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1

NASA Astrophysics Data System (ADS)

Magnetic Resonance Imaging (MRI) techniques have achieved much importance in providing visual and quantitative information of human body. Diffusion MRI is the only non-invasive tool to obtain information of the neural fiber networks of the human brain. The traditional Diffusion Tensor Imaging (DTI) is only capable of characterizing Gaussian diffusion. High Angular Resolution Diffusion Imaging (HARDI) extends its ability to model more complex diffusion processes. Spherical harmonic series truncated to a certain degree is used in recent studies to describe the measured non-Gaussian Apparent Diffusion Coefficient (ADC) profile. In this study, we use the sampling theorem on band-limited spherical harmonics to choose a suitable degree to truncate the spherical harmonic series in the sense of Signal-to-Noise Ratio (SNR), and use Monte Carlo integration to compute the spherical harmonic transform of human brain data obtained from icosahedral schema.

Cao, Ning; Liang, Xuwei; Zhuang, Qi; Zhang, Jun

2009-02-01

2

High resolution angular sensor

NASA Astrophysics Data System (ADS)

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.

1981-06-01

3

Supernovae at the Highest Angular Resolution

NASA Technical Reports Server (NTRS)

The study of supernovae (SNe) and their environments in host galaxies at the highest possible angular resolution in a number of wavelength regimes is providing vital clues to the nature of their progenitor stars.

Dyk, S. Van; Weiler, K.; Sramek, R.; Panagia, N.; Lacey, C.; Montes, M.; Mercaide, J.; Lewin, W.; Fox, D.; Filippenko, A.; Peng, C.

2000-01-01

4

Asymptotic Approximations to Angular-Spectrum Representations.

National Technical Information Service (NTIS)

Under rather general conditions, a time-harmonic wave field u(x,y,z) can be represented in a half-space z>0 by a double integral known as the angular spectrum of plane waves. The representation divides naturally into the sum of two double integrals, one o...

G. C. Sherman J. J. Stamnes E. Lalor

1975-01-01

5

HST Astrometry Angular Resolution Test

NASA Astrophysics Data System (ADS)

The ability of the HST FGS to detect and resolve close faint binary stars and measure their orbits is unique and unchallenged by current ground-based techniques. SMOV tests with FGS1R have revealed except- ional S curve morphology at pickle center. This test is designed to measure and compare the resolution of the TRANSFER mode of the new FGS1R and FGS3. A known binary will be observed in TRANS mode at multiple orientations in each instrument in order to sample the sensitivity along each FGS axis. Some POS mode observations will be obtained during each orbit in order to indepen- dently determine the relative orientation of each observation.

Nelan, Edmund

1997-12-01

6

Angular Resolution of Multi-Lisa Constellations

NASA Astrophysics Data System (ADS)

In this article, we present a detailed derivation of the angular resolution of arbitrary sets of LISA (Laser Interferometer Space Antenna) constellations with a toy model for gravitational wave signals, and further generalized to more complicated cases with slowly varying gravitational wave signals of well-defined frequency at any time instant. For future space-borne LISA-like gravitational wave detectors, our results may serve as a conservative quick estimate of the detector's angular resolution and hopefully moreover a reference for the configuration designs.

Wang, Yan; Gong, Xue-Fei

2010-04-01

7

X-ray astronomy with ultra-high-angular resolution

We present new schemes for a next-generation X-ray telescope for the energy range between approximately 1 and 10 keV providing an angular resolution of at least 1 milli-arcsec. Its technology will be based on diffractive transmission optics, e.g. Fresnel zone plates and their derivatives. Beside near-diffraction limited imaging, these devices hold the potential of a large collecting area well beyond

Christoph Braig; Peter Predehl

2004-01-01

8

Enhanced angular resolution from multiply scattered waves

NASA Astrophysics Data System (ADS)

Multiply scattered waves are often neglected in imaging methods, largely because of the inability of standard algorithms to deal with the associated non-linear models. This paper shows that by incorporating a known environment into the background model, we not only retain the benefits of imaging techniques based on linear models, but also obtain different views of the target scatterer. The net result is an enhanced angular resolution of the target to be imaged. We carry out our analysis in the context of high-frequency radar imaging, in which a steerable beam from a moving platform is used to produce an image of a region on the earth's surface (the target scatterers being buildings, etc). We consider the case where the target we want to image is situated in the vicinity of an a priori known reflecting wall. This is one of the simplest possible multipathing environments for the scatterer, and in the case when the illuminating beam is narrow enough to isolate different scattering paths, we will show that the imaging process achieves enhanced angular resolution. Although we carry out our analysis here in the context of radar, our technique is general enough that it can be adapted to many imaging modalities, such as acoustics, ultrasound, elasticity, etc. The extension of the method to other more complicated environments is also possible.

Nolan, Clifford J.; Cheney, Margaret; Dowling, Thomas; Gaburro, Romina

2006-10-01

9

The Universe at High Angular Resolution

NASA Astrophysics Data System (ADS)

Sub-milliarsecond resolution in the UV-optical domain, combined with the unique spectral diagnostics available at these wavelengths, will be an invaluable resource for many areas of astrophysical research in the 21st century. Increasing the angular resolution to the sub-milliarsecond level will result in an advance of at least two orders of magnitude compared to that provided by HST and will lead to unprecedented opportunities for astrophysical studies of the observable Universe. Simultanous attainment of ultra high resolution and observation of faint objects is technically very difficult, and the inevitable compromises must be driven by the science goals. In this talk I will highlight the potential of these capabilities to address current observational challenges. Examples include direct imaging of inner disk regions and planet forming environments within several stellar radii of YSOs, and of the atmospheric structures in evolved stars; studies of origins of winds and outflows in large variety of sources ranging from stars to AGNs; exploring accretion processes in protostars and in a variety of interacting binaries; improvement of the cosmic distance scale, and others.

Karovska, M.

2004-05-01

10

Drawing Trees with Perfect Angular Resolution and Polynomial Area.

National Technical Information Service (NTIS)

We study methods for drawing trees with perfect angular resolution, i.e., with angles at each vertex, v, equal to 2p=d(v). We show: 1. Any unordered tree has a crossing-free straight-line drawing with perfect angular resolution and polynomial area. 2. The...

C. A. Duncan D. Eppstein M. Nollenburg M. T. Goodrich S. G. Kobourov

2010-01-01

11

Angular and time resolution of neutron time of flight spectrometers

NASA Astrophysics Data System (ADS)

We show that the angular resolution ?? and time resolution ?t of neutron time-of-flight spectrometers can be determined accurately by measuring the scattering spectrum of superfluid 4He at low temperature. The method is used to determine ?? and ?t of the IRIS spectrometer at ISIS (UK), yielding the values (FWHM) ??=0.118 rad (6.8°) and ?t=212 ?s, and to reinterpret the results of Blagoveshchenskii et al., showing that their measured linewidths for superfluid 4He can be ascribed solely to the effect of the angular resolution of their time-of-flight spectrometer.

Crevecoeur, Roelof; de Schepper, Ignatz; de Graaf, Leo; Montfrooij, Wouter; Svensson, Eric; Carlile, Colin

1995-02-01

12

Microbeam High Angular Resolution Diffraction Applied to Optoelectronic Devices

Collimating perfect crystal optics in a combination with the X-ray focusing optics has been applied to perform high angular resolution microbeam diffraction and scattering experiments on micron-size optoelectronic devices produced by modern semiconductor technology. At CHESS, we used capillary optics and perfect Si/Ge crystal(s) arrangement to perform X-ray standing waves, high angular-resolution diffraction and high resolution reciprocal space mapping analysis. At the APS, 2ID-D microscope beamline, we employed a phase zone plate producing a beam with the size of 240 nm in the horizontal plane and 350 nm in the vertical (diffraction) plane and a perfect Si (004) analyzer crystal to perform diffraction analysis of selectively grown InGaAsP and InGaAlAs-based waveguides with arc sec angular resolution.

Kazimirov, A.; Bilderback, D. H. [Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, NY, 14853 (United States); Sirenko, A. A. [Department of Physics, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Cai, Z.-H.; Lai, B. [Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, IL 60439 (United States)

2007-01-19

13

Angular Resolution of Pachmarhi Array of Cerenkov Telescopes

NASA Astrophysics Data System (ADS)

Pachmarhi Array of ?Cerenkov Telescopes(PACT), consisting of a distributed array of 25 telescopes is used to sample the atmospheric ?Cerenkov Photon showers. The shower front is fitted to a plane and the direction of arrival of primary particle is obtained. The accuracy in the estimation of the arrival direction of showers has been estimated to be 0° .1 using `split' array method. The angular resolution is expected to be even better when a spherical front is used for direction reconstruction or correction for the curvature of the front is applied. This is the best angular resolution among all the currently operating atmospheric ?Cerenkov telescopes in the world.

Majumdar, P.; Acharya, B. S.; Bhat, P. N.; Chitnis, V. R.; Rahman, M. A.; Singh, B. B.; Vishwanath, P. R.

2001-08-01

14

Angular and time resolution of neutron time of flight spectrometers

We show that the angular resolution ?? and time resolution ?t of neutron time-of-flight spectrometers can be determined accurately by measuring the scattering spectrum of superfluid 4He at low temperature. The method is used to determine ?? and ?t of the IRIS spectrometer at ISIS (UK), yielding the values (FWHM) ??=0.118 rad (6.8°) and ?t=212 ?s, and to reinterpret the

Roelof Crevecoeur; Ignatz de Schepper; Leo de Graaf; Wouter Montfrooij; Eric Svensson; Colin Carlile

1995-01-01

15

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

16

Higher signal harmonics, LISA's angular resolution, and dark energy

It is generally believed that the angular resolution of the Laser Interferometer Space Antenna (LISA) for binary supermassive black holes (SMBH) will not be good enough to identify the host galaxy or galaxy cluster. This conclusion, based on using only the dominant harmonic of the binary SMBH signal, changes substantially when higher signal harmonics are included in assessing the parameter estimation problem. We show that in a subset of the source parameter space the angular resolution increases by more than a factor of 10, thereby making it possible for LISA to identify the host galaxy/galaxy cluster. Thus, LISA's observation of certain binary SMBH coalescence events could constrain the dark energy equation of state to within a few percent, comparable to the level expected from other dark energy missions.

Arun, K. G. [LAL, Universite Paris-Sud, IN2P3/CNRS, Orsay (France); GReCO, Institut d'Astrophysique de Paris-C.N.R.S., Paris (France); Iyer, Bala R. [Raman Research Institute, Bangalore, 560 080 (India); Sathyaprakash, B. S.; Broeck, Chris van den [School of Physics and Astronomy, Cardiff University, 5, The Parade, Cardiff, CF24 3YB (United Kingdom); Sinha, Siddhartha [Raman Research Institute, Bangalore, 560 080 (India); Department of Physics, Indian Institute of Science, Bangalore, 560 012 (India)

2007-11-15

17

Dusty Blue Supergiants: News from High-Angular Resolution Observations

NASA Astrophysics Data System (ADS)

An overview is presented of the recent advances in understanding the B[e] phenomenon among blue supergiant stars in light of high-angular resolution observations and with an emphasis on the results obtained by means of long baseline optical stellar interferometry. The focus of the review is on the circumstellar material and evolutionary phase of B[e] supergiants, but recent results on dust production in regular blue supergiants are also highlighted.

de Wit, W. J.; Oudmaijer, R. D.; Vink, J. S.

18

High Angular Resolution Electron Detection in the Inner Heliosphere

NASA Astrophysics Data System (ADS)

Measurement of low-energy (<5keV) electron distribution functions in the inner heliosphere is of prime importance for understanding solar wind acceleration and heating processes. Solar Orbiter and Solar Probe Plus missions will provide the high-angular resolution electron measurements which are needed for improving our understanding of the sources of fast and slow solar wind, of the distribution of open and closed magnetic field structures, and of the origin and evolution of electron strahl. We present the main characteristics of the high-angular resolution electron detector that has been developed, prototyped, and tested at LPP for the Solar Orbiter mission. Our detector is using a pixelated anode that is HV coupled to a low power multi-channel hard-rad full custom ASIC that performs charge amplification and discrimination from noise. Using embedded capacitance technology, it provides a generic ultra-compact and low mass solution for high-angular resolution electron measurements in solar system plasmas.

Berthomier, M.; Zouganelis, I.; Techer, J.; Leblanc, F.; Verdeil, C.

2011-12-01

19

Approximation for the Rayleigh Resolution of a Circular Aperture

NASA Astrophysics Data System (ADS)

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,1 the first minimum for a rectangular slit of width a is located at angular position ? = sin-1 (?/a) for light of wavelength ?. If the angular separation of the two sources is small, we can use the small-angle approximation sin ? ~ ? to conclude that the resolution is ?min = ?/a for a rectangular aperture. On the other hand, for a circular aperture of diameter D, the limiting angle is shown in optics texts2 to be ?min = 1.22 ?/D. The derivation of the numerical prefactor of 1.22 involves finding the zero of a Bessel function and is beyond the reach of introductory physics students. Consequently, elementary texts simply pull that prefactor out of thin air. The purpose of the present paper is to briefly explain why we expect a prefactor larger than unity and to make simple estimates of its value, using only algebra.

Mungan, Carl E.

2009-05-01

20

Holographic Imaging: A Versatile Tool for High Angular Resolution Imaging

NASA Astrophysics Data System (ADS)

Speckle holography can be used to reconstruct high angular resolution images from long series of short exposures if the point spread function (PSF) from each frame can be measured reliably. We show that through use of multiple reference stars and iterative PSF subtraction, we can obtain highly accurate PSFs. The technique is optimised for crowded fields and results in images with excellent cosmetics and high Strehl ratio from the optical to the mid-infrared regimes. With examples from NACO, VISIR, and HAWK-I we show that holography opens up novel and unforeseen possibilities and can be an attractive alternative to adaptive optics.

Schödel, R.; Girard, J. H.

2012-12-01

21

High-energy resolution, high-angular acceptance crystal monochromator

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

22

High-energy resolution, high-angular acceptance crystal monochromator

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

23

A hard x-ray spectrometer for high angular resolution observations of cosmic sources

LAXRIS (large area x-ray imaging spectrometer) is an experimental, balloon-borne, hard x-ray telescope that consists of a coaligned array of x-ray imaging spectrometer modules capable of obtaining high angular resolution (1--3 arcminutes) with moderate energy resolution in the 20- to 300-keV region. Each spectrometer module consists of a CsI(Na) crystal coupled to a position-sensitive phototube with a crossed-wire, resistive readout. Imaging is provided by a coded aperture mask with a 4-m focal length. The high angular resolution is coupled with rather large area (/approximately/800 cm/sup 2/) to provide good sensitivity. Results are presented on performance and overall design. Sensitivity estimates are derived from a Monte-Carlo code developed to model the LAXRIS response to background encountered at balloon altitudes. We discuss a variety of observations made feasible by high angular resolution. For instance, spatially resolving the nonthermal x-ray emission from clusters of galaxies is suggested as an ideal program for LAXRIS. 15 refs., 5 figs.

Hailey, C.J.; Ziock, K.P.; Harrison, F.; Kahn, S.M.; Liedahl, D.; Lubin, P.M.; Seiffert, M.

1988-08-12

24

An estimator of the Orientation Probability Density Function (OPDF) of fiber tracts in the white matter of the brain from High Angular Resolution Diffusion data is presented. Unlike Q-Balls, which use the Funk-Radon transform to estimate the radial projection of the 3D Probability Density Function, the Jacobian of the spherical coordinates is included in the Funk-Radon approximation to the radial integral. Thus, true angular marginalizations are computed, which allows a strict probabilistic interpretation. Extensive experiments with both synthetic and real data show the better capability of our method to characterize complex micro-architectures compared to other related approaches (Q-Balls and Diffusion Orientation Transform), especially for low values of the diffusion weighting parameter. PMID:19393321

Tristán-Vega, Antonio; Westin, Carl-Fredrik; Aja-Fernández, Santiago

2009-08-15

25

Apparent diffusion profile estimation from high angular resolution diffusion images

NASA Astrophysics Data System (ADS)

High angular resolution diffusion imaging (HARDI) has recently been of great interest to characterize non-Gaussian diffusion process. In the white matter of the brain, this occurs when fiber bundles cross, kiss or diverge within the same voxel. One of the important goal is to better describe the apparent diffusion process in these multiple fiber regions, thus overcoming the limitations of classical diffusion tensor imaging (DTI). In this paper, we design the appropriate mathematical tools to describe noisy HARDI data. Using a meaningful modified spherical harmonics basis to capture the physical constraints of the problem, we propose a new regularization algorithm to estimate a smoother and closer diffusivity profile to the true diffusivities without noise. We exploit properties of the spherical harmonics to define a smoothing term based on the Laplace-Beltrami for functions defined on the unit sphere. An additional contribution of the paper is the derivation of the general transformation taking the spherical harmonics coefficients to the high order tensor independent elements. This allows the careful study of the state of the art high order anisotropy measures computed from either spherical harmonics or tensor coefficients. We analyze their ability to characterize the underlying diffusion process. We are able to recover voxels with isotropic, single fiber anisotropic and multiple fiber anisotropic diffusion. We test and validate the approach on diffusion profiles from synthetic data and from a biological rat phantom.

Descoteaux, Maxime; Angelino, Elaine; Fitzgibbons, Shaun; Deriche, Rachid

2006-03-01

26

ISMI: a classification index for high angular resolution diffusion imaging

NASA Astrophysics Data System (ADS)

Magnetic resonance diffusion imaging provides a unique insight into the white matter architecture of the brain in vivo. Applications include neurosurgical planning and fundamental neuroscience. Contrary to diffusion tensor imaging (DTI), high angular resolution diffusion imaging (HARDI) is able to characterize complex intra-voxel diffusion distributions and hence provides more accurate information about the true diffusion profile. Anisotropy indices aim to reduce the information of the diffusion probability function to a meaningful scalar representation that classifies the underlying diffusion and thereby the neuronal fiber configuration within a voxel. These indices can be used to answer clinical questions such as the integrity of certain neuronal pathways. Information about the underlying fiber distribution can be beneficial in tractography approaches, reconstructing neuronal pathways using local diffusion orientations. Therefore, an accurate classification of diffusion profiles is of great interest. However, the differentiation between multiple fiber orientations and isotropic diffusion is still a challenging task. In this work, we introduce ISMI, an index which successfully differentiates isotropic diffusion and single and multiple fiber populations. The classifier is based on the orientation distribution function (ODF) resulting from Q-ball imaging. We compare our results with the well-known general fractional anisotropy (GFA) index using a fiber phantom comprising challenging diffusion profiles such as crossing, fanning and kissing fiber configurations and a human brain dataset considering the centrum semiovale. Additionally, we visualize the results directly on the fibers represented by streamtubes using a heat color map.

Röttger, D.; Dudai, D.; Merhof, D.; Müller, S.

2012-02-01

27

With the rapid progress in metallicity gradient studies at high redshift, it is imperative that we thoroughly understand the systematics in these measurements. This work investigates how the [N II]/H{alpha}-ratio-based metallicity gradients change with angular resolution, signal to noise (S/N), and annular binning parameters. Two approaches are used: (1) we downgrade the high angular resolution integral-field data of a gravitationally lensed galaxy and re-derive the metallicity gradients at different angular resolution; (2) we simulate high-redshift integral field spectroscopy observations under different angular resolution and S/N conditions using a local galaxy with a known gradient. We find that the measured metallicity gradient changes systematically with angular resolution and annular binning. Seeing-limited observations produce significantly flatter gradients than higher angular resolution observations. There is a critical angular resolution limit beyond which the measured metallicity gradient is substantially different to the intrinsic gradient. This critical angular resolution depends on the intrinsic gradient of the galaxy and is {<=}0.''02 for our simulated galaxy. We show that seeing-limited high-redshift metallicity gradients are likely to be strongly affected by resolution-driven gradient flattening. Annular binning with a small number of annuli produces a more flattened gradient than the intrinsic gradient due to weak line smearing. For three-annulus bins, a minimum S/N of {approx}5 on the [N II] line is required for the faintest annulus to constrain the gradients with meaningful errors.

Yuan, T.-T.; Kewley, L. J. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Rich, J. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

2013-04-20

28

NASA Technical Reports Server (NTRS)

The Markov approximation to the propagation of waves in an extended, irregular medium is discussed in an astrophysical context. A new derivation is presented which is simple and which shows that the assumption of Gaussian statistics used by previous authors is irrelevant. We discuss the relevance of the approximation and show that it may apply in many situations of interest, including interstellar scintillations of pulsar signals. The approximation does not require the assumption of weak scattering or Gaussian correlation functions. The Markov equation for the angular spectrum is particularly simple, and solutions are discussed for typical turbulence spectra. It is found that the equation for the angular spectrum is very nearly that used by previous authors, and the present discussion shows that these results are much more general than previously thought. A possible observational test for distinguishing between Gaussian and power-law interstellar density spectra is discussed.

Lee, L. C.; Jokipii, J. R.

1975-01-01

29

Spatially Regularized Compressed Sensing for High Angular Resolution Diffusion Imaging

Despite the relative recency of its inception, the theory of compressive sampling (aka compressed sensing) (CS) has already revolutionized multiple areas of applied sciences, a particularly important instance of which is medical imaging. Specifically, the theory has provided a different perspective on the important problem of optimal sampling in magnetic resonance imaging (MRI), with an ever-increasing body of works reporting stable and accurate reconstruction of MRI scans from the number of spectral measurements which would have been deemed unacceptably small as recently as five years ago. In this paper, the theory of CS is employed to palliate the problem of long acquisition times, which is known to be a major impediment to the clinical application of high angular resolution diffusion imaging (HARDI). Specifically, we demonstrate that a substantial reduction in data acquisition times is possible through minimization of the number of diffusion encoding gradients required for reliable reconstruction of HARDI scans. The success of such a minimization is primarily due to the availability of spherical ridgelet transformation, which excels in sparsifying HARDI signals. What makes the resulting reconstruction procedure even more accurate is a combination of the sparsity constraints in the diffusion domain with additional constraints imposed on the estimated diffusion field in the spatial domain. Accordingly, the present paper describes an original way to combine the diffusion-and spatial-domain constraints to achieve a maximal reduction in the number of diffusion measurements, while sacrificing little in terms of reconstruction accuracy. Finally, details are provided on an efficient numerical scheme which can be used to solve the aforementioned reconstruction problem by means of standard and readily available estimation tools. The paper is concluded with experimental results which support the practical value of the proposed reconstruction methodology.

Rathi, Yogesh; Dolui, Sudipto

2013-01-01

30

Accommodation measurement according to angular resolution density in three-dimensional display

NASA Astrophysics Data System (ADS)

Accommodative response measurement according to angular resolution in autostereoscopic display based on lenticular lens and lens array method is presented. Conflict between accommodation and convergence is one of the most dominant factors leading to visual fatigue in viewing three-dimensional display. The conflict originates from directional rays that do not have enough angular resolution density. Therefore the purpose of this paper is to verify the relationship between angular resolution density of elemental images and accommodation-convergence conflict. For measurement of accommodation response of a single eye, we used lens arrays and elemental images with different resolution densities.

Kim, Youngmin; Hong, Keehoon; Kim, Jongshin; Yang, Hee Kyung; Hwang, Jeong-Min; Lee, Byoungho

2011-02-01

31

Approximate scaling formula for collisional angular-momentum mixing of Rydberg atoms

An approximate scaling formula has been determined that permits the rapid estimation of cross sections for angular-momentum-changing collisions of Rydberg atoms with a variety of targets, using information about low-energy-electron scattering from the target. The formula is obtained by fitting the results of coupled-channel and Born-approximation calculations to functions of reduced parameters. Application to Na(nd)+He, Ne, Ar, N/sub 2/, CH/sub 4/, C/sub 3/H/sub 8/; Rb(nf)+He, Ar, Xe; and Xe(nf)+CO/sub 2/, suggests that the accuracy is about a factor of 2.

Hickman, A.P.

1981-01-01

32

Angular sensing resolution provided by accelerometers in Micron, a physiological tremor compensation instrument, is determined by noise levels of accelerometer outputs and placement of the accelerometers. The angular sensing resolution can be increased by properly placing accelerometers in the instrument. In this paper, propositions for the placement of accelerometers to obtain the highest possible angular sensing resolution in micro manipulation

W. T. Latt; U.-X. Tan; F. Widjaja; W. T. Ang

2009-01-01

33

High Angular Resolution Microwave Sensing with Large, Sparse, Random Arrays.

National Technical Information Service (NTIS)

This document describes progress toward development of a general capability for high resolution microwave surveillance and imaging using large, sparse, self-cohering arrays. During the last five years progress has been made in the following areas: underst...

C. N. Dorny

1983-01-01

34

High energy resolution, high angular acceptance crystal monochromator

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 .mu.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.

Alp, Ercan E. (Bolingbrook, IL); Mooney, Timothy M. (Westmont, IL); Toellner, Thomas (Green Bay, WI)

1996-06-04

35

High energy resolution, high angular acceptance crystal monochromator

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

36

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

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

Approximate angular distribution and spectra for geomagnetically trapped protons in low-earth orbit

NASA Technical Reports Server (NTRS)

The highly anisotropic nature of the radiation in the low-earth orbit has been ignored for most spacecraft shielding calculations made to date because the standard environmental models describe the omnidirectional flux only, because the varying attitude of the spacecraft in the environment is assumed to average out the effect and because of the added complexity of the calculation. The Space Station is planned to be stabilized with respect to the velocity vector and local vertical. Thus it will pass through the South Atlantic Anomaly where most of the radiation flux is encountered in much the same attitude on each pass. Any calculation including a complex shielding geometry should thus consider the angular distributuon of the incident radiation. An approximate trapped proton angular distribution is presented which includes both the 'pan caked' distribution relative to the magnetic field direction and the east-west effect which is energy dependent. This distribution is then used with a planar shielding geometry to obtain an estimate of the effect of the anisotropy on radiation dose rates in spacecraft.

Watts, J. W.; Parnell, T. A.; Heckman, H. H.

1989-01-01

38

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

39

High angular resolution X-ray astronomy in the next 50 years. Back to the future

NASA Astrophysics Data System (ADS)

The 0.5 arc second angular resolution of the Chandra X-Ray Observatory is likely to be the best that can be obtained with grazing incidence optics, especially when larger effective area is required. We describe a telescope concept based upon transmitting diffractive-refractive optics that appears to be capable of providing better than mili arc second angular resolution. However, focal lengths are of the order of 1000 km, which requires long distance formation-flying between two spacecraft. In order to counteract gravity gradient forces to maintain alignment of optics with the detector and change targets,one of the spacecraft must contain engines for propulsion.

Gorenstein, P.

40

HST/FGS High Angular Resolution Observations of Binary Asteroids

NASA Astrophysics Data System (ADS)

Binary or multiple asteroids are important bodies that provide insight into the physical properties of asteroids in general. The knowledge of the components orbit in a binary provides the total mass with high accuracy and generally permits a rough bulk-density estimate [1,2]. We have observed 10 selected binary or multiple asteroids (22 Kalliope, 45 Eugenia, 87 Sylvia, 90 Antiope, 107 Camilla, 121 Hermione, 283 Emma, 379 Huenna, 617 Patroclus, 762 Pulcova) with the HST/FGS interferometer in order to obtain high resolution data on the size and shape of their primaries (HST proposal ID 10614). All these systems except the Jupiter Trojan 617 Patroclus are located in the main-belt of asteroids. Combining these HST/FGS data to topographic models obtained from lightcurve inversion [3,4] yields the volume and hence the bulk density of these bodies with unprecedented accuracy [5]. This work will allow us to obtain important information on their internal structure, and insight into the possible gravitational re-accumulation process after a catastrophic disruptive collision [e.g. 6,7,8].In particular, one can see whether or not the surfaces of theses bodies closely follow an effective equipotential surface, and under what circumstances such a correspondence is or is not attained . We will present the preliminary results for the data reduction and the size and bulk density determination. [1] Merline et al. (2003). In: Asteroids III, pp 289. [2] Marchis et al. (2005) ACM 2005, Buzios, Brazil. [3] Kaasalainen et al. (2002) Icarus 159, 359. [4] Torppa et al. (2003) Icarus 164, 346. [5] Hestroffer et al. (2003) ACM 2002, ESA-SP 500, 493. [6] Michel et al. (2004) P&SS 52, 1109. [7] Durda et al. (2004) Icarus 167, 342. [8] Paolicchi et al. (1993) Cel. Mech., 57, 49.

Hestroffer, Daniel; Tanga, P.; Cellino, A.; Kaasalainen, M.; Torppa, J.; Marchis, F.; Richardson, D. C.; Elankumaran, P.; Berthier, J.; Colas, F.; Lounis, S.

2006-09-01

41

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

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

42

Beating the Rayleigh limit: Orbital-angular-momentum-based super-resolution diffraction tomography

NASA Astrophysics Data System (ADS)

This paper reports a super-resolution imaging approach based on orbital-angular-momentum diffraction tomography (OAM-DT), which makes an important breakthrough on the Rayleigh limit associated with conventional diffraction tomography (DT) technique. It is well accepted that orbital-angular momentum (OAM) provides additional electromagnetic degrees of freedom. This concept has been widely applied in science and technology. In this paper we revisit the DT problem extended with OAM, and demonstrate theoretically and numerically that there is no physical limit on imaging resolution with OAM-DT. The physical mechanism behind it is that either the near field or superoscillation of the transmitter is employed to super-resolve probed objects. This super-resolution OAM-DT imaging paradigm does not require near-field measurement, a subtle focusing lens, or complicated postprocessing, etc., thus providing an approach to realize the wave-field imaging of universal objects with subwavelength resolution.

Li, Lianlin; Li, Fang

2013-09-01

43

Beating the Rayleigh limit: orbital-angular-momentum-based super-resolution diffraction tomography.

This paper reports a super-resolution imaging approach based on orbital-angular-momentum diffraction tomography (OAM-DT), which makes an important breakthrough on the Rayleigh limit associated with conventional diffraction tomography (DT) technique. It is well accepted that orbital-angular momentum (OAM) provides additional electromagnetic degrees of freedom. This concept has been widely applied in science and technology. In this paper we revisit the DT problem extended with OAM, and demonstrate theoretically and numerically that there is no physical limit on imaging resolution with OAM-DT. The physical mechanism behind it is that either the near field or superoscillation of the transmitter is employed to super-resolve probed objects. This super-resolution OAM-DT imaging paradigm does not require near-field measurement, a subtle focusing lens, or complicated postprocessing, etc., thus providing an approach to realize the wave-field imaging of universal objects with subwavelength resolution. PMID:24125378

Li, Lianlin; Li, Fang

2013-09-01

44

HIGH-RESOLUTION ASYMPTOTICS FOR THE ANGULAR BISPECTRUM OF SPHERICAL RANDOM FIELDS1

In this paper we study the asymptotic behavior of the angular bispectrum of spherical random fields. Here, the asymptotic theory is developed in the framework of fixed-radius fields, which are observed with increasing resolution as the sample size grows. The results we present are then exploited in a set of procedures aimed at testing non- Gaussianity; for these statistics, we

Domenico Marinucci

2006-01-01

45

National Technical Information Service (NTIS)

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 ...

I. Ambats D. Ayres W. Barrett K. Barron J. Dawson

1987-01-01

46

A nonparametric Riemannian framework for processing high angular resolution diffusion images (HARDI)

High angular resolution diffusion imaging has become an important magnetic resonance technique for in vivo imaging. Most current research in this field focuses on developing methods for computing the orientation distribution function (ODF), which is the probability distribution function of water molecule diffusion along any angle on the sphere. In this paper, we present a Riemannian framework to carry out

Alvina Goh; Christophe Lenglet; Paul M. Thompson; R. Vidal

2009-01-01

47

Evaluation of the accuracy and angular resolution of q-ball imaging.

Q-ball imaging (QBI) has been proposed for the mapping of multiple intravoxel fiber structures using the Funk-Radon transform on high angular resolution diffusion images (HARDI). However, the accuracy and the angular resolution of QBI to define fiber orientations and its dependence on diffusion imaging parameters remain unclear. The phantom models, made up of sheets of parallel capillaries filled with water, were designed to evaluate the accuracy and the angular resolution of QBI at different |q| values. With an inner diameter of 20 mum and an outer diameter of 90 mum, the capillaries afforded a restrictive environment compared with the diffusion measurement scale. Further, the angular resolutions of QBI at various |q| value were also quantified on the corpus callosum in the human brain. The full width at half maximum (FWHM) of the main lobe of normalized orientation distribution function (nODF) was calculated and adopted to quantify the angular resolution of QBI. With the phantom model, a higher |q| value resulted in worse accuracy but better angular resolution for QBI. The same trend where a higher |q| value yielded a better angular resolution was also observed in the human study. Upon comparison of QBI with T2WI, QBI with |q|=277 cm(-1) (b=3000 s/mm(2)) was found to be insufficient to differentiate capillaries crossing at 45 degrees . However, when encoding with |q|=320, 358, and 392 cm(-1) (b=4000, 5000, and 6000 s/mm(2)), the deviation angles between the primary ODF and the 45 degrees phantoms were -4.91 degrees +/-2.72 degrees , -1.37 degrees +/-2.32 degrees , and -0.69 degrees +/-1.54 degrees with adequate signal-to-noise ratio (SNR). These results were consistent with the FWHM-nODF, which showed that a |q| value of 320 cm(-1) was the threshold to resolve capillaries intersecting at 45 degrees . Additionally, it was demonstrated in both the phantom model and the human brain that QBI encoding with lower |q| values may result in underestimation of the orientations of the crossing fibers. In conclusion, QBI was found to accurately resolve crossing fiber orientations and was highly dependent on the selected |q| value. PMID:18502152

Cho, Kuan-Hung; Yeh, Chun-Hung; Tournier, Jacques-Donald; Chao, Yi-Ping; Chen, Jyh-Horng; Lin, Ching-Po

2008-08-01

48

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

49

We report for the first time a method-independent geometrical expression for the angular resolution of an arbitrary network of interferometric gravitational wave (GW) detectors when the arrival-time of a GW is unknown. We discuss the implications of our results on how to improve angular resolutions of a GW network and on improvements of localization methods. An example of an improvement

Linqing Wen; Xilong Fan; Yanbei Chen

2008-01-01

50

Orbital angular momentum of Laguerre-Gaussian beams beyond the paraxial approximation.

We derive a full field solution for Laguerre-Gaussian beams consistent with the Helmholtz equation using the angular spectrum method. Field components are presented as an order expansion in the ratio of the wavelength to the beam waist, f=?/(2?w?), which is typically small. The result is then generalized to a beam of arbitrary polarization. This result is then used to reproduce the signature angular momentum properties of Laguerre-Gaussian beams in the paraxial limit. The subsequent higher-order term is similarly obtained, which does not display a clear separation of orbital and spin angular momentum components. PMID:22048292

Cerjan, Alexander; Cerjan, Charles

2011-11-01

51

A Future Generation High Angular Resolution X-ray Telescope Based Upon Physical Optics

NASA Astrophysics Data System (ADS)

Although the highest priority objective for the next major X-ray mission is high resolution spectroscopy we will ultimately want the next generation high angular resolution X-ray observatory. This author believes that the 0.5 arc second angular resolution of the Chandra X-Ray Observatory is likely to be close to the best that can be obtained with grazing incidence optics, especially with larger effective area. Telescopes based upon physical optics, diffraction and refraction that transmit rather than reflect X-rays can have an angular resolution of a mili arc second or better. Combining the diffractive and refractive components into one unit can neutralize the chromatic aberration of each individually over a ~15% bandwidth at 6 keV. The aperture could be divided into several diffractive-refractive pairs to broaden the bandwidth. Furthermore these telescopes would be very low cost, very light weight, and more tolerant of figure errors and surface roughness than grazing incidence telescopes. However, focal lengths are of the order of 1000 km, which requires a new mission architecture consisting of long distance formation-flying between two spacecraft, one hosting the optics, the other, the detector. One of the spacecraft requires propulsion, provided by, for example, ion engines to maintain the optics-detector alignment by counteracting gravity gradient forces, and for changing targets. Although their effective area can be large and their angular resolution very high diffractive-refractive telescopes are not necessarily more sensitive than Chandra because their large focal plane scale (1 mili arc second ~ 1 mm) subjects them to a higher level of cosmic ray background and their opacity results in a lower energy limit of 2 keV. The intrinsic field of view is wide but the large focal length scale and practical limits on the size of the detector array results in a small field of view.

