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1

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

2

Photoelectron angular distributions beyond the dipole approximation  

SciTech Connect

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

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

1996-08-01

3

Complex angular momentum approximation to hard-core scattering  

NASA Technical Reports Server (NTRS)

The complex angular momentum (CAM) approximation for nonrelativistic quantum scattering by a hard sphere - a union of the recently developed CAM uniform approximation with a semiclassical WKB-like approximation valid at large angles - is shown to be remarkably accurate over the complete range of scattering angles and down to size parameters (circumference to de Broglie wavelength ratios) of order unity. The best approximations previously derivable (Fock-type) cannot reach large scattering angles where semiclassical approximations are useful; even at angles where Fock-type approximations are valid, they are typically two or more orders of magnitude less accurate than CAM. The crucial new feature responsible for the high accuracy of the CAM approximation is the treatment of large-angle diffraction associated with (1) tunneling near the edge of the scatterer, and (2) anomalous reflection.

Nussenzveig, H. M.; Wiscombe, W. J.

1991-01-01

4

Resolution analysis of an angular domain imaging system with two dimensional angular filters  

NASA Astrophysics Data System (ADS)

Angular Domain Imaging (ADI) employs an angular filter to distinguish between quasi-ballistic and scattered photons based on trajectory. A 2D angular filter array was constructed using 3D printing technology to generate an array of micro-channels 500 ?m x 500 ?m with a length of 12 cm. The main barrier to 2D imaging with the 2D angular filter array was the shadows cast on the image by the 500 ?m walls of the angular filter. The objective of this work was to perform a resolution analysis of the 2D angular filter array. The approach was to position the AFA with a two dimensional positioning stage to obtain images of areas normally obstructed by the walls of the AFA. A digital light processor was also incorporated to generate various light patterns to improve the contrast of the images. A resolution analysis was completed by imaging a knife edge submerged in various uniform scattering media (Intralipid® dilutions with water). The edge response functions obtained were then used to compute the line spread function and the theoretical resolution of the imaging system. The theoretical system resolution was measured to be between 110 ?m - 180 ?m when the scattering level was at or below 0.7% Intralipid®. The theoretical resolution was in agreement with a previous resolution analysis of a silicon-based angular filter with a similar aspect ratio. The measured resolution was also found to be smaller than the size of an individual channel, suggesting that the resolution of an AFA based ADI system is not dependent on the size of the micro-channel.

Ng, Eldon; Carson, Jeffrey J. L.

2013-02-01

5

Angular resolution obtained with a LaBr3-based rotational modulator  

NASA Astrophysics Data System (ADS)

A Rotational Modulator (RM) gamma ray imager, consisting of a single grid of lead slats rotating above an array of detectors with diameter equal to the slat spacing, has the capability of providing angular resolution significantly better than the geometric resolution (i.e., the ratio of detector diameter to mask/detector separation). The sensitivity, weight, and angular resolution are comparable to that of a coded aperture device, but with significantly less complexity. As the grid rotates, the transmission from a source is modulated on each detector between 0 and 100%. The count profile is cross-correlated with precalculated modulation profiles to produce an approximate source image. Deconvolution of this image with the known imager response can accurately resolve point sources and complex emissions. The appropriate deconvolution technique can achieve angular resolution better than the basic geometrical resolution of the instrument. A prototype RM developed at Louisiana State University features high sensitivity and energy resolution, functional angular resolution of 15, and a simple readout system. The detector array consists of 19 1.5 × 1 thick cerium-doped lanthanum bromide (LaBr3:Ce) crystals. LaBr3 produces significantly more light than other common scintillators, offering < 3% FWHM energy resolution at 662 keV. A grid spaced ~1.2 m from the detection plane with slat width 1.5 offers a 13.8° field of view. We present our reconstruction technique, deconvolution algorithms, and simulated and experimental imaging results.

Budden, Brent S.; Case, Gary L.; Cherry, Michael L.

2009-08-01

6

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

SciTech Connect

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

7

Distance-based tractography in high angular resolution diffusion MRI  

Microsoft Academic Search

High angular resolution diffusion imaging (HARDI) is a magnetic resonance imaging (MRI) technique, determining the diffusion\\u000a of water molecules in tissue in vivo. HARDI is advantageous over the well-known diffusion tensor imaging (DTI), since it is\\u000a able to extract more than one fiber orientation within a voxel and can therefore resolve crossing, kissing or fanning fiber\\u000a tracts. However, multiple orientations

Diana Röttger; Viktor Seib; Stefan Müller

2011-01-01

8

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, 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

9

The AT20G high-angular-resolution catalogue  

NASA Astrophysics Data System (ADS)

We present the high-angular-resolution catalogue for the Australia Telescope 20 GHz (AT20G) survey, using the high-angular-resolution 6-km antenna data at the baselines of ˜4500 m of the Australia Telescope Compact Array. We have used the data to produce the visibility catalogue that separates the compact active galactic nuclei (AGNs) from the extended radio sources at the 0.15 arcsec angular scale, corresponding to the linear size scale of 1 kpc at redshifts higher than 0.7. We find the radio population at 20 GHz to be dominated by compact AGNs constituting 77 per cent of the total sources in the AT20G. We introduce the visibility-spectra diagnostic plot, produced using the AT20G cross-matches with lower frequency radio surveys at 1 GHz [the NRAO VLA Sky Survey (NVSS) and the Sydney University Molonglo Sky Survey (SUMSS)], that separates the 20 GHz population into distinct sub-populations of the compact AGNs, the compact steep-spectrum (CSS) sources, the extended AGN-powered sources and extended flat-spectrum sources. The extended flat-spectrum sources include a local thermal emitting population of high-latitude planetary nebulae and also gravitational lens and binary black hole candidates among the AGNs. We find a smooth transition in properties between the CSS sources and the AGN populations. The visibility catalogue, together with the main AT20G survey, provides an estimate of angular size scales for sources in the AT20G and an estimate of the flux arising from central cores of extended radio sources. The identification of the compact AGNs in the AT20G survey provides high-quality calibrators for high-frequency radio telescope arrays and very large baseline interferometry observations.

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

2013-09-01

10

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

11

SYSTEMATICS IN METALLICITY GRADIENT MEASUREMENTS. I. ANGULAR RESOLUTION, SIGNAL TO NOISE, AND ANNULAR BINNING  

SciTech Connect

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

12

A Nonparametric Riemannian Framework for Processing High Angular Resolution Diffusion Images (HARDI)  

E-print Network

) [4]. In DTI, the diffusivity profile is characterized by a single oriented 3D Gaussian probabilityA Nonparametric Riemannian Framework for Processing High Angular Resolution Diffusion Images (HARDI@loni.ucla.edu Abstract High angular resolution diffusion imaging has become an important magnetic resonance technique

13

Spatially Regularized Compressed Sensing for High Angular Resolution Diffusion Imaging  

PubMed Central

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. PMID:21536524

Rathi, Yogesh; Dolui, Sudipto

2013-01-01

14

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

National Technical Information Service (NTIS)

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-...

A. Carlotti, F. Martinache, G. Knapp, J. E. Gunn, M. Galvin, M. Hayashi, M. Janson, M. A. Carr, M. A. Peters, M. W. McElwain, N. Takato, N. J. Kasdin, O. Guyon, Q. Gong, R. Lupton, T. Brandt, T. Groff

2012-01-01

15

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

SciTech Connect

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

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

2013-05-10

16

High Angular Resolution X-Ray Astronomy with Diffractive-Refractive Elements  

Microsoft Academic Search

No future grazing incidence X-ray telescope is likely to have an angular resolution that is signficantly superior to the Chandra X-Ray Observatory s Better angular resolution requires a new technology I describe an X-ray imaging system that has the potential to do based upon diffractive-refractive optics that transmit rather than reflect X-rays These optics are much less sensitive to figure

P. Gorenstein

2006-01-01

17

Apparent Diffusion Coefficients from High Angular Resolution Diffusion Imaging: Estimation and  

E-print Network

Apparent Diffusion Coefficients from High Angular Resolution Diffusion Imaging: Estimation resolution diffusion imaging has recently been of great interest in characterizing non-Gaussian diffusion pro- cesses. One important goal is to obtain more accurate fits of the apparent diffusion processes

Chen, Yiling

18

High energy resolution, high angular acceptance crystal monochromator  

DOEpatents

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

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

1996-06-04

19

High energy resolution, high angular acceptance crystal monochromator  

DOEpatents

A 4-bounce dispersive crystal monochromator reduces the bandpass of synchrotron radiation to a 10-50 meV range without sacrificing angular acceptance. The monochromator includes the combination of an asymmetrical channel-cut single crystal of lower order reflection and a symmetrical channel-cut single crystal of higher order reflection in a nested geometric configuration. In the disclosed embodiment, a highly asymmetrically cut (.alpha.=20) outer silicon crystal (4 2 2) with low order reflection is combined with a symmetrically cut inner silicon crystal (10 6 4) with high order reflection to condition a hard x-ray component (5-30 keV) of synchrotron radiation down to the .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

20

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

SciTech Connect

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

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

2010-04-15

21

The High Angular Resolution Multiplicity of Massive Stars  

E-print Network

We present the results of a speckle interferometric survey of Galactic massive stars that complements and expands upon a similar survey made over a decade ago. The speckle observations were made with the KPNO and CTIO 4 m telescopes and USNO speckle camera, and they are sensitive to the detection of binaries in the angular separation regime between 0.03" and 5" with relatively bright companions (Delta V < 3). We report on the discovery of companions to 14 OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37 Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary sample that we selected for future orbital determinations). We made a statistical analysis of the binary frequency among the subsample that are listed in the Galactic O Star Catalog by compiling published data on other visual companions detected through adaptive optics studies and/or noted in the Washington Double Star Catalog and by collecting published information on radial velocities and spectroscopic binaries. We find that the binary frequency is much higher among O-stars in clusters and associations compared to the numbers for field and runaway O-stars, consistent with predictions for the ejection processes for runaway stars. We present a first orbit for the O-star Delta Orionis, a linear solution of the close, apparently optical, companion of the O-star Iota Orionis, and an improved orbit of the Be star Delta Scorpii. Finally, we list astrometric data for another 249 resolved and 221 unresolved targets that are lower mass stars that we observed for various other science programs.

Brian D. Mason; William I. Hartkopf; Douglas R. Gies; Todd J. Henry; John W. Helsel

2008-11-04

22

Low Power Compact Radio Galaxies at High Angular Resolution  

SciTech Connect

We present sub-arcsecond resolution multi-frequency (8 and 22 GHz) VLA images of five low power compact (LPC) radio sources, and phase referenced VLBA images at 1.6 GHz of their nuclear regions. At the VLA resolution we resolve the structure and identify component positions and flux densities. The phase referenced VLBA data at 1.6 GHz reveals flat-spectrum, compact cores (down to a few milliJansky) in four of the five sources. The absolute astrometry provided by the phase referencing allows us to identify the center of activity on the VLA images. Moreover, these data reveal rich structures, including two-sided jets and secondary components. On the basis of the arcsecond scale structures and of the nuclear properties, we rule out the presence of strong relativistic effects in our LPCs, which must be intrinsically small (deprojected linear sizes {approx}< 10 kpc). Fits of continuous injection models reveal break frequencies in the GHz domain, and ages in the range 10{sup 5}-10{sup 7} yrs. In LPCs, the outermost edge may be advancing more slowly than in more powerful sources or could even be stationary; some LPCs might also have ceased their activity. In general, the properties of LPCs can be related to a number of reasons, including, but not limited to: youth, frustration, low kinematic power jets, and short-lived activity in the radio.

Giroletti, Marcello; Giovannini, G.; /Bologna U. /Bologna, Ist. Radioastronomia; Taylor, G.B.; /KIPAC, Menlo Park /NRAO, Socorro

2005-06-30

23

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

24

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

SciTech Connect

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

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

1987-01-01

25

NTU-90: A high angular resolution brain atlas constructed by q-space diffeomorphic reconstruction  

Microsoft Academic Search

We present a high angular resolution brain atlas constructed by averaging 90 diffusion spectrum imaging (DSI) datasets in the ICBM-152 space. The spatial normalization of the diffusion information was conducted by a novel q-space diffeomorphic reconstruction method, which reconstructed the spin distribution function (SDF) in the ICBM-152 space from the diffusion MR signals. The performance of this method was examined

Fang-Cheng Yeh; Wen-Yih Isaac Tseng

2011-01-01

26

Local Water Diffusion Phenomenon Clustering From High Angular Resolution Diffusion Imaging (HARDI)  

E-print Network

of water molecules in biological tissues such as the human brain white matter. The great success of DWLocal Water Diffusion Phenomenon Clustering From High Angular Resolution Diffusion Imaging (HARDI of neurodegenerative diseases un- doubtedly passes through the study of human brain white matter fiber tracts. To date

Boyer, Edmond

27

The Future of High Angular Resolution Star and Planet Formation Science in the Optical/Infrared  

E-print Network

This presentation summarizes how some of the most pressing questions in the field of star and planet formation can be addressed by high angular resolution optical/infrared capabilities, and how many of these capabilities will in fact be available with realization of the space and ground facilities currently being planned for the 2005-2020 time frame.

Lynne A. Hillenbrand

2003-12-06

28

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

Microsoft Academic Search

Diffusion tensor magnetic resonance imaging (DTI) can resolve white matter fiber orientations within voxels in which the diffusion is characterized by Gaussian diffusion process. High angular resolution diffusion imaging (HARDI) adds the capability of describing the apparent diffusion coefficient (ADC) profile of voxels that contain kissing, branching and crossing fiber configurations. We present a new method for recovering BiGaussian model

Ning Cao; Qi Zhuang; Xuwei Liang; Ruiwang Huang; Jun Zhang

2007-01-01

29

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

E-print Network

profile is always shown as a surface in a 3D space, it is defined on the 2-sphere. The diffusion tensorComputing White Matter Fiber Orientations in High Angular Resolution Diffusion-Weighted MRI Ning 40506-0046, U.S.A. IME Research Center Juelich, Germany Abstract Diffusion tensor magnetic resonance

Zhang, Jun

30

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

31

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

32

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

PubMed

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

33

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

34

Formation and evolution of planetary systems: the impact of high angular resolution optical techniques  

E-print Network

The direct images of giant extrasolar planets recently obtained around several main sequence stars represent a major step in the study of planetary systems. These high-dynamic range images are among the most striking results obtained by the current generation of high angular resolution instruments, which will be superseded by a new generation of instruments in the coming years. It is therefore an appropriate time to review the contributions of high angular resolution visible/infrared techniques to the rapidly growing field of extrasolar planetary science. During the last 20 years, the advent of the Hubble Space Telescope, of adaptive optics on 4- to 10-m class ground-based telescopes, and of long-baseline infrared stellar interferometry has opened a new viewpoint on the formation and evolution of planetary systems. By spatially resolving the optically thick circumstellar discs of gas and dust where planets are forming, these instruments have considerably improved our models of early circumstellar environments...

Absil, Olivier; 10.1007/s00159-009-0028-y

2009-01-01

35

Method for improving the angular resolution of a neutron scatter camera  

DOEpatents

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

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

2012-12-25

36

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

37

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

38

Geometrical Expression of the Angular Resolution of a Network of Gravitational-Wave Detectors and Improved Localization Methods  

E-print Network

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 to the null-stream localization method for GWs of unknown waveforms is demonstrated.

Linqing Wen; Xilong Fan; Yanbei Chen

2007-11-05

39

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 observatories—Chandra, XMM-Newton, and Suzaku—are 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

40

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

41

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

NASA Astrophysics Data System (ADS)

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

Zhang, William; NGXO

2014-01-01

42

Quality assessment of High Angular Resolution Diffusion Imaging data using bootstrap on Q-ball reconstruction  

PubMed Central

Purpose To develop a bootstrap method to assess the quality of High Angular Resolution Diffusion Imaging (HARDI) data using Q-Ball imaging (QBI) reconstruction. Materials and Methods HARDI data were re-shuffled using regular bootstrap with jackknife sampling. For each bootstrap dataset, the diffusion orientation distribution function (ODF) was estimated voxel-wise using QBI reconstruction based on spherical harmonics functions. The reproducibility of the ODF was assessed using the Jensen-Shannon divergence (JSD) and the angular confidence interval was derived for the first and the second ODF maxima. The sensitivity of the bootstrap method was evaluated on a human subject by adding synthetic noise to the data, by acquiring a map of image signal-to-noise ratio (SNR) and by varying the echo time and the b-value. Results The JSD was directly linked to the image SNR. The impact of echo times and b-values was reflected by both the JSD and the angular confidence interval, proving the usefulness of the bootstrap method to evaluate specific features of HARDI data. Conclusion The bootstrap method can effectively assess the quality of HARDI data and can be used to evaluate new hardware and pulse sequences, perform multi-fiber probabilistic tractography, and provide reliability metrics to support clinical studies. PMID:21509879

Cohen-Adad, J.; Descoteaux, M.; Wald, L.L.

2011-01-01

43

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

PubMed Central

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

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

2013-01-01

44

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

45

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

46

HIGH ANGULAR RESOLUTION OBSERVATIONS OF FOUR CANDIDATE BLAST HIGH-MASS STARLESS CORES  

SciTech Connect

We discuss high angular resolution observations of ammonia toward four candidate high-mass starless cores (HMSCs). The cores were identified by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) during its 2005 survey of the Vulpecula region where 60 compact sources were detected simultaneously at 250, 350, and 500 {mu}m. Four of these cores, with no IRAS-PSC or MSX counterparts, were mapped with the NRAO Very Large Array and observed with the Effelsberg 100 m telescope in the NH{sub 3}(1,1) and (2,2) spectral lines. Our observations indicate that the four cores are cold (T {sub k} < 16 K) and show a filamentary and/or clumpy structure. They also show a significant velocity substructure within {approx}1 km s{sup -1}. The four BLAST cores appear to be colder and more quiescent than other previously observed HMSC candidates, suggesting an earlier stage of evolution.

Olmi, Luca; Poventud, Carlos M. [Physics Department, Rio Piedras Campus, University of Puerto Rico, Box 23343, UPR Station, San Juan, Puerto Rico (United States); Araya, Esteban D. [Physics Department, Western Illinois University, 1 University Circle, Macomb, IL 61455 (United States); Chapin, Edward L.; Gibb, Andrew [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Hofner, Peter [Physics Department, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801 (United States); Martin, Peter G., E-mail: olmi.luca@gmail.co, E-mail: olmi@arcetri.astro.i [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada)

2010-06-01

47

Spatial normalization of the fiber orientation distribution based on high angular resolution diffusion imaging data.  

PubMed

Comparison of high angular resolution diffusion imaging (HARDI) measurements between subjects or between timepoints for the same subject are facilitated by spatial normalization. In this work an algorithm was developed to transform the fiber orientation distribution (FOD) function, based on HARDI data, taking into account not only translation, but also rotation, scaling, and shearing effects of the spatial transformation. The algorithm was tested using simulated data and intrasubject and intersubject normalization of in vivo human data. All cases demonstrated reliable transformation of the FOD. This technique makes it possible to compare the intravoxel fiber distribution between subjects, between groups, or between timepoints for a single subject, which will be helpful in HARDI studies of white matter disease. PMID:19353649

Hong, Xin; Arlinghaus, Lori R; Anderson, Adam W

2009-06-01

48

Accretion and outflow in massive star formation: Observational studies at high angular resolution  

NASA Astrophysics Data System (ADS)

This thesis examines the process of massive star formation by observations of the molecular gas surrounding young H II regions at the highest angular resolution. Because the regions that form massive stars are more complicated and more distant than low-mass-star forming regions, high angular resolution is essential. We achieve this resolution through the use of radio interferometry. While an evolutionary sequence for the formation of isolated low-mass stars has been well established over the last decade, a unified picture of massive-star formation remains elusive. Fundamental questions about the nature of accretion in massive star formation, and the chronology of different observed stages remain. We present several pieces of this slowly coalescing picture. First, we show in the case of W51, that high mass star formation can occur roughly coevally over a 1 pc size scale, without being part of a single gravitational collapse. Second, we present observations of a bipolar outflow coincident with an expanding UCH II region, G5.89-0.39. Because bipolar outflows are generally thought to be a signpost of ongoing accretion, and because the spherical expansion of the UCH II region must mean that actual accretion must have stopped, the source presented a mystery. This source shows strong evidence for the compressed time-scales and chronology involved in massive star formation. Third, a clear case can be made for the existence of disks around young massive stars. These disks are different in character than the accretion disks around low mass protostars, being much more massive relative to the central object, and not always rotationally supported. We show observations of such a disk in G28.20-0.05, seen at higher resolution than in any previous work. Fourth, we present observations of a group of young stars in G10.62-0.38, forming in a single gravitational potential. Because massive stars form in clusters, it is understood that the formation of a massive star can effect the formation of surrounding protostars. We show that the existence of massive young stars can also effect their own accretion process, leading to a new physical regime in which both molecular gas and ionized gas are part of a single accretion flow.

Sollins, Peter K..

49

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

50

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

E-print Network

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 140x140 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 microns) 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 th...

Peters, Mary Anne; 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

51

Conceptual design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) for the Subaru telescope  

NASA Astrophysics Data System (ADS)

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 exo-planets on the Subaru telescope. The IFS will provide spectral information for 140x140 spatial elements over a 1.75 arcsecs x 1.75 arcsecs field of view (FOV). CHARIS will operate in the near infrared (? = 0.9-2.5?m) 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 A.; 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

2012-09-01

52

High angular resolution measurements of K shell x-ray emission created by electron channeling in the analytical electron microscope.  

SciTech Connect

Since the original observations by Duncumb in 1962, a number of studies have been conducted on the effects of electron channel on characteristic x-ray emission and microanalysis. Most of the recent studies have concentrated upon using the phenomenon to perform site specific distributions of impurity elements in ordered compounds using the ALCHEMI methodology. Very few studies have attempted to accurately measure the effect as a function of orientation and compare these results to theories. In this study, two dimensional high angular resolution studies of channeling enhance x-ray emission were performed and herein the results are compared to theoretical calculations of Allen et al. All experimental measurements presented here were conducted on a Philips EM 420T analytical electron microscope. The instrument was operated in the TEM mode, at 120 kV using an LaB6 electron source. The characteristic x-ray emission was measured using an EDAX ultra thin window Si(Li) detector having a FWHM of {approximately}145 eV at Mn Km Nominal probe sizes used during the study were 200-500 nm with beam convergence half angle defined by the Condenser apertures. Control of the relative orientation of the incident probe was accomplished via direct computer control of the beam tilt coils, after the specimen was first manually oriented to an appropriate zone axis using the specimen tilt stage. Two dimensional measurements were carried out using a 128 x 100 pixel scan corresponding to an angular range of {approximately}100 by 80 mR using customized computer program running on a EDAX 9900 microanalyzer system. Careful alignment and manual optimization/adjustments of beam tilt pivot coils, minimized probe wobble during data acquisition. The effects of this were additionally mitigated due to the relative uniformity of the specimen thickness in the analyzed zone. Typical acquisition times for a complete two dimensional scan were 18-24 hours. Essential to the success of these measurements was the stability of the probe current, minimal specimen drift, and absence of hydrocarbon contamination. The latter being accomplished using argon plasma processing of the specimen (MgAl{sub 2}O{sub 4}) which was initially prepared by mechanical tripod polishing.

Zaluzec, N. J.

1999-03-10

53

Trade-off between angular resolution and straylight contamination in the PLANCK Low Frequency Instrument. I. Pattern simulations  

NASA Astrophysics Data System (ADS)

The study of cosmic microwave background (CMB) anisotropies represents one of the most powerful cosmological tools. After the great success of the two NASA satellite missions COBE and WMAP, PLANCK is the third generation of mm-wave instruments designed for space observations of CMB anisotropies within the new Cosmic Vision 2020 ESA Science Programme. PLANCK will map the whole sky with unprecedented sensitivity, angular resolution and frequency coverage, using two instruments that share the focal region of a 1.5 m off-axis dual reflector telescope: the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI). In the optimisation of the optical interfaces of the LFI two concurrent demands have to be satisfied: the very good angular resolution (which affects the ability to reconstruct the angular power spectrum of the CMB anisotropies at high multipoles) and a very low level of straylight contamination (which may be one of the most serious sources of systematic effects). We present the results of the optical simulations aimed at establishing the trade-off between angular resolution and straylight rejection, carried out for the 100 GHz channel of the PLANCK LFI. Antenna patterns of different models of dual profiled corrugated conical feed horns have been simulated using advanced simulation techniques, considering the whole spacecraft geometry in order to obtain reliable sidelobe predictions. We show the optical computation accuracy necessary to provide strong straylight evaluation in reasonable computational time and demonstrate the inadequacy of a Gaussian feed model in realistic far beam predictions.

Sandri, M.; Villa, F.; Nesti, R.; Burigana, C.; Bersanelli, M.; Mandolesi, N.

2004-12-01

54

Long-Distance Dependency Resolution in Automatically Acquired Wide-Coverage PCFG-Based LFG Approximations  

Microsoft Academic Search

This paper shows how finite approximations of long distance dependency (LDD) resolution can be obtained automatically for wide-coverage, robust, probabilistic Lexical-Functional Grammar (LFG) resources acquired from treebanks. We extract LFG subcategorisation frames and paths linking LDD reentrancies from f-structures generated automati- cally for the Penn-II treebank trees and use them in an LDD resolution algorithm to parse new text. Unlike

Aoife Cahill; Michael Burke; Ruth O'donovan; Josef Van Genabith

2004-01-01

55

Sex differences in the human connectome: 4Tesla high angular resolution diffusion imaging (HARDI) tractography in 234 young adult twins  

Microsoft Academic Search

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 ± 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

56

Angular resolution of GRAPES3 array obtained from the shadow of Moon and Sun in extensive air showers  

Microsoft Academic Search

The GRAPES-3 experiment observes extensive air showers using a high-density array of scintillators and a large area tracking muon detector. The array consists of 300 scintillation detectors (each 1m2 in area) and 16 modules of muon detectors having a total area of 560m2. Good angular resolution of the array is a key requirement for detection of point sources of gamma

A. Oshima; S. K. Gupta; K. Hayashi

2008-01-01

57

Southern Massive Stars at High Angular Resolution: Observational Campaign and Companion Detection  

NASA Astrophysics Data System (ADS)

Multiplicity is one of the most fundamental observable properties of massive O-type stars and offers a promising way to discriminate between massive star formation theories. Nevertheless, companions at separations between 1 and 100 milliarcsec (mas) remain mostly unknown due to intrinsic observational limitations. At a typical distance of 2 kpc, this corresponds to projected physical separations of 2-200 AU. The Southern MAssive Stars at High angular resolution survey (SMaSH+) was designed to fill this gap by providing the first systematic interferometric survey of Galactic massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162 O-type stars with NACO/Sparse Aperture Masking (SAM), probing the separation ranges 1-45 and 30-250 mas and brightness contrasts of ?H < 4 and ?H < 5, respectively. Taking advantage of NACO's field of view, we further uniformly searched for visual companions in an 8'' radius down to ?H = 8. This paper describes observations and data analysis, reports the discovery of almost 200 new companions in the separation range from 1 mas to 8'' and presents a catalog of detections, including the first resolved measurements of over a dozen known long-period spectroscopic binaries. Excluding known runaway stars for which no companions are detected, 96 objects in our main sample (? < 0° H < 7.5) were observed both with PIONIER and NACO/SAM. The fraction of these stars with at least one resolved companion within 200 mas is 0.53. Accounting for known but unresolved spectroscopic or eclipsing companions, the multiplicity fraction at separation ? < 8'' increases to f m = 0.91 ± 0.03. The fraction of luminosity class V stars that have a bound companion reaches 100% at 30 mas while their average number of physically connected companions within 8'' is f c = 2.2 ± 0.3. This demonstrates that massive stars form nearly exclusively in multiple systems. The nine non-thermal radio emitters observed by SMaSH+ are all resolved, including the newly discovered pairs HD 168112 and CPD–47°2963. This lends strong support to the universality of the wind-wind collision scenario to explain the non-thermal emission from O-type stars.

Sana, H.; Le Bouquin, J.-B.; Lacour, S.; Berger, J.-P.; Duvert, G.; Gauchet, L.; Norris, B.; Olofsson, J.; Pickel, D.; Zins, G.; Absil, O.; de Koter, A.; Kratter, K.; Schnurr, O.; Zinnecker, H.

2014-11-01

58

High-angular resolution observations towards OMC-2 FIR 4: Dissecting an intermediate-mass protocluster  

NASA Astrophysics Data System (ADS)

Context. Intermediate-mass stars are an important ingredient of our Galaxy and a key to understanding how high- and low-mass stars form in clusters. One of the closest known young intermediate-mass protoclusters is OMC-2 FIR 4, which is located at a distance of 420 pc in Orion. This region is one of the few where the complete 500-2000 GHz spectrum has been observed with the heterodyne spectrometer HIFI on board the Herschel satellite, and unbiased spectral surveys at 0.8, 1, 2, and 3 mm have been obtained with the JCMT and IRAM 30-m telescopes. Aims: We aim to disentangle the core multiplicity, to investigate the morphology of this region in order to study the formation of a low- and intermediate-mass protostar cluster, and to aid in interpretation of the single-dish line profiles already in our hands. Methods: We used the IRAM Plateau de Bure Interferometer to image OMC-2 FIR 4 in the 2-mm continuum emission, as well as in DCO+(2-1), DCN(2-1), C34S(3-2), and several CH3OH lines. In addition, we analysed observations of the NH3(1, 1) and (2, 2) inversion transitions that used the Very Large Array of the NRAO. The resulting maps have an angular resolution that allows us to resolve structures of 5?, which is equivalent to ~2000 AU. Results: Our observations reveal three spatially resolved sources within OMC-2 FIR 4, of one or several solar masses each, with hints of further unresolved substructure within them. Two of these sources have elongated shapes and are associated with dust continuum emission peaks, thus likely containing at least one molecular core each. One of them also displays radio continuum emission, which may be attributed to a young B3-B4 star that dominates the overall luminosity output of the region. The third identified source displays a DCO+(2-1) emission peak and weak dust continuum emission. Its higher abundance of DCO+ relative to the other two regions suggests a lower temperature, hence its possible association with either a younger low-mass protostar or a starless core. It may alternatively be part of the colder envelope of OMC-2 FIR 4. Conclusions: Our interferometric observations show the complexity of the intermediate-mass protocluster OMC-2 FIR 4, where multiple cores, chemical differentiation, and an ionised region all coexist within an area of only 10 000 AU. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by the INSU/CNRS (France), MPG (Germany), and IGN (Spain).

