIUM.  

SciTech Connect

The Equal Channel Angular Extrusion (ECAE) technique has been applied to a P/M source Be alloy. Single and two-pass extrusions have been successfully completed, using two different processing routes, on Ni-canned billets of Be at 400 C. No cracking was observed in the billet and significant grain refinement was achieved. In this paper, microstructural features and dislocation structures are discussed for the single-pass material, including evidence of and dislocations. Significant crystallographic texture developed during ECAE, which will be discussed in terms of this unique deformation processing technique and the underlying physical processes which sustained the deformation.

Field, R. D. (Richard D.); Hartwig, K. T.; Necker, C. T. (Carl T.); Bingert, J. F. (John F.); Agnew, S. R. (Sean R.)

2001-01-01

351

Matter & Interactions Practice Problems: Angular Momentum  

NSDL National Science Digital Library

This web page contains problems to supplement the introductory textbook Matter and Interactions by Ruth Chabay and Bruce Sherwood. These problems are designed for use with Volume 1, Chapter 10 on angular momentum. Topics include multiparticle systems, conservation, torque, and collisions. Each problem can be viewed separately, with solutions, or downloaded as a pdf file. The site includes videos showing solutions to many of the problems. These can be followed with RSS or as podcasts from iTunes. Instructors are encouraged to submit their own problems and solutions. Problems should be submitted in LaTeX format; ample support for this process is provided by the web site.

Titus, Aaron

2010-01-11

352

Angular resolved time delay in photoemission  

NASA Astrophysics Data System (ADS)

We investigate theoretically the relative time delay of photoelectrons originating from different atomic subshells of noble gases. This quantity was measured via attosecond streaking and studied theoretically by Schultze et al (2010 Science 328 1658) for neon. A substantial discrepancy was found between the measured and the calculated values of the relative time delay. Several theoretical studies were put forward to resolve this issue, e.g., by including correlation effects. In the present paper we explore a further aspect, namely the directional dependence of time delay. In contrast to neon, for argon target a strong angular dependence of the time delay is found near the Cooper minimum.

Wätzel, J.; Moskalenko, A. S.; Pavlyukh, Y.; Berakdar, J.

2015-01-01

353

Linear and angular retroreflecting interferometric alignment target  

DOEpatents

The present invention provides a method and apparatus for measuring both the linear displacement and angular displacement of an object using a linear interferometer system and an optical target comprising a lens, a reflective surface and a retroreflector. The lens, reflecting surface and retroreflector are specifically aligned and fixed in optical connection with one another, creating a single optical target which moves as a unit that provides multi-axis displacement information for the object with which it is associated. This displacement information is useful in many applications including machine tool control systems and laser tracker systems, among others.

Maxey, L. Curtis (Powell, TN)

2001-01-01

354

Angularly anisotropic correlation in granular packings  

NASA Astrophysics Data System (ADS)

We present an x-ray microtomography study of the three-dimensional structural correlations in monodisperse granular packings. By measuring an orientation-dependent pair correlation function, we find that the local structure shows an angularly anisotropic orientation correlation. The correlation is strongest along the major axis of the local Minkowski tensor of the Voronoi cell. It turns out that this anisotropic correlation is consistent with the existence of some locally favored structures. The study suggests the importance of high-order structural correlations in random granular packings.

Xia, Chengjie; Cao, Yixin; Kou, Binquan; Li, Jindong; Wang, Yujie; Xiao, Xianghui; Fezzaa, Kamel

2014-12-01

355

High resolution grazing incidence telescopes for the EUV-regime  

NASA Astrophysics Data System (ADS)

With the aim of building high-resolution grazing incidence telescopes for the EUV regime, much work has been done over the past two decades to improve the angular resolution of an X-ray mirror and to understand its point spread function. Based on the performance data of the best X-ray optics (ATMS-054), Einstein-Observatory, MPI, EXOSAT), the requirements for building an EUV telescope with sub-arcsec angular resolution are estimated, and problem areas in manufacturing these telescopes are discussed. In particular, the effect of an imperfect mirror system on imaging quality is discussed, with consideration to both surface microroughness and macroscopic manufacturing tolerances. Finally, values of optical fabrication tolerances for existing X-ray mirrors are given, and means of improving these values are outlined

Aschenbach, B.

1981-12-01

356

Approximate Bayesian Computation  

PubMed Central

Approximate Bayesian computation (ABC) constitutes a class of computational methods rooted in Bayesian statistics. In all model-based statistical inference, the likelihood function is of central importance, since it expresses the probability of the observed data under a particular statistical model, and thus quantifies the support data lend to particular values of parameters and to choices among different models. For simple models, an analytical formula for the likelihood function can typically be derived. However, for more complex models, an analytical formula might be elusive or the likelihood function might be computationally very costly to evaluate. ABC methods bypass the evaluation of the likelihood function. In this way, ABC methods widen the realm of models for which statistical inference can be considered. ABC methods are mathematically well-founded, but they inevitably make assumptions and approximations whose impact needs to be carefully assessed. Furthermore, the wider application domain of ABC exacerbates the challenges of parameter estimation and model selection. ABC has rapidly gained popularity over the last years and in particular for the analysis of complex problems arising in biological sciences (e.g., in population genetics, ecology, epidemiology, and systems biology). PMID:23341757

Sunnåker, Mikael; Corander, Jukka; Foll, Matthieu; Dessimoz, Christophe

2013-01-01

357

Angular distribution in two-particle emission induced by neutrinos and electrons  

E-print Network

The angular distribution of the phase space arising in two-particle emission reactions induced by electrons and neutrinos is computed in the laboratory (Lab) system by boosting the isotropic distribution in the center of mass (CM) system used in Monte Carlo generators. The Lab distribution has a singularity for some angular values, coming from the Jacobian of the angular transformation between CM and Lab systems. We recover the formula we obtained in a previous calculation for the Lab angular distribution. This is in accordance with the Monte Carlo method used to generate two-particle events for neutrino scattering\\cite{Sob12}. Inversely, by performing the transformation to the CM system, it can be shown that the phase-space function, which is proportional to the two particle-two hole (2p-2h) hadronic tensor for a constant current operator, can be computed analytically in the frozen nucleon approximation, if Pauli blocking is absent. The results in the CM frame confirm our previous work done using an alternative approach in the Lab frame. The possibilities of using this method to compute the hadronic tensor by a boost to the CM system are analyzed.

I. Ruiz Simo; C. Albertus; J. E. Amaro; M. B. Barbaro; J. A. Caballero; T. W. Donnelly

2014-07-26

358

Calculation of multiple-scattering angular distributions of electrons and positrons  

NASA Astrophysics Data System (ADS)

A robust numerical algorithm for the calculation of multiple-scattering angular distributions of high-energy electrons and positrons is described. This algorithm implements the multiple-scattering theories of Goudsmit-Saunderson, which disregards energy losses, and of Lewis, which accounts for energy losses within the continuous slowing down approximation. We have used partial-wave elastic scattering differential cross sections, generated with a recently developed program ELSEPA, in the calculations. The contribution of inelastic collisions to multiple-scattering angular distributions is treated in detail using inelastic scattering angular differential cross sections obtained from the Sternheimer-Liljequist generalised oscillator strength model. The stopping powers adopted in the calculations are consistent with the values recommended in the ICRU 37 report. The coefficients in the Legendre expansion of the single-scattering distribution are calculated by using the N-point Gauss-Legendre integration formula, coded in such a way that it allows the generation of a large number of expansion coefficients simultaneously. A computer program has been written to calculate angular multiple-scattering distributions for given path lengths, which can be readily adopted for class I Monte Carlo simulations.

Negreanu, C.; Llovet, X.; Chawla, R.; Salvat, F.

2005-12-01

359

Dangerous angular Kaluza-Klein/glueball relics in string theory cosmology  

NASA Astrophysics Data System (ADS)

The presence of Kaluza-Klein (KK) particles in the universe is a potential manifestation of string theory cosmology. In general, they can be present in the high temperature bath of the early universe. In particular examples, string theory inflation often ends with brane-antibrane annihilation followed by the energy cascading through massive closed string loops to KK modes which then decay into lighter standard model particles. However, massive KK modes in the early universe may become dangerous cosmological relics if the inner manifold contains warped throat(s) with approximate isometries. In the complimentary picture, in the AdS/CFT dual gauge theory with extra isometries, massive glueballs of various spins become the dangerous cosmological relics. The decay of these angular KK modes/glueballs, located around the tip of the throat, is caused by isometry breaking which results from gluing the throat to the compact Calabi-Yau (CY) manifold. We address the problem of these angular KK particles/glueballs, studying their interactions and decay channels, from the theory side, and the resulting cosmological constraints on the warped compactification parameters, from the phenomenology side. The abundance and decay time of the long-lived nonrelativistic angular KK modes depend strongly on the parameters of the warped geometry, so that observational constraints rule out a significant fraction of the parameter space. In particular, the coupling of the angular KK particles can be weaker than gravitational.

Dufaux, J. F.; Kofman, L.; Peloso, M.

2008-07-01

360

Microstructure evolution during semi continuous equal channel angular extrusion process of interstitial- free steel  

NASA Astrophysics Data System (ADS)

In order to produce ultrafine grained structures, interstitial-free steel sheets have been processed using a novel severe plastic deformation technique semi continuous equal channel angular extrusion (SC-ECAE) which is based on equal channel angular extrusion (ECAE) in an incremental way. The deformation was carried out at room temperature and individual specimen was repeatedly processed to various passes. An overall grain size which is 0.55 ?m was achieved after 10 passes (or an equivalent total strain of 4.8). The present paper reports the evolution of microstructures during deformation, which were examined and characterized using high resolution EBSD in a field emission gun SEM. The mechanisms of grain refinement are discussed.

Yan, Bo; Jiao, Sihai; Zhang, Dianhua

2014-08-01

361

Canopus Angular Diameter Revisited by the AMBER Instrument of the VLT Interferometer  

NASA Astrophysics Data System (ADS)

We used the VLTI/AMBER instrument to obtain interferometric data on the F0I star Canopus (visibilities and closure phases in the H and K bands with spectral resolution of 35). The adopted baselines (100 m) and the high quality of the VLTI/AMBER observations allowed us to measure fringe visibilities up to the third visibility lobe of Canopus.The angular diameter has been measured from the visibility and set to be (6.95 ± 0.15) mas. From this measured angular diameter we derive a stellar radius R=(72± 4) Rsun and an effective temperature Teff=(7272± 107) K or Teff=(7570± 250) K depending on the considered bolometric flux and its precision. Contrarily to the theory, our VLTI/AMBER data do not reveal any limb darkening on Canopus in the near-IR. Our observations set new constraints on the physical parameters of this star.

Bendjoya, P.; Domiciano de Souza, A.; Vakili, F.; Millour, F.; Petrov, R.

2009-08-01

362

X-ray line profile analysis of equal channel angular pressing processed Cu  

NASA Astrophysics Data System (ADS)

The effect of equal channel angular pressing on the microstructure of copper samples was studied by X-ray line profile analysis. Pure Cu samples were processed by equal channel angular pressing with 3 passes in route A. Samples were taken from the vicinity of the channel intersection, and along a profile across the deformation zone, microhardness and XRD measurements were performed. For the high resolution line profile analysis of the diffraction spectra, convolutional-multiple-whole-profile CMWP method was applied, dislocation density and grain size were calculated, furthermore the density of twin boundaries were determined. Results show a rearrangement in the dislocations in the third pass leading to a rise in the density of twin boundaries.

Jóni, B.; Gonda, V.; Verö, B.; Ungár, T.

2014-08-01

363

Fragment angular correlation in the breakup of 16O ions at 95 MeV/A  

NASA Astrophysics Data System (ADS)

Fragment angular correlations in projectile breakup reactions are very sensitive to interference between different multipolarities entering in the excitation-dissociation process of the projectile. In particular, it was proposed to disentangle L=1 and L=2 contributions in direct breakup reactions of 16O with low relative energy between the ? and 12C fragment, which are of astrophysical interest. We studied the experimental aspects of extracting those angular correlations in extreme kinematical conditions usually encountered in breakup experiments of astrophysical interest. The breakup of 95 MeV/A 16O projectiles induced by a 208Pb target was measured using the high-resolution spectrometer SPEG at Ganil for the coincident detection of the fragments. Sequential breakup via the 12.53 MeV level of 16O is analyzed in this framework and it favors an one-step M2 excitation of this level.