Gorenstein, Paul

2013-04-01

52

The factorisation approximation in electron-atom scattering usually consists of eliminating the exchange contribution to the scattering by writing the scattering cross section as the product of the square of a direct scattering target form factor times the Mott cross section for electron-electron scattering. It is shown that a factorisation approximation is only possible for scattering angles less than 30' and

R. A. Bonham

1990-01-01

53

NASA Astrophysics Data System (ADS)

The mirror design for the International X-ray Observatory (IXO) is currently following two paths: a segmented slumped glass shell Wolter-I design, and a Silicon Pore Optics (SPO) conical approximation to the Wolter-I design. The conical approximation used for the SPO imposes a lower limit to the angular resolution which puts this option at a potential disadvantage. In this paper we describe ways in which this can be circumvented. We analyse the surface profile modifications that can be made to lift this limitation and show that a much closer approximation to the Wolter I ideal is possible. We describe several ways in which a much tighter angular resolution limit could be achieved in practice and discuss ways in which this can be implemented in the manufacture of the SPO.

Willingale, Richard; Spaan, Frank H. P.

2010-07-01

54

CHARRON: Code for High Angular Resolution of Rotating Objects in Nature

NASA Astrophysics Data System (ADS)

Rotation is one of the fundamental physical parameters governing stellar physics and evolution. At the same time, spectrally resolved optical/IR long-baseline interferometry has proven to be an important observing tool to measure many physical effects linked to rotation, in particular, stellar flattening, gravity darkening, differential rotation. In order to interpret the high angular resolution observations from modern spectro-interferometers, such as VLTI/AMBER and VEGA/CHARA, we have developed an interferometry-oriented numerical model: CHARRON (Code for High Angular Resolution of Rotating Objects in Nature). We present here the characteristics of CHARRON, which is faster (?q10-30 s per model) and thus more adapted to model-fitting than the first version of the code presented by Domiciano de Souza et al. (2002).

Domiciano de Souza, A.; Zorec, J.; Vakili, F.

2012-12-01

55

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

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

56

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

57

A Hamilton-Jacobi-Bellman Approach to High Angular Resolution Diffusion Tractography

This paper describes a new framework for white matter trac- tography in high angular resolution diusion data. A direction-dependent local cost is defined based on the diusion data for every direction on the unit sphere. Minimum cost curves are determined by solving the Hamilton-Jacobi-Bellman using an ecient algorithm. Classical costs based on the diusion tensor field can be seen as

Eric Pichon; Carl-fredrik Westin; Allen Tannenbaum

2005-01-01

58

Method for improving the angular resolution of a neutron scatter camera

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

59

Angular versus spatial resolution trade-offs for diffusion imaging under time constraints.

Diffusion weighted magnetic resonance imaging (DW-MRI) are now widely used to assess brain integrity in clinical populations. The growing interest in mapping brain connectivity has made it vital to consider what scanning parameters affect the accuracy, stability, and signal-to-noise of diffusion measures. Trade-offs between scan parameters can only be optimized if their effects on various commonly-derived measures are better understood. To explore angular versus spatial resolution trade-offs in standard tensor-derived measures, and in measures that use the full angular information in diffusion signal, we scanned eight subjects twice, 2 weeks apart, using three protocols that took the same amount of time (7 min). Scans with 3.0, 2.7, 2.5 mm isotropic voxels were collected using 48, 41, and 37 diffusion-sensitized gradients to equalize scan times. A specially designed DTI phantom was also scanned with the same protocols, and different b-values. We assessed how several diffusion measures including fractional anisotropy (FA), mean diffusivity (MD), and the full 3D orientation distribution function (ODF) depended on the spatial/angular resolution and the SNR. We also created maps of stability over time in the FA, MD, ODF, skeleton FA of 14 TBSS-derived ROIs, and an information uncertainty index derived from the tensor distribution function, which models the signal using a continuous mixture of tensors. In scans of the same duration, higher angular resolution and larger voxels boosted SNR and improved stability over time. The increased partial voluming in large voxels also led to bias in estimating FA, but this was partially addressed by using "beyond-tensor" models of diffusion. PMID:22522814

Zhan, Liang; Jahanshad, Neda; Ennis, Daniel B; Jin, Yan; Bernstein, Matthew A; Borowski, Bret J; Jack, Clifford R; Toga, Arthur W; Leow, Alex D; Thompson, Paul M

2013-10-01

60

High-resolution angular and displacement sensing based on the excitation of surface plasma waves.

The possibility of building angular and displacement sensors based on the phenomenon of attenuated total reflection (ATR) is explored both numerically and experimentally. ATR occurs when a surface wave is excited by an incoming TM electromagnetic wave through a resonant phase-matching process, as in the Kretschmann coupling scheme. The reflected intensity strongly depends on the angle of incidence of the beam. We first show some computations of the sensitivity and the linearity of an ATR-based sensor, then proceed to the experiment, illustrating how an angular resolution of the order of 0.1 arc sec can be obtained with moderate effort. Finally we show how the sensor, combined with a simple optical arrangement, can be used to detect and measure nanometric displacements, as those provided by piezoelectric actuators. PMID:18259245

Margheri, G; Mannoni, A; Quercioli, F

1997-07-01

61

Avalanche photodiode arrays for a high-angular resolution X-ray and gamma-ray imaging telescopes

Avalanche photodiodes (APDs) have been investigated as the basis for a very high angular resolution coded aperture telescope with sensitivity over a wide energy range. Using custom electronics, software and a unique shadow-masking technique, we have achieved angular resolution from an X-ray point source of about 30arcsec. In addition we have demonstrated imaging of higher gamma-ray energies by coupling to

M. R. Squillante; R. A. Myers; F. Robertson; R. Farrell; J. F. Christian; G. Entine

2007-01-01

62

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

NASA Astrophysics Data System (ADS)

Since its beginning 50 years ago, X-ray astronomy has advanced by leaps and bounds, culminating in its current golden age in which three major observatoriesChandra, XMM-Newton, and Suzakuare operating simultaneously and addressing some of the most important astronomical and astrophysical problems of our time. Building upon this success, the recent Decadal Survey of Astronomy and Astrophysics has defined objectives for x-ray astronomy whose realization requires both new optics and new detector technologies. The development of these technologies has been identified as one of the highest priorities for funding to enable future x-ray missions. X-ray optics technology based on precision glass slumping is on the verge of revolutionizing x-ray telescope making. It has shown that extremely thin (< 0.4mm) and lightweight (areal density < 1 kg/m2) true Wolter-I mirror segments with angular resolutions better than 7 arc-seconds can be fabricated consistently, efficiently, and inexpensively. In comparison with those of XMM-Newton, these mirror segments represent a factor of 10 reduction in mass while achieving slightly better angular resolution. In comparison with those of Suzaku, they represent a factor of 20 improvement in angular resolution while maintaining the same mass areal density. These advances have been demonstrated with x-ray images from aligned and bonded mirror segments. In short, this technology is approaching TRL-5 for making the mirror assemblies required for a 10 arc-second observatory. In this poster we will present the latest x-ray and environment test results obtained with technology development modules which are substantially similar to flight modules in the way they constructed and tested.

Zhang, William

2013-01-01

63

Examining young stellar systems in birth by high angular resolution observations

NASA Astrophysics Data System (ADS)

We present a high angular resolution survey of young T Tauri binaries on the northern sky. The binaries were discovered in the early 1990s, using speckle interferometry or lucky imaging techniques. The aim of our survey is to reobserve about 30 T Tauri pairs using a fast Andor iXon EMCCD camera mounted on our 1 m RCC telescope at the Piszkéstet? Mountain Station, Hungary, and determine whether the orbital motion of the companion could be revealed by speckle interferometry or lucky imaging. %

Csépány, G.; Ábrahám, P.; Regály, Zs.; Mez?, Gy.; Brandner, W.; Hormuth, F.

2014-03-01

64

X-Ray Phase-Contrast Imaging with Nanoradian Angular Resolution

NASA Astrophysics Data System (ADS)

We present a new quantitative x-ray phase-contrast imaging method based on the edge illumination principle, which allows achieving unprecedented nanoradian sensitivity. The extremely high angular resolution is demonstrated theoretically and through experimental images obtained at two different synchrotron radiation facilities. The results, achieved at both very high and very low x-ray energies, show that this highly sensitive technique can be efficiently exploited over a very broad range of experimental conditions. This method can open the way to new, previously inaccessible scientific applications in various fields including biology, medicine and materials science.

Diemoz, P. C.; Endrizzi, M.; Zapata, C. E.; Pei?, Z. D.; Rau, C.; Bravin, A.; Robinson, I. K.; Olivo, A.

2013-03-01

65

Optimal short-time acquisition schemes in high angular resolution diffusion-weighted imaging.

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/mm(2)) 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

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

67

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

68

NASA Astrophysics Data System (ADS)

We present the results of near-IR lunar occultation measurements of three well-known, large angular diameter, cool giant stars, namely X Cnc (CII), U Ori (M8III) and eta Gem (M3III). Their 2.2 mu m angular diameters, derived under the assumption of a uniform circular disk, are 8.26+/-0.04, 15.14+/-0.05 and 12.57+/-0.04 milliarcsec, respectively. In the case of U Ori, we find a significant deviation of the brightness profile from circular symmetry, as well as a faint signature of extended emission. The asymmetry of the brightness profile cannot be explained by scintillation effects in the lunar occultation lightcurve, and could have contributed to the important differences in previous determinations of the angular diameter of U Ori in the near-IR. Also in the case of eta Gem, significant differences exist among the available angular diameter determinations. Based on observations collected at TIRGO (Gornergrat, Switzerland). TIRGO is operated by CNR - CAISMI Arcetri, Italy.

Richichi, A.; Calamai, G.

2003-02-01

69

The utility of several approximate scattering methods for predicting collision induced spectral pressure broadening has been tested by comparison with accurate close coupling results. In particular, broadening of the pure rotational spectra of HD, HCl, CO, and HCN - all perturbed by low energy collisions with He atoms - has been computed using the effective potential formalism of Rabitz, the

Sheldon Green; Louis Monchick; D. J. Kouri; R. Goldflam

1977-01-01

70

The angular resolution of the GRAPES-3 array from the shadows of the Moon and the Sun

NASA Astrophysics Data System (ADS)

The absence of a well established point source of very high energy (?10TeV) ?-rays in the sky, makes the measurement of the angular resolution and the absolute pointing accuracy of an extensive air shower (EAS) array a challenging task. In the past, several groups have utilized the reduction in the isotropic flux of cosmic rays due to the shadows of the Moon and the Sun, to measure the angular resolution and the absolute pointing accuracy of their arrays. The data collected from the GRAPES-3 EAS array, over the period of 4 years from 2000 to 2003, has been used to observe the shadow of the Moon at a level of 5? and that of the Sun at a lower level of significance. The high density of the detectors in GRAPES-3 enabled an angular resolution of 0.7° to be obtained at energies as low as 30 TeV. The angular resolution studies were further extended by using two other techniques, namely, the even-odd and the left-right methods. All three techniques have yielded nearly identical results on the energy dependent angular resolution.

Oshima, A.; Dugad, S. R.; Goswami, U. D.; Gupta, S. K.; Hayashi, Y.; Ito, N.; Iyer, A.; Jagadeesan, P.; Jain, A.; Kawakami, S.; Minamino, M.; Mohanty, P. K.; Morris, S. D.; Nayak, P. K.; Nonaka, T.; Ogio, S.; Rao, B. S.; Ravindran, K. C.; Tanaka, H.; Tonwar, S. C.; GRAPES-3 Collaboration

2010-03-01

71

NASA Astrophysics Data System (ADS)

Due to the temporal resolution of available numerical weather analyses, the effect of the atmosphere on Earth rotation at daily and sub-daily periods is usually investigated using 6-hourly atmospheric angular momentum (AAM) functions. During the period of CONT08, however, atmospheric analysis data were provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) also on an hourly basis. In this paper, we, therefore, determine two sets of AAM functions from ECMWF dataone for CONT08 with hourly resolution and one for the year 2008 with 6-hourly resolution. The comparisons of the AAM functions to high-resolution Earth rotation parameters (ERP) from VLBI and GPS observations are carried out in the frequency domain. Special attention is paid to the preparation of the high-resolution data sets for the geodetic purposes, as there are jump discontinuities at 12 h intervals. Hence, the hourly AAM functions need to be concatenated. The revised functions yield much smaller amplitudes than their 6-hourly counterparts, as can be seen from the equatorial and the axial frequency spectra of atmospheric excitation in Earth rotation. This decrease of spectral power in the hourly AAM functions is found to be associated with a strong counteraction of pressure and wind terms, which originates from atmospheric circulation on short time scales. The results are compared to previous findings published by Brzezi?ski and Petrov (IERS Tech Note 28:53-60, 2000) based on the data from the U.S. National Centers for Environmental Prediction (NCEP).

Schindelegger, Michael; Böhm, Johannes; Salstein, David; Schuh, Harald

2011-07-01

72

High Angular Resolution Observations of the Massive Stars in Cyg OB2

NASA Astrophysics Data System (ADS)

It is a widely accepted fact that massive stars love company and have a significant affect on the evolution of the Universe, from galactic dynamics and structure to star formation. However, our knowledge of O-type multiple systems with periods in the range from years to thousands of years is incomplete. The Fine Guidance Sensors (FGS) on the Hubble Space Telescope and Adaptive Optics at the Gemini Observatory North are ideal for finding widely separated binaries at high angular resolution with separations of at least 0.?1. At a distance of 1.7 kpc, Cyg OB2 provides a nearby, young stellar environment, rich in high-mass stars. We observed 75 O- and early B-type stars and determined that 42% of the sample have at least one physical companion. We present these initial results as part of an ongoing survey of O stars with FGS.

Caballero-Nieves, S. M.; Gies, D. R.; Nelan, E. P.

2012-12-01

73

NASA Technical Reports Server (NTRS)

The utility of several approximate scattering methods for predicting collision induced spectral pressure broadening has been tested by comparison with accurate close coupling results. In particular, broadening of the pure rotational spectra of HD, HCl, CO, and HCN - all perturbed by low energy collisions with He atoms - has been computed using the effective potential formalism of Rabitz, the decoupled l-dominant approximation of DePristo and Alexander, and the j(2)-conserving coupled states method of McGuire and Kouri. For this last method, pressure broadening cross sections have been obtained with the new, correct expression recently derived by Goldflam and Kouri as well as with an earlier formalism based on an incorrect labeling of the scattering matrices. These methods were found to be generally diasppointing for predicting pressure broadening with the exception of the new, correctly formulated j(2)-conserving coupled states method which was found to agree quantitatively (better than 5%) with close coupling values for all cases studied.

Green, S.; Monchick, L.; Kouri, D. J.; Goldflam, R.

1977-01-01

74

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

75

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

76

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(?). Experiment has proved its feasibility and practicability. PMID:24784662

Tang, Shanzhi; Wang, Zhao; Gao, Jianmin; Guo, Junjie

2014-04-01

77

We have used momentum imaging techniques to measure in high resolution the kinetic energy release spectra and angular distributions of coincident O+ and N+ ion pairs produced by short laser pulses (8-35 fs) on targets of N2 and O2 at peak intensities between 1 and 12 × 1014 W cm-2. We record the full momentum vectors of both members of

S. Voss; A. S. Alnaser; X.-M. Tong; C. Maharjan; P. Ranitovic; B. Ulrich; B. Shan; Z. Chang; C. D. Lin; C. L. Cocke

2004-01-01

78

Sub-Airy disk angular resolution with high dynamic range in the near-infrared

NASA Astrophysics Data System (ADS)

Lunar occultations (LO) are a simple and effective high angular resolution method, with minimum requirements in instrumentation and telescope time. They rely on the analysis of the diffraction fringes created by the lunar limb. The diffraction phenomen occurs in space, and as a result LO are highly insensitive to most of the degrading effects that limit the performance of traditional single telescope and long-baseline interferometric techniques used for direct detection of faint, close companions to bright stars. We present very recent results obtained with the technique of lunar occultations in the near-IR, showing the detection of companions with very high dynamic range as close as few milliarcseconds to the primary star. We discuss the potential improvements that could be made, to increase further the current performance. Of course, LO are fixed-time events applicable only to sources which happen to lie on the Moon's apparent orbit. However, with the continuously increasing numbers of potential exoplanets and brown dwarfs beign discovered, the frequency of such events is not negligible. I will list some of the most favorable potential LO in the near future, to be observed from major observatories.

Richichi, A.

2011-07-01

79

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.

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.

2014-01-01

80

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

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

81

NASA Astrophysics Data System (ADS)

This dissertation presents the results of several observational projects designed to explore AGNs, on scales of about 100 pc and smaller, in nearby galaxies. High angular resolution spectroscopy acquired from HST STIS and Keck LGS AO OSIRIS observations are used to study the kinematic structure of gas disks and stars on scales comparable to the gravitational sphere of influence of the supermassive black hole. Specifically, I use multi-slit STIS data of low-luminosity AGNs to map out the emission-line kinematics, and to look for regularly rotating velocity fields suitable for future gas dynamical black hole mass measurements. The HST data is further useful for searching for electron-density gradients and for examining how the emission-line velocity dispersion varies as a function of aperture size. In another project, I aim to resolve a discrepancy between two previous gas dynamical measurements of the black hole in the elliptical galaxy M84. I perform new measurements of the gas kinematics from archival multi-slit STIS data, and carry out a more comprehensive dynamical model of the emission-line disk than had been previously attempted. With the most recent project, I measure high-resolution stellar kinematics from LGS AO OSIRIS data and large-scale kinematics from long-slit LRIS data of the S0 galaxy NGC 3998. Using triaxial orbit-based stellar dynamical models, I determine the black hole mass. The stellar dynamical value is then compared to a previous gas dynamical determination in order to test the consistency between these two main mass measurement methods. In addition to using high spatial resolution spectroscopy, AGN variability can be used to probe the inner regions of AGNs. The Lick AGN Monitoring Project targeted 12 galaxies expected to harbor low-mass black holes. Through reverberation mapping, the collaboration measured the masses of nine black holes, and learned about the geometry and kinematics of the broad-line region in several of the objects. I discuss my contribution to the project: measuring the AGN continuum from broadband B and V images. I also examine continuum variability characteristics, search for time lags between B - and V -band variations, and look for fluctuations in the AGN color.

Walsh, Jonelle L.

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

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

Cortical connectivity is associated with cognitive and behavioral traits that are thought to vary between sexes. Using high-angular resolution diffusion imaging at 4 Tesla, we scanned 234 young adult twins and siblings (mean age: 23.4 ą 2.0 SD years) with 94 diffusion-encoding directions. We applied a novel Hough transform method to extract fiber tracts throughout the entire brain, based on

Neda Jahanshad; Iman Aganj; Christophe Lenglet; Anand Joshi; Yan Jin; Marina Barysheva; Katie L. McMahon; Greig I. de Zubicaray; Nicholas G. Martin; Margaret J. Wright; Arthur W. Toga; Guillermo Sapiro; Paul M. Thompson

2011-01-01

85

In vivo DTI of the healthy and injured cat spinal cord at high spatial and angular resolution

Spinal cord diffusion tensor imaging (DTI) is challenging in many ways: the small size of the cord, physiological motion and susceptibility artifacts pose daunting obstacles to the acquisition of high-quality data. Here, we present DTI results computed from in vivo studies of the healthy and injured spinal cord of five cats. Both high spatial (1.1 mm3) and angular (55 directions) resolutions

J. Cohen-Adad; H. Benali; R. D. Hoge; S. Rossignol

2008-01-01

86

Due to strong electron correlation effects and electron coupling with nuclear motion, the molecular inner-valence photoionization is still a challenge in electron spectroscopy, resulting in several interesting phenomena such as drastic changes of angular dependencies, spin-orbit induced predissociation, and complex interplay between adiabatic and nonadiabatic transitions. We investigated the excited electronic states of HCl(+) in the binding energy range 27.5-30.5 eV using synchrotron radiation based high-resolution inner-valence photoelectron spectroscopy with angular resolution and interpreted the observations with the help of ab initio calculations. Overlapping electronic states in this region were disentangled through the analysis of photoelectron emission anisotropies. For instance, a puzzling transition, which does not seem to obey either an adiabatic or a nonadiabatic picture, has been identified at ?28.6 eV binding energy. By this study, we show that ultrahigh-resolution photoelectron spectroscopy with angular selectivity represents a powerful tool to probe the highly excited ionic molecular electronic states and their intricate couplings. PMID:25007894

Patanen, M; Nicolas, C; Linguerri, R; Simőes, G; Travnikova, O; Liu, X-J; Hochlaf, M; Bozek, J D; Miron, C

2014-07-10

87

Properties of dense cores in clustered massive star-forming regions at high angular resolution

NASA Astrophysics Data System (ADS)

We aim at characterizing dense cores in the clustered environments associated with intermediate-/high-mass star-forming regions. For this, we present a uniform analysis of Very Large Array NH3 (1,1) and (2,2) observations towards a sample of 15 intermediate-/high-mass star-forming regions, where we identify a total of 73 cores, classify them as protostellar, quiescent starless, or perturbed starless, and derive some physical properties. The average sizes and ammonia column densities of the total sample are 0.06 pc and 1015 cm-2, respectively, with no significant differences between the starless and protostellar cores, while the linewidth and rotational temperature of quiescent starless cores are smaller, 1.0 km s-1 and 16 K, than linewidths and temperatures of protostellar (1.8 km s-1 and 21 K), and perturbed starless (1.4 km s-1 and 19 K) cores. Such linewidths and temperatures for these quiescent starless cores in the surroundings of intermediate-/high-mass stars are still significantly larger than the typical linewidths and rotational temperatures measured in starless cores of low-mass star-forming regions, implying an important non-thermal component. We confirm at high angular resolutions (spatial scales 0.05 pc) the correlations previously found with single-dish telescopes (spatial scales ? 0.1 pc) between the linewidth and the rotational temperature of the cores, as well as between the rotational temperature and the linewidth with respect to the bolometric luminosity. In addition, we find a correlation between the temperature of each core and the incident flux from the most massive star in the cluster, suggesting that the large temperatures measured in the starless cores of our sample could be due to heating from the nearby massive star. A simple virial equilibrium analysis seems to suggest a scenario of a self-similar, self-gravitating, turbulent, virialized hierarchy of structures from clumps (0.1-10 pc) to cores (0.05 pc). A closer inspection of the dynamical state taking into account external pressure effects reveals that relatively strong magnetic field support may be needed to stabilize the cores, or that they are unstable and thus on the verge of collapse.

Sánchez-Monge, Álvaro; Palau, Aina; Fontani, Francesco; Busquet, Gemma; Juárez, Carmen; Estalella, Robert; Tan, Jonathan C.; Sepúlveda, Inma; Ho, Paul T. P.; Zhang, Qizhou; Kurtz, Stan

2013-07-01

88

NASA Astrophysics Data System (ADS)

Scan-MUSIC algorithm, developed by the U.S. Army Research Laboratory (ARL), improves angular resolution for target detection with the use of a single rotatable radar scanning the angular region of interest. This algorithm has been adapted and extended from the MUSIC algorithm that has been used for a linear sensor array. Previously, it was shown that the SMUSIC algorithm and a Millimeter Wave radar can be used to resolve two closely spaced point targets that exhibited constructive interference, but not for the targets that exhibited destructive interference. Therefore, there were some limitations of the algorithm for the point targets. In this paper, the SMUSIC algorithm is applied to a problem of resolving real complex scatterer-type targets, which is more useful and of greater practical interest, particular for the future Army radar system. The paper presents results of the angular resolution of the targets, an M60 tank and an M113 Armored Personnel Carrier (APC), that are within the mainlobe of a ??-band radar antenna. In particular, we applied the algorithm to resolve centroids of the targets that were placed within the beamwidth of the antenna. The collected coherent data using the stepped-frequency radar were compute magnitudely for the SMUSIC calculation. Even though there were significantly different signal returns for different orientations and offsets of the two targets, we resolved those two target centroids when they were as close as about 1/3 of the antenna beamwidth.

Ly, Canh

2004-08-01

89

Characterization of anisotropy in high angular resolution diffusion-weighted MRI

The methods of group theory are applied to the problem of characterizing the diffusion measured in high angular resolu- tion MR experiments. This leads to a natural representation of the local diffusion in terms of spherical harmonics. In this rep- resentation, it is shown that isotropic diffusion, anisotropic diffusion from a single fiber, and anisotropic diffusion from multiple fiber directions

Lawrence R. Frank

2002-01-01

90

High-angular-resolution diffusion-weighted imaging (HARDI) is one of the most common MRI acquisition schemes for use with higher order models of diffusion. However, the optimal b value and number of diffusion-weighted (DW) directions for HARDI are still undetermined, primarily as a result of the large number of available reconstruction methods and corresponding parameters, making it impossible to identify a single criterion by which to assess performance. In this study, we estimate the minimum number of DW directions and optimal b values required for HARDI by focusing on the angular frequency content of the DW signal itself. The spherical harmonic (SH) series provides the spherical analogue of the Fourier series, and can hence be used to examine the angular frequency content of the DW signal. Using high-quality data acquired along 500 directions over a range of b values, we estimate that SH terms above l = 8 are negligible in practice for b values up to 5000 s/mm(2), implying that a minimum of 45 DW directions is sufficient to fully characterise the DW signal. l > 0 SH terms were found to increase as a function of b value, levelling off at b = 3000 s/mm(2), suggesting that this value already provides the highest achievable angular resolution. In practice, it is recommended to acquire more than the minimum of 45 DW directions to avoid issues with imperfections in the uniformity of the DW gradient directions and to meet signal-to-noise requirements of the intended reconstruction method. PMID:24038308

Tournier, J-Donald; Calamante, Fernando; Connelly, Alan

2013-12-01

91

The perturbation of angular correlations by a fluctuating distribution of electric quadrupole interactions has been calculated with Blume's stochastic theory for an ensemble of 10 states differing in magnitude and orientation of an electric field gradient as a function of the fluctuation rate w for different values of the fluctuating and the static components of the distribution. By fits to

M. Forker; W. Herz; D. Simon

1994-01-01

92

NASA Astrophysics Data System (ADS)

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared (30-90 microns) interferometer designed to fly on a high altitude balloon. BETTII uses a double-Fourier Michelson interferometer to simultaneously obtain spatial and spectral information on science targets; the long baseline permits subarcsecond angular resolution, a capability unmatched by other far-infrared facilities. The first BETTII flight will make use of this unique capability to address key questions about star formation. Here, we present the overall design of the BETTII gondola and science instrument, and provide an overview of the current status of the project.

Rinehart, Stephen; Barclay, R.; Barry, R. K.; Benford, D. J.; Fixsen, D. J.; Gorman, E.; Jackson, M.; Jhabvala, C.; Leisawitz, D.; Mentzell, E.; Mundy, L. G.; Rizzo, M.; Silverberg, R. F.; Staguhn, J.; Willingham, A.; BETTII Team

2013-06-01

93

NASA Astrophysics Data System (ADS)

A lunar occultation (LO) technique in the near-infrared (NIR) provides angular resolution down to milliarcseconds for an occulted source, even with ground-based 1 m class telescopes. LO observations are limited to brighter objects because they require a high signal-to-noise ratio (S/N ~40) for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and wavelet transforms have been explored in this study. A sample of 54 NIR LO light curves observed with the IR camera at Mt Abu Observatory has been used. It is seen that both Fourier and wavelet methods have shown an improvement in S/N compared to the original data. However, the application of wavelet transforms causes a slight smoothing of the fringes and results in a higher value for angular diameter. Fourier transforms which reduce discrete noise frequencies do not distort the fringe. The Fourier transform method seems to be effective in improving the S/N, as well as improving the model fit, particularly in the fainter regime of our sample. These methods also provide a better model fit for brighter sources in some cases, though there may not be a significant improvement in S/N.

Baug, Tapas; Chandrasekhar, Thyagarajan

2013-11-01

94

This paper presents a novel family of linear transforms that can be applied to data collected from the surface of a 2-sphere in three-dimensional Fourier space. This family of transforms generalizes the previously-proposed Funk-Radon Transform (FRT), which was originally developed for estimating the orientations of white matter fibers in the central nervous system from diffusion magnetic resonance imaging data. The new family of transforms is characterized theoretically, and efficient numerical implementations of the transforms are presented for the case when the measured data is represented in a basis of spherical harmonics. After these general discussions, attention is focused on a particular new transform from this family that we name the Funk-Radon and Cosine Transform (FRACT). Based on theoretical arguments, it is expected that FRACT-based analysis should yield significantly better orientation information (e.g., improved accuracy and higher angular resolution) than FRT-based analysis, while maintaining the strong characterizability and computational efficiency of the FRT. Simulations are used to confirm these theoretical characteristics, and the practical significance of the proposed approach is illustrated with real diffusion weighted MRI brain data. These experiments demonstrate that, in addition to having strong theoretical characteristics, the proposed approach can outperform existing state-of-the-art orientation estimation methods with respect to measures such as angular resolution and robustness to noise and modeling errors.

Haldar, Justin P.; Leahy, Richard M.

2013-01-01

95

The high angular resolution view of local X-ray selected AGN in the mid-infrared

NASA Astrophysics Data System (ADS)

Hard X-ray and mid-infrared observations probe the peaks in broadband spectra of active galactic nucle (AGN), sampling the bulk of their accretion energy. But bolometric emission measurements of Seyfert galaxies can be strongly biased by unresolved nuclear stellar emission. Disentangling these components using emission line proxies for the intrinsic AGN power suffers from various uncertainties. Here, we show that fundamental new insights into AGN are enabled by using high angular resolution observations of Seyferts with the largest telescopes currently available. We have imaged the 9 month Swift/BAT selected AGN sample using the VLT, Gemini and Subaru at their diffraction-limit at 12°. Collecting all high angular resolution data yields a large database of 150 AGN of all types with a point-like detected nucleus. This sample serves as a benchmark for studies on unification issues and accurate (unbiased) AGN bolometric corrections. We discuss some key results, including new inferences on the structures of Seyfert nuclei from the enlarged infrared/Xray correlation and show that the MIR to X-ray flux ratio is independent of the Eddington fraction (lEdd) over about 4 orders of magnitude down to lEdd 10^{-4} at least, which appears to be the threshold below which accretion properties change.

Gandhi, Poshak; Asmus, D.; Hönig, S. F.; Smette, A.; Duschl, W. J.; Matsuta, K.; Ichikawa, K.; Ueda, Y.; Terashima, Y.; Gilli, R.; Comastri, A.; Vignali, C.

2012-09-01

96

This paper presents a novel family of linear transforms that can be applied to data collected from the surface of a 2-sphere in three-dimensional Fourier space. This family of transforms generalizes the previously-proposed Funk-Radon Transform (FRT), which was originally developed for estimating the orientations of white matter fibers in the central nervous system from diffusion magnetic resonance imaging data. The new family of transforms is characterized theoretically, and efficient numerical implementations of the transforms are presented for the case when the measured data is represented in a basis of spherical harmonics. After these general discussions, attention is focused on a particular new transform from this family that we name the Funk-Radon and Cosine Transform (FRACT). Based on theoretical arguments, it is expected that FRACT-based analysis should yield significantly better orientation information (e.g., improved accuracy and higher angular resolution) than FRT-based analysis, while maintaining the strong characterizability and computational efficiency of the FRT. Simulations are used to confirm these theoretical characteristics, and the practical significance of the proposed approach is illustrated with real diffusion weighted MRI brain data. These experiments demonstrate that, in addition to having strong theoretical characteristics, the proposed approach can outperform existing state-of-the-art orientation estimation methods with respect to measures such as angular resolution and robustness to noise and modeling errors. PMID:23353603

Haldar, Justin P; Leahy, Richard M

2013-05-01

97

Resolution enhancement by aerial image approximation with 2D-TCC

NASA Astrophysics Data System (ADS)

A newly developed sub-resolution assist feature (SRAF) placement technique with two-dimensional transmission cross coefficient (2D-TCC) is described in this paper. In SRAF placement with 2D-TCC, Hopkins' aerial image equation with four-dimensional TCC is decomposed into the sum of Fourier transforms of diffracted light weighted by 2D-TCC, introducing an approximated aerial image so as to place SRAFs into a given reticle layout. SRAFs are placed at peak positions of the approximated aerial image for enhanced resolution. Since the approximated aerial image can handle the full optical model, SRAFs can be automatically optimized to the given optical condition to generate the optimized reticle. The validity of this technique was confirmed by experiment using a Canon FPA6000-ES6a, 248 nm with a numerical aperture (NA) of 0.86. A binary reticle optimized by this technique with mild off-axis illumination was used in the experiment. Both isolated and dense 100 nm contacts (k1 = 0.35) were simultaneously resolved with the aid of this technique.

Yamazoe, Kenji; Sekine, Yoshiyuki; Kawashima, Miyoko; Hakko, Manabu; Ono, Tomomi; Honda, Tokuyuki

2007-10-01

98

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

99

NASA Astrophysics Data System (ADS)

Context: The massive black hole Sgr A* at the very center of the Galaxy, and its immediate stellar and non-stellar environment, have been studied in the past decade with increasing intensity and wavelength coverage, revealing surprising results. This research requires the highest angular resolution available to avoid source confusion and to study the physical properties of the objects. Aims: GCIRS 7 is the dominating star of the central cluster in the NIR, so it has been used as wavefront and astrometric reference. Our studies investigate, for the first time, its properties at 2 and 10 ?m using the VLTI. We aim at analyzing the suitability of GCIRS 7 as an interferometric phase-reference for the upcoming generation of dual-field facilities at optical interferometers. Methods: VLTI-AMBER and MIDI instruments were used to spatially resolve GCIRS 7 and to measure the wavelength dependence of the visibility using the low spectral resolution mode (? / ? ? ? 30) and projected baseline lengths of about 50 m, resulting in an angular resolution of about 9 mas and 45 mas for the NIR and MIR, respectively. Results: The first K-band fringe detection of a GC star suggests that GCIRS 7 could be marginally resolved at 2 micron, which would imply that the photosphere of the supergiant is enshrouded by a molecular and dusty envelope. At 10 ?m, GCIRS 7 is strongly resolved with a visibility of approximately 0.2. The MIR is dominated by moderately warm (200 K), extended dust, mostly distributed outside of a radius of about 120 AU (15 mas) around the star. A deep 9.8 ?m-silicate absorption in excess of the usual extinction law with respect to the NIR extinction has been found. Conclusions: Our VLTI observations show that interferometric NIR phase-referencing experiments with mas resolution using GCIRS 7 as phase reference appear to be feasible, but more such studies are required to definitely characterize the close environment around this star. The MIR data confirm recent findings of a relatively enhanced, interstellar 9.8 ?m-silicate absorption with respect to the NIR extinction towards another star in the central arc-seconds, suggesting an unusual dust composition in that region. We demonstrate that the resolution and sensitivity of modern large-aperture optical telescope arrays is required to resolve the innermost environment of stars at the Galactic center. Based on observations collected at the European Southern Observatory, Paranal, Chile (programs 076.B-0863, 077.D-0709).

Pott, J.-U.; Eckart, A.; Glindemann, A.; Kraus, S.; Schödel, R.; Ghez, A. M.; Woillez, J.; Weigelt, G.

2008-08-01

100

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

101

A High Angular Resolution Search for the Progenitor of the Type Ic Supernova 2004gt

We report the results of a high spatial resolution search for the progenitor of Type Ic supernova SN 2004gt, using the newly commissioned Keck laser guide star adaptive optics (LGSAO) system along with archival Hubble Space Telescope data. This is the deepest search yet performed for the progenitor of any Type Ib\\/c event in a wide wavelength range stretching from

Avishay Gal-Yam; D. B. Fox; S. R. Kulkarni; K. Matthews; D. C. Leonard; D. J. Sand; D.-S. Moon; S. B. Cenko; A. M. Soderberg

2005-01-01

102

Spatiotemporal multi-resolution approximation of the Amari type neural field model.

Neural fields are spatially continuous state variables described by integro-differential equations, which are well suited to describe the spatiotemporal evolution of cortical activations on multiple scales. Here we develop a multi-resolution approximation (MRA) framework for the integro-difference equation (IDE) neural field model based on semi-orthogonal cardinal B-spline wavelets. In this way, a flexible framework is created, whereby both macroscopic and microscopic behavior of the system can be represented simultaneously. State and parameter estimation is performed using the expectation maximization (EM) algorithm. A synthetic example is provided to demonstrate the framework. PMID:23116813

Aram, P; Freestone, D R; Dewar, M; Scerri, K; Jirsa, V; Grayden, D B; Kadirkamanathan, V

2012-10-30

103

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

104

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

105

NASA Astrophysics Data System (ADS)

In this paper, using the exponential function transformation approach along with an approximation for the centrifugal potential, the radial Klein-Gordon equation with the vector and scalar Hulthén potential is transformed to a hypergeometric differential equation. The approximate analytical solutions of t-waves scattering states are presented. The normalized wave functions expressed in terms of hypergeometric functions of scattering states on the k/2? scale and the calculation formula of phase shifts are given. The physical meaning of the approximate analytical solution is discussed.