López-Sepulcre, A.; Taquet, V.; Sánchez-Monge, Á.; Ceccarelli, C.; Dominik, C.; Kama, M.; Caux, E.; Fontani, F.; Fuente, A.; Ho, P. T. P.; Neri, R.; Shimajiri, Y.

2013-08-01

59

Assessment of Anisotropic Tissue Elasticity of Cortical Bone from High-Resolution, Angular Acoustic Measurements  

Microsoft Academic Search

Assessment of anisotropic elastic properties at the tissue level is still one of the major challenges in bone research. In previous studies, bone sections were cut in different directions relative to a principle axis of symmetry. This causes a high preparation and measurement effort. We have developed a new acoustic scanning procedure that allows one to measure the angular dependence

Sannachi Lakshmanan; Andreas Bodi; Kay Raum

2007-01-01

60

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

NASA Technical Reports Server (NTRS)

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

Rinehart, Stephen A.

2008-01-01

61

High angular-resolution automated visible-wavelength scanning angle Raman microscopy.  

PubMed

A scanning angle (SA) Raman microscope with 532-nm excitation is reported for probing chemical content perpendicular to a sample interface. The instrument is fully automated to collect Raman spectra across a range of incident angles from 20.50 to 79.50° with an angular spread of 0.4±0.2° and an angular uncertainty of 0.09°. Instrumental controls drive a rotational stage with a fixed axis of rotation relative to a prism-based sample interface mounted on an inverted microscope stage. Three benefits of SA Raman microscopy using visible wavelengths, compared to near infrared wavelengths are: (i) better surface sensitivity; (ii) increased signal due to the frequency to the fourth power dependence of the Raman signal, and the possibility for resonant enhancement; (iii) the need to scan a reduced angular range to shorten data collection times. These benefits were demonstrated with SA Raman measurements of thin polymer films of polystyrene or a diblock copolymer of polystyrene and poly(3-hexylthiophene-2,5-diyl). Thin film spectra were collected with a signal-to-noise ratio of 30 using a 0.25s acquisition time. PMID:25263117

Lesoine, Michael D; Bobbitt, Jonathan M; Zhu, Shaobin; Fang, Ning; Smith, Emily A

2014-10-27

62

Noise reduction methods in the analysis of near infrared lunar occultation light curves for high angular resolution measurements  

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

63

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

E-print Network

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

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

2006-10-16

64

Linear transforms for Fourier data on the sphere: application to high angular resolution diffusion MRI of the brain.  

PubMed

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

65

The Multiplicity of Massive Stars: A High Angular Resolution Survey with the HST Fine Guidance Sensor  

E-print Network

We present the results of an all-sky survey made with the Fine Guidance Sensor on Hubble Space Telescope to search for angularly resolved binary systems among the massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and Luminous Blue Variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to detection of companions with an angular separation between 0."01 and 1."0 and brighter than $\\triangle m = 5$. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations...

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

2014-01-01

66

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

PubMed

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

Xiahou, Chengkui; Connor, J N L

2014-06-01

67

Milliarcsecond angular resolution of reddened stellar sources in the vicinity of the Galactic center  

Microsoft Academic Search

Aims: For the first time, the lunar occultation technique has been employed on a very large telescope in the near-IR with the aim of systematically achieving milliarcsecond resolution on stellar sources. Methods: We have demonstrated the burst mode of the ISAAC instrument, using a fast read-out on a small area of the detector to record many tens of seconds of

A. Richichi; O. Fors; E. Mason; J. Stegmeier; T. Chandrasekhar

2008-01-01

68

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

69

CC2 excitation energy calculations on large molecules using the resolution of the identity approximation  

NASA Astrophysics Data System (ADS)

A new implementation of the approximate coupled cluster singles and doubles method CC2 is reported, which is suitable for large scale integral-direct calculations. It employs the resolution of the identity (RI) approximation for two-electron integrals to reduce the CPU time needed for calculation and I/O of these integrals. We use a partitioned form of the CC2 equations which eliminates the need to store double excitation cluster amplitudes. In combination with the RI approximation this formulation of the CC2 equations leads to a reduced scaling of memory and disk space requirements with the number of correlated electrons (n) and basis functions (N) to, respectively, O(N2) and O(nN2), compared to O(n2N2) in previous implementations. The reduced CPU, memory and disk space requirements make it possible to perform CC2 calculations with accurate basis sets on large molecules, which would not be accessible with conventional implementations of the CC2 method. We present an application to vertical excitation energies of alkenes C2nH2n+2, for n=1-12, and report results for the lowest lying dipole-allowed transitions for the TZVPP basis sets, which for n=12 contain 1108 basis functions. Comparison with conventional CC2 results for the smaller alkenes show that for CC2 ground state energies and for excitation energies of valence states, the error due to the RI approximation is negligible compared to the usual basis set error, if auxiliary basis sets are used, which have been optimized for MP2 energy calculations.

Hättig, Christof; Weigend, Florian

2000-10-01

70

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

NASA Astrophysics Data System (ADS)

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

Dutt, Ranabir; Mukherji, Uma

1982-08-01

71

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

72

Next generation astronomical x-ray optics: high angular resolution, light weight, and low production cost  

NASA Astrophysics Data System (ADS)

X-ray astronomy depends upon the availability of telescopes with high resolution and large photon colleX-ray astronomy depends upon the availability of telescopes with high resolution and large photon collecting areas. As astronomical x-ray observations can only be carried out above the atmosphere, these telescopes must necessarily be lightweight. Compounding the lightweight requirement is that an x-ray telescope consists of many nested concentric shells, which further requires that x-ray mirrors must be geometrically thin to achieve high packing efficiency. This double requirement—lightweight and geometrically thin—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 program to develop x-ray optics meeting these technical challenges at modest cost. The objective of this technology program is 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.ing areas. As astronomical x-ray observations can only be carried out above the atmosphere, these telescopes must necessarily be lightweight. Compounding the lightweight requirement is that an x-ray telescope consists of many nested concentric shells, which further requires that x-ray mirrors must be geometrically thin to achieve high packing efficiency. This double requirement—lightweight and geometrically thin—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 program to develop x-ray optics meeting these technical challenges at modest cost. The objective of this technology program is 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.

2012-09-01

73

The Stellar Imager (SI): An Ultra-High Angular Resolution UV/Optical Observatory  

NASA Technical Reports Server (NTRS)

The Stellar Imager (SI) is envisioned as a space-based, UV-optical interferometer composed of 10 or more one-meter class elements distributed with a maximum baseline of 0.5-km and providing a resolution of 60 micro-arcseconds at 1550 A. It will image stars and binaries with one hundred to one thousand resolution elements on their surface and enable long-term studies of stellar magnetic activity patterns and their evolution with time, for comparison with those on the sun. It will also sound their interiors through asteroseismology to image internal structure, differential rotation, and large-scale circulations. SI will enable us to understand the various effects of magnetic fields of stars, the dynamos that generate these fields, and the internal structure and dynamics of the stars in which these dynamos operate. The ultimate goal of the mission is to achieve the best-possible forecasting of solar activity as a driver of climate and space weather on times scales ranging from months up to decades, and an understanding of the impact of stellar magnetic activity on life in the Universe. The road to that goal will revolutionize our understanding of stars and stellar systems, the building blocks of the Universe. Fitting naturally within the NASA and ESA long-term time lines, SI complements defined missions, and with them will show us entire other solar systems, from the central star to their orbiting planets. In this paper we will describe the scientific goals of the mission, the performance requirements needed to address those goals, and the design concepts now under study.

Carpenter, Kenneth G.; Schrijver, Carolus J.; Oegerle, William R. (Technical Monitor)

2002-01-01

74

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

NASA Astrophysics Data System (ADS)

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

Demidov, V. I.; Kudryavtsev, A. A.

2014-09-01

75

High angular resolution imaging and infrared spectroscopy of CoRoT candidates  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

76

Improving the angular resolution of an ultra-high-energy gamma-ray telescope by the addition of thin lead sheets above its detectors  

Microsoft Academic Search

The prediction made by Linsley (1986,7) that the angular resolution of a scintillator array can be improved by placing lead sheets over its constituent detectors has been tested experimentally with the gamma-ray telescope at Haverah Park. The authors find that the addition of lead significantly improves the prompt timing and density response of detectors, and that the optimum thickness of

S. D. Bloomer; J. Linsley; A. A. Watson

1988-01-01

77

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

PubMed Central

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

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

2014-01-01

78

High angular resolution near-infrared integral field observations of young star cluster complexes in NGC 1365  

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

79

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

NASA Astrophysics Data System (ADS)

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

Ibach, Harald

2014-12-01

80

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

81

Optic Radiation Fiber Tractography in Glioma Patients Based on High Angular Resolution Diffusion Imaging with Compressed Sensing Compared with Diffusion Tensor Imaging - Initial Experience  

PubMed Central

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. PMID:23923036

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

2013-01-01

82

Providing stringent star formation rate limits of z$\\sim$2 QSO host galaxies at high angular resolution  

E-print Network

We present integral field spectrograph (IFS) with laser guide star adaptive optics (LGS-AO) observations of z=2 quasi-stellar objects (QSOs) designed to resolve extended nebular line emission from the host galaxy. Our data was obtained with W. M. Keck and Gemini-North Observatories using OSIRIS and NIFS coupled with the LGS-AO systems. We have conducted a pilot survey of five QSOs, three observed with NIFS+AO and two observed with OSIRIS+AO at an average redshift of z=2.15. We demonstrate that the combination of AO and IFS provides the necessary spatial and spectral resolutions required to separate QSO emission from its host. We present our technique for generating a PSF from the broad-line region of the QSO and performing PSF subtraction of the QSO emission to detect the host galaxy. We detect H$\\alpha$ and [NII] for two sources, SDSS J1029+6510 and SDSS J0925+06 that have both star formation and extended narrow-line emission. Assuming that the majority of narrow-line H$\\alpha$ is from star formation, we inf...

Vayner, Andrey; Do, Tuan; Larkin, James E; Armus, Lee; Gallagher, Sarah C

2014-01-01

83

Nondipolar photoelectron angular distributions  

SciTech Connect

The deviations of photoelectron angular distributions from the simple, highly symmetric shapes predicted within the electric-dipole approximation are investigated. The admixture of an electric-quadrupole component in the photon-atom interaction causes an asymmetry in the angular distribution with respect to the direction of photon propagation. The reported measurement of the angular distributions of argon {ital 1s}, krypton {ital 2s}, and krypton {ital 2p} photoemission within 2-3 keV above their respective thresholds reveal pronounced asymmetries which are present even at low electron kinetic energies. The measured asymmetry parameters are in good agreement with recent predictions from nonrelativistic calculations.

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

1996-12-31

84

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

NASA Technical Reports Server (NTRS)

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

Young, David T.

1991-01-01

85

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

E-print Network

We present direct radii measurements of the well-known transiting exoplanet host stars HD 189733 and HD 209458 using the CHARA Array interferometer. We find the limb-darkened angular diameters to be theta_LD = 0.3848 +/- 0.0055 and 0.2254 +/- 0.0072 milliarcsec for HD 189733 and HD 209458, respectively. HD 189733 and HD 209458 are currently the only two transiting exoplanet systems where detection of the respective planetary companion's orbital motion from high resolution spectroscopy has revealed absolute masses for both star and planet. We use our new measurements together with the orbital information from radial velocity and photometric time series data, Hipparcos distances, and newly measured bolometric fluxes to determine the stellar effective temperatures (T_eff = 4875 +/- 43, 6093 +/- 103 K), stellar linear radii (R_* = 0.805 +/- 0.016, 1.203 +/- 0.061 R_sun), mean stellar densities (rho_* = 1.62 +/- 0.11, 0.58 +/- 0.14 rho_sun), planetary radii (R_p = 1.216 +/- 0.024, 1.451 +/- 0.074 R_Jup), and mean ...

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

2014-01-01

86

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

87

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

88

The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations  

NASA Astrophysics Data System (ADS)

We present low spectral resolution molecular interferometric observations at 1.2 mm obtained with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) towards the C-rich AGB star IRC+10216. We have mapped the emission of several lines of SiS, H13CN, SiO and SiC2 in the ground and first excited vibrational states with a high angular resolution of 0.25 arcsec. These observations have allowed us to partially resolve the emission of the envelope at distances from the star ?50 stellar radii (R?), where the stellar wind is mainly accelerated. The structure of the molecular emission has been modelled with a 3D radiation transfer code. The emission of line SiS (v = 0, J = 14-13) is best reproduced with a set of maser emitting arcs arranged between 5 and 20R?. The abundance of H13CN with respect to H2 decreases from 8 × 10-7 at 1-5R? to 3 × 10-7 at 20R?. The SiO observations are explained with an abundance ?2 × 10-8 in the shell-like region between 1 and 5R?. At this point, the SiO abundance sharply increases up to (2-3) × 10-7. The vibrational temperature of SiO increases by a factor of 2 due north-east between 20 and 50R?. SiC2 is formed at the stellar surface with an abundance of 8 × 10-7 decreasing down to 8 × 10-8 at 20R? probably due to depletion on to dust grains. Several asymmetries are found in the abundance distributions of H13CN, SiO and SiC2 which define three remarkable directions (north-east, south-southwest, and south-east) in the explored region of the envelope. There are some differences between the redshifted and blueshifted emissions of these molecules suggesting the existence of additional asymmetries in their abundance distributions along the line of sight.

Fonfría, J. P.; Fernández-López, M.; Agúndez, M.; Sánchez-Contreras, C.; Curiel, S.; Cernicharo, J.

2014-12-01

89

High Angular Resolution, Sensitive CS J = 2-1 and J = 3-2 Imaging of the Protostar L1551 NE: Evidence for Outflow-triggered Star Formation?  

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

90

Enhanced angular current intensity from Schottky emitters.  

PubMed

Even though the Schottky emitter is a high-brightness source of choice for electron beam systems, its angular current intensity is substantially lower than that of thermionic cathodes, rendering the emitter impractical for applications that require high beam current. In this study, two strategies were attempted to enhance its angular intensity, and their experimental results are reported. The first scheme is to employ a higher extraction field for increasing the brightness. However, the tip shape transformation was found to induce undesirably elevated emission from the facet edges at high fields. The second scheme exploits the fact that the angular intensity is proportional to the square of the electron gun focal length [Fujita, S. & Shimoyama, H. (2005) Theory of cathode trajectory characterization by canonical mapping transformation. J. Electron Microsc. 54, 331-343], which can be increased by scaling-up the emitter tip radius. A high angular current intensity (J(Omega) approximately 1.5 mA sr(-1)) was obtained from a scaled-up emitter. Preliminary performance tests were conducted on an electron probe-forming column by substituting the new emitter for the original tungsten filament gun. The beam current up to a few microamperes was achieved with submicron spatial resolution. PMID:20701659

Fujita, S; Wells, T R C; Ushio, W; Sato, H; El-Gomati, M M

2010-09-01

91

Approximation Theory Approximation Practice  

E-print Network

. Orthogonal polynomials, 123 18. Polynomial roots and colleague matrices, 132 19. Clenshaw­Curtis and Gauss-squares, 219 27. Pad´e approximation, 232 28. Analytic continuation and convergence acceleration, 247 Appendix. Everything is practical and fast, so we will routinely compute polynomial interpolants or Gauss quadrature

Morrow, James A.

92

Measurements of the Sunyaev-Zel'dovich Effect in MACS J0647.7+7015 and MACS J1206.2-0847 at High Angular Resolution with MUSTANG  

E-print Network

We present high resolution (9$^{\\prime \\prime}$) imaging of the Sunyaev-Zel'dovich Effect (SZE) toward two massive galaxy clusters, MACS J0647.7+7015 ($z=0.591$) and MACS J1206.2-0847 ($z=0.439$). We compare these 90 GHz measurements, taken with the MUSTANG receiver on the Green Bank Telescope, with generalized Navarro-Frenk-White (gNFW) models derived from Bolocam 140 GHz SZE data as well as maps of the thermal gas derived from {\\it Chandra} X-ray observations. For MACS J0647.7+7015, we find a gNFW profile with core slope parameter $\\gamma= 0.9$ fits the MUSTANG image with $\\chi^{2}_{red}=1.005$ and probability to exceed (PTE) = 0.34. For MACS J1206.2-0847, we find $\\gamma=0.7$, $\\chi^{2}_{red}=0.993$, and PTE = 0.70. In addition, we find a significant ($>$3-$\\sigma$) residual SZE feature in MACS J1206.2-0847 coincident with a group of galaxies identified in VLT data and filamentary structure found in a weak-lensing mass reconstruction. We suggest the detected sub-structure may be the SZE decrement from a lo...

Young, Alexander H; Romero, Charles; Sayers, Jack; Balestra, Italo; Clarke, Tracy E; Czakon, Nicole; Devlin, Mark; Dicker, Simon R; Ferrari, Chiara; Girardi, Marisa; Golwala, Sunil; Intema, Huib; Korngut, Phillip M; Mason, Brian S; Mercurio, Amata; Nonino, Mario; Reese, Erik D; Rosati, Piero; Sarazin, Craig; Umetsu, Keiichi

2014-01-01

93

A high angular-resolution and time-of-flight detector system for recoil protons from the reactions p(?, ?)p and p( ?, ?0)p  

NASA Astrophysics Data System (ADS)

Using the Mainz NaI(Tl)?BaF 2 photon spectrometer CATS (Compton And Two photon Spectrometer) together with the prototype of a universal spectrometer for recoil protons TRAJAN (TRAjectory ANalyser) we have studied different methods to disentangle Compton scattering by the proton from the large ? 0 background through the energy range of the ? resonance. CATS is a modular 48 cm ? × 64 cm NaI(Tl) detector with an energy resolution of 1.5% combined with a 2? array of 61 BaF 2 detectors. TRAJAN consists of a hodoscope with two planes, a wire chamber with horizontal and vertical wires and a grid of horizontal and vertical plastic scintillator strips, followed by a wall of nine NaI(Tl) detectors. By this arrangement the proton energy was obtained via a time-of-flight analysis and the recoil angle of the protons via a trajectory reconstruction. Additionally, a ?E- E analysis of the detected particles allows us to suppress the electromagnetic background. By reconstructing the proton trajectory the segment of the scattering target can be determined where the Compton scattering process or the ? 0 production process had taken place. In this way it is possible to correct the event distributions for the smearing-out caused by the finite target length and thus to improve on the separation of the two types of events.

Hünger, A.; Kordsmeier, R.; Schumacher, M.; Selke, O.; Ahrens, J.; Peise, J.; Schmitz, M.; Schneider, M.; Wissmann, F.; Dolbilkin, B.; Kondratjev, R.; Lisin, V.; Polonski, A.

1996-02-01

94

A detection system with broad angular acceptance for particle identification and angular distribution measurements  

NASA Astrophysics Data System (ADS)

A new detection system for time-optimized heavy-ion angular distribution measurements has been designed and constructed. This device is composed by an ionization chamber with a segmented-grid anode and three position-sensitive silicon detectors. This particular arrangement allows identifying reaction products emitted within a 30° wide angular range with better than 1° angular resolution. As a demonstration of its capabilities, angular distributions of the elastic scattering cross-section and the production of alpha particles in the 7Li+27Al system, at an energy above the Coulomb barrier, are presented.

Carnelli, P. F. F.; Arazi, A.; Fernández Niello, J. O.; Capurro, O. A.; Cardona, M. A.; de Barbará, E.; Figueira, J. M.; Hojman, D.; Martí, G. V.; Martinez Heimann, D.; Negri, A. E.; Pacheco, A. J.

2013-10-01

95

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

96

Quasiclassical Born–Oppenheimer Approximations  

Microsoft Academic Search

We discuss several problems in quasiclassical physics for which approximate solutions were recently obtained by a new method, and which can also be solved by novel versions of the Born–Oppenheimer approximation. These cases include the so-called bouncing ball modes, low angular momentum states in perturbed circular billiards, resonant states in perturbed rectangular billiards, and whispering gallery modes. Some rare, special

Oleg Zaitsev; R. Narevich; R. E. Prange

2001-01-01

97

Analytic approximations to the 2-60 microns infrared continua for standard calibration stars - With application to the calibration of spectroscopy and photometry, and the determination of effective temperature and angular size from IR measurements  

Microsoft Academic Search

Convenient two-parameter analytic expressions approximating the long-wavelength (2-60 mum) infrared continua expected from over a dozen stellar calibration standards are derived. These analytic spectral functions are based on the implicit scaling of a semiempirical solar atmospheric temperature profile to differing effective temperatures, a procedure believed to be theoretically valid for stars with effective temperature lower than 6000 K. The generalized

C. W. Engelke

1992-01-01

98

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

99

Piezoelectric angular acceleration sensor  

Microsoft Academic Search

This paper deals with a piezoelectric angular acceleration sensor, which might be proposed by us, first, as a new concept of the sensor to detect a rotational motion only. In the first part of this paper are dealt with some concrete constructions of this new concept of angular acceleration sensor, composed of piezoelectric transducers. The second part contains their basic

Y. Tomikawa; S. Okada

2003-01-01

100

Angular shear plate  

Microsoft Academic Search

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

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

2009-01-01

101

Quark orbital angular momentum from lattice QCD  

SciTech Connect

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

102

Metamaterial broadband angular selectivity  

E-print Network

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

Shen, Yichen

103

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

104

Approximate schedule  

E-print Network

Oct 8, 2014 ... Binomial theorem (1), definition of probability (2.3) , properties of probability, examples ... Distribution function of random variables (4.10). Sep 25 ... Poisson random variables, Poisson approximation to binomial distribution ...

Alex Misiats

2014-08-25

105

Absolute measurement of hyperspectral and angular reflection.  

PubMed

A new instrument for absolute measurement of hyperspectral and angular reflection is presented. The instrument determines absolute values of angular reflection quantities in a wavelength range from 380 to 780 nm with a 3 nm spectral resolution by using a white source and a CCD-based spectroradiometer. Through uncertainty evaluation, the measurement uncertainty is determined as 1.4%-2.9% (k=2) for white diffuse material of Spectralon. The gonioreflectometric determination and an integrating-sphere-based reflection measurement traceable to KRISS spectral reflectance scale are compared by determining hemispherical reflectance, which results in agreement in their uncertainties. PMID:25322100

Hwang, Jisoo

2014-09-20

106

Approximating pi  

NSDL National Science Digital Library

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

British Broadcasting Corporation (BBC)

2003-01-01

107

Approximate (Euclidean)  

E-print Network

Approximate Nearest Neighbor in High Dimensions via Hashing Aris Gionis Piotr Indyk Rajeev Motwani­tree Guttman '84 LSD­tree Henrich, Six, Widmayer '89 R \\Lambda ­tree Beckmann, Kriegel et al '90 hB­tree Lomet #12; The curse of dimensionality ``Theorem:'' For dimensionality ``high enough'', any data structure

108

Introduction Approximating  

E-print Network

to predict forward model output from WRF grids 4 In real time, input WRF to NN, obtain satellite visible a Satellite Visible Image from Model Output Visualizing Model Data Using a Fast Approximation of a Radiative Transfer Model Valliappa Lakshmanan1,2 Robert Rabin2 Jason Otkin3 John Kain2 1Cooperative Institute

Lakshmanan, Valliappa

109

Wissenschaftliches Approximation  

E-print Network

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

Auzinger, Winfried

110

Metamaterial broadband angular selectivity  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

111

Creating High-Harmonic Beams with Controlled Orbital Angular Momentum  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

112

Angular correlations and high energy evolution  

SciTech Connect

We address the question of to what extent JIMWLK evolution is capable of taking into account angular correlations in a high energy hadronic wave function. Our conclusion is that angular (and indeed other) correlations in the wave function cannot be reliably calculated without taking into account Pomeron loops in the evolution. As an example we study numerically the energy evolution of angular correlations between dipole scattering amplitudes in the framework of the large N{sub c} approximation to JIMWLK evolution (the 'projectile dipole model'). Target correlations are introduced via averaging over an (isotropic) ensemble of anisotropic initial conditions. We find that correlations disappear very quickly with rapidity even inside the saturation radius. This is in accordance with our physical picture of JIMWLK evolution. The actual correlations inside the saturation radius in the target QCD wave function, on the other hand, should remain sizable at any rapidity.

Kovner, Alex [Physics Department, University of Connecticut, 2152 Hillside Road, Storrs, Connecticut 06269-3046 (United States); Lublinsky, Michael [Physics Department, Ben-Gurion University of the Negev, Beer Sheva 84105 (Israel); Physics Department, University of Connecticut, 2152 Hillside Road, Storrs, Connecticut 06269-3046 (United States)

2011-11-01

113

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

114

Gears: Determining Angular Velocity  

NSDL National Science Digital Library

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

AMPS GK-12 Program,

115

Quantifying Angular Momentum in Planetary Systems and Host Stars  

NASA Astrophysics Data System (ADS)

For decades it has been known that the spin angular momentum of early-type stars may be related to the stellar mass by the empirically derived power law J ? M^?. Late-type stars, however, break the power law with a significantly smaller value of ?. In particular, the Sun's spin angular momentum is consistent with the late-type break, whereas the total angular momentum of the Solar System falls near an extension of the early-type power law for single stars. We examine existing stellar inertial models, use them to approximate the spin angular momentum of host stars of newly discovered planetary systems, and calculate the orbital angular momentum of their planets from available observational data. Ratios of planetary to total system angular momentum are also presented. Results are discussed in the context of star and planet formation.

Irwin, Stacy; Durrance, Samuel T.

2014-11-01

116

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

SciTech Connect

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

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

1996-10-01

117

Approximate resolution of hard numbering problems  

SciTech Connect

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

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

1996-12-31

118

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

SciTech Connect

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

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

2004-09-01

119

Quantum Heuristics of Angular Momentum  

ERIC Educational Resources Information Center

Discusses the quantization of angular momentum components, Heisenberg-type inequalities for their spectral dispersions, and the quantization of the angular momentum modulus, without using operators or commutation relations. (MLH)

Levy-Leblond, Jean-Marc

1976-01-01

120

Angular momentum of rotating beams  

NASA Astrophysics Data System (ADS)

Light beams rotating about their axis can be created using rotating optical elements. We analyze the properties of rotating beams by expanding the mode function in eigenfunctions of angular momentum. Both the spin angular momentum, arising from the polarization, and orbital angular momentum, arising from the circulating phase gradient, are considered.

Nienhuis, Gerard

2006-02-01

121

Nanofabricated quartz cylinders for angular  

E-print Network

Nanofabricated quartz cylinders for angular trapping: DNA supercoiling torque detection Christopher nanofabricated quartz cylinders well suited for torque application and detection in an angular optical trap. We that nanofabricated quartz cylinders, when used with an angular trapping instrument, allow direct and simultaneous

Wang, Michelle

122

ANGULAR MOMENTUM ACQUISITION IN GALAXY HALOS  

SciTech Connect

We use high-resolution cosmological hydrodynamic simulations to study the angular momentum acquisition of gaseous halos around Milky-Way-sized galaxies. We find that cold mode accreted gas enters a galaxy halo with {approx}70% more specific angular momentum than dark matter averaged over cosmic time (though with a very large dispersion). In fact, we find that all matter has a higher spin parameter when measured at accretion than when averaged over the entire halo lifetime, and is well characterized by {lambda} {approx} 0.1, at accretion. Combined with the fact that cold flow gas spends a relatively short time (1-2 dynamical times) in the halo before sinking to the center, this naturally explains why cold flow halo gas has a specific angular momentum much higher than that of the halo and often forms ''cold flow disks.'' We demonstrate that the higher angular momentum of cold flow gas is related to the fact that it tends to be accreted along filaments.

Stewart, Kyle R. [Department of Natural and Mathematical Sciences, California Baptist University, 8432 Magnolia Ave., Riverside, CA 92504 (United States); Brooks, Alyson M. [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706 (United States); Bullock, James S. [Center for Cosmology, Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697 (United States); Maller, Ariyeh H. [Department of Physics, New York City College of Technology, 300 Jay St., Brooklyn, NY 11201 (United States); Diemand, Juerg [Institute for Theoretical Physics, University of Zurich, 8057, Zurich (Switzerland); Wadsley, James [Department of Physics and Astronomy, McMaster University, Main Street West, Hamilton L85 4M1 (Canada); Moustakas, Leonidas A. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2013-05-20

123

Angular displacement measuring device  

NASA Technical Reports Server (NTRS)

A system for measuring the angular displacement of a point of interest on a structure, such as aircraft model within a wind tunnel, includes a source of polarized light located at the point of interest. A remote detector arrangement detects the orientation of the plane of the polarized light received from the source and compares this orientation with the initial orientation to determine the amount or rate of angular displacement of the point of interest. The detector arrangement comprises a rotating polarizing filter and a dual filter and light detector unit. The latter unit comprises an inner aligned filter and photodetector assembly which is disposed relative to the periphery of the polarizer so as to receive polarized light passing the polarizing filter and an outer aligned filter and photodetector assembly which receives the polarized light directly, i.e., without passing through the polarizing filter. The purpose of the unit is to compensate for the effects of dust, fog and the like. A polarization preserving optical fiber conducts polarized light from a remote laser source to the point of interest.

Seegmiller, H. Lee B. (inventor)

1992-01-01

124

Temporal resolution improvement using PICCS in MDCT cardiac imaging.  