Tatischeff, V.; Kiener, J.; Aguer, P.; Bogaert, G.; Coc, A.; Disdier, D.; Ichihara, T.; Kraus, L.; Lefebvre, A.; Linck, I.; Mittig, W.; Motobayashi, T.; de Oliveira Santos, F.; Roussel-Chomaz, P.; Stephan, C.; Thibaud, J. P.

1998-04-01

364

X-ray Reflectivity Measurements of Nanoscale Structures: Limits of the Effective Medium Approximation  

SciTech Connect

Specular X-ray reflectivity (SXR) can be used, in the limit of the effective medium approximation (EMA), as a high-resolution shape metrology for periodic patterns on a smooth substrate. The EMA means that the density of the solid patterns and the spaces separating the periodic patterns are averaged together. In this limit the density profile as a function of pattern height obtained by SXR can be used to extract quantitative pattern profile information. Here we explore the limitations of SXR as a pattern shape metrology by studying a series of linear grating structures with periodicities ranging from 300 nm to 16 {mu}m and determining at which length scales the EMA breaks down. We also study the angular dependence of the grating orientation with respect to the incident X-ray beam. The gratings systematically are rotated through a series of azimuthal angles with the incident X-ray beams ranging from 0 deg. to 90 deg. . The applicability of the EMA is related to the coherence length of the X-ray source. When the coherence length of beam is larger than the physical dimension of grating periodicities, EMA can be applied for characterizing nanostructures. For our slit-collimated X-ray source, the coherence length in the direction parallel to the long axis of the slit is on the order of 900 nm while the coherence length along the main axis of the beam appears to be in the range of (22 to 26) {mu}m.

Lee, Hae-Jeong; Soles, Christopher L.; Kang, Shuhui; Wook Ro, Hyun; Lin, Eric K.; Wu, Wen-li [NIST Polymers Division, 100 Bureau Drive, MS 8541, Gaithersburg, MD, 20899 (United States)

2007-09-26

365

Axions and the galactic angular momentum distribution  

NASA Astrophysics Data System (ADS)

We analyze the behavior of axion dark matter before it falls into a galactic gravitational potential well. The axions thermalize sufficiently fast by gravitational self-interactions that almost all go to their lowest-energy state consistent with the total angular momentum acquired from tidal torquing. That state is a state of rigid rotation on the turnaround sphere. It predicts the occurrence and detailed properties of the caustic rings of dark matter for which observational evidence had been found earlier. We show that the vortices in the axion Bose-Einstein condensate (BEC) are attractive, unlike those in superfluid He4 and dilute gases. We expect that a large fraction of the vortices in the axion BEC join into a single big vortex along the rotation axis of the galaxy. The resulting enhancement of caustic rings explains the typical size of the rises in the Milky Way rotation curve attributed to caustic rings. We show that baryons and ordinary cold dark matter particles are entrained by the axion BEC and acquire the same velocity distribution. The resulting baryonic angular momentum distribution gives a good qualitative fit to the distributions observed in dwarf galaxies. We give estimates of the minimum fraction of dark matter that is composed of axions.

Banik, N.; Sikivie, P.

2013-12-01

366

Mapping spin-polarized transitions with atomic resolution  

NASA Astrophysics Data System (ADS)

The coupling of angstrom-sized electron probes with spin-polarized electronic transitions shows that the inelastically scattered probe electron is in a mixed state containing electron vortices with nonzero orbital angular momentum. These electrons create an asymmetric intensity distribution in energy filtered diffraction patterns, giving access to maps of the magnetic moments with atomic resolution. A feasibility experiment shows evidence of the predicted effect. Potential applications are column-by-column maps of magnetic ordering, and the creation of angstrom-sized free electrons with orbital angular momentum by inelastic scattering in a thin ferromagnetic foil.

Schattschneider, P.; Schaffer, B.; Ennen, I.; Verbeeck, J.

2012-04-01

367

Resolution limits for wave equation imaging  

NASA Astrophysics Data System (ADS)

Formulas are derived for the resolution limits of migration-data kernels associated with diving waves, primary reflections, diffractions, and multiple reflections. They are applicable to images formed by reverse time migration (RTM), least squares migration (LSM), and full waveform inversion (FWI), and suggest a multiscale approach to iterative FWI based on multiscale physics. That is, at the early stages of the inversion, events that only generate low-wavenumber resolution should be emphasized relative to the high-wavenumber resolution events. As the iterations proceed, the higher-resolution events should be emphasized. The formulas also suggest that inverting multiples can provide some low- and intermediate-wavenumber components of the velocity model not available in the primaries. Finally, diffractions can provide twice or better the resolution than specular reflections for comparable depths of the reflector and diffractor. The width of the diffraction-transmission wavepath is approximately ? at the diffractor location for the diffraction-transmission wavepath.

Huang, Yunsong; Schuster, Gerard T.

2014-08-01

368

Angular distribution of Au and U L x-rays induced by 22.6-keV photons  

SciTech Connect

The angular distribution of the L x-ray fluorescent lines from Au and U induced by 22.6-keV x rays from a {sup 109}Cd has been measured. A Si(Li) detector having a resolution of 160 eV at 5.90 keV was used to detect these L lines over the angular range of 70 degree sign -150 degree sign . No strong anisotropy was observed as mentioned by some groups. In the case of Au, a maximum anisotropy of 5% was observed while for U it was within experimental errors (2%). From the angular distribution of the L1 line of Au, the alignment parameter was obtained and its value was found to be 0.10{+-}0.14.

Santra, S.; Mitra, D.; Sarkar, M.; Bhattacharya, D. [Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India)

2007-02-15

369

Ordinances and Resolutions ORDINANCES, RESOLUTIONS AND REGULATIONS  

E-print Network

come into effect on the day on 27th October 2000. #12;Page 2.2 Ordinances and Resolutions III. DEGREE of its approval by Her Majesty in Council. II. AWARD OF POSTGRADUATE DIPLOMAS AND DEGREES Resolution) the degree of Doctor of Languages (D.Lang.), (c) the degree of Doctor of Philosophy in Arts, Divinity

Brierley, Andrew

370

SPECT imaging with resolution recovery  

SciTech Connect

Single-photon emission computed tomography (SPECT) is a method of choice for imaging spatial distributions of radioisotopes. Many applications of this method are found in nuclear industry, medicine, and biomedical research. We study mathematical modeling of a micro-SPECT system by using a point-spread function (PSF) and implement an OSEM-based iterative algorithm for image reconstruction with resolution recovery. Unlike other known implementations of the OSEM algorithm, we apply en efficient computation scheme based on a useful approximation of the PSF, which ensures relatively fast computations. The proposed approach can be applied with the data acquired with any type of collimators, including parallel-beam fan-beam, cone-beam and pinhole collimators. Experimental results obtained with a micro SPECT system demonstrate high efficiency of resolution recovery. (authors)

Bronnikov, A. V. [Bronnikov Algorithms, P.O. Box 77, 6800AB Arnhem (Netherlands)

2011-07-01

371

Angular distributions of photoelectrons from free Na clusters  

SciTech Connect

We explore, from a theoretical perspective, photoelectron angular distributions (PADs) of the Na clusters Na{sub 8}, Na{sub 10}, Na{sub 12}, Na{sub 18}, Na{sub 3}{sup +}, Na{sub 11}{sup +}, Na{sub 13}{sup +}, and Na{sub 19}{sup +}. The basis of the description is the time-dependent local-density approximation (TDLDA), augmented by a self-interaction correction (SIC) to describe ionization properties correctly. The scheme is solved on a numerical grid in coordinate space with absorbing bounds. We assume for each cluster system an isotropic ensemble of free clusters and develop for the case of one-photon emission analytical formulas for computing the orientation-averaged PAD on the basis of a few TDLDA-SIC calculations for properly chosen reference orientations. It turns out that all the information in the averaged PAD is contained in one anisotropy parameter. We find that this parameter varies very little with system size, but as a whole is crucially influenced by the detailed ionic structure. We also make comparisons with direct orientation averaging and consider one example reaching outside the perturbative regime.

Wopperer, P.; Dinh, P. M. [Universite de Toulouse, UPS, Laboratoire de Physique Theorique, IRSAMC, F-31062 Toulouse Cedex, France and CNRS, UMR 5152, F-31062 Toulouse Cedex (France); Faber, B.; Reinhard, P.-G. [Institut fuer Theoretische Physik, Universitaet Erlangen, D-91058 Erlangen (Germany); Suraud, E. [Universite de Toulouse, UPS, Laboratoire de Physique Theorique, IRSAMC, F-31062 Toulouse Cedex, France and CNRS, UMR 5152, F-31062 Toulouse Cedex (France); Institut fuer Theoretische Physik, Universitaet Erlangen, D-91058 Erlangen (Germany)

2010-12-15

372

The angular momentum transport by unstable toroidal magnetic fields  

NASA Astrophysics Data System (ADS)

We demonstrate with a nonlinear magnetohydrodynamic (MHD) code that angular momentum can be transported because of the magnetic instability of toroidal fields under the influence of differential rotation, and that the resulting effective viscosity may be high enough to explain the almost rigid-body rotation observed in radiative stellar cores. We only consider stationary, current-free fields, and only those combinations of rotation rates and magnetic field amplitudes which provide maximal numerical values of the viscosity. We find that the dimensionless ratio of the effective over molecular viscosity, ?T/?, linearly grows with the Reynolds number of the rotating fluid multiplied by the square-root of the magnetic Prandtl number, which is approximately unity for the considered red subgiant star KIC 7341231. For the interval of magnetic Reynolds numbers considered - which is restricted by numerical constraints of the nonlinear MHD code - the magnetic Prandtl number has a remarkable influence on the relative importance of the contributions of the Reynolds stress and the Maxwell stress to the total viscosity, which is magnetically dominated only for Pm ? 0.5. We also find that the magnetized plasma behaves as a non-Newtonian fluid, i.e., the resulting effective viscosity depends on the shear in the rotation law. The decay time of the differential rotation thus depends on its shear and becomes longer and longer during the spin-down of a stellar core.

Rüdiger, G.; Gellert, M.; Spada, F.; Tereshin, I.

2015-01-01

373

Effect of angular quadrature on results of two-dimensional space power reactor shield calculations.  

NASA Technical Reports Server (NTRS)

Study of the effect of angular quadrature on the results of two-dimensional transport calculations made to evaluate radiation environment in the vicinity of a shielded space power reactor. The application considered is for a manned space-station; crew shielding must be provided within a 25 deg cone angle. The asymmetric shield layout is evaluated using the two-dimensional transport code DOT. Within the shield, an S sub 6 angular quadrature yields satisfactory results. For regions where the ray effect may occur it is not apparent that an S sub 10 quadrature is adequate. Anomalies in results due to transport of particles in a void and necessary geometric approximations were observed.

Connolley, D. J.; Lahti, G. P.

1971-01-01

374

Angular dependence of the energy loss of ions in solids: Computer simulations and analysis of models  

NASA Astrophysics Data System (ADS)

The angular dependence of the electronic energy loss of light ions in solids is analyzed in the frame of the binary collision approximation (BCA) using an analytical formalism based on multiple scattering (MS) functions, as well as with Monte Carlo (MC) simulations. These simulations have been performed for different collisional models of ions in the solid. A variation of the mean number of collisions with the observation angle is found, for a frequently used random distribution of interatomic distances, which may originate an angular dependence of the energy loss. Additionally the effect of impact parameter restrictions has been investigated, and again a change in the mean number of collisions with the observation angle has been observed. As this variation depends on the model of the solid and the impact parameter criteria applied, uncertainties in the single collision energy loss appear.

Famá, M.; Lantschner, G. H.; Eckardt, J. C.; Arista, N. R.

2001-03-01

375

Photoelectron angular distributions from polar molecules probed by intense femtosecond lasers  

SciTech Connect

We present numerical calculations of molecular-frame photoelectron angular distributions in strong-field ionization of oriented polar HF and LiF molecules by linearly polarized laser pulses with durations of about 20 fs (seven cycles at 800 nm). The calculations are performed within the single-active-electron and frozen-nuclei approximations. Our analysis shows that for the HF and LiF molecules, anisotropies in the molecular potential and the probed orbital lead to enhanced ionization during laser half cycles with the field pointing antiparallel to the permanent dipole of the dipole term in a multipolar expansion of the anisotropic molecular potential. This is manifested as a strong asymmetry in the computed photoelectron angular distributions: The photoelectrons are preferentially detected opposite to the permanent dipole of the molecular potential. This phenomenon is very sensitive to the probed system (the probed orbital and the molecular potential) and the orientation angle between the molecular axis and the laser polarization.