Chen, Chang-Yuan; Lu, Fa-Lin; Sun, Dong-Sheng

2008-12-01

106

Mid-infrared properties of nearby low-luminosity AGN at high angular resolution

We present high spatial resolution mid-infrared (MIR) 12 mum continuum imaging of low-luminosity active galactic nuclei (LLAGN) obtained with VLT\\/VISIR. Our goal is to determine whether the nuclear MIR emission of LLAGN is consistent with the existence of a dusty obscuring torus, the key component of the unification model for AGN. Based on available hard X-ray luminosities and the previously

D. Asmus; P. Gandhi; A. Smette; S. F. Hönig; W. J. Duschl

2011-01-01

107

Chandra's Ultimate Angular Resolution: Studies of the HRC-I Point Spread Function

NASA Astrophysics Data System (ADS)

The Chandra High Resolution Camera (HRC) should provide an ideal imaging match to the High-Resolution Mirror Assembly (HRMA). The laboratory-measured intrinsic resolution of the HRC is 20 microns FWHM. HRC event positions are determined via a centroiding method rather than by using discrete pixels. This event position reconstruction method and any non-ideal performance of the detector electronics can introduce distortions in event locations that, when combined with spacecraft dither, produce artifacts in source images. We compare ray-traces of the HRMA response to "on-axis" observations of AR Lac and Capella as they move through their dither patterns to images produced from filtered event lists to characterize the effective intrinsic PSF of the HRC-I. A two-dimensional Gaussian, which is often used to represent the detector response, is NOT a good representation of the intrinsic PSF of the HRC-I; the actual PSF has a sharper peak and additional structure which will be discussed. This work was supported under NASA contract NAS8-03060.

Juda, Michael; Karovska, M.

2010-02-01

108

By using the 45 m millimeter-wave telescope, we have observed the CO bipolar flow source associated with an infrared source, GL 490, in the J = 1-0 line of carbon monosulfide. The high angular resolution of the telescope, 30'', has allowed us to find a compact CS cloud about 0.3 pc x 0.13 pc in extent around GL 490, which is elongated orthogonally to the direction of the CO bipolar flow. Part of the cloud shows signs of expansion at velocities of < or approx. =4 km s/sup -1/, although the total outgoing momentum of the CS cloud is smaller than that of the CO flow by an order of magnitude. This implies that the CS compact cloud has not been responsible for collimating the bipolar flow in this object.

Kawabe, R.; Ogawa, H.; Fukui, Y.; Takano, T.; Takaba, H.; Fujimoto, Y.; Sugitani, K.; Fujimoto, M.

1984-07-15

109

Angular resolution of an EAS array for gamma ray astronomy energies 5 X 10 (13) eV

NASA Astrophysics Data System (ADS)

A 24 detector extensive air shower array is being operated at Ootacamund (2300 m altitude, 11.4 deg N latitude) in southern India for a study of arrival directions of showers of energies greater than 5 x 10 to the 13th power eV. Various configurations of the array of detectors have been used to estimate the accuracy in determination of arrival angle of showers with such an array. These studies show that it is possible to achieve an angular resolution of better than 2 deg with the Ooty array for search for point sources of Cosmic gamma rays at energies above 5 x 10 to the 13th power eV.

Apte, A. R.; Gopalakrishnan, N. V.; Tonwar, S. C.; Uma, V.

1985-08-01

110

NASA Astrophysics Data System (ADS)

Analytic expressions for the direct, resonant, and interference contributions to the differential cross section of a resonant Auger process, produced by the inner-shell photoionization of a linear molecule either fixed in space or belonging to a gas of randomly oriented molecules, have been derived following Dills procedures [ Dill , Phys. Rev. Lett. 45, 1393 (1980) ], but going beyond the two-step approximation. Angle-resolved Auger spectra of the C2H2 molecule measured on top of the C1s??* resonance [ Kivimäki , J. Phys. B 30, 4279 (1997) ] have been calculated together with asymmetry parameters, analyzing also the different contributions to the electron angular distributions.

Colle, Renato; Embriaco, Davide; Massini, Michol; Simonucci, Stefano; Taioli, Simone

2004-10-01

111

High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

NASA Technical Reports Server (NTRS)

The authors present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3--0.5 resolution from 4.7 (micro)m to 22 (micro)m. The young stellar objects designed infrared source n and radio source I are believed to dominate the BN/KL region. They have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L(sub (center-dot)).

Greenhill, L. J.; Gezari, D. Y.; Danchi, W. C.; Najita, J.; Monnier, J. D.

2004-01-01

112

NASA Astrophysics Data System (ADS)

A laser beam induced current (LBIC) map of a photoactive surface is a very useful tool when it is necessary to study the spatial variability of properties such as photoconverter efficiency or factors connected with the recombination of carriers. Obtaining high spatial resolution LBIC maps involves irradiating the photoactive surface with a photonic beam with Gaussian power distribution and with a low dispersion coefficient. Laser emission fulfils these characteristics, but against it is the fact that it is highly monochromatic and therefore has a spectral distribution different to solar emissions. This work presents an instrumental system and procedure to obtain high spatial resolution LBIC maps in conditions approximating solar irradiation. The methodology developed consists of a trichromatic irradiation system based on three sources of laser excitation with emission in the red, green, and blue zones of the electromagnetic spectrum. The relative irradiation powers are determined by either solar spectrum distribution or Planck's emission formula which provides information approximate to the behavior of the system if it were under solar irradiation. In turn, an algorithm and a procedure have been developed to be able to form images based on the scans performed by the three lasers, providing information about the photoconverter efficiency of photovoltaic devices under the irradiation conditions used. This system has been checked with three photosensitive devices based on three different technologies: a commercial silicon photodiode, a commercial photoresistor, and a dye-sensitized solar cell. These devices make it possible to check how the superficial quantum efficiency has areas dependent upon the excitation wavelength while it has been possible to measure global incident photon-to-current efficiency values approximating those that would be obtained under irradiation conditions with sunlight.

Navas, F. J.; Alcántara, R.; Fernández-Lorenzo, C.; Martín-Calleja, J.

2010-03-01

113

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

114

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

115

Transfer Scan Angular Resolution Assessment of FGS1R and FGS3

NASA Astrophysics Data System (ADS)

The ability of the HST FGS to detect and resolve close faint binary stars and measure their orbits is unique and unchallenged by current ground-based techniques. SMOV tests with FGS1R have revealed except- ional S curve morphology at pickle center. This test is designed to measure and compare the resolution of the TRANSFER mode of the new FGS1R and FGS3. A known binary will be observed in TRANS mode at multiple orientations in each instrument in order to sample the sensitivity along each FGS axis. Some POS mode observations will be obtained during each orbit in order to indepen- dently determine the relative orientation of each observation.

Lupie, Olivia

1997-12-01

116

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

117

NASA Astrophysics Data System (ADS)

We present resolved images of four massive clusters of galaxies through the Sunyaev-Zel'dovich effect (SZE). These measurements, made at 90 GHz with the MUSTANG receiver on the Green Bank Telescope (GBT), reveal pressure substructure to the intracluster medium (ICM) in three of the four systems. The SZE and X-ray morphology of MACS0744.8+3927 are suggestive of the presence of a weak shock outside the cluster core. By fitting the Rankine-Hugoniot density jump conditions in a complementary SZE/X-ray analysis, we asses the feasibility of this interpretation. We conclude that a weak shock with a Mach number of {M} = 1.2^{+0.2}_{-0.2} and a shock velocity of 1827+267 - 195 km s-1 adequately describes the observed phenomenology. Deeper Chandra data are needed for confirmation. In RXJ1347.5-1145, we present a new reduction of previously reported data and confirm the presence of a southeast SZE enhancement with a significance of 13.9? when smoothed to 18'' resolution. This too is likely caused by shock-heated gas produced in a recent merger. In our highest redshift system, CL1226.9+3332, we detect substructure at a peak significance of 4.6? in the form of a ridge oriented orthogonally to the vector connecting the main mass peak and a subclump revealed by weak lensing. We also conclude that the gas distribution is elongated in a southwest direction, consistent with a previously proposed merger scenario. The SZE image of the cool core cluster A1835 is, in contrast, consistent with azimuthally symmetric signal only. This pilot study demonstrates the potential of high-resolution SZE images to complement X-ray data and probe the dynamics of galaxy clusters.

Korngut, P. M.; Dicker, S. R.; Reese, E. D.; Mason, B. S.; Devlin, M. J.; Mroczkowski, T.; Sarazin, C. L.; Sun, M.; Sievers, J.

2011-06-01

118

Using High Angular Resolution Diffusion Imaging Data to Discriminate Cortical Regions

Brodmanns 100yearold summary map has been widely used for cortical localization in neuroscience. There is a pressing need to update this map using noninvasive, highresolution and reproducible data, in a way that captures individual variability. We demonstrate here that standard HARDI data has sufficiently diverse directional variation among grey matter regions to inform parcellation into distinct functional regions, and that this variation is reproducible across scans. This characterization of the signal variation as nonrandom and reproducible is the critical condition for successful cortical parcellation using HARDI data. This paper is a first step towards an individual cortexwide map of grey matter microstructure, The gray/white matter and pial boundaries were identified on the highresolution structural MRI images. Two HARDI data sets were collected from each individual and aligned with the corresponding structural image. At each vertex point on the surface tessellation, the diffusionweighted signal was extracted from each image in the HARDI data set at a point, half way between gray/white matter and pial boundaries. We then derived several features of the HARDI profile with respect to the local cortical normal direction, as well as several fully orientationally invariant features. These features were taken as a fingerprint of the underlying grey matter tissue, and used to distinguish separate cortical areas. A supportvector machine classifier, trained on three distinct areas in repeat 1 achieved 8082% correct classification of the same three areas in the unseen data from repeat 2 in three volunteers. Though gray matter anisotropy has been mostly overlooked hitherto, this approach may eventually form the foundation of a new cortical parcellation method in living humans. Our approach allows for further studies on the consistency of HARDI based parcellation across subjects and comparison with independent microstructural measures such as exvivo histology.

Nagy, Zoltan; Alexander, Daniel C.; Thomas, David L.; Weiskopf, Nikolaus; Sereno, Martin I.

2013-01-01

119

We present 0.''15 resolution observations of the 227 GHz continuum emission from the circumstellar disk around the FU Orionis star PP 13S*. The data were obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) Paired Antenna Calibration System (C-PACS), which measures and corrects the atmospheric delay fluctuations on the longest baselines of the array in order to improve the sensitivity and angular resolution of the observations. A description of the C-PACS technique and the data reduction procedures are presented. C-PACS was applied to CARMA observations of PP 13S*, which led to a factor of 1.6 increase in the observed peak flux of the source, a 36% reduction in the noise of the image, and a 52% decrease in the measured size of the source major axis. The calibrated complex visibilities were fitted with a theoretical disk model to constrain the disk surface density. The total disk mass from the best-fit model corresponds to 0.06 M{sub sun}, which is larger than the median mass of a disk around a classical T Tauri star. The disk is optically thick at a wavelength of 1.3 mm for orbital radii less than 48 AU. At larger radii, the inferred surface density of the PP 13S* disk is an order of magnitude lower than that needed to develop a gravitational instability.

Perez, Laura M.; Carpenter, John M.; Isella, Andrea [Department of Astronomy, California Institute of Technology, 1200 East California Blvd, Pasadena, CA 91125 (United States); Lamb, James W.; Woody, David P.; Leitch, Erik M.; Muchovej, Stephen J.; Scott, Stephen L. [Owens Valley Radio Observatory, California Institute of Technology, Big Pine, CA 93513 (United States); Zauderer, B. Ashley; Bolatto, Alberto D.; Teuben, Peter J. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Bock, Douglas C. [Combined Array for Research in Millimeter-wave Astronomy, P.O. Box 968, Big Pine, CA 93513 (United States); Carlstrom, John; Culverhouse, Thomas L.; Marrone, Daniel P. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave. Chicago, IL 60637 (United States); Joy, Marshall [Space Sciences-VP62, NASA Marshall Space Flight Center, Huntsville, AL 35812 (United States); Kwon, Woojin [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Plambeck, Richard L.; Wright, Melvyn C. H. [Astronomy Department, University of California at Berkeley, Berkeley, CA 94720-3411 (United States)

2010-11-20

120

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

121

Introduction Diffusion tensor imaging (DTI) measures in patients with multiple sclerosis (MS), particularly those measures associated with a specific white matter pathway, have consistently shown correlations with function. This study sought to investigate correlations between DTI measures in the fornix and common cognitive deficits in MS patients, including episodic memory, working memory and attention. Materials and Methods Patients with MS and group age- and sex-matched controls underwent high-resolution diffusion scanning (1-mm isotropic voxels) and cognitive testing. Manually drawn forniceal regions of interest were applied to individual maps of tensor-derived measures, and mean values of transverse diffusivity (TD), mean diffusivity (MD), longitudinal diffusivity (LD) and fractional anisotropy (FA) were calculated. Results In 40 patients with MS [mean ageąS.D.=42.55ą9.1 years; Expanded Disability Status Scale (EDSS)=2.0ą1.2; Multiple Sclerosis Functional Composite (MSFC) score=0.38ą0.46] and 20 healthy controls (mean ageąS.D.=41.35ą9.7 years; EDSS=0.0ą0; MSFC score=0.74ą0.24), we found that FA, MD and TD values in the fornix were significantly different between groups (P<.03), and patient performance on the Brief Visuospatial Memory Test-Revised (BVMT-R) was correlated with DTI measures (P<.03). Discussion These results are consistent with findings of axonal degeneration in MS and support the use of DTI as an indicator of disease progression.

Koenig, Katherine A.; Sakaie, Ken E.; Lowe, Mark J.; Lin, Jian; Stone, Lael; Bermel, Robert A.; Beall, Erik B.; Rao, Stephen M.; Trapp, Bruce D.; Phillips, Micheal D.

2013-01-01

122

Development of high angular resolution x-ray telescopes based on slumped glass foils

NASA Astrophysics Data System (ADS)

The mirrors of the International X-ray Observatory (IXO) were based on a large number of high quality segments, aiming at achieving a global spatial resolution better than 5 HEW while giving a large collecting area (around 3m2@ 1 keV). A study concerning the hot slumping of thin glass foils was started in Europe, funded by ESA and led by the Brera Astronomical Observatory (INAF-OAB), for the development of a replication technology based on glass material. The study is currently continuing even after the IXO program has been descoped and renamed ATHENA, in the perspective of using the technology under development for other future missions or applications. INAF-OAB efforts have been focused on the "Direct" slumping approach with convex moulds, meaning that during the thermal cycle the optical surface of the glass is in direct contact with the mould surface. The single mirror segments are made of thin glass plates (0.4 mm thick), with a reflecting area of 200 mm × 200 mm. The adopted integration process foresees the use of glass reinforcing ribs for bonding together the plates in such a way to form a rigid and stiff stack of segmented mirror shells; the stack is supported by a thick backplane. During the bonding process, the plates are constrained in close contact with the surface of a precisely figured integration master by the application of vacuum pump suction. In this way, the springback deformations and the low frequency errors still present in the plates' profile after slumping can be corrected. The status of the technology development is presented in this paper, together with the description and metrology of the prototypes already realized or under construction at the Observatory laboratories.

Ghigo, M.; Basso, S.; Borsa, F.; Citterio, O.; Civitani, M.; Conconi, P.; Pagano, G.; Pareschi, G.; Proserpio, L.; Salmaso, B.; Sironi, G.; Spiga, D.; Tagliaferri, G.; Zambra, A.; Parodi, G.; Martelli, F.; Gallieni, D.; Tintori, M.; Bavdaz, M.; Wille, E.

2012-09-01

123

NASA Astrophysics Data System (ADS)

We studied the X-ray dust scattering halos around 17 bright X-ray point sources using Chandra data. All sources were observed with the Advanced CCD Imaging Spectrometer and High Energy Transmission Grating in continuous clocking mode (CC mode) or timed exposure mode (TE mode). We use an iterative method to resolve the halos at small scattering angles from the zeroth-order data in CC mode or the first-order data in TE mode, which is not, or less, piled up. Using the interstellar grain models of Weingartner and Draine and Mathis and coworkers to fit the halo profiles, we get the hydrogen column densities and the spatial distributions of the scattering dust grains along the lines of sight (LOSs) to these sources. We find that the scattering dust density very close to these sources is much higher than the normal interstellar medium. For X-ray pulsars GX 301-2 and Vela X-1 with companions of strong stellar winds, the X-ray absorption column densities are much higher than the derived scattering column densities, because the dense media around the X-ray sources produce extremely small angle scatterings that are indistinguishable from point sources, even with Chandra's angular resolution. For LMC X-1, most of the scattering and absorption occur in the Large Magellanic Cloud, rather than in the Milky Way. From the obtained X-ray spectra, the cold gas absorption and thus the equivalent hydrogen column are determined. We have obtained the linear correlation between the NH derived from spectral fits and that derived from the grain models of Weingartner and Draine and Mathis and coworkers (except for GX 301-2 and Vela X-1): NH,WD01=(0.720+/-0.009)NH,abs+(0.051+/-0.013) and NN,MRN=(1.156+/-0.016)NH,abs+(0.062+/-0.024) in units of 1022 cm-2. High angular resolution X-ray dust scattering halos offer an excellent potential for probing the spatial distributions of the interstellar dust medium.

Xiang, Jingen; Zhang, Shuang Nan; Yao, Yangsen

2005-08-01

124

High angular resolution diffusion imaging (HARDI) has become an important technique for imaging complex oriented structures in the brain and other anatomical tissues. This has motivated the recent development of several methods for computing the orientation probability density function (PDF) at each voxel. However, much less work has been done on developing techniques for filtering, interpolation, averaging and principal geodesic analysis of orientation PDF fields. In this paper, we present a Riemannian framework for performing such operations. The proposed framework does not require that the orientation PDFs be represented by any fixed parameterization, such as a mixture of von Mises-Fisher distributions or a spherical harmonic expansion. Instead, we use a nonparametric representation of the orientation PDF. We exploit the fact that under the square-root re-parameterization, the space of orientation PDFs forms a Riemannian manifold: the positive orthant of the unit Hilbert sphere. We show that various orientation PDF processing operations, such as filtering, interpolation, averaging and principal geodesic analysis, may be posed as optimization problems on the Hilbert sphere, and can be solved using Riemannian gradient descent. We illustrate these concepts with numerous experiments on synthetic, phantom and real datasets. We show their application to studying left/right brain asymmetries.

Goh, Alvina; Lenglet, Christophe; Thompson, Paul M.; Vidal, Rene

2011-01-01

125

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

126

In this paper, we propose a novel large deformation diffeomorphic registration algorithm to align high angular resolution diffusion images (HARDI) characterized by orientation distribution functions (ODFs). Our proposed algorithm seeks an optimal diffeomorphism of large deformation between two ODF fields in a spatial volume domain and at the same time, locally reorients an ODF in a manner such that it remains consistent with the surrounding anatomical structure. To this end, we first review the Riemannian manifold of ODFs. We then define the reorientation of an ODF when an affine transformation is applied and subsequently, define the diffeomorphic group action to be applied on the ODF based on this reorientation. We incorporate the Riemannian metric of ODFs for quantifying the similarity of two HARDI images into a variational problem defined under the large deformation diffeomorphic metric mapping framework. We finally derive the gradient of the cost function in both Riemannian spaces of diffeomorphisms and the ODFs, and present its numerical implementation. Both synthetic and real brain HARDI data are used to illustrate the performance of our registration algorithm. PMID:22156979

Du, Jia; Goh, Alvina; Qiu, Anqi

2012-05-01

127

High angular resolution diffusion imaging (HARDI) has become an important technique for imaging complex oriented structures in the brain and other anatomical tissues. This has motivated the recent development of several methods for computing the orientation probability density function (PDF) at each voxel. However, much less work has been done on developing techniques for filtering, interpolation, averaging and principal geodesic analysis of orientation PDF fields. In this paper, we present a Riemannian framework for performing such operations. The proposed framework does not require that the orientation PDFs be represented by any fixed parameterization, such as a mixture of von Mises-Fisher distributions or a spherical harmonic expansion. Instead, we use a nonparametric representation of the orientation PDF. We exploit the fact that under the square-root re-parameterization, the space of orientation PDFs forms a Riemannian manifold: the positive orthant of the unit Hilbert sphere. We show that various orientation PDF processing operations, such as filtering, interpolation, averaging and principal geodesic analysis, may be posed as optimization problems on the Hilbert sphere, and can be solved using Riemannian gradient descent. We illustrate these concepts with numerous experiments on synthetic, phantom and real datasets. We show their application to studying left/right brain asymmetries. PMID:21292013

Goh, Alvina; Lenglet, Christophe; Thompson, Paul M; Vidal, René

2011-06-01

128

NASA Astrophysics Data System (ADS)

X-rays are absorbed and scattered by dust grains when they travel through the interstellar medium. The scattering within small angles results in an X-ray ``halo''. The halo properties are significantly affected by the energy of radiation, the optical depth of the scattering, the grain size distributions and compositions, and the spatial distribution of dust along the line of sight (LOS). Therefore analyzing the X-ray halo properties is an important tool to study the size distribution and spatial distribution of interstellar grains, which plays a central role in the astrophysical study of the interstellar medium, such as the thermodynamics and chemistry of the gas and the dynamics of star formation. With excellent angular resolution, good energy resolution and broad energy band, the Chandra ACIS is so far the best instrument for studying the X-ray halos. But the direct images of bright sources obtained with ACIS usually suffer from severe pileup which prevents us from obtaining the halos in small angles. We first improve the method proposed by Yao et al to resolve the X-ray dust scattering halos of point sources from the zeroth order data in CC-mode or the first order data in TE mode with Chandra HETG/ACIS. Using this method we re-analyze the Cygnus X-1 data observed with Chandra. Then we studied the X-ray dust scattering halos around 17 bright X-ray point sources using Chandra data. All sources were observed with the HETG/ACIS in CC-mode or TE-mode. Using the interstellar grain models of WD01 model and MRN model to fit the halo profiles, we get the hydrogen column densities and the spatial distributions of the scattering dust grains along the line of sights (LOS) to these sources. We find there is a good linear correlation not only between the scattering hydrogen column density from WD01 model and the one from MRN model, but also between N_{H} derived from spectral fits and the one derived from the grain models WD01 and MRN (except for GX 301-2 and Vela X-1): N_{H,WD01} = (0.720ą0.009) × N_{H,abs} + (0.051ą0.013) and N_{H, MRN} = (1.156ą0.016) × N_{H,abs} + (0.062ą0.024) in the units 10^{22} cm^{-2}. Then the correlation between FHI and N_{H} is obtained. Both WD01 model and MRN model fits show that the scattering dust density very close to these sources is much higher than the normal interstellar medium and we consider it is the evidence of molecular clouds around these X-ray binaries. We also find that there is the linear correlation between the effective distance through the galactic dust layer and hydrogen scattering olumn density N_{H} excluding the one in x=0.99-1.0 but the correlation does not exist between he effective distance and the N_{H} in x=0.99-1.0. It shows that the dust nearby the X-ray sources is not the dust from galactic disk. Then we estimate the structure and density of the stellar wind around the special X-ray pulsars Vela X-1 and GX 301-2. Finally we discuss the possibility of probing the three dimensional structure of the interstellar using the X-ray halos of the transient sources, probing the spatial distributions of interstellar dust medium nearby the point sources, even the structure of the stellar winds using higher angular resolution X-ray dust scattering halos and testing the model that the black hole can be formed from the direct collapse of a massive star without supernova using the statistical distribution of the dust density nearby the X-ray binaries.

Xiang, Jingen

129

NASA Astrophysics Data System (ADS)

One of the most difficult requests to be accomplished from the technological point of view for next generation x-ray telescopes is to combine high angular resolution and effective area. A significant increase of effective area can be reached with high precision but at the same time thin (2-3 mm thickness for mirror diameters of 30-110 cm) glass mirror shells. In the last few years the Brera Observatory has lead a development program for realizing this kind of monolithic thin glass shell. The fused silica has been chosen as shell substrate due to its thermal and mechanical properties. To bring the mirror shells to the needed accuracy, we have adopted a deterministic direct polishing method (already used for past missions as Einstein, Rosat, Chandra) to ten time thinner shells. The technological challenge has been solved using a temporary stiffening structure that allows the handling and the machining of so thin glass shells. The results obtained with a prototype shell at an intermediate stage of its development (17'' HEW measured in full illumination mode with x-ray) indicate that the working concept is feasible and can be further exploited using the very large Ion Beam Facility available in our labs for the final high accuracy figuring of the thin shells. In this paper we present the required tolerances for the shell realization, the shells production chain flow and the ion beam facility up grading. Forecast on figuring time and expected performances of the figuring will also be given on the basis on the metrological data collected during past shell development.

Civitani, M. M.; Citterio, O.; Ghigo, M.; Mattaini, E.; Pareschi, G.; Parodi, G.

2013-09-01

130

A pre-processing step is proposed as a general method to enhance resolution properties of low order numerical differentiation and interpolation. Pre-processing operators are designed by taking two or more terms in the approximate deconvolution formula and using a local filter whose response characteristics are close to those of the numerical operation considered; operators for second order central differencing for first

Florian Schwertfirm; Joseph Mathew; Michael Manhart

2008-01-01

131

NASA Astrophysics Data System (ADS)

This paper presents and examines new near-infrared integral field observations of the three so-called "embedded star clusters" located in the nuclear region of NGC 1365. Adaptive-optics-corrected K-band data cubes were obtained with the ESO/VLT instrument SINFONI. The continuum in the K-band and emission lines such as He I, Br?, and several H2 lines were mapped at an achieved angular resolution of 0.2'' over a field of 3 × 3''2 around each source. We find that the continuum emission of the sources is spatially resolved. This means that they are indeed cluster complexes confined to regions of about 50 pc extension. We performed robust measurements of the equivalent width of the CO absorption band at 2.3 ?m and of Br?. For the main mid-infrared bright sources, the data only allow us to determine an upper limit to the equivalent width of the CO bands. Under the assumption of an instantaneously formed standard initial mass function Starburst99 model, the new measurements are found to be incompatible with previously published mid-infrared line ratios. We show that an upper mass limit of 25 to 30 M?, lower than the typically assumed 100 M?, allows one to simply remove this inconsistency. For such a model, the measurements are consistent with ages in the range of 5.5 Myr to 6.5 Myr, implying masses in the range from 3 to 10 × 106 M?. We detect extended gas emission both in H ii and H2. We argue that the central cluster complexes are the sources of excitation for the whole nebulae, through ionisation and shock heating. We detect a blue wing on the Br? emission profile, suggesting the existence of gas outflows centred on the cluster complexes. We do not find any evidence for the presence of a lower mass cluster population, which would fill up a "traditional" power law cluster mass function. Figure 9 and Tables 1-4 are available in electronic form at http://www.aanda.org

Galliano, E.; Kissler-Patig, M.; Alloin, D.; Telles, E.

2012-09-01

132

NASA Astrophysics Data System (ADS)

In the past decade, interferometric observations of the circumstellar dust shells of 15 late-type stars at a wavelength of 11.15 mum have been made at the Infrared Spatial Interferometer (ISI) as part of a systematic investigation of dust shell properties. The incomplete spatial frequency coverage of the ISI data, especially at spatial frequencies less than 0.65 cycles arcsec -1, has resulted in some uncertainty in the interpretation of the data. Using TNTCAM at WIRO, we have imaged 12 stars with circumstellar dust at a wavelength of 11.5 mum. We have used data reduction techniques similar to those used in speckle interferometry to extract source visibilities at frequencies between 0.0 and 0.75 cycles arcsec-1 from the images. We review the ISI models for six of the sources that we have observed in common with the ISI, alpha Ori, VY CMa, chi Cyg, IRC+10216, IK Tau, and NML Cyg. Measurements of the inner radii of dust shells set important constraints on current theoretical models of mass-loss. Dust shell inner radii are inferred from model fits to the available data. The angular diameter of the parent star is one component of these models; the uncertainty in the solution for the inner radius of the dust shell is consequently a function of the uncertainty in the stellar angular diameter. The angular diameters of the late-type stars are poorly known, largely because the atmospheres of these stars are extended. Measured angular diameters vary with wavelength, and a model is necessary to correct the measured diameters to a single, well-defined diameter. Detailed models of stellar atmospheres of late-type stars which predict variations in angular diameter with wavelength are just now becoming available. We constructed a near-infrared beam combiner at the NPOI. With this instrument, we observed delta2 Lyrae at wavelengths of 1.25 and 1.65 mum on a 22 meter baseline. We have used the results of these observations and the results of observations at other interferometers at other wavelengths to test recent, detailed models of stellar atmospheres and to illustrate the potential of mufti-wavelength angular diameter data in understanding the structures of the atmospheres of late-type stars.

Sudol, Jeffrey Joseph

133

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

134

Implications of a High Angular Resolution Image of the Sunyaev-Zel'Dovich Effect in RXJ1347-1145

NASA Astrophysics Data System (ADS)

The most X-ray luminous cluster known, RXJ1347-1145 (z = 0.45), has been the object of extensive study across the electromagnetic spectrum. We have imaged the Sunyaev-Zel'dovich effect (SZE) at 90 GHz (? = 3.3 mm) in RXJ1347-1145 at 10'' resolution with the 64 pixel MUSTANG bolometer array on the Green Bank Telescope, confirming a previously reported strong, localized enhancement of the SZE 20'' to the southeast of the center of X-ray emission. This enhancement of the SZE has been interpreted as shock-heated (>20 keV) gas caused by an ongoing major (low mass ratio) merger event. Our data support this interpretation. We also detect a pronounced asymmetry in the projected cluster pressure profile, with the pressure just east of the cluster core ~1.6× higher than just to the west. This is the highest resolution image of the SZE made to date.

Mason, B. S.; Dicker, S. R.; Korngut, P. M.; Devlin, M. J.; Cotton, W. D.; Koch, P. M.; Molnar, S. M.; Sievers, J.; Aguirre, J. E.; Benford, D.; Staguhn, J. G.; Moseley, H.; Irwin, K. D.; Ade, P.

2010-06-01

135

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

136

National Technical Information Service (NTIS)

An angular accelerometer with a blade damper on a torsion arm was examined. A comparative evaluation was conducted with a conventional inertia angular accelerometer for sensitivity. Relationships for parameter selection are given. The possibility of obtai...

V. M. Subbotin

1972-01-01

137

The random phase approximation (RPA) is an increasingly popular post-Kohn-Sham correlation method, but its high computational cost has limited molecular applications to systems with few atoms. Here we present an efficient implementation of RPA correlation energies based on a combination of resolution of the identity (RI) and imaginary frequency integration techniques. We show that the RI approximation to four-index electron repulsion integrals leads to a variational upper bound to the exact RPA correlation energy if the Coulomb metric is used. Auxiliary basis sets optimized for second-order Mřller-Plesset (MP2) calculations are well suitable for RPA, as is demonstrated for the HEAT [A. Tajti et al., J. Chem. Phys. 121, 11599 (2004)] and MOLEKEL [F. Weigend et al., Chem. Phys. Lett. 294, 143 (1998)] benchmark sets. Using imaginary frequency integration rather than diagonalization to compute the matrix square root necessary for RPA, evaluation of the RPA correlation energy requires O(N(4) log N) operations and O(N(3)) storage only; the price for this dramatic improvement over existing algorithms is a numerical quadrature. We propose a numerical integration scheme that is exact in the two-orbital case and converges exponentially with the number of grid points. For most systems, 30-40 grid points yield muH accuracy in triple zeta basis sets, but much larger grids are necessary for small gap systems. The lowest-order approximation to the present method is a post-Kohn-Sham frequency-domain version of opposite-spin Laplace-transform RI-MP2 [J. Jung et al., Phys. Rev. B 70, 205107 (2004)]. Timings for polyacenes with up to 30 atoms show speed-ups of two orders of magnitude over previous implementations. The present approach makes it possible to routinely compute RPA correlation energies of systems well beyond 100 atoms, as is demonstrated for the octapeptide angiotensin II. PMID:20572696

Eshuis, Henk; Yarkony, Julian; Furche, Filipp

2010-06-21

138

Objective Up to now, fiber tractography in the clinical routine is mostly based on diffusion tensor imaging (DTI). However, there are known drawbacks in the resolution of crossing or kissing fibers and in the vicinity of a tumor or edema. These restrictions can be overcome by tractography based on High Angular Resolution Diffusion Imaging (HARDI) which in turn requires larger numbers of gradients resulting in longer acquisition times. Using compressed sensing (CS) techniques, HARDI signals can be obtained by using less non-collinear diffusion gradients, thus enabling the use of HARDI-based fiber tractography in the clinical routine. Methods Eight patients with gliomas in the temporal lobe, in proximity to the optic radiation (OR), underwent 3T MRI including a diffusion-weighted dataset with 30 gradient directions. Fiber tractography of the OR using a deterministic streamline algorithm based on DTI was compared to tractography based on reconstructed diffusion signals using HARDI+CS. Results HARDI+CS based tractography displayed the OR more conclusively compared to the DTI-based results in all eight cases. In particular, the potential of HARDI+CS-based tractography was observed for cases of high grade gliomas with significant peritumoral edema, larger tumor size or closer proximity of tumor and reconstructed fiber tract. Conclusions Overcoming the problem of long acquisition times, HARDI+CS seems to be a promising basis for fiber tractography of the OR in regions of disturbed diffusion, areas of high interest in glioma surgery.

Kuhnt, Daniela; Bauer, Miriam H. A.; Sommer, Jens; Merhof, Dorit; Nimsky, Christopher

2013-01-01

139

... of angular cheilitis is usually undertaken with topical antifungals such as nystatin, clotrimazole, or econazole. Combinations of a topical antifungal and a topical steroid such as MycostatinŽ and ...

140

NASA Astrophysics Data System (ADS)

The approximate analytical bound and scattering state solutions of the arbitrary l-wave Klein-Gordon equation for the second Pöschl-Teller like potential are carried out by a new approximation to the centrifugal term. The analytical radial wave functions of the l-wave Klein-Gordon equation with the second Pöschl-Teller like potential are presented and the corresponding energy equations for bound states and phase shifts for scattering states are derived. It is well shown that the poles of S-matrix in the complex energy plane correspond to bound states for real poles and scattering states for complex poles in the lower half of the energy plane. Some numerical results are calculated to show the improved accuracy of our results and the special case for s-wave is also studied briefly.

Chen, Wen-Li; Wei, Gao-Feng; Qiang, Wen-Chao

141

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

142

NASA Astrophysics Data System (ADS)

We present the results of a 74 kilosecond X-ray observation with Chandra of the northwestern rim complex of the Galactic supernova remnant G266.2-1.2. This SNR is a member of the small but growing class of sources known to feature X-ray spectra dominated by non-thermal emission: a detailed analysis of this emission is crucial in gaining new insights on the phenomenon of cosmic-ray acceleration by SNRs. Our high angular resolution X-ray image of this rim complex reveals new fine structure including a remarkably well-defined leading shock structure. We have also extracted spectra from seven discrete regions in the complex and fit this spectra with several different models, including a power law as well as the synchrotron models SRCUT and SRESC. Clear variations are seen in the derived fit parameters for the different regions, indicating differences in the cosmic-ray acceleration conditions in this complex. A summary and discussion of these results will be presented. We acknowledge support for this work from the Chandra General Observer Grant GO3-4072Z.

Pannuti, T. G.; Allen, G. E.

2005-05-01

143

Q-ball imaging (QBI) is a high angular resolution diffusion-weighted imaging (HARDI) technique for reconstructing the orientation distribution function (ODF). Some form of smoothing or regularization is typically required in the ODF reconstruction from low signal-to-noise ratio HARDI data. The amount of smoothing or regularization is usually set a priori at the discretion of the investigator. In this article, we apply an adaptive and objective means of smoothing the raw HARDI data using the smoothing splines on the sphere method with generalized cross-validation (GCV) to estimate the diffusivity profile in each voxel. Subsequently, we reconstruct the ODF, from the smoothed data, based on the Funk-Radon transform (FRT) used in QBI. The spline method was applied to both simulated data and in vivo human brain data. Simulated data show that the smoothing splines on the sphere method with GCV smoothing reduces the mean squared error in estimates of the ODF as compared with the standard analytical QBI approach. The human data demonstrate the utility of the method for estimating smooth ODFs. PMID:20573465

Metwalli, Nader S; Hu, Xiaoping P; Carew, John D

2010-09-01

144

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

145

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

146

NASA Astrophysics Data System (ADS)

Two related methods to calculate the Kohn-Sham correlation energy within the framework of the adiabatic-connection fluctuation-dissipation theorem are presented. The required coupling-strength-dependent density-density response functions are calculated within exact-exchange time-dependent density-functional theory, i.e., within time-dependent density-functional response theory using the full frequency-dependent exchange kernel in addition to the Coulomb kernel. The resulting resolution-of-identity exact-exchange random-phase approximation (RI-EXXRPA) methods in contrast to previous EXXRPA methods employ an auxiliary basis set (RI basis set) to improve the computational efficiency, in particular, to reduce the formal scaling of the computational effort with respect to the system size N from N6 to N5. Moreover, the presented RI-EXXRPA methods, in contrast to previous ones, do not treat products of occupied times unoccupied orbitals as if they were linearly independent. Finally, terms neglected in previous EXXRPA methods can be included, which leads to a method designated RI-EXXRPA+, while the method without these extra terms is simply referred to as RI-EXXRPA. Both EXXRPA methods are shown to yield total energies, reaction energies of small molecules, and binding energies of noncovalently bonded dimers of a quality that is similar and in some cases even better than that obtained with quantum chemistry methods such as Mřller-Plesset perturbation theory of second order (MP2) or with the coupled cluster singles doubles method. In contrast to MP2 and to conventional density-functional methods, the presented RI-EXXRPA methods are able to treat static correlation.