PubMed

The current paradigm for temporal resolution improvement is to add more source-detector units and/or increase the gantry rotation speed. The purpose of this article is to present an innovative alternative method to potentially improve temporal resolution by approximately a factor of 2 for all MDCT scanners without requiring hardware modification. The central enabling technology is a most recently developed image reconstruction method: Prior image constrained compressed sensing (PICCS). Using the method, cardiac CT images can be accurately reconstructed using the projection data acquired in an angular range of about 120 degrees, which is roughly 50% of the standard short-scan angular range (approximately 240 degrees for an MDCT scanner). As a result, the temporal resolution of MDCT cardiac imaging can be universally improved by approximately a factor of 2. In order to validate the proposed method, two in vivo animal experiments were conducted using a state-of-the-art 64-slice CT scanner (GE Healthcare, Waukesha, WI) at different gantry rotation times and different heart rates. One animal was scanned at heart rate of 83 beats per minute (bpm) using 400 ms gantry rotation time and the second animal was scanned at 94 bpm using 350 ms gantry rotation time, respectively. Cardiac coronary CT imaging can be successfully performed at high heart rates using a single-source MDCT scanner and projection data from a single heart beat with gantry rotation times of 400 and 350 ms. Using the proposed PICCS method, the temporal resolution of cardiac CT imaging can be effectively improved by approximately a factor of 2 without modifying any scanner hardware. This potentially provides a new method for single-source MDCT scanners to achieve reliable coronary CT imaging for patients at higher heart rates than the current heart rate limit of 70 bpm without using the well-known multisegment FBP reconstruction algorithm. This method also enables dual-source MDCT scanner to achieve higher temporal resolution without further hardware modifications. PMID:19610302

Chen, Guang-Hong; Tang, Jie; Hsieh, Jiang

2009-06-01

125

High angular resolution cosmic X-ray astronomy observations in the energy range 0.15-2 keV and XUV observations of nearby stars from an attitude controlled rocket  

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

126

Angular Momenta of the Planets.  

National Technical Information Service (NTIS)

The angular momentum densities of planet-satellite systems (including the asteroids but excepting Venus, Mercury, Mars, and Neptune), viewed as a rest in their solar orbits, exhibit a regularity expressed by A=k(M to the 2/3 power, where A is the angular ...

F. F. Fish

1967-01-01

127

The Angular Gyrus  

PubMed Central

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

2013-01-01

128

The angular momentum of baryons and dark matter halos revisited  

Microsoft Academic Search

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

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

2011-01-01

129

A High Resolution Micro-Electro-Mechanical Resonant Tilt Sensor  

E-print Network

of DC polarization voltage noise on the frequency stability. For the tilt sensor using batteries as the DC polarization source, the equivalent angular resolution is approximately 500 nano-radian. 22 Figure 14 Modified Allan deviation results... ), (2010) 3 pp.- pp. pp. [4] D. Inaudi, B. Glisic, Interferometric inclinometer for structural monitoring, 2002 15th Optical Fiber Sensors Conference Technical Digest OFS 2002(Cat No02EX533), (2002) 391-4 vol.14 vol.1. [5] C. Yang, G.J. Shropshire, C...

Zou, Xudong; Thiruvenkatanathan, Pradyumna; Seshia, Ashwin A.

2014-01-01

130

Digital Instrumentation for Angular Velocity and Acceleration  

Microsoft Academic Search

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

131

Spatial-spectral volume holographic systems: resolution dependence on effective thickness.  

PubMed

The resolution dependence of spatial-spectral volume holographic imaging systems on angular and spectral bandwidth of nonuniform gratings is investigated. Modeling techniques include a combination of the approximate coupled-wave analysis and the transfer-matrix method for holograms recorded in absorptive media. The effective thickness of the holograms is used as an estimator of the resolution of the imaging systems. The methodology, which assists in the design and optimization of volume holographic simulation results based on our approach, are confirmed with experiments and show proof of consistency and usefulness of the proposed models. PMID:21364728

Castro, Jose M; Brownlee, John; Luo, Yuan; de Leon, Erich; Barton, Jennifer K; Barbastathis, George; Kostuk, Raymond K

2011-03-01

132

The angular distribution of diffusely backscattered light  

NASA Astrophysics Data System (ADS)

The diffusion approximation predicts the angular distribution of light diffusely transmitted through an opaque slab to depend only on boundary reflectivity, independent of scattering anisotropy, and this has been verified by experiment(M.U. Vera and D.J. Durian, Phys. Rev. E 53) 3215 (1996). Here, by contrast, we demonstrate that the angular distribution of diffusely backscattered light depends on scattering anisotropy as well as boundary reflectivity. To model this observation scattering anisotropy is added to the diffusion approximation by a discontinuity in the photon concentration at the source point that is proportional to the average cosine of the scattering angle. We compare the resulting predictions with random walk simulations and with measurements of diffusely backscattered intensity versus angle for glass frits and aqueous suspensions of polystyrene spheres held in air or immersed in a water bath. Increasing anisotropy and boundary reflectivity each tend to flatten the predicted distributions, and for different combinations of anisotropy and reflectivity the agreement between data and predictions ranges from qualitatively to quantitatively good.

Vera, M. U.; Durian, D. J.

1997-03-01

133

3D digital hologram synthesis based on angular spectrum  

Microsoft Academic Search

This paper presents a ne method to calculate an image hologram pattern for a 3D object modeled as a stack of horizontally sliced 2D images. It is shown that the proposed method manipulates data on the angular spectrum domain, just as a recently presented method by Leseberg and thus it is regarded as an approximation to the Leseberg's method. Major

Hoon Gee Yang; Kyu-Tae Kim; Jae-Hoon Kim; Eun-Soo Kim

1998-01-01

134

Stepwise angular spectrum method for curved surface diffraction.  

PubMed

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

135

Practical Aspects of Calibration Near-Infrared Interferometer Data: Predicting Stellar Angular Sizes  

NASA Technical Reports Server (NTRS)

Reliable prediction of stellar diameters, particularly angular diameters, is a useful and necessary tool for the increasing number of milliarcsecond resolution studies being carried out in the astronomical community.

van Belle, G.

1999-01-01

136

Angular Momentum Profiles of Warm Dark Matter Halos  

E-print Network

We compare the specific angular momentum profiles of virialized dark halos in cold dark matter (CDM) and warm dark matter (WDM) models using high-resolution dissipationless simulations. The simulations were initialized using the same set of modes, except on small scales, where the power was suppressed in WDM below the filtering length. Remarkably, WDM as well as CDM halos are well-described by the two-parameter angular momentum profile of Bullock et al. (2001), even though the halo masses are below the filtering scale of the WDM. Although the best-fit shape parameters change quantitatively for individual halos in the two simulations, we find no systematic variation in profile shapes as a function of the dark matter type. The scatter in shape parameters is significantly smaller for the WDM halos, suggesting that substructure and/or merging history plays a role producing scatter about the mean angular momentum distribution, but that the average angular momentum profiles of halos originate from larger-scale phenomena or a mechanism associated with the virialization process. The known mismatch between the angular momentum distributions of dark halos and disk galaxies is therefore present in WDM as well as CDM models. Our WDM halos tend to have a less coherent (more misaligned) angular momentum structure and smaller spin parameters than do their CDM counterparts, although we caution that this result is based on a small number of halos.

James S. Bullock; Andrey V. Kravtsov; Pedro Colin

2001-09-25

137

The Angular Momentum of Light  

NASA Astrophysics Data System (ADS)

Preface D. L. Andrews and M. Babiker; 1. Light beams carrying orbital angular momentum J. B. Götte and S. M. Barnett; 2. Vortex transformation and vortex dynamics in optical fields G. Molina-Terriza; 3. Vector beams in free space E. J. Galvez; 4. Optical beams with orbital angular momentum in nonlinear media A. S. Desyatnikov and Y. S. Kivshar; 5. Ray optics, wave optics and quantum mechanics G. Nienhuis; 6. Quantum formulation of angle and orbital angular momentum J. B. Götte and S. M. Barnett; 7. Dynamic rotational frequency shift I. Bialynicki-Birula and Z. Bialynicka-Birula; 8. Spin-orbit interactions of light in isotropic media K. Y. Bliokh, A. Aiello and M. A. Alonso; 9. Quantum electrodynamics, angular momentum and chirality D. L. Andrews and M. Babiker; 10. Trapping of charged particles by Bessel beams I. Bialynicki-Birula, Z. Bialynicka-Birula and N. Drozd; 11. Theory of atoms in twisted light M. Babiker, D. L. Andrews and V. E. Lembessis; 12. An experimentalist's introduction to orbital angular momentum for quantum optics J. Romero, D. Giovannini, S. Franke-Arnold and M. J. Padgett; 13. Measurement of light's orbital angular momentum M. P. J. Lavery, J. Courtial and M. J. Padgett; 14. Efficient generation of optical twisters using helico-conical beams V. R. Daria, D. Palima and J. Glückstad; 15. Self similar modes of coherent diffusion with orbital angular momentum O. Firstenberg, M. Shuker, R. Pugatch and N. Davidson; 16. Dimensionality of azimuthal entanglement M. van Exter, E. Eliel and H. Woerdman; Index.

Andrews, David L.; Babiker, Mohamed

2012-11-01

138

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

139

"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

140

Photoelectron spectrometer for high-resolution angular resolved studies  

SciTech Connect

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

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

1982-01-01

141

High-angular resolution observations of stellar binary systems  

NASA Technical Reports Server (NTRS)

A long-term program designed to investigate the spatial structure of centimetric radio emission from close binary systems using multistation VLBI array is discussed. Eleven binaries, including eight RS CVn systems, Algol, LSI 61 deg 303, and Cyg X-1, have been detected. The measured brightness temperatures vary from T(B) about 10 exp 8.5 K during periods of low activity to T(B) about 10 exp 10.5 K during flares. Extensive observation of a few sources has shown that the spatial structure is 'core-halo' with linear dimensions of about a stellar radius and the binary system, respectively. The observations are consistent with gyrosynchrotron emission of mildly relativistic electrons in magnetic fields of about 10 exp 1.5 + or - 0.5 gauss. The core sources appear to be optically thick, while the halo component is optically thin.

Lestrade, J.-F.; Mutel, R. L.; Preston, R. A.; Phillips, R. B.

1985-01-01

142

AT20G high-angular-resolution catalogue (Chhetri+, 2013)  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

143

Factors influencing perceived angular velocity  

NASA Technical Reports Server (NTRS)

Angular velocity perception is examined for rotations both in depth and in the image plane and the influence of several object properties on this motion parameter is explored. Two major object properties are considered, namely, texture density which determines the rate of edge transitions for rotations in depth, i.e., the number of texture elements that pass an object's boundary per unit of time, and object size which determines the tangential linear velocities and 2D image velocities of texture elements for a given angular velocity. Results of experiments show that edge-transition rate biased angular velocity estimates only when edges were highly salient. Element velocities had an impact on perceived angular velocity; this bias was associated with 2D image velocity rather than 3D tangential velocity. Despite these biases judgements were most strongly determined by the true angular velocity. Sensitivity to this higher order motion parameter appeared to be good for rotations both in depth (y-axis) and parallel to the line of sight (z-axis).

Kaiser, Mary K.; Calderone, Jack B.

1991-01-01

144

Refined Error Estimates for the Riccati Equation with Applications to the Angular Teukolsky Equation  

E-print Network

We derive refined rigorous error estimates for approximate solutions of Sturm-Liouville and Riccati equations with real or complex potentials. The approximate solutions include WKB approximations, Airy and parabolic cylinder functions, and certain Bessel functions. Our estimates are applied to solutions of the angular Teukolsky equation with a complex aspherical parameter in a rotating black hole Kerr geometry.

Felix Finster; Joel Smoller

2013-07-24

145

Angular Differential Imaging at the Subaru Telescope  

NASA Astrophysics Data System (ADS)

We present Angular Differential Imaging (ADI) commissioning results using the next-generation high contrast instrumentation at the Subaru Telescope. The Subaru high contrast instrumentation consists of a 188 actuator AO system (AO188), classical Lyot coronagraph, and near infrared differential imaging science camera (HiCIAO). This system was designed specifically to achieve the requisite high angular resolution and contrast to directly detect the thermal emission of extrasolar planets. ADI suppresses optical speckle features by fixing the telescope PSF with respect to the science camera detector, while allowing the field with any companions to rotate freely. In post processing, the sequence of images are registered and combined to produce a reference PSF that is subtracted from each image. The final images are de-rotated and to realign the field with a fixed position angle. We implement ADI PSF subtraction algorithms, including the LOCI algorithm introduced in Lafrenière et al. 2007. The sensitivity of our results is compared with high contrast observations at other telescopes.

Dressing, Courtney D.; Turner, E.; McElwain, M.; Knapp, G.; SEEDS Collaboration

2010-01-01

146

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

147

Phenomenology of preequilibrium angular distributions  

SciTech Connect

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

148

Interferometric measurement of angular motion.  

PubMed

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°. PMID:23635175

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

2013-04-01

149

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/sqrt{textrm {Hz}} from audioband down to 100 mHz and an angular measurement range of more than ±1°.

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

2013-04-01

150

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

151

Angular momentum in QGP holography  

NASA Astrophysics Data System (ADS)

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

McInnes, Brett

2014-10-01

152

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.

153

Fast Approximate Convex Decomposition  

E-print Network

Approximate convex decomposition (ACD) is a technique that partitions an input object into "approximately convex" components. Decomposition into approximately convex pieces is both more efficient to compute than exact convex decomposition and can...

Ghosh, Mukulika

2012-10-19

154

Angular Momentum Transfer in Catastrophic Asteroid Impacts  

NASA Astrophysics Data System (ADS)

Incomplete knowledge of angular momentum transfer in asteroid impacts has hampered efforts to deduce asteroid collisional histories from their rotation rates. This problem traditionally has been investigated using impact experiments on cm-scale, strength-dominated targets. Recent evidence, however, indicates that impacts on asteroids of km size and larger may be controlled by gravity rather than strength, and that the analogy to laboratory impacts may not hold. Accordingly, we have modelled catastrophic impacts on gravitating asteroids to better understand angular momentum transfer in such events. We employ a 3--D, strengthless, gravitating SPH computer code. Target bodies are 10 to 1000 km in diameter and do not initially rotate. Impact speeds are 3--7 km/s; impact angles are 15--75(deg) . Each target is composed of 1791 mass elements: spatial resolution is coarse but acceptable for large scale energy transfer. We simulate the hydrodynamic phase of each impact, after which particle motions are ballistic and treated analytically. Escaping particles have kinetic energy greater than the gravitational energy binding them to the rest of the system; the others reaccrete to form a ``rubble pile'' which is assumed spherical. The rubble pile's size, mass, and angular momentum define its rotation rate. Spin rates for ejected fragments cannot be determined. The target's final spin period depends on the impact angle and the fraction of target mass ejected, but not on impact speed or target size in the ranges tested. The lack of size dependence cannot explain the observed excess of slowly rotating asteroids of ~ 100 km diameter. The fraction of projectile angular momentum retained by the target varies dramatically with impact speed and angle and with target size and fraction of mass removed, complicating its use in models where collision geometry varies. The final spin period of an asteroid losing 50% of its mass is 6--10 hours, comparable to the asteroidal mean of 8 hours. More destructive impacts yield spin rates approaching the 2-hour rotational breakup limit for strengthless stone bodies. We speculate that the observed decreasing trend in spin rate from C to S to M class asteroids results from an increasing trend in density.

Love, S. G.; Ahrens, T. J.

1996-09-01

155

Angular-domain imaging of fluorescence sources within tissue phantoms  

NASA Astrophysics Data System (ADS)

Conventional fluorescence imaging often does not have a mechanism to remove the scattering effect in biological tissue. We use Angular Domain Imaging (ADI) to improve the detection of smaller structures in fluorescence layer over that can be provided by existing systems. ADI is a high resolution, ballistic imaging method that utilizes the angular spectrum of photons to filter multiple-scattered photons and accepts only photons with small angular deviation from their original trajectory. Advantages of the ADI technique are that it is insensitive to wavelength and the sources are not required to be high quality, coherent, or pulse, as with OCT or time domain. Our target is to perform fluorescence ADI at shallow tissue such as skin (~ 1mm) with a buried collagen layer. To experimentally model shallow tissue with phantoms, a thin layer of scattering medium with similar scattering characteristic (?s = 200cm-1, g = 0.85) is placed on top fluorescence plastic (415nm excitation, ~ 555-585nm emission) which is patterned by strips of non-emitting structures (200-400?m). Positioning multiple collimated arrays with acceptance angles of 5.71° on top of the scattering medium, test structures (200?m wide) can be detected at shallow scattering medium thickness (1mm). Monte Carlo simulation confirms that fluorescence ADI can image structures at shallow tissue depth by using collimator array with modest filtration angles. Results show micromachined collimator arrays provide both high spatial resolution and angular filtration on scattered photons.

Cheng, Rongen L. K.; Tsui, Polly; Chapman, Glenn H.; Qarehbaghi, Reza; Pfeiffer, Nick

2011-03-01

156

Dissociating the effects of angular disparity and image similarity in mental rotation and object recognition.  

PubMed

Performance is often impaired linearly with increasing angular disparity between two objects in tasks that measure mental rotation or object recognition. But increased angular disparity is often accompanied by changes in the similarity between views of an object, confounding the impact of the two factors in these tasks. We examined separately the effects of angular disparity and image similarity on handedness (to test mental rotation) and identity (to test object recognition) judgments with 3-D novel objects. When similarity was approximately equated, an effect of angular disparity was only found for handedness but not identity judgments. With a fixed angular disparity, performance was better for similar than dissimilar image pairs in both tasks, with a larger effect for identity than handedness judgments. Our results suggest that mental rotation involves mental transformation procedures that depend on angular disparity, but that object recognition is predominately dependent on the similarity of image features. PMID:19665109

Cheung, Olivia S; Hayward, William G; Gauthier, Isabel

2009-10-01

157

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

158

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

159

Resolution-Tunable Angle-Resolved X-ray Imaging  

SciTech Connect

A resolution-tunable double-crystal device was successfully applied to angle-resolved x-ray imaging. The angular resolution of a Si (220) double-crystal analyzer was tuned between 0.5'' and 2.3'' through the offset angle at {lambda} = 0.0733nm. The throughput of the analyzer was higher than 90%. The angle-resolved images of a spider were recorded on nuclear emulsion plates at various angular resolutions. It was clearly observed that the quality of the angle-resolved image varies with the angular resolution of the analyzer.

Hirano, Keiichi [Institute of Materials Structure Science, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

2004-05-12

160

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

SciTech Connect

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

161

State-to-state and state-to-all-states reactive scattering angular distributions: F+H /sub 2/. -->. HF+H  

SciTech Connect

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

162

Longitudinal Profile Diagnostic Scheme with Subfemtosecond Resolution for High-Brightness Electron Beams  

SciTech Connect

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

163

The angular power spectra of polarized Galactic synchrotron  

Microsoft Academic Search

We derive the angular power spectra of intensity and polarization of Galactic synchrotron emission in the range 36???103 from the Parkes survey mapping the southern Galactic plane at 2.4 GHz. The polarization spectra of both electric and magnetic parity up to ??103 are approximated very well by power laws with slope coefficients ?1.4, quite different from the CMB spectra. We

M. Tucci; E. Carretti; S. Cecchini; R. Fabbri; M. Orsini; E. Pierpaoli

2000-01-01

164

Spin Angular Momentum Imparted by Gravitational Waves  

E-print Network

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

M Sharif

2007-01-23

165

Approximation Via Value Unification  

Microsoft Academic Search

Numerical function approximation over a Boolean domain is a classical problem with wide application to data modeling tasks and various forms of learning. A great many function approximation algorithms have been devised over the years. Because the goal is to produce an approximating function that has low expected error, algorithms are typically guided by error reduction. This guiding force, to

Paul E. Utgoff; David J. Stracuzzi

1999-01-01

166

Fabricating High Resolution Mirrors for Hand X-Ray Astronomy  

NASA Technical Reports Server (NTRS)

We describe the fabrication process for producing high-resolution conical mirrors for hard x-ray astronomy. When flown aboard stratospheric balloons, these high-resolution reflective mirrors focus hard x-rays (10-70 keV) emitted from cosmic sources such as supernovae, neutron stars, and quasars onto imaging focal plane detectors. Focused hard x-ray images allow scientists to determine the elemental compositions, temperatures, magnetic fields, velocities, and gravitational fields of these celestial bodies. The fabrication process involves generating super-polished mandrels, mandrel metrology, mirror shell nickel electroforming, and mirror testing. Each mandrel is a cylinder consisting of two conical segments; each segment is approximately 305-mm long. Through precision grinding these mandrels before super polishing, we have achieved 30 arc seconds, half power diameter replicated mirrors. During a May 2001 high atmosphere balloon flight, these mirrors focused high energy x-rays from three different celestial sources. However, we seek to improve the angular resolutions of future mirror shells by a factor of two. To achieve this goal, we have begun single point diamond turning the mandrels before super polishing. This has allowed greater precision tolerances on mandrel surface roughness and axial figure errors before super polishing. Surface roughnesses before polishing have been reduced from approximately 60 nm to approximately 15 nm. The peak to valley axial figure profile errors have been reduced from approximately 1.0 micrometers to approximately 0.4 micrometers. We are currently in Phase 2 of the HERO (high energy replicated optics) program which entails the production of sixteen 6-m-focal-length mirror modules, each containing a nested array of 15 mirror shells of diameters ranging from 50-mm to 94-mm. This flight is slated for the fall of 2003.

Speegle, Chet O.; Ramsey, Brian D.; Engelhaupt, Darell; Six, N. Frank (Technical Monitor)

2001-01-01

167

A test of galaxy evolutionary models via angular sizes  

NASA Technical Reports Server (NTRS)

The relationship between angular size, magnitude, and redshift of faint galaxies is explored as a potential tool to distinguish between galaxy evolutionary models. Different models, based on merging, mild luminosity evolution, and no evolution, lead to different predictions of the angular size distribution, redshift- size relation, and magnitude-size relation. The merging model predicts significantly smaller sizes for faint galaxies than the standard model, because of the requirement for more intrinsically small faint objects at high redshift. A dwarf-rich no-evolution model also predicts small sizes for faint galaxies. The mild luminosity evolution model predicts more luminous galaxies of large angular size at high redshift, as does a standard no-evolution model. Prefurbishment Hubble Space Telescope (HST) Medium Deep Survey observations of magnitudes and sizes of faint galaxies indicate an excess of small versus large faint galaxies, favoring the dwarf rich, no evolution model with respect to the merging model; the other two models are more discrepant with the data. While these results cannot yet rule out with certainty any of the proposed models, they demonstrate the potential of angular size to discriminate between models of galaxy evolution, especially with the high-resolution HST wide field/planetary camera-2 (WFPC2) data.

Im, Myungshin; Casertano, Stefano; Griffiths, Richard E.; Ratnatunga, Kavan U.; Tyson, J. Anthony

1995-01-01

168

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

169

Two-axis angular effector  

DOEpatents

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

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

1997-01-21

170

Estimation of the angular coordinates of radiation sources by a spectral-analysis method  

NASA Astrophysics Data System (ADS)

The paper examines the estimation of the angular coordinates of radiation sources by the spectral analysis of space-time samples using Prony's method. The application of the Prony method to the analysis of the spatial-frequency spectrum yields an algorithm which provides for the separate estimation of the angular coordinates of coherent and incoherent radiation sources within the limits of an angular resolution element. Computer simulation for different signal cross-correlations is used to study the proposed algorithm for two radiation sources. Results are presented for a linear equidistant antenna array.

Dzhavadov, G. G.; Sychev, M. I.

1987-02-01

171

Many-body theory for angular resolved photoelectron spectra of metal clusters  

E-print Network

Angular resolved photoelectron spectra of metal clusters have been experimentally measured for the first time only recently. These measurements have been performed systematically for sodium clusters in a broad range of cluster sizes. This work attracted a lot of attention and was reported practically at all major international cluster conferences because it revealed a very non-trivial behavior of the angular anisotropy parameter with respect to photon energy and provided a method for probing the angular momentum character of the valence orbitals of free nanoclusters. Initial attempts to explain these observations within single particle approximations fail completely. In this Letter we present a consistent many-body theory for the description of angular resolved photoelectron spectra of metal clusters. Jellium model formalism is employed. Our calculations demonstrate the dominant role of the many-body effects in the formation of angular distributions of photoelectrons emitted from sodium clusters and are in a ...

Solov'yov, Andrey V; Ivanov, Vadim K

2009-01-01

172

Compound Poisson process approximation  

Microsoft Academic Search

Compound Poisson processes are often useful as approximate models, when describing the occurrence of rare events. In this paper, we develop a method for showing how close such approximations are. Our approach is to use Stein's method directly, rather than by way of declumping and a marked Poisson process; this has conceptual advantages, but entails technical difficulties. Several applications are

A. D. Barbour; Marianne Månsson

2002-01-01

173

Approximation of Hopf bifurcation  

Microsoft Academic Search

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

174

Constructive Function Approximation1  

Microsoft Academic Search

The problem of automatically constructing features for use in a learned evaluation function is visited. Issues of feature overlap, independence, and coverage are addressed. Three algorithms are applied to two tasks, measuring the error in the approximated function as learning proceeds. The issues are discussed in the context of their apparent effects on the function approximation pro cess.

Paul E. Utgoff; Doina Precup

175

Approximate spatial reasoning  

NASA Technical Reports Server (NTRS)

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

Dutta, Soumitra

1988-01-01

176

On-demand generation of propagation-invariant photons with orbital angular momentum  

NASA Astrophysics Data System (ADS)

We study the generation of propagation invariant photons with orbital angular momentum by spontaneous parametric down conversion (SPDC) using a Bessel-Gauss pump beam. The angular and conditional angular spectra are calculated for an uniaxial crystal optimized for type I SPDC with standard Gaussian pump beams. It is shown that, as the mean value of the magnitude of the transverse wave vector of the pump beam increases, the emission cone is deformed into two non-coaxial cones that touch each other along a line determined by the orientation of the optical axis of the nonlinear crystal. At this location, the conditional spectrum becomes maximal for a pair of photons, one of which is best described by a Gaussian-like photon with a very small transverse wave vector, and the other a Bessel-Gauss photon with a distribution of transverse wave vectors similar in amplitude to that of the incident pump beam. A detailed analysis is then performed of the angular momentum content of SPDC photons by the evaluation of the corresponding transition amplitudes. As a result, we obtain conditions for the generation of heralded single photons which are approximately propagation invariant and have orbital angular momentum. A discussion is given about the difficulties in the interpretation of the results in terms of conservation of optical orbital angular momentum along the vector normal to the crystal surface. The angular spectra and the conditional angular spectra are successfully compared with available experimental data recently reported in the literature.

Jerónimo-Moreno, Y.; Jáuregui, R.

2014-07-01

177

Angular distributions as lifetime probes  

NASA Astrophysics Data System (ADS)

If new TeV scale particles are discovered, it will be important to determine their width. There is, however, a problematic region, where the width is too small to be determined directly, and too large to generate a secondary vertex. For a collection of colored, spin polarized particles, hadronization depolarizes the particles prior to their decay. The amount of depolarization can be used to probe the lifetime in the problematic region. In this paper we apply this method to a realistic scenario of a top-like particle that can be produced at the LHC. We study how depolarization affects the angular distributions of the decay products and derive an equation for the distributions that is sensitive to the lifetime.

Dror, Jeff Asaf; Grossman, Yuval

2014-06-01

178

Relativistic Statistical Mechanics with Angular Momentum  

E-print Network

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

Tadas K Nakamura

2011-12-01

179

Orbital angular momentum in phase space  

SciTech Connect

Research Highlights: > We propose a comprehensive Weyl-Wigner formalism for the canonical pair angle-angular momentum. > We present a simple and useful toolkit for the practitioner. > We derive simple evolution equations in terms of a star product in the semiclassical limit. - Abstract: A comprehensive theory of the Weyl-Wigner formalism for the canonical pair angle-angular momentum is presented. Special attention is paid to the problems linked to rotational periodicity and angular-momentum discreteness.

Rigas, I. [Departamento de Optica, Facultad de Fisica, Universidad Complutense, 28040 Madrid (Spain); Sanchez-Soto, L.L., E-mail: lsanchez@fis.ucm.es [Departamento de Optica, Facultad de Fisica, Universidad Complutense, 28040 Madrid (Spain); Klimov, A.B. [Departamento de Fisica, Universidad de Guadalajara, 44420 Guadalajara, Jalisco (Mexico); Rehacek, J.; Hradil, Z. [Department of Optics, Palacky University, 17. Listopadu 12, 746 01 Olomouc (Czech Republic)

2011-02-15

180

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.

2006-02-01

181

Angular correlations in Auger and fluorescence cascades  

NASA Astrophysics Data System (ADS)

Angular correlations in cascades of Auger electrons and X-rays (fluorescence) are discussed. These correlations can be studied by angle-resolved coincidence measurements of two sequential emissions of Auger electrons and/or fluorescence photons. A general expression for the angular correlation function for two sequential radiation is obtained using the density matrix and statistical tensor formalism. As an example, the cascades in inner-shell atomic photoionization and photoexcitation are considered. Spectroscopic and dynamic information which can be gained from angular correlation measurement in cascade transitions is discussed. Finally, the alignment transfer and non-coincidence measurements of the angular distribution of any radiation from a cascade are discussed.

Kabachnik, Nicolai M.

1997-01-01

182

Modular Approach to Physics: Angular Velocity  

NSDL National Science Digital Library

This web page contains an interactive simulation for introductory physics students describing different types of motion in term of angular coordinates. It consists of a moving car, a graph of angular velocity vs. time, and real-time values for areal and angular velocity. The path of the car can be a straight line, a circle, or a parabola with the angular motion given relative to a fixed point. This item is part of a larger collection of physics simulations sponsored by the MAP project (Modular Approach to Physics).