Abu-samha, M.; Madsen, L. B. [Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark)

2010-10-15

376

The Wide-Field Imaging Interferometry Testbed: Enabling Techniques for High Angular Resolution Astronomy  

NASA Technical Reports Server (NTRS)

The Wide-Field Imaging Interferometry Testbed (WIIT) was designed to develop techniques for wide-field of view imaging interferometry, using "double-Fourier" methods. These techniques will be important for a wide range of future spacebased interferometry missions. We have provided simple demonstrations of the methodology already, and continuing development of the testbed will lead to higher data rates, improved data quality, and refined algorithms for image reconstruction. At present, the testbed effort includes five lines of development; automation of the testbed, operation in an improved environment, acquisition of large high-quality datasets, development of image reconstruction algorithms, and analytical modeling of the testbed. We discuss the progress made towards the first four of these goals; the analytical modeling is discussed in a separate paper within this conference.

Rinehart, S. A.; Armstrong, T.; Frey, Bradley J.; Jung, J.; Kirk, J.; Leisawitz, David T.; Leviton, Douglas B.; Lyon, R.; Maher, Stephen; Martino, Anthony J.; Pauls, T.

2007-01-01

377

Galaxies and their constituents at the highest angular resolutions ASP Conference Series, Vol. ???, 2001  

E-print Network

.P. Krichbaum 1 , H. Falcke 1 , & E.J.M. Colbert 6 1 MPIfR, Bonn, Germany, aroy@mpifr-bonn.mpg.de 2 NRAO, PO Box scale H I disc; Carilli et al. 1998). In powerful radio jets the one-sidedness is usually explained = 1.000E­03 (­1.50, ­1, ­0.500, 0.500, 1, 1.500, 2, 2.500, 3, 3.500, 4, 4.500, 5, 5.500) DECLINATION

Roy, Alan

378

An Integrated Framework for High Angular Resolution Diffusion Imaging–Based Investigation of Structural Connectivity  

PubMed Central

Abstract Structural connectivity models hold great promise for expanding what is known about the ways information travels throughout the brain. The physiologic interpretability of structural connectivity models depends heavily on how the connections between regions are quantified. This article presents an integrated structural connectivity framework designed around such an interpretation. The framework provides three measures to characterize the structural connectivity of a subject: (1) the structural connectivity matrix describing the proportion of connections between pairs of nodes, (2) the nodal connection distribution (nCD) characterizing the proportion of connections that terminate in each node, and (3) the connection density image, which presents the density of connections as they traverse through white matter (WM). Individually, each possesses different information concerning the structural connectivity of the individual and could potentially be useful for a variety of tasks, ranging from characterizing and localizing group differences to identifying novel parcellations of the cortex. The efficiency of the proposed framework allows the determination of large structural connectivity networks, consisting of many small nodal regions, providing a more detailed description of a subject's connectivity. The nCD provides a gray matter contrast that can potentially aid in investigating local cytoarchitecture and connectivity. Similarly, the connection density images offer insight into the WM pathways, potentially identifying focal differences that affect a number of pathways. The reliability of these measures was established through a test/retest paradigm performed on nine subjects, while the utility of the method was evaluated through its applications to 20 diffusion datasets acquired from typically developing adolescents. PMID:22500705

Ingalhalikar, Madhura; Batmanghelich, Nematollah K.; Schultz, Robert T.; Roberts, Timothy P.L.; Verma, Ragini

2012-01-01

379

VizieR Online Data Catalog: AT20G high-angular-resolution catalogue (Chhetri+, 2013)  

NASA Astrophysics Data System (ADS)

For data processing we used the Multichannel Image Reconstruction, Image Analysis and Display (MIRIAD; Sault, Teuben & Wright, 1995, ASP Conf. Ser., Vol. 77, p. 433) software package. We used the AT20G survey data after the initial data quality checks implemented in an automated custom analysis pipeline as described by Murphy et al. (2010MNRAS.402.2403M). We then calculated the visibilities on the 4500m baselines in a separate custom pipeline. (2 data files).

Chhetri, R.; Ekers, R. D.; Jones, P. A.; Ricci, R.

2014-08-01

380

Next Generation X-ray Optics: High Angular Resolution, Light Weight, and Low Production Cost  

NASA Astrophysics Data System (ADS)

X-ray optics is an essential enabling component of nearly every future x-ray astronomical mission concept. In this poster we will present the rationale, technical approach, and status of an x-ray optics technology development program that has been underway at Goddard Space Flight Center and Marshall Space Flight Center.

Zhang, William

2013-04-01

381

High angular resolution mm- and submm-observations of dense molecular gas in M82  

NASA Technical Reports Server (NTRS)

Researchers observed CO(7-6), CO(3-2), HCN(3-2) and HCO+(3-2) line emission toward the starburst nucleus of M82 and have obtained an upper limit to H13CN(3-2). These are the first observations of the CO(7-6), HCN(3-2) and HCO+(3-2) lines in any extragalactic source. Researchers took the CO(7-6) spectrum in January 1988 at the Infrared Telescope Facility (IRTF) with the Max Planck Institute for Extraterrestrial Physics/Univ. of California, Berkeley 800 GHz Heterodyne Receiver. In March 1989 researchers used the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope to observe the CO(3-2) line with the new MPE 350 GHz Superconductor Insulator Superconductor (SIS) receiver and the HCN(3-2) and HCO+(3-2) lines with the (IRAM) 230 GHz SIS receiver (beam 12" FWHM, Blundell et al. 1988). The observational parameters are summarized.

Wild, W.; Eckart, Andreas; Genzel, Reinhard; Harris, Andrew I.; Jackson, James M.; Jaffe, D. T.; Lugten, J. B.; Stutzki, J.

1990-01-01

382

The surface of small solar system bodies: Spectroscopic observatons and high-angular resolution imaging  

Microsoft Academic Search

I present some observational results using near-infrared reflectance spectroscopy and adaptive optics to study the nature of the surface of some selected minor bodies. The spectroscopic observations of dark asteroids were motivated by the recent discovery of a strong absorption band in the reflection spectrum of Pholus. Pholus is one of the most pristine object of our solar system, a

C. Dumas

1997-01-01

383

Comparison of FBP and Iterative Algorithms with Non-Uniform Angular Sampling  

PubMed Central

Some people may believe that the filtered backprojection (FBP) algorithm does not work if the projection data are measured non-uniformly. Some may also believe that iterative algorithms can automatically handle the non-uniformly sampled data in the projector/backprojector. This paper claims that the FBP algorithm can effectively handle the situation where the angular sampling is not uniform. This paper compares the images that are reconstructed by both the FBP and the iterative Landweber algorithms when the angular sampling is nonuniform. When the iteration number is low, the iterative algorithms do not handle the non-uniform sampling properly. A weighting strategy is then suggested and it makes the image resolution more isotropic. In few-view tomography, the FBP and iterative algorithms both perform poorly if no other prior information is used. We have made the following observations: 1) When using an iterative algorithm, one must use early solutions due to noise amplification. 2) An early solution can have anisotropic spatial resolution if the angular sampling is not uniform. 3) The anisotropic resolution problem can be solved by introducing angle dependent weighting, which is not noise dependent. 4) The weighting is not effective when the iteration number is large. The weighting only affects the early solutions, and does not affect the converged solution. 5) When the iteration number is large, the model-mismatch errors are amplified and cause artifacts in the image. 6) The FBP algorithm is not sensitive to the model-mismatch errors, and does not have the “early solution” problems. 7) In few-view tomography, both FBP and iterative algorithms perform poorly, while the FBP algorithm gives a sharper image than the iterative algorithm does.

Zeng, Gengsheng L.

2014-01-01

384

The coupled states approximation for scattering of two diatoms  

NASA Technical Reports Server (NTRS)

The paper presents a detailed development of the coupled-states approximation for the general case of two colliding diatomic molecules. The high-energy limit of the exact Lippman-Schwinger equation is applied, and the analysis follows the Shimoni and Kouri (1977) treatment of atom-diatom collisions where the coupled rotor angular momentum and projection replace the single diatom angular momentum and projection. Parallels to the expression for the differential scattering amplitude, the opacity function, and the nondiagonality of the T matrix are reported. Symmetrized expressions and symmetrized coupled equations are derived. The present correctly labeled coupled-states theory is tested by comparing its calculated results with other computed results for three cases: H2-H2 collisions, ortho-para H2-H2 scattering, and H2-HCl.

Heil, T. G.; Kouri, D. J.; Green, S.

1978-01-01

385

Application of Gaussian Approximation Potentials to Barium Titanate  

NASA Astrophysics Data System (ADS)

The computational study of complex phenomena over long time and distance scales not accessible to first principles calculations requires empirical potentials usually derived by integrating out the electronic degree of freedoms. Recently, a parameter free approach called Gaussian Approximation Potentials (GAP) has been shown that it can duplicate first principles density functional theory (DFT) total energies and atomic forces accurately [1]. In a GAP the atomic neighborhood of an atom is projected onto the angular momentum channels of Wigner-D functions, yielding a bispectrum of the expansion coefficients of the atomic density. A non-parametric Gaussian Process regression is used to fit a database of total energies and forces to the combination of angular momentum channels constituting the bispectrum. We report initial results of using a GAP to describe the ferroelectric perovskite Barium Titanate (BaTiO3). [4pt] [1] A. P. Bartok, M. C. Payne, R. Kondor, and G. Csanyi, Phys. Rev. Lett. 104 136403 (2010).

Vielma, Jason; Schneider, Guenter

2012-02-01

386

Approximate nonlinear self-adjointness and approximate conservation laws  

E-print Network

In this paper, approximate nonlinear self-adjointness for perturbed PDEs is introduced and its properties are studied. Consequently, approximate conservation laws which cannot be obtained by the approximate Noether theorem are constructed by means of the method. As an application, a class of perturbed nonlinear wave equations is considered to illustrate the effectiveness.

Zhi-Yong Zhang

2011-10-31

387

Exploring Machin's Approximation of Exploring Machin's Approximation of  

E-print Network

#12;Exploring Machin's Approximation of Precursors Method of Exhaustion `a la Archimedes Archimedes of Precursors Method of Exhaustion `a la Archimedes Archimedes of Syracuse ( 287­212 BC) approximated la Archimedes Archimedes of Syracuse ( 287­212 BC) approximated by the Method of Exhaustion: 3

Knaust, Helmut

388

Angular-momentum-dominated electron beams and flat-beam generation  

SciTech Connect

In the absence of external forces, if the dynamics within an electron beam is dominated by its angular momentum rather than other effects such as random thermal motion or self Coulomb-repulsive force (i.e., space-charge force), the beam is said to be angular-momentum-dominated. Such a beam can be directly applied to the field of electron-cooling of heavy ions; or it can be manipulated into an electron beam with large transverse emittance ratio, i.e., a flat beam. A flat beam is of interest for high-energy electron-positron colliders or accelerator-based light sources. An angular-momentum-dominated beam is generated at the Fermilab/NICADD photoinjector Laboratory (FNPL) and is accelerated to an energy of 16 MeV. The properties of such a beam is investigated systematically in experiment. The experimental results are in very good agreement with analytical expectations and simulation results. This lays a good foundation for the transformation of an angular-momentum-dominated beam into a flat beam. The round-to-flat beam transformer is composed of three skew quadrupoles. Based on a good knowledge of the angular-momentum-dominated beam, the quadrupoles are set to the proper strengths in order to apply a total torque which removes the angular momentum, resulting in a flat beam. For bunch charge around 0.5 nC, an emittance ratio of 100 {+-} 5 was measured, with the smaller normalized root-mean-square emittance around 0.4 mm-mrad. Effects limiting the flat-beam emittance ratio are investigated, such as the chromatic effects in the round-to-flat beam transformer, asymmetry in the initial angular-momentum-dominated beam, and space-charge effects. The most important limiting factor turns out to be the uncorrelated emittance growth caused by space charge when the beam energy is low, for example, in the rf gun area. As a result of such emittance growth prior to the round-to-flat beam transformer, the emittance ratio achievable in simulation decreases from orders of thousands to hundreds. Finally, factors that might spoil the smaller transverse emittance such as beamline misalignments and dispersions caused by magnetic elements are discussed. The limit of the emittance measurement system, such as camera resolution, is also studied.

Sun, Yin-e; /Chicago U.; ,

2005-06-01

389

Space-angle approximations in the variational nodal method.  