Bleiziffer, Patrick; Heßelmann, Andreas; Görling, Andreas

2012-04-01

147

NASA Astrophysics Data System (ADS)

Photoelectron angular distributions (PADs) are obtained for a pair of 4s14p66p1 (a singlet and a triplet) autoionizing states in atomic krypton. A high-order harmonic pulse is used to excite the pair of states and a time-delayed 801 nm ionization pulse probes the PADs to the final 4s14p6 continuum with femtosecond time resolution. The ejected electrons are detected with velocity map imaging to retrieve the time-resolved photoelectron spectrum and PADs. The PAD for the triplet state is inherently separable by virtue of its longer autoionization lifetime. Measuring the total signal over time allows for the PADs to be extracted for both the singlet state and the triplet state. Anisotropy parameters for the triplet state are measured to be ?2 = 0.55 +/- 0.17 and ?4 = -0.01 +/- 0.10, while the singlet state yields ?2 = 2.19 +/- 0.18 and ?4 = 1.84 +/- 0.14. For the singlet state, the ratio of radial transition dipole matrix elements, X, of outgoing S to D partial waves and total phase shift difference between these waves, ?, are determined to be X = 0.56 +/- 0.08 and ? = 2.19 +/- 0.11 rad. The continuum quantum defect difference between the S and D electron partial waves is determined to be -0.15 +/- 0.03 for the singlet state. Based on previous analyses, the triplet state is expected to have anisotropy parameters independent of electron kinetic energy and equal to ?2 = 5/7 and ?4 = -12/7. Deviations from the predicted values are thought to be a result of state mixing by spin-orbit and configuration interactions in the intermediate and final states; theoretical calculations are required to quantify these effects.

Doughty, Benjamin; Haber, Louis H.; Hackett, Christina; Leone, Stephen R.

2011-03-01

148

There is a growing interest in understanding alterations to the interhemispheric transfer of information as a result of brain injury and neurological disease. To facilitate research, we have developed a fully automated method for the accurate extraction of commissural pathways (corpus callosum (CC) and anterior commissure (AC)) and functional parcellation of the CC using a high angular resolution diffusion imaging (HARDI) based probabilistic tractography approach that is applicable to clinical populations. The CC was divided into 33 functional divisions based on its connections to cortical parcellations derived from individual structural images in 8 healthy participants. Probabilistic CC population maps acquired at two different b-values (1000 s mm(-2) and 3000 s mm(-2)) are presented. Topography of the CC was consistent with histology reports. We show that HARDI data acquired at a higher b-value reveals more callosal-temporal connections than low b-value data. With respect to intra-subject precision, data acquired using a higher b-value show superior reproducibility of the delineated CC area on the midsagittal plane (MSP), as well as the total number of callosal streamlines and the number of clustered callosal streamlines. The AC was delineated in all 8 participants using high b-value HARDI tractography. Cortical projections of the AC were analysed and are in agreement with known anatomy. We conclude that, while data acquired at a lower b-value may be used, this is associated with a loss in quality, both in the delineation of commissural pathways and, potentially, the reproducibility of results over time. PMID:20079446

Pannek, Kerstin; Mathias, Jane L; Bigler, Erin D; Brown, Greg; Taylor, Jamie D; Rose, Stephen

2010-04-15

149

NASA Astrophysics Data System (ADS)

High angular resolution and sensitive aperture synthesis observations of CS (J=2-1) and CS (J=3-2) emissions toward L1551 NE, the second brightest protostar in the Taurus molecular cloud, made with the Nobeyama Millimeter Array are presented. L1551 NE is categorized as a Class 0 object deeply embedded in the redshifted outflow lobe of L1551 IRS 5. Previous studies of the L1551 NE region in CS emission revealed the presence of shell-like components open toward L1551 IRS 5, which seem to trace low-velocity shocks in the swept-up shell driven by the outflow from L1551 IRS 5. In this study, significant CS emission around L1551 NE was detected at the eastern tip of the swept-up shell from Vlsr=5.3 to 10.1 km s-1, and the total mass of the dense gas is estimated to be 0.14+/-0.02 Msolar. In addition, the following new structures were successfully revealed: a compact disklike component with a size of ~1000 AU just at L1551 NE, an arc-shaped structure around L1551 NE, open toward L1551 NE, with a size of ~5000 AU, i.e., a bow shock, and a distinct velocity gradient of the dense gas, i.e., deceleration along the outflow axis of L1551 IRS 5. These features suggest that the CS emission traces the postshocked region where the dense gas associated with L1551 NE and the swept-up shell of the outflow from L1551 IRS 5 interact. Since the age of L1551 NE is comparable to the timescale of the interaction, it is plausible that the formation of L1551 NE was induced by the outflow impact. The compact structure of L1551 NE with a tiny envelope was also revealed, suggesting that the outer envelope of L1551 NE has been blown off by the outflow from L1551 IRS 5. Based on observations made at the Nobeyama Radio Observatory (NRO), which is a branch of the National Astronomical Observatory, an interuniversity research institute operated by the Ministry of Education, Science, Sports, Culture, and Technology.

Yokogawa, Sozo; Kitamura, Yoshimi; Momose, Munetake; Kawabe, Ryohei

2003-09-01

150

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

151

Angular encoding with Larmor precession

NASA Astrophysics Data System (ADS)

The first test of angular encoding of a neutron beam with Larmor precession was performed at the spin-echo set-up of ZETA on IN3 (ILL, Grenoble, France). The polymer multilayer sample exhibits specular and off-specular scattering previously measured with reflectometry. The Yoneda scattering was discriminated from the specular reflection employing the angular encoding. The scans of the reflected and the off-specular scattered intensities as a function of the spin-echo length reveal its sinusoidal intensity dependence and the phase relation with respect to each other. The phase shift between the off-specular scattering and specular reflected intensity produced the wanted and necessary angular resolution. An estimation of the effective resolution abilities of this method in reflectometry kinematics yields that the angular encoding including subsequent deconvolution is useful for any divergent or convergent incoming or outgoing beam in order to separate signals.

Jernenkov, M.; Lauter, H.; Lauter-Pasyuk, V.; Toperverg, B.; Klimko, S.; Gähler, R.

2005-02-01

152

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.

153

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.1-3 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

154

NASA Astrophysics Data System (ADS)

Within general circulation models (GCMs), domain average radiative fluxes are computed using plane-parallel radiative transfer algorithms that rely on cloud overlap schemes to account for clouds not resolved at the horizontal resolution of a grid cell. These parameterizations have a strong statistical approach and have difficulty being applied well to all cloudy conditions. A more physically based superparameterization has been developed that captures subgrid cloud variability using an embedded cloud system resolving model (CSRM) within each GCM grid cell. While plane-parallel radiative transfer computations are generally appropriate at the scale of a GCM grid cell, their suitability for the much higher spatially resolved CSRMs (2-4 km) is unknown because they ignore photon horizontal transport effects. The purpose of this study is to examine the relationship between model horizontal resolution and 3D radiative effects by computing the differences between independent column approximations (ICA) and 3D Monte Carlo estimates of shortwave surface irradiance and atmospheric heating rate.Shortwave radiative transfer computations are performed on a set of six 2D fields composed of stratiform and convective liquid water and ice clouds. To establish how 3D effects vary with the size of a grid cell, this process is repeated as the model resolution is progressively degraded from 200 to 20 km. For shortwave surface irradiance, the differences between the 3D and ICA results can reach 500 W m-2. At model resolutions of between 2.0 and 5.0 km the difference for almost all columns is reduced to a maximum of ą100 W m-2. For atmospheric heating rates assessed at the level of individual model cells, 3D radiative effects can approach a maximum value of ą1.2 K h-1 when the horizontal column size is 200 m. However, between model resolutions of 2.0 and 5.0 km, 3D radiative effects are reduced to well below ą0.1 K h-1 for a large majority of the cloudy cells. While this finding seems to bode well for the CSRM, the results ultimately need to be understood within the context of how 3D radiative effects impact not only heating rates but also cloud dynamics.

O'Hirok, William; Gautier, Catherine

2005-08-01

155

We have observed the CO bipolar flow source near NGC 2071 in the J = 1-0 line of carbon monosulfide with 30'' resolution provided by the new 45 m Nobeyama telescope. We find a compact cloud with a size of approx.0.3 pc x 0.15 pc embedded in an extended cloud. This compact molecular cloudd is more than 4 times smaller than ws indicated in previously published coarser resolution observations, is elongated orthogonally to the bipolar flow, and shows strong signs of rotation. However, we estimate the mass of the compact cloud to be approx.10 M/sub sun/, much less than expected if it has been focusing the flow. We therefore conclude that collimation of the flow is taking place at considerably smaller scales unresolved with the 30'' beam.

Takano, T.; Fukui, Y.; Ogawa, H.; Takaba, H.; Kawabe, R.; Fujimoto, Y.; Sugitani, K.; Fujimoto, M.

1984-07-15

156

NASA Astrophysics Data System (ADS)

We present the results of N-band spectro-interferometric observations of the silicate carbon star IRAS08002-3803 with the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO). The observations were carried out using two unit telescopes (UT2 and UT3) with projected baseline lengths ranging from 39 to 47 m. Our observations of IRAS08002-3803 have spatially resolved the dusty environment of a silicate carbon star for the first time and revealed an unexpected wavelength dependence of the angular size in the N band: the uniform-disk diameter is found to be constant and 36 mas (72 Rstar) between 8 and 10 ?m, while it steeply increases longward of 10 ?m to reach 53 mas (106 Rstar) at 13 ?m. Model calculations with our Monte Carlo radiative transfer code show that neither spherical shell models nor axisymmetric disk models consisting of silicate grains alone can simultaneously explain the observed wavelength dependence of the visibility and the spectral energy distribution (SED). We propose that the circumstellar environment of IRAS08002-3803 may consist of two grain species coexisting in the disk: silicate and a second grain species, for which we consider amorphous carbon, large silicate grains, and metallic iron grains. Comparison of the observed visibilities and SED with our models shows that such disk models can fairly - though not entirely satisfactorily - reproduce the observed SED and N-band visibilities. Our MIDI observations and the radiative transfer calculations lend support to the picture where oxygen-rich material around IRAS08002-3803 is stored in a circumbinary disk surrounding the carbon-rich primary star and its putative low-luminosity companion.

Ohnaka, K.; Driebe, T.; Hofmann, K.-H.; Leinert, Ch.; Morel, S.; Paresce, F.; Preibisch, Th.; Richichi, A.; Schertl, D.; Schöller, M.; Waters, L. B. F. M.; Weigelt, G.; Wittkowski, M.

2006-01-01

157

Full three dimensional (3D) translational distributions for quantum state-resolved scattering dynamics at the gas-liquid interface are presented for experimental and theoretical studies of CO(2) + perfluorinated surfaces. Experimentally, high resolution absorption profiles are measured as a function of incident (?(inc)) and scattering (?(scat)) angles for CO(2) that has been scattered from a 300 K perfluorinated polyether surface (PFPE) with an incident energy of E(inc) = 10.6(8) kcal mol(-1). Line shape analysis of the absorption profiles reveals non-equilibrium dynamics that are characterized by trapping-desorption (TD) and impulsive scattering (IS) components, with each channel simply characterized by an effective "temperature" that compares very well with previous results from rotational state analysis [Perkins and Nesbitt, J. Phys. Chem. A, 2008, 112, 9324]. From a theoretical perspective, molecular dynamics (MD) simulations of CO(2) + fluorinated self-assembled monolayer surface (F-SAMs) yield translational probability distributions that are also compared with experimental results. Trajectories are parsed by ?(scat) and J, with the results rigorously corrected by flux-to-density transformation and providing comparisons in near quantitative agreement with experiment. 3D flux and velocity distributions obtained from MD simulations are also presented to illustrate the role of in- and out-of-plane scattering. PMID:20890492

Perkins, Bradford G; Nesbitt, David J

2010-11-14

158

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

159

NSDL National Science Digital Library

After using the historical development of concepts of conserved motion to develop introductory understanding, students are directed to a series of activities to gain a better understanding of momentum, conservation of momenta, angular momentum, and conservation of angular momenta.

Trapp, David

160

High Angular Resolution Astronomy on a Shoestring

NASA Astrophysics Data System (ADS)

Introduction; Lessons From Single-Telescope Interferometry; Interferometry with Single Telescopes; Astronomical applications; Desiderata For a Second-Generation Array; Astronomical goals; COAST - Lessons From a Prototype Array; Design elements of COAST; Suggestions For a Next-Generation Array (NGA); Collectors; Transport; Path Equalization; Optics; Operation; Summary

Haniff, Chris

161

Aspheric mirror with constant angular magnification II.

Differential equations for a constant-angular-magnification aspheric-mirror surface shape are derived for a general dependence of the camera image height on the camera field angle. The explicit equations of the constant-angular-magnification mirror surface are given for some particular values of the angular magnification. For a series of odd integer values of the angular magnification, 10th-order polynomial approximations of the mirror surface are presented. The imaging performance of such a mirror with an angular magnification of 7 is analyzed and compared with a spherical mirror. The main cause of image blur in all-sky cameras at the edge of the field of view was found to be a strong image curvature. We show that increasing the camera-to-mirror distance and/or stopping down the camera lens reduces the image blur. PMID:20935771

Andrei?, Z; Radi?, N

1994-07-01

162

Phonons with orbital angular momentum

Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

Ayub, M. K. [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan); National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Ali, S. [National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Mendonca, J. T. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

2011-10-15

163

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

164

Photoelectron angular distributions (PADs) are obtained for a pair of 4s{sup 1}4p{sup 6}6p{sup 1} (a singlet and a triplet) autoionizing states in atomic krypton. A high-order harmonic pulse is used to excite the pair of states and a time-delayed 801 nm ionization pulse probes the PADs to the final 4s{sup 1}4p{sup 6} continuum with femtosecond time resolution. The ejected electrons are detected with velocity map imaging to retrieve the time-resolved photoelectron spectrum and PADs. The PAD for the triplet state is inherently separable by virtue of its longer autoionization lifetime. Measuring the total signal over time allows for the PADs to be extracted for both the singlet state and the triplet state. Anisotropy parameters for the triplet state are measured to be {beta}{sub 2}= 0.55 {+-} 0.17 and {beta}{sub 4}=-0.01 {+-} 0.10, while the singlet state yields {beta}{sub 2}= 2.19 {+-} 0.18 and {beta}{sub 4}= 1.84 {+-} 0.14. For the singlet state, the ratio of radial transition dipole matrix elements, X, of outgoing S to D partial waves and total phase shift difference between these waves, {Delta}, are determined to be X= 0.56 {+-} 0.08 and {Delta}= 2.19 {+-} 0.11 rad. The continuum quantum defect difference between the S and D electron partial waves is determined to be -0.15 {+-} 0.03 for the singlet state. Based on previous analyses, the triplet state is expected to have anisotropy parameters independent of electron kinetic energy and equal to {beta}{sub 2}= 5/7 and {beta}{sub 4}=-12/7. Deviations from the predicted values are thought to be a result of state mixing by spin-orbit and configuration interactions in the intermediate and final states; theoretical calculations are required to quantify these effects.

Doughty, Benjamin; Haber, Louis H.; Hackett, Christina; Leone, Stephen R. [Departments of Chemistry and Physics and Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)

2011-03-07

165

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

166

Angular velocity measuring interferome.

A novel optical system to measure angular velocity based on the Doppler effect is presented. The system was developed to investigate the effect of rotation in the process of experimental modal analysis. PMID:20555859

Ben-Levy, M; Braun, S G; Shamir, J

1989-10-15

167

National Technical Information Service (NTIS)

The video describes how to choose the correct grinding wheel, adjust the swivel table for grinding the angular teeth of the cutter, adjust for clearance angle, and check the teeth for accuracy of the angle.

1994-01-01

168

Quark orbital angular momentum from lattice QCD

The authors calculate the quark orbital angular momentum of the nucleon from the quark energy-momentum tensor form factors on the lattice. The disconnected insertion is estimated stochastically which employs the Z{sub 2} noise with an unbiased subtraction. This reduced the error by a factor of 4 with negligible overhead. The total quark contribution to the proton spin is found to be 0.30{+-}0.07. From this and the quark spin content the authors deduce the quark orbital angular momentum to be 0.17{+-}0.06 which is {approximately} 34% of the proton spin. The authors further predict that the gluon angular momentum to be 0.20{+-}0.07, i. e. {approximately} 40% of the proton spin is due to the glue.

Liu, K.F.

2000-01-10

169

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

170

National Technical Information Service (NTIS)

A simple approach employing properties of solutions of differential equations is adopted to derive an appropriate extension of the WKBJ method. Some of the earlier techniques that are commonly in use are unified, whereby the general approximate solution t...

M. El Sawi

1983-01-01

171

National Technical Information Service (NTIS)

Methods for representing multi-dimensional objects, such as functions of several variables and, more generally, (hyper-)surfaces is the main objective. One goal of such representation, whether approximate or exact, is the efficient evaluation of the objec...

C. DE Boor A. Ron

1998-01-01

172

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, E.; Parisi, G.; Spinello, F.; Romanato, F.

2014-02-01

173

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

174

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

175

Scaled angular spectrum method.

The angular spectrum method (ASM) calculates diffraction calculation in a high numerical aperture, unlike Fresnel diffraction. However, this method does not allow us to calculate at different sampling rates on source and destination planes. In this Letter, we propose a scaled ASM that calculates diffraction at different sampling rates on source and destination planes using the nonuniform fast Fourier transform. PMID:23027301

Shimobaba, Tomoyoshi; Matsushima, Kyoji; Kakue, Takashi; Masuda, Nobuyuki; Ito, Tomoyoshi

2012-10-01

176

ERIC Educational Resources Information Center

Discusses, classically and quantum mechanically, the angular momentum induced in the bound motion of an electron by an external magnetic field. Calculates the current density and its magnetic moment, and then uses two methods to solve the first-order perturbation theory equation for the required eigenfunction. (Author/GA)

Parker, G. W.

1978-01-01

177

NASA Astrophysics Data System (ADS)

We predict the possibility of observing integer and fractional self-imaging (Talbot) phenomena on the discrete angular spectrum of periodic diffraction gratings illuminated by a suitable spherical wave front. Our predictions are experimentally validated, reporting what we believe to be the first observation of self-imaging effects in the far-field diffraction regime.

Azańa, José; Guillet de Chatellus, Hugues

2014-05-01

178

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

179

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 LEGOÂŽ MINDSTORMSÂŽ 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,

180

Quark orbital angular momentum from lattice QCD

We calculate the quark orbital angular momentum of the nucleon from the quark energy-momentum tensor form factors on the lattice with the quenched approximation. The disconnected insertion is estimated stochastically which employs the Z{sub 2} noise with an unbiased subtraction. This reduced the error by a factor of 3--4 with negligible overhead. The total quark contribution to the proton spin is found to be 0.30{+-}0.07. From this and the quark spin content we deduce the quark orbital angular momentum to be 0.17{+-}0.06 which is {approx}34% of the proton spin. We further predict that the gluon angular momentum is 0.20{+-}0.07; i.e., {approx}40% of the proton spin is due to the glue.

Mathur, N.; Dong, S. J.; Liu, K. F.; Mankiewicz, L.; Mukhopadhyay, N. C.

2000-12-01

181

Intravenous pyogenic granuloma of the angular vein.

A 47-year-old woman presented with a painful mass below her left medial canthus. Examination revealed a 1-cm tender, smooth, pulseless, mobile mass inferior to the level of the anterior lacrimal crest. CT imaging was performed. Excision of the involved angular vein revealed a smooth, intralumenal lesion. Histopathologic examination demonstrated intravenous pyogenic granuloma (IVPG). There are approximately 30 reported cases of IVPG in the English literature, 2 of which arise in the periocular angular vein. The ultrasound and MRI characteristics of IVPG have been previously described. We describe the CT profile of this rare, benign tumor as a mildly heterogeneic, contrast-enhancing cylindrical lesion within, and conforming to the shape of, the angular vein. There is dilatation of the vein proximal to the lesion with marked narrowing distal to it secondary to obstruction of flow. On noncontrast imaging, the lesion is isodense with nasal mucosa and without calcifications. PMID:19617809

Winn, Bryan J; Herreid, Peter A; Sires, Bryan S

2009-01-01

182

NASA Astrophysics Data System (ADS)

Starting from the simplest possible building blocks--a ket, a bra, a time-reversed ket, and a time-reversed bra--a diagrammatic formalism is developed for angular momentum coupling problems. The formalism comprises Clebsch-Gordan coefficients as well as 3jm-symbols. The idea of constructing invariants (internal lines) by contracting contragredient pairs of quantities is emphasized throughout. The Clebsch-Gordan series, and its extension to the coupling of more than two angular momenta, is introduced algebraically and diagrammatically. Recoupling between bases obtained in different coupling schemes is introduced and the connection between recoupling coefficients and irreducible 3nj-symbols is derived diagrammatically. The well-known diagrammatic rules due to Jucys and co-workers are derived by group theoretical means and simple rules for their practical exploitation are presented.

Wormer, Paul E. S.; Paldus, Josef

183

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

184

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

185

Improving the resolution of chopper spectrometers at pulsed neutron sources

NASA Astrophysics Data System (ADS)

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.

Carpenter, J. M.; Mildner, D. F. R.

1993-02-01

186

POLYCAPILLARY OPTICS FOR ANGULAR FILTERING OF X-RAYS AND NEUTRONS IN TWO DIMENSIONS

The ability of polycapillary optics to reject radiation incident outside the critical angle for total external reflection while efficiently transmitting radiation within the critical angle make them ideal two-dimensional angular filters for X-rays and neutrons. The use of such angular filters is shown to be important for medical imaging to give contrast and resolution improvement, for improved spatial resolution and

W. M. GibsonaTb; H. HuahgaYb; J. Nicolich; P. Klein; C. A. MacDonald

187

Balanced angular profile analysis.

To evaluate current preferences and ethnic differences of female soft-tissue profiles, 71 profile photographs of famous female models were collected from Internet Web pages and divided into four groups (Korean, 22; Japanese, 15; Chinese, 16; and Western, 18). Eleven soft-tissue landmarks were recorded on each photograph and 16 angular measurements were made by using V-ceph (CyberMed, Inc., Seoul, Korea). Data from each group are presented to show the means, ranges, p and F values, standard deviations, and standard errors of each measurement. In addition, individual measurements for each group were compared with those of the other groups by one-way analysis of variance using a p value corrected for multivariable testing. Between-group mean value differences were calculated using a Tukey's studentized range test (HSD), at a significance level of p = 0.05. Most of the variables were similar in the groups. Significant between-group differences (p < 0.05) were found for angle of alar curvature point, profile convexity, interlabial contour, and nasolabial contour. In addition, we divided all data into two groups (Western and Asian). The t test (with significance level set to p = 0.05) was performed to compare the two. Significant between-group differences (p < 0.05) were found for angle of alar curvature, angle of labiale inferius, profile convexity, and lower lip projection angle, but no significant racial differences were found in terms of several profile angles. These findings suggest that point of ala curvature point, subnasale, and the labiale inferius of Asian models may differ from those of Western models. These peculiar angular patterns of Asian models led the authors to create a new characteristic angular concept, termed the "ethnic pyramid," which is composed of soft-tissue profile points of alar curvature point, subnasale, pronasale, and labiale inferius. This ethnic pyramid describes the characteristic patterns of the ethnic differences. The results of this study suggest that the soft-tissue profiles of famous female models have some common features but also show differences among ethnic groups and races. This simple method of profile analysis may provide aesthetic surgeons with a simple formula and reference data for creation and application of an attractive face. On the basis of their balanced angular profile analysis data, the authors suggest that appropriate and harmonious aesthetic operations reflecting these differences should be considered. PMID:15277828

Rhee, Seung Chul; Kang, So Ra; Park, Heung Sik

2004-08-01

188

Ultra high resolution soft x-ray tomography

Ultra high resolution three dimensional images of a microscopic test object were made with soft x-rays using a scanning transmission x-ray microscope. The test object consisted of two different patterns of gold bars on silicon nitride windows that were separated by {approximately}5{mu}m. A series of nine 2-D images of the object were recorded at angles between {minus}50 to +55 degrees with respect to the beam axis. The projections were then combined tomographically to form a 3-D image by means of an algebraic reconstruction technique (ART) algorithm. A transverse resolution of {approximately}1000 {Angstrom} was observed. Artifacts in the reconstruction limited the overall depth resolution to {approximately}6000 {Angstrom}, however some features were clearly reconstructed with a depth resolution of {approximately}1000 {Angstrom}. A specially modified ART algorithm and a constrained conjugate gradient (CCG) code were also developed as improvements over the standard ART algorithm. Both of these methods made significant improvements in the overall depth resolution bringing it down to {approximately}1200 {Angstrom} overall. Preliminary projection data sets were also recorded with both dry and re-hydrated human sperm cells over a similar angular range.

Haddad, W.S.; Trebes, J.E.; Goodman, D.M. [and others

1995-07-19

189

Ultrahigh-resolution soft x-ray tomography

NASA Astrophysics Data System (ADS)

Ultra high resolution three-dimensional images of a microscopic test object were made with soft x rays using a scanning transmission x-ray microscope. The test object consisted of two different patterns of gold bars on silicon nitride windows that were separated by approximately 5 micrometer. A series of nine 2-D images of the object were recorded at angles between -5 to +55 degrees with respect to the beam axis. The projections were then combined tomographically to form a 3-D image by means of an algebraic reconstruction technique (ART) algorithm. A transverse resolution of approximately 1000 angstrom was observed. Artifacts in the reconstruction limited the overall depth resolution to approximately 6000 angstrom, however some features were clearly reconstructed with a depth resolution of approximately 1000 angstrom. A specially modified ART algorithm and a constrained conjugate gradient (CCG) code were also developed as improvements over the standard ART algorithm. Both of these methods made significant improvements in the overall depth resolution, bringing it down to approximately 1200 angstrom overall. Preliminary projection data sets were also recorded with both dry and re-hydrated human sperm cells over a similar angular range.

Haddad, Waleed S.; Trebes, James E.; Goodman, Dennis M.; Lee, Heung-Rae; McNulty, Ian; Anderson, Erik H.; Zalensky, Andrei O.

1995-09-01

190

Estimating energy-momentum and angular momentum near null infinity

The energy-momentum and angular momentum contained in a spacelike two-surface of spherical topology are estimated by joining the two-surface to null infinity via an approximate no-incoming-radiation condition. The result is a set of gauge-invariant formulas for energy-momentum and angular momentum which should be applicable to much numerical work; it also gives estimates of the finite-size effects.

Helfer, Adam D. [Department of Mathematics, University of Missouri, Columbia, Missouri 65211 (United States)

2010-04-15

191

Angular probe based on using Fabry-Perot etalon and scanning technique.

A novel angular probe using the Fabry-Perot etalon and angular scanning technique is proposed for absolute angular displacement determinations in this paper. The measurement theory is first derived, a setup constructed to implement the angular probe is then introduced and analyzed, and the experimental results from the uses of the setup are finally presented. The setup analyses reveal that the probe is with high measurement resolution and sensitivity. The experimental results not only confirm the validity, stability, accuracy, and repeatability, but also show an application of the angular probe. PMID:20174008

Lin, Shyh-Tsong; Yeh, Sheng-Lih; Lin, Zhi-Feng

2010-02-01

192

Fragment angular momenta in alpha-induced fission of 238U

NASA Astrophysics Data System (ADS)

Fragment angular momenta are deduced from the radiochemically determined independent isomeric yield ratios of the antimony isotopes 126,128,130Sb in the alpha-particle-induced fission of 238U at various initial excitation energies (18.3-30.2 MeV) and angular momenta (7.86-13.9?). It is found that the fragment angular momenta increase with increasing excitation energy and angular momentum of the fissioning nucleus. Calculations of fragment angular momenta are performed based on the Fermi gas approximation for the fissioning nucleus, taking into account the contribution of fissioning nucleus' angular momentum into that of the fragment. The calculated values agree reasonably well with the experimental values indicating that the fragment angular momenta increase with the increasing initial excitation energy and angular momentum of the fissioning nucleus, with the former playing the dominant role through increased fragment moment of inertia and temperature.

Tomar, B. S.; Goswami, A.; Das, S. K.; Srivastava, B. K.; Guin, R.; Sahakundu, S. M.; Prakash, Satya

1988-10-01

193

NASA Technical Reports Server (NTRS)

The construction of a two dimensional focusing Wolter Type I mirror system for X-ray and XUV astronomical observations from an Astrobee F sounding rocket is described. The mirror design goal will have a one degree field, a 20-arc seconds resolution, an effective area of about 50 sq cm at 1 keV and 10 sq cm at 0.25 keV on axis. A star camera provides aspect data to about 15-arc seconds. Two detectors are placed at the focus with an interchange mechanism to allow a detector change during flight. The following specific developments are reported: (1) position sensitive proportional counter development; (2) channel plate multiplier development; (3) telescope mirror development and payload structure; (4) Australian rocket flight results; (5) Comet Kohoutek He I observation; and (6) Vela, Puppis A, and Gem-Mon bright patch observations.

Garmire, G. P.

1974-01-01

194

Angular Velocimeter for Aerospace Applications.

National Technical Information Service (NTIS)

Low-level broad-band angular vibration measurement applications are continually developing. This has generated a pressing need for a low-level angular vibration sensor capable of measuring 0.000001 radians at frequencies from 0 to 10kHz, with a total size...

P. W. Whaley

1983-01-01

195

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

196

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.

2013-01-01

197

Supersensitive measurement of angular displacements using entangled photons

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

198

Angular-dependent core hole screening effects have been found in the cobalt K -edge x-ray absorption spectrum of LiCoO2 , using high-resolution data and parameter-free general gradient approximation plus U calculations. The Co1s core hole on the absorber causes strong local attraction. The core hole screening on the cobalt nearest-neighbors induces a 2 eV shift in the density of states with

Amélie Juhin; Frank de Groot; György Vankó; Matteo Calandra; Christian Brouder

2010-01-01

199

Digital Instrumentation for Angular Velocity and Acceleration

An instrument is described for the measurement of angular velocity and angular acceleration of a rotating shaft, based upon an optical angular transducer and an associated operational digital (pulse rate) system. The angular transducer produces a pulse rate directly proportional to the instantaneous angular velocity and this quantity and its rate of change are processed by the pulse rate system

Alan Dunworth

1969-01-01

200

Exploring angular distance in protein-protein docking algorithms.

We present a two-stage hybrid-resolution approach for rigid-body protein-protein docking. The first stage is carried out at low-resolution (15°) angular sampling. In the second stage, we sample promising regions from the first stage at a higher resolution of 6°. The hybrid-resolution approach produces the same results as a 6° uniform sampling docking run, but uses only 17% of the computational time. We also show that the angular distance can be used successfully in clustering and pruning algorithms, as well as the characterization of energy funnels. Traditionally the root-mean-square-distance is used in these algorithms, but the evaluation is computationally expensive as it depends on both the rotational and translational parameters of the docking solutions. In contrast, the angular distances only depend on the rotational parameters, which are generally fixed for all docking runs. Hence the angular distances can be pre-computed, and do not add computational time to the post-processing of rigid-body docking results. PMID:23437194

Vreven, Thom; Hwang, Howook; Weng, Zhiping

2013-01-01

201

NASA Astrophysics Data System (ADS)

We implement an interferometric method using two angular slits to measure the orbital-angular-momentum (OAM) mode spectrum of a field with partial angular coherence. As the angular separation of the slits changes, an interference pattern for a particular OAM mode is obtained. The visibility of this interference pattern as a function of angular separation is equivalent to the angular correlation function of the field. By Fourier transforming the angular correlation function obtained from the double-angular-slit interference, we are able to calculate the OAM spectrum of the partially coherent field. This method has potential application for characterizing the OAM spectrum in high-dimensional quantum information protocols.

Malik, Mehul; Murugkar, Sangeeta; Leach, Jonathan; Boyd, Robert W.

2012-12-01

202

Angular momentum in subbarrier fusion

We have measured the ratio of the isomer to ground-state yields of {sup 137}Ce produced in the fusion reactions {sup 128}Te({sup 12}C,3n), {sup 133}Cs({sup 7}Li,3n), {sup 136}Ba({sup 3}He,2n), {sup 136}Ba({sup 4}He,3n), and {sup 137}Ba({sup 3}He,3n), from energies above the Coulomb barrier to energies typically 20--30% below the barrier by observing the delayed x- and {gamma}-ray emission. We deduce the average angular momentum, {lt}J{gt}, from the measured isomer ratios with a statistical model. In the first three reactions we observe that the values of {lt}J{gt} exhibit the behavior predicted for low energies and the expected variation with the reduced mass of the entrance channel. We analyze these data and the associated cross sections with a barrier penetration model that includes the coupling of inelastic channels. Measurements of average angular momenta and cross sections made on other systems using the {gamma}-multiplicity and fission-fragment angular correlation techniques are then analyzed in a similar way with this model. The discrepancies with theory for the {gamma}-multiplicity data show correlations in cross section and angular momentum that suggest a valid model can be found. The measurements of angular momentum using the fission fragment angular correlation technique, however, do not appear reconcilable with the energy dependence of the cross sections. This systematic overview suggests, in particular, that our current understanding of the relationship of angular momentum and anisotropy in fission fragment angular correlations is incomplete. 26 refs.

DiGregorio, D.E.; Lesko, K.T.; Harmon, B.A.; Norman, E.B.; Pouliot, J.; Sur, B.; Chan, Y.D.; Stokstad, R.G.

1990-05-01

203

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 19.96ą0.03 milliarcsec for the uniform disk diameter. The corresponding limb-darkened value is 20.58ą0.03 milliarcsec, or 44.2ą0.9 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

204

Stepwise angular spectrum method for curved surface diffraction.

We present a method to calculate wave propagation between arbitrary curved surfaces using a staircase approximation approach. The entire curved surface is divided into multiple subregions and each curved subregion is approximated by a piecewise flat subplane allowing the application of conventional diffraction theory. In addition, in order to reflect the local curvature of each subregion, we apply the phase compensation technique. Analytical expressions are derived based on the angular spectrum method and numerical studies are conducted to validate our method. PMID:24921383

Hwang, Chi-Young; Oh, Seungtaik; Jeong, Il-Kwon; Kim, Hwi

2014-05-19

205

Angular pattern and binary angular pattern for shape retrieval.

In this paper, we propose two novel shape descriptors, angular pattern (AP) and binary angular pattern (BAP), and a multiscale integration of them for shape retrieval. Both AP and BAP are intrinsically invariant to scale and rotation. More importantly, being global shape descriptors, the proposed shape descriptors are computationally very efficient, while possessing similar discriminability as state-of-the-art local descriptors. As a result, the proposed approach is attractive for real world shape retrieval applications. The experiments on the widely used MPEG-7 and TARI-1000 data sets demonstrate the effectiveness of the proposed method in comparison with existing methods. PMID:24144665

Hu, Rong-Xiang; Jia, Wei; Ling, Haibin; Zhao, Yang; Gui, Jie

2014-03-01

206

Spectrally encoded angular light scattering.