Austin, David; Martin, Brian

2008-08-03

183

MEASURING GAS ACCRETION AND ANGULAR MOMENTUM NEAR SIMULATED SUPERMASSIVE BLACK HOLES  

SciTech Connect

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

184

APPROXIMATE CHEMISTRY 113  

E-print Network

APPROXIMATE CHEMISTRY 113 Spring 2014 Forensic Science Professors James T. Spencer (jtspence SKILLS: Chemistry 113, Forensic Science, is focused upon the application of scientific methods specifically relevant to crime detection and analysis will be presented. No prior chemistry instruction

Doyle, Robert

185

Tsunami Travel Time Approximation  

NSDL National Science Digital Library

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

Grosfils, Eric

186

Relative Value Function Approximation  

Microsoft Academic Search

A form of temporal difference learning is presented that learns the relative utility of states,instead of the absolute utility. This formulation backs up decisions instead of values, makingit possible to learn a simpler function for defining a decision-making policy. A nonlinearrelative value function can be learned without increasing the dimensionality of the inputs.Contents1 Introduction 12 Approximating Absolute Utility 13 Approximating

Doina Precup; Paul E. Utgoff

1997-01-01

187

Variations in atmospheric angular momentum and the length of day  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

188

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

189

Galerkin discontinuous approximation of the MHD equations  

E-print Network

Galerkin discontinuous approximation of the MHD equations Altmann, Belat, Gutnic, Helluy, Mathis, Sonnendr¨ucker Contents 1 Some properties of the MHD system 2 1.1 Equations . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.4 Symmetric form of the MHD system . . . . . . . . . . . . 7 2 Numerical resolution

Paris-Sud XI, Université de

190

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

191

Optical angular motion sensor, phase 1  

Microsoft Academic Search

The optical angular motion sensor (OAMS) program, phase I, consisted of the design, fabrication, test and analysis of a triaxial angular motion sensor. A brassboard system was fabricated and assembled. It included a transmitter, a receiver assembly and an electronics assembly. The alignment information was transmitted between the transmitter and receiver on three discrete polarized light beams. The detail design

H. T. Braswell; J. W. Fontenot; L. L. Hartley; B. F. Heinrich; W. E. Miller; N. J. Ockman; S. W. Paulson; J. R. Taylor

1975-01-01

192

Angular-Rate Estimation Using Quaternion Measurements  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

193

Specific Angular Momentum of Extrasolar Planetary Systems  

E-print Network

As the number of known planetary systems increases, the ability to follow-up and characterize the extent of any system becomes limited. This paper considers the use of specific angular momentum as a metric to prioritize future observations. We analyze 431 planets in 367 known extrasolar planetary systems from Butler et al. (2006) (including updates to their online catalog, current to April, 2011) and estimate each system's orbital angular momentum. The range of partition- ing of specific angular momentum in these systems is found to be large, spanning several orders of magnitude. The analysis shows that multi-planet systems tend to have the highest values of specific angular momentum normalized against the planetary masses. This suggests that in high angular momentum systems, the dominant contributors have already been discovered, and that single-planet sys- tems with low observed angular momentum may be the most likely candidates for additional undiscovered companions compared to their high angular momentum, single-planet counterparts. The multi-planet system, GJ 581, is considered as a historical case study to demonstrate the concept, examining how the specific angular momentum of the know planetary system evolved with each discovery.

John C. Armstrong; Shane L. Larson; Rhett R. Zollinger

2007-08-13

194

Angular momentum decomposition of Richardson's pairs  

SciTech Connect

The angular momentum decomposition of pairs obtained using Richardson's exact solution of the pairing Hamiltonian for the deformed {sup 174}Yb nucleus are displayed. The probabilities for low angular momenta of the collective pairs are strikingly different from the ones obtained in the BCS ground state.

Dussel, G. G.; Sofia, H. M. [Departamento de Fisica Juan Jose Giambiagi, Universidad de Buenos Aires and CONICET Ciudad Universitaria, Pabellon 1, 1428 Buenos Aires (Argentina); Departamento de Fisica, Comision Nacional de Energia Atomica, and CONICET Avda. del Lbertador 8250, 1429 Buenos Aires (Argentina)

2008-07-15

195

Fine Aggregate Angularity from Geotechnical Perspective  

Microsoft Academic Search

Particle angularity is an important aspect in the performance of asphalt concrete pavements. When rounded materials are used, the shear strength is reduced resulting in rutting and shoving of the asphalt concrete mixtures. Currently, the Superpave design method stipulates that the fine aggregate angularity (FAA) via AASHTO T304 be used as a test specification for fine aggregate. The objectives of

Stan Vitton; Jason P. Bausano; R. Christopher Williams; Vernon Schafer

2008-01-01

196

The Angular Momentum-Energy Space  

E-print Network

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

Dan Comanescu

2007-02-09

197

Angular momentum in the global atmospheric circulation  

Microsoft Academic Search

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

Joseph Egger; Klaus Weickmann; Klaus-Peter Hoinka

2007-01-01

198

Asymptotic Diffusion-Limit Accuracy of Sn Angular Differencing Schemes  

SciTech Connect

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

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

2009-11-05

199

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.

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

2014-05-01

200

Amplification of Angular Rotations Using Weak Measurements  

E-print Network

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.

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

2013-12-10

201

Covariant approximation averaging  

E-print Network

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

Shintani, Eigo; Blum, Thomas; Izubuchi, Taku; Jung, Chulwoo; Lehner, Christoph

2014-01-01

202

Approximate programmable quantum processors  

E-print Network

A quantum processor is a programmable quantum circuit in which both the data and the program, which specifies the operation that is carried out on the data, are quantum states. We study the situation in which we want to use such a processor to approximate a set of unitary operators to a specified level of precision. We measure how well an operation is performed by the process fidelity between the desired operation and the operation produced by the processor. We show how to find the program for a given processor that produces the best approximation of a particular unitary operation. We also place bounds on the dimension of the program space that is necessary to approximate a set of unitary operators to a specified level of precision.

Mark Hillery; Mario Ziman; Vladimir Buzek

2005-10-20

203

Covariant approximation averaging  

E-print Network

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

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

2014-02-02

204

On Stochastic Approximation.  

ERIC Educational Resources Information Center

This paper deals with a stochastic process for the approximation of the root of a regression equation. This process was first suggested by Robbins and Monro. The main result here is a necessary and sufficient condition on the iteration coefficients for convergence of the process (convergence with probability one and convergence in the quadratic…

Wolff, Hans

205

Multicriteria approximation through decomposition  

SciTech Connect

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

206

Extended Abstract Approximating Visibility  

E-print Network

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

Franklin, W. Randolph

207

Multicriteria approximation through decomposition  

SciTech Connect

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

208

Monitoring Location and Angular Orientation of a Pill  

NASA Technical Reports Server (NTRS)

A mobile pill transmitter system moves through, or adjacent to, one or more organs in an animal or human body, while transmitting signals from its present location and/or present angular orientation. The system also provides signals from which the present roll angle of the pill, about a selected axis, can be determined. When the location coordinates angular orientation and the roll angle of the pill are within selected ranges, an aperture on the pill container releases a selected chemical into, or onto, the body. Optionally, the pill, as it moves, provides a sequence of visually perceptible images. The times for image formation may correspond to times at which the pill transmitter system location or image satisfies one of at least four criteria. This invention provides and supplies an algorithm for exact determination of location coordinates and angular orientation coordinates for a mobile pill transmitter (PT), or other similar device that is introduced into, and moves within, a GI tract of a human or animal body. A set of as many as eight nonlinear equations has been developed and applied, relating propagation of a wireless signal between either two, three, or more transmitting antennas located on the PT, to four or more non-coplanar receiving antennas located on a signal receiver appliance worn by the user. The equations are solved exactly, without approximations or iterations, and are applied in several environments: (1) association of a visual image, transmitted by the PT at each of a second sequence of times, with a PT location and PT angular orientation at that time; (2) determination of a position within the body at which a drug or chemical substance or other treatment is to be delivered to a selected portion of the body; (3) monitoring, after delivery, of the effect(s) of administration of the treatment; and (4) determination of one or more positions within the body where provision and examination of a finer-scale image is warranted.

Schipper, John F.

2012-01-01

209

Angular momentum dependence of complex fragment emission  

NASA Astrophysics Data System (ADS)

The angular momentum dependence of large fragment production in long-lived reactions is studied by measurements of fragment cross sections from reactions with substantially different angular momentum distributions and the coincident ?-ray multiplicity distributions. The results indicate that the primary l-wave distributions move to larger mean values and decrease in width and skewness with increasing mass symmetry in the decay channel. The results also confirm that the partition of angular momentum kinetic energy relaxed heavy-ion reactions is that expected for a rigidly rotating intermediate.

Sobotka, L. G.; Sarantites, D. G.; Li, Ze; Dines, E. L.; Halbert, M. L.; Hensley, D. C.; Lisle, J. C.; Schmitt, R. P.; Majka, Z.; Nebbia, G.; Griffin, H. C.; Sierk, A. J.

1987-12-01

210

Angular momentum in the Local Group  

SciTech Connect

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

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

1994-04-01

211

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

212

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

213

Importance of high-angular-momentum channels in pseudopotentials for quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

Quantum Monte Carlo methods provide in principle a highly accurate treatment of the many-body problem of calculating the ground and excited states of condensed systems. In practice, however, uncontrolled errors, such as those arising from the fixed-node and pseudopotential approximations can be problematic. We show that the accuracy of some quantum Monte Carlo calculations is limited by the properties of currently available pseudopotentials. The use of pseudopotentials involves several approximations, and we will focus on one that is relatively simple to correct during the pseudopotential design phase. It is necessary to include angular-momentum channels in the pseudopotential for excited angular-momentum states and to choose the local channel appropriately to obtain accurate results. Variational and diffusion Monte Carlo calculations for Zn, O, and Si atoms and ions demonstrate these issues. Adding higher-angular-momentum channels into the pseudopotential description reduces such errors without a significant increase in computational cost.

Tipton, William W.; Drummond, Neil D.; Hennig, Richard G.

2014-09-01

214

Approximate strip packing  

SciTech Connect

We present an approximation scheme for strip-packing, or packing rectangles into a rectangle of fixed width and minimum height, a classical NP-hard cutting-stock problem. The algorithm finds a packing of n rectangles whose total height is within a factor of (1 + {epsilon}) of optimal, and has running time polynomial both in n and in 1/{epsilon}. It is based on a reduction to fractional bin-packing, and can be performed by 5 stages of guillotine cuts.

Kenyon, C. [CNRS, Lyon (France); Remila, E. [LASPI, Roanne (France)

1996-12-31

215

l ?Approximation via Subdominants  

Microsoft Academic Search

Given a vector u and a certain subset K of a real vector space E, the problem of l?-approximation involves determining an element u in K nearest to u in the sense of the l?-error norm. The subdominant u? of u is the upper bound (if it exists) of the set {x?K:x?u} (we let x?y if all coordinates of x

Victor Chepoi; Bernard Fichet

2000-01-01

216

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

217

Light Gluino And Tevatroin Dijet Angular Distributions  

E-print Network

We consider the effects of a light gluino on the dijet angular distributions in p - pbar collisions at sqrt(s)=1800 GeV. We show that the slower running of alpha_s and the production q qbar, g g -> Gino Gino do not significantly alter the expected angular distributions. On the other hand, single U, D squark production q g -> Q Gino with subsequent Q -> q g results in dijets whose angular distributions are dramatically different from that in SM. The CDF data on dijet angular distributions with integrated luminosity of 106 pb^(-1) exclude U, D squarks in the mass ranges 170 < m < 650 and 190 < m < 600 GeV, We consider lower energies as well and show that in a future experimental analysis for dijet mass below 240 GeV squarks could be observed or ruled out.

Igor V. Terekhov

1997-02-11

218

The physics of angular momentum radio  

E-print Network

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

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

2014-01-01

219

Angular momentum effects in weak gravitational fields  

E-print Network

It is shown that, contrary to what is normally expected, it is possible to have angular momentum effects on the geometry of space time at the laboratory scale, much bigger than the purely Newtonian effects. This is due to the fact that the ratio between the angular momentum of a body and its mass, expressed as a length, is easily greater than the mass itself, again expressed as a length.

A. Tartaglia

2002-01-02

220

Optimal design of graded x-ray multilayer mirrors in the angular and spectral domains  

Microsoft Academic Search

The shape of the angular and spectral reflection curves of depth-graded x-ray multilayer mirrors may be controlled by the proper variation of the layer thicknesses. The determination of the thickness distribution of the layers that gives the best possible approximation to the desired reflection curve profile is a complicated mathematical problem. The present work reports on the application of the

Vladimir V. Protopopov; Alexander V. Tikhonravov; Andrei V. Voronov; Michael K. Trubetskov; Gary W. Debell

1999-01-01

221

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

SciTech Connect

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

222

Approximate option pricing  

SciTech Connect

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

223

Berkeley High-Resolution Ball  

SciTech Connect

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

Diamond, R.M.

1984-10-01

224

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

PubMed

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

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

2014-10-01

225

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

226

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

227

Femtolensing: Beyond the semiclassical approximation  

NASA Technical Reports Server (NTRS)

Femtolensoing is a gravitational lensing effect in which the magnification is a function not only of the position and sizes of the source and lens, but also of the wavelength of light. Femtolensing is the only known effect of 10(exp -13) - 10(exp -16) solar mass) dark-matter objects and may possibly be detectable in cosmological gamma-ray burst spectra. We present a new and efficient algorithm for femtolensing calculation in general potentials. The physical optics results presented here differ at low frequencies from the semiclassical approximation, in which the flux is attributed to a finite number of mutually coherent images. At higher frequencies, our results agree well with the semicalssical predictions. Applying our method to a point-mass lens with external shear, we find complex events that have structure at both large and small spectral resolution. In this way, we show that femtolensing may be observable for lenses up to 10(exp -11) solar mass, much larger than previously believed. Additionally, we discuss the possibility of a search femtolensing of white dwarfs in the Large Magellanic Cloud at optical wavelengths.

Ulmer, Andrew; Goodman, Jeremy

1995-01-01

228

Ultrafast angular momentum transfer in multisublattice ferrimagnets.  

PubMed

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

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

2014-01-01

229

Angular momentum conservation for dynamical black holes  

SciTech Connect

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

230

DISTRIBUTION OF ACCRETING GAS AND ANGULAR MOMENTUM ONTO CIRCUMPLANETARY DISKS  

SciTech Connect

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

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

2012-03-01

231

Angular Filters for Angular Domain Imaging Optical Tomography in Highly Scattering Media  

E-print Network

under you, and not an insignificant assortment of science-fiction trivia and tech news due OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the School of Engineering Science © Paulman Chan Konn Yan Chan Degree: Master of Applied Science Title of Thesis: Angular Filters for Angular Domain

Chapman, Glenn H.

232

Angular distribution of quasi-ballistic light measured through turbid media using angular domain optical imaging  

E-print Network

Angular distribution of quasi-ballistic light measured through turbid media using angular domain of minimally deviated quasi-ballistic photons versus multiply scattered photons in a turbid medium. The study-machined arrays of micro-tunnels each with a different range of acceptance angles. The balance between quasi-ballistic

Chapman, Glenn H.

233

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

234

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

SciTech Connect

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

235

Surface angular momentum of light beams.  

PubMed

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

236

Angular Dependence of Betatron X-Ray Spectra from a Laser-Wakefield Accelerator  

NASA Astrophysics Data System (ADS)

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.

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

237

Uncovering the Ultrafast Angular Momentum Transfer Channels on the Nanoscale in GdFeCo  

NASA Astrophysics Data System (ADS)

The ultrafast control of electron spins is of both fundamental scientific and technological interest. Recent experiments have shown that femtosecond laser excitation can act as a stimulus to switch the magnetization direction in ferrimagnetic GdFeCo, called all-optical switching. However, how angular momentum is transferred to result in a switched state remains unknown. To further understand this mechanism, we use 80fs x-ray pulses from LCLS to study how angular momentum transfer is triggered in GdFeCo by fs laser excitation using time-, element- and spatially-resolved x-ray resonant magnetic scattering. We present here the first-ever measurement of the fs magnetic response in GdFeCo with spatial resolution down to 10nm. Our results reveal drastically different behaviors on the nanoscale as compared to the bulk and provide insight into the angular momentum transfer channels.

Graves, Catherine; Reid, Alex; Wu, Benny; Wang, Tianhan; de Jong, Sanne; Radu, Ilie; Epp, Sasha; Hartmann, Robert; Tsukamoto, Arata; Coffee, Ryan; Bionta, Mina; Turner, Joshua; Schlotter, William; Acremann, Yves; Kimel, Alexey; Kirilyuk, Andrei; Stöhr, Joachim; Rasing, Theo; Dürr, Hermann; Scherz, Andreas

2012-02-01

238

Electronic sputtering from HOPG: A study of angular dependence  

NASA Astrophysics Data System (ADS)

The angular distribution of the sputtering yield from highly oriented pyrolytic graphite sample irradiated with a 130 MeV Ag beam is studied. The beam was incident perpendicular to the sample and the sputtered carbon was collected on Si catcher foils which were studied using a high resolution ERDA set up. An anisotropic distribution of sputtering is observed with a distribution C= Acos 1.3?+ Bexp(-( ?-53) 2/ ?2) which shows that a peak lies at around 53° on a distribution which otherwise is a over-cosine function. The maximum sputtering yield is observed at 53°, falling rapidly to almost zero at 90°, with an average sputter yield of 5.5 × 10 5 atoms/ion. It is suggested that this anisotropy may be due to the crystal structure and formation of a pressure pulse.

Tripathi, A.; Khan, S. A.; Srivastava, S. K.; Kumar, M.; Kumar, S.; Rao, S. V. S. N.; Lakshmi, G. B. V. S.; Siddiqui, Azhar. M.; Bajwa, N.; Nagaraja, H. S.; Mittal, V. K.; Szokefalvi, A.; Kurth, M.; Pandey, A. C.; Avasthi, D. K.; Carstanjen, H. D.

2003-12-01

239

Total angular momentum from Dirac eigenspinors  

NASA Astrophysics Data System (ADS)

The eigenvalue problem for Dirac operators, constructed from two connections on the spinor bundle over closed spacelike 2-surfaces, is investigated. A class of divergence-free vector fields, built from the eigenspinors, are found, which, for the lowest eigenvalue, reproduce the rotation Killing vectors of metric spheres, and provide rotation BMS vector fields at future null infinity. This makes it possible to introduce a well-defined, gauge invariant spatial angular momentum at null infinity, which reduces to the standard expression in stationary spacetimes. The general formula for the angular momentum flux carried away by the gravitational radiation is also derived.

Szabados, László B.

2008-01-01

240

Total angular momentum from Dirac eigenspinors  

E-print Network

The eigenvalue problem for Dirac operators, constructed from two connections on the spinor bundle over closed spacelike 2-surfaces, is investigated. A class of divergence free vector fields, built from the eigenspinors, are found, which, for the lowest eigenvalue, reproduce the rotation Killing vectors of metric spheres, and provide rotation BMS vector fields at future null infinity. This makes it possible to introduce a well defined, gauge invariant spatial angular momentum at null infinity, which reduces to the standard expression in stationary spacetimes. The general formula for the angular momentum flux carried away be the gravitational radiation is also derived.

Laszlo B. Szabados

2007-09-07

241

Angular Dispersion and Deflection Function for Heavy Ion Elastic Scattering  

Microsoft Academic Search

The differential cross sections for elastic scattering products of 17F on 208Pb have been measured. The angular dispersion plots of ln(d?\\/d?) versus ?2 are obtained from the angular distribution of the elastic scattering differential cross sections. Systematical analysis on the angular dispersion for the available experimental data indicates that there is an angular dispersion turning angle at forward angular range

Zhen Bai; Qi Wang; Jian-Long Han; Zhi-Gang Xiao; Hu-Shan Xu; Zhi-Yu Sun; Zheng-Guo Hu; Xue-Ying Zhang; Hong-Wei Wang; Rui-Shi Mao; Xiao-Hua Yuan; Zhi-Guo Xu; Hong-Bin Zhang; Hua-Gen Xu; Hui-Rong Qi; Yue Wang; Fei Jia; Li-Jie Wu; Xian-Li Ding; Qi Gao; Hui Gao; Song-Lin Li; Jun-Qing Li; Ya-Peng Zhang; Guo-Qing Xiao; Gen-Ming Jin; Zhong-Zhou Ren; Shan-Gui Zhou; Wang Xu; Gong-Tao Fan; Shuang-Quan Zhang; Dan-Yang Pang; Yu-Kun Sergey

2007-01-01

242

PHYSICAL REVIEW A 86, 063806 (2012) Measurement of the orbital-angular-momentum spectrum of fields with partial angular coherence  

E-print Network

the angular correlation function obtained from the double-angular-slit interference, we are able to calculate pattern obtained from double-angular-slit interference, one can calculate the degree of angular coherence of the constituent modes using a forked hologram [13]. More novel methods that involve interfering the field

Boyd, Robert W.

243

Approximations based on the adiabatic treatment of rotation for resonances  

SciTech Connect

In the adiabatic treatment of overall rotational motion, the rotational energy is obtained by diagonalization of the inertia tensor at each nuclear configuration, and subsequent insertion of the rotation constants into the standard formalism for the energy for a symmetric or asymmetric top. We have tested this approximation previously for bound states and resonances in HCO, and found it to be quite accurate. This adiabatic approximation is justified here by deriving an approximation very similar to it (but less accurate) for a triatomic molecule. We then consider further approximations to the adiabatic rotation approximation. In one we assume that rotation constants for each resonance are independent of the angular momentum state J. This approximation requires a minimum of two calculations of resonance positions and widths for nonzero J in addition to the one for J=0. The second approximation we consider is standard first-order perturbarion theory. The adiabatic rotational energy is the perturbation relative to the J=0 Hamiltonian, and the complex L{sup 2} eigenfunctions of this Hamiltonian are the zero-order states. These two approximations are tested for HCO bound states and resonances, where those obtained from the full adiabatic rotation approximation are assumed to be the benchmark calculations. {copyright} {ital 1997 American Institute of Physics.}

Qi, J.; Bowman, J.M. [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)] [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)

1997-12-01

244

Optimization of Angular-Momentum Biases of Reaction Wheels  

NASA Technical Reports Server (NTRS)

RBOT [RWA Bias Optimization Tool (wherein RWA signifies Reaction Wheel Assembly )] is a computer program designed for computing angular momentum biases for reaction wheels used for providing spacecraft pointing in various directions as required for scientific observations. RBOT is currently deployed to support the Cassini mission to prevent operation of reaction wheels at unsafely high speeds while minimizing time in undesirable low-speed range, where elasto-hydrodynamic lubrication films in bearings become ineffective, leading to premature bearing failure. The problem is formulated as a constrained optimization problem in which maximum wheel speed limit is a hard constraint and a cost functional that increases as speed decreases below a low-speed threshold. The optimization problem is solved using a parametric search routine known as the Nelder-Mead simplex algorithm. To increase computational efficiency for extended operation involving large quantity of data, the algorithm is designed to (1) use large time increments during intervals when spacecraft attitudes or rates of rotation are nearly stationary, (2) use sinusoidal-approximation sampling to model repeated long periods of Earth-point rolling maneuvers to reduce computational loads, and (3) utilize an efficient equation to obtain wheel-rate profiles as functions of initial wheel biases based on conservation of angular momentum (in an inertial frame) using pre-computed terms.

Lee, Clifford; Lee, Allan

2008-01-01

245

Angular momentum transport by internal waves in the solar interior.  

NASA Astrophysics Data System (ADS)

The internal gravity waves of low frequency which are emitted at the base of the solar convection zone are able to extract angular momentum from the radiative interior. We evaluate this transport with some simplifying assumptions: we ignore the Coriolis force, approximate the spectrum of turbulent convection by the Kolmogorov law, and couple this turbulence to the internal waves through their pressure fluctuations, following Press (1981ApJ...245..286P) and Garcia Lopez & Spruit (1991ApJ...377..268G). The local frequency of an internal wave varies with depth in a differentially rotating star, and it can vanish at some location, thus leading to enhanced damping (Goldreich & Nicholson 1989ApJ...342.1079G). It is this dissipation mechanism only that we take into account in the exchange of momentum between waves and stellar rotation. The flux of angular momentum is then an implicit function of depth, involving the local rotation rate and an integral representing the cumulative effect of radiative dissipation. We find that the efficiency of this transport process is rather high: it operates on a timescale of 10^7^ years, and is probably responsible for the flat rotation profile which has been detected through helioseismology.

Zahn, J.-P.; Talon, S.; Matias, J.

1997-06-01

246

Flavor stability analysis of dense supernova neutrinos with flavor-dependent angular distributions  

E-print Network

Numerical simulations of the supernova (SN) neutrino self-induced flavor conversions, associated with the neutrino-neutrino interactions in the deepest stellar regions, have been typically carried out assuming the "bulb-model". In this approximation, neutrinos are taken to be emitted half-isotropically by a common neutrinosphere. In the recent Ref. \\cite{Mirizzi:2011tu} we have removed this assumption by introducing flavor-dependent angular distributions for SN neutrinos, as suggested by core-collapse simulations. We have found that in this case a novel multi-angle instability in the self-induced flavor transitions can arise. In this work we perform an extensive study of this effect, carrying out a linearized flavor stability analysis for different SN neutrino energy fluxes and angular distributions, in both normal and inverted neutrino mass hierarchy. We confirm that spectra of different nu species which cross in angular space (where F_{\

Alessandro Mirizzi; Pasquale Dario Serpico

2012-08-01

247

Energy spreading and angular distribution of a beam of electrons in molecular hydrogen  

NASA Technical Reports Server (NTRS)

A Monte Carlo approach is used to obtain the energy spreading and angular distribution of initially monoenergetic and monodirectional beams of electron incident on a gas of molecular hydrogen. Several beams of primary electrons and the resultant secondaries are degraded in a step-by-step procedure which utilizes a detailed set of cross sections, together with reasonable approximations for the creation of secondary electrons. Particular attention is paid to the initial angular distribution of secondary electrons. An analytic function which characterizes current experimental differential cross-section data is used to provide realistic inputs into our calculations. The results for energy distribution as a function of distance and angular distribution at selected energies and distances are illustrated.

Heaps, M. G.; Green, A. E. S.

1975-01-01

248

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

249

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

SciTech Connect

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

QIAN,S.

1999-07-23

250

Angular distribution of atoms ejected by laser ablation of different metals  

SciTech Connect

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

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

2009-07-01

251

Combining angular response classification and backscatter imagery segmentation for benthic biological habitat mapping  

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

252

Spacecraft Angular State Estimation After Sensor Failure  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

253

Heteromodal conceptual processing in the angular gyrus  

PubMed Central

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

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

2013-01-01

254

Diffraction at a plane angular sector  

Microsoft Academic Search

A closed form solution is presented for the scattering in the far zone by a vertex at the interconnection between the two edges of a plane angular sector, when it is illuminated by a plane wave. The solution is obtained as a superposition of simple interaction mechanisms between the two adjacent edges. The spectral representation of the field diffracted by

S. Maci; R. Tiberio; A. Toccafondi

1994-01-01

255

Angular momentum and vortices in paraxial beams  

NASA Astrophysics Data System (ADS)

The free propagation of a paraxial light beam can be exactly mapped on the free evolution of a 2D harmonic oscillator over half an oscillation period. We apply this mapping to give an analytical description of the dynamics of vortices and their relation to the orbital angular momentum of light.

Nienhuis, Gerard; Visser, Jorrit

2004-05-01

256

Angular spectrum of quantized light beams  

NASA Astrophysics Data System (ADS)

We introduce a generalized angular spectrum representation for quantized light beams. By using our formalism, we are able to derive simple expressions for the electromagnetic vector potential operator in the case of (a) time-independent paraxial fields, (b) time-dependent paraxial fields, and (c) nonparaxial fields. For the first case the well-known paraxial results are fully recovered.

Aiello, A.; Visser, J.; Nienhuis, G.; Woerdman, J. P.

2006-02-01

257

The angular appearance of white holes  

Microsoft Academic Search

It is shown that non-radial light rays emitted from the surface of a white hole can emerge from inside the Schwarzschild barrier. The upper limit on their impact parameter is calculated under the requirement that such rays are blueshifted. The apparent angular size of the white hole determined by blueshifted rays is shown to grow so rapidly in the early

J. V. Narlikar; R. C. Kapoor

1978-01-01

258

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

259

Energy Versus Angular Momentum in Black Hole Binaries  

NASA Astrophysics Data System (ADS)

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 ENR(j) curve with the predictions of several analytic approximation schemes, we find that, while the canonically defined, nonresummed post-Newtonian-expanded EPN(j) relation exhibits large and growing deviations from ENR(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.

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

2012-03-01

260

Energy versus angular momentum in black hole binaries.  

PubMed

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

261

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

E-print Network

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

Knaust, Helmut

262

Forms of Approximate Radiation Transport  

SciTech Connect

Photon radiation transport is described by the Boltzmann equation. Because this equation is difficult to solve, many different approximate forms have been implemented in computer codes. Several of the most common approximations are reviewed, and test problems illustrate the characteristics of each of the approximations. This document is designed as a tutorial so that code users can make an educated choice about which form of approximate radiation transport to use for their particular simulation.

BRUNNER, THOMAS A.

2002-06-01

263

The angular momentum content of dwarf galaxies: new challenges for the theory of galaxy formation  

Microsoft Academic Search

We compute the specific angular momentum distributions for a sample of low-mass disc galaxies observed by Swaters. We compare these distributions to those of dark matter haloes obtained by Bullock et al. from high-resolution N-body simulations of structure formation in a LambdaCDM universe. We find that although the disc mass fractions are significantly smaller than the universal baryon fraction, the

Frank C. van den Bosch; Andreas Burkert; Rob A. Swaters

2001-01-01

264

The Angular Momentum Content of Dwarf Galaxies: New Challenges for the Theory of Galaxy Formation  

Microsoft Academic Search

We compute the specific angular momentum distributions of a sample of low\\u000amass disk galaxies observed by Swaters. We compare these distributions to those\\u000aof dark matter haloes obtained by Bullock et al. from high resolution N-body\\u000asimulations of structure formation in a LCDM Universe. We find that although\\u000athe disk mass fractions are significantly smaller than the Universal baryon

Frank C. van den Bosch; Andreas Burkert; Rob A. Swaters

2001-01-01

265

A multiwire proportional chamber for precision studies of neutron ? decay angular correlations  

NASA Astrophysics Data System (ADS)

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

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

2007-02-01

266

Noncommutative lattices as finite approximations  

Microsoft Academic Search

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

267

Approximations of fractional Brownian motion  

E-print Network

Approximations of fractional Brownian motion using Poisson processes whose parameter sets have the same dimensions as the approximated processes have been studied in the literature. In this paper, a special approximation to the one-parameter fractional Brownian motion is constructed using a two-parameter Poisson process. The proof involves the tightness and identification of finite-dimensional distributions.

Li, Yuqiang; 10.3150/10-BEJ319

2012-01-01

268

Networks for approximation and learning  

Microsoft Academic Search

The problem of the approximation of nonlinear mapping, (especially continuous mappings) is considered. Regularization theory and a theoretical framework for approximation (based on regularization techniques) that leads to a class of three-layer networks called regularization networks are discussed. Regularization networks are mathematically related to the radial basis functions, mainly used for strict interpolation tasks. Learning as approximation and learning as

T. Poggio; F. Girosi

1990-01-01

269

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

SciTech Connect

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

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

2013-07-20

270

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

271

Angular Momentum Loss Via Stellar Winds  

NASA Astrophysics Data System (ADS)

The evolution of stellar spin rates observed during star formation is not yet understood, due primarily to the fact that it is still not clear which mechanism(s) is responsible for removing angular momentum. Stellar winds may exert significant torques during pre-main-sequence evolution, provided that the mass loss rates are enhanced by several orders of magnitude relative to their main sequence values. This may be possible, if the winds are powered by the accretion process. We present new calculations of the angular momentum loss from enhanced stellar winds and address how this may help our understanding of young star spins. SPM was supported by an appointment to the NASA Postdoctoral Program at Ames Research Center, administered by ORAU through a contract with NASA.