SciTech Connect

The variational nodal method is formulated such that the angular and spatial approximations maybe examined separately. Spherical harmonic, simplified spherical harmonic, and discrete ordinate approximations are coupled to the primal hybrid finite element treatment of the spatial variables. Within this framework, two classes of spatial trial functions are presented: (1) orthogonal polynomials for the treatment of homogeneous nodes and (2) bilinear finite subelement trial functions for the treatment of fuel assembly sized nodes in which fuel-pin cell cross sections are represented explicitly. Polynomial and subelement trial functions are applied to benchmark water-reactor problems containing MOX fuel using spherical harmonic and simplified spherical harmonic approximations. The resulting accuracy and computing costs are compared.

Lewis, E. E.; Palmiotti, G.; Taiwo, T.

1999-03-12

390

Approximation Bayesian Computation  

PubMed Central

Approximation Bayesian computation [ABC] is an analysis approach that has arisen in response to the recent trend to collect data that is of a magnitude far higher than has been historically the case. This has led to many existing methods become intractable because of difficulties in calculating the likelihood function. ABC circumvents this issue by replacing calculation of the likelihood with a simulation step in which it is estimated in one way or another. In this review we give an overview of the ABC approach, giving examples of some of the more popular specific forms of ABC. We then discuss some of the areas of most active research and application in the field, specifically, choice of low-dimensional summaries of complex datasets and metrics for measuring similarity between observed and simulated data. Next, we consider the question of how to do model selection in an ABC context. Finally, we discuss an area of growing prominence in the ABC world, use of ABC methods in genetic pathway inference.

Marjoram, Paul

2014-01-01

391

Moon influence on equatorial atmospheric angular momentum  

NASA Astrophysics Data System (ADS)

The variation of the equatorial atmospheric angular momentum function, coordinated with respect to a star-fixed system, is investigated in relation with the lunar tide. We isolate the rapid fluctuations, below 30 days, where Moon motion has a possible influence. First we notice that pressure term and wind term are almost proportional, by contrast to celestial seasonal band (S1). This would mean that, in this frequency band, the torque of the atmosphere on the solid Earth mostly results from the equatorial bulge. Spectrum reveals sharp lunar tidal peaks at 13.66 days (O1 diurnal tide in the terrestrial frame) and 13.63 days, reflecting the Moon influence on meridional circulation. We also observe powerful episodic fluctuations between 5 and 8 days (up to 10 mas), possibly resulting from non linear effect of the O1 tide, or tidal waves 2Q1 (6.86 days) and ?1 (7.095 days).

Bizouard, Christian; Zotov, Leonid; Sidorenkov, Nikolay

2014-05-01

392

Angular momentum effects in subbarrier fusion  

SciTech Connect

Angular-momentum distributions sigma/sub L/ for the compound nucleus /sup 164/Yb were deduced from measurements of ..gamma..-ray multiplicity for all significant evaporation residues from fusion of /sup 64/Ni and /sup 100/Mo at and below the Coulomb barrier. The excitation functions can be reproduced with coupled-channels calculations only if additional coupling beyond the known inelastic strengths is included. Even with this augmented coupling, however, at the lowest bombarding energies the experimental sigma/sub L/ extend to higher L values than the predictions. Single-barrier penetration models for a potential with an energy-dependent depth and shape fitted to the excitation function likewise underestimate the role of high-L partial waves. Somewhat better success is achieved with models in which fission is allowed to occur at distances comparable with or even larger than the Coulomb barrier radius. 24 refs., 3 figs., 2 tabs.

Halbert, M.L.; Beene, J.R.; Hensley, D.C.; Honkanen, K.; Semkow, T.M.; Abenante, V.; Sarantites, D.G.; Li, Z.

1988-01-01

393

Angular Size-Redshift: Experiment and Calculation  

E-print Network

In this paper the next attempt is made to clarify the nature of the Euclidean behavior of the boundary in the angular size-redshift cosmological test. It is shown experimentally that this can be explained by the selection determined by anisotropic morphology and anisotropic radiation of extended radio sources. A catalogue of extended radio sources with minimal flux densities of about 0.01 Jy at 1.4 GHz was compiled for conducting the test. Without the assumption of their size evolution, the agreement between the experiment and calculation was obtained both in the Lambda CDM model (Omega_m=0.27 , Omega_v=0.73.) and the Friedman model (Omega = 0.1 ).

Amirkhanyan, V R

2015-01-01

394

Noncontacting method for measuring angular deflection  

NASA Technical Reports Server (NTRS)

An apparatus is described for indicating the instantaneous angular deflection of an object about a selected axis without mechanical contact with the object. Light from a light source is transmitted through a flat refractor to a converging lens which focuses the light through another flat refractor onto a differential photocell. The first flat refractor is attached to the object such that when the object is deflected about the selected axis the refractor is also deflected about that axis. The two flat refractors are identical and they are placed an equal distance from the converging lens as are the light source and the photocell. The output of the photocell which is a function of image displacement is fed to a high gain amplifier that drives a galvanometer which rotates the second flat refractor. The second refractor is rotated so that the image displacement is very nearly zero making the galvanometer current a measure of the deflection of the object about the selected axis.

Bryant, E. L. (inventor)

1980-01-01

395

Orbital angular momentum photonic quantum interface  

E-print Network

High dimensional orbital angular momentum (OAM) light states are very important in enhancing the information carrying capacity in optical communications and quantum key distributions. Light at wavelengths of fiber communication windows or free space communication windows are suitable for long distance quantum communication, but most quantum processing tasks are performed in the visible wavelength ranges. The interface to bridge the wavelength gap of single photon with Gaussian shape has been realized, however, to create such interface for OAM-carrying light is a great challenge. We report the demonstration of such an interface to frequency up-conversion of herald single photon OAM state from 1560nm to 525nm with high efficiency by using nonlinear crystal in an external cavity. We show that different single photon OAM light shapes are observed directly by using single photon counting camera and the single photon entangled property is retained in the conversion process.

Yan Li; Zhi-Yuan Zhou; Dong-Sheng Ding; Wei Zhang; Shuai Shi; Bao-Sen Shi; Guang-Can Guo

2014-10-28

396

The SKA as a Doorway to Angular Momentum  

E-print Network

Angular momentum is one of the most fundamental physical quantities governing galactic evolution. Differences in the colours, morphologies, star formation rates and gas fractions amongst galaxies of equal stellar/baryon mass M are potentially widely explained by variations in their specific stellar/baryon angular momentum j. The enormous potential of angular momentum science is only just being realised, thanks to the emergence of the first simulations of galaxies with converged spins, paralleled by a dramatic increase in kinematic observations. Such observations are still challenged by the fact that most of the stellar/baryon angular momentum resides at large radii. In fact, the radius that maximally contributes to the angular momentum of an exponential disk (3Re-4Re) is twice as large as the radius that maximally contributes to the disk mass; thus converged measurements of angular momentum require either extremely deep IFS data or, alternatively, kinematic measurements of neutral atomic hydrogen (HI), which ...

Obreschkow, D; Popping, A; Power, C; Quinn, P; Staveley-Smith, L

2015-01-01

397

Scaling of spin relaxation and angular momentum dissipation in permalloy nanowires  

NASA Astrophysics Data System (ADS)

We study the relationship between the damping (?) and the nonadiabaticity of the spin transport (?) in permalloy nanowires. ? is engineered by Ho doping, and from the characteristics of the current-induced domain-wall velocity, determined by high-resolution x-ray magnetic circular-dichroism photoemission electron microscopy, ? due to spin relaxation is measured. We find that ? scales with ? and conclude that the spin relaxation that leads to nonadiabatic spin torque originates from the same underlying mechanism as the angular momentum dissipation that causes viscous damping.

Moore, T. A.; Kläui, M.; Heyne, L.; Möhrke, P.; Backes, D.; Rhensius, J.; Rüdiger, U.; Heyderman, L. J.; Thiele, J.-U.; Woltersdorf, G.; Back, C. H.; Fraile Rodríguez, A.; Nolting, F.; Mentes, T. O.; Niño, M. Á.; Locatelli, A.; Potenza, A.; Marchetto, H.; Cavill, S.; Dhesi, S. S.

2009-10-01

398

Angular asymmetries as a probe for anomalous contributions to HZZ vertex at the LHC  

E-print Network

In this article, the prospects for studying the tensor structure of the HZZ vertex with the LHC experiments are presented. The structure of tensor couplings in Higgs di-boson decays is investigated by measuring the asymmetries and by studing the shapes of the final state angular distributions. The expected background contributions, detector resolution, and trigger and selection efficiencies are taken into account. The potential of the LHC experiments to discover sizeable non-Standard Model contributions to the HZZ vertex with $300\\;{\\rm fb}^{-1}$ and $3000\\;{\\rm fb}^{-1}$ is demonstrated.

Belyaev, N; Pedersen, L Egholm; Prokofiev, K

2015-01-01

399

Angular asymmetries as a probe for anomalous contributions to HZZ vertex at the LHC  

E-print Network

In this article, the prospects for studying the tensor structure of the HZZ vertex with the LHC experiments are presented. The structure of tensor couplings in Higgs di-boson decays is investigated by measuring the asymmetries and by studing the shapes of the final state angular distributions. The expected background contributions, detector resolution, and trigger and selection efficiencies are taken into account. The potential of the LHC experiments to discover sizeable non-Standard Model contributions to the HZZ vertex with $300\\;{\\rm fb}^{-1}$ and $3000\\;{\\rm fb}^{-1}$ is demonstrated.

N. Belyaev; R. Konoplich; L. Egholm Pedersen; K. Prokofiev

2015-02-10

400

?-SHAKE: An extension to SHAKE for the explicit treatment of angular constraints  

NASA Astrophysics Data System (ADS)

This paper presents ?-SHAKE, an extension to SHAKE, an algorithm for the resolution of holonomic constraints in molecular dynamics simulations, which allows for the explicit treatment of angular constraints. We show that this treatment is more efficient than the use of fictitious bonds, significantly reducing the overlap between the individual constraints and thus accelerating convergence. The new algorithm is compared with SHAKE, M-SHAKE, the matrix-based approach described by Ciccotti and Ryckaert and P-SHAKE for rigid water and octane.

Gonnet, Pedro; Walther, Jens H.; Koumoutsakos, Petros

2009-03-01

401

First Year Wilkinson Microwave Anisotropy Probe(WMAP)Observations: The Angular Power Spectrum  

NASA Technical Reports Server (NTRS)

We present the angular power spectrum derived from the first-year Wilkinson Microwave Anisotropy Probe (WMAP) sky maps. We study a variety of power spectrum estimation methods and data combinations and demonstrate that the results are robust. The data are modestly contaminated by diffuse Galactic foreground emission, but we show that a simple Galactic template model is sufficient to remove the signal. Point sources produce a modest contamination in the low frequency data. After masking approximately 700 known bright sources from the maps, we estimate residual sources contribute approximately 3500 mu sq Kappa at 41 GHz, and approximately 130 mu sq Kappa at 94 GHz, to the power spectrum [iota(iota + 1)C(sub iota)/2pi] at iota = 1000. Systematic errors are negligible compared to the (modest) level of foreground emission. Our best estimate of the power spectrum is derived from 28 cross-power spectra of statistically independent channels. The final spectrum is essentially independent of the noise properties of an individual radiometer. The resulting spectrum provides a definitive measurement of the CMB power spectrum, with uncertainties limited by cosmic variance, up to iota approximately 350. The spectrum clearly exhibits a first acoustic peak at iota = 220 and a second acoustic peak at iota approximately 540, and it provides strong support for adiabatic initial conditions. Researchers have analyzed the CT(sup Epsilon) power spectrum, and present evidence for a relatively high optical depth, and an early period of cosmic reionization. Among other things, this implies that the temperature power spectrum has been suppressed by approximately 30% on degree angular scales, due to secondary scattering.

Hinshaw, G.; Spergel, D. N.; Verde, L.; Hill, R. S.; Meyer, S. S.; Barnes, C.; Bennett, C. L.; Halpern, M.; Jarosik, N.; Kogut, A.

2003-01-01

402

Simulation of LANDSAT multispectral scanner spatial resolution with airborne scanner data  

NASA Technical Reports Server (NTRS)

A technique for simulation of low spatial resolution satellite imagery by using high resolution scanner data is described. The scanner data is convolved with the approximate point spread function of the low resolution data and then resampled to emulate low resolution imagery. The technique was successfully applied to Daedalus airborne scanner data to simulate a portion of a LANDSAT multispectra scanner scene.

Hlavka, C. A.