The angular light scattering profile of microscopic particles significantly depends on their morphological parameters, such as size and shape. This dependency is widely used in state-of-the-art flow cytometry methods for particle classification. We introduce a new spectrally encoded angular light scattering method, with potential application in scanning flow cytometry. We show that a one-to-one wavelength-to-angle mapping enables the measurement of the angular dependence of scattered light from microscopic particles over a wide dynamic range. Improvement in dynamic range is obtained by equalizing the angular dependence of scattering via wavelength equalization. Continuous angular spectrum is obtained without mechanical scanning enabling single-shot measurement. Using this information, particle morphology can be determined with improved accuracy. We derive and experimentally verify an analytic wavelength-to-angle mapping model, facilitating rapid data processing. As a proof of concept, we demonstrate the method's capability of distinguishing differently sized polystyrene beads. The combination of this technique with time-stretch dispersive Fourier transform offers real-time and high-throughput (high frame rate) measurements and renders the method suitable for integration in standard flow cytometers. PMID:24514410

Adam, Jost; Mahjoubfar, Ata; Diebold, Eric D; Buckley, Brandon W; Jalali, Bahram

2013-11-18

207

Defining Electron Backscatter Diffraction Resolution

Automated electron backscatter diffraction (EBSD) mapping systems have existed for more than 10 years [1,2], and due to their versatility in characterizing multiple aspects of microstructure, they have become an important tool in microscale crystallographic studies. Their increasingly widespread use however raises questions about their accuracy in both determining crystallographic orientations, as well as ensuring that the orientation information is spatially correct. The issue of orientation accuracy (as defined by angular resolution) has been addressed previously [3-5]. While the resolution of EBSD systems is typically quoted to be on the order of 1{sup o}, it has been shown that by increasing the pattern quality via acquisition parameter adjustment, the angular resolution can be improved to sub-degree levels. Ultimately, the resolution is dependent on how it is identified. In some cases it can be identified as the orientation relative to a known absolute, in others as the misorientation between nearest neighbor points in a scan. Naturally, the resulting values can be significantly different. Therefore, a consistent and universal definition of resolution that can be applied to characterize any EBSD system is necessary, and is the focus of the current study. In this work, a Phillips (FEI) XL-40 FEGSEM coupled to a TexSEM Laboratories OIM system was used. The pattern capturing hardware consisted of both a 512 by 512 pixel SIT CCD camera and a 1300 by 1030 pixel Peltier cooled CCD camera. Automated scans of various sizes, each consisting of 2500 points, were performed on a commercial-grade single crystal silicon wafer used for angular resolution measurements. To adequately quantify angular resolution for all possible EBSD applications we define two angular values. The first is {omega}{sub center}, the mean of the misorientation angle distribution between all scan points and the scan point coincident to the calibration source (typically the scan center). The {omega}{sub center} value is used to describe the overall system resolution, as it effectively quantifies the deviation of all orientations in the scan relative to the diffraction pattern least affected by distortions. The second is {omega}{sub max}, the largest misorientation angle possible between any pair of points in the dataset, and describes the worst possible case. Fig. 1 shows the effects of scan size and captured pattern resolution (bin size) on both angular values, illustrating that smaller scan and bin sizes have the effect of increasing angular resolution. However, it can be observed that the benefits of utilizing smaller bin sizes (and consequently slower data collection) diminish with scan size. Fig. 2 shows the effect of the number of pixels used in the Hough transform (defined as the ratio of pixels used to maximum possible pixels) on the angular values. It can be seen that the best angular resolutions are achieved at a pixel ratio of 0.80, again illustrating that the use of higher resolutions is not always beneficial. As evidenced by the results, the use of {omega}{sub center} and {omega}{sub max} not only permits the characterization of the angular resolution of an EBSD system, but they allow for a more efficient utilization of the system by identifying appropriate settings depending on the desired angular resolution [6].

El-Dasher, B S; Rollett, A D

2005-02-07

208

A Role for Improved Angular Observations in Geosynchronous Orbit Determination

NASA Astrophysics Data System (ADS)

The goal of this thesis is to show that improved angular observations can aid in the determination of satellite position and velocity in the geosynchronous orbit regime. Raven is a new sensor being developed by the U.S. Air Force Research Laboratory which should allow for angular observations of satellites to be made with a standard deviation of 1 arcsecond (which maps into approximately 170 meters at geosynchronous altitude); this is an order of magnitude improvement over traditional angular observation techniques and represents state of the art accuracy of angular observations for geosynchronous orbit determination work. Simulation studies are undertaken to show that these angular observations can be used in the orbit determination process both as the only cracking data source and as a supplement to other tracking data sources such as radar and radio transponder ranges. Results from the radio transponder range analysis are extended to cover Satellite Laser Ranging (SLR) and Global Positioning System (GPS) observation types as well. The studies target both space surveillance and owner/operator mission support aspects of orbit determination although the emphasis will be on mission support satellite operations. Parameters varied in the simulation studies include the number of observing stations, the density of the angular observations, and the number of nights of optical tracking. The data simulations are calibrated based on real data results from a geosynchronous satellite to ensure the integrity of the simulations and the accuracy of the results. The studies show that including the improved angular observations with traditional high accuracy range observations produces a significant improvement in orbit determination accuracy over the range observations alone. The studies also show single site geosynchronous orbit determination is an attractive alternative when combining improved angular and high accuracy range observations.

Sabol, Christopher Andrew

1998-12-01

209

High angular resolution and position determinations by infrared interferometry

NASA Technical Reports Server (NTRS)

Interferometer systems are described in the form of publications and reports. 'Distance Meter Helps Track the Stars', 'Berkeley Heterodyne Interferometer', 'Infrared Heterodyne Spectroscopy of CO2 on Mars', and 'A 10 micron Heterodyne Stellar Interferometer' are papers reported.

1974-01-01

210

An Acousto-Optical Sensor with High Angular Resolution

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.

Kaloshin, Gennady; Lukin, Igor

2012-01-01

211

Progress toward light weight high angular resolution multilayer coated optics

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

212

"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

213

Interferometric measurement of angular motion

NASA Astrophysics Data System (ADS)

This paper describes the design and realization of a homodyne polarization interferometer for measuring angular motion. The optical layout incorporates carefully designed cat's eye retroreflectors that maximize the measurable range of angular motion and facilitate initial alignment. The retroreflectors are optimized and numerically characterized in terms of defocus and spherical aberrations using Zemax software for optical design. The linearity of the measurement is then calculated in terms of the aberrations. The actual physical interferometer is realized as a compact device with optical components from stock and without relying on adjustable holders. Evaluation of its performance using a commercial autocollimator confirmed a reproducibility within 0.1%, a non-linearity of less than 1 ppm with respect to the autocollimator, an upper limit to its sensitivity of about 5 × 10-11 rad/Hz from audioband down to 100 mHz and an angular measurement range of more than +/-1°.

Peńa Arellano, Fabián Erasmo; Panjwani, Hasnain; Carbone, Ludovico; Speake, Clive C.

2013-04-01

214

Phenomenology of preequilibrium angular distributions

The systematics of continuum angular distributions from a wide variety of light ion nuclear reactions have been studied. To first order, the shape of the angular distributions have been found to depend only on the energy of the outgoing particle and on the division of the cross section into multi-step direct and multi-step compound parts. The angular distributions can be described in terms of Legendre polynomials with the reduced polynomial coefficients exhibiting a simple dependence on the outgoing particle energy. Two integer and four continuous parameters with universal values are needed to describe the coefficients for outgoing energies of 2 to 60 MeV in all the reaction types studied. This parameterization combined with a modified Griffin model computer code permits the calculation of double differential cross sections for light ion continuum reactions where no data is available.

Kalbach, C.; Mann, F.M.

1980-05-01

215

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

216

The angular distribution of ion flux around an ionospheric satellite.

NASA Technical Reports Server (NTRS)

Ion measurements from the Explorer 31 satellite were used to determine the angular distribution of ions around the satellite. The ion distributions were compared with the electron distributions measured on the same satellite. It is shown that the electron currents (fluxes) in the wake are always larger than the ion currents for a wide domain of plasma parameters. A quantitative comparison of the ion fluxes with a neutral approximation model for the angular distribution is considered. It is found that the ion fluxes become progressively larger than the corresponding computed neutral fluxes as the angle of attack increases from 0 to 180 deg.

Samir, U.; Maier, E. J.; Troy, B. E., Jr.

1973-01-01

217

Scaling rotationally inelastic collisions with an effective angular momentum parameter

NASA Astrophysics Data System (ADS)

A new formulation of the base rate and the adiabatic energy correction used in the energy corrected sudden approximation is proposed. Explicitly, the common energy gap laws are replaced with an angular momentum gap law. This law is based upon the introduction of an effective angular momentum parameter (? c=2?) limiting the collision-induced intra-molecular rotational energy transfer (RET) due to the finite interaction time. The experimental results of collision induced RET for the N 2-N 2, CO-CO and N 2-He systems obtained by the application of femtosecond coherent anti-Stokes Raman spectroscopy (fs-CARS) are in excellent agreement with the proposed model.

Beaud, P.; Knopp, G.

2003-03-01

218

Non-Colinearity of Angular Velocity and Angular Momentum

ERIC Educational Resources Information Center

Discusses the principles, construction, and operation of an apparatus which serves to demonstrate the non-colinearity of the angular velocity and momentum vectors as well as the inertial tensors. Applications of the apparatus to teaching of advanced undergraduate mechanics courses are recommended. (CC)

Burr, A. F.

1974-01-01

219

Measuring Angular Size and Distance

NSDL National Science Digital Library

This is an activity about measuring angular size and understanding the solar and lunar proportions that result in solar eclipses. Learners will use triangles and proportions to create a shoebox eclipse simulator. They will then apply what they learn about angular size to predict the diameter and distance of one object that can be eclipsed by another. They will also complete three journal assignments to record observations and conceptual understanding. This activity derives from those demonstrated in the NASA CONNECT television series episode, titled Path of Totality.

220

Nanoradian angular stabilization of x-ray optical components

An x-ray free-electron laser oscillator (XFELO) has been recently proposed [K. Kim et al., Phys. Rev. Lett. 100, 244802 (2008)]. Angular orientation and position in space of Bragg mirrors of the XFELO optical cavity must be continuously adjusted to compensate for the instabilities and maximize the output intensity. An angular stability of about 10 nrad (rms) is required [K. Kim and Y. Shvyd'ko, Phys. Rev. ST Accel. Beams 12, 030703 (2009)]. To approach this goal, a feedback loop based on a null-detection principle was designed and used for stabilization of a high-energy-resolution x-ray monochromator ({Delta}E/E{approx_equal}4x10{sup -8}, E=23.7 keV) and a high-heat-load monochromator. Angular stability of about 13 nrad (rms) has been demonstrated for x-ray optical elements of the monochromators.

Stoupin, Stanislav; Lenkszus, Frank; Laird, Robert; Goetze, Kurt; Kim, Kwang-Je; Shvyd'ko, Yuri [Advanced Photon Source, Argonne National Laboratory, Illinois 60439 (United States)

2010-05-15

221

Angular distributions of solar protons and electrons

NASA Technical Reports Server (NTRS)

High angular-resolution measurements of directional fluxes of solar particles in space have been obtained with detectors aboard OGO-5 during the cosmic ray event of Nov. 18, 1968. This is the only case on record for which sharply-defined directional observations of protons and electrons covering a wide rigidity range (0.3 MV to 1.5 GV) are available. The satellite experiment provided data for determining pitch-angle distributions with respect to the direction of the local interplanetary magnetic field lines during the lengthy highly anisotropic phase of the event. The results have been interpreted in the light of the temporal flux profiles and the state of the interplanetary medium.

Nielsen, E.; Pomerantz, M. A.; West, H. I., Jr.

1975-01-01

222

We propose a generalization of quasi-phase-matching of quadratic nonlinear processes that we call angular quasi-phase-matching (AQPM). It corresponds to a propagation of three collinear interacting electromagnetic waves in a periodically poled nonlinear medium at any angle with respect to the grating vector. AQPM directions are analyzed using groups theory.

Petit, Yannick; Boulanger, Benoit; Segonds, Patricia [Institut Neel / CNRS-UJF, Boite Postale 166, F 38042 Grenoble Cedex 9 (France); Taira, Takunori [Institute for Molecular Science, 38 Nishigonaka, Myodaiji, Okazaki, 444-8585 (Japan)

2007-12-15

223

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

224

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

225

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

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)] [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)] [Mitsubishi Heavy Industries, Ltd., Wadasakicho1-1-1, Hyogo-ku, Kobe, 652-8585 (Japan)

2013-07-01

226

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

227

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

228

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

229

Optical design for laser Doppler angular encoder with sub-nanoradian sensitivity

A novel laser angular encoder system has been developed based on the principles of radar, the Doppler effect, optical heterodyning, and self aligning multiple reflection optics. Using this novel three dimensional multiple reflection optical path, a 10 to 20 times better resolution has been reached compared to commercially available laser Doppler displacement meters or laser interferometer systems. With the new angular encoder, sub-nanoradian resolution has been attained in the 8 degree measuring range in a compact setup about 60 mm (H) x 150 mm (W) x 370 mm (L) in size for high energy resolution applications at the Advanced Photon Source undulator beamline 3-ID.

Shu, D.; Alp, E.E.; Barraza, J.; Kuzay, T.M.; Mooney, T.

1997-09-01

230

How each state-to-state reactive transition determines nonundulatory ''state-to-all-states'' angular distribution has not yet been investigated. Here we present a complete exposure of state-to-state distorted-wave Born-approximation angular distributions in order to examine how the nonoscillatory and backward-peaked state-to-all-states reactive scattering angular distribution occurs.

Emmons, R.W.; Suck, S.H.

1983-04-01

231

High Resolution Study of Pionic 0- State in 16O

NASA Astrophysics Data System (ADS)

The cross sections and analyzing powers of the 16O(p,p')16O(0-,T = 1) scattering were measured at a bombarding energy of 295 MeV and an angular range of 14° <= ?lab <= 30°. The isovector 0- state at Ex = 12.80 MeV is clearly separated from the neighboring states with an energy resolution of ?E ~= 30 keV. The data have been compared with distorted wave impulse approximation (DWIA) calculations. The analyzing powers are sensitve to the effective nucleon-nucleon (NN) interaction used in DWIA calculations, and our data support the medium modification of the NN interaction in nuclei. The DWIA calculation employing a random phase approximation (RPA) response function predicts an enhancement of the cross sections around a momentum transfer of q ~= 1.7 fm-1, and it gives a reasonable agreement with the data.

Wakasa, T.; Berg, G. P. A.; Fujimura, H.; Fujita, K.; Hatanaka, K.; Itoh, M.; Kamiya, J.; Kawabata, T.; Kitamura, Y.; Obayashi, E.; Sakaguchi, H.; Sakamoto, N.; Sakemi, Y.; Shimizu, Y.; Takeda, H.; Uchida, M.; Yasuda, Y.; Yoshida, H. P.; Yosoi, M.

2003-07-01

232

High Resolution Study of Pionic 0- State in 16O

NASA Astrophysics Data System (ADS)

The cross sections and analyzing powers of the 16O(p,p')16O(0-,T = 1) scattering were measured at a bombarding energy of 295 MeV and an angular range of 14 ° ? ?lab ? 30°. The isovector 0- state at Ex = 12.80 MeV is clearly separated from the neighboring states with an energy resolution of ?E ? 30 keV. The data have been compared with distorted wave impulse approximation (DWIA) calculations. The analyzing powers are sensitive to the effective nucleon-nucleon (NN) interaction used in DWIA calculations, and our data support the medium modification of the NN interaction in nuclei. The DWIA calculation employing a random phase approximation (RPA) response function predicts an enhancement of the cross sections around a momentum transfer of q ? 1.7 fm-1, and it gives a reasonable agreement with the data.

Wakasa, T.; Berg, G. P. A.; Fujimura, H.; Fujita, K.; Hatanaka, K.; Itoh, M.; Kamiya, J.; Kitamura, Y.; Obayashi, E.; Sakamoto, N.; Sakemi, Y.; Shimizu, Y.; Yoshida, H. P.; Sakaguchi, H.; Takeda, H.; Uchida, M.; Yasuda, Y.; Yosoi, M.; Kawabata, T.

2003-04-01

233

Angular correlation patterns in double Auger decay

The angular distribution of two emitted electrons in the double Auger process in atoms has been theoretically investigated. In particular, the double Auger decay of a 1s vacancy in Ne and a 2p vacancy in Ar is considered. In analogy with double photoionization, we present a convenient parametrization of the angular correlation patterns for all possible angular momenta of the

A N Grum-Grzhimailo; N M Kabachnik

2004-01-01

234

Double Auger decay in atoms: Probability and angular distribution

Within many-body perturbation theory (MBPT), the correlated decay of an inner-shell vacancy, namely, the double Auger effect, is considered. Expressions for the amplitude and probabilities are obtained in the lowest order of MBPT. The approximate formulas, in particular the ``shakeoff'' model, are discussed. The calculations are performed for the 1s-1-->2s-22p-1+q1+q2 transition in Ne. It is shown that the angular distribution

M. Ya. Amusia; I. S. Lee; V. A. Kilin

1992-01-01

235

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

236

Global uniform semiclassical approximation for Clebsch-Gordan coefficients

NASA Astrophysics Data System (ADS)

Semiclassical integral representations, analogous to initial value expressions for the propagator, are presented for the Clebsch-Gordan angular momentum coupling coefficients. Two forms (L and R types) of the approximation are presented. For each form, new non-Gaussian expressions, which are specifically adapted to the nature of angular momentum variables, are proposed in place of the familiar Gaussian coherent state functions. With these non-Gaussian kernels, it is found that the present treatments are capable of accuracy similar to that obtained from a uniform Airy approximation. Although the present semiclassical approximations involve only real-valued angle variables, associated with sets of angular momenta that are related by ordinary, real, classical transformations, the treatments produce accurate results not only for classically allowed choices of quantum numbers but also for very strongly classically forbidden values.

Engel, Hamutal; Kay, Kenneth G.

2008-03-01

237

Practical formula for the radiated angular momentum

NASA Astrophysics Data System (ADS)

We present a simple formula for the radiated angular momentum based on a spin-weighted spherical harmonic decomposition of the Weyl scalar ?4 representing outgoing radiation in the Kinnersley tetrad. We test our formula by measuring the radiated angular momentum from three simulations of nonspinning equal-mass black-hole binaries with orbital angular momentum aligned along the x, y, and z axes, respectively. We find that the radiated angular momentum agrees with the differences in the remnant horizon spins and the initial angular momentum for each system.

Lousto, Carlos O.; Zlochower, Yosef

2007-08-01

238

High-resolution measurement of the longitudinal profile of a relativistic electron beam is of utmost importance for linac based free-electron lasers and other advanced accelerator facilities that employ ultrashort bunches. In this paper, we investigate a novel scheme to measure ultrashort bunches (subpicosecond) with exceptional temporal resolution (hundreds of attoseconds) and dynamic range. The scheme employs two orthogonally oriented deflecting sections. The first imparts a short-wavelength (fast temporal resolution) horizontal angular modulation on the beam, while the second imparts a long-wavelength (slow) angular kick in the vertical dimension. Both modulations are observable on a standard downstream screen in the form of a streaked sinusoidal beam structure. We demonstrate, using scaled variables in a quasi-1D approximation, an expression for the temporal resolution of the scheme and apply it to a proof-of-concept experiment at the UCLA Neptune high-brightness injector facility. The scheme is also investigated for application at the SLAC NLCTA facility, where we show that the subfemtosecond resolution is sufficient to resolve the temporal structure of the beam used in the echo-enabled free-electron laser. We employ beam simulations to verify the effect for typical Neptune and NLCTA parameter sets and demonstrate the feasibility of the concept.

Andonian, G.; /UCLA /RadiaBeam Tech.; Hemsing, E.; /UCLA; Xiang, D.; /SLAC; Musumeci, P.; /UCLA; Murokh, A.; /RadiaBeam Tech.; Tochitsky, S.; /UCLA; Rosenzweig, J.B.; /UCLA

2012-05-03

239

Effects of merging histories on angular momentum distribution of dark matter haloes

NASA Astrophysics Data System (ADS)

The effects of merging histories of proto-objects on the angular momentum distributions of the present-time dark matter haloes are analysed. An analytical approach to the analysis of the angular momentum distributions assumes that the haloes are initially homogeneous ellipsoids and that the growth of the angular momentum of the haloes halts at their maximum expansion time. However, the maximum expansion time cannot be determined uniquely, because in the hierarchical clustering scenario each progenitor, or subunit, of the halo has its own maximum expansion time. Therefore the merging history of the halo may be important in estimating its angular momentum. Using the merger tree model by Rodrigues & Thomas, which takes into account the spatial correlations of the density fluctuations, we have investigated the effects of the merging histories on the angular momentum distributions of dark matter haloes. It was found that the merger effects, that is, the effects of the inhomogeneity of the maximum expansion times of the progenitors which finally merge together into a halo, do not strongly affect the final angular momentum distributions, so that the homogeneous ellipsoid approximation happens to be good for the estimation of the angular momentum distribution of dark matter haloes. This is because the effect of the different directions of the angular momenta of the progenitors cancels out the effect of the inhomogeneity of the maximum expansion times of the progenitors. The contribution of the orbital angular momentum to the total angular momentum when two or more pre-existing haloes merge together was also investigated. It is shown that this contribution is more important than that of the angular momentum of diffuse accreting matter to the total angular momentum, especially when the mergers occur many times.

Nagashima, Masahiro; Gouda, Naoteru

1998-12-01

240

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

241

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

242

Optical Diffractive Memories: Angular Selectivity and Diffraction Efficiency in Dichromated Gelatin

Two thousand images of resolution 512×512 pixels as a regular matrix pattern of 10×10 elements are stored, where each element is angularly multiplexed 20 times in a 25 ?m thickness of dichromated gelatin emulsion without cross-talk effect. The surface area of the matrix is 1 cm2. We show good concordance of the angular selectivity between the experimental result and theory.

Harry Ramenah; Poul Bertrand; Patrick Meyrueis

1995-01-01

243

Polynomial Approximation: The Weierstrass Approximation Theorem.

National Technical Information Service (NTIS)

In this paper we will look at three proofs of the Weierstrass Approximation Theorem. The first proof is in much the same form in which Weierstrass originally proved his theorem. The next is due to Lebesgue. It is by far the easiest proof to follow, with o...

S. J. Nichols

1982-01-01

244

Multivariate Padé approximants revisited

Several definitions of multivariate Padé approximants have been introduced during the last decade. We will here consider all types of definitions based on the choice that the coefficients in numerator and denominator of the multivariate Padé approximant are defined by means of a linear system of equations. In this case a determinant representation for the multivariate Padé approximant exists. We

Annie Cuyt

1986-01-01

245

Quasicrystals and crystalline approximants

Over the past seven years, many examples of periodic crystals closely related to quasicrystalline alloys have been discovered. These crystals have been termed approximants, since the arrangements of atoms within their unit cells closely approximate the local atomic structures in quasicrystals. This colloquium focuses on these approximant structures, their description, and their relationship to quasicrystals.

A. I. Goldman; R. F. Kelton

1993-01-01

246

Approximate Posterior Distributions

This paper proposes the use of approximate posterior distributions resulting from operational prior distributions chosen with regard to the realized likelihood function. L.J. Savage's precise measurement is generalized for approximation in terms of an arbitrary operational prior density, including mixed-type prior distributions with positive probabilities on singular subsets. A new approximation is also given relating such distributions to absolutely continuous

James M. Dickey

1976-01-01

247

NASA Astrophysics Data System (ADS)

Approximation of laws is an important theme in the philosophy of science. If we can make sense of the idea that two scientific laws are "close" to each other, then we can also analyze such methodological notions as approximate explanation of laws, approximate reduction of theories, approximate empirical success of theories, and approximate truth of laws. Proposals for measuring the distance between quantitative scientific laws were given in Niiniluoto (1982, 1987). In this paper, these definitions are reconsidered as a response to the interesting critical remarks by Liu (1999).

Niiniluoto, Ilkka

2014-03-01

248

Over-cosine angular distributions of sputtered atoms at normal incidence

NASA Astrophysics Data System (ADS)

The angular distribution of sputtered atoms for normal incidence ions has been investigated theoretically and by computer simulation. For low energy ions the angular distribution is under-cosine, while for relatively high energy ions we obtain an over-cosine angular distribution for the sputtered atoms. It is found that the outward-peakness of the angular distribution for relatively high energy ions is due to the geometrical asymmetry near the surface. Using the Monte Carlo simulation code ACAT, which is based on the binary collision approximation, the angular distributions of sputtered atoms are calculated for various incident energies of Ar ions incident normally on an Fe target. It is found that one needs to take into account the surface roughness in order to obtain good agreement with experiment. The surface roughness is believed to reduce the degree of the over-cosine distribution because a rough surface has a larger effective surface area as compared with an unirradiated surface.

Yamamura, Y.; Muraoka, K.

1989-06-01

249

Tunneling probability: an evaluation of different approximations

NASA Astrophysics Data System (ADS)

Before the recent developments in the quantum-defect theoryootnotetextB. Gao, Phys. Rev. A 78, 012702 (2008). and the related analytic solutions for 1/r^n type of long-range potentials, there were virtually no exact result of tunneling for physically realistic systems, which made the evaluation of different approximations, such as the ubiquitous semiclassical approximation, difficult. By comparing with the exact analytic results of tunneling for -1/r^6 and -1/r^4 types of potentials, we carefully evaluate the validity of the semiclassical and the top-of-barrierootnotetextS. J. Ward and J. H. Macek, Phys. Rev. A 62, 052715 (2000). approximations for tunneling through the angular momentum barrier in atom-atom, ion-atom, and electron-atom interactions.

Li, Ming; Makrides, Constantinos; Gao, Bo

2010-03-01

250

Photoelectron angular distributions: energy dependence for s subshells

An overview of the theory of photoelectron angular distributions for atoms is presented. Its features, which are embodied in a single asymmetry parameter ..beta.. in the electric dipole approximation, are examined within the framework of the angular momentum transfer formulation. The ..beta.. parameter is in principle always energy dependent. Within the LS coupling approximation, however, there are instances, each representing a multitude of particular photoionization processes, in which ..beta.. is an analytically determined constant. The energy dependence of the ..beta.. parameters in such instances is due entirely to spin-orbit and other relativistic interactions. It is shown that the asymmetry parameters for atomic s subshells are particularly suitable for distinguishing between purely geometrical effects on the photoelectron angular distribution, resulting from physical conservation laws, and dynamical effects arising from relativistic interactions and electron exchange and correlation. In general, the ..beta.. parameters for s subshells vary with energy; such variation is largest near minima in the cross sections for the corresponding photoelectron channels and in the vicinity of resonances. However, a number of atomic photoionization transitions are identified for which ..beta.. would be a constant (equal to one of the three values 2, 1/5, or -1) were it not for relativistic interactions and (in some cases) final-state interchannel coupling and/or initial-state electron correlations. Measurement or calculation of the ..beta.. parameters for such transitions thus provides a sensitive measure of the strength of relativistic interactions as well as of electron correlations.

Manson, S.T.; Starace, A.F.

1982-04-01

251

Practical formula for the radiated angular momentum

We present a simple formula for the radiated angular momentum based on a spin-weighted spherical harmonic decomposition of the Weyl scalar representing outgoing radiation in the Kinnersley tetrad. We test our formula by measuring the radiated angular momentum from three simulations of nonspinning equal-mass-black-hole binaries with orbital angular momentum aligned along the x, y, and z axes, respectively. We find

Carlos O. Lousto; Yosef Zlochower

2007-01-01

252

Practical formula for the radiated angular momentum

We present a simple formula for the radiated angular momentum based on a spin-weighted spherical harmonic decomposition of the Weyl scalar psi4 representing outgoing radiation in the Kinnersley tetrad. We test our formula by measuring the radiated angular momentum from three simulations of nonspinning equal-mass black-hole binaries with orbital angular momentum aligned along the x, y, and z axes, respectively.

Carlos O. Lousto; Yosef Zlochower

2007-01-01

253

Measurement of polarization with the Degree Angular Scale Interferometer.

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

254

Angularly resolved light scattering from aerosolized spores: observations and calculations.

Angularly resolved elastic light scattering patterns from individual aerosolized Bacillus subtilis spores were qualitatively compared with simulations. Two-dimensional angular optical scattering patterns of the spores were collected for polar scattering angles varying from approximately 77 degrees to 130 degrees and azimuthal angles varying from 0 degrees to 360 degrees . Computations were performed with single T-matrix formalism by simulating a spore with three different particle shapes: (1) a finite-length cylinder with spherical end caps, (2) a spheroid, and (3) two spheres in contact. Excellent agreement between computation and measurement was found for the finite-length cylinder with spherical end caps, poorer agreement was found for the spheroids, and the poorest agreement was for the two spheres in contact. PMID:18026307

Auger, Jean-Claude; Aptowicz, Kevin B; Pinnick, Ronald G; Pan, Yong-Le; Chang, Richard K

2007-11-15

255

Quantitative phase-contrast microscopy by angular spectrum digital holography

NASA Astrophysics Data System (ADS)

Techniques of digital holography are improved in order to obtain high-resolution, high-fidelity images of quantitative phase-contrast microscopy. In particular, the angular spectrum method of calculating the holographic optical field is seen to have several advantages over the more commonly used Fresnel transformation or Huygens convolution method. Spurious noise and interference components can be tightly controlled through the analysis and filtering of the angular spectrum. The reconstruction distance does not have a lower limit and the off-axis angle between the object and reference can be lower than the Fresnel requirement and still be able to cleanly separate out the zero-order background. Holographic phase images are largely immune from the coherent noise common in amplitude images. Together with the use of a miniature pulsed laser, the resulting images have 0.5?m diffraction-limited lateral resolution and the phase profile is accurate to about 30 nm of optical path length. SKOV-3 (ovarian cancer cells) and HUVEC (human umbilical vein endothelial cells) are imaged that display intra-cellular and intra-nuclear organelles with clarity and quantitative accuracy. The technique clearly exceeds currently available methods in phase-contrast optical microscopy in the level of resolution and detail, and provides a new modality for imaging morphology of cellular and intracellular structures that is not currently available.

Mann, C. J.; Kim, M. K.

2006-03-01

256

Approximations of satellite stability

NASA Technical Reports Server (NTRS)

Modifications and corrections are presented to relations obtained in an investigation conducted by Szebehely (1978), who has discussed the problem of Hill's (1878) stability of satellites in the restricted problem of three bodies. Attention is given to an approximation of the Jacobian constant for the satellite, the critical value of the Jacobian constant, and approximate solutions.

Markellos, V. V.; Szebehely, V.

1981-01-01

257

National Technical Information Service (NTIS)

In order to analyze the accuracy of a fixed, finite-dimensional approximation space which is not uniform over its domain Omega, we define approximation error map, a description of how the error is distributed over Omega-not for a single test function but ...

A. Gomide J. Stolfi

2001-01-01

258

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

259

Approximation of Hopf bifurcation

Summary We make several assumptions on a nonlinear evolution problem, ensuring the existence of a Hopf bifurcation. Under a fairly general approximation condition, we define a discrete problem which retains the bifurcation property and we prove an error estimate between the branches of exact and approximate periodic solutions.

C. Bernardi; M. Curie

1982-01-01

260

Geometric Approximation via Coresets

The paradigm of coresets has recently emerged as a powerful tool for eciently approximating various extent measures of a point set P. Using this paradigm, one quickly computes a small subset Q of P, called a coreset, that approximates the original set P and and then solves the problem on Q using a relatively inecient algorithm. The solution for Q

PANKAJ K. AGARWAL; SARIEL HAR-PELED; KASTURI R. VARADARAJAN

261

Imaging the Earth's Interior: the Angular Distribution of Terrestrial Neutrinos

NASA Astrophysics Data System (ADS)

Decays of radionuclides throughout the earths interior produce geothermal heat, but also are a source of antineutrinos; these geoneutrinos are now becoming observable in experiments such as KamLAND. The (angle-integrated) geoneutrino flux has been shown to provide a unique probe of geothermal heating due to decays, and an integral constraint on the distribution of radionuclides in the earth. In this paper, we calculate the angular distribution of geoneutrinos, which opens a window on the differential radial distribution of terrestrial radionuclides. We develop the general formalism for the neutrino angular distribution. We also present the inverse transformation which recovers the terrestrial radioisotope distribution given a measurement of the neutrino angular distribution. Thus, geoneutrinos not only allow a means to image the earths interior, but offer a direct measure of the radioactive earth, both revealing the earths inner structure as probed by radionuclides, and allowing a complete determination of the radioactive heat generation as a function of radius. Turning to specific models, we emphasize the very useful approximation in which the earth is modeled as a series of shells of uniform density. Using this multishell approximation, we present the geoneutrino angular distribution for the favored earth model which has been used to calculate the geoneutrino flux. In this model the neutrino generation is dominated by decays of potassium, uranium, and thorium in the earths mantle and crust; this leads to a very peripheral angular distribution, in which 2/3 of the neutrinos come from angles ? ? 60° away from the nadir. We note that a measurement of the neutrino intensity in peripheral directions leads to a strong lower limit to the central intensity. We briefly discuss the challenges facing experiments to measure the geoneutrino angular distribution. Currently available techniques using inverse beta decay of protons require a (for now) unfeasibly large number of events to recover with confidence the forward scattering signal from the background of subsequent elastic scatterings. Nevertheless, it is our hope that future large experiments, and/or more sensitive techniques, can resolve an image of the earths radioactive interior.

Fields, Brian D.; Hochmuth, Kathrin A.

2006-12-01

262

MEASURING GAS ACCRETION AND ANGULAR MOMENTUM NEAR SIMULATED SUPERMASSIVE BLACK HOLES

Using cosmological simulations with a dynamic range in excess of 10{sup 7}, we study the transport of gas mass and angular momentum through the circumnuclear region of a disk galaxy containing a supermassive black hole (SMBH). The simulations follow fueling over relatively quiescent phases of the galaxy's evolution (no mergers) and without feedback from active galactic nuclei (AGNs), as part of the first stage of using state-of-the-art, high-resolution cosmological simulations to model galaxy and black hole co-evolution. We present results from simulations at different redshifts (z = 6, 4, and 3) and three different black hole masses (3 x 10{sup 7}, 9 x 10{sup 7}, and 3 x 10{sup 8} M{sub sun}; at z = 4), as well as a simulation including a prescription that approximates optically thick cooling in the densest regions. The interior gas mass throughout the circumnuclear disk shows transient and chaotic behavior as a function of time. The Fourier transform of the interior gas mass follows a power law with slope -1 throughout the region, indicating that, in the absence of the effects of galaxy mergers and AGN feedback, mass fluctuations are stochastic with no preferred timescale for accretion over the duration of each simulation ({approx}1-2 Myr). The angular momentum of the gas disk changes direction relative to the disk on kiloparsec scales over timescales less than 1 Myr, reflecting the chaotic and transient gas dynamics of the circumnuclear region. Infalling clumps of gas, which are driven inward as a result of the dynamical state of the circumnuclear disk, may play an important role in determining the spin evolution of an SMBH, as has been suggested in stochastic accretion scenarios.

Levine, Robyn [CITA, 60 St. George St., Toronto, ON, M5S 3H8 (Canada); Gnedin, Nickolay Y. [Particle Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Hamilton, Andrew J. S., E-mail: levine@cita.utoronto.c [JILA, University of Colorado, Boulder, CO 80309 (United States)

2010-06-20

263

Amplified dispersive delay generator using angular dispersion amplification.

Angular dispersion amplification can be used to design compact dispersive delay generators with delay amplification. A specific design is presented that can be used to generate 1 ns delay for two wavelengths separated by 1 nm. The delay generator can be easily switched from a positive to a negative group velocity delay and can be used as a pulse compressor, a pulse stretcher, or a pulse shaper in chirped pulse amplification, high-resolution time-gated spectroscopy as well as other applications. PMID:19823234

Basu, Santanu

2009-10-10

264

Pendulum Micromechanical Angular Accelerometer with Force Feedback

This paper bring forward a kind of pendulum micromechanical angular accelerometer with force feedback, which might be proposed by us, first. The sensor adopts a pendulum with mass joined to the anchors by a pair torsion-spring beams as sensing device, differential-capacitor device for detecting the angular acceleration about the X axis, an electrostatic force device for feedback loop. The sensor's

Li Jianli; Fang Jiancheng; Sheng Wei

2007-01-01

265

Angular momentum in the global atmospheric circulation

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

266

Angular momenta of modeled ocean gyres

Total angular momentum of fluid within an ocean basin consists of a part due to center of mass of the fluid rotating about Earth's axis and a part due to relative motion within the basin. In rotating planar geometry (f plane) the relative angular momentum due to motion within a basin can be expressed as an integral of mass transport

Greg Holloway; Peter Rhines

1991-01-01

267

Harmonized Profiloplasty Using Balanced Angular Profile Analysis

To evaluate outcomes of aesthetic facial plastic surgery objectively the authors developed a photogrammetric profile analysis method, which they call balanced angular profile analysis (BAPA). To develop standards and ways to determine the conformation of various soft tissue segments analytically, 19 mean angular values acquired from the photographs of 71 famous female models (53 Eastern models and 18 Western models)

Heung Sik Park; Seung Chul Rhee; So Ra Kang; Ji Hyuck Lee

2004-01-01

268

Stellar angular diameters from occultation observations.