Matt, Sean; Pinzon, G.; Greene, T. P.

2010-01-01

272

Approximate equivalence and approximate synchronization of metric transition systems  

Microsoft Academic Search

In this paper, we consider metric transition systems which are transition systems equipped with metrics for observation and synchronization labels. The existence of metrics leads to the introduction of two new concepts, (i) (epsi, delta)-approximate (bi)simulation of transition systems and (ii) approximate synchronization of transition systems. We show that the notion of (epsi, delta)-approximate (bi)simulation can be thought of as

A. Agung Julius; George J. Pappas

2006-01-01

273

Angular Momentum Transfer in a Protolunar Disk  

Microsoft Academic Search

The Moon would have formed through accretion from an impact-debris disk. N-body simulations (Ida et al. 1997, Nature, 389, 353; Kokubo et al. 2000, Icarus, in press) showed that time scale of lunar accretion is regulated by diffusion of material out from the Roche limit due to angular momentum transfer. Ida et al.(N ~ 1,000) and Kokubo et al. (2000)

T. Takeda; S. Ida

2000-01-01

274

Chirality and angular momentum in optical radiation  

E-print Network

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 multi-mode 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.

Matt M. Coles; David L. Andrews

2012-03-08

275

NASA/JPL-Caltech angular size  

E-print Network

#12;#12; : -- © NASA/JPL-Caltech #12; angular size SZ CC -- 3.0 CC © © NASA/JPL-Caltech/University of Arizona © Lynn Laux© NASA M4© M51© NASA/ESA M87© Juan. /Goddard Space Flight Center, JPL-Caltech, SDSS, NASA Abell 370© NASA, ESA, the Hubble SM4 ERO Team

Wang, Ming-Jye

276

A Neural Circuit for Angular Velocity Computation  

PubMed Central

In one of the most remarkable feats of motor control in the animal world, some Diptera, such as the housefly, can accurately execute corrective flight maneuvers in tens of milliseconds. These reflexive movements are achieved by the halteres, gyroscopic force sensors, in conjunction with rapidly tunable wing steering muscles. Specifically, the mechanosensory campaniform sensilla located at the base of the halteres transduce and transform rotation-induced gyroscopic forces into information about the angular velocity of the fly's body. But how exactly does the fly's neural architecture generate the angular velocity from the lateral strain forces on the left and right halteres? To explore potential algorithms, we built a neuromechanical model of the rotation detection circuit. We propose a neurobiologically plausible method by which the fly could accurately separate and measure the three-dimensional components of an imposed angular velocity. Our model assumes a single sign-inverting synapse and formally resembles some models of directional selectivity by the retina. Using multidimensional error analysis, we demonstrate the robustness of our model under a variety of input conditions. Our analysis reveals the maximum information available to the fly given its physical architecture and the mathematics governing the rotation-induced forces at the haltere's end knob. PMID:21228902

Snider, Samuel B.; Yuste, Rafael; Packer, Adam M.

2010-01-01

277

Angular Momentum Transport in Circumplanetary Disks  

NASA Astrophysics Data System (ADS)

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

Mitchell, Tyler R.

2014-11-01

278

Superplastic properties of an aluminum-based alloy after equal-channel angular pressing  

SciTech Connect

It is now recognized that superplasticity requires a very small grain size, typically < 10 {micro}m. A further reduction in grain size, to the submicrometer or nanometer level, offers the potential for attaining superplasticity at both faster strain rates and lower temperatures. This paper reports an investigation of the microstructure and tensile behavior of an Al-3% Mg-0.5% Zr alloy after processing by equal-channel angular pressing to an equivalent true strain of {approximately}8.

Wang, J.; Berbon, P.B.; Xu, Y.; Wang, L.; Langdon, T.G.

2000-07-01

279

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

PubMed Central

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

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

2011-01-01

280

Supporting Text Approximation of the Multinomial. Using Stirling's approximation  

E-print Network

Supporting Text Approximation of the Multinomial. Using Stirling's approximation n! (n/e)n 2n! . [S12] To calculate B L (^n) limN BN L (^n), we apply Stirling's formula to N!, n0!, and n1!, which that r Stirling's formula

Peterson, Carsten

281

Parallel solution of block angular LP problems using Kaul's algorithm  

E-print Network

Parallel solution of block angular LP problems using Kaul's algorithm Ilkay Boduro~glu1 , Julian, University of Edinburgh November 7th 2007 Parallel solution of block angular LP problems using Kaul problems parallel simplex · Kaul's algorithm #12;Overview · Introduction to block angular LP problems

Hall, Julian

282

3Angular Size and Similar Triangles The corresponding  

E-print Network

: The sun is 400 times the diameter of the moon. Explain why they appear to have about the same angular size of the Moon. Explain why they appear to have the same angular size if the moon is at a distance of 3843Angular Size and Similar Triangles The corresponding sides of similar triangles are proportional

283

LABORATORY EVALUATION OF THE FINE AGGREGATE ANGULARITY (FAA) TEST  

Microsoft Academic Search

The performance of hot-mix asphalt (HMA) pavements depends on the properties and proportions of the major components, i.e., mineral aggregates, asphalt cement and air voids. The performance of dense asphalt mixtures is influenced mainly by fine aggregate characteristics, such as shape, angularity and surface texture. The Fine Aggregate Angularity test (FAA), adopted by Superpave to evaluate the shape, angularity and

J. L. Fernandes Jr

284

Angular solution to FPGA-based high speed synchro  

Microsoft Academic Search

Synchro is a kind of angular measuring devices with high reliability widely used in avigation, spaceflight, military affairs and other fields. It aims to test positions, displacements and other angular information. CORDIC algorithm and its pipeline architecture were utilized by correcting the compensating factor based on FPGA. During the angular solution, we proposed a new method for angle mapping to

Li Mingwei; Mao Zhen; Sui Yongsheng

2008-01-01

285

Computer Science Approximately Uniform Random  

E-print Network

. Byers and Jeffrey Considine #12;Computer Science Motivation Data aggregation Approximations to COUNT sketches (Considine et al. 2004) Randomized algorithms e.g. randomized routing #12;Computer Science

Massachusetts at Amherst, University of

286

Critique of the angular momentum sum rules and a new angular momentum sum rule  

SciTech Connect

We present a study of the tensorial structure of the hadronic matrix elements of the angular momentum operators J. Well known results in the literature are shown to be incorrect, and we have taken pains to derive the correct expressions in three different ways, two involving explicit physical wave packets and the third, totally independent, based upon the rotational properties of the state vectors. Surprisingly it turns out that the results are very sensitive to the type of relativistic spin state used to describe the motion of the particle, i.e., whether a canonical (i.e., boost) state or a helicity state is utilized. We present results for the matrix elements of the angular momentum operators, valid in an arbitrary Lorentz frame, for both helicity states and canonical states. These results are relevant for the construction of angular momentum sum rules, relating the angular momentum of a nucleon to the spin and orbital angular momentum of its constituents. It turns out that it is necessary to distinguish carefully whether the motion of the partons is characterized via canonical or helicity spin states. Fortunately, for the simple parton model interpretation, when the proton moves along OZ, our results for the sum rule based upon the matrix elements of J{sub z} agree with the often used sum rule found in the literature. But for the components J{sub x},J{sub y} the results are different and lead to a new and very intuitive sum rule for transverse polarization.

Bakker, B.L.G. [Department of Physics and Astronomy, Vrije Universiteit, Amsterdam (Netherlands); Leader, E. [Imperial College London, SW7 2BW (United Kingdom); Trueman, T.L. [Physics Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)

2004-12-01

287

Quadrupole Approximation for Para-Positronium in Relativistic Schrödinger Theory  

E-print Network

The non-relativistic energy levels of para-positronium are calculated in the quadrupole approximation of the interaction potential. This approximation technique takes into account the anisotropy of the electrostatic electron-positron interaction in the lowest order. The states due to different values of the quantum number $(l_z)$ of angular momentum are found to be no longer degenerate as is the case in the conventional theory. The physical origin of this elimination of the conventional degeneracy may intuitively be attributed to the state-dependent inertial \\emph{broadening} of the rotating charge clouds; the corresponding \\emph{anisotropic} deformation (in the quadrupole approximation) lowers then the negative electrostatic interaction energy. The result of this influence of anisotropy is that the states with $l_z=0$ adopt smaller binding energy whereas the states with maximal value of $|l_z|$ (for fixed principal quantum number $n$) have the largest binding energy within the angular momentum multiplet $(-|l_{z,\\mathrm{max}}| \\le l_z \\le |l_{z,\\mathrm{max}}|)$. This yields a certain kind of electric fine-structure splitting with the splitted RST levels being placed in a relatively narrow band around the (highly degenerated) conventional levels.

M. Mattes; M. Sorg

2011-09-11

288

Extreme nonlinear optical processes with beams carrying orbital angular momentum  

NASA Astrophysics Data System (ADS)

Light beams carrying an isolated point singularity with a screw-type phase distribution are called an optical vortex (OV). The fact that in free space the Poynting vector of the beam gives the momentum flow leads to an orbital angular momentum (OAM) of the photons in such a singular beam, independent on the spin angular momentun1. There are many applications of optical OAM shown in literature that would benefit from the availability of optical vortex beams in all spectral regions. For example it was shown that transitions forbidden by selection rules in dipole approximation appear allowed when using photons with the additional degree of freedom of optical OAM2. However, the common techniques of producing new light frequencies by nonlinear optical processes seem problematic in conserving the optical vortex when the nonlinearity becomes large. We show that with the extremely nonlinear process of High Harmonic Generation (HHG) it is possible to transfer OVs from the near-infrared to the extreme ultraviolet (XUV)3 at wavelengths down to ~30 nm. The observed XUV light was examined spatially and spectrally. The spatial profile showed the expected singular behavior, a dark region in the center. A comparison of the far-field fringe pattern caused by a thin wire with corresponding simulations suggests that the XUV vortex beam carries a unit topological charge. A screw-like phase evolution around the profile was also verified by employing a Hartmann type measurement. The generated spectrum revealed that in all Harmonic orders an OV was present. The profile, however, looked the same in all orders, indicating identical topological charge, which runs counterintuitive to the assumption that the phase of exp(-il?) is multiplied by the harmonic order in a frequency up-conversion experiment.

Kern, C.; Zürch, M.; Hansinger, P.; Dreischuh, A.; Spielmann, Ch.

2014-03-01

289

Angular-spectral distribution of the emission of electrons moving in a plane weak-field magnetic undulator  

Microsoft Academic Search

The spontaneous emission of an electron moving in an infinite plane magnetic undulator is examined. The angular-spectral distribution of the emission is found in explicit form in the weak-field approximation for an arbitrary structure of the undulator field and is the product of a factor, which depends only on the harmonic, and a function of the angles and the velocity

Yu. M. Nikitina

1991-01-01

290

A comparison of FEM and upper-bound type analysis of equal-channel angular pressing (ECAP)  

Microsoft Academic Search

In this paper the pressures needed for non-friction equal-channel angular pressing (ECAP) of perfectly plastic or strain-hardening materials are analysed using analytical approximations (upper-bound type) and numerical (finite-elements) methods. The approximate solutions agree very well with the FEM results for different ECAP die angles or materials. The convenience of using back-pressure for improving the strain pattern homogeneity of deformed strain-hardening

Jon Alkorta; Javier Gil Sevillano

2003-01-01

291

Fuzzy systems as universal approximators  

Microsoft Academic Search

The author shows that an additive fuzzy system can approximate any continuous function on a compact domain to any degree of accuracy. Fuzzy systems are dense in the space of continuous functions. The fuzzy system approximates the function by covering its graph with fuzzy patches in the input-output state space. Each fuzzy rule defines a fuzzy patch and connects commonsense

Bart Kosko

1992-01-01

292

) Hermite approximation for conic sections  

E-print Network

An O(h 2n ) Hermite approximation for conic sections Michael Floater SINTEF P.O. Box 124, Blindern 0314 Oslo, NORWAY November 1994, Revised March 1996 Abstract. Given a segment of a conic section order approximation, conic sections, splines §1. Introduction It was described in a recent paper [6

Floater, Michael S.

293

Fuzzy systems are universal approximators  

Microsoft Academic Search

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

294

Angular-momentum evolution in laser-plasma accelerators.  

PubMed

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

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

2013-09-27

295

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

296

ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED  

SciTech Connect

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{sub *} and mass M{sub *} (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{sub *} reliably. Our results contravene suggestions that ellipticals could harbor large reservoirs of hidden j{sub *} 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 {approx}100 nearby bright galaxies of all types, placing them on a diagram of j{sub *} versus M{sub *}. The ellipticals and spirals form two parallel j{sub *}-M{sub *} tracks, with log-slopes of {approx}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 {approx}3-4 if mass-to-light ratio variations are neglected for simplicity, and {approx}7 if they are included. We decompose the spirals into disks and bulges and find that these subcomponents follow j{sub *}-M{sub *} 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{sub *}-M{sub *} 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{sub *}, but that the observations are reproduced well if these galaxies simply retained different fractions of their initial j complement ({approx}60% and {approx}10%, respectively). We consider various physical mechanisms for the simultaneous evolution of j{sub *} and M{sub *} (including outflows, stripping, collapse bias, and merging), emphasizing that the vector sum of all such processes must produce the observed j{sub *}-M{sub *} 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. [University of California Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States); Fall, S. Michael [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2012-12-15

297

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" (TT1ex" ), 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

298

Linear Upconversion of Orbit Angular Momentum  

E-print Network

We experimentally demonstrate that an infrared light imprinted the orbit angular momentum is linearly converted into a visible light using Four-wave mixing (FWM) via a Ladder-type configuration in Rb85 atoms. Simultaneously, we theoretically simulate this linear conversion process, and theoretical analysis is in reasonable agreement with the experimental result. A large single-photon detuning is used to reduce the absorption of the atoms to the up-converted light and to avoid the pattern formation in FWM process. The multi-mode image linear conversion is important for applications in image communications, astrophysics and quantum information so on.

Ding, Dong-Sheng; Shi, Bao-Sen; Zou, Xu-Bo; Guo, Guang-Can

2012-01-01

299

EQUAL CHANNEL ANGULAR EXTRUSION (ECAE) OF BERYLLIUM.  

SciTech Connect

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

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

2001-01-01

300

Linear and angular retroreflecting interferometric alignment target  

DOEpatents

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

Maxey, L. Curtis (Powell, TN)

2001-01-01

301

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

302

Existence of solutions and diffusion approximation for a model Fokker-Planck equation  

Microsoft Academic Search

We study a simplified model of the Fokker-Planck equation of plasma physics. This model only involves a linear angular diffusion for a monoenergetic beam. We discuss the problem of existence and uniqueness of solutions in both the evolution and the stationary cases; Then we justify the diffusion approximation, with either the Dirichlet, or the Robin boundary conditions. For that purpose,

Pierre Degond; Sylvie Mas-Gallic

1987-01-01

303

Small-angle scattering in a Reissner-Nordstrem field. Quasiclassical approximation  

SciTech Connect

Phases, amplitude and differential cross section of charged particle scattering by a Reissner-Nordstrem black hole are obtained for small scattering angles in a quasiclassical approximation of the Klein-Gordon equation. The approximation is legitimate in the shortwave case, where the situation is considered when the Coulomb and gravitational effects are commensurate in magnitude. It is shown that for relativistic particles the angular scattering distribution differs from the Rutherford distribution in terms /approx/ /theta//sup /minus/3/.

Gaina, A.B.

1989-01-01

304

TECHNICAL DESIGN NOTE: Precision angular velocity response of a fiber-optic gyroscope using a piezo-nano-rotation table  

NASA Astrophysics Data System (ADS)

Modern fiber-optic gyroscopes are calibrated using the Earth's rotation or stepper motor actuated rotation tables. We investigated the angular velocity resolution of the Optolink SRS-1000 fiber-optic gyroscope using a piezo-activated rotation table down to angular velocity steps of 1 × 10-7 rad s-1 with an accuracy of 1.5 × 10-8 rad s-1. To our knowledge, these are the smallest velocity steps resolved and reported in the literature so far. Our results show that such a gyroscope may be also used for nanopositioning purposes in addition to its usual navigation application.

Tajmar, M.; Plesescu, F.; Seifert, B.

2009-02-01

305

Neutron Emission and Angular Distribution in Compact Plasma Focus Devices Operating at Hundreds of Joules  

SciTech Connect

Measurement of anisotropy and neutron energy of the very small device PF-400J (880 nF, 30 kV, 120 kA, 400 J, 300 ns time to peak current, dI/dt{approx}4x1011 A/s) are presented. Neutron emission with the device operating in deuterium has been obtained and the maximum total neutron yield measured is of the order of 106 per shot at 9mbar. The following diagnostics have been applied: time of flight (TOF) to estimate the neutron mean energy, and angular distribution of the neutron emission using CR-39 nuclear track detectors covered with polyethylene located at several positions (between -90 deg. to 90 deg. ). Discharges were performed at different pressures, 5-12 mbar, with a charging voltage of 30{+-}2 KV ({approx}400J). With the results of the TOF measurements a mean neutron energy of (2.4{+-}0.4) MeV was obtained. The angular measurements are compared with the total neutron yield (integral of the angular measurements). The results are consistent with an angular uniform plateau (isotropic emission) plus a shape peaked in the direction of the axis of the discharge (anisotropic emission). Isotropic components accounts for 57.5% of the accumulative emission, while the anisotropy component accounts for the remaining 42.5%. Anisotropic component appears between +50 deg. and -50 deg. approximately.

Silva, Patricio; Moreno, Jose; Soto, Leopoldo [Comision Chilena de Energia Nuclear, Casilla 188-D, Santiago (Chile); Pavez, Cristian [Comision Chilena de Energia Nuclear, Casilla 188-D, Santiago (Chile); Universidad de Concepcion, Facultad de Ciencias, Departamento de Fisica, Concepcion (Chile); Castillo, Fermin; Herrera, Julio [Universidad Nacional Autonoma de Mexico, Ciudad de Mexico (Mexico)

2006-12-04

306

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

E-print Network

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

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

2014-07-26

307

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

E-print Network

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

Simo, I Ruiz; Amaro, J E; Barbaro, M B; Caballero, J A; Donnelly, T W

2014-01-01

308

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

NASA Astrophysics Data System (ADS)

The angular distribution of the phase space arising in two-particle emission reactions induced by electrons and neutrinos is computed in the laboratory (Lab) system by boosting the isotropic distribution in the center of mass (CM) system used in Monte Carlo generators. The Lab distribution has a singularity for some angular values, coming from the Jacobian of the angular transformation between CM and Lab systems. We recover the formula we obtained in a previous calculation for the Lab angular distribution. This is in accordance with the Monte Carlo method used to generate two-particle events for neutrino scattering [J. T. Sobczyk, Phys. Rev. C 86, 015504 (2012)]. Inversely, by performing the transformation to the CM system, it can be shown that the phase-space function, which is proportional to the two-particle-two-hole (2p-2h) hadronic tensor for a constant current operator, can be computed analytically in the frozen nucleon approximation, if Pauli blocking is absent. The results in the CM frame confirm our previous work done using an alternative approach in the Lab frame. The possibilities of using this method to compute the hadronic tensor by a boost to the CM system are analyzed.

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

2014-09-01

309

Orbital angular momentum of general astigmatic modes  

NASA Astrophysics Data System (ADS)

We present an operator method to obtain complete sets of astigmatic Gaussian solutions of the paraxial wave equation. In case of general astigmatism, the astigmatic intensity and phase distribution of the fundamental mode differ in orientation. As a consequence, the fundamental mode has a nonzero orbital angular momentum, which is not due to phase singularities. Analogous to the operator method for the quantum harmonic oscillator, the corresponding astigmatic higher-order modes are obtained by repeated application of raising operators on the fundamental mode. The nature of the higher-order modes is characterized by a point on a sphere, in analogy with the representation of polarization on the Poincaré sphere. The north and south poles represent astigmatic Laguerre-Gaussian modes, similar to circular polarization on the Poincaré sphere, while astigmatic Hermite-Gaussian modes are associated with points on the equator, analogous to linear polarization. We discuss the propagation properties of the modes and their orbital angular momentum, which depends on the degree of astigmatism and on the location of the point on the sphere.

Visser, Jorrit; Nienhuis, Gerard

2004-07-01

310

Angular Power Spectra with Finite Counts  

E-print Network

Angular anisotropy techniques for cosmic diffuse radiation maps are powerful probes, even for quite small data sets. A popular observable is the angular power spectrum; we present a detailed study applicable to any unbinned source skymap S(n) from which N random, independent events are observed. Its exact variance, which is due to the finite statistics, depends only on S(n) and N; we also derive an unbiased estimator of the variance from the data. First-order effects agree with previous analytic estimates. Importantly, heretofore unidentified higher-order effects are found to contribute to the variance and may cause the uncertainty to be significantly larger than previous analytic estimates---potentially orders of magnitude larger. Neglect of these higher-order terms, when significant, may result in a spurious detection of the power spectrum. On the other hand, this would indicate the presence of higher-order spatial correlations, such as a large bispectrum, providing new clues about the sources. Numerical si...

Campbell, Sheldon S

2014-01-01

311

Orbital angular momentum of general astigmatic modes  

SciTech Connect

We present an operator method to obtain complete sets of astigmatic Gaussian solutions of the paraxial wave equation. In case of general astigmatism, the astigmatic intensity and phase distribution of the fundamental mode differ in orientation. As a consequence, the fundamental mode has a nonzero orbital angular momentum, which is not due to phase singularities. Analogous to the operator method for the quantum harmonic oscillator, the corresponding astigmatic higher-order modes are obtained by repeated application of raising operators on the fundamental mode. The nature of the higher-order modes is characterized by a point on a sphere, in analogy with the representation of polarization on the Poincare sphere. The north and south poles represent astigmatic Laguerre-Gaussian modes, similar to circular polarization on the Poincare sphere, while astigmatic Hermite-Gaussian modes are associated with points on the equator, analogous to linear polarization. We discuss the propagation properties of the modes and their orbital angular momentum, which depends on the degree of astigmatism and on the location of the point on the sphere.

Visser, Jorrit; Nienhuis, Gerard [Huygens Laboratorium, Universiteit Leiden, Postbus 9504, 2300 RA Leiden (Netherlands)

2004-07-01

312

Approximate Correspondences in High Dimensions  

E-print Network

Pyramid intersection is an efficient method for computing an approximate partial matching between two sets of feature vectors. We introduce a novel pyramid embedding based on a hierarchy of non-uniformly shaped bins that ...

Grauman, Kristen

2006-06-15

313

Greedy approximation in convex optimization  

E-print Network

Jun 2, 2012 ... continuous functions. One more important argument that motivates us to ... In optimization theory an energy function E(x) is given and we should find an approximate ..... of matrices with nuclear norm not exceeding 1. We are ...

2012-06-02

314

method and approximate sparse inverses  

Microsoft Academic Search

Application of algebraic multigrid method and approximate sparse inverses are applied as preconditioners for large algebraic systems arising in approximation of diusion-reaction problems in 3-dimensional complex domains. Here we report the results of numerical experiments when using highly graded and locally rened meshes for problems with non-homogeneous and anisotropic coecien ts that have small features and almost singular solutions. For

Veselin Dobrev; Richard Ewing; Raytcho Lazarov; Joseph Pasciak

315

Fuzzy Systems as Universal Approximators  

Microsoft Academic Search

An additive fuzzy system can uniformly approximate any real continuous function on a compact domain to any degree of accuracy. An additive fuzzy system approximates the function by covering its graph with fuzzy patches in the input-output state space and averaging patches that overlap. The fuzzy system computes a conditional expectation E|Y|X| if we view the fuzzy sets as random

Bart Kosko

1994-01-01

316

Approximate Data Structures with Applications  

E-print Network

. INSERT(~) inserts i recursively into the appropriate Sk. If Sk was previously empty, it creates the data structure for Sk and recursively inserts k into T. DELETE(N) recursively deletes the element from the appropriate Sk. If Sk becomes empty... the same dynamic operations as the standard van Emde Boas data structure [28, 201, except that answers to queries are approximate. The variants support all operations in constant time provided the error of approximation is l/polylog(n), and in O...

Matias, Yossi; Vitter, Jeffrey Scott; Young, Neal E.

1994-01-01

317

Exponential approximations in optimal design  

NASA Technical Reports Server (NTRS)

One-point and two-point exponential functions have been developed and proved to be very effective approximations of structural response. The exponential has been compared to the linear, reciprocal and quadratic fit methods. Four test problems in structural analysis have been selected. The use of such approximations is attractive in structural optimization to reduce the numbers of exact analyses which involve computationally expensive finite element analysis.

Belegundu, A. D.; Rajan, S. D.; Rajgopal, J.

1990-01-01

318

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

NASA Astrophysics Data System (ADS)

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

Yan, Bo; Jiao, Sihai; Zhang, Dianhua

2014-08-01

319

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

320

Prototype of an angular-selective photoelectron calibration source for the KATRIN experiment  

NASA Astrophysics Data System (ADS)

The method of direct neutrino mass determination based on the kinematics of tritium beta decay, which is adopted by the KATRIN experiment, makes use of a large, high-resolution electrostatic spectrometer with magnetic adiabatic collimation. In order to target a sensitivity on m(?) of 0.2eV/c2, a detailed understanding of the electromagnetic properties of the electron spectrometer is essential, requiring comprehensive calibration measurements with dedicated electron sources. In this paper we report on a prototype of a photoelectron source providing a narrow energy spread and angular selectivity. Both are key properties for the characterisation of the spectrometer. The angular selectivity is achieved by applying non-parallel strong electric and magnetic fields: Directly after being created, photoelectrons are accelerated rapidly and non-adiabatically by a strong electric field before adiabatic magnetic guiding takes over.

Valerius, K.; Hein, H.; Baumeister, H.; Beck, M.; Bokeloh, K.; Bonn, J.; Glück, F.; Ortjohann, H.-W.; Ostrick, B.; Zbo?il, M.; Weinheimer, Ch

2011-01-01

321

Approximating random quantum optimization problems  

NASA Astrophysics Data System (ADS)

We report a cluster of results regarding the difficulty of finding approximate ground states to typical instances of the quantum satisfiability problem k-body quantum satisfiability (k-QSAT) on large random graphs. As an approximation strategy, we optimize the solution space over “classical” product states, which in turn introduces a novel autonomous classical optimization problem, PSAT, over a space of continuous degrees of freedom rather than discrete bits. Our central results are (i) the derivation of a set of bounds and approximations in various limits of the problem, several of which we believe may be amenable to a rigorous treatment; (ii) a demonstration that an approximation based on a greedy algorithm borrowed from the study of frustrated magnetism performs well over a wide range in parameter space, and its performance reflects the structure of the solution space of random k-QSAT. Simulated annealing exhibits metastability in similar “hard” regions of parameter space; and (iii) a generalization of belief propagation algorithms introduced for classical problems to the case of continuous spins. This yields both approximate solutions, as well as insights into the free energy “landscape” of the approximation problem, including a so-called dynamical transition near the satisfiability threshold. Taken together, these results allow us to elucidate the phase diagram of random k-QSAT in a two-dimensional energy-density-clause-density space.

Hsu, B.; Laumann, C. R.; Läuchli, A. M.; Moessner, R.; Sondhi, S. L.

2013-06-01

322

Analysis of resolution criterion and aberrations for Fizeau interferometer  

Microsoft Academic Search

The quest for higher angular resolution in astronomy will inevitably require the telescope with large aperture. However, the primary mirror diameter is limited by the fabrication problems, and the cost of monolithic optics increases faster than diameter squared. The Fizeau interferometer imaging system represents a promising new technology to overcome the above-mentioned problems. The sub-apertures of the system are phased

Shengqian Wang; Changhui Rao; Wenhan Jiang

2008-01-01

323

The two-dimensional angular momentum distribution in a protostellar core L1527  

NASA Astrophysics Data System (ADS)

In star formation at the early phase, angular momentum distribution of a natal core is crucial to determine the evolution of the core such as binary formation and disk formation. We have not yet fully understood the angular momentum distribution of such dense cores. We therefore mapped a 6 arcmin x6 arcmin region (0.2 pc x 0.2 pc) of the protostellar core L1527 in C18O(1-0) with 0.1 km/s resolution with the Nobeyama 45m Telescope in order to derive rotation properties. In the C18O(1-0) integrated intensity map, the emission distribution is centered on the protostar. We introduced a new method to calculate the two-dimensional specific angular momentum distribution of a core and derived the direction of the rotation axis as a function of the core radius. We found that the direction of the angular momentum vector changes from outside to inside and thus, we have confirmed that the dense core L1527 cannot be described by a single rotation axis. Since the inner rotational axis direction is especially important with formation and evolution of the inner rotating disk (Tobin+2013), we think that analysis of the two dimensional specific angular momentum distributions is required. Our method has advantages over the previous analysis of dense cores. First the linear or planar fitting of the line of sight velocity to derive a velocity gradient cannot detect change of the rotational axis (Goodman+1993, Ohashi+1997, and Caselli+2002). Second the position-velocity diagrams can distinguish between rigid-rotation or differential rotation of the core, but only the cut direction. (Belloch+2002). Indeed our analysis results agree with Tobin+2011 who firstly showed the different directions of the velocity gradient on between large- and small-scales.

Kiyokane, Kazuhiro; Saito, Masao; Saigo, Kazuya; Kurono, Yasutaka

2013-07-01

324

Dependence of the angular distributions in photoionization of H+2 on the initial and final state representation  

NASA Astrophysics Data System (ADS)

We present a detailed study of the angular distribution in photoionization of H+2 in different geometrical arrangements between the internuclear axis and the polarization vector. We compare the results of an exact calculations with those obtained employing approximate initial and final state wave functions. We find large and unexpected differences if we employ the 2C or exact final state continuum wave functions with the same initial state. We find also that the results depend on the accuracy of the initial bound state. As the quality of the final state is improved we obtain results in closer agreement with the exact angular distributions.