1986-01-01

403

Angular momentum exchange between coherent light and matter fields  

E-print Network

Full, three dimensional, time-dependent simulations are presented demonstrating the quantized transfer of angular momentum to a Bose-Einstein condensate from a laser carrying orbital angular momentum in a Laguerre-Gaussian mode. The process is described in terms of coherent Bragg scattering of atoms from a chiral optical lattice. The transfer efficiency and the angular momentum content of the output coupled vortex state are analyzed and compared with a recent experiment.

T. P. Simula; N. Nygaard; S. X. Hu; L. A. Collins; B. I. Schneider; K. Molmer

2007-07-25

404

Angular momenta creation in relativistic electron-positron plasma.  

PubMed

Creation of angular momentum in a relativistic electron-positron plasma is explored. It is shown that a chain of angular momentum carrying vortices is a robust asymptotic state sustained by the generalized nonlinear Schrödinger equation characteristic to the system. The results may suggest a possible electromagnetic origin of angular momenta when it is applied to the MeV epoch of the early Universe. PMID:12935260

Tatsuno, T; Berezhiani, V I; Pekker, M; Mahajan, S M

2003-07-01

405

Computer simulation on spatial resolution of X-ray bright-field imaging by dynamical diffraction theory for a Laue-case crystal analyzer  

SciTech Connect

Recently, dark-field imaging (DFI) and bright-field imaging (BFI) have been proposed and applied to visualize X-ray refraction effects yielded in biomedical objects. In order to clarify the spatial resolution due to a crystal analyzer in Laue geometry, a program based on the Takagi-Taupin equation was modified to be used for carrying out simulations to evaluate the spatial resolution of images coming into a Laue angular analyzer (LAA). The calculation was done with a perfect plane wave for diffraction wave-fields, which corresponded to BFI, under the conditions of 35 keV and a diffraction index 440 for a 2100 {mu}m thick LAA. As a result, the spatial resolution along the g-vector direction showed approximately 37.5 {mu}m. 126 {mu}m-thick LAA showed a spatial resolution better than 3.1 {mu}m under the conditions of 13.7 keV and a diffraction index 220.

Suzuki, Yoshifumi; Chikaura, Yoshinori [Graduate School of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550 (Japan); Ando, Masami [Research Institute for Science and Technology, Tokyo University of Science, 2461 Yamasaki, Noda, Chiba 278-8510 (Japan)

2011-10-15

406

Ultrahigh resolution absolute Cartesian electronic autocollimator  

NASA Astrophysics Data System (ADS)

The development of a compact, ultra-high resolution, electronic autocollimator with excellent readout stability, linearity, and coordinate orthogonality is presented. This optical metrology tool relies on new advances in Cartesian optical encoders based on pattern recognition technology. Readout instabilities characteristic of conventional electronic autocollimators whose lateral effect photodetectors and operational amplifiers exhibit temporal and thermal drifts, are absent in this new technology. An autocollimator with a form factor similar to conventional alignment telescopes has been demonstrated with an angular resolution of 0.02 arcseconds peak-to-peak and less than 0.01 arcseconds rms. Various optical metrology applications for the laboratory and for space flight, including cryostatic ones, are described.

Leviton, Douglas B.

2003-11-01

407

Approximation by hinge functions  

SciTech Connect

Breiman has defined {open_quotes}hinge functions{close_quotes} for use as basis functions in least squares approximations to data. A hinge function is the max (or min) function of two linear functions. In this paper, the author assumes the existence of smooth function f(x) and a set of samples of the form (x, f(x)) drawn from a probability distribution {rho}(x). The author hopes to find the best fitting hinge function h(x) in the least squares sense. There are two problems with this plan. First, Breiman has suggested an algorithm to perform this fit. The author shows that this algorithm is not robust and also shows how to create examples on which the algorithm diverges. Second, if the author tries to use the data to minimize the fit in the usual discrete least squares sense, the functional that must be minimized is continuous in the variables, but has a derivative which jumps at the data. This paper takes a different approach. This approach is an example of a method that the author has developed called {open_quotes}Monte Carlo Regression{close_quotes}. (A paper on the general theory is in preparation.) The author shall show that since the function f is continuous, the analytic form of the least squares equation is continuously differentiable. A local minimum is solved for by using Newton`s method, where the entries of the Hessian are estimated directly from the data by Monte Carlo. The algorithm has the desirable properties that it is quadratically convergent from any starting guess sufficiently close to a solution and that each iteration requires only a linear system solve.

Faber, V.

1997-05-01

408

Correction of measured Gamma-Knife output factors for angular dependence of diode detectors and PinPoint ionization chamber.  

PubMed

Dosimetry for Gamma-Knife requires detectors with high spatial resolution and minimal angular dependence of response. Angular dependence and end effect time for p-type silicon detectors (PTW Diode P and Diode E) and PTW PinPoint ionization chamber were measured with Gamma-Knife beams. Weighted angular dependence correction factors were calculated for each detector. The Gamma-Knife output factors were corrected for angular dependence and end effect time. For Gamma-Knife beams angle range of 84°-54°. Diode P shows considerable angular dependence of 9% and 8% for the 18 mm and 14, 8, 4 mm collimator, respectively. For Diode E this dependence is about 4% for all collimators. PinPoint ionization chamber shows angular dependence of less than 3% for 18, 14 and 8 mm helmet and 10% for 4 mm collimator due to volumetric averaging effect in a small photon beam. Corrected output factors for 14 mm helmet are in very good agreement (within ±0.3%) with published data and values recommended by vendor (Elekta AB, Stockholm, Sweden). For the 8 mm collimator diodes are still in good agreement with recommended values (within ±0.6%), while PinPoint gives 3% less value. For the 4 mm helmet Diodes P and E show over-response of 2.8% and 1.8%, respectively. For PinPoint chamber output factor of 4 mm collimator is 25% lower than Elekta value which is generally not consequence of angular dependence, but of volumetric averaging effect and lack of lateral electronic equilibrium. Diodes P and E represent good choice for Gamma-Knife dosimetry. PMID:25266988

Hršak, Hrvoje; Majer, Marija; Grego, Timor; Bibi?, Juraj; Heinrich, Zdravko

2014-12-01

409

A mathematical analysis of the theory of interplanetary scintillation in the weak scattering approximation  

Microsoft Academic Search

We present a simplified analytic technique for modeling the interplanetary scintillation of radio sources of finite angular size with a power law electron density fluctuation power spectrum. The simplification results from the representation of the scintillation spectrum in confluent hypergeometric functions. The approximations presented allow fast numerical evaluation of a spectrum for a weak scattering but extended medium with <10%

D. G. Mitchell; E. C. Roelof

1976-01-01

410

Equivalence of physical optics and aperture field integration method for reflectors approximated by polyhedra  

Microsoft Academic Search

The equivalence of physical optics (PO) and the aperture field integration method (AFIM) in the full 360° angular region of reflector antennas is discussed from two viewpoints. One is how to approximate the equivalent surface currents and the other is how to select the integration surface. The former was already discussed by Oodo and Ando (see IEEE AP-S Int. Symp.,

M. Ooda; Makoto Ando

1996-01-01

411

a Discrete Ordinates Approximation to the Neutron Transport Equation Applied to Generalized Geometries  

Microsoft Academic Search

A method for applying the discrete ordinates method for solution of the neutron transport equation in arbitrary two-dimensional meshes has been developed. The finite difference approach normally used to approximate spatial derivatives in extrapolating angular fluxes across a cell is replaced by direct solution of the characteristic form of the transport equation for each discrete direction. Thus, computational cells are

Mark David Dehart

1992-01-01

412

"High Resolution Solar Physics: Theory, Observations, and Techniques", Eds. T. Rimmele, K. Balasubramiam and R. Radick, Procs. NSO/SP Summer Workshop Astron. Soc. Pac. Conf.  

E-print Network

"High Resolution Solar Physics: Theory, Observations, and Techniques", Eds. T. Rimmele, K resolution. Adding liquid-crystal polarization encoding before the fiber pickup would permit multi- line full. In the solar case, the fibers should map the focal plane with angular resolution at the diffraction limit

Rutten, Rob

413

Changes in angular momentum during the tennis serve.  

PubMed

Three-dimensional cinematography and the direct linear transformation method were used to obtain the coordinates of the landmarks of five right-handed collegiate tennis players. A 15-segment model was used to calculate the total body angular momentum about three orthogonal axes (X, parallel to the baseline; Y, normal to baseline and pointing towards the net; and Z, pointing upwards) passing through the centre of mass and to obtain the segmental contribution of the trunk, arms and legs. Most of the clockwise angular momentum about the X-axis was concentrated in the trunk and the racket-arm. Between the events of maximum external rotation and ball impact, the clockwise angular momentum about the X-axis of rotation of most body segments was reduced and the racket-arm gained clockwise angular momentum. The body angular momentum about the Y-axis of rotation had two distinct patterns and was the result of the lateral rotation of the trunk as the racket shoulder was elevated in preparation for impact. This body angular momentum was clockwise from the event of maximum external rotation to impact for the players with the greatest ball speed, whereas it was counterclockwise for the other players. The angular momentum about the Z-axis of rotation was small and lacked a consistent pattern. The largest source of angular momentum in the tennis serve derives from the remote angular momentum about the X- and Y-axes of rotation, which are then transferred from the trunk to the racket-arm and finally to the racket. Near impact, most of the angular momentum (75.1%) was concentrated in the racket-arm. Of the angular momentum of the racket-arm, the largest percentages were concentrated in the racket (35.9%) and the forearm segment (25.7%). PMID:10972409

Bahamonde, R E

2000-08-01

414

A spinning mirror for fast angular scans of EBW emission for magnetic pitch profile measurements  

SciTech Connect

A tilted spinning mirror rapidly steers the line of sight of the electron Bernstein wave (EBW) emission radiometer at the Mega-Amp Spherical Tokamak (MAST). In order to resist high mechanical stresses at rotation speeds of up to 12 000 rpm and to avoid eddy current induced magnetic braking, the mirror consists of a glass-reinforced nylon substrate of a special self-balanced design, coated with a reflecting layer. By completing an angular scan every 2.5-10 ms, it allows one to characterize with good time resolution the Bernstein-extraordinary-ordinary mode-conversion efficiency as a function of the view angles. Angular maps of conversion efficiency are directly related to the magnetic pitch angle at the cutoff layer for the ordinary mode. Hence, measurements at various frequencies provide the safety factor profile at the plasma edge. Initial measurements and indications of the feasibility of the diagnostic are presented. Moreover, angular scans indicate the best launch conditions for EBW heating.

Volpe, Francesco [Department of Engineering Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2010-10-15

415

Angular neutron transport investigation in the HZETRN free-space ion and nucleon transport and shielding computer program  

SciTech Connect

Extension of the high charge and energy (HZE) transport computer program HZETRN for angular transport of neutrons is considered. For this paper, only light ion transport, He{sup 4} and lighter, will be analyzed using a pure solar proton source. The angular transport calculator is the ANISN/PC program which is being controlled by the HZETRN program. The neutron flux values are compared for straight-ahead transport and angular transport in one dimension. The shield material is aluminum and the target material is water. The thickness of these materials is varied; however, only the largest model calculated is reported which is 50 gm/cm{sup 2} of aluminum and 100 gm/cm{sup 2} of water. The flux from the ANISN/PC calculation is about two orders of magnitude lower than the flux from HZETRN for very low energy neutrons. It is only a magnitude lower for the neutrons in the 10 to 20 MeV range in the aluminum and two orders lower in the water. The major reason for this difference is in the transport modes: straight-ahead versus angular. The angular treatment allows a longer path length than the straight-ahead approximation. Another reason is the different cross section sets used by the ANISN/PC-BUGLE-80 mode and the HZETRN mode. The next step is to investigate further the differences between the two codes and isolate the differences to just the angular versus straight-ahead transport mode. Then, create a better coupling between the angular neutron transport and the charged particle transport.

Singleterry, R.C. Jr. [Argonne National Lab. - West, Idaho Falls, ID (United States); Wilson, J.W. [National Aeronautics and Space Administration, Hampton, VA (United States). Langley Research Center

1997-05-01

416

Angular neutron transport investigation in the HZETRN free-space ion and nucleon transport and shielding computer program  

NASA Technical Reports Server (NTRS)

Extension of the high charge and energy (HZE) transport computer program HZETRN for angular transport of neutrons is considered. For this paper, only light ion transport, He4 and lighter, will be analyzed using a pure solar proton source. The angular transport calculator is the ANISN/PC program which is being controlled by the HZETRN program. The neutron flux values are compared for straight-ahead transport and angular transport in one dimension. The shield material is aluminum and the target material is water. The thickness of these materials is varied; however, only the largest model calculated is reported which is 50 gm/sq cm of aluminum and 100 gm/sq cm of water. The flux from the ANISN/PC calculation is about two orders of magnitude lower than the flux from HZETRN for very low energy neutrons. It is only a magnitude lower for the neutrons in the 10 to 20 MeV range in the aluminum and two orders lower in the water. The major reason for this difference is in the transport modes: straight-ahead versus angular. The angular treatment allows a longer path length than the straight-ahead approximation. Another reason is the different cross section sets used by the ANISN/PC-BUGLE-80 mode and the HZETRN mode. The next step is to investigate further the differences between the two codes and isolate the differences to just the angular versus straight-ahead transport mode. Then, create a better coupling between the angular neutron transport and the charged particle transport.