NASA Astrophysics Data System (ADS)

This paper reviews the history of measuring stellar angular diameters from lunar occultation observations and the techniques of data analysis. Several effects which can affect the results of measurement are discussed. The author finds that there may be systematic errors in angular diameters measured by various observatories for Aldebaran.

Qian, B.-C.

269

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

270

Selection Sample Size Approximations.

National Technical Information Service (NTIS)

Two conservative sample size approximations are given for the Bechhofer formulation of the problem of selecting the population with the largest mean, when the populations have a common known variance. A table of numerical comparisons of these approximatio...

J. S. Ramberg

1972-01-01

271

Angular behavior of synchrotron radiation harmonics

NASA Astrophysics Data System (ADS)

The detailed analysis of angular dependence of the synchrotron radiation (SR) is presented. Angular distributions of linear and circular polarization integrated over all harmonics, well known for relativistic electron energies, are extended to include radiation from electrons that are not fully relativistic. In particular, we analyze the angular dependence of the integral SR intensity and peculiarities of the angular dependence of the first harmonics SR. Studying spectral SR intensities, we have discovered their unexpected angular behavior, completely different from that of the integral SR intensity; namely, for any given synchrotron frequency, maxima of the spectral SR intensities recede from the orbit plane with increasing particle energy. Thus, in contrast with the integral SR intensity, the spectral ones have the tendency to deconcentrate themselves on the orbit plane.

Bagrov, V. G.; Bulenok, V. G.; Gitman, D. M.; Jara, Jose Acosta; Tlyachev, V. B.; Jarovoi, A. T.

2004-04-01

272

Amplification of Angular Rotations Using Weak Measurements

NASA Astrophysics Data System (ADS)

We present a weak measurement protocol that permits a sensitive estimation of angular rotations based on the concept of weak-value amplification. The shift in the state of a pointer, in both angular position and the conjugate orbital angular momentum bases, is used to estimate angular rotations. This is done by an amplification of both the real and imaginary parts of the weak-value of a polarization operator that has been coupled to the pointer, which is a spatial mode, via a spin-orbit coupling. Our experiment demonstrates the first realization of weak-value amplification in the azimuthal degree of freedom. We have achieved effective amplification factors as large as 100, providing a sensitivity that is on par with more complicated methods that employ quantum states of light or extremely large values of orbital angular momentum.

Magańa-Loaiza, Omar S.; Mirhosseini, Mohammad; Rodenburg, Brandon; Boyd, Robert W.

2014-05-01

273

NASA Technical Reports Server (NTRS)

Much of human reasoning is approximate in nature. Formal models of reasoning traditionally try to be precise and reject the fuzziness of concepts in natural use and replace them with non-fuzzy scientific explicata by a process of precisiation. As an alternate to this approach, it has been suggested that rather than regard human reasoning processes as themselves approximating to some more refined and exact logical process that can be carried out with mathematical precision, the essence and power of human reasoning is in its capability to grasp and use inexact concepts directly. This view is supported by the widespread fuzziness of simple everyday terms (e.g., near tall) and the complexity of ordinary tasks (e.g., cleaning a room). Spatial reasoning is an area where humans consistently reason approximately with demonstrably good results. Consider the case of crossing a traffic intersection. We have only an approximate idea of the locations and speeds of various obstacles (e.g., persons and vehicles), but we nevertheless manage to cross such traffic intersections without any harm. The details of our mental processes which enable us to carry out such intricate tasks in such apparently simple manner are not well understood. However, it is that we try to incorporate such approximate reasoning techniques in our computer systems. Approximate spatial reasoning is very important for intelligent mobile agents (e.g., robots), specially for those operating in uncertain or unknown or dynamic domains.

Dutta, Soumitra

1988-01-01

274

Asymptotic Diffusion-Limit Accuracy of Sn Angular Differencing Schemes

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

275

Very High Resolution Solar X-ray Imaging Using Diffractive Optics

NASA Technical Reports Server (NTRS)

This paper describes the development of X-ray diffractive optics for imaging solar flares with better than 0.1 arcsec angular resolution. X-ray images with this resolution of the greater than or equal to 10 MK plasma in solar active regions and solar flares would allow the cross-sectional area of magnetic loops to be resolved and the coronal flare energy release region itself to be probed. The objective of this work is to obtain X-ray images in the iron-line complex at 6.7 keV observed during solar flares with an angular resolution as fine as 0.1 arcsec - over an order of magnitude finer than is now possible. This line emission is from highly ionized iron atoms, primarily Fe xxv, in the hottest flare plasma at temperatures in excess of approximately equal to 10 MK. It provides information on the flare morphology, the iron abundance, and the distribution of the hot plasma. Studying how this plasma is heated to such high temperatures in such short times during solar flares is of critical importance in understanding these powerful transient events, one of the major objectives of solar physics.We describe the design, fabrication, and testing of phase zone plate X-ray lenses with focal lengths of approximately equal to 100 m at these energies that would be capable of achieving these objectives. We show how such lenses could be included on a two-spacecraft formation-flying mission with the lenses on the spacecraft closest to the Sun and an X-ray imaging array on the second spacecraft in the focal plane approximately equal to 100 m away. High resolution X-ray images could be obtained when the two spacecraft are aligned with the region of interest on the Sun. Requirements and constraints for the control of the two spacecraft are discussed together with the overall feasibility of such a formation-flying mission.

Dennis, B. R.; Skinner, G. K.; Li, M. J.; Shih, A. Y.

2012-01-01

276

High Resolution Imaging of Circumstellar Disks at Millimeter Wavelengths

NASA Technical Reports Server (NTRS)

We summarize progress on our program to use high angular resolution imaging of thermal dust continuum emission at millimeter and submillimeter wavelengths to probe the structure of protoplanetary disks and debris disks around nearby stars.

Wilner, David J.

2004-01-01

277

Hybridization of angular-momentum eigenstates in nonspherical sodium clusters

NASA Astrophysics Data System (ADS)

Angle-resolved photoelectron spectra of low-temperature sodium clusters Na33- and Na34- have been measured as a function of photon energy. The experiments in combination with density functional theory calculations demonstrate that despite the strongly oblate shape of the clusters, most of the occupied valence orbitals are close to angular-momentum eigenstates. Some states, however, exhibit a strongly mixed character. This mixing follows the selection rules ?l=ą2 and ?m=0, which result from the approximate symmetry of the cluster deformation.

Bartels, C.; Hock, C.; Kuhnen, R.; Walter, M.; v. Issendorff, B.

2013-10-01

278

Frequency dependence of photoelectron angular distributions in small Na clusters

NASA Astrophysics Data System (ADS)

We investigate from a theoretical perspective photoelectron angular distributions (PADs) in small Na clusters in relation to recently available experimental results. We consider various (increasingly refined) levels of theory in order to better understand relevant physical trends. It is found that PADs are extremely sensitive to all details of the modeling such that a detailed description of the final state and the ionic background is necessary. Finally, we compare the theoretical description with recent experimental data on the cluster anion Na7- and find a satisfying agreement for full time-dependent local-density approximation (TDLDA) with ionic background.

Wopperer, P.; Dinh, P. M.; Suraud, E.; Reinhard, P.-G.

2012-01-01

279

A new all-digital time differential ?-? angular correlation spectrometer

NASA Astrophysics Data System (ADS)

A new digital time differential perturbed angular correlation spectrometer, designed to measure the energy of and coincidence time between correlated detector signals, here correlated ? photons, is presented. The system overcomes limitations of earlier digital approaches and features improved performance and handling. By consequently separating the data recording and evaluation, it permits the simultaneous measurement of decays with several ?-ray cascades at once and avoids the necessity of premeasurement configuration. Tests showed that the spectrometer reaches a time resolution of 460 ps [using a 60Co sample and Lu1.8Y0.2SiO5:Ce (LYSO) scintillators, otherwise better than 100 ps], an energy resolution that is equivalent to the limit of the used scintillation material, and a processing capability of more than 200 000 ? quanta per detector and second. Other possible applications of the presented methods include nuclear spectroscopy, positron emission tomography, time of flight studies, lidar, and radar.

Nagl, Matthias; Vetter, Ulrich; Uhrmacher, Michael; Hofsäss, Hans

2010-07-01

280

Approximation for the Rayleigh Resolution of a Circular Aperture.

National Technical Information Service (NTIS)

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 ...

C. E. Mungan

2009-01-01

281

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

282

The angular spectrum approach is evaluated for the simulation of focused ultrasound fields produced by large thermal therapy arrays. For an input pressure or normal particle velocity distribution in a plane, the angular spectrum approach rapidly computes the output pressure field in a three dimensional volume. To determine the optimal combination of simulation parameters for angular spectrum calculations, the effect of the size, location, and the numerical accuracy of the input plane on the computed output pressure is evaluated. Simulation results demonstrate that angular spectrum calculations performed with an input pressure plane are more accurate than calculations with an input velocity plane. Results also indicate that when the input pressure plane is slightly larger than the array aperture and is located approximately one wavelength from the array, angular spectrum simulations have very small numerical errors for two dimensional planar arrays. Furthermore, the root mean squared error from angular spectrum simulations asymptotically approaches a nonzero lower limit as the error in the input plane decreases. Overall, the angular spectrum approach is an accurate and robust method for thermal therapy simulations of large ultrasound phased arrays when the input pressure plane is computed with the fast nearfield method and an optimal combination of input parameters.

Zeng, Xiaozheng; McGough, Robert J.

2009-01-01

283

The angular spectrum approach is evaluated for the simulation of focused ultrasound fields produced by large thermal therapy arrays. For an input pressure or normal particle velocity distribution in a plane, the angular spectrum approach rapidly computes the output pressure field in a three dimensional volume. To determine the optimal combination of simulation parameters for angular spectrum calculations, the effect of the size, location, and the numerical accuracy of the input plane on the computed output pressure is evaluated. Simulation results demonstrate that angular spectrum calculations performed with an input pressure plane are more accurate than calculations with an input velocity plane. Results also indicate that when the input pressure plane is slightly larger than the array aperture and is located approximately one wavelength from the array, angular spectrum simulations have very small numerical errors for two dimensional planar arrays. Furthermore, the root mean squared error from angular spectrum simulations asymptotically approaches a nonzero lower limit as the error in the input plane decreases. Overall, the angular spectrum approach is an accurate and robust method for thermal therapy simulations of large ultrasound phased arrays when the input pressure plane is computed with the fast nearfield method and an optimal combination of input parameters. PMID:19425640

Zeng, Xiaozheng; McGough, Robert J

2009-05-01

284

Two-dimensional electron angular distributions from aligned molecules

NASA Astrophysics Data System (ADS)

We report the measurement of 2D electron angular distributions from multiphoton single ionization of aligned CS2 molecules. CS2 molecules were cooled in a supersonic expansion and aligned non-adiabatically using a Ti:Sapphire laser pulse (800 nm, 0.5 ps, 2.9x10^12 W/cm^2) without significant ionization, and a time-delayed second pulse (25 fs, 7.7x10^13 W/cm^2 ) was used to singly ionize the molecules at best alignment at the first half-revival. 2D electron momentum spectra were measured using velocity map imaging as a function of angle between the alignment axis and the polarization vector of the ionizing pulse. The angular distribution was found to depend significantly on this angle. Calculations using molecular strong-field approximation were found to account for some, but not all, of the features seen in the experiment. The measurement of molecular-frame photoelectron angular distributions provides new challenges and more stringent tests for theoretical description of molecular ionization by intense lasers.

Kumarappan, Vinod; Holmegaard, Lotte; Martiny, Christian; Madsen, Christian; Kjeldsen, Thomas; Viftrup, Simon; Madsen, Lars; Stapelfeldt, Henrik

2008-05-01

285

The Stellar Angular Correlation: Clues to Wide Binary Star Properties

NASA Astrophysics Data System (ADS)

The angular distribution of stars brighter than visual magnitude 14 is analyzed for evidence of gravitationally bound systems with widely separated components. Binary stars with separations on the order of 0.1 parsec are interesting as probes of Galactic dynamics, disk dark matter, the Oort comet cloud, and the postulated solar companion star, Nemesis. Catalogs of stars, complete to a resolution limit of four arcseconds, were constructed from digitized Schmidt telescope plates covering over 600 square degrees of the sky in four directions. I analyze the clustering properties of stars and star pairs using two-point and three-point angular correlation functions. Significant correlation (assumed to be due to binary stars) is detected only for angular separations less than 40 arcseconds. No significant numbers of ternary systems are detected. Employing a modified Wasserman-Weinberg technique, I directly compare the angular correlation functions with a simple model of wide binary star properties. The wide binary semimajor axis distribution at low Galactic latitudes is best described as a single power law of index -1.3. Near the North Galactic Pole (NGP), the power law is less steep and the distribution is consistent with a cutoff near 0.1~parsec. The derived wide binary density is unrealistically large, suggesting that the basic model inadequately characterizes wide binary properties. I also study a sample of stars from the Space Telescope Guide Star Catalog (GSC). The region analyzed lies within thirty degrees of the NGP and covers 2500 square degrees of sky. This large, low-resolution sample complements the smaller, more uniform plate catalogs. I identify many systematic errors in the GSC and attempt to account for image misclassifications and poorly defined resolution limits. The corrected stellar correlation function from the GSC is found to be consistent with a wide binary separation cutoff near 0.1parsec. The dissolution of a poor Galactic cluster at the NGP may explain the observed wide binary distribution in that direction. Evidence for weak clustering on scales of one degree is seen in the pair-pair correlation function. The unphysically large wide binary density derived from magnitude-limited samples is explained well by a luminosity correlation between the binary components. An alternative solution requires all F to K dwarfs to be members of wide binaries. Based on the observed properties of wide binary stars, the probability that the Sun has a stellar companion capable of inducing periodic mass extinctions on Earth is only 0.05 percent. In an analogy with Oort cloud dynamics, I suggest a mechanism that can substantially reduce the number of wide binaries with separations greater than 0.1 parsec. (SECTION: Dissertation Abstracts)

Garnavich, Peter M.

1993-03-01

286

The stellar angular correlation: Clues to wide binary star properties

NASA Astrophysics Data System (ADS)

The angular distribution of stars brighter than visual magnitude 14 is analyzed for evidence of gravitationally bound systems with widely separated components. Binary stars with separations on the order of 0.1 parsec are interesting as probes of Galactic dynamics, disk dark matter, the Oort comet cloud and the postulated Solar compannion star, Nemesis. Catalogs of stars, complete to a resolution limit of four arcseconds, were constructed from digitized Schmidt telescope plates covering over 600 square degrees of the sky in four directions. I analyze the clustering properties of stars and star pairs using two-point and three-point angular correlation functions. Significant correlation (assumed to be due to binary stars) is detected only for angular separations less than 40 arcseconds. No significant numbers of ternary systems are detected. Employing a modified Wasserman-Weinberg technique, I directly compare the angular correlation functions with a simple model of wide binary star properties. The wide binary semimajor axis distribution at low Galactic latitudes is best described as a single power law of index -1.3. Near the north Galactic pole (NGP), the power law is less steep and the distribution is consistent with a cutoff near 0.1 parsec. The derived wide binary density is unrealistically large, suggesting that the basic model inadequately characterizes wide binary properties. I also study a sample of stars from the Space Telescope Guide Star Catalog (GSC). The region analyzed lies within thirty degrees of the NGP and covers 2500 square degrees of sky. This large, low resolution sample complements the smaller, more uniform plate catalogs. I identify many systematic errors in the GSC and attempt to account for image misclassifications and poorly defined resolution limits. The corrected stellar correlation function from the GSC is found to be consistent with a wide binary separation cutoff 0.1 parsec. The dissolution of a poor Galactic cluster at the NGP may explain the observed wide binary distribution in that direction. Evidence for weak clustering on scales of one degree is seen in the pair-pair correlation function. The unphysically large wide binary density derived from magnitude-limited samples is explained well by luminosity correlation between the binary components.

Garnavich, Peter Marcus

287

Calculate engine crankshaft angular acceleration based on original flywheel data

This paper presented a new method to obtain crankshaft angular acceleration using MATLAB. The original flywheel data was processed through a self-developed MATLAB code to generate crankshaft angular velocity which was differentiated to generate crankshaft angular acceleration. High frequency components in angular acceleration were eliminated through a zero-phase IIR low pass filter. The angular acceleration obtained using MATLAB code was

Longxin Zhen; Zijun An; Qiang Li; Baocheng Wang

2010-01-01

288

Longitudinal write-process modeling including measured angular-dependent coercivity

NASA Astrophysics Data System (ADS)

Recent angular VSM measurements indicate that the remanent coercivity of various types of longitudinal media has an applied field angular dependence that approximates the behavior of Stoner-Wohlfarth particles with easy axes oriented isotropically in-plane. This is in contrast to the Kondorsky style switching (in-plane field, domain wall switching) inherently assumed in most models of the write process. In this article, we incorporate the measured angular dependent switching into a Williams-Comstock style write model. We find that the vertical spacing dependence of the transition width or ``a'' parameter can be much lower than that expected when only the in-plane component of the head field participates in switching the media. This phenomena is verified experimentally by writing at different spacings and reading at a constant spacing. We find that the experimental data can only be matched if the measured angular dependent switching is taken into account.

Olson, Terry; Hsiao, Wenchien; Lu, Danzhu

2003-05-01

289

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

290

The digital measurement of low values of angular velocity and acceleration

An algorithm and the microprocessor implementation thereof for the measurement of angular velocity and acceleration of rotating machinery are presented. The speed reference signal is derived from a pulse train at a frequency of only one pulse per revolution. This fact places severe constraints on the resolution and measuring time of the instrument. To detect a rate of change of

G. P. Hancke; C. F. T. Viljoen

1990-01-01

291

Dynamical Cluster Approximation

NASA Astrophysics Data System (ADS)

The dynamical cluster approximation (DCA) is a method which systematically incorporates nonlocal corrections to the dynamical mean-field approximation. Here we present a pedagogical discussion of the DCA by describing it as a ?-derivable coarse-graining approximation in k-space, which maps an infinite lattice problem onto a periodic finite-sized cluster embedded in a self-consistently determined effective medium. We demonstrate the method by applying it to the two-dimensional Hubbard model. From this application, we show evidences of the presence of a quantum critical point (QCP) at a finite doping underneath the superconducting dome. The QCP is associated with the second-order terminus of a line of first order phase separation transitions. This critical point is driven to zero temperature by varying the band parameters, generating the QCP. The effect of the proximity of the QCP to the superconducting dome is also discussed.

Fotso, H.; Yang, S.; Chen, K.; Pathak, S.; Moreno, J.; Jarrell, M.; Mikelsons, K.; Khatami, E.; Galanakis, D.

292

Nonlinear instabilities in ring-based vibratory angular rate sensors

NASA Astrophysics Data System (ADS)

Nonlinear dynamic response and associated instabilities of rotating thin circular rings for use in vibratory angular rate sensors is investigated via analytical and experimental methods. The governing equations of in-plane motion of rotating thin circular rings are developed via the Hamilton's principle for the purpose of investigating nonlinear dynamic behaviour and associated instabilities of rotating thin circular rings. Effects of input angular rate fluctuations have been incorporated in the model by considering the input angular rate as a time-periodic function. The derived ordinary differential equations represent a two-degree-of-freedom time-varying nonlinear gyroscopic system. The effect of imperfection due to the ring asymmetry is considered for quantifying its effects on the nonlinear dynamic response and associated instabilities. In addition, the effect of the elastic support of the ring, and the thermal expansion effect is included in the model. Nonlinear dynamic behaviour of the system which is subjected to external excitations is examined via analytical and experimental methods. When the ring is subjected to an input angular rate, the natural frequency variations caused by gyroscopic coupling in the system matrix have been investigated. Then, the approximate solutions obtained via the method of averaging have been shown to exhibit the presence of softening type of nonlinearities. A decoupling technique suitable for decoupling the gyroscopic coupling is employed in the present analysis. Further effect of sensor parameters, such as presence of mass mismatch, stiffness of elastic foundation, and presence of thermal expansion, are quantified. In addition, an experimental setup is built for examining the nonlinear dynamic behaviour of a rotating cylindrical structure. Using a precision rate table which is fitted with a slip ring and non-contact sensors/actuators, an experiment which closely represents the actual physical operating condition of angular rate sensors is developed. A thin cylindrical structure is employed for examining the nonlinear dynamic behaviour of rotating thin circular rings via experiments. Natural frequency variations due to the input angular rate changes are observed in the time and the frequency domains. Typical nonlinear phenomena of a rotating thin circular cylinder are observed experimentally. In particular, the jump phenomena and the presence of softening-type of nonlinearities are observed and have been compared with the theoretical predictions. The calculated predictions and measured values are generally found to be in good agreement. For the system under an influence of periodic input angular speed perturbations of small-intensity, nonlinear dynamic behaviour is investigated via an analytical method. Approximate steady state solutions and associated stability conditions are shown to depend on the excitation as well as system natural frequencies. The cases of subharmonic as well as combination resonance have been considered for this purpose. Subsequently, the presence of softening type of nonlinearity in the system is observed, and associated stability conditions are found and illustrated. Further effects of sensor parameters such as presence of mass mismatch and stiffness of elastic foundation, are quantified. Results from the present study, in particular, the effects of sensor parameters on the response and stability are expected to provide further insight into the design and operation of this class of devices. Keywords. nonlinear dynamic response; dynamic stability; rotating thin circular ring; MEMS angular rate sensor; gyroscopic system; method of averaging; external harmonic excitation; parametric harmonic perturbation.

Cho, Jihyun

293

Clustering, angular size, and dark energy

The influence of dark matter inhomogeneities on the angular size-redshift test is investigated for a large class of flat cosmological models driven by dark energy plus a cold dark matter component (XCDM). The results are presented in two steps. First, the mass inhomogeneities are modeled by a generalized Zeldovich-Kantowski-Dyer-Roeder distance which is characterized by a smoothness parameter {alpha}(z) and a power index {gamma}, and, second, we provide a statistical analysis to angular size data for a large sample of milliarcsecond compact radio sources. As a general result, we have found that the {alpha} parameter is totally unconstrained by this sample of angular-diameter data.

Santos, R. C.; Lima, J. A. S. [Departamento de Astronomia, Universidade de Sao Paulo, 05508-900 Sao Paulo, SP (Brazil)

2008-04-15

294

Wave angular momentum in nonneutral plasmas

Angular momentum and energy are added (or removed) when exciting a mode, such as a diocotron, Trivelpiece-Gould, or Dubin mode, and we discuss rates at which mode angular momentum and energy are added by applied fields. Excitation of a plasma mode is an effective way to transfer angular momentum and energy to the plasma because it is a resonant process. We relate this to recent experiments on compression and expansion of plasmas using a 'rotating wall' field. We also calculate the torque on a Coulomb crystal which is phase-locked to a 'rotating wall' field and describe phase oscillations and the maximum rate of acceleration which can be achieved.

Gould, Roy W. [California Institute of Technology, Pasadena, California 91125 (United States)

1999-12-10

295

Stellar accretion of matter possessing angular momentum

Observations of novae and theoretical results, in which the authors studied the nova outburst by radially accreting H-rich matter onto an He white dwarf, have convinced them that realistic nova models must be based on accretion that includes the angular momentum of the accreting matter. In the present paper the authors develop the theory of accretion onto stars of matter possessing angular momentum, including the shear forces between the accreting matter and the star (assumed to be nonrotating), distribution of accreted matter and its angular momentum by turbulent mixing, thermalizing of rotational kinetic energy, and loss of energy by horizontal expansion. 25 references.

Kutter, G.S.; Sparks, W.M.

1987-10-01

296

Clustering, angular size, and dark energy

NASA Astrophysics Data System (ADS)

The influence of dark matter inhomogeneities on the angular size-redshift test is investigated for a large class of flat cosmological models driven by dark energy plus a cold dark matter component (XCDM). The results are presented in two steps. First, the mass inhomogeneities are modeled by a generalized Zeldovich-Kantowski-Dyer-Roeder distance which is characterized by a smoothness parameter ?(z) and a power index ?, and, second, we provide a statistical analysis to angular size data for a large sample of milliarcsecond compact radio sources. As a general result, we have found that the ? parameter is totally unconstrained by this sample of angular-diameter data.

Santos, R. C.; Lima, J. A. S.

2008-04-01

297

Multicriteria approximation through decomposition

The authors propose a general technique called solution decomposition to devise approximation algorithms with provable performance guarantees. The technique is applicable to a large class of combinatorial optimization problems that can be formulated as integer linear programs. Two key ingredients of their technique involve finding a decomposition of a fractional solution into a convex combination of feasible integral solutions and devising generic approximation algorithms based on calls to such decompositions as oracles. The technique is closely related to randomized rounding. Their method yields as corollaries unified solutions to a number of well studied problems and it provides the first approximation algorithms with provable guarantees for a number of new problems. The particular results obtained in this paper include the following: (1) the authors demonstrate how the technique can be used to provide more understanding of previous results and new algorithms for classical problems such as Multicriteria Spanning Trees, and Suitcase Packing; (2) they also show how the ideas can be extended to apply to multicriteria optimization problems, in which they wish to minimize a certain objective function subject to one or more budget constraints. As corollaries they obtain first non-trivial multicriteria approximation algorithms for problems including the k-Hurdle and the Network Inhibition problems.

Burch, C. [Carnegie Mellon Univ., Pittsburgh, PA (United States). School of Computer Science; Krumke, S. [Univ. of Wuerzburg (Germany). Dept. of Computer Science; Marathe, M. [Los Alamos National Lab., NM (United States); Phillips, C. [Sandia National Labs., Albuquerque, NM (United States). Applied Mathematics Dept.; Sundberg, E. [Rutgers Univ., NJ (United States). Dept. of Computer Science

1998-06-01

298

Multicriteria approximation through decomposition

The authors propose a general technique called solution decomposition to devise approximation algorithms with provable performance guarantees. The technique is applicable to a large class of combinatorial optimization problems that can be formulated as integer linear programs. Two key ingredients of the technique involve finding a decomposition of a fractional solution into a convex combination of feasible integral solutions and devising generic approximation algorithms based on calls to such decompositions as oracles. The technique is closely related to randomized rounding. The method yields as corollaries unified solutions to a number of well studied problems and it provides the first approximation algorithms with provable guarantees for a number of new problems. The particular results obtained in this paper include the following: (1) The authors demonstrate how the technique can be used to provide more understanding of previous results and new algorithms for classical problems such as Multicriteria Spanning Trees, and Suitcase Packing. (2) They show how the ideas can be extended to apply to multicriteria optimization problems, in which they wish to minimize a certain objective function subject to one or more budget constraints. As corollaries they obtain first non-trivial multicriteria approximation algorithms for problems including the k-Hurdle and the Network Inhibition problems.

Burch, C. [Carnegie Mellon Univ., Pittsburgh, PA (United States). School of Computer Sciences]|[Sandia National Labs., Albuquerque, NM (United States); Krumke, S. [Univ. of Wuerzburg (Germany). Dept. of Computer Science; Marathe, M. [Los Alamos National Lab., NM (United States); Phillips, C. [Sandia National Labs., Albuquerque, NM (United States). Applied Mathematics Dept.; Sundberg, E. [Rutgers Univ., NJ (United States). Dept. of Computer Science]|[Sandia National Labs., Albuquerque, NM (United States)

1997-12-01

299

Multidimensional Stochastic Approximation Methods

Multidimensional stochastic approximation schemes are presented, and conditions are given for these schemes to converge a.s. (almost surely) to the solutions of $k$ stochastic equations in $k$ unknowns and to the point where a regression function in $k$ variables achieves its maximum.

Julius R. Blum

1954-01-01

300

Interpolation by Pade Approximants.

National Technical Information Service (NTIS)

The interpolation problem for error affected complex functions in order to best extrapolate them in the cutcomplex plane is studied. The methods used for interpolation are the diagonal and near-diagonal Pade approximants (PA) of the second type (PA2) and ...

N. Bogdanova F. Nichitiu

1983-01-01

301

About Accuracy and Approximation

NSDL National Science Digital Library

Students learn about the concepts of accuracy and approximation as they pertain to robotics, gain insight into experimental accuracy, and learn how and when to estimate values that they measure. Students also explore sources of error stemming from the robot setup and rounding numbers.

Applying Mechatronics to Promote Science (AMPS) GK-12 Program,

302

Approximating the Selection Process.

National Technical Information Service (NTIS)

The article describes research performed by the author on his own time in response to a problem posed by animal geneticists. The problem is that of approximating the consequences of the types of artificial selection to which domestic animals are subjected...

D. A. Harville

1969-01-01

303

Angular Momenta of Collided Rarefied Preplanetesimals

NASA Astrophysics Data System (ADS)

The angular momenta of rarefied preplanetesimals needed for formation of small-body binaries can be obtained at collisions of preplanetesimals. Trans-Neptunian objects, including trans-Neptunian binaries, could be formed from contracting rarefied preplanetesimals.

Ipatov, Sergei I.

2014-04-01

304

Angular distribution of atoms sputtered from alloys

NASA Astrophysics Data System (ADS)

The angular distribution of atoms sputtered from Co 5Sm alloy under 3 keV Ar + and 10 keV Xe + ion bombardment (normal incidence) has been studied experimentally. RBS was used to analyze a material deposited on a collector. The surface composition of Ni xPd y alloys ( x, y = 1, 3, 5) irradiated by 3 keV Ar + ions was also investigated in situ by Auger electron spectroscopy. Results of these measurements compared with our previous data on component angular distributions sputtered from Ni 5Pd alloy. Sm segregation was found to effect on component angular distributions sputtered from Co 5Sm alloy. It has been found by using AES that Pd segregates to the surface in Ni 5Pd-NiPd 3 alloys, while Ni - in NiPd 5 alloy. A new approach to description of component angular distributions sputtered from Ni xPd y and Co 5Sm alloys presented.

Chernysh, V. S.; Patrakeev, A. S.

2012-01-01

305

Anisotropic angular distribution of sputtered atoms

NASA Astrophysics Data System (ADS)

The sputtering yield angular distributions have been calculated on the basis of the ion energy dependence of total sputtering yields for Ni and Mo targets bombarded by low-energy Hg+ ions. The calculated curves show excellent agreement with the corresponding Wehner's experimental results of sputtering yield angular distributions. This fact clearly demonstrates the intrinsic relation between the ion energy dependence of total sputtering yields and the sputtering yield angular distribution. This intrinsic relation had been ignored in Yamamura's papers [Yamamura, Y. (1982). Theory of sputtering and comparison to experimental data, Nucl. Instr. and Meth. , 194 , 515-522; Yamamura, Y. (1981). Contribution of anisotropic velocity distribution of recoil atoms to sputtering yields and angular distributions of sputtered atoms, Rad. Eff. , 55 , 49-55.] due to some obvious mistakes.

Zhang, Z. L.; Zhang, L.

2004-05-01

306

Molecular-frame photoelectron angular distributions of strong-field tunneling from inner orbitals

NASA Astrophysics Data System (ADS)

Using photoelectron angular streaking by strong circularly polarized laser pulses, we measure angular-dependent tunneling rates from the inner orbitals of O2 in the molecular frame, which correlate with the strong-field molecular dissociative ionization process. We show that the electronic density of molecular inner orbitals can be visualized by angular tunneling rates in the molecular frame. We demonstrate the orbital-by-orbital characterization of tunneling ionization from randomly oriented molecules. Compared with the single-active-electron approximation theories, i.e., the molecular strong-field approximation and the molecular Ammosov-Delone-Krainov model, the experiment shows that the tunneling from the excited states and the state coupling might play an important role in strong-field molecular tunneling ionization. Our results suggest major advances in quantum theory needed for molecular inner orbital tunneling and open intriguing perspectives to probe quantum dynamics related with molecular core electrons.

Liu, Hong; Zhao, Song-Feng; Li, Min; Deng, Yongkai; Wu, Chengyin; Zhou, Xiao-Xin; Gong, Qihuang; Liu, Yunquan

2013-12-01

307

Electron angular distributions above the dayside auroral oval

NASA Technical Reports Server (NTRS)

An electrostatic analyzer was employed on the Ariel 4 satellite to determine pitch angle distributions of electron intensities over the dayside auroral oval. Two major precipitation zones were encountered: an equatorward zone of broad spectra with intensities of approximately 1000 electrons/(sq cm-sec-sr-eV) and a poleward zone, the polar cusp, with intensities typical of those of the magnetosheath. Angular distributions within the equatorward zone are generally isotropic outside of the atmospheric backscatter cone. The precipitation mechanism appears to be pitch angle scattering near the distant magnetic equator. In contrast, pitch angle distributions within the polar cusp are often found to be strongly field aligned with intensities within the atmospheric loss cone greater by factors of approximately 10 than the mirroring intensities. These distributions are qualititatively similar to those for the inverted V precipitation events at later local times, and probably share a common acceleration mechanism with the inverted V phenomenon.

Craven, J. D.; Frank, L. A.

1975-01-01

308

Angular-averaged consistency relations of large-scale structures

NASA Astrophysics Data System (ADS)

The cosmological dynamics of gravitational clustering satisfies an approximate invariance with respect to the cosmological parameters that is often used to simplify analytical computations. We describe how this approximate symmetry gives rise to angular-averaged consistency relations for the matter density correlations. This allows one to write the (?+n) density correlation, with ? large-scale linear wave numbers that are integrated over angles, and n fixed small-scale nonlinear wave numbers, in terms of the small-scale n-point density correlation and ? prefactors that involve the linear power spectra at the large-scale wave numbers. These relations, which do not vanish for equal-time statistics, go beyond the already known kinematic consistency relations. They could be used to detect primordial non-Gaussianities, modifications of gravity, limitations of galaxy biasing schemes, or to help design analytical models of gravitational clustering.

Valageas, Patrick

2014-06-01

309

Angular momentum decomposition of nonparaxial light beams.

The total angular momentum per unit length of a general non-paraxial beam is decomposed into an orbital component associated with the spiral spectrum at the far field and a component concerning the balance between right- and left-handed circular-polarization content of the angular spectrum. Expressions for the linear momentum and energy per unit length are also provided. The well-known division into orbital and spin components is shown to be recovered in the paraxial limit. PMID:20588639

Martínez-Herrero, R; Mejías, P M

2010-04-12

310

Angular performance measure for tighter uncertainty relations

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

311

Neutrino angular momentum loss in rotating stars

NASA Technical Reports Server (NTRS)

We consider how an axisymmetric, uniformly and slowly rotating homogeneous star might be affected by the loss of energy and angular momentum via neutrino emission. For example, these losses can cause a collapsing, rotating star to flatten either faster or slower than would be the case if these losses were not taken fully into account, depending on the efficiency of the angular momentum loss mechanism.

Epstein, R.

1978-01-01

312

Optimizing the Zeldovich approximation

NASA Technical Reports Server (NTRS)

We have recently learned that the Zeldovich approximation can be successfully used for a far wider range of gravitational instability scenarios than formerly proposed; we study here how to extend this range. In previous work (Coles, Melott and Shandarin 1993, hereafter CMS) we studied the accuracy of several analytic approximations to gravitational clustering in the mildly nonlinear regime. We found that what we called the 'truncated Zeldovich approximation' (TZA) was better than any other (except in one case the ordinary Zeldovich approximation) over a wide range from linear to mildly nonlinear (sigma approximately 3) regimes. TZA was specified by setting Fourier amplitudes equal to zero for all wavenumbers greater than k(sub nl), where k(sub nl) marks the transition to the nonlinear regime. Here, we study the cross correlation of generalized TZA with a group of n-body simulations for three shapes of window function: sharp k-truncation (as in CMS), a tophat in coordinate space, or a Gaussian. We also study the variation in the crosscorrelation as a function of initial truncation scale within each type. We find that k-truncation, which was so much better than other things tried in CMS, is the worst of these three window shapes. We find that a Gaussian window e(exp(-k(exp 2)/2k(exp 2, sub G))) applied to the initial Fourier amplitudes is the best choice. It produces a greatly improved crosscorrelation in those cases which most needed improvement, e.g. those with more small-scale power in the initial conditions. The optimum choice of kG for the Gaussian window is (a somewhat spectrum-dependent) 1 to 1.5 times k(sub nl). Although all three windows produce similar power spectra and density distribution functions after application of the Zeldovich approximation, the agreement of the phases of the Fourier components with the n-body simulation is better for the Gaussian window. We therefore ascribe the success of the best-choice Gaussian window to its superior treatment of phases in the nonlinear regime. We also report on the accuracy of particle positions and velocities produced by TZA.

Melott, Adrian L.; Pellman, Todd F.; Shandarin, Sergei F.