Della Picca, R.; Fainstein, P. D.; Martiarena, M. L.; Dubois, A.

2008-11-01

325

Chiral symmetries associated with angular momentum  

NASA Astrophysics Data System (ADS)

In quantum mechanics courses, symmetries of a physical system are usually introduced as operators which commute with the Hamiltonian. In this paper we will consider chiral symmetries which anticommute with the Hamiltonian. Typically, introductory courses at the (under)graduate level do not discuss these simple, useful and beautiful symmetries at all. The first time a student encounters them is when the Dirac equation is discussed in a course on relativistic quantum mechanics, or when particle-hole symmetry is studied in the context of superconductivity. In this paper, we will show how chiral symmetries can be simply elucidated using the theory of angular momentum, which is taught in virtually all introductory quantum mechanics courses.

Bhattacharya, M.; Kleinert, M.

2014-03-01

326

Orbital angular momentum photonic quantum interface  

E-print Network

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

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

2014-01-01

327

Chiral symmetries associated with angular momentum  

E-print Network

In beginning quantum mechanics courses, symmetries of a physical system are usually introduced as operators which commute with the Hamiltonian. In this article we will consider chiral symmetries which anticommute with the Hamiltonian. Typically, introductory courses at the (under)graduate level do not discuss these simple, useful and beautiful symmetries at all. The first time a student typically encounters them is when the Dirac equation is discussed in a course on relativistic quantum mechanics, or when particle-hole symmetry is studied in the context of superconductivity. In this article, we will show how chiral symmetries can be simply elucidated using the theory of angular momentum, which is taught in virtually all introductory quantum mechanics courses.

M. Bhattacharya; M. Kleinert

2013-11-29

328

Moon influence on equatorial atmospheric angular momentum  

NASA Astrophysics Data System (ADS)

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

Bizouard, Christian; Zotov, Leonid; Sidorenkov, Nikolay

2014-05-01

329

?-decay angular correlations with neutral atom traps  

NASA Astrophysics Data System (ADS)

We review the use of laser cooling and trapping techniques for nuclear beta-decay angular correlations. Coincidences between the beta (?) and recoiling nucleus allow the determination of the neutrino (?) momentum more directly than previously possible. Highly spin-polarized samples are also possible, with polarization known from atomic observables, and the nuclear recoils both in singles and in coincidence with the ? add interesting observables. Ongoing experiments are trapping elements that provide pure Fermi, pure Gamow–Teller, and mixed Gamow–Teller transitions to distinguish sources of new physics. To compete with the next generation of neutron ?-decay experiments, cases are being carefully chosen to minimize or at least know recoil-order corrections.

Behr, J. A.; Gorelov, A.

2014-11-01

330

The Angular Momentum of Accreting Neutron Stars  

E-print Network

I review the rotation measurements of accreting neutron stars. Many of the highly magnetic accreting X-ray pulsars have been continuously observed with the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory (CGRO) since April 1991. These observations show that the accretion torque exerted on many disk-fed accreting X-ray pulsars changes sign on a monthly to yearly timescale. This results in alternating periods of spin-up and spin-down with nearly the same torques, leading to little net angular momentum gained by accretion. I also summarize recent discoveries with the Rossi X-Ray Timing Explorer (RXTE) of periodicities during Type I X-ray bursts. These seem to indicate that many of the rapidly accreting and weakly magnetic neutron stars in our galaxy are rotating at frequencies greater than 250 Hertz. Most remarkable is that they all rotate within a rather narrow range of frequencies.

Lars Bildsten

1998-01-07

331

Angular biasing in implicit Monte-Carlo  

SciTech Connect

Calculations of indirect drive Inertial Confinement Fusion target experiments require an integrated approach in which laser irradiation and radiation transport in the hohlraum are solved simultaneously with the symmetry, implosion and burn of the fuel capsule. The Implicit Monte Carlo method has proved to be a valuable tool for the two dimensional radiation transport within the hohlraum, but the impact of statistical noise on the symmetric implosion of the small fuel capsule is difficult to overcome. We present an angular biasing technique in which an increased number of low weight photons are directed at the imploding capsule. For typical parameters this reduces the required computer time for an integrated calculation by a factor of 10. An additional factor of 5 can also be achieved by directing even smaller weight photons at the polar regions of the capsule where small mass zones are most sensitive to statistical noise.

Zimmerman, G.B.

1994-10-20

332

Angular momentum effects in subbarrier fusion  

SciTech Connect

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

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

1988-01-01

333

Spectro-angular light scattering measurements of individual microscopic objects.  

PubMed

The spectro-angular light scattering measurements of individual microscopic objects are presented. Using spectroscopic quantitative phase microscopy and Fourier transform light scattering, the 2D angle-resolved light scattering intensity and phase patterns are measured in a spectral range of 450-750 nm and an angular range of -70-70°. The spectro-angular light scattering measurements of individual polystyrene beads are demonstrated with high sensitivity and precision. PMID:24663733

Jung, JaeHwang; Park, YongKeun

2014-02-24

334

Measurement of angular correlations based on secondary vertex reconstruction at  

Microsoft Academic Search

A measurement of the angular correlations between beauty and anti-beauty hadrons () produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the\\u000a region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their\\u000a decays. The B hadron angular separation

V. Khachatryan; A. M. Sirunyan; A. Tumasyan; W. Adam; T. Bergauer; M. Dragicevic; J. Erö; C. Fabjan; M. Friedl; R. Frühwirth; V. M. Ghete; J. Hammer; S. Hänsel; C. Hartl; M. Hoch; N. Hörmann; J. Hrubec; M. Jeitler; G. Kasieczka; W. Kiesenhofer; M. Krammer; D. Liko; I. Mikulec; M. Pernicka; H. Rohringer; R. Schöfbeck; J. Strauss; A. Taurok; F. Teischinger; P. Wagner; W. Waltenberger; G. Walzel; E. Widl; C.-E. Wulz; V. Mossolov; N. Shumeiko; J. Suarez Gonzalez; L. Benucci; K. Cerny; E. A. De Wolf; X. Janssen; T. Maes; L. Mucibello; S. Ochesanu; B. Roland; R. Rougny; M. Selvaggi; H. Van Haevermaet; P. Van Mechelen; N. Van Remortel; S. Beauceron; F. Blekman; S. Blyweert; J. D’Hondt; O. Devroede; R. Gonzalez Suarez; A. Kalogeropoulos; J. Maes; M. Maes; S. Tavernier; W. Van Doninck; P. Van Mulders; G. P. Van Onsem; I. Villella; O. Charaf; B. Clerbaux; G. De Lentdecker; V. Dero; A. P. R. Gay; G. H. Hammad; T. Hreus; P. E. Marage; L. Thomas; C. Vander Velde; P. Vanlaer; J. Wickens; V. Adler; S. Costantini; M. Grunewald; B. Klein; A. Marinov; J. Mccartin; D. Ryckbosch; F. Thyssen; M. Tytgat; L. Vanelderen; P. Verwilligen; S. Walsh; N. Zaganidis; S. Basegmez; G. Bruno; J. Caudron; L. Ceard; J. De Favereau De Jeneret; C. Delaere; P. Demin; D. Favart; A. Giammanco; G. Grégoire; J. Hollar; V. Lemaitre; J. Liao; O. Militaru; S. Ovyn; D. Pagano; A. Pin; K. Piotrzkowski; N. Schul; N. Beliy; T. Caebergs; E. Daubie; G. A. Alves; D. De Jesus Damiao; M. E. Pol; M. H. G. Souza; W. Carvalho; E. M. Da Costa; C. De Oliveira Martins; S. Fonseca De Souza; L. Mundim; H. Nogima; V. Oguri; W. L. Prado Da Silva; A. Santoro; S. M. Silva Do Amaral; A. Sznajder; F. Torres Da Silva De Araujo; F. A. Dias; M. A. F. Dias; T. R. Fernandez Perez Tomei; E. M. Gregores; F. Marinho; S. F. Novaes; Sandra S. Padula; N. Darmenov; L. Dimitrov; V. Genchev; P. Iaydjiev; S. Piperov; M. Rodozov; S. Stoykova; G. Sultanov; V. Tcholakov; R. Trayanov; I. Vankov; M. Dyulendarova; R. Hadjiiska; V. Kozhuharov; L. Litov; E. Marinova; M. Mateev; B. Pavlov; P. Petkov; J. G. Bian; G. M. Chen; H. S. Chen; C. H. Jiang; D. Liang; S. Liang; J. Wang; X. Wang; Z. Wang; M. Xu; M. Yang; J. Zang; Z. Zhang; Y. Ban; S. Guo; Y. Guo; W. Li; Y. Mao; S. J. Qian; H. Teng; L. Zhang; B. Zhu; W. Zou; A. Cabrera; B. Gomez Moreno; A. A. Ocampo Rios; A. F. Osorio Oliveros; J. C. Sanabria; N. Godinovic; D. Lelas; K. Lelas; R. Plestina; D. Polic; I. Puljak; Z. Antunovic; M. Dzelalija; V. Brigljevic; S. Duric; K. Kadija; S. Morovic; A. Attikis; M. Galanti; J. Mousa; C. Nicolaou; F. Ptochos; P. A. Razis; H. Rykaczewski; M. Finger; Y. Assran; M. A. Mahmoud; A. Hektor; M. Kadastik; K. Kannike; M. Müntel; M. Raidal; L. Rebane; V. Azzolini; P. Eerola; S. Czellar; J. Härkönen; A. Heikkinen; V. Karimäki; R. Kinnunen; J. Klem; M. J. Kortelainen; T. Lampén; K. Lassila-Perini; S. Lehti; T. Lindén; P. Luukka; T. Mäenpää; E. Tuominen; J. Tuominiemi; E. Tuovinen; D. Ungaro; L. Wendland; K. Banzuzi; A. Korpela; T. Tuuva; D. Sillou; M. Besancon; S. Choudhury; M. Dejardin; D. Denegri; B. Fabbro; J. L. Faure; F. Ferri; S. Ganjour; F. X. Gentit; A. Givernaud; P. Gras; G. Hamel de Monchenault; P. Jarry; E. Locci; J. Malcles; M. Marionneau; L. Millischer; J. Rander; A. Rosowsky; I. Shreyber; M. Titov; P. Verrecchia; S. Baffioni; F. Beaudette; L. Bianchini; M. Bluj; C. Broutin; P. Busson; C. Charlot; T. Dahms; L. Dobrzynski; R. Granier de Cassagnac; M. Haguenauer; P. Miné; C. Mironov; C. Ochando; P. Paganini; D. Sabes; R. Salerno; Y. Sirois; C. Thiebaux; B. Wyslouch; A. Zabi; J.-L. Agram; J. Andrea; A. Besson; D. Bloch; D. Bodin; J.-M. Brom; M. Cardaci; E. C. Chabert; C. Collard; E. Conte; F. Drouhin; C. Ferro; J.-C. Fontaine; D. Gelé; U. Goerlach; S. Greder; P. Juillot; M. Karim; A.-C. Le Bihan; Y. Mikami; P. Van Hove; F. Fassi; D. Mercier; C. Baty; N. Beaupere; M. Bedjidian; O. Bondu; G. Boudoul; D. Boumediene; H. Brun; N. Chanon; R. Chierici; D. Contardo; P. Depasse; H. El Mamouni; A. Falkiewicz; J. Fay; S. Gascon; B. Ille; T. Kurca; T. Le Grand; M. Lethuillier; L. Mirabito; S. Perries; V. Sordini; S. Tosi; Y. Tschudi; P. Verdier; H. Xiao; L. Megrelidze; V. Roinishvili; D. Lomidze; G. Anagnostou; M. Edelhoff; L. Feld; N. Heracleous; O. Hindrichs; R. Jussen; K. Klein; J. Merz; N. Mohr; A. Ostapchuk; A. Perieanu; F. Raupach; J. Sammet; S. Schael; D. Sprenger; H. Weber; M. Weber; B. Wittmer; M. Ata; W. Bender; M. Erdmann; J. Frangenheim; T. Hebbeker; A. Hinzmann; K. Hoepfner; C. Hof; T. Klimkovich; D. Klingebiel; P. Kreuzer; D. Lanske; C. Magass; G. Masetti; M. Merschmeyer; A. Meyer; P. Papacz; H. Pieta; H. Reithler; S. A. Schmitz; L. Sonnenschein; J. Steggemann; D. Teyssier; M. Bontenackels; M. Davids; M. Duda; G. Flügge; H. Geenen; M. Giffels; W. Haj Ahmad; D. Heydhausen; T. Kress; Y. Kuessel; A. Linn; A. Nowack; L. Perchalla; O. Pooth; J. Rennefeld

2011-01-01

335

X-ray multilayer mirrors with an extended angular range  

Microsoft Academic Search

The shape of the reflection curve of depth-graded X-ray multilayer mirrors may be controlled in an angular region several times greater than the angular width of traditionally periodical X-ray multilayer mirrors. Mirrors of this type may be used in X-ray collimators, focusing devices and scanners. In addition, very narrow angular gaps in the reflection curves may be obtained, which may

V. V. Protopopov; V. A. Kalnov

1998-01-01

336

Can torsion play a role in angular momentum conservation law?  

E-print Network

In Einstein-Cartan theory, by the use of the general Noether theorem, the general covariant angular-momentum conservation law is obtained with the respect to the local Lorentz transformations. The corresponding conservative Noether current is interpreted as the angular momentum tensor of the gravity-matter system including the spin density. It is pointed out that, assuming the tetrad transformation given by eq. (15), torsion tensor can not play a role in the conservation law of angular momentum.

Yishi Duan; Ying Jiang

1998-09-02

337

Angular Momentum Conservation Law for Randall-Sundrum Models  

E-print Network

In Randall-Sundrum models, by the use of general Noether theorem, the covariant angular momentum conservation law is obtained with the respect to the local Lorentz transformations. The angular momentum current has also superpotential and is therefore identically conserved. The space-like components $J_{ij}$ of the angular momentum for Randall-Sundrum models are zero. But the component $J_{04}$ is infinite.

Yu-Xiao Liu; Yi-Shi Duan; Li-Jie Zhang

2005-08-27

338

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

NASA Technical Reports Server (NTRS)

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

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

1971-01-01

339

Measuring the Angular Momentum Distribution in Core-Collapse Supernova Progenitors with Gravitational Waves  

E-print Network

The late collapse, core bounce, and the early postbounce phase of rotating core collapse leads to a characteristic gravitational wave (GW) signal. The precise shape of the signal is governed by the interplay of gravity, rotation, nuclear equation of state (EOS), and electron capture during collapse. We explore the dependence of the signal on total angular momentum and its distribution in the progenitor core by means of a large set of axisymmetric general-relativistic core collapse simulations in which we vary the initial angular momentum distribution in the core. Our simulations include a microphysical finite-temperature EOS, an approximate electron capture treatment during collapse, and a neutrino leakage scheme for the postbounce evolution. We find that the precise distribution of angular momentum is relevant only for very rapidly rotating cores with T/|W|>~8% at bounce. We construct a numerical template bank from our baseline set of simulations, and carry out additional simulations to generate trial waveforms for injection into simulated advanced LIGO noise at a fiducial galactic distance of 10 kpc. Using matched filtering, we show that for an optimally-oriented source and Gaussian noise, advanced Advanced LIGO could measure the total angular momentum to within ~20%, for rapidly rotating cores. For most waveforms, the nearest known degree of precollapse differential rotation is correctly inferred by both our matched filtering analysis and an alternative Bayesian model selection approach. We test our results for robustness against systematic uncertainties by injecting waveforms from simulations using a different EOS and and variations in the electron fraction in the inner core. The results of these tests show that these uncertainties significantly reduce the accuracy with which the total angular momentum and its precollapse distribution can be inferred from observations.

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

2013-11-14

340

A Revised Prescription for the Tayler-Spruit Dynamo: Magnetic Angular Momentum Transport in Stars  

NASA Astrophysics Data System (ADS)

Angular momentum transport by internal magnetic fields is an important ingredient for stellar interior models. In this paper we critically examine the basic heuristic assumptions in the model of the Tayler-Spruit dynamo, which describes how a pinch-type instability of a toroidal magnetic field in differentially rotating stellar radiative zones may result in large-scale fluid motion. We agree with prior published work both on the existence of the instability and its nearly horizontal geometry for perturbations. However, the approximations in the original Acheson dispersion relation are valid only for small length scales, and we disagree that the dispersion relation can be extrapolated to horizontal length scales of order the radius of the star. We contend that dynamical effects, in particular, angular momentum conservation, limit the maximum horizontal length scale. We therefore present transport coefficients for chemical mixing and angular momentum redistribution by magnetic torques that are significantly different from previous published values. The new magnetic viscosity is reduced by 2-3 orders of magnitude compared to the old one, and we find that magnetic angular momentum transport by this mechanism is very sensitive to gradients in the mean molecular weight. The revised coefficients are more compatible with empirical constraints on the timescale of core-envelope coupling in young stars than the previous ones. However, solar models including only this mechanism possess a rapidly rotating core, in contradiction with helioseismic data. Previous studies had found strong core-envelope coupling, both for solar models and for the cores of massive evolved stars. We conclude that the Tayler-Spruit mechanism may be important for envelope angular momentum transport but that some other process must be responsible for efficient spin-down of stellar cores.

Denissenkov, Pavel A.; Pinsonneault, Marc

2007-02-01

341

Solving the Darwin problem in the first post-Newtonian approximation of general relativity  

E-print Network

We analytically calculate the equilibrium sequence of the corotating binary stars of incompressible fluid in the first post-Newtonian(PN) approximation of general relativity. By calculating the total energy and total angular momentum of the system as a function of the orbital separation, we investigate the innermost stable circular orbit for corotating binary(we call it ISCCO). It is found that by the first PN effect, the orbital separation of the binary at the ISCCO becomes small with increase of the compactness of each star, and as a result, the orbital angular velocity at the ISCCO increases. These behaviors agree with previous numerical works.

Keisuke Taniguchi; Masaru Shibata

1997-05-13

342

Ideal linear-chain polymers with fixed angular momentum.  

PubMed

The statistical mechanics of a linear noninteracting polymer chain with a large number of monomers is considered with fixed angular momentum. The radius of gyration for a linear polymer is derived exactly by functional integration. This result is then compared to simulations done with a large number of noninteracting rigid links at fixed angular momentum. The simulation agrees with the theory up to finite-size corrections. The simulations are also used to investigate the anisotropic nature of a spinning polymer. We find universal scaling of the polymer size along the direction of the angular momentum, as a function of rescaled angular momentum. PMID:21867202

Brunner, Matthew; Deutsch, J M

2011-07-01

343

Mechanical memory for photons with orbital angular momentum  

NASA Astrophysics Data System (ADS)

We propose to use an acoustic surface wave as a memory for a photon carrying orbital angular momentum. We clarify the physical mechanism that enables the transfer of information, derive the angular momentum selection rule that must be obeyed in the process and show how to optimize the optoacoustic coupling. We theoretically demonstrate that high fidelities can be achieved, using realistic parameters, for the transfer of a coherent optical Laguerre-Gaussian state, associated with large angular momentum, to a mechanical shear mode. Our results add a significant possibility to the ongoing efforts towards the implementation of quantum information processing using photonic orbital angular momentum.

Shi, H.; Bhattacharya, M.

2013-08-01

344

Entropic uncertainty minimum for angle and angular momentum  

NASA Astrophysics Data System (ADS)

Uncertainty relations are key components in the understanding of the nature of quantum mechanics. In particular, entropic relations are preferred in the study of angular position and angular momentum states. We propose a new form of angle–angular momentum state that provides, for all practical purposes, a lower bound on the entropic uncertainty relation, {{H}\\varphi }+{{H}m}, for any given angular uncertainty, thus improving upon previous bounds. We establish this by comparing this sum with the absolute minimum value determined by a global numerical search. These states are convenient to work with both analytically and experimentally, which suggests that they may be of use for quantum information purposes.

Yao, Alison M.; Brougham, Thomas; Eleftheriadou, Electra; Padgett, Miles J.; Barnett, Stephen M.

2014-10-01

345

Heat pipe transient response approximation.  

SciTech Connect

A simple and concise routine that approximates the response of an alkali metal heat pipe to changes in evaporator heat transfer rate is described. This analytically based routine is compared with data from a cylindrical heat pipe with a crescent-annular wick that undergoes gradual (quasi-steady) transitions through the viscous and condenser boundary heat transfer limits. The sonic heat transfer limit can also be incorporated into this routine for heat pipes with more closely coupled condensers. The advantages and obvious limitations of this approach are discussed. For reference, a source code listing for the approximation appears at the end of this paper.

Reid, R. S. (Robert Stowers)

2001-01-01

346

Representing and selecting vibrational angular momentum states for quasiclassical trajectory chemical dynamics simulations.  

PubMed

Linear molecules with degenerate bending modes have states, which may be represented by the quantum numbers N and L. The former gives the total energy for these modes and the latter identifies their vibrational angular momentum jz. In this work, the classical mechanical analog of the N,L-quantum states is reviewed, and an algorithm is presented for selecting initial conditions for these states in quasiclassical trajectory chemical dynamics simulations. The algorithm is illustrated by choosing initial conditions for the N = 3 and L = 3 and 1 states of CO2. Applications of this algorithm are considered for initial conditions without and with zero-point energy (zpe) included in the vibrational angular momentum states and the C-O stretching modes. The O-atom motions in the x,y-plane are determined for these states from classical trajectories in Cartesian coordinates and are compared with the motion predicted by the normal-mode model. They are only in agreement for the N = L = 3 state without vibrational angular momentum zpe. For the remaining states, the Cartesian O-atom motions are considerably different from the elliptical motion predicted by the normal-mode model. This arises from bend-stretch coupling, including centrifugal distortion, in the Cartesian trajectories, which results in tubular instead of elliptical motion. Including zpe in the C-O stretch modes introduces considerable complexity into the O-atom motions for the vibrational angular momentum states. The short-time O-atom motions for these trajectories are highly irregular and do not appear to have any identifiable characteristics. However, the O-atom motions for trajectories integrated for substantially longer period of times acquire unique properties. With C-O stretch zpe included, the long-time O-atom motion becomes tubular for trajectories integrated to approximately 14 ps for the L = 3 states and to approximately 44 ps for the L = 1 states. PMID:17824675

Lourderaj, Upakarasamy; Martínez-Núñez, Emilio; Hase, William L

2007-10-18

347

Super-resolution processing for HF surface wave radar based on pre-whitened MUSIC  

Microsoft Academic Search

Owing to the decametric wavelength, the angular resolution of high-frequency surface wave radar (HFSWR) is usually coarse, especially when dimensions of antenna arrays are restricted such as in shipborne HFSWR applications. In this paper, the relative strength of atmospheric noise and sea clutter that will heavily degrade the capabilities of HFSWR in target detection and resolution are calculated, then a

Junhao Xie; Yeshu Yuan; Yongtan Liu

1998-01-01

348

Improving Resolution and Depth-of-Field of Light Field Cameras Using a Hybrid Imaging System  

E-print Network

Improving Resolution and Depth-of-Field of Light Field Cameras Using a Hybrid Imaging System Vivek, Kaushik.Mitra, vashok] @rice.edu Abstract Current light field (LF) cameras provide low spatial res megapixels no angular information. Figure 1: Fundamental resolution trade-off in light-field imaging: Given

Mellor-Crummey, John

349

Evaluation of a CCD-based high resolution autocollimator for use as a slope sensor  

E-print Network

Evaluation of a CCD-based high resolution autocollimator for use as a slope sensor Rohan Isaac the focused beam profile to broaden and decrease its peak intensity Project: Evaluation of a compact CCD lenses in front of CCD increase angular resolution while decreasing installation space. By changing

Baltisberger, Jay H.

350

Approximate Parameterized Matching Carmit Hazay  

E-print Network

was a postdoctoral student at Bar-Ilan University; partially supported by the Israel Science Foun- dation Grant 282 applications in image processing and computational biology. For example, approximate parameterized matching,moshe}@cs.biu.ac.il The second author was partially supported by an IBM faculty award grant. § Brooklyn College of the City

Lewenstein, Moshe

351

Conic approximation of planar curves  

Microsoft Academic Search

An upper bound of the Hausdorff distance between planar curve and conic section can be expressed by the maximum norm of error function from the conic section to the planar curve (Comput. Aided Geomet. Design, 14 (1997) 135–151). With respect to the maximum norm we characterize the necessary and sufficient condition for the conic section to be optimal approximation of

Young Joon Ahn

2001-01-01

352

The WKB Approximation without Divergences  

E-print Network

In this paper, the WKB approximation to the scattering problem is developed without the divergences which usually appear at the classical turning points. A detailed procedure of complexification is shown to generate results identical to the usual WKB prescription but without the cumbersome connection formulas.

D. Cocolicchio; M. Viggiano

1997-10-01

353

Approximation Algorithms for Combinatorial Problems  

Microsoft Academic Search

Simple, polynomial-time, heuristic algorithms for finding approximate solutions to various polynomial complete optimization problems are analyzed with respect to their worst case behavior, measured by the ratio of the worst solution value that can be chosen by the algorithm to the optimal value. For certain problems, such as a simple form of the knapsack problem and an optimization problem based

David S. Johnson

1973-01-01

354

Approximation Algorithms for Combinatorial Problems  

Microsoft Academic Search

Simple, polynomial-time, heuristic algorithms for finding approximate solutions to various polynomial complete optimization problems are analyzed with respect to their worst case behavior, measured by the ratio of the worst solution value that can be chosen by the algorithm to the optimal value. For certain problems, such as a simple form of the knapsack problem and an optimization problem based

David S. Johnson

1974-01-01

355

Pythagorean Approximations and Continued Fractions  

ERIC Educational Resources Information Center

In this article, we will show that the Pythagorean approximations of [the square root of] 2 coincide with those achieved in the 16th century by means of continued fractions. Assuming this fact and the known relation that connects the Fibonacci sequence with the golden section, we shall establish a procedure to obtain sequences of rational numbers…

Peralta, Javier

2008-01-01

356

Some issues of linguistic approximation  

Microsoft Academic Search

Summary form only given. Two of the most exemplary capabilities of the human mind are the capability of using perceptions in purposeful ways and the capability of approximating perceptions by statements in natural language. Understanding these capabilities and emulating them by machines is the crux of intelligent systems. To construct intelligent systems, we need to develop appropriate methodological tools for

George J. Klir

2004-01-01

357

Quantized mean-field approximation  

Microsoft Academic Search

An extension of the quantum–classical mean-field (MF) approximation is developed by application of quantized Hamilton dynamics (QHD) to the classical subsystem. The resulting quantized MF (QMF) approach supplements the classical position and momentum variables with higher order moments. In the limit of all moments exact quantum dynamics is achieved. Already with second order variables, QMF properly treats zero point energy

Craig Brooksby; Oleg V. Prezhdo

2001-01-01

358

Approximate dynamic programming for management  

E-print Network

Approximate dynamic programming for management of high-value spare parts Hugo Simao and Warren Jersey, USA Abstract Purpose ­ An aircraft manufacturer faces the problem of allocating inventory interest in managing high value, low volume spare parts which must be available to respond to low

Powell, Warren B.

359

Normal Approximation to Poisson Distribution  

NSDL National Science Digital Library

This applet, created by Ivo Dinov of the University of California, Los Angeles, demonstrates the normal approximation to the Poisson distribution. Users can set the rate, lambda, and the number of trials, n, and observe how the shape of the distribution changes. The Poisson distribution is shown in blue, and the Normal distribution is shown in red.

Dinov, Ivo

2009-01-14

360

APPROXIMATION CLASSES FOR ADAPTIVE METHODS  

Microsoft Academic Search

Adaptive Finite Element Methods (AFEM) are numerical proce- dures that approximate the solution to a partial differential equation (PDE) by piecewise polynomials on adaptively generated triangulations. Only re- cently has any analysis of the convergence of these methods (10, 13) or their rates of convergence (2) become available. In the latter paper it is shown that a certain AFEM for

Peter Binev; Wolfgang Dahmen; Ronald DeVore; Pencho Petrushev

2002-01-01

361

Angular Dependance of Auger Decay of Double Core Vacancies in N2  

NASA Astrophysics Data System (ADS)

We present a first experimental step toward angle-resolved multiple-core vacancy Auger electron spectroscopy. We observe Auger decay for both single-site and double-site K-2 vacancy pairs in N2 and find that the single-site double vacancy undergoes an Auger process whose angular pattern qualitatively resembles previous measurements of 1?g-1 Auger decay. In addition, we measure the angle dependence of the Auger decay of single core vacancies to quasi-bound molecular dication states. Ultimately, the combination of impulsive molecular alignment and x-ray free-electron lasers enables angle resolution for few femtosecond chemical dynamics.

Cryan, James; Glownia, James; Bucksbaum, Philip; Coffee, Ryan

2010-03-01

362

The explicit representation for the angular flux solution in the simplified P{sub N} (SP{sub N}) theory  

SciTech Connect

The current SP{sub n} theory formulation, via either the asymptotic method or the variational method, does not provide an explicit and calculable representation for the corresponding angular flux solution. It is therefore not possible to reconstruct from the SP{sub n} solution the corresponding angular flux solution, or to extract from a reference transport solution the corresponding SP{sub n} solution. This makes it impossible to calculate the necessary surface discontinuity factors to force consistency between the SP{sub n} solution and the higher level transport solution. Without discontinuity factors, the superiority of SP{sub n} over diffusion could be significantly degraded in practical applications. In this paper we present a different SP{sub n} formulation that provides the explicit angular flux solution such that the physical picture for the SP{sub n} approximation is transparent and the SP{sub n} discontinuity factors can be calculated. (authors)

Chao, Y. A. [Apartment 101, Building 2, 788 Hong Xu Road, Shanghai 201103 (China); Yamamoto, A. [Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan)

2012-07-01

363

Comptonization of low-frequency radiation in accretion disks Angular distribution and polarization of hard X-ray radiation  

SciTech Connect

Analytical consideration is given to the comptonization of photons and its effects on the radiation emitted from accretion disks of compact X-ray sources, such as black holes and neutron stars. Attention is given to the photon distribution during escape from the disk, the angular distribution of hard radiation from the disk, the polarization of hard radiation and the electron temperature distribution over the optical depth. It is shown that the hard radiation spectrum is independent of the low-frequency photon source distribution. The angular distribution and polarization of the outgoing X-rays are a function of the optical depth. A Thomson approximation is used to estimate the angular distribution of the hard radiation and the polarization over the disk. The polarization results are compared with OSO-8 satellite data for Cyg X-1 and show good agreement at several energy levels. 17 references.