Singleterry, R. C., Jr.; Wilson, J. W.

1997-01-01

417

Research to improve extension ladder angular positioning.  

PubMed

A leading cause for extension ladder fall incidents is a slide-out event usually related to suboptimal ladder inclination. An improved ladder positioning method or procedure could reduce the risk of ladder stability failure and the related fall injury. The objective of the study was to comparatively evaluate the effectiveness of a multimodal angle indicator with other existing methods for extension ladder angular positioning. Twenty experienced and 20 inexperienced ladder users participated in the study. Four ladder positioning methods were tested in a controlled laboratory environment with 4.88 m (16 ft) and 7.32 m (24 ft) ladders in extended and retracted positions. The positioning methods included a no-instruction method, the current standard anthropometric method, and two instrumental methods - a bubble level indicator, and a multimodal indicator providing direct feedback with visual and sound signals. Performance measures included positioning angle and time. The results indicated that the anthropometric method was effective in improving the extension ladder positioning angle (p < 0.001); however, it was associated with considerable variability and required 50% more time than no-instruction. The bubble level indicator was an accurate positioning method (with very low variability), but required more than double the time of the no-instruction method (p < 0.001). The multimodal indicator improved the ladder angle setting as compared to the no-instruction and anthropometry methods (p < 0.001) and required the least time for ladder positioning among the tested methods (p < 0.001). An indicator with direct multimodal feedback is a viable approach for quick and accurate ladder positioning. The main advantage of the new multimodal method is that it provides continuous feedback on the angle of the device and hence does not require repositioning of the ladder. Furthermore, this indicator can be a valuable tool for training ladder users to correctly apply the current ANSI A14 standard anthropometric method in ladder angular positioning. The multimodal indicator concept has been further developed to become a hand-held tool in the form of a smart phone application. PMID:23177178

Simeonov, P; Hsiao, H; Powers, J; Kim, I-J; Kau, T-Y; Weaver, D

2013-05-01

418

Simulated cosmic microwave background maps at 0.5 deg resolution: Basic results  

NASA Technical Reports Server (NTRS)

We have simulated full-sky maps of the cosmic microwave background (CMB) anisotropy expected from cold dark matter (CDM) models at 0.5 deg and 1.0 deg angular resolution. Statistical properties of the maps are presented as a function of sky coverage, angular resolution, and instrument noise, and the implications of these results for observability of the Doppler peak are discussed. The rms fluctuations in a map are not a particularly robust probe of the existence of a Doppler peak; however, a full correlation analysis can provide reasonable sensitivity. We find that sensitivity to the Doppler peak depends primarily on the fraction of sky covered, and only secondarily on the angular resolution and noise level. Color plates of the simulated maps are presented to illustrate the anisotropies.

Hinshaw, G.; Bennett, C. L.; Kogut, A.

1995-01-01

419

Angular dependence of metamagnetic transitions in HoNi2B2C  

E-print Network

interference device ~SQUID! magnetometer. A modified version of the QD sample rotator probe, that allows for the rotation of the sample in a manner that keeps the c axis approximately perpendicular to the applied field at all times, was used. Due...356.6 kG/sinf as determine from Fig. 2~b!. 973F METAMAGNETIC . . . manifest by Hc3!. These angular dependences are consistent with the Ho moment being fully along the @110# direction. This would lead to the longitudinal moment measured by the SQUID...

Canfield, PC; Budko, SL; Cho, BK; Lacerda, A.; Farrell, D.; JohnstonHalperin, E.; Kalatsky, VA; Pokrovsky, Valery L.

1997-01-01

420

Non Resonant Two Photon Ionization of Atomic Hydrogen: Exact Expressions of Angular Distribution  

NASA Astrophysics Data System (ADS)

Within the framework of second order time dependent perturbation theory and non relativistic dipole approximation, the exact expressions of the radial transition amplitude from 3d, 3p and 3s excited states, were obtained from the integral representation of the Green Coulomb function. Below threshold and above one photon ionization threshold, it can be expressed as an analytic combination of three Appell hypergeometric functions of first order, one of which is degenerated; while at threshold, it can be obtained in terms of an expansion of Gauss confluent hypergeometric functions. The angular coefficients are numerically evaluated and analysed for some available laser wavelengths.

Faye, M.; Wane, S. T.; Ndiaye, S.

421

Motion of a Ball in Angular-Contact Ball Bearing  

Microsoft Academic Search

The author carried out an experimental investigation on the motion of a ball in an angular-contact ball bearing under thrust load by measuring change in magnetic flux induced by a magnetized ball. The observed data of the angular velocity of the ball and that of the cage were adequate for analyzing the kinematical condition in the bearing. It is noted

Fujio Hirano

1965-01-01

422

Spatial Angular Compounding for Elastography without the Incompressibility Assumption  

PubMed Central

Spatial-angular compounding is a new technique that enables the reduction of noise artifacts in ultrasound elastography. Previous results using spatial angular compounding, however, were based on the use of the tissue incompressibility assumption. Compounded elastograms were obtained from a spatially-weighted average of local strain estimated from radiofrequency echo signals acquired at different insonification angles. In this paper, we present a new method for reducing the noise artifacts in the axial strain elastogram utilizing a least-squares approach on the angular displacement estimates that does not use the incompressibility assumption. This method produces axial strain elastograms with higher image quality, compared to noncompounded axial strain elastograms, and is referred to as the least-squares angular-compounding approach for elastography. To distinguish between these two angular compounding methods, the spatial-angular compounding with angular weighting based on the tissue incompressibility assumption is referred to as weighted compounding. In this paper, we compare the performance of the two angular-compounding techniques for elastography using beam steering on a linear-array transducer. Quantitative experimental results demonstrate that least-squares compounding provides comparable but smaller improvements in both the elastographic signal-to-noise ratio and the contrast-to-noise ratio, as compared to the weighted-compounding method. Ultrasound simulation results suggest that the least-squares compounding method performs better and provide accurate and robust results when compared to the weighted compounding method, in the case where the incompressibility assumption does not hold. PMID:16761786

Rao, Min; Varghese, Tomy

2007-01-01

423

Nonlinear effects of particle shape angularity in sheared granular media.  

PubMed

We analyze the effects of particle shape angularity on the macroscopic shear behavior and texture of granular packings simulated by means of the contact dynamics method. The particles are regular polygons with an increasing number of sides ranging from 3 (triangles) to 60. The packings are analyzed in the steady shear state in terms of their shear strength, packing fraction, connectivity, and fabric and force anisotropies, as functions of the angularity. An interesting finding is that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below six sides). In contrast, the packing fraction declines towards a constant value, so that the packings of more angular particles are looser but have higher shear strength. We show that the increase of the shear strength at low angularity is due to an increase of both contact and force anisotropies and the saturation of the shear strength for higher angularities is a consequence of a rapid falloff of the contact and normal force anisotropies compensated for by an increase of the tangential force anisotropy. This transition reflects clearly the rather special geometrical properties of these highly angular shapes, implying that the stability of the packing relies strongly on the side-side contacts and the mobilization of friction forces. PMID:23214574

Azéma, Emilien; Estrada, Nicolas; Radjaï, Farhang

2012-10-01

424

Boston University Physics Applets: Orbits and Angular Momentum  

NSDL National Science Digital Library

This web page is an interactive physics simulation relating to conservation of angular momentum in an orbiting object. The user can choose between an elliptical or circular orbit to observe why angular momentum is conserved in either case. This item is part of a larger collection of simulation-based activities developed for students of introductory physics.

Duffy, Andrew

2008-08-22

425

Angular correlation function and scattering coefficient of electromagnetic waves  

E-print Network

Angular correlation function and scattering coefficient of electromagnetic waves scattered We study three-dimensional (3-D) electromagnetic wave scattering from a buried object under a two. The study of 3-D electromagnetic scattering allows the use of azimuthal angular averaging and the study

Zhang, Guifu

426

Distilling angular momentum nonclassical states in trapped ions  

SciTech Connect

In the spirit of quantum nondemolition measurements, we show that by exploiting suitable vibronic couplings and repeatedly measuring the atomic population of a confined ion, it is possible to distill center-of-mass vibrational states with a well-defined square of angular momentum or, alternatively, angular momentum projection Schroedinger cat states.

Militello, B.; Messina, A. [INFM, MIUR, and Dipartimento di Scienze Fisiche ed Astronomiche dell'Universita di Palermo, Via Archirafi, 36, I-90123 Palermo (Italy)

2004-09-01

427

EBG-ANTENNA ANALYSIS : UNIFICATION OF FREQUENCY AND ANGULAR DEPENDENCIES  

E-print Network

][2][3][4] deal with directive antennas based on EBG (Electronic Band Gap) structures. In these worksEBG-ANTENNA ANALYSIS : UNIFICATION OF FREQUENCY AND ANGULAR DEPENDENCIES H. BOUTAYEB, K. MAHDJOUBI antennas. From this method, which unifies the frequency and angular dependencies of the EBG structure, we

Boyer, Edmond

428

Full angular profile of the coherent polarization opposition effect  

E-print Network

Full angular profile of the coherent polarization opposition effect Michael I. Mishchenko NASA M. Nieuwenhuizen Van der Waals-Zeeman Laboratorium, Valckenierstraat 65, 1018 XE Amsterdam the full angular profile of the polarization opposition effect. The effect is caused by coherent

429

Modification of the DSN radio frequency angular tropospheric refraction model  

NASA Technical Reports Server (NTRS)

The previously derived DSN Radio Frequency Angular Tropospheric Refraction Model contained an assumption which was subsequently seen to be at a variance with the theoretical basis of angular refraction. The modification necessary to correct the model is minor in that the value of a constant is changed.

Berman, A. L.

1977-01-01

430

VAlidation of angular finite element techniques for neutron transport calculations  

Microsoft Academic Search

A great deal of attention is being devoted to the numerical problems of the discrete ordinate method. This paper describes a new numerical technique, based on angular finite element methods, in which the main shortcomings of S{sub N} methods are efficiently dealt with. The obtained results show the high accuracy and effectiveness of our angular finite element method that in

G. Lapenta; G. G. Coppa; P. Ravetto

1993-01-01

431

Student understanding of the angular momentum of classical particles  

NSDL National Science Digital Library

Students in introductory calculus-based physics were asked about the angular momentum of a particle traveling in a straight line. The tendency to state that the angular momentum is identically zero was widespread, and few students applied l = r à p correctly. The common errors reflect a tendency to conflate angular momentum with angular velocity or with linear momentum. Many students assume that linear and angular momentum are jointly conserved, an error that appears to be linked to their thinking about energy. A tutorial was developed to help students recognize that linear momentum and angular momentum are separately conserved. The results suggest that helping students understand why angular momentum is attributed to a particle moving in a straight line may be more effective in helping them to apply the concept than instructing them only on its correct use. In addition to providing insights into student learning of the concept of angular momentum, we illustrate how studentsâ own ideas can be the basis for more effective instruction.

Close, Hunter G.; Heron, Paula R.

2013-08-05

432

Adaptive and anisotropic finite element approximation : Theory and algorithms  

E-print Network

Mesh adaption procedures for finite element approximation allows one to adapt the resolution, by local refinement in the regions of strong variation of the function of interest. This procedure plays a key role in numerous applications of scientific computing. The use of anisotropic triangles allows to improve the efficiency of the procedure by introducing long and thin triangles that fit in particular the directions of the possible curves of discontinuity. Given a norm X of interest and a function f to be approximated, we formulate the problem of optimal mesh adaptation, as minimizing the approximation error over all (possibly anisotropic) triangulations of prescribed cardinality. We address the four following questions related to this problem: I. How does the approximation error behave in the asymptotic regime when the number of triangles N tends to infinity, when f is a smooth function ? II. Which classes of functions govern the rate of decay of the approximation error as N grows, and are in that sense natu...