1994-01-01

313

Angular Momentum Dependent Orbital Free Density Functional Theory

NASA Astrophysics Data System (ADS)

We report a novel and general formalism for linear scaling, angular momentum dependent (AMD) orbital free (OF) density functional theory (DFT) to advance the accuracy and applicability of OFDFT. To introduce angular momentum dependence in OFDFT, we devise a hybrid scheme by partitioning the system into muffin-tin spheres and an interstitial region: the electron density inside the spheres is expressed by a set of Kohn-Sham (KS) DFT derived atom-centered basis functions combined with an on-site density matrix NR. A general OFDFT total energy functional is introduced with a crucial nonlocal energy term E^NL which is neglected in conventional implementations of OFDFT. E^NL corrects the errors due to the use of approximate kinetic energy density functionals and local pseudopotentials for ion-electron interactions. We approximate E^NL to include AMD contributions inside the spheres: as a first step, a linear dependence on the NR is considered with a set of AMD energies E^lR. E^lR are determined by fitting a small set of bulk properties to KSDFT. We find AMD-OFDFT offers substantial improvements over conventional OFDFT, as we show for various properties of the transition metal Ti and its alloys (TixAl1-x).

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

2013-03-01

314

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

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

315

Variational truncated Wigner approximation

NASA Astrophysics Data System (ADS)

In this paper we reconsider the notion of an optimal effective Hamiltonian for the semiclassical propagation of the Wigner distribution in phase space. An explicit expression for the optimal effective Hamiltonian is obtained in the short-time limit by minimizing the Hilbert-Schmidt distance between the semiclassical approximation and the real state of the system. The method is illustrated for the quartic oscillator.

Sels, Dries; Brosens, Fons

2014-04-01

316

Variational truncated Wigner approximation.

In this paper we reconsider the notion of an optimal effective Hamiltonian for the semiclassical propagation of the Wigner distribution in phase space. An explicit expression for the optimal effective Hamiltonian is obtained in the short-time limit by minimizing the Hilbert-Schmidt distance between the semiclassical approximation and the real state of the system. The method is illustrated for the quartic oscillator. PMID:24827193

Sels, Dries; Brosens, Fons

2014-04-01

317

Fuzzy approximately cubic mappings

We establish some stability results concerning the cubic functional equationf(2x+y)+f(2x-y)=2f(x+y)+2f(x-y)+12f(x)in fuzzy normed spaces. We discuss the fuzzy continuity of the cubic mappings and show that the existence of a solution for any approximately cubic mapping guarantees the completeness of the fuzzy normed space.

Alireza Kamel Mirmostafaee; Mohammad Sal Moslehian

2008-01-01

318

NASA Technical Reports Server (NTRS)

Population models for dependence between two angular measurements and for dependence between an angular and a linear observation are proposed. The method of canonical correlations first leads to new population and sample measures of dependence in this latter situation. An example relating wind direction to the level of a pollutant is given. Next, applied to pairs of angular measurements, the method yields previously proposed sample measures in some special cases and a new sample measure in general.

Johnson, R. A.; Wehrly, T.

1976-01-01

319

An angular multigrid method for computing mono-energetic particle beams in Flatland

Beams of microscopic particles penetrating scattering background matter play an important role in several applications. The parameter choices made here are motivated by the problem of electron-beam cancer therapy planning. Mathematically, a steady particle beam penetrating matter, or a configuration of several such beams, is modeled by a boundary value problem for a Boltzmann equation. Grid-based discretization of such a problem leads to a system of algebraic equations. This system is typically very large because of the large number of independent variables in the Boltzmann equation-six if no dimension-reducing assumptions other than time independence are made. If grid-based methods are to be practical for these problems, it is therefore necessary to develop very fast solvers for the discretized problems. For beams of mono-energetic particles interacting with a passive background, but not with each other, in two space dimensions, the first author proposed such a solver, based on angular domain decomposition, some time ago. Here, we propose and test an angular multigrid algorithm for the same model problem. Our numerical experiments show rapid, grid-independent convergence. For high-resolution calculations, our method is substantially more efficient than the angular domain decomposition method. In addition, unlike angular domain decomposition, the angular multigrid method works well even when the angular diffusion coefficient is fairly large.

Boergers, Christoph [Department of Mathematics, Tufts University, Medford, MA 02155 (United States)], E-mail: christoph.borgers@tufts.edu; MacLachlan, Scott [Department of Mathematics, Tufts University, Medford, MA 02155 (United States)

2010-04-20

320

Photoelectron Angular Distributions of s Electrons in Open-Shell Atoms

It is shown that the photoelectron angular distribution of s electrons in an open-shell atom, having outer configuration ns2npq, is not described by the asymmetry parameter beta=2, as predicted by more approximate theories, but has dramatic variations with energy even within LS coupling. Calculations for the 3s subshell in Cl are presented as an example.

Anthony F. Starace; Robert H. Rast; Steven T. Manson

1977-01-01

321

Photoelectron angular distributions of s electrons in open-shell atoms

It is shown that the photoelectron angular distribution of s electrons in an open-shell atom, having outer configuration nsÂ˛np\\/sup q\\/, is not described by the asymmetry parameter ..beta.. = 2, as predicted by more approximate theories, but has dramatic variations with energy even within LS coupling. Calculations for the 3s subshell in Cl are presented as an example.

Anthony Starace; Robert Rast; Steven Manson

1977-01-01

322

NASA Astrophysics Data System (ADS)

We measured the angular diameter of the lithium-rich K giant star HD 148293 using Georgia State University's Center for High Angular Resolution Astronomy Array interferometer. We used our measurement to calculate the star's effective temperature, which allowed us to place it on an H-R diagram to compare it with other Li-rich giants. Its placement supports the evidence presented by Charbonnel & Balachandran that it is undergoing a brief stage in its evolution where Li is being created.

Baines, Ellyn K.; McAlister, Harold A.; ten Brummelaar, Theo A.; Turner, Nils H.; Sturmann, Judit; Sturmann, Laszlo; Goldfinger, P. J.; Farrington, Christopher D.; Ridgway, Stephen T.

2011-04-01

323

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

324

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

325

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.

326

As increasingly large volumes of sophisticated options (called derivative securities) are traded in world financial markets, determining a fair price for these options has become an important and difficult computational problem. Many valuation codes use the binomial pricing model, in which the stock price is driven by a random walk. In this model, the value of an n-period option on a stock is the expected time-discounted value of the future cash flow on an n-period stock price path. Path-dependent options are particularly difficult to value since the future cash flow depends on the entire stock price path rather than on just the final stock price. Currently such options are approximately priced by Monte carlo methods with error bounds that hold only with high probability and which are reduced by increasing the number of simulation runs. In this paper the authors show that pricing an arbitrary path-dependent option is {number_sign}-P hard. They show that certain types f path-dependent options can be valued exactly in polynomial time. Asian options are path-dependent options that are particularly hard to price, and for these they design deterministic polynomial-time approximate algorithms. They show that the value of a perpetual American put option (which can be computed in constant time) is in many cases a good approximation to the value of an otherwise identical n-period American put option. In contrast to Monte Carlo methods, the algorithms have guaranteed error bounds that are polynormally small (and in some cases exponentially small) in the maturity n. For the error analysis they derive large-deviation results for random walks that may be of independent interest.

Chalasani, P.; Saias, I. [Los Alamos National Lab., NM (United States); Jha, S. [Carnegie Mellon Univ., Pittsburgh, PA (United States)

1996-04-08

327

The angular spectrum method is an accurate and computationally efficient method for modeling acoustic wave propagation. The use of the typical 2D fast Fourier transform algorithm makes this a fast technique but it requires that the source pressure (or velocity) be specified on a plane. Here the angular spectrum method is extended to calculate pressure from a spherical transducer-as used extensively in applications such as magnetic resonance-guided focused ultrasound surgery-to a plane. The approach, called the Ring-Bessel technique, decomposes the curved source into circular rings of increasing radii, each ring a different distance from the intermediate plane, and calculates the angular spectrum of each ring using a Fourier series. Each angular spectrum is then propagated to the intermediate plane where all the propagated angular spectra are summed to obtain the pressure on the plane; subsequent plane-to-plane propagation can be achieved using the traditional angular spectrum method. Since the Ring-Bessel calculations are carried out in the frequency domain, it reduces calculation times by a factor of approximately 24 compared to the Rayleigh-Sommerfeld method and about 82 compared to the Field II technique, while maintaining accuracies of better than 96% as judged by those methods for cases of both solid and phased-array transducers. PMID:22087896

Vyas, Urvi; Christensen, Douglas A

2011-11-01

328

Approximate Bayesian Computation

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).

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

2013-01-01

329

Angular momentum conservation for dynamical black holes

Angular momentum can be defined by rearranging the Komar surface integral in terms of a twist form, encoding the twisting around of space-time due to a rotating mass, and an axial vector. If the axial vector is a coordinate vector and has vanishing transverse divergence, it can be uniquely specified under certain generic conditions. Along a trapping horizon, a conservation law expresses the rate of change of angular momentum of a general black hole in terms of angular momentum densities of matter and gravitational radiation. This identifies the transverse-normal block of an effective gravitational-radiation energy tensor, whose normal-normal block was recently identified in a corresponding energy conservation law. Angular momentum and energy are dual, respectively, to the axial vector and a previously identified vector, the conservation equations taking the same form. Including charge conservation, the three conserved quantities yield definitions of an effective energy, electric potential, angular velocity and surface gravity, satisfying a dynamical version of the so-called first law of black-hole mechanics. A corresponding zeroth law holds for null trapping horizons, resolving an ambiguity in taking the null limit.

Hayward, Sean A. [Center for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234 (China)

2006-11-15

330

Angular correlation between proton and neutron rotors

NASA Astrophysics Data System (ADS)

A brief review is given on the controversy and its solution about the fact that the angular momentum vector of protons and that of neutrons in well-deformed nuclei at low total angular momenta have a strong correlation that they are oriented in opposite directions. In a simple two-rotor model in 2-dimensional space, this fact is explained as originating from the quantum mechanical uncertainty relation between the angle and the angular momentum for the relative rotation of the two rotors. As the second topic, a more realistic model consisting of two triaxial rotors in 3-dimensional space coupled with a QQ interaction is employed to investigate a possible shears-band-like collective rotation predicted by T. Otsuka, in which the angle at which the angular momentum of protons and that of neutrons intersect changes continuously from 180° at spin zero toward 0° at high spins within the same rotational band. The probability distributions of the angle between the two angular momenta and the angle between the longest principal axes of two rotors are calculated to examine the participation of the scissors mode in the evolution of the ground rotational band versus spin.

Tajima, N.

2013-07-01

331

Angular-planar CMB power spectrum

Gaussianity and statistical isotropy of the Universe are modern cosmology's minimal set of hypotheses. In this work we introduce a new statistical test to detect observational deviations from this minimal set. By defining the temperature correlation function over the whole celestial sphere, we are able to independently quantify both angular and planar dependence (modulations) of the CMB temperature power spectrum over different slices of this sphere. Given that planar dependence leads to further modulations of the usual angular power spectrum C{sub l}, this test can potentially reveal richer structures in the morphology of the primordial temperature field. We have also constructed an unbiased estimator for this angular-planar power spectrum which naturally generalizes the estimator for the usual C{sub l}'s. With the help of a chi-square analysis, we have used this estimator to search for observational deviations of statistical isotropy in WMAP's 5 year release data set (ILC5), where we found only slight anomalies on the angular scales l=7 and l=8. Since this angular-planar statistic is model-independent, it is ideal to employ in searches of statistical anisotropy (e.g., contaminations from the galactic plane) and to characterize non-Gaussianities.

Pereira, Thiago S.; Abramo, L. Raul [Instituto de Fisica Teorica, UNESP-Universidade Estadual Paulista, Caixa Postal 70532-2, 01140-070, Sao Paulo (Brazil); Instituto de Fisica, Universidade de Sao Paulo, CP 66318, 05314-970, Sao Paulo (Brazil)

2009-09-15

332

Ultrafast angular momentum transfer in multisublattice ferrimagnets

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

333

Ultrafast angular momentum transfer in multisublattice ferrimagnets.

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

334

Multispectral angular domain imaging with a tunable pulsed laser

NASA Astrophysics Data System (ADS)

Angular Domain Imaging (ADI) is an imaging technique that is capable of generating three dimensional images of attenuating targets embedded in a scattering medium. In ADI, an angular filter is positioned between the sample and the detector to discriminate between quasi-ballistic photons and scattered photons. Quasi-ballistic photons have undergone relatively few forward directed scattering events, and can be used to generate a projection image representative of the imaging target. Scattered photons have undergone many scattering events and contain little information regarding the imaging target, thereby leading to decreased image contrast. Our implementation of ADI utilizes a silicon micro-channel array to reject scattered photons based on the angle at which they exit the sample. The objective of this work was to collect ADI images with a tunable pulsed laser within the visible range. Samples were illuminated at 13 wavelengths between 460 nm and 700 nm. An angular filter array of 80 ?m × 80 ?m tunnels 2-cm long was used to select the quasiballistic photons. Images were detected with a linear 16-bit linear CCD. The phantom consisted of a 0.7 mm attenuating target submerged in one of four IntralipidR dilutions (0.15%-0.3%) contained within a 1 cm path length cuvette. Image contrast ranged from 0.02 at 460 nm and 0.3% IntralipidR to 1 at 680 nm at 0.15% IntralipidR. For a given scattering level, contrast increased at longer wavelengths. Resolution varied minimally with wavelength. The results suggested that multispectral ADI with a tunable pulsed laser is feasible and may find utility in imaging thin tissue samples in the future.

Ng, Eldon; Vasefi, Fartash; Carson, Jeffrey J. L.

2012-02-01

335

Distribution of Accreting Gas and Angular Momentum onto Circumplanetary Disks

NASA Astrophysics Data System (ADS)

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 L1 and L2. 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; Machida, Masahiro N.

2012-03-01

336

DISTRIBUTION OF ACCRETING GAS AND ANGULAR MOMENTUM ONTO CIRCUMPLANETARY DISKS

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

337

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

338

Sivers function in the quasiclassical approximation

NASA Astrophysics Data System (ADS)

We calculate the Sivers function in semi-inclusive deep inelastic scattering (SIDIS) and in the Drell-Yan process (DY) by employing the quasiclassical Glauber-Mueller/McLerran-Venugopalan approximation. Modeling the hadron as a large "nucleus" with nonzero orbital angular momentum (OAM), we find that its Sivers function receives two dominant contributions: one contribution is due to the OAM, while another one is due to the local Sivers function density in the nucleus. While the latter mechanism, being due to the "lensing" interactions, dominates at large transverse momentum of the produced hadron in SIDIS or of the dilepton pair in DY, the former (OAM) mechanism is leading in saturation power counting and dominates when the above transverse momenta become of the order of the saturation scale. We show that the OAM channel allows for a particularly simple and intuitive interpretation of the celebrated sign flip between the Sivers functions in SIDIS and DY.

Kovchegov, Yuri V.; Sievert, Matthew D.

2014-03-01

339

Approximation by Hill Functions: II.

National Technical Information Service (NTIS)

The problem of the approximation in Sobolev spaces by piecewise smooth function is considered. This approach deals with the problems of approximation on less dimensional manifolds and simultaneous approximation on manifolds of different dimensions.

I. Babuska

1971-01-01

340

Estimating q_0 from angular size statistics

NASA Astrophysics Data System (ADS)

Compact radio sources, being relatively small (parsec-scale) and short-lived, are likely to be little affected by evolutionary changes, and are therefore good probes of the angular size-redshift relation. Kellermann has analysed a sample of 82 compact radio sources and finds that they are consistent with q_0=1/2. We develop a likelihoods method for analysing angular size data without having to bin them, and apply the method to an updated version of Kellermann's sample. From this analysis we argue that, while the angular size data are consistent with q_0=1/2, they do not at present rule out extreme values such as q_0~5.

Stepanas, Paulius G.; Saha, Prasenjit

1995-02-01

341

Surface angular momentum of light beams.

Traditionally, the angular momentum of light is calculated for "bullet-like" electromagnetic wave packets, although in actual optical experiments "pencil-like" beams of light are more commonly used. The fact that a wave packet is bounded transversely and longitudinally while a beam has, in principle, an infinite extent along the direction of propagation, renders incomplete the textbook calculation of the spin/orbital separation of the angular momentum of a light beam. In this work we demonstrate that a novel, extra surface part must be added in order to preserve the gauge invariance of the optical angular momentum per unit length. The impact of this extra term is quantified by means of two examples: a Laguerre-Gaussian and a Bessel beam, both circularly polarized. PMID:24664007

Ornigotti, Marco; Aiello, Andrea

2014-03-24

342

Angular momentum generation by parity violation

NASA Astrophysics Data System (ADS)

We generalize our holographic derivation of spontaneous angular momentum generation in 2+1 dimensions in several directions. We consider cases when a parity-violating perturbation responsible for the angular momentum generation can be nonmarginal (while in our previous paper we restricted to a marginal perturbation), including all possible two-derivative interactions, with parity violations triggered both by gauge and gravitational Chern-Simons terms in the bulk. We make only a minimal assumption about the bulk geometry that it is asymptotically AdS, respects the Poincaré symmetry in 2+1 dimensions, and has a horizon. In this generic setup, we find a remarkably concise and universal formula for the expectation value of the angular momentum density, to all orders in the parity violating perturbation.

Liu, Hong; Ooguri, Hirosi; Stoica, Bogdan

2014-05-01

343

Electromagnetic angular momentum transport in Saturn's rings

NASA Technical Reports Server (NTRS)

It is shown here that submicrometer dust particles sporadically elevated above Saturn's ring are subject to electromagnetic forces which will reduce their angular momentum inside synchronous orbit and increase it outside. When the dust is reabsorbed by the ring the angular momentum of the ring is decreased (increased) inside (outside) of synchronous orbit. For the case of the spokes in Saturn's B-ring it is estimated that the timescale for transporting ring material due to this angular momentum coupling effect is comparable to the viscous transport time or even smaller. It is suggested that the minimum in the optical depth of the B-ring at synchronous orbit is due to this effect.

Goertz, C. K.; Morfill, G. E.; Ip, W.; Gruen, E.; Havnes, O.

1986-01-01

344

NASA Astrophysics Data System (ADS)

We illustrate the possibility for calculation of bremsstrahlung tip angular destributions and polarization correlations from corresponding photoeffect results with an extension of the method for connecting bremsstrahlung tip and direct-radiative-recombination (DRR) cross sections developed by Lee and Pratt. The agreement between results obtained with this method and results from our numerical partial-wave calculations is, in general, satisfactory. We note features of the distributions and correlations, and once again point out the inadequacies of the nonrelativistic dipole approximation for the evaluation of bremsstrahlung or DRR angular distributions.

Feng, I. J.; Goldberg, I. B.; Kim, Young Soon; Pratt, R. H.

1983-08-01

345

Mechanism of Angular Momentum Exchange between Molecules and Laguerre-Gaussian Beams

We derive the interaction Hamiltonian between a diatomic molecule and a Laguerre-Gaussian beam under the assumption of a small spread of the center of mass wave function of the molecule in comparison with the beam waist. Considering the dynamical variables of the center of mass, vibrational, rotational, and electronic motion, we show that, within the electronic dipole approximation, the orbital angular momentum of the field couples with the rotational and electronic motion. The changes in the transition probabilities and selection rules induced by the field orbital angular momentum and the applicability of the derived interaction mechanisms for polyatomic molecules are discussed.

Alexandrescu, Adrian [Department of Mathematics, E.T.S.I.I., University of Castilla - La Mancha, 13071 Ciudad Real (Spain); CCO - Optoelectronics Research Center, 'Politehnica' University of Bucharest, 61071 Bucharest (Romania); Cojoc, Dan [CNR - Istituto Nazionale per la Fisica della Materia, Laboratorio Nazionale TASC, Area Science Park, 34012 Basovizza (TS) (Italy); CCO - Optoelectronics Research Center, 'Politehnica' University of Bucharest, 61071 Bucharest (Romania); Fabrizio, Enzo Di [BIONEM Laboratory, University of Magna Graecia, Campus Germaneto Viale Europa, 88100 Catanzaro (Italy); CNR - Istituto Nazionale per la Fisica della Materia, Laboratorio Nazionale TASC, Area Science Park, 34012 Basovizza (TS) (Italy)

2006-06-23

346

Angular Diameters and Effective Temperatures of 25 K Giant Stars from the CHARA Array

NASA Astrophysics Data System (ADS)

Using Georgia State University's Center for High Angular Resolution Astronomy Array interferometer, we measured angular diameters for 25 giant stars, six of which host exoplanets. The combination of these measurements and Hipparcos parallaxes produces physical linear radii for the sample. Except for two outliers, our values match angular diameters and physical radii estimated using photometric methods to within the associated errors with the advantage that our uncertainties are significantly lower. We also calculated the effective temperatures for the stars using the newly measured diameters. Our values do not match those derived from spectroscopic observations as well, perhaps due to the inherent properties of the methods used or because of a missing source of extinction in the stellar models that would affect the spectroscopic temperatures.

Baines, Ellyn K.; Döllinger, Michaela P.; Cusano, Felice; Guenther, Eike W.; Hatzes, Artie P.; McAlister, Harold A.; ten Brummelaar, Theo A.; Turner, Nils H.; Sturmann, Judit; Sturmann, Laszlo; Goldfinger, P. J.; Farrington, Christopher D.; Ridgway, Stephen T.

2010-02-01

347

Angular dependence of betatron x-ray spectra from a laser-wakefield accelerator.

We present the first measurements of the angular dependence of the betatron x-ray spectrum produced by electrons inside the cavity of a laser-wakefield accelerator. Electrons accelerated up to 300 MeV energies produce a beam of broadband, forward-directed betatron x-ray radiation extending up to 80 keV. The angular resolved spectrum from an image plate-based spectrometer with differential filtering provides data in a single laser shot. The simultaneous spectral and spatial x-ray analysis allows for a three-dimensional reconstruction of electron trajectories with micrometer resolution, and we find that the angular dependence of the x-ray spectrum is showing strong evidence of anisotropic electron trajectories. PMID:24476282

Albert, F; Pollock, B B; Shaw, J L; Marsh, K A; Ralph, J E; Chen, Y-H; Alessi, D; Pak, A; Clayton, C E; Glenzer, S H; Joshi, C

2013-12-01

348

Establishing an IERS Sub-Center for Ocean Angular Momentum

NASA Technical Reports Server (NTRS)

With the objective of establishing the Special Bureau for the Oceans (SBO), a new archival center for ocean angular momentum (OAM) products, we have computed and analyzed a number of OAM products from several ocean models, with and without data assimilation. All three components of OAM (axial term related to length of day variations and equatorial terms related to polar motion) have been examined in detail, in comparison to the respective Earth rotation parameters. An 11+ year time series of OAM given at 5-day intervals has been made publicly available. Other OAM products spanning longer periods and with higher temporal resolution, as well as products calculated from ocean model/data assimilation systems, have been prepared and should become part of the SBO archives in the near future.

Ponte, Rui M.

2001-01-01

349

Color holography using the angular selectivity of volume recording media

NASA Astrophysics Data System (ADS)

A display hologram of an object can be recorded and reconstructed in three primary colors if the angular selectivity of volume recording media is exploited. Three holograms are recorded in the same medium, each at a different primary color. These three holograms are reconstructed by simultaneous illumination of the hologram with the original reference beams. By proper choice of the angles that the reference beams make to the hologram, it is possible to suppress strongly cross talk between the different reconstructions (e.g., the red object reconstruction in green light). The technique exhibits high resolution, high diffraction efficiency, and vivid colors. Through the addition of three holographically recorded volume gratings it is possible to reconstruct the hologram with a beam of white light. The saturation and brightness of each primary color in the reconstruction can be adjusted by selection of an appropriate thickness for the corresponding grating.

Zhu, Peiping; Xu, Zhizhan; Liu, Xinsen

1995-02-01

350

This paper presents a general method for reducing the effective rotational Hamiltonian for molecules H /sub rot/ to the empirically constructed form in the (J + or -, J /sub z/) representation (molecules of the asymmetric-top type), applicable to Hamiltonians having improved convergence with nonpolynomial dependence on the angular momentum J /sub a/. Rational forms for the reduced H /sub rot/ and reduced Pade approximants for the rotational energy operator of the molecules are proposed.

Tyuterev, V.G.; Durenin, A.V.; Perevalov, V.I.; Starikov, V.I.

1986-02-01

351

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

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

352

BAYESIAN ANGULAR POWER SPECTRUM ANALYSIS OF INTERFEROMETRIC DATA

We present a Bayesian angular power spectrum and signal map inference engine which can be adapted to interferometric observations of anisotropies in the cosmic microwave background (CMB), 21 cm emission line mapping of galactic brightness fluctuations, or 21 cm absorption line mapping of neutral hydrogen in the dark ages. The method uses Gibbs sampling to generate a sampled representation of the angular power spectrum posterior and the posterior of signal maps given a set of measured visibilities in the uv-plane. We use a mock interferometric CMB observation to demonstrate the validity of this method in the flat-sky approximation when adapted to take into account arbitrary coverage of the uv-plane, mode-mode correlations due to observations on a finite patch, and heteroschedastic visibility errors. The computational requirements scale as O(n{sub p} log n{sub p}) where n{sub p} measures the ratio of the size of the detector array to the inter-detector spacing, meaning that Gibbs sampling is a promising technique for meeting the data analysis requirements of future cosmology missions.

Sutter, P. M.; Wandelt, Benjamin D. [Department of Physics, 1110 West Green Street, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Malu, Siddarth S. [Raman Research Institute, C V Raman Avenue, Bangalore 560080 (India)

2012-09-15

353

Effect of head posture on cephalometric sagittal angular measures.

The definitions of cephalometric landmarks include relative terms that are dependent on the orientation of the head (e.g., lowest, most posterior) and head orientation differ widely during cephalometry (e.g., Frankfort plane horizontal, natural head posture). The purpose of this study was to quantify the effect of head posture changes on the commonly used sagittal angular measures SNA, SNB, and SNPogonion (SNPg). The sample comprised 30 Chinese skulls. Cephalograms were taken in a purpose designed skull holder with the Frankfort plane horizontal and at +10 degrees, +20 degrees, +30 degrees, -10 degrees, -20 degrees, and -30 degrees. A geometric grid was used to locate the deepest landmarks, and the landmarks were digitized followed by computer superimposition on the S-N line. To compare the values of the SNA, SNB, and SNPg angles in the different head postures, t tests were used. Head (skull) posture changes produced significant effects on the cephalometric values even at +/- 10 degrees of tilting. Overall, the angles were underestimated by approximately 1 degrees. In general, the angular differences and their standard deviations increased as the skull rotation increased with most of the differences for the SNB and the SNPg angles being clinically significant and also statistically significant at the 0.1% level. It was concluded that head posture needs to be standardized during cephalometry. Changes in posture significantly affect the location of some landmarks and the subsequent data obtained. PMID:8213654

Tng, T T; Chan, T C; Cooke, M S; Hägg, U

1993-10-01

354

Self-similar factor approximants.

The problem of reconstructing functions from their asymptotic expansions in powers of a small variable is addressed by deriving an improved type of approximants. The derivation is based on the self-similar approximation theory, which presents the passage from one approximant to another as the motion realized by a dynamical system with the property of group self-similarity. The derived approximants, because of their form, are called self-similar factor approximants. These complement the obtained earlier self-similar exponential approximants and self-similar root approximants. The specific feature of self-similar factor approximants is that their control functions, providing convergence of the computational algorithm, are completely defined from the accuracy-through-order conditions. These approximants contain the Padé approximants as a particular case, and in some limit they can be reduced to the self-similar exponential approximants previously introduced by two of us. It is proved that the self-similar factor approximants are able to reproduce exactly a wide class of functions, which include a variety of nonalgebraic functions. For other functions, not pertaining to this exactly reproducible class, the factor approximants provide very accurate approximations, whose accuracy surpasses significantly that of the most accurate Padé approximants. This is illustrated by a number of examples showing the generality and accuracy of the factor approximants even when conventional techniques meet serious difficulties. PMID:12636750

Gluzman, S; Yukalov, V I; Sornette, D

2003-02-01

355

Behavior of Nuclei at High Angular Momentum.

National Technical Information Service (NTIS)

The present report begins with a brief overview of nuclear shapes and level structures at high-spin values. The new spectroscopy associated with angular-momentum alignments is described, and some of the exciting possibilities of this spectroscopy are expl...

F. S. Stephens

1982-01-01

356

Heteromodal conceptual processing in the angular gyrus

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.

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

2013-01-01

357

Representations of SO(3) and angular polyspectra

We characterize the angular polyspectra, of arbitrary order, associated with isotropic fields defined on the sphere S2 = ? (x, y, z) : x2 + y2 + z2 = 1 ? . Our techniques rely heavily on group representation theory, and specifically on the properties of Wigner matrices and Clebsch-Gordan coefficients. The findings of the present paper constitute a basis

Domenico Marinucci; Giovanni Peccati

2010-01-01

358

The Role of Angularity in Route Choice

NASA Astrophysics Data System (ADS)

The paths of 2425 individual motorcycle trips made in London were analyzed in order to uncover the route choice decisions made by drivers. The paths were derived from global positioning system (GPS) data collected by a courier company for each of their drivers, using algorithms developed for the purpose of this paper. Motorcycle couriers were chosen due to the fact that they both know streets very well and that they do not rely on the GPS to guide their navigation. Each trace was mapped to the underlying road network, and two competing hypotheses for route choice decisions were compared: (a) that riders attempt to minimize the Manhattan distance between locations and (b) that they attempt to minimize the angular distance. In each case, the distance actually traveled was compared to the minimum possible either block or angular distance through the road network. It is usually believed that drivers who know streets well will navigate trips that reduce Manhattan distance; however, here it is shown that angularity appears to play an important role in route choice. 63% of trips made took the minimum possible angular distance between origin and destination, while 51% of trips followed the minimum possible block distance. This implies that impact of turns on cognitive distance plays an important role in decision making, even when a driver has good knowledge of the spatial network.

Turner, Alasdair

359

Vectorial measurements of the angular coercive field

NASA Astrophysics Data System (ADS)

Two of the most important parameters in magnetic measurements are the coercive field, Hc, and the remanent coercive field, Hr. In this paper we will look at these parameters in relation to vector measurements taken at an angle with the (mean) anisotropy direction. We will show that the definition and interpretation of these parameters should be reconsidered for angular measurements.

Samwel, E. O.; Bolhuis, T.; Speliotis, D.; Lodder, J. C.

1999-03-01

360

The measurement of instantaneous angular speed

NASA Astrophysics Data System (ADS)

Many different methods have been developed for the measurement of angular speed. Each successive method has attempted to improve measurement performance using a different strategy to process encoder signals based on two basic principles: counting the number of pulses in a given time duration and measuring the elapsed time for a single cycle of encoder signal. A review of existing methods reveals that little effort has been made in the measurement of instantaneous, multi-channel, wide-range angular speed. As a result, this paper aims to develop a method that provides instantaneous speed information in the form of angular displacement. It addresses the general process and considerations that ensure effective measurement of instantaneous angular speed (IAS). The paper then presents two different techniques: one is based on a general-purpose data acquisition system, another uses pure software implementation. Both methods aim to maximise the use of hardware resources without incurring additional costs in the form of upgrades to the measurement system. Finally, an optimisation of measurement system parameters for a reliable IAS measurement has been carried out based on measurement error analysis.

Li, Yuhua; Gu, Fengshou; Harris, Georgina; Ball, Andrew; Bennett, Nick; Travis, Ken

2005-07-01

361

Angular Motion of Spinning Almost Symmetric Missiles.

National Technical Information Service (NTIS)

An almost symmetric missile is a missile whose zero-spin pitch and yaw frequencies are 'nearly' equal. The angular motion of a spinning almost symmetric missile can be described by five rotating modal vectors. Two of these vectors vanish when the frequenc...

C. H. Murphy

1978-01-01

362

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

363

Approximation by hinge functions

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

364

NASA Astrophysics Data System (ADS)

Backscatter information from multibeam echosounders (MBES) have been shown to contain useful information for the characterisation of benthic habitats. Compared to backscatter imagery, angular response of backscatter has shown advantages for feature discrimination. However its low spatial resolution inhibits the generation of fine scale habitat maps. In this study, angular backscatter response was combined with image segmentation of backscatter imagery to characterise benthic biological habitats in Discovery Bay Marine National Park, Victoria, Australia. Angular response of backscatter data from a Reson Seabat 8101 MBES (240 kHz) was integrated with georeferenced underwater video observations for constructing training data. To produce benthic habitat maps, decision tree supervised classification results were combined with mean shift image segmentation for class assignment. The results from mean angular response characteristics show effects of incidence angle at the outer angle for invertebrates (INV) and mixed red and invertebrates (MRI) classes, whilst mixed brown algae (MB) and mixed brown algae and invertebrates (MBI) showed similar responses independent from incidence angle. Automatic segmentation processing produce over segmented results but showed good discrimination between heterogeneous regions. Accuracy assessment from habitat maps produced overall accuracies of 79.6% (Kappa coefficient = 0.66) and 80.2% (Kappa coefficient = 0.67) for biota and substratum classifications respectively. MRI and MBI produced the lowest average accuracy while INV the highest. The ability to combine angular response and backscatter imagery provides an alternative approach for investigating biological information from acoustic backscatter data.

Che Hasan, Rozaimi; Ierodiaconou, Daniel; Laurenson, Laurie

2012-01-01

365

Angular distribution of atoms ejected by laser ablation of different metals

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

366

Unexpectedly low angular extent of journal bearing pressures: experiment and theory

NASA Astrophysics Data System (ADS)

Journal bearings have been studied for a long time. Pressure solutions for the same, as presented in textbooks, typically have angular extents exceeding 150°. Here, for a bearing with a relatively larger clearance ratio (0.01 as opposed to, say, 0.001), our experiments show an angular extent of about 50° only. Such small angular extents cannot be predicted, even approximately, by the existing simple theories for journal bearing pressures. However, such theories are based on assumptions whereby only the relative speed between bearing and journal surfaces enters the governing equations. We discuss how these same assumptions motivate some new combinations of boundary conditions that allow reasonably simple numerical treatment. In this paper, the resulting families of possible solutions are computed semi-numerically using a Fourier series expansion in one direction and finite differences and numerical continuation in the other. We find that one such solution family contains small-extent solutions similar to those observed experimentally.

Sharma, Nikhil; Vimal, T.; Chatterjee, Anindya

2014-03-01

367

Angles in fuzzy disc and angular noncommutative solitons

NASA Astrophysics Data System (ADS)

The fuzzy disc, introduced by the authors of [1], is a disc-shaped region in a noncommutative plane, and is a fuzzy approximation of a commutative disc. In this paper we show that one can introduce a concept of angles to the fuzzy disc, by using the phase operator and phase states known in quantum optics. We gave a description of the fuzzy disc in terms of operators and their commutation relations, and studied properties of angular projection operators. A similar construction for the fuzzy annulus is also given. As an application, we constructed fan-shaped soliton solutions of a scalar field theory on the fuzzy disc. We also applied this concept to the theory of noncommutative gravity we proposed in [2]. In addition, possible connections to some systems in physics are suggested.

Kobayashi, Shinpei; Asakawa, Tsuguhiko

2013-04-01

368

Energy versus angular momentum in black hole binaries.

Using accurate numerical-relativity simulations of (nonspinning) black-hole binaries with mass ratios 1:1, 2:1, and 3:1, we compute the gauge-invariant relation between the (reduced) binding energy E and the (reduced) angular momentum j of the system. We show that the relation E(j) is an accurate diagnostic of the dynamics of a black-hole binary in a highly relativistic regime. By comparing the numerical-relativity E(NR)(j) curve with the predictions of several analytic approximation schemes, we find that, while the canonically defined, nonresummed post-Newtonian-expanded E(PN)(j) relation exhibits large and growing deviations from E(NR)(j), the prediction of the effective one body formalism, based purely on known analytical results (without any calibration to numerical relativity), agrees strikingly well with the numerical-relativity results. PMID:22540688

Damour, Thibault; Nagar, Alessandro; Pollney, Denis; Reisswig, Christian

2012-03-30

369

Angular Momentum Transport in Double White Dwarf Binaries

NASA Astrophysics Data System (ADS)

We present simulations of dynamical mass transfer in a double white dwarf binary with an initial mass ratio of 0.4. The binary components are approximated as polytropes of index n = 3/2 and the synchronously rotating, semi-detached equilibrium binary is evolved hydrodynamically with the gravitational potential being computed through the solution of Poisson's equation. Upon initiating deep contact, the mass transfer rate grows by more than an order of magnitude over approximately ten orbits, as would be expected for dynamically unstable mass transfer. However, the mass transfer rate then reaches a peak value, the binary expands and the mass transfer event subsides over approximately 30 orbits. Despite the loss of orbital angular momentum into the spin of the accreting star, we find that the accretor's spin saturates and the binary responds as one would expect for a system with an accretion disk filling a substantial fraction of the accretor's Roche lobe. It appears that double white dwarf binaries may be more resilient against merger than previously anticipated though our simulations do not include radiation forces which may ultimately fill a common envelope which dooms the binary.