Suniaev, R.A.; Titarchuk, L.G.

1984-01-01

364

Holographic imaging of crowded fields: high angular resolution imaging with excellent quality at very low cost  

NASA Astrophysics Data System (ADS)

We present a method for speckle holography that is optimized for crowded fields. Its two key features are an iterative improvement of the instantaneous point spread functions (PSFs) extracted from each speckle frame and the (optional) simultaneous use of multiple reference stars. In this way, high signal-to-noise ratio and accuracy can be achieved on the PSF for each short exposure, which results in sensitive, high-Strehl reconstructed images. We have tested our method with different instruments, on a range of targets, and from the N[10 ?m] to the I[0.9 ?m] band. In terms of PSF cosmetics, stability and Strehl ratio, holographic imaging can be equal, and even superior, to the capabilities of currently available adaptive optics (AO) systems, particularly at short near-infrared to optical wavelengths. It outperforms lucky imaging because it makes use of the entire PSF and reduces the need for frame selection, thus, leading to higher Strehl and improved sensitivity. Image reconstruction a posteriori, the possibility to use multiple reference stars and the fact that these reference stars can be rather faint means that holographic imaging offers a simple way to image large, dense stellar fields near the diffraction limit of large telescopes, similar to, but much less technologically demanding than, the capabilities of a multiconjugate AO system. The method can be used with a large range of already existing imaging instruments and can also be combined with AO imaging when the corrected PSF is unstable.

Schödel, R.; Yelda, S.; Ghez, A.; Girard, J. H.; Labadie, L.; Rebolo, R.; Pérez-Garrido, A.; Morris, M. R.

2013-02-01

365

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

NASA Astrophysics Data System (ADS)

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

Zhang, William

2013-04-01

366

Status of the development of the miniaturized digital high angular resolution laser irradiation detectors (HARLIDtm) technology  

Microsoft Academic Search

Miniaturized digital HARLID modules integrating linear silicon and indium gallium arsenide arrays have been developed by the Defence Research Establishment Valcartier in collaboration with EG&G Optoelectronics Canada. These modules are designed to locate a laser source within +\\/- 1 degree(s) over a 90 degree(s) field of view either in azimuth or elevation. The principle of operation of these modules is

Andre Cantin; G. Pelletier; Paul P. Webb; M. Cordray; Daniel Pomerleau; Jack H. Parker; Mark L. Delong; S. A. Milligan

1998-01-01

367

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

368

Star Formation at High Angular Resolution ASP Conference Series, Vol. S-221, 2003  

E-print Network

. Jayawardhana & T.L. Bourke The Structure of Cold Molecular Cloud Cores D. Ward-Thompson & D. J. Nutter Dept of Physics, Cardiff University, PO Box 913, Cardiff, UK J. M. Kirk Dept of Astronomy, University of Illinois Andr´e, Ward-Thompson & Barsony 2000). Many studies of cold cores have been carried out to attempt

Ward-Thompson, Derek

369

Ultra High Angular Resolution and sub-mas Astrometry with HST's FGS1r  

Microsoft Academic Search

The 3 Fine Guidance Sensors (FGS) - white-light shearing interferometers - are critical to the mission of the Hubble Space Telescope (HST) by providing highly accurate guiding for the observatory. Moreover, FGS1r in particular is a capable science instrument. Its two observing modes - Position Mode and Transfer Mode - support wide angle and narrow angle astrometry respectively. In Position

M. Lallo; R. B. Makidon; D. Jong; E. Nelan

2001-01-01

370

Tracking the Cortico-Spinal Tract from Low Spatial and Angular Resolution Diusion MRI  

E-print Network

the spinal cord to the motor cortex. The proposed method combines a new geometry-based multi the spinal cord to the cerebral motor cortex, is one of the most impor- tant fascicles because it carries that are connected to the spinal cord via straight line sub-fascicles but also of more lateral regions

Boyer, Edmond

371

Scene Reconstruction from High Spatio-Angular Resolution Light Fields Changil Kim1,2  

E-print Network

1,2 Yael Pritch1 Alexander Sorkine-Hornung1 Markus Gross1,2 1 Disney Research Zurich 2 ETH Zurich, and archiving the real world, in the movie and game industry as well as in architecture, archaeology, arts, and many other areas. For example, in movie production considerable efforts are invested to create accurate

Zimmer, Henning

372

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

PubMed Central

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

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

2012-01-01

373

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

E-print Network

of diffusion MRI, which images the 3D profile of diffusion at each im- aged location in the brain. At each ­ yielding an entire spherical function at each point in a 3D image ­ the statistical study of diffusion the whole brain, and their varia- tional derivative may be computed with respect to tunable parameters of 3D

Wang, Yalin

374

F. Combes and D. Barret (eds) HIGH ANGULAR RESOLUTION IN 20102020: POSSIBLE  

E-print Network

and Strehl ratio; photometric range for high dynamics imaging (HDI), coronagraphy; spectral bandpass (V to N di#culties to over­ come for ELTs. Although several works show its feasibility, MCAO with high Strehl

Lardière, Olivier

375

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

376

Towards a Full-sky, High-resolution Dust Extinction Map with WISE and Planck  

NASA Astrophysics Data System (ADS)

We have recently completed a custom processing of the entire WISE 12 micron All-sky imaging data set. The result is a full-sky map of diffuse, mid-infrared Galactic dust emission with angular resolution of 15 arcseconds, and with contaminating artifacts such as compact sources removed. At the same time, the 2013 Planck HFI maps represent a complementary data set in the far-infrared, with zero-point relatively immune to zodiacal contamination and angular resolution superior to previous full-sky data sets at similar frequencies. Taken together, these WISE and Planck data products present an opportunity to improve upon the SFD (1998) dust extinction map, by virtue of enhanced angular resolution and potentially better-controlled systematics on large scales. We describe our continuing efforts to construct and test high-resolution dust extinction and temperature maps based on our custom WISE processing and Planck HFI data.

Meisner, Aaron M.; Finkbeiner, D. P.

2014-01-01

377

THe Very High Resolution Whipple Gamma Ray Camera  

NASA Astrophysics Data System (ADS)

The Whipple Gamma Ray Collaboration has been involved in the development of atmospheric Cherenkov imaging cameras since 1982. In the latest planned upgrade the Whipple Observatory 109 pixel camera on the 10m optical reflector which has a 3 degree full field of view will be replaced by a 541 pixel camera with 6 degree full field. The higher resolution will increase the angular resolution and reduce the energy threshold. The larger field of view will permit the observation of extended sources, improve the angular resolution and permit a sky survey to be made. It can also be used to search for delayed emission from gamma-ray bursts. The 109 pixel camera on the 11m optical reflector will be expanded to 169 pixels to maximise the overlap for stereo operation. Both telescopes will include an intelligent trigger to preferentially select gamma-ray events and reduce the background. Supported in part by the U.S. Dept. of Energy

Gaidos, J.

1994-12-01

378

High resolution imaging at Palomar  

NASA Technical Reports Server (NTRS)

For the last two years we have embarked on a program of understanding the ultimate limits of ground-based optical imaging. We have designed and fabricated a camera specifically for high resolution imaging. This camera has now been pressed into service at the prime focus of the Hale 5 m telescope. We have concentrated on two techniques: the Non-Redundant Masking (NRM) and Weigelt's Fully Filled Aperture (FFA) method. The former is the optical analog of radio interferometry and the latter is a higher order extension of the Labeyrie autocorrelation method. As in radio Very Long Baseline Interferometry (VLBI), both these techniques essentially measure the closure phase and, hence, true image construction is possible. We have successfully imaged binary stars and asteroids with angular resolution approaching the diffraction limit of the telescope and image quality approaching that of a typical radio VLBI map. In addition, we have carried out analytical and simulation studies to determine the ultimate limits of ground-based optical imaging, the limits of space-based interferometric imaging, and investigated the details of imaging tradeoffs of beam combination in optical interferometers.

Kulkarni, Shrinivas R.

1992-01-01

379

Nuclear Shells: Angular and Magnetic Momenta of Nuclei  

Microsoft Academic Search

Part I. Angular momenta. The experimental data on the number of isotopes per atom show marked regularities, which suggest closed shells in the nucleus. These regularities have been rigorously followed in arranging the first thirty elements into an isotopic system, with proton and neutron shells. In order to correlate both the angular and magnetic momenta of nuclei, it is necessary

P. Gerald Kruger

1935-01-01

380

Parallel solution of block angular LP problems using Kaul's algorithm  

E-print Network

Parallel solution of block angular LP problems using Kaul's algorithm Ilkay Boduro~glu1 , Julian, University of Edinburgh November 7th 2007 Parallel solution of block angular LP problems using Kaul parallel simplex · Kaul's algorithm · Dense parallel scheme for Kaul's algorithm · Results · Sparse

Hall, Julian

381

Hot Jupiters and the evolution of stellar angular momentum  

Microsoft Academic Search

Context. Giant planets orbiting main-sequence stars closer than 0.1 AU are called hot Jupiters. They interact with their stars affecting their angular momentum. Aims: Recent observations provide evidence of excess angular momentum in stars with hot Jupiters in comparison to stars with distant and less massive planets. This has been attributed to tidal interaction, but needs to be investigated in

A. F. Lanza

2010-01-01

382

Student understanding of the angular momentum of classical particles  

NSDL National Science Digital Library

Students in introductory calculus-based physics were asked about the angular momentum of a particle traveling in a straight line. The tendency to state that the angular momentum is identically zero was widespread, and few students applied l = r à p correctly. The common errors reflect a tendency to conflate angular momentum with angular velocity or with linear momentum. Many students assume that linear and angular momentum are jointly conserved, an error that appears to be linked to their thinking about energy. A tutorial was developed to help students recognize that linear momentum and angular momentum are separately conserved. The results suggest that helping students understand why angular momentum is attributed to a particle moving in a straight line may be more effective in helping them to apply the concept than instructing them only on its correct use. In addition to providing insights into student learning of the concept of angular momentum, we illustrate how studentsâ own ideas can be the basis for more effective instruction.

Close, Hunter G.; Heron, Paula R.

2013-08-05

383

Boston University Physics Applets: Orbits and Angular Momentum  

NSDL National Science Digital Library

This web page is an interactive physics simulation relating to conservation of angular momentum in an orbiting object. The user can choose between an elliptical or circular orbit to observe why angular momentum is conserved in either case. This item is part of a larger collection of simulation-based activities developed for students of introductory physics.

Duffy, Andrew

2008-08-22

384

Stellar Angular Diameter Calibration Cycle 3 Instrument Scientist Calibration  

Microsoft Academic Search

The pirmary goal of this proposal is to demonstrate and calibrate the capability of the FGSs to perform absolute angular diameter measurements of stars larger than 15 mas. Three stars of different, known, angular sizes will be observed in the center of the astrometer FGS.

Laurence Taff

1993-01-01

385

Angular neutron transport investigation in the HZETRN free-space ion and nucleon transport and shielding computer program  

NASA Technical Reports Server (NTRS)

Extension of the high charge and energy (HZE) transport computer program HZETRN for angular transport of neutrons is considered. For this paper, only light ion transport, He4 and lighter, will be analyzed using a pure solar proton source. The angular transport calculator is the ANISN/PC program which is being controlled by the HZETRN program. The neutron flux values are compared for straight-ahead transport and angular transport in one dimension. The shield material is aluminum and the target material is water. The thickness of these materials is varied; however, only the largest model calculated is reported which is 50 gm/sq cm of aluminum and 100 gm/sq cm of water. The flux from the ANISN/PC calculation is about two orders of magnitude lower than the flux from HZETRN for very low energy neutrons. It is only a magnitude lower for the neutrons in the 10 to 20 MeV range in the aluminum and two orders lower in the water. The major reason for this difference is in the transport modes: straight-ahead versus angular. The angular treatment allows a longer path length than the straight-ahead approximation. Another reason is the different cross section sets used by the ANISN/PC-BUGLE-80 mode and the HZETRN mode. The next step is to investigate further the differences between the two codes and isolate the differences to just the angular versus straight-ahead transport mode. Then, create a better coupling between the angular neutron transport and the charged particle transport.

Singleterry, R. C., Jr.; Wilson, J. W.

1997-01-01

386

Perturbed angular correlation investigation of zirconia ceramics  

SciTech Connect

A four-detector time differential perturbed angular correlation (PAC) spectrometer was built and has been used to characterize phases and study local properties and defect dynamics of pure zirconia, yttria-stabilized cubic zirconia, and yttria partially stabilized zirconia (Y-PSZ). The PAC spectra of pure zirconia were characterized by discrete frequencies. The electric field gradient (EFG) magnitude, the asymmetry parameter, and the EFG distribution were determined from the spectra by a least-square fitting procedure. The EFG in the monoclinic and tetragonal phase is weakly temperature-dependent and in larger in the tetragonal phase. The EFG was calculated using a point-ion charge model. The results agree qualitatively with the experimental data, but the calculated EFG magnitudes were typically 40-50% smaller than the experimental field gradients. PAC spectra in cubic stabilized zirconia are characterized by a wide frequency distribution. While spectra at highest and lowest temperatures are static, the spectra in the intermediate temperature range show relaxation phenomena arising from oxygen vacancy diffusion. PAC spectra in Y-PSZ show two components, one tetragonal-like, the other cubic-like. From a least-squares fitting procedure the phase boundary between the cubic and tetragonal-cubic mixed region was determined.

Jaeger, H.

1987-01-01

387

CLASS: the cosmology large angular scale surveyor  

NASA Astrophysics Data System (ADS)

The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to measure the signature of a gravitationalwave background from inflation in the polarization of the cosmic microwave background (CMB). CLASS is a multi-frequency array of four telescopes operating from a high-altitude site in the Atacama Desert in Chile. CLASS will survey 70% of the sky in four frequency bands centered at 38, 93, 148, and 217 GHz, which are chosen to straddle the Galactic-foreground minimum while avoiding strong atmospheric emission lines. This broad frequency coverage ensures that CLASS can distinguish Galactic emission from the CMB. The sky fraction of the CLASS survey will allow the full shape of the primordial B-mode power spectrum to be characterized, including the signal from reionization at low ?. Its unique combination of large sky coverage, control of systematic errors, and high sensitivity will allow CLASS to measure or place upper limits on the tensor-to-scalar ratio at a level of r = 0:01 and make a cosmic-variance-limited measurement of the optical depth to the surface of last scattering, ? .

Essinger-Hileman, Thomas; Ali, Aamir; Amiri, Mandana; Appel, John W.; Araujo, Derek; Bennett, Charles L.; Boone, Fletcher; Chan, Manwei; Cho, Hsiao-Mei; Chuss, David T.; Colazo, Felipe; Crowe, Erik; Denis, Kevin; Dünner, Rolando; Eimer, Joseph; Gothe, Dominik; Halpern, Mark; Harrington, Kathleen; Hilton, Gene C.; Hinshaw, Gary F.; Huang, Caroline; Irwin, Kent; Jones, Glenn; Karakla, John; Kogut, Alan J.; Larson, David; Limon, Michele; Lowry, Lindsay; Marriage, Tobias; Mehrle, Nicholas; Miller, Amber D.; Miller, Nathan; Moseley, Samuel H.; Novak, Giles; Reintsema, Carl; Rostem, Karwan; Stevenson, Thomas; Towner, Deborah; U-Yen, Kongpop; Wagner, Emily; Watts, Duncan; Wollack, Edward J.; Xu, Zhilei; Zeng, Lingzhen

2014-07-01

388

Inhomogeneity Through Warm Equal Channel Angular Pressing  

NASA Astrophysics Data System (ADS)

In this study, the hardness inhomogeneity of billets during multi-passes of equal channel angular pressing (ECAP) at elevated temperatures is investigated and the effect of large strain deformation during ECAP on the hardness inhomogeneity characteristics due to dynamic aging of aluminum 6061 under a variety of temperatures and ram speed was studied by TEM and hardness measurements. The hardness results showed that the hardness distribution is more homogenous after four passes using the pressing route Bc. However, when the deformation temperature was considered, performing ECAP at 100 °C may provide the most homogeneous microstructure after multi-pressing as long as the total number of pressing passes is four. This indicates that a lower temperature (in the range of warm working) is favorable for achieving an ultrafine-grained/nanomaterial with a more homogenous microstructure. In order to quantify the inhomogeneity in the cross section of the as-pressed sample, an inhomogeneity index has been defined. The results show an increase in the hardness in the first pass with significant inhomogeneous deformation and a transition toward a more homogeneous structure with subsequent passes.

Vaseghi, Majid; Kim, Hyoung Seop; Karimi Taheri, Ali; Momeni, Amir

2013-06-01

389

CLASS: The Cosmology Large Angular Scale Surveyor  

E-print Network

The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to measure the signature of a gravita-tional-wave background from inflation in the polarization of the cosmic microwave background (CMB). CLASS is a multi-frequency array of four telescopes operating from a high-altitude site in the Atacama Desert in Chile. CLASS will survey 70\\% of the sky in four frequency bands centered at 38, 93, 148, and 217 GHz, which are chosen to straddle the Galactic-foreground minimum while avoiding strong atmospheric emission lines. This broad frequency coverage ensures that CLASS can distinguish Galactic emission from the CMB. The sky fraction of the CLASS survey will allow the full shape of the primordial B-mode power spectrum to be characterized, including the signal from reionization at low $\\ell$. Its unique combination of large sky coverage, control of systematic errors, and high sensitivity will allow CLASS to measure or place upper limits on the tensor-to-scalar ratio at a level of $r=0.01$ and make a cosmi...

Essinger-Hileman, Thomas; Amiri, Mandana; Appel, John W; Araujo, Derek; Bennett, Charles L; Boone, Fletcher; Chan, Manwei; Cho, Hsiao-Mei; Chuss, David T; Colazo, Felipe; Crowe, Erik; Denis, Kevin; Dünner, Rolando; Eimer, Joseph; Gothe, Dominik; Halpern, Mark; Harrington, Kathleen; Hilton, Gene; Hinshaw, Gary F; Huang, Caroline; Irwin, Kent; Jones, Glenn; Karakla, John; Kogut, Alan J; Larson, David; Limon, Michele; Lowry, Lindsay; Marriage, Tobias; Mehrle, Nicholas; Miller, Amber D; Miller, Nathan; Moseley, Samuel H; Novak, Giles; Reintsema, Carl; Rostem, Karwan; Stevenson, Thomas; Towner, Deborah; U-Yen, Kongpop; Wagner, Emily; Watts, Duncan; Wollack, Edward; Xu, Zhilei; Zeng, Lingzhen

2014-01-01

390

Effect of acquisition parameters on digital breast tomosynthesis: Total angular range and number of projection views  

NASA Astrophysics Data System (ADS)

The purpose of this study was to investigate the effect of different acquisition parameters and to determine the optimal set of acquisition parameters of projection views (PVs) for the new developed digital breast tomosynthesis (DBT) system. The DBT imaging parameters were optimized using 32 different acquisition sets with six angular ranges (±5°, ±10°, ±13°, ±17°, ±21°, and ±25°) and eight projection views (5, 11, 15, 21, 25, 31, 41, and 51 prjections). In addition to the contrastto-noise ratio (CNR), the artifact spread function (ASF) was used to quantify the in-focus plane artifacts along the z-direction in order to explore the relationship between the acquisition parameters and the image quality. A commercially, available breast-mimicking phantom was imaged to qualitatively verify our results. Our results show that a wide angular range improved the reconstructed image quality in the z-direction. If a large number of projections are acquired, then the electronic noise may dominate the CNR due to reduce the radiation dose per projection. Although increasing angular range was found to improve the vertical resolution, due to greater effective breast thickness, the image quality of microcalcifications in the in-focus plane was also found not to be improved by increasing the noise. Therefore, potential trade-offs of these physical imaging properties must be considered to optimize the acquisition configuration of a DBT system. Our results suggest possible directions for further improvements in DBT systems for high quality imaging.

Choi, Young-Wook; Park, Hye-Suk; Kim, Ye-seul; Kim, Hee-Joung; Choi, Jae-Gu

2012-12-01

391

Linear approximations of nonlinear systems  

NASA Technical Reports Server (NTRS)

A method for designing an automatic flight controller for short and vertical takeoff aircraft is presently being developed at NASA Ames Research Center. This technique involves transformations of nonlinear systems to controllable linear systems and takes into account the nonlinearities of the aircraft. In general, the transformations cannot always be given in closed form. Using partial differential equations, an approximate linear system, called the modified tangent model, was recently introduced. A linear transformation of this tangent model to Brunovsky canonical form can be constructed, and from this an approximation of an exact transformation for the nonlinear system can be found. It is shown that a canonical expansion in Lie brackets about the point x(0) yields the same modified tangent model.

Hunt, L. R.; Su, R.

1983-01-01

392

One sign ion mobile approximation  

NASA Astrophysics Data System (ADS)

The electrical response of an electrolytic cell to an external excitation is discussed in the simple case where only one group of positive and negative ions is present. The particular case where the diffusion coefficients of the negative ions, Dm, is very small with respect to that of the positive ions, Dp, is considered. In this framework, it is discussed under what conditions the one mobile approximation, in which the negative ions are assumed fixed, works well. The analysis is performed by assuming that the external excitation is sinusoidal with circular frequency ?, as that used in the impedance spectroscopy technique. In this framework, we show that there exists a circular frequency, ?*, such that for ? > ?*, the one mobile ion approximation works well. We also show that for Dm << Dp, ?* is independent of Dm.

Barbero, G.

2011-12-01

393

Suitability of the parametric model RPV to assess canopy structure and heterogeneity from multi-angular CHRIS-PROBA data  

Microsoft Academic Search

The spaceborne ESA-mission CHRIS-PROBA (Compact High Resolution Imaging Spectrometer- Project for On-board Autonomy) provides hyperspectral and multi-angular data of selected terrestrial targets (Barnsley et al. 2004). For vegetated surfaces, the spectral information content of CHRIS data may yield the biochemical and biophysical properties of a vegetation canopy, while the directional component may deliver additional information on its canopy structure. Here,

B. Koetz; J.-L. Widlowski; F. Morsdorf; J. Verrelst; M. E. Schaepman

2007-01-01

394

High-dimensional quantum nature of ghost angular Young's diffraction  

SciTech Connect

We propose a technique to characterize the dimensionality of entangled sources affected by any environment, including phase and amplitude masks or atmospheric turbulence. We illustrate this technique on the example of angular ghost diffraction using the orbital angular momentum (OAM) spectrum generated by a nonlocal double slit. We realize a nonlocal angular double slit by placing single angular slits in the paths of the signal and idler modes of the entangled light field generated by parametric down-conversion. Based on the observed OAM spectrum and the measured Shannon dimensionality spectrum of the possible quantum channels that contribute to Young's ghost diffraction, we calculate the associated dimensionality D{sub total}. The measured D{sub total} ranges between 1 and 2.74 depending on the opening angle of the angular slits. The ability to quantify the nature of high-dimensional entanglement is vital when considering quantum information protocols.

Chen Lixiang [State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275 (China); Department of Physics and Astronomy, SUPA, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Leach, Jonathan; Jack, Barry; Padgett, Miles J.; Franke-Arnold, Sonja [Department of Physics and Astronomy, SUPA, University of Glasgow, Glasgow G12 8QQ (United Kingdom); She Weilong [State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275 (China)

2010-09-15

395

Photon beam polarization and non-dipolar angular distributions  

SciTech Connect

Angular distributions of ejecta from unoriented atoms and molecules depend upon the polarization state of the incident x-rays as well as upon the dynamics of the physical systems being studied. I recommend a simple geometrical way of looking at the polarization and its effects upon angular distributions. The polarization is represented as a vector in a parameter space that faithfully represents the polarization of the beam. The simple dependence of the angular dependence of the angular distributions on the polarization vector enables easy extraction of the dynamical information contained in those angular distributions. No new physical results emerge from this geometrical approach, but known consequences of the symmetries appear in an easily visualized form that I find pleasing and that has proved to be useful for planning experiments and for analyzing data.

Peshkin, M

1996-08-01

396

Transferring orbital and spin angular momenta of light to atoms  

E-print Network

Light beams carrying orbital angular momentum, such as Laguerre-Gaussian beams, give rise to the violation of the standard dipolar selection rules during the interaction with matter yielding, in general, an exchange of angular momentum larger than hbar per absorbed photon. By means of ab initio 3D numerical simulations, we investigate in detail the interaction of a hydrogen atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the dependence of the angular momentum exchange with the polarization, the orbital angular momentum, and the carrier-envelope phase of light, as well as with the relative position between the atom and the light vortex. In addition, a quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum mechanics is used to gain physical insight into the absorption of angular momentum by the hydrogen atom.

Picón, Antonio; Mompart, Jordi; de Aldana, Javier R Vázquez; Plaja, Luis; Calvo, Gabriel F; Roso, Luis

2010-01-01

397

Simulating bioterrorism through epidemiology approximation  

Microsoft Academic Search

Bioterrorism represents a significant threat to society. The lack of successful attacks that have resulted in true epidemics have created a need for data that can be generated from existing known factors. We have taken the popular susceptible-infected-recovery model and created a hybridized model that balances the simplicity of the original with an approximation of what more complex agent-based models

Ryan Layfield; Murat Kantarcioglu; Bhavani M. Thuraisingham

2008-01-01

398

Finite approximations in fluid mechanics  

Microsoft Academic Search

This book contains twenty papers on work which was conducted between 1983 and 1985 in the Priority Research Program ''Finite Approximations in Fluid Mechanics'' of the German Research Society (Deutsche Forschungsgemeinschaft). Scientists from numerical mathematics, fluid mechanics, and aerodynamics present their research on boundary-element methods, factorization methods, higher-order panel methods, multigrid methods for elliptical and parabolic problems, two-step schemes for

Hirschel

1986-01-01

399

Simultaneous approximation by greedy algorithms  

Microsoft Academic Search

We study nonlinear m-term approximation with regard to a redundant dictionary D in a Hilbert space H. It is known that the Pure Greedy Algorithm (or, more generally, the Weak Greedy Algorithm) provides for each f 2 H and any dictionary D an expansion into a series f = 1 X j=1 cj(f)'j(f); 'j(f) 2 D; j = 1;2;::: with

Dany Leviatan; Vladimir N. Temlyakov

2006-01-01

400

Approximate calculations for heat exchangers  

Microsoft Academic Search

Estimates were developed for the total heat transfer coefficient for various types of heat exchangers. These estimates were not meant to replace more accurate calculations for individual heat exchangers, but to provide quick approximations for situations in which great accuracy was not required. The heat transfer coefficients k (in kcal\\/m²\\/hr\\/°C) were calculated based on assumed average values for input and

Matz

2008-01-01

401

Best Approximation with Walsh Atoms  

Microsoft Academic Search

.    We consider the approximation in L\\u000a \\u000a 2\\u000a \\u000a R of a given function using finite linear combinations of Walsh atoms, which are Walsh functions localized to dyadic intervals,\\u000a also called Haar—Walsh wavelet packets. It is shown that up to a constant factor, a linear combination of K atoms can be represented to relative error ? by a linear combination

L. F. Villemoes

1997-01-01

402

Weyl-Wigner formalism for rotation-angle and angular-momentum variables in quantum mechanics  

NASA Astrophysics Data System (ADS)

A comprehensive study is presented on the Weyl-Wigner formalism for rotation-angle and angular-momentum variables: the elements of kinematics are extended, the elements of dynamics are established, and the implications of rotational perodicity and angular-momentum quantization are investigated. Particular attention is paid to discreteness, and two of its consequences are emphasized: the importance of evenness and oddness, and the need to use two difference operators in a discrete domain, whereas one differential operator suffices in a continuous domain. These consequences are shown to strongly distinguish the Weyl-Wigner formalism for rotation-angle and angular-momentum variables from the well-known Weyl-Wigner formalism for Cartesian-position and linear-momentum variables. The point is made clear that the first of these formalisms cannot be regarded as a trivial and straightforward extension of the second. The rotational Wigner function is derived as the only bilinear form of the state vector that is real, has the natural invariances for rotational motion, and yields the correct distributions for the rotation-angle and angular-momentum variables as well as the appropriate expression for the transition probability between states. The conditions for its uniqueness are thus established. Its properties are described in detail and, in particular, its uniform boundedness is demonstrated. The rotational Wigner function and the associated correspondence between quantum operators and classical-like functions, as well as the relations they obey, are explored and are written so as to clearly exhibit the distinct contributions of evenness and oddness in the discrete domain of the angular-momentum eigenvalues, thus providing a most natural way to account for periodicity. Using the derivative, which acts on the continuous rotation-angle variable, and the forward and backward differences, which act on the discrete angular-momentum variable, the equation of motion for the rotational Wigner function is established. This equation is detailed for the following Hamiltonian forms: those that depend only on the angular-momentum variable, including, in particular, the free rotator, and those that are in the cosine of the rotation-angle variable. It is verified that the Weyl-Wigner formalism for rotation-angle and angular-momentum variables has the correct nonperiodic limit and that it properly reduces to the Weyl-Wigner formalism for Cartesian-position and linear-momentum variables. In order to illustrate the formalism, a careful analysis is carried out for the rotational Wigner function representing the energy eigenstates of a hindered rotator whose Hamiltonian is the sum of a term in the absolute value of the angular-momentum variable with a term in the cosine of the rotation-angle variable. For this hindered rotator, and within the approximation of a large absolute value of the angular-momentum variable, the equation of motion for the rotational Wigner function is solved for its stationary solutions, and the time-independent Schrödinger equation is also solved.

Bizarro, João P.