Mirebeau, Jean-Marie

2011-01-01

433

Quantifying and containing the curse of high resolution coronal imaging  

E-print Network

Future missions such as Solar Orbiter (SO), InterHelioprobe, or Solar Probe aim at approaching the Sun closer than ever before, with on board some high resolution imagers (HRI) having a subsecond cadence and a pixel area of about $(80km)^2$ at the Sun during perihelion. In order to guarantee their scientific success, it is necessary to evaluate if the photon counts available at these resolution and cadence will provide a sufficient signal-to-noise ratio (SNR). We perform a first step in this direction by analyzing and characterizing the spatial intermittency of Quiet Sun images thanks to a multifractal analysis. We identify the parameters that specify the scale-invariance behavior. This identification allows next to select a family of multifractal processes, namely the Compound Poisson Cascades, that can synthesize artificial images having some of the scale-invariance properties observed on the recorded images. The prevalence of self-similarity in Quiet Sun coronal images makes it relevant to study the ratio between the SNR present at SoHO/EIT images and in coarsened images. SoHO/EIT images thus play the role of 'high resolution' images, whereas the 'low-resolution' coarsened images are rebinned so as to simulate a smaller angular resolution and/or a larger distance to the Sun. For a fixed difference in angular resolution and in Spacecraft-Sun distance, we determine the proportion of pixels having a SNR preserved at high resolution given a particular increase in effective area. If scale-invariance continues to prevail at smaller scales, the conclusion reached with SoHO/EIT images can be transposed to the situation where the resolution is increased from SoHO/EIT to SO/HRI resolution at perihelion.

Véronique Delouille; Pierre Chainais; Jean-François Hochedez

2008-08-22

434

The Angular Trispectrum of the CMB  

E-print Network

We study the general properties of the CMB temperature four-point function, specifically its harmonic analogue the angular trispectrum, and illustrate its utility in finding optimal quadratic statistics through the weak gravitational lensing effect. We determine the general form of the trispectrum, under the assumptions of rotational, permutation, and parity invariance, its estimators on the sky, and their Gaussian noise properties. The signal-to-noise in the trispectrum can be highly configuration dependent and any quadratic statistic used to compress the information to a manageable two-point level must be carefully chosen. Through a systematic study, we determine that for the case of lensing a specific statistic, the divergence of a filtered temperature-weighted temperature-gradient map, contains the maximal signal-to-noise and reduces the variance of estimates of the large-scale convergence power spectrum by over an order of magnitude over previous gradient-gradient techniques. The total signal-to-noise for lensing with the Planck satellite is of order 60 for a LCDM cosmology.

Wayne Hu

2001-05-07

435

Angular-momentum effects in subbarrier fusion  

SciTech Connect

It has been known since about 1980 that fusion of heavy ions is greatly enhanced below the Coulomb barrier compared with normal barrier-penetration expectations. The excitation function for fusion of {sup 64}Ni + {sup 100}Mo measured in collaboration with a group at Washington University shows the effect clearly. The barrier energy is about 142 MeV; the lowest point is at about 90% of the barrier energy. The dotted curve is the prediction of a one-dimensional-barrier-penetration calculation of a type that reproduces the fusion of light projectiles very well. Several theoretical approaches have been successful in explaining the enhancement seen in much of the excitation-function data, but it cannot be said that a full understanding of the physics is in hand even after more than a decade of hard work. In fact, the reasonable success of several rather different models shows that the underlying phenomena are not well understood. Other types of data might be helpful in distinguishing among the many different theoretical approaches. An important kind of information not measured in most of the experiments is the dependence on {ell}, the angular momentum of the fusing system. We obtained such information on the cross sections, {sigma}{ell}, as a function of {ell} for the fusion of {sup 64}Ni and {sup 100}Mo using the Spin Spectrometer. This paper will first review the experimental method and data and then present results from a more sophisticated analysis of the same data.

Halbert, M.L.; Beene, J.R.

1993-11-01

436

Angular velocity and centripetal acceleration relationship  

NASA Astrophysics Data System (ADS)

During the last few years, the growing boom of smartphones has given rise to a considerable number of applications exploiting the functionality of the sensors incorporated in these devices. A sector that has unexpectedly taken advantage of the power of these tools is physics teaching, as reflected in several recent papers. In effect, the use of smartphones has been proposed in several physics experiments spanning mechanics, electromagnetism, optics, oscillations, and waves, among other subjects. Although mechanical experiments have received considerable attention, most of them are based on the use of the accelerometer. An aspect that has received less attention is the use of rotation sensors or gyroscopes. An additional advance in the use of these devices is given by the possibility of obtaining data using the accelerometer and the gyroscope simultaneously. The aim of this paper is to consider the relation between the centripetal acceleration and the angular velocity. Instead of using a formal laboratory setup, in this experiment a smartphone is attached to the floor of a merry-go-round, found in many playgrounds. Several experiments were performed with the roundabout rotating in both directions and with the smart-phone at different distances from the center. The coherence of the measurements is shown.

Monteiro, Martín; Cabeza, Cecilia; Marti, Arturo C.; Vogt, Patrik; Kuhn, Jochen

2014-05-01

437

The Dynamics of Equatorial Atmospheric Angular Momentum  

NASA Astrophysics Data System (ADS)

The physical processes that drive intraseasonal equatorial atmospheric angular momentum (EAAM) fluctuations are examined with data from an aquaplanet GCM run and with NCEP/NCAR reanalysis data. The GCM has an all-ocean lower boundary with a zonally symmetric sea surface temperature field. The EAAM budget is dominated by the equatorial bulge torque in both the GCM and in observations. For the GCM and the atmosphere, both components of the EAAM vector exhibit a strong spectral peak near a period of 10 days. An analysis with the linearized shallow water model equations on the sphere shows that this 10-day period can be interpreted as arising from the westward propagation of a free, antisymmetric, zonal wavenumber one, Rossby wave. The amplitude fluctuations of the EAAM vector are found to be related to tropical convection in both the GCM and the atmosphere. For the GCM, this convection is associated with an equatorial mixed Rossby-gravity wave. In the atmosphere, in addition to mixed Rossby-gravity waves, EAAM amplitude fluctuations are also related to both the Madden-Julian Oscillation (MJO) and to constructive and destructive interference between the propagating and stationary components of EAAM vector. The latter two processes arise because of the large, nonzero, seasonal mean values of the components of the EAAM vector. The above findings collectively suggest that the latent heat release in the tropics excites poleward Rossby wave propagation which alters the amplitude of the EAAM vector.

Feldstein, S. B.

2003-12-01

438

High-resolution imaging using ultrasound-modulated optical tomography  

Microsoft Academic Search

We present an implementation of ultrasound-modulated optical tomography that has the potential to provide high resolution images of tissue structures at a penetration depth of several millimeters. Light and pulsed ultrasound are focused on an approximately 100 mum wide area below the sample surface. With this configuration, the length of the ultrasonic pulses determines the axial resolution, and the lateral

Sava Sakadzic; Konstantin Maslov; Jun Li; Vikram K. Kinra; Lihong V. Wang

2004-01-01

439

Precise Canopus angular diameter measurement from AMBER/VLTI, photospheric structures suspected  

NASA Astrophysics Data System (ADS)

% Context {Direct measurements of fundamental parameters and photospheric structures of post-main-sequence intermediate-mass stars are required for a deeper understanding of their evolution. } % Aims {Based on near-IR long-baseline interferometry we aim to resolve the stellar surface of the F0 supergiant star Canopus, and to precisely measure its angular diameter and related physical parameters.} % Methods {We used the AMBER/VLTI instrument to record interferometric data on Canopus: visibilities and closure phases in the H and K bands with a spectral resolution of 35. The available baselines (?60-110 m) and the high quality of the AMBER/VLTI observations allowed us to measure fringe visibilities as far as in the third visibility lobe.} % Results {We determined an angular diameter of ?=6.93±0.15 mas by adopting a linearly limb-darkened disk model. From this angular diameter and Hipparcos distance we derived a stellar radius R=71.4±4.0 R_{?}.} % Conclusions {In addition to providing the most precise angular diameter obtained to date, the AMBER interferometric data point towards additional photospheric structures on Canopus beyond the limb-darkened model alone. A promising explanation for such surface structures is the presence of convection cells. We checked such a hypothesis using first order star-cell models and concluded that the observations are compatible with the presence of surface convective structures. This direct detection of convective cells on Canopus from interferometry can provide strong constraints to radiation-hydrodynamics models of photospheres of F-type supergiants.}

Bendjoya, Ph.; Domiciano de Souza, A.; Vakili, F.; Millour, F.; Petrov, R. G.

2008-11-01

440

Angular correlation of cosmic neutrinos with ultrahigh-energy cosmic rays and implications for their sources  

E-print Network

Cosmic neutrino events detected by the IceCube Neutrino Observatory with energy $\\gtrsim 30$ TeV have poor angular resolutions to reveal their origin. Ultrahigh-energy cosmic rays (UHECRs), with better angular resolutions at $>60$ EeV energies, can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test this hypothesis, with statistical methods which emphasize invariant quantities, by using data from the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments. We find that the arrival directions of the cosmic neutrinos are correlated with $\\ge 100$ EeV UHECR arrival directions at confidence level $\\approx 93\\%$. The strength of the correlation decreases with decreasing UHECR energy and no correlation exists at energy $\\sim 60$ EeV. A search in astrophysical databases within $3^\\circ$ of the arrival directions of UHECRs with energy $\\ge 100$ EeV, that are correlated with the IceCube cosmic neutrinos, resulted in 18 sources from the S...

Moharana, Reetanjali

2015-01-01

441

Preliminary determination of Newtonian gravitational constant with angular acceleration feedback method.  

PubMed

This paper describes the preliminary measurement of the Newtonian gravitational constant G with the angular acceleration feedback method at HUST. The apparatus has been built, and preliminary measurement performed, to test all aspects of the experimental design, particularly the feedback function, which was recently discussed in detail by Quan et al. The experimental results show that the residual twist angle of the torsion pendulum at the signal frequency introduces 0.4?ppm to the value of G. The relative uncertainty of the angular acceleration of the turntable is approximately 100?ppm, which is mainly limited by the stability of the apparatus. Therefore, the experiment has been modified with three features: (i) the height of the apparatus is reduced almost by half, (ii) the aluminium shelves were replaced with shelves made from ultra-low expansion material and (iii) a perfect compensation of the laboratory-fixed gravitational background will be carried out. With these improvements, the angular acceleration is expected to be determined with an uncertainty of better than 10?ppm, and a reliable value of G with 20?ppm or below will be obtained in the near future. PMID:25201996

Xue, Chao; Quan, Li-Di; Yang, Shan-Qing; Wang, Bing-Peng; Wu, Jun-Fei; Shao, Cheng-Gang; Tu, Liang-Cheng; Milyukov, Vadim; Luo, Jun

2014-10-13

442

Development of a high resolution scintillating fiber gamma ray telescope  

Microsoft Academic Search

We report on the initia development and testing of a Compton telescope that is composed of scintillating fibers and position sensitive photomultiphers. Initial tests of the telescope result in a 17.5 mrad (rms) angular resolution for 1.2 MeV photons from a collimated 60Co gamma source. This type of device can be used for constructing large area telescopes for gamma ray

P. Antich; M. Atac; R. Chaney; D. Chrisman; D. Cline; E. Fenyves

1990-01-01

443

A high resolution scintillating fiber gamma-ray-telescope  

Microsoft Academic Search

The design of a large-area gamma-ray detector with high angular and energy resolution for space-based experiments, using scintillating fibers and recently developed position-sensitive photomultiplier tubes, is presented. The structural and functional characteristics of the telescope instruments, a Compton-pair production converter, gas drift time projection chamber (TPC), and calorimeter, are given. It is concluded that with this design the Compton electron

M. Atac; D. B. Cline; E. J. Fenyves; R. C. Chaney

1989-01-01

444

Supporting Text Approximation of the Multinomial. Using Stirling's approximation  

E-print Network

Supporting Text Approximation of the Multinomial. Using Stirling's approximation n! (n/e)n 2n! . [S12] To calculate B L (^n) limN BN L (^n), we apply Stirling's formula to N!, n0!, and n1!, which that r Stirling's formula

Peterson, Carsten

445

Angular dependent light emission from planar waveguides  

NASA Astrophysics Data System (ADS)

We have investigated the angular dependence of amplified spontaneous emission (ASE) and laser emission from an asymmetric and free-standing polymer thin films doped with rhodamine 6G, which is transversely pumped by a pulsed Nd:YAG laser. A semi-leaky waveguide or quasi-waveguide structure has been developed by spin coating technique. In these waveguides, the light was confined by the film/air-film/glass substrate interfaces. At the film/substrate interface, a portion of light will reflect back into the film (guided mode) and the remaining refracted to the substrate resulting in cutoff modes. A blue-shift in ASE has been observed when the pump power was increased from 8 to 20 mW allowing a limited range of tuning of emission wavelength. To study the directionality of the ASE from the waveguide, we have measured the output intensity and FWHM of emission spectra as a function of viewing angle (?) from the plane parallel to film. From the detailed examination of the output emission spectra, as +? increases from 0° there has been an initial decrease in output intensity, but at a particular angle ?10° an increase in output intensity was observed. This additional peak in output intensity as +? is a clear indication of coexistence of the cutoff mode. We also present a compact solid-state laser based on leaky mode propagation from the dye-doped polymer free-standing film (˜50 ?m thickness) waveguide. The partial reflections from the broad lateral surfaces of the free-standing films provided the optical feedback for the laser emission with high directionality. For a pump power of 22 mW, an intense line with FWHM <0.2 nm was observed at 578 nm.