Motl, Patrick M.; Tohline, Joel E.; Frank, Juhan

2006-11-01

370

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

371

Interpolation function for approximating knee joint behavior in human gait

NASA Astrophysics Data System (ADS)

Starting from the importance of analyzing the kinematic data of the lower limb in gait movement, especially the angular variation of the knee joint, the paper propose an approximation function that can be used for processing the correlation among a multitude of knee cycles. The approximation of the raw knee data was done by Lagrange polynomial interpolation on a signal acquired using Zebris Gait Analysis System. The signal used in approximation belongs to a typical subject extracted from a lot of ten investigated subjects, but the function domain of definition belongs to the entire group. The study of the knee joint kinematics plays an important role in understanding the kinematics of the gait, this articulation having the largest range of motion in whole joints, in gait. The study does not propose to find an approximation function for the adduction-abduction movement of the knee, this being considered a residual movement comparing to the flexion-extension.

Toth-Ta?c?u, Mirela; Pater, Flavius; Stoia, Dan Ioan

2013-10-01

372

Angular spectrum detection instrument for label-free photonic crystal sensors.

An angular spectrum analysis system was demonstrated to monitor the optical resonant mode of a photonic crystal (PC) sensor comprised of a one-dimensional grating structure. Exposed to solutions with different refractive indices or adsorbed with biomaterials, the PC sensor exhibited changes of the optical resonant modes. The developed detection system utilized a focused laser beam to detect shifts of the resonant angle, and thereby allowed a kinetic analysis of chemical absorption. Such a detection apparatus offers an adjustable angular resolution and a tunable detection range for a wide variety of refractometric sensing applications. A limit of detection of 6.57×10^{-5} refractive index unit has been observed. The instrument also offers an imaging capability of rapidly characterizing low-contrast samples deposited on the PC surface with a spatial resolution of 10 ?m. PMID:24784094

Liu, Longju; Xu, Zhen; Dong, Liang; Lu, Meng

2014-05-01

373

Resolution performance of the extra ultraviolet telescopes

NASA Astrophysics Data System (ADS)

The Extreme Ultraviolet Telescopes (EUT) Operates at wavelengths between 100-1000 Ĺ. As an important parameter of the telescope system, before the launch, angular resolution is necessary to be calibrated for testing the imaging performance of EUT. However, the difficulty and expense of fabricating optical testing systems capable of imaging the characteristic EUV wavelengths, has precluded in working wavelength resolution testing. This article taken a Ritchey-Chrétien normal incidence optical system as sample and resolution tests were carried out at visible wavelength. Based on this measurement, the angular resolution error budget at visible wavelength was calculated. At working wavelength, we added the squares of the pointing jitter error, the resolution focusing error and the scattering error, to the theoretical Rayleigh diffraction limit at the wavelength of operation, and then take the square root of this sum, an upper limit estimate of telescope's resolution was obtained about 0.4705 arcsec. This result proved that the EUT worked at diffraction-limited level and the resolution performance has met the demand of design.

Fu, Huai-yang; Zhou, Sizhong; Jiang, Kai; Mei, Chao

2013-08-01

374

National Technical Information Service (NTIS)

This collision probabilistic method is broadly used in cylindrical geometry (in one- or two-dimensions). It constitutes a powerful tool for the heterogeneous Response Method where, the coupling current is of the cosine type, that is, without angular depen...

E. A. Villarino

1990-01-01

375

Rapid Generation of Angular Momentum in Bounded Magnetized Plasma

Direct numerical simulations of two-dimensional decaying MHD turbulence in bounded domains show the rapid generation of angular momentum in nonaxisymmetric geometries. It is found that magnetic fluctuations enhance this mechanism. On a larger time scale, the generation of a magnetic angular momentum, or angular field, is observed. For axisymmetric geometries, the generation of angular momentum is absent; nevertheless, a weak magnetic field can be observed. The derived evolution equations for both the angular momentum and angular field yield possible explanations for the observed behavior.

Bos, Wouter J. T. [LMFA, UMR CNRS 5509, Ecole Centrale de Lyon-Universite de Lyon, Ecully (France); M2P2, UMR 6181 CNRS and CMI, Universites d'Aix-Marseille, Marseille (France); Neffaa, Salah; Schneider, Kai [M2P2, UMR 6181 CNRS and CMI, Universites d'Aix-Marseille, Marseille (France)

2008-12-05

376

Angular momentum redistribution by SASI spiral modes and consequences for neutron star spins

NASA Astrophysics Data System (ADS)

In the collapsing core of massive stars, the standing accretion shock instability (SASI) can drive spiral modes that efficiently redistribute angular momentum. This process can impart a spin to the forming neutron star even when the progenitor star is non-rotating. Here we develop the first analytical description of the angular momentum redistribution driven by a spiral mode of the SASI. Our analysis, valid in the limit of small mode amplitude, shows that the angular momentum separation is driven by the Reynolds stress generated by the spiral mode. The resulting solutions compare favourably with previous 3D hydrodynamic simulations of the SASI in the linear and weakly non-linear phases. Reasonable agreement is also found when extrapolating the solutions into the fully non-linear phase. A Reynolds decomposition of the flow is performed in the saturated state of these simulations, showing that outward angular momentum transport by the Reynolds stress and the fluctuating component of the mass flux balance inward transport by advection. We derive an approximate analytic expression for the maximum angular momentum deposited in the neutron star as a function of the mass accretion rate, shock radius, shock compression ratio, and amplitude of the spiral mode at the time of explosion. Implications for the birth spin periods of neutron stars are discussed.

Guilet, Jérôme; Fernández, Rodrigo

2014-07-01

377

Momentum measurement by the angular method in the Emulsion Cloud Chamber

We present the first automated momentum measurement in an Emulsion Cloud Chamber, consisting of multiple sandwiches of lead plates and nuclear emulsion sheets. The measurement is based on the detection of the multiple Coulomb scattering analysed by the so-called angular method. A 3X0 chamber was exposed to 2, 3 and 4GeV\\/c ??. A pion momentum resolution of 36% at 4GeV\\/c,

M. De Serio; M. Ieva; S. Simone; M. Giorgini; M. Sioli; G. Sirri; S. Buontempo; N. D'Ambrosio; G. De Lellis; G. Rosa; S. Mangano; P. Migliozzi; C. Pistillo; L. Scotto Lavina; V. Tioukov; P. Righini; E. Barbuto; C. Bozza; C. Sirignano

2003-01-01

378

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

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.

Marquez, Jose Manuel Andujar; Bohorquez, Miguel Angel Martinez; Garcia, Jonathan Medina; Nieto, Francisco Jose Aguilar

2010-01-01

379

Multifocus lemniscates: Approximation of curves

NASA Astrophysics Data System (ADS)

A focal method for the continuous approximation of smooth closed plane curves is proposed. Multifocus lemniscates are used as the approximating functions. The curve to be approximated is represented by a finite set of foci inside the curve; the number and the location of the foci provide the degrees of freedom for the focal approximation. An algorithmic solution of this problem in various modifications is constructed. Proximity criteria for curves are proposed. A comparative analysis of the approximative capabilities of the focal method with the capabilities of the classical harmonic approximation method is performed.

Rakcheeva, T. A.

2010-11-01

380

On uniform approximation of elliptic functions by Pade approximants

Diagonal Pade approximants of elliptic functions are studied. It is known that the absence of uniform convergence of such approximants is related to them having spurious poles that do not correspond to any singularities of the function being approximated. A sequence of piecewise rational functions is proposed, which is constructed from two neighbouring Pade approximants and approximates an elliptic function locally uniformly in the Stahl domain. The proof of the convergence of this sequence is based on deriving strong asymptotic formulae for the remainder function and Pade polynomials and on the analysis of the behaviour of a spurious pole. Bibliography: 23 titles.

Khristoforov, Denis V [Steklov Mathematical Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2009-06-30

381

On uniform approximation of elliptic functions by Padé approximants

NASA Astrophysics Data System (ADS)

Diagonal Padé approximants of elliptic functions are studied. It is known that the absence of uniform convergence of such approximants is related to them having spurious poles that do not correspond to any singularities of the function being approximated. A sequence of piecewise rational functions is proposed, which is constructed from two neighbouring Padé approximants and approximates an elliptic function locally uniformly in the Stahl domain. The proof of the convergence of this sequence is based on deriving strong asymptotic formulae for the remainder function and Padé polynomials and on the analysis of the behaviour of a spurious pole. Bibliography: 23 titles.

Khristoforov, Denis V.

2009-06-01

382

Approximation for Bayesian Ability Estimation.

National Technical Information Service (NTIS)

An approximation is proposed for the posterior mean and standard deviation of the ability parameter in an item response model. The procedure assumes that approximations to the posterior mean and covariance matrix of item parameters are available. It is ba...

R. K. Tsutakawa M. J. Soltys

1987-01-01

383

Satellite Angular Rate Estimation From Vector Measurements

NASA Technical Reports Server (NTRS)

This paper presents an algorithm for estimating the angular rate vector of a satellite which is based on the time derivatives of vector measurements expressed in a reference and body coordinate. The computed derivatives are fed into a spacial Kalman filter which yields an estimate of the spacecraft angular velocity. The filter, named Extended Interlaced Kalman Filter (EIKF), is an extension of the Kalman filter which, although being linear, estimates the state of a nonlinear dynamic system. It consists of two or three parallel Kalman filters whose individual estimates are fed to one another and are considered as known inputs by the other parallel filter(s). The nonlinear dynamics stem from the nonlinear differential equation that describes the rotation of a three dimensional body. Initial results, using simulated data, and real Rossi X ray Timing Explorer (RXTE) data indicate that the algorithm is efficient and robust.

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

1996-01-01

384

Behavior of nuclei at high angular momentum

The present report begins with a brief overview of nuclear shapes and level structures at high-spin values. The new spectroscopy associated with angular-momentum alignments is described, and some of the exciting possibilities of this spectroscopy are explored. Nuclear moments of inertia are discussed and a somewhat different one is defined, together with a method for measuring it and some early results. Finally a few comments on the future prospects for high-spin physics are offered.

Stephens, F.S.

1982-07-01

385

Results on angular correlations with ALICE

NASA Astrophysics Data System (ADS)

Angular correlations are a sensitive probe of the transport properties of the system produced in nucleus-nucleus collisions. Similar studies performed in p-Pb collisions have recently revealed intriguing features as well. In this article, we review the latest results on charged and identified particle correlations obtained with the ALICE detector at the LHC in both Pb-Pb and p-Pb events.

Christakoglou, Panos; Alice Collaboration

2014-05-01

386

Angular synchronization by eigenvectors and semidefinite programming

The angular synchronization problem is to obtain an accurate estimation (up to a constant additive phase) for a set of unknown angles ?1, ,?n from m noisy measurements of their offsets ?i??jmod 2?. Of particular interest is angle recovery in the presence of many outlier measurements that are uniformly distributed in [0,2?) and carry no information on the true offsets. We introduce

Amit Singer

2011-01-01

387

Angular strain estimation method for elastography

In the conventional cross-correlation-based strain estimation, there is a trade-off between the interpolation accuracy and the computational requirement. On the other hand, the autocorrelation-based method does not need interpolation, but it cannot estimate the wide range of displacements for elastography. We have developed a new strain estimator, called the angular strain estimation method, which does not need any interpolation and

Unmin Bae; Yongmin Kim

2007-01-01

388

Chirality and angular momentum in optical radiation

NASA Astrophysics Data System (ADS)

This paper develops, in precise quantum electrodynamic terms, photonic attributes of the optical chirality density, one of several measures long known to be conserved quantities for a vacuum electromagnetic field. The analysis lends insights into some recent interpretations of chiroptical experiments, in which this measure, and an associated chirality flux, have been treated as representing physically distinctive superchiral phenomena. In the fully quantized formalism the chirality density is promoted to operator status, whose exploration with reference to an arbitrary polarization basis reveals relationships to optical angular momentum and helicity operators. Analyzing multimode beams with complex wave-front structures, notably Laguerre-Gaussian modes, affords a deeper understanding of the interplay between optical chirality and optical angular momentum. By developing theory with due cognizance of the photonic character of light, it emerges that only the spin-angular momentum of light is engaged in such observations. Furthermore, it is shown that these prominent measures of the helicity of chiral electromagnetic radiation have a common basis in differences between the populations of optical modes associated with angular momenta of opposite sign. Using a calculation of the rate of circular dichroism as an example, with coherent states to model the electromagnetic field, it is discovered that two terms contribute to the differential effect. The primary contribution relates to the difference in left- and right-handed photon populations; the only other contribution, which displays a sinusoidal distance dependence corresponding to the claim of nodal enhancements, is connected with the quantum photon number-phase uncertainty relation. From the full analysis, it appears that the term superchiral can be considered redundant.

Coles, Matt M.; Andrews, David L.

2012-06-01

389

Noncommutative lattices as finite approximations

Lattice discretizations of continuous manifolds are common tools used in a variety of physical contexts. Conventional discrete approximations, however, cannot capture all aspects of the original manifold, notably its topology. In this paper we discuss an approximation scheme due to Sorkin (1991) which correctly reproduces important topological aspects of continuum physics. The approximating topological spaces are partially ordered sets (posets),

A. P. Balachandran; G. Bimonte; E. Ercolessi; G. Landi; F. Lizzi; G. Sparano; P. Teotonio-Sobrinho

1996-01-01

390

Combining global and local approximations

A method based on a linear approximation to a scaling factor, designated the 'global-local approximation' (GLA) method, is presented and shown capable of extending the range of usefulness of derivative-based approximations to a more refined model. The GLA approach refines the conventional scaling factor by means of a linearly varying, rather than constant, scaling factor. The capabilities of the method

Raphael T. Haftka

1991-01-01

391

Taylor Approximations and Definite Integrals

ERIC Educational Resources Information Center

We investigate the possibility of approximating the value of a definite integral by approximating the integrand rather than using numerical methods to approximate the value of the definite integral. Particular cases considered include examples where the integral is improper, such as an elliptic integral. (Contains 4 tables and 2 figures.)

Gordon, Sheldon P.

2007-01-01

392

Time-dependent photoelectron angular distributions

NASA Astrophysics Data System (ADS)

I show that the angular distribution of electrons photoionized from gas phase targets by short light pulses is time-dependent, when the orbital momentum composition of the photocurrent changes with excitation energy so evolves with the time of detection. A theory of time- dependent photoionization is outlined and general formulas of time-dependent photoelectron flux and angular distribution are given. Two general propagator methods suitable to describe the time-dependent photoionization and scattering processes are developed. The photoionization process is viewed as a local excitation followed by a half scattering. The local excitation process is solved theoretically in a small region around the target core. This approach has been generalized to describe the evolution of a wavepacket in an unbound system. An asymptotic propagator theorem is discovered and used to derive analytic expressions for asymptotic propagators. The origin of the time dependence is explored by parameterizing the time delay and orbital momentum coupling in a two channel model. K-shell photoionization of N2 and CO are calculated with this time- dependent photoionization theory, implemented using a multiple scattering model. Numerical results demonstrate that the time dependence of photoelectron angular distributions is a realistic effect.

Wang, Xiangyang

1999-09-01

393

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

394

Optical angular momentum in a rotating frame.

It is well established that light carrying orbital angular momentum (OAM) can be used to induce a mechanical torque causing an object to spin. We consider the complementary scenario: will an observer spinning relative to the beam axis measure a change in OAM as a result of their rotational velocity? Remarkably, although a linear Doppler shift changes the linear momentum of a photon, the angular Doppler shift induces no change in the angular momentum. Further, we examine the rotational Doppler shift in frequency imparted to the incident light due to the relative motion of the beam with respect to the observer and consider what must happen to the measured wavelength if the speed of light c is to remain constant. We show specifically that the OAM of the incident beam is not affected by the rotating observer and that the measured wavelength is shifted by a factor equal and opposite to that of the frequency shift induced by the rotational Doppler effect. PMID:24978243

Speirits, Fiona C; Lavery, Martin P J; Padgett, Miles J; Barnett, Stephen M

2014-05-15

395

Angular craniometry in craniocervical junction malformation.

The craniometric linear dimensions of the posterior fossa have been relatively well studied, but angular craniometry has been poorly studied and may reveal differences in the several types of craniocervical junction malformation. The objectives of this study were to evaluate craniometric angles compared with normal subjects and elucidate the main angular differences among the types of craniocervical junction malformation and the correlation between craniocervical and cervical angles. Angular craniometries were studied using primary cranial angles (basal and Boogard's) and secondary craniocervical angles (clivus canal and cervical spine lordosis). Patients with basilar invagination had significantly wider basal angles, sharper clivus canal angles, larger Boogard's angles, and greater cervical lordosis than the Chiari malformation and control groups. The Chiari malformation group does not show significant differences when compared with normal controls. Platybasia occurred only in basilar invagination and is suggested to be more prevalent in type II than in type I. Platybasic patients have a more acute clivus canal angle and show greater cervical lordosis than non-platybasics. The Chiari group does not show significant differences when compared with the control, but the basilar invagination groups had craniometric variables significantly different from normal controls. Hyperlordosis observed in the basilar inavagination group was associated with craniocervical kyphosis conditioned by acute clivus canal angles. PMID:23640096

Botelho, Ricardo Vieira; Ferreira, Edson Dener Zandonadi

2013-10-01

396

NASA Astrophysics Data System (ADS)

The photodetachment spectrum of O2- has been measured at a number of wavelengths using velocity-map imaging. The electron kinetic-energy resolution (< 5 meV) is sufficient to resolve the anion fine-structure splitting, vibrational and electronic structure. The electron angular distribution varies with the electron kinetic-energy, with a different behaviour for each vibronic band.

Gibson, S. T.; Cavanagh, S. J.; Lewis, B. R.; Gascooke, J. R.; Mabbs, R.; Sanov, A.

2009-11-01

397

Measuring Angular Accelerations of a Model Head Using Linear Accelerometers.

National Technical Information Service (NTIS)

Angular accelerations are considered responsible for certain types of common brain injuries. It is therefore of great importance that they can be measured in conjunction with testing of protective headgear. Angular accelerometers presently on the market a...

C. Ljung

1983-01-01

398

Temporal resolution enhancement from motion

NASA Astrophysics Data System (ADS)

We describe progress in the third year of the EMRS DTC TEP theme project entitled "Temporal Resolution Enhancement from Motion". The aim is to develop algorithms that combine evidence over time from a sequence of images in order to improve spatial resolution and reduce unwanted artefacts. Years one and two of this project developed and demonstrated an efficient algorithm that provided good resolution enhancement of a scene viewed in the far field (approximately flat) [1]. This paper reports a new algorithm which is applicable to a three dimensional scene where substantial depth variation causes parallax within the imagery. The new algorithm is demonstrated using airborne infra-red imagery.

Rollason, M. P.; Watson, G. H.; Strens, M. J. A.

2009-09-01

399

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

400

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

401

Angular momentum primitives for human walking: biomechanics and control

Towards the goal of developing stable humanoid robots and leg prostheses, we present a biologically motivated control strategy for walking where system angular momentum is explicitly controlled. Using human kinematic gait data, we calculate the distribution of spin angular momentum throughout the human body at slow and self-selected walking speeds. Principal component analysis reveals three angular momentum primitives that explain

Marko Popovic; Amy Englehart

2004-01-01

402

Photoelectron angular distributions at the ionization of atoms by intense sub-one-cycle laser pulses

NASA Astrophysics Data System (ADS)

The phase sensitivity of the photoelectron angular distributions by intense sub-one-cycle linearly polarized laser pulses has been discussed within the analytic Landau-Dykhne approximation. In both cases of sine and cosine laser pulses most of the electrons are ejected along the polarization axis of the laser field. Nevertheless the electron yield and the electron kinetic energies are much larger for the cosine waveform pulse.

Rastunkov, V. S.; Krainov, V. P.

2009-04-01

403

On the use of an absorption layer for the angular spectrum approach (L).

Reducing the spatial aliasing error of the angular spectrum method by using an absorption layer is investigated in this paper. The acoustic equation including the absorption layer is presented and is transformed in the spatial frequency domain, where an implicit analytic solution is readily available. Its approximation, which is more suitable for numerical simulation, is derived and is numerically implemented. The comparisons between the present method and available methods demonstrate its validity and advantages. PMID:22352473

Jing, Yun

2012-02-01

404

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.

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

2011-01-01

405

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

406

Angular Momentum Exchange in White Dwarf Binaries Accreting Through Direct Impact

NASA Astrophysics Data System (ADS)

We examine the exchange of angular momentum between the component spins and the orbit in semi-detached double white dwarf binaries undergoing mass transfer through direct impact of the transfer stream. We approximate the stream as a series of discrete massive particles ejected in the ballistic limit at the inner Lagrangian point of the donor toward the accretor. This work improves upon similar earlier studies in a number of ways. First, we self-consistently calculate the total angular momentum of the orbit at all times. This includes changes in the orbital angular momentum during the ballistic trajectory of the ejected mass, as well as changes during the ejection/accretion due to the radial component of the particle's velocity. Second, we calculate the particle's ballistic trajectory for each system, which allows us to determine the precise position and velocity of the particle upon accretion. We can then include specific information about the radius of the accretor as well as the angle of impact. Finally, we ensure that the total angular momentum is conserved, which requires the donor star spin to vary self-consistently. With these improvements, we calculate the angular momentum change of the orbit and each binary component across the entire parameter space of direct impact double white dwarf binary systems. We find a significant decrease in the amount of angular momentum removed from the orbit during mass transfer, as well as cases where this process increases the angular momentum of the orbit at the expense of the spin angular momentum of the donor. We conclude that, unlike earlier claims in the literature, mass transfer through direct impact need not destabilize the binary and that the quantity and sign of the orbital angular momentum transfer depends on the binary properties, particularly the masses of the double white dwarf binary component stars. This stabilization may significantly impact the population synthesis calculations of the expected numbers of events/systems for which double white dwarfs may be a progenitor, e.g., Type Ia supernovae, Type.Ia supernovae, and AM CVn.

Sepinsky, J. F.; Kalogera, V.

2014-04-01

407

Natural roller bearing fault detection by angular measurement of true instantaneous angular speed

NASA Astrophysics Data System (ADS)

The challenge in many production activities involving large mechanical devices like power transmissions consists in reducing the machine downtime, in managing repairs and in improving operating time. Most online monitoring systems are based on conventional vibration measurement devices for gear transmissions or bearings in mechanical components. In this paper, we propose an alternative way of bearing condition monitoring based on the instantaneous angular speed measurement. By the help of a large experimental investigation on two different applications, we prove that localized faults like pitting in bearing generate small angular speed fluctuations which are measurable with optical or magnetic encoders. We also emphasize the benefits of measuring instantaneous angular speed with the pulse timing method through an implicit angular sampling which ensures insensitivity to speed fluctuation. A wide range of operating conditions have been tested for the two applications with varying speed, load, external excitations, gear ratio, etc. The tests performed on an automotive gearbox or on actual operating vehicle wheels also establish the robustness of the proposed methodology. By the means of a conventional Fourier transform, angular frequency channels kinematically related to the fault periodicity show significant magnitude differences related to the damage severity. Sideband effects are evidently seen when the fault is located on rotating parts of the bearing due to load modulation. Additionally, slip effects are also suspected to be at the origin of enlargement of spectrum peaks in the case of double row bearings loaded in a pure radial direction.

Renaudin, L.; Bonnardot, F.; Musy, O.; Doray, J. B.; Rémond, D.

2010-10-01

408

The optically driven angular alignment of micromachined components (microlenses and microprisms) within a single-beam optical trap using a linearly-polarized laser is presented. This optically induced angular alignment around the laser beam axis results from the spin angular momentum of the laser beam produced by the birefringence of the trapped microcomponents. The microcomponents are fabricated by reactive ion etching of an

E. Higurashi; R. Sawada; T. Ito

2001-01-01

409

High-resolution infrared mapping of the Galactic center - Imaging and lunar occultations

This paper presents 2.2-micron observations of lunar occultations of the Galactic center that occurred in September 1988 and February 1989. These observations were used to determine the angular size of sources in and near IRS 16 with an accuracy of about 0.02 arcsec (or about 200 AU). Also presented are high-resolution images of IRS 16 at 1.65 and 2.2 micron and an analysis of the September 1986 occultation data originally published by Adams et al. (1988). The combined results of the analyses indicate that the major components of IRS 16, namely IRS 16NE, 16C, 16SW, and 16 NW are all compact, with diameters less than about 200 AU. They all have absolute 2.2-micron magnitudes of approximately -8. 30 refs.

Simons, D.A.; Hodapp, K.W.; Becklin, E.E. (Hawaii Univ., Honolulu (USA))

1990-09-01

410

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

411

Model-independent forecasts of CMB angular power spectra for the Planck mission

NASA Astrophysics Data System (ADS)

The Planck mission, designed for making measurements of the cosmic microwave background (CMB) radiation with unprecedented accuracy and angular resolution, is expected to release its entire data in the near future. In this paper, we provide model-independent forecasts for the TT, EE, and TE angular power spectra for the Planck mission using synthetic data based on the best-fit Lambda cold dark matter (?CDM) model. The nonparametric function estimation methodology we use here is based on the agnostic viewpoint of allowing the data to speak for themselves rather than letting the models decide what is inferred from the data. Our analysis indicates that the three Planck angular power spectra will be determined sufficiently well for 2?l ?lmax, where lmax=25001ex" stretchy="true">(TT1ex" stretchy="true">), 1377(EE), and 1727(TE) respectively. A key signature of reionization, namely, a bump at low values of l, is evident in our forecasts for the EE and TE power spectra. Nonparametric confidence bands in the phase shift (?m) versus acoustic scale (lA) plane, corresponding to the first eight peaks in the TT power spectrum, show a confluence region for 300?lA?305 which is in good agreement with the estimate lA=300 based on the best-fit ?CDM model. From our results, we expect that the final Planck data should lead to accurate model-independent estimates of CMB angular power spectra using our nonparametric regression formalism.

Aghamousa, Amir; Arjunwadkar, Mihir; Souradeep, Tarun

2014-01-01

412

Whole-body angular momentum during stair ascent and descent.

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

413

Angular distributions of neutron-nucleus collisions

We derive the total and the differential cross sections with respect to angle for neutron-induced reactions from an analytical model having a simple functional form to demonstrate the quantitative agreement with the measured cross sections. The energy dependence of the neutron-nucleus interaction cross sections are estimated successfully for energies ranging from 5 to 600 MeV. In this work, the effect of the imaginary part of the nuclear potential is treated more appropriately compared to our earlier work. The angular distributions for neutron scattering also agree reasonably well with the experimental data at forward angles.

Mukhopadhyay, Tapan; Lahiri, Joydev; Basu, D. N. [Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700 064 (India)

2011-06-15

414

Angular momentum flux of counterpropagating paraxial beams.

We study the angular momentum (AM) of the arbitrary superposition of counterpropagating paraxial beams that have the same magnitude of the wavenumber. We derive compact analytical expressions for the total AM in a transverse cross section (linear AM density) and the total AM flux through the cross section. We demonstrate that whereas for the time-averaged linear AM density its separation into the spin and orbital parts is not, generally, observed, the total time-averaged AM flux is separated into well-identifiable spin and orbital constituents. Moreover, we show that such a flux is also naturally separated into the fluxes of forward- and backward-propagating beams. PMID:18311232

Alexeyev, Constantine N; Yavorsky, Maxim A; Shvedov, Vladlen G

2008-03-01

415

Angular Momentum Sensitive Two-Center Interference

NASA Astrophysics Data System (ADS)

In quantum mechanics the Young-type double-slit experiment can be performed with electrons either traveling through a double slit or being coherently emitted from two inversion symmetric molecular sites. In the latter one the valence photoionization cross sections of homonuclear diatomic molecules were predicted to oscillate over kinetic energy almost 50 years ago. Beyond the direct proof of the oscillatory behavior of these photoionization cross sections ?, we show that the angular distribution of the emitted electrons reveals hitherto unexplored information on the relative phase shift between the corresponding partial waves through two-center interference patterns.

Ilchen, M.; Glaser, L.; Scholz, F.; Walter, P.; Deinert, S.; Rothkirch, A.; Seltmann, J.; Viefhaus, J.; Decleva, P.; Langer, B.; Knie, A.; Ehresmann, A.; Al-Dossary, O. M.; Braune, M.; Hartmann, G.; Meissner, A.; Tribedi, L. C.; AlKhaldi, M.; Becker, U.

2014-01-01

416

Linear and angular retroreflecting interferometric alignment target

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

417

Nonstandard Higgs couplings from angular distributions in

NASA Astrophysics Data System (ADS)

We compute the fully differential rate for the Higgs-boson decay , with . For these processes we assume the most general matrix elements within an effective Lagrangian framework. The electroweak chiral Lagrangian we employ assumes minimal particle content and Standard Model gauge symmetries, but it is otherwise completely general. We discuss how information on new physics in the decay form factors may be obtained that is inaccessible in the dilepton-mass spectrum integrated over angular variables. The form factors are related to the coefficients of the effective Lagrangian, which are used to estimate the potential size of new-physics effects.

Buchalla, Gerhard; Catŕ, Oscar; D'Ambrosio, Giancarlo

2014-03-01

418

The Cosmology Large Angular Scale Surveyor (CLASS)

NASA Astrophysics Data System (ADS)

The Cosmology Large Angular Scale Surveyor (CLASS) is an array of telescopes designed to search for the signature of inflation in the polarization of the Cosmic Microwave Background (CMB). By combining the strategy of targeting large scales (>2 deg) with novel front-end polarization modulation and novel detectors at multiple frequencies, CLASS will pioneer a new frontier in ground-based CMB polarization surveys. In this talk, I give an overview of the CLASS instrument, survey, and outlook on setting important new limits on the energy scale of inflation.

Eimer, Joseph; Ali, A.; Amiri, M.; Appel, J. W.; Araujo, D.; Bennett, C. L.; Boone, F.; Chan, M.; Cho, H.; Chuss, D. T.; Colazo, F.; Crowe, E.; Denis, K.; Dünner, R.; Essinger-Hileman, T.; Gothe, D.; Halpern, M.; Harrington, K.; Hilton, G.; Hinshaw, G. F.; Huang, C.; Irwin, K.; Jones, G.; Karakla, J.; Kogut, A. J.; Larson, D.; Limon, M.; Lowry, L.; Marriage, T.; Mehrle, N.; Miller, A. D.; Miller, N.; Moseley, S. H.; Novak, G.; Reintsema, C.; Rostem, K.; Stevenson, T.; Towner, D.; U-Yen, K.; Wagner, E.; Watts, D.; Wollack, E.; Xu, Z.; Zeng, L.

2014-01-01

419

Angular Momentum Distribution of Fission Fragments

NASA Astrophysics Data System (ADS)

Latest generation fission experiments provide an excellent testing ground for theoretical models. In this contribution we compare the measurements obtained with the DANCE calorimeter at LANSCE with our full-scale simulation of the primary fragment de-excitation, using the recently developed CGMF code, based on a Monte-Carlo implementation of the Hauser-Feshbach theoretical model. We compute the isomeric ratios as a function of the initial angular momentum of the fission fragments. Comparison with the available experimental data allows us to determine the initial spin distribution. Finally, we study the sensitivity to the discrete spectra input.

Stetcu, I.; Talou, P.; Kawano, T.; Jandel, M.

2014-04-01

420

Angular distributions of high-order ATI

The above-threshold ionization (ATI), a strong-field behavior, can be studied using kilohertz lasers. This paper reports a study of electron angular distributions (AD) for Xe and Kr excited by a 50 ps, 1.05 {mu}m strong field. ADs are presented for ATI orders up to 30 and show a new intensity-dependent structure. A physical picture is proposed that has its source in one-electron, and not two-electron, dynamics. 2 figs, 5 refs.

Yang, Baorui; Walker, B.; DiMauro, L.F. [Brookhaven National Lab., Upton, NY (United States); Schafer, K.J.; Kulander, K.C. [Lawrence Livermore National Lab., CA (United States); Agostini, P. [Service de Recherches sur les Surfaces et l`Irradiation de la Matiere, Centre d`Etudes Nucleaires de Saclay, 91 - Gif-sur-Yvette (France)

1993-08-01

421

Angular Rate Estimation Using a Distributed Set of Accelerometers

A distributed set of accelerometers based on the minimum number of 12 accelerometers allows for computation of the magnitude of angular rate without using the integration operation. However, it is not easy to extract the magnitude of angular rate in the presence of the accelerometer noises, and even worse, it is difficult to determine the direction of a rotation because the angular rate is present in its quadratic form within the inertial measurement system equations. In this paper, an extended Kalman filter scheme to correctly estimate both the direction and magnitude of the angular rate through fusion of the angular acceleration and quadratic form of the angular rate is proposed. We also provide observability analysis for the general distributed accelerometers-based inertial measurement unit, and show that the angular rate can be correctly estimated by general nonlinear state estimators such as an extended Kalman filter, except under certain extreme conditions.

Park, Sungsu; Hong, Sung Kyung

2011-01-01

422

Angular rate estimation using a distributed set of accelerometers.

A distributed set of accelerometers based on the minimum number of 12 accelerometers allows for computation of the magnitude of angular rate without using the integration operation. However, it is not easy to extract the magnitude of angular rate in the presence of the accelerometer noises, and even worse, it is difficult to determine the direction of a rotation because the angular rate is present in its quadratic form within the inertial measurement system equations. In this paper, an extended Kalman filter scheme to correctly estimate both the direction and magnitude of the angular rate through fusion of the angular acceleration and quadratic form of the angular rate is proposed. We also provide observability analysis for the general distributed accelerometers-based inertial measurement unit, and show that the angular rate can be correctly estimated by general nonlinear state estimators such as an extended Kalman filter, except under certain extreme conditions. PMID:22346651

Park, Sungsu; Hong, Sung Kyung

2011-01-01

423

The advent of high angular resolution diffusion imaging (HARDI) has opened up new perspectives for the delineation of crossing and branching fiber pathways. However, image acquisition under clinical conditions with limited measurement time faces the problem of poor spatial and angular resolution and the technique's high susceptibility to noise. In this paper we present a straightforward spatial filter for ODF fields that uses the data-inherent structural information around a voxel as part of a directionally selective method for angular smoothing and radial regularization (ASRR). Especially in regions where fibers cross (multimodal voxels), the method allows us to reduce noise, improve the accuracy of ODF diffusion peaks, and strengthen signals of non-dominant fibers. Moreover, we propose a dynamic scheme in which regularization is applied only to ODFs classified as multimodal. The approach is quantitatively evaluated on synthetic datasets of various configurations. With an in vivo dataset of a human subject, measured under clinical imaging conditions, we demonstrate the method's ability to improve tractography of non-dominant transcallosal fiber pathways and the long fibers of the superior longitudinal fasciculus. PMID:22051017

Otto, K M; Ehricke, H-H; Kumar, V; Klose, U

2013-01-01

424

Fuzzy systems are universal approximators

The author proves that fuzzy systems are universal approximators. The Stone-Weierstrass theorem is used to prove that fuzzy systems with product inference, centroid defuzzification, and a Gaussian membership function are capable of approximating any real continuous function on a compact set to arbitrary accuracy. This result can be viewed as an existence theorem of an optimal fuzzy system for a

Li-Xin Wang

1992-01-01

425

Beta approximations for bridge sampling

We consider the problem of simulating X conditional on the value of X +Y , when X and Y are independent positive random variables. We propose approximate methods for sampling (X|X+Y) by approximating the fraction (X\\/z|X+ Y = z) with a beta random variable. We discuss applications to Levy processes and infinitely divisible distributions, and we report numerical tests for

Paul Glasserman; Kyoung-kuk Kim

2008-01-01

426

Parameterized Complexity and Approximation Algorithms

Approximation algorithms and parameterized complexity are usually considered to be two separate ways of dealing with hard algorithmic problems. In this paper, our aim is to investigate how these two fields can be combined to achieve better algorithms than what any of the two theories could offer. We discuss the different ways parameterized complexity can be extended to approximation algorithms,

Dániel Marx

2008-01-01

427

Secure Multiparty Computation of Approximations

Approximation algorithms can sometimes provide efficient solutions when no efficient exact computation is known. In particular, approximations are often useful in a distributed setting where the inputs are held by different parties and are extremely large. Furthermore, for some applications, the parties want to cooperate to compute a function of their inputs without revealing more information than necessary. If

Joan Feigenbaum; Yuval Ishai; Tal Malkin; Kobbi Nissim; Martin J. Strauss; Rebecca N. Wright

2001-01-01