Peter, Jaison; Prabhu, Radhakrishna; Radhakrishnan, P.; Vallabhan, C. P. G.; Nampoori, V. P. N.; Kailasnath, M.

2015-01-01

446

Resolution recovery for list-mode reconstruction in SPECT  

NASA Astrophysics Data System (ADS)

We developed an iterative reconstruction method for SPECT which uses list-mode data instead of binned data. It uses a more accurate model of the collimator structure. The purpose of the study was to evaluate the resolution recovery and to compare its performance to other iterative resolution recovery methods in the case of high noise levels The source distribution is projected onto an intermediate layer. Doing this we obtain the complete emission radiance distribution as an angular sinogram. This step is independent of the acquisition system. To incorporate the resolution of the system we project the individual list-mode events over the collimator wells to the intermediate layer. This projection onto the angular sinogram will define the probability a photon from the source distribution will reach this specific location on the surface of the crystal, thus being accepted by the collimator hole. We compared the SPECT list-mode reconstruction to MLEM, OSEM and RBI. We used Gaussian shaped point sources with different FWHM at different noise levels. For these distributions we calculated the reconstructed images at different number of iterations. The modeling of the resolution in this algorithm leads to a better resolution recovery compared to other methods, which tend to overcorrect.

Bouwens, Luc; Gifford, Howard C.; Van de Walle, Rik; King, Michael A.; Lemahieu, Ignace L.; Dierckx, Rudi A.

2001-07-01

447

A compact high-resolution X-ray powder diffractometer  

PubMed Central

A new powder diffractometer operating in transmission mode is described. It can work as a rapid very compact instrument or as a high-resolution instrument, and the sample preparation is simplified. The incident beam optics create pure Cu K?1 radiation, giving rise to peak widths of ?0.1° in 2? in compact form with a sample-to-detector minimum radius of 55?mm, reducing to peak widths of <0.05° in high-resolution mode by increasing the detector radius to 240?mm. The resolution of the diffractometer is shown to be governed by a complex mixture of angular divergence, sample size, diffraction effects and the dimensions of the detector pixels. The data can be collected instantaneously, which combined with trivial sample preparation and no sample alignment, makes it a suitable method for very rapid phase identification. As the detector is moved further from the sample, the angular step from the pixel dimension is reduced and the resolution improves significantly for very detailed studies, including structure determination and analysis of the microstructure. The advantage of this geometry is that the resolution of the diffractometer can be calculated precisely and the instrumental artefacts can be analysed easily without a sample present. The performance is demonstrated with LaB6 and paracetamol, and a critical appraisal of the uncertainties in the measurements is presented. The instantaneous data collection offers possibilities in dynamic experiments. PMID:24282331

Fewster, Paul F.; Trout, David R. D.

2013-01-01

448

Angular Momentum Transport by Gravity Waves in the Solar Interior  

E-print Network

We present self-consistent numerical simulations of the sun's convection zone and radiative interior using a two-dimensional model of its equatorial plane. The background reference state is a one-dimensional solar structure model. Turbulent convection in the outer convection zone continually excites gravity waves which propagate throughout the stable radiative interior and deposit their angular momentum. We find that angular velocity variations in the tachocline are driven by angular momentum transported by overshooting convective plumes rather than the nonlinear interaction of waves. The mean flow in the tachocline is time dependent but not oscillatory in direction. Since the forcing in this shallow region can not be described by simple linear waves, it is unlikely that the interaction of such waves is responsible for the solar cycle or the 1.3 year oscillation. However, in the deep radiative interior, the interaction of low amplitude gravity waves, continually excited by the overshooting plumes, is responsible for the angular velocity deviations observed there. Near the center of the model sun the angular velocity deviation is about two orders of magnitude greater than that in the bulk of the radiative region and reverses its direction (prograde to retrograde or vice versa) in the opposite sense of the angular velocity deviations that occur in the tachocline. Our simulations thus demonstrate how angular velocity variations in the solar core are linked to those in the tachocline, which themselves are driven by convective overshooting.

Tamara M. Rogers; Gary A. Glatzmaier

2005-11-25

449

Smoothed dissipative particle dynamics with angular momentum conservation  

NASA Astrophysics Data System (ADS)

Smoothed dissipative particle dynamics (SDPD) combines two popular mesoscopic techniques, the smoothed particle hydrodynamics and dissipative particle dynamics (DPD) methods, and can be considered as an improved dissipative particle dynamics approach. Despite several advantages of the SDPD method over the conventional DPD model, the original formulation of SDPD by Español and Revenga (2003) [9], lacks angular momentum conservation, leading to unphysical results for problems where the conservation of angular momentum is essential. To overcome this limitation, we extend the SDPD method by introducing a particle spin variable such that local and global angular momentum conservation is restored. The new SDPD formulation (SDPD+a) is directly derived from the Navier-Stokes equation for fluids with spin, while thermal fluctuations are incorporated similarly to the DPD method. We test the new SDPD method and demonstrate that it properly reproduces fluid transport coefficients. Also, SDPD with angular momentum conservation is validated using two problems: (i) the Taylor-Couette flow with two immiscible fluids and (ii) a tank-treading vesicle in shear flow with a viscosity contrast between inner and outer fluids. For both problems, the new SDPD method leads to simulation predictions in agreement with the corresponding analytical theories, while the original SDPD method fails to capture properly physical characteristics of the systems due to violation of angular momentum conservation. In conclusion, the extended SDPD method with angular momentum conservation provides a new approach to tackle fluid problems such as multiphase flows and vesicle/cell suspensions, where the conservation of angular momentum is essential.

Müller, Kathrin; Fedosov, Dmitry A.; Gompper, Gerhard

2015-01-01

450

Approximating Functions with Exponential Functions  

ERIC Educational Resources Information Center

The possibility of approximating a function with a linear combination of exponential functions of the form e[superscript x], e[superscript 2x], ... is considered as a parallel development to the notion of Taylor polynomials which approximate a function with a linear combination of power function terms. The sinusoidal functions sin "x" and cos "x"…

Gordon, Sheldon P.

2005-01-01

451

Uniform approximations for fermionic densities  

E-print Network

Uniform semiclassical approximations for the number and kinetic-energy densities are derived for many non-interacting fermions in one-dimensional potentials with two turning points. The resulting simple, closed-form expressions contain the leading corrections to Thomas-Fermi theory, involve neither sums nor derivatives, are spatially uniform approximations, and are exceedingly accurate.

Raphael F. Ribeiro; Donghyung Lee; Attila Cangi; Peter Elliott; Kieron Burke

2014-09-24

452

Approximation Capabilities of Folding Networks  

E-print Network

on inputs with restricted height, but the resources necessarily increase at least ex­ ponentially. If the maximum in­ put height is restricted any mapping can be approximated, but the resources increase in the input height. In general, approximation on arbitrary inputs is not possible in the maximum norm. 1

Hammer, Barbara

453

Approximating Directed Multicuts Joseph Cheriyan  

E-print Network

multicommodity flow network, and give the first non- trivial upper bounds on the max flow-to-min multicut ratio and Rao (1988) and subsequent papers presented approximate min- max theorems relating multicommodity flow approximation algorithms, and generated novel tools for utilizing linear programming relaxations. Yet, despite

Cheriyan, Joseph

454

Lexical Ambiguity Resolution  

E-print Network

Lexical Ambiguity Resolution: Perspectives from Psycholinguistics, Neuropsychology, and Artificial throughout the short history of psycholinguistics. In what follows, we organize old and present new evidence

455

USGS aerial resolution targets.  

USGS Publications Warehouse

It is necessary to measure the achievable resolution of any airborne sensor that is to be used for metric purposes. Laboratory calibration facilities may be inadequate or inappropriate for determining the resolution of non-photographic sensors such as optical-mechanical scanners, television imaging tubes, and linear arrays. However, large target arrays imaged in the field can be used in testing such systems. The USGS has constructed an array of resolution targets in order to permit field testing of a variety of airborne sensing systems. The target array permits any interested organization with an airborne sensing system to accurately determine the operational resolution of its system. -from Author

Salamonowicz, P.H.

1982-01-01

456

Angular and radial mode analyzer for optical beams.  

PubMed

We describe an approach to determining both the angular and the radial modal content of a scalar optical beam in terms of optical angular momentum modes. A modified Mach-Zehnder interferometer that incorporates a spatial rotator to determine the angular modes and an optical realization of the fractional Hankel transform (fHT) to determine the radial modes is analyzed. Varying the rotation angle and the order of the fHT produces a two-dimensional (2D) interferogram from which we extract the modal coefficients by simple 2D Fourier analysis. PMID:22139283

Abouraddy, Ayman F; Yarnall, Timothy M; Saleh, Bahaa E A

2011-12-01

457

Indirect precise angular control using four-wave mixing  

SciTech Connect

Here, we show indirect precise angular control using a four-wave mixing (FWM) process. This was performed with a superposition of light with orbital angular momentum in an M-Type configuration of a hot {sup 85}Rb atomic ensemble. A gear-shaped interference pattern is observed at FWM light with a donut-shaped input signal. The gear could be rotated and is controlled through the change of the polarization of the pump laser. Our experimental results that are based on nonlinear coherent interactions have applications in image processing and precise angular control.

Zhang, Wei; Ding, Dong-Sheng; Shi, Bao-Sen, E-mail: drshi@ustc.edu.cn; Guo, Guang-Can [Key Laboratory of Quantum Information, CAS, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Jiang, Yun-Kun [Fuzhou University, Fuzhou, Fujian 350108 (China)

2014-04-28

458

Indirect precise angular control using four-wave mixing  

E-print Network

Here we show indirect precise angular control using a four-wave mixing (FWM) process. This was performed with a superposition of light with orbital angular momentum (OAM) in an M-Type configuration of a hot 85Rb atomic ensemble. A gear-shaped interference pattern is observed at FWM light with a donut-shaped input signal. The gear could be rotated and is controlled through the change of the polarization of the pump laser. Our experimental results that are based on nonlinear coherent interactions have applications in image processing and precise angular control.

Wei Zhang; Dong-Sheng Ding; Yun-Kun Jiang; Bao-Sen Shi; Guang-Can Guo

2014-05-08

459

Observation of Orbital Angular Momentum Sidebands due to Optical Reflection  

NASA Astrophysics Data System (ADS)

We investigate how the orbital angular momentum of a paraxial light beam is affected upon reflection at a planar interface. Theoretically, the unavoidable angular spread of the beam leads to orbital angular momentum sidebands, which are found to be already significant for a modest beam spread (0.05). In analogy to the polarization Fresnel coefficients, we develop an analytical theory based upon spatial Fresnel coefficients; this allows a straightforward prediction of the strength of the sidebands. We confirm this by experiment and numerical simulation.

Löffler, W.; Aiello, Andrea; Woerdman, J. P.

2012-09-01

460

VAlidation of angular finite element techniques for neutron transport calculations  

SciTech Connect

A great deal of attention is being devoted to the numerical problems of the discrete ordinate method. This paper describes a new numerical technique, based on angular finite element methods, in which the main shortcomings of S{sub N} methods are efficiently dealt with. The obtained results show the high accuracy and effectiveness of our angular finite element method that in all tested situations performs by far better than usual S{sub N} codes. These results, along with the ease of the numerical implementation of these new angular finite element methods, strongly suggest their application to actual fusion machine design codes.

Lapenta, G.; Coppa, G.G.; Ravetto, P. [Politecnico di Torino (Italy)

1993-12-31