1994-05-01

403

Spatial and Angular Moment Analysis of Continuous and Discretized Particle Transport Problems  

NASA Astrophysics Data System (ADS)

A spatial and angular moment analysis of the linear Boltzmann transport equation is used to compute exact flux-weighted average spatial quantities such as the 'center of mass' and 'radius of gyration' of the flux distribution. This moment analysis is valid for multidimensional general-geometry analytic transport problems, posed in an infinite homogeneous medium, with multiple energy groups and anisotropic scattering. The results from the analysis are used in this thesis to assess how accurately approximations to the transport equation compute these flux-weighted average spatial quantities. The first part of this thesis addresses the theoretical analysis of spatial differencing schemes used to discretize the discrete ordinates approximation of the linear Boltzmann transport equation. Discrete ordinates methods have been utilized for many years to obtain numerical solutions of neutron transport problems in which the optical width of the spatial cells is small. The traditional truncation analysis can be used to assess the accuracy of spatial differencing schemes for these problems. The same discrete ordinates methods have in recent years been utilized for radiative transfer problems characterized by optically thick spatial cells and scattering ratios near unity. In this case, an asymptotic diffusion limit analysis has been applied to discretized transport problems in order to assess the accuracy of spatial differencing schemes. At present, theoretical methods for analyzing discretized transport problems with optically intermediate and thick spatial cells and arbitrary scattering ratios are not available. We develop a moment analysis method for theoretically analyzing discrete ordinates spatial differencing schemes that makes no assumptions on the optical thickness of the spatial cells or on the value of the scattering ratio. The second part of this thesis concerns the Simplified PN (SPN) approximation, a multidimensional generalization of the one-dimensional planar geometry PN approximation. The SPN approximation was proposed in the early 1960's but has not gained wide acceptance because of its weak theoretical basis. Our goal is to establish a sound theoretical basis for the Simplified PN approximation, in the hopes that it will find broader application with increased confidence. In particular, we examine the Simplified P3 approximation and show that it more accurately computes higher-order spatial and angular moments than the P1 (diffusion) approximation. Then, we derive the multigroup Simplified P3 approximation using a variational analysis that yields the SP3 equations along with interface and Marshak-like boundary conditions. We also develop an efficient explicit iterative algorithm for solving the multigroup SP3 equations. Finally, we present numerical solutions of transport problems that verify the accuracy of the multigroup SP3 approximation.

Brantley, Patrick Shawn

1998-08-01

404

Computer Experiments for Function Approximations  

SciTech Connect

This research project falls in the domain of response surface methodology, which seeks cost-effective ways to accurately fit an approximate function to experimental data. Modeling and computer simulation are essential tools in modern science and engineering. A computer simulation can be viewed as a function that receives input from a given parameter space and produces an output. Running the simulation repeatedly amounts to an equivalent number of function evaluations, and for complex models, such function evaluations can be very time-consuming. It is then of paramount importance to intelligently choose a relatively small set of sample points in the parameter space at which to evaluate the given function, and then use this information to construct a surrogate function that is close to the original function and takes little time to evaluate. This study was divided into two parts. The first part consisted of comparing four sampling methods and two function approximation methods in terms of efficiency and accuracy for simple test functions. The sampling methods used were Monte Carlo, Quasi-Random LP{sub {tau}}, Maximin Latin Hypercubes, and Orthogonal-Array-Based Latin Hypercubes. The function approximation methods utilized were Multivariate Adaptive Regression Splines (MARS) and Support Vector Machines (SVM). The second part of the study concerned adaptive sampling methods with a focus on creating useful sets of sample points specifically for monotonic functions, functions with a single minimum and functions with a bounded first derivative.

Chang, A; Izmailov, I; Rizzo, S; Wynter, S; Alexandrov, O; Tong, C

2007-10-15

405

Approximate reasoning using terminological models  

NASA Technical Reports Server (NTRS)

Term Subsumption Systems (TSS) form a knowledge-representation scheme in AI that can express the defining characteristics of concepts through a formal language that has a well-defined semantics and incorporates a reasoning mechanism that can deduce whether one concept subsumes another. However, TSS's have very limited ability to deal with the issue of uncertainty in knowledge bases. The objective of this research is to address issues in combining approximate reasoning with term subsumption systems. To do this, we have extended an existing AI architecture (CLASP) that is built on the top of a term subsumption system (LOOM). First, the assertional component of LOOM has been extended for asserting and representing uncertain propositions. Second, we have extended the pattern matcher of CLASP for plausible rule-based inferences. Third, an approximate reasoning model has been added to facilitate various kinds of approximate reasoning. And finally, the issue of inconsistency in truth values due to inheritance is addressed using justification of those values. This architecture enhances the reasoning capabilities of expert systems by providing support for reasoning under uncertainty using knowledge captured in TSS. Also, as definitional knowledge is explicit and separate from heuristic knowledge for plausible inferences, the maintainability of expert systems could be improved.

Yen, John; Vaidya, Nitin

1992-01-01

406

Evaluation of a radiative transfer equation and diffusion approximation hybrid forward solver for fluorescence molecular imaging  

NASA Astrophysics Data System (ADS)

The solution of the forward problem in fluorescence molecular imaging strongly influences the successful convergence of the fluorophore reconstruction. The most common approach to meeting this problem has been to apply the diffusion approximation. However, this model is a first-order angular approximation of the radiative transfer equation, and thus is subject to some well-known limitations. This manuscript proposes a methodology that confronts these limitations by applying the radiative transfer equation in spatial regions in which the diffusion approximation gives decreased accuracy. The explicit integro differential equations that formulate this model were solved by applying the Galerkin finite element approximation. The required spatial discretization of the investigated domain was implemented through the Delaunay triangulation, while the azimuthal discretization scheme was used for the angular space. This model has been evaluated on two simulation geometries and the results were compared with results from an independent Monte Carlo method and the radiative transfer equation by calculating the absolute values of the relative errors between these models. The results show that the proposed forward solver can approximate the radiative transfer equation and the Monte Carlo method with better than 95% accuracy, while the accuracy of the diffusion approximation is approximately 10% lower.

Gorpas, Dimitris; Andersson-Engels, Stefan

2012-12-01

407

Influence of Talc Concentration on Angular Deformation in Injection Molded Parts of Talc and Rubber Filled Polypropylene  

NASA Astrophysics Data System (ADS)

Polypropylene (PP), filled with talc and rubber, is one of the most popular resins used for automotive plastic parts. The influence of talc concentration in PP compounds on the angular deformation of L-shaped specimens is discussed. The experimental and analytical results are as follows 1) Angular deformation increases sharply with increasing talc concentration until approximately 10 wt% of talc. The angle reaches a maximum at 10 wt% of talc, and then decreases above the critical concentration. 2) The shrinkage in the in-plane direction of the plate specimens shows a decrease until the talc concentration reaches approximately 10 wt%, and then becomes constant above the critical concentration. On the other hand, the shrinkage in the thickness direction increases sharply until talc concentration approaches 5 %, and then decreases gradually above that concentration. 3) The strains for each sample are calculated using Hooke's Law. In this case, the force that induces angular deformation is assumed to be the difference of shrinkage between the thickness and in-plane directions. The tendencies of calculated strains are quite qualitatively consistent with measured angular deformations. 4) A deformation angle peak can be explained by the difference of shrinkage in the thickness and in-plane directions, which increase sharply until 5 wt% talc concentration. Above this concentration, shrinkage will remain constant despite an increasing flexural modulus.

Takahara, Tadayoshi; Koyama, Kiyohito

408

Hydraulic conductance and viscous coupling of three-phase layers in angular capillaries  

NASA Astrophysics Data System (ADS)

Predicting three-phase relative permeability by network models requires reliable models for hydraulic conductance of films and layers stabilized by capillary forces at the pore level. We solve the creeping flow approximation of the Navier-Stokes equation for stable wetting and intermediate layers in the corner of angular capillaries by using a continuity boundary condition at the layer interface. We find significant coupling between the condensed phases and calculate the generalized mobilities by solving cocurrent and countercurrent flow of wetting and intermediate layers. Finally, we present a simple heuristic model for the generalized mobilities as a function of the geometry and viscosity ratio.

Dehghanpour, H.; Aminzadeh, B.; Dicarlo, D. A.

2011-06-01

409

Angular dependence of metamagnetic transitions in HoNi2B2C  

E-print Network

interference device ~SQUID! magnetometer. A modified version of the QD sample rotator probe, that allows for the rotation of the sample in a manner that keeps the c axis approximately perpendicular to the applied field at all times, was used. Due...356.6 kG/sinf as determine from Fig. 2~b!. 973F METAMAGNETIC . . . manifest by Hc3!. These angular dependences are consistent with the Ho moment being fully along the @110# direction. This would lead to the longitudinal moment measured by the SQUID...

Canfield, PC; Budko, SL; Cho, BK; Lacerda, A.; Farrell, D.; JohnstonHalperin, E.; Kalatsky, VA; Pokrovsky, Valery L.

1997-01-01

410

Effect of angular inflow on the vibratory response of a counter-rotating propeller  

NASA Technical Reports Server (NTRS)

This report presents the results of a propeller vibratory stress survey on the Fairey Gannet aircraft aimed at giving an assessment of the difference in vibratory response between single and counter-rotating propeller operation in angular inflow. The survey showed that counter-rotating operation of the propeller had the effect of increasing the IP response of the rear propeller by approximately 25 percent over comparable single-rotation operation while counter-rotating operation did not significantly influence the IP response of the front propeller.

Turnberg, J. E.; Brown, P. C.

1985-01-01

411

On the non-uniform distribution of the angular elements of near-Earth objects  

NASA Astrophysics Data System (ADS)

We examine the angular distributions of near-Earth objects (NEOs) which are often regarded as uniform. The apparent distribution of the longitude of ascending node, ?, is strongly affected by well-known seasonal effects in the discovery rate of NEOs. The deviation from the expected ?-periodicity in the apparent distribution of ? indicates that its intrinsic distribution is slightly enhanced along a mean direction, ??=111°; approximately 53% of NEOs have ? values within ±90° of ??. We also find that each subgroup of NEOs (Amors, Apollos and Atens) has different observational selection effects which cause different non-uniformities in the apparent distributions of their arguments of perihelion ?, and longitudes of perihelion ?. For their intrinsic distributions, our analysis reveals that the Apollo asteroids have non-uniform ? due to secular dynamics associated with inclination-eccentricity-? coupling, and the Amors’ ? distribution is peaked towards the secularly forced eccentricity vector. The Apollos’ ? distribution is axial, favoring values near 0° and 180°; the two quadrants centered at 0° and 180° account for 55% of the Apollos’ ? values. The Amors’ ? distribution peaks near ??=4°; 61% of Amors have ? within ±90° of this peak. We show that these modest but statistically significant deviations from uniform random distributions of angular elements are owed to planetary perturbations, primarily Jupiter’s. It is remarkable that this strongly chaotic population of minor planets reveals the presence of Jupiter in its angular distributions.

JeongAhn, Youngmin; Malhotra, Renu

2014-02-01

412

Preliminary determination of Newtonian gravitational constant with angular acceleration feedback method.  

PubMed

This paper describes the preliminary measurement of the Newtonian gravitational constant G with the angular acceleration feedback method at HUST. The apparatus has been built, and preliminary measurement performed, to test all aspects of the experimental design, particularly the feedback function, which was recently discussed in detail by Quan et al. The experimental results show that the residual twist angle of the torsion pendulum at the signal frequency introduces 0.4?ppm to the value of G. The relative uncertainty of the angular acceleration of the turntable is approximately 100?ppm, which is mainly limited by the stability of the apparatus. Therefore, the experiment has been modified with three features: (i) the height of the apparatus is reduced almost by half, (ii) the aluminium shelves were replaced with shelves made from ultra-low expansion material and (iii) a perfect compensation of the laboratory-fixed gravitational background will be carried out. With these improvements, the angular acceleration is expected to be determined with an uncertainty of better than 10?ppm, and a reliable value of G with 20?ppm or below will be obtained in the near future. PMID:25201996

Xue, Chao; Quan, Li-Di; Yang, Shan-Qing; Wang, Bing-Peng; Wu, Jun-Fei; Shao, Cheng-Gang; Tu, Liang-Cheng; Milyukov, Vadim; Luo, Jun

2014-10-13

413

Rotating wave approximation and entropy  

E-print Network

This paper studies composite quantum systems, like atom-cavity systems and coupled optical resonators, in the absence of external driving by resorting to methods from quantum field theory. Going beyond the rotating wave approximation, it is shown that the usually neglected counter-rotating part of the Hamiltonian relates to the entropy operator and generates an irreversible time evolution. The vacuum state of the system is shown to evolve into a generalized coherent state exhibiting entanglement of the modes in which the counter-rotating terms are expressed. Possible consequences at observational level in quantum optics experiments are currently under study.

Andreas Kurcz; Antonio Capolupo; Almut Beige; Emilio Del Giudice; Giuseppe Vitiello

2010-01-22

414

Deep-Subwavelength Spatial Characterization of Angular Emission from Single-Crystal Au Plasmonic Ridge Nanoantennas  

E-print Network

We use spatially and angle-resolved cathodoluminescence imaging spectroscopy to study, with deep subwavelength resolution, the radiation mechanism of single plasmonic ridge antennas with lengths ranging from 100 to 2000 nm. We measure the antenna's standing wave resonances up to the fifth order and measure the dispersion of the strongly confined guided plasmon mode. By directly detecting the emitted antenna radiation with a 2D CCD camera we are able to measure the angular emission patterns associated with each individual antenna resonance. We demonstrate that the shortest ridges can be modeled as a single point dipole emitter oriented either upward (m=0) or in-plane (m=1). The far-field emission pattern for longer antennas (m>2) is well described by two interfering in-plane point dipoles at the end facets giving rise to an angular fringe pattern, where the number of fringes increases as the antenna becomes longer. Taking advantage of the deep subwavelength excitation resolution of the cathodoluminescence tech...

Coenen, Toon; Polman, Albert; 10.1021/nn204750d

2013-01-01

415

On the convergence of difference approximations to scalar conservation laws  

NASA Technical Reports Server (NTRS)

A unified treatment of explicit in time, two level, second order resolution, total variation diminishing, approximations to scalar conservation laws are presented. The schemes are assumed only to have conservation form and incremental form. A modified flux and a viscosity coefficient are introduced and results in terms of the latter are obtained. The existence of a cell entropy inequality is discussed and such an equality for all entropies is shown to imply that the scheme is an E scheme on monotone (actually more general) data, hence at most only first order accurate in general. Convergence for total variation diminishing-second order resolution schemes approximating convex or concave conservation laws is shown by enforcing a single discrete entropy inequality.

Osher, S.; Tadmor, E.

1985-01-01

416

Knee abduction angular impulses during prolonged running with wedged insoles.  

PubMed

Wedged insoles may produce immediate effects on knee abduction angular impulses during running; however, it is currently not known whether these knee abduction angular impulse magnitudes are maintained throughout a run when fatigue sets in. If changes occur, this could affect the clinical utility of wedged insoles in treating conditions such as patellofemoral pain. Thus, the purpose of this study was to determine whether knee abduction angular impulses are altered during a prolonged run with wedged insoles. It was hypothesized that knee abduction angular impulses would be reduced following a prolonged run with wedged insoles. Nine healthy runners participated. Runners were randomly assigned to either a 6-mm medial wedge condition or a 6-mm lateral wedge condition and then ran continuously overground for 30 min. Knee abduction angular impulses were quantified at 0 and 30 min using a gait analysis procedure. After 2 days, participants returned to perform the same test but with the other wedge type. Two-way repeated-measures analysis of variance was used to evaluate main effects of wedge condition and time and interactions between wedge condition and time (? = 0.05). Paired t-tests were used for post hoc analysis (? = 0.01). No interaction effects (p = 0.958) were found, and knee abduction angular impulses were not significantly different over time (p = 0.384). Lateral wedge conditions produced lesser knee abduction angular impulses than medial conditions at 0 min (difference of 2.79 N m s, p = 0.006) and at 30 min (difference of 2.76 N m s, p < 0.001). It is concluded that significant knee abduction angular impulse changes within wedge conditions do not occur during a 30-min run. Additionally, knee abduction angular impulse differences between wedge conditions are maintained during a 30-min run. PMID:23636760

Lewinson, Ryan T; Worobets, Jay T; Stefanyshyn, Darren J

2013-07-01

417

Approximating distributions in stochastic learning.  

PubMed

On-line machine learning algorithms, many biological spike-timing-dependent plasticity (STDP) learning rules, and stochastic neural dynamics evolve by Markov processes. A complete description of such systems gives the probability densities for the variables. The evolution and equilibrium state of these densities are given by a Chapman-Kolmogorov equation in discrete time, or a master equation in continuous time. These formulations are analytically intractable for most cases of interest, and to make progress a nonlinear Fokker-Planck equation (FPE) is often used in their place. The FPE is limited, and some argue that its application to describe jump processes (such as in these problems) is fundamentally flawed. We develop a well-grounded perturbation expansion that provides approximations for both the density and its moments. The approach is based on the system size expansion in statistical physics (which does not give approximations for the density), but our simple development makes the methods accessible and invites application to diverse problems. We apply the method to calculate the equilibrium distributions for two biologically-observed STDP learning rules and for a simple nonlinear machine-learning problem. In all three examples, we show that our perturbation series provides good agreement with Monte-Carlo simulations in regimes where the FPE breaks down. PMID:22418034

Leen, Todd K; Friel, Robert; Nielsen, David

2012-08-01

418

Approximate simulation of quantum channels  

NASA Astrophysics Data System (ADS)

Earlier, we proved a duality between two optimizations problems [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.104.120501 104, 120501 (2010)]. The primary one is, given two quantum channels M and N, to find a quantum channel R such that R?N is optimally close to M as measured by the worst-case entanglement fidelity. The dual problem involves the information obtained by the environment through the so-called complementary channels M? and N?, and consists in finding a quantum channel R' such that R'?M? is optimally close to N?. It turns out to be easier to find an approximate solution to the dual problem in certain important situations, notably when M is the identity channel—the problem of quantum error correction—yielding a good near-optimal worst-case entanglement fidelity as well as the corresponding near-optimal correcting channel. Here we provide more detailed proofs of these results. In addition, we generalize the main theorem to the case where there are certain constraints on the implementation of R, namely, on the number of Kraus operators. We also offer a simple algebraic form for the near-optimal correction channel in the case M=id. For approximate error correction, we show that any ?-correctable channel is, up to appending an ancilla, ?-close to an exactly correctable one. We also demonstrate an application of our theorem to the problem of minimax state discrimination.

Bény, Cédric; Oreshkov, Ognyan

2011-08-01

419

High Resolution Imaging of Circumstellar Disks at Millimeter Wavelengths  

NASA Technical Reports Server (NTRS)

We update progress on our research 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. Observations at these wavelengths are advantageous because the dust emission is generally optically thin and directly proportional to mass, contrast with stellar photospheres is not problematic, and the wavelength dependence provides information on an important regime of grain sizes. We employ several facilities for state-of-the-art high resolution observations, including the Very Large Array (VLA), the Australia Telescope Compact Array (ATCA), the Plateau de Bure Interferometer (PdBI) of the Institut de RadioAstronomie Millimetrique, the Submillimeter Array (SMA) of the Smithsonian Astrophysical Observatory, and the Caltech Submillimeter Observatory (CSO). Many recent highlights of our program were presented in an invited review on High Angular Resolution Studies of Disks- the Millimetre at IAU Symposium 221, Star Formation at High Angular Resolution, in July 2003.

Wilner, David J.

2003-01-01

420

Blue Stragglers as Stellar Collision Products: the Angular Momentum Question  

E-print Network

We investigate the structure and evolution of blue stragglers stars which were formed from direct stellar collisions between main sequence stars in globular clusters. In particular, we look at the rotational evolution of the products of off-axis collisions. As found in previous work, such blue stragglers initially have too high an angular momentum to contract down to the main sequence. We consider angular momentum loss through either disc locking or locking to an outflowing wind and show that both methods allow the merged object to shed sufficient angular momentum to contract down to the main sequence.

Alison Sills; Tim Adams; Melvyn B. Davies

2005-01-10

421

Statistical prescission point model of fission fragment angular distributions  

NASA Astrophysics Data System (ADS)

In light of recent developments in fission studies such as slow saddle to scission motion and spin equilibration near the scission point, the theory of fission fragment angular distribution is examined and a new statistical prescission point model is developed. The conditional equilibrium of the collective angular bearing modes at the prescission point, which is guided mainly by their relaxation times and population probabilities, is taken into account in the present model. The present model gives a consistent description of the fragment angular and spin distributions for a wide variety of heavy and light ion induced fission reactions.

John, Bency; Kataria, S. K.

1998-03-01

422

The spectrum of random ICRF source angular velocities  

NASA Astrophysics Data System (ADS)

The spectrum of the random angular velocities of ICRF sources is analyzed. This spectrum is calculated assuming that the apparent angular velocities of the sources are random and uncorrelated, and that the directions of the motions of each source are uniformly distributed over a circle. The amplitudes of the vector spherical harmonics display a white-noise spectrum. Published observational data are considered, and preliminary conclusions are drawn about the nature of the observed dipole and quadrupole harmonics in the spectrum of angular velocities.

Sazhin, M. V.; Sazhina, O. S.; Marakulin, A. O.

2011-11-01

423

Angular Momentum Mixing in a Non-spherical Color Superconductor  

E-print Network

We study the angular momentum mixing effects in the color superconductor with non-spherical pairing. We first clarify the concept of the angular momentum mixing with a toy model for non-relativistic and spinless fermions. Then we derive the gap equation for the polar phase of dense QCD by minimizing the CJT free energy. The solution of the gap equation consists of all angular momentum partial waves of odd parity. The corresponding free energy is found to be lower than that reported in the literature with p-wave only.

Bo Feng; Defu Hou; Hai-cang Ren

2007-11-04

424

Coupled grating reflectors with highly angular tolerant reflectance.  

PubMed

We report on stacked high-contrast grating reflectors with virtually angular independent reflectance for transverse-magnetic polarized light. The investigated structure consists of two-layer pairs of amorphous silicon and silicondioxide that are designed for a wavelengths of 1550 nm. The large angular tolerance results from coupling of the two involved silicon gratings and is achieved if the modal fields in the reflectors are matched. With this approach, a reflectance of more than 96% in the entire angular spectrum is feasible. Experimentally we demonstrate a reflectance of more than 98% for incidence angles up to 60° and more than 90% up to 80°. PMID:23988950

Kroker, Stefanie; Käsebier, Thomas; Kley, Ernst-Bernhard; Tünnermann, Andreas

2013-09-01

425

Orbital angular momentum in optical fibers  

NASA Astrophysics Data System (ADS)

Internet data traffic capacity is rapidly reaching limits imposed by nonlinear effects of single mode fibers currently used in optical communications. Having almost exhausted available degrees of freedom to orthogonally multiplex data in optical fibers, researchers are now exploring the possibility of using the spatial dimension of fibers, via multicore and multimode fibers, to address the forthcoming capacity crunch. While multicore fibers require complex manufacturing, conventional multi-mode fibers suffer from mode coupling, caused by random perturbations in fibers and modal (de)multiplexers. Methods that have been developed to address the problem of mode coupling so far, have been dependent on computationally intensive digital signal processing algorithms using adaptive optics feedback or complex multiple-input multiple-output algorithms. Here we study the possibility of using the orbital angular momentum (OAM), or helicity, of light, as a means of increasing capacity of future optical fiber communication links. We first introduce a class of specialty fibers designed to minimize mode coupling and show their potential for OAM mode generation in fibers using numerical analysis. We then experimentally confirm the existence of OAM states in these fibers using methods based on fiber gratings and spatial light modulators. In order to quantify the purity of created OAM states, we developed two methods based on mode-image analysis, showing purity of OAM states to be 90% after 1km in these fibers. Finally, in order to demonstrate data transmission using OAM states, we developed a 4-mode multiplexing and demultiplexing systems based on free-space optics and spatial light modulators. Using simple coherent detection methods, we successfully transmit data at 400Gbit/s using four OAM modes at a single wavelength, over 1.1 km of fiber. Furthermore, we achieve data transmission at 1.6Tbit/s using 10 wavelengths and two OAM modes. Our study indicates that OAM light can exist, and be long lived, in a special class of fibers and our data transmission demonstrations show that OAM could be considered an additional degree of freedom for data multiplexing in future optical fiber communication links. Our studies open the doors for other applications such as micro-endoscopy and nanoscale imaging which require fiber based remote delivery of OAM light.

Bozinovic, Nenad

426

Resolution limits for wave equation imaging  

NASA Astrophysics Data System (ADS)

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

Huang, Yunsong; Schuster, Gerard T.

2014-08-01

427

CMB likelihood approximation by a Gaussianized Blackwell-Rao estimator  

E-print Network

We introduce a new CMB temperature likelihood approximation called the Gaussianized Blackwell-Rao (GBR) estimator. This estimator is derived by transforming the observed marginal power spectrum distributions obtained by the CMB Gibbs sampler into standard univariate Gaussians, and then approximate their joint transformed distribution by a multivariate Gaussian. The method is exact for full-sky coverage and uniform noise, and an excellent approximation for sky cuts and scanning patterns relevant for modern satellite experiments such as WMAP and Planck. A single evaluation of this estimator between l=2 and 200 takes ~0.2 CPU milliseconds, while for comparison, a single pixel space likelihood evaluation between l=2 and 30 for a map with ~2500 pixels requires ~20 seconds. We apply this tool to the 5-year WMAP temperature data, and re-estimate the angular temperature power spectrum, $C_{\\ell}$, and likelihood, L(C_l), for l<=200, and derive new cosmological parameters for the standard six-parameter LambdaCDM model. Our spectrum is in excellent agreement with the official WMAP spectrum, but we find slight differences in the derived cosmological parameters. Most importantly, the spectral index of scalar perturbations is n_s=0.973 +/- 0.014, 1.9 sigma away from unity and 0.6 sigma higher than the official WMAP result, n_s = 0.965 +/- 0.014. This suggests that an exact likelihood treatment is required to higher l's than previously believed, reinforcing and extending our conclusions from the 3-year WMAP analysis. In that case, we found that the sub-optimal likelihood approximation adopted between l=12 and 30 by the WMAP team biased n_s low by 0.4 sigma, while here we find that the same approximation between l=30 and 200 introduces a bias of 0.6 sigma in n_s.

Ø. Rudjord; N. E. Groeneboom; H. K. Eriksen; Greg Huey; K. M. Górski; J. B. Jewell

2008-09-26

428

On certain quasi-local spin-angular momentum expressions for small spheres  

NASA Astrophysics Data System (ADS)

The Ludvigsen-Vickers and two recently suggested quasi-local spin-angular momentum expressions, based on holomorphic and anti-holomorphic spinor fields, are calculated for small spheres of radius r about a point o. It is shown that, apart from the sign in the case of anti-holomorphic spinors in non-vacuum, the leading terms of all these expressions coincide. In non-vacuum spacetimes this common leading term is of order r4, and it is the product of the contraction of the energy-momentum tensor and an average of the approximate boost-rotation Killing vector that vanishes at o and of the 3-volume of the ball of radius r. In vacuum spacetimes the leading term is of order r6, and the factor of proportionality is the contraction of the Bel-Robinson tensor and another average of the same approximate boost-rotation Killing vector.

Szabados, LászlóB

1999-09-01

429

On certain quasi-local spin-angular momentum expressions for small spheres  

E-print Network

The Ludvigsen-Vickers and two recently suggested quasi-local spin-angular momentum expressions, based on holomorphic and anti-holomorphic spinor fields, are calculated for small spheres of radius $r$ about a point $o$. It is shown that, apart from the sign in the case of anti-holomorphic spinors in non-vacuum, the leading terms of all these expressions coincide. In non-vacuum spacetimes this common leading term is of order $r^4$, and it is the product of the contraction of the energy-momentum tensor and an average of the approximate boost-rotation Killing vector that vanishes at $o$ and of the 3-volume of the ball of radius $r$. In vacuum spacetimes the leading term is of order $r^6$, and the factor of proportionality is the contraction of the Bel-Robinson tensor and an other average of the same approximate boost-rotation Killing vector.

Laszlo B Szabados

1999-01-24

430

Linear approximations of nonlinear systems  

NASA Technical Reports Server (NTRS)

The development of a method for designing an automatic flight controller for short and vertical take off aircraft is discussed. This technique involves transformations of nonlinear systems to controllable linear systems and takes into account the nonlinearities of the aircraft. In general, the transformations cannot always be given in closed form. Using partial differential equations, an approximate linear system called the modified tangent model was introduced. A linear transformation of this tangent model to Brunovsky canonical form can be constructed, and from this the linear part (about a state space point x sub 0) of an exact transformation for the nonlinear system can be found. It is shown that a canonical expansion in Lie brackets about the point x sub 0 yields the same modified tangent model.

Hunt, L. R.; Su, R.

1983-01-01

431

Communication: The distinguishable cluster approximation.  

PubMed

We present a method that accurately describes strongly correlated states and captures dynamical correlation. It is derived as a modification of coupled-cluster theory with single and double excitations (CCSD) through consideration of particle distinguishability between dissociated fragments, whilst retaining the key desirable properties of particle-hole symmetry, size extensivity, invariance to rotations within the occupied and virtual spaces, and exactness for two-electron subsystems. The resulting method, called the distinguishable cluster approximation, smoothly dissociates difficult cases such as the nitrogen molecule, with the modest N(6) computational cost of CCSD. Even for molecules near their equilibrium geometries, the new model outperforms CCSD. It also accurately describes the massively correlated states encountered when dissociating hydrogen lattices, a proxy for the metal-insulator transition, and the fully dissociated system is treated exactly. PMID:23862916

Kats, Daniel; Manby, Frederick R

2013-07-14

432

Wavelets and distributed approximating functionals  

NASA Astrophysics Data System (ADS)

A general procedure is proposed for constructing father and mother wavelets that have excellent time-frequency localization and can be used to generate entire wavelet families for use as wavelet transforms. One interesting feature of our father wavelets (scaling functions) is that they belong to a class of generalized delta sequences, which we refer to as distributed approximating functionals (DAFs). We indicate this by the notation wavelet-DAFs. Correspondingly, the mother wavelets generated from these wavelet-DAFs are appropriately called DAF-wavelets. Wavelet-DAFs can be regarded as providing a pointwise (localized) spectral method, which furnishes a bridge between the traditional global methods and local methods for solving partial differential equations. They are shown to provide extremely accurate numerical solutions for a number of nonlinear partial differential equations, including the Korteweg-de Vries (KdV) equation, for which a previous method has encountered difficulties (J. Comput. Phys. 132 (1997) 233).

Wei, G. W.; Kouri, D. J.; Hoffman, D. K.

1998-07-01

433

IONIS: Approximate atomic photoionization intensities  

NASA Astrophysics Data System (ADS)

A program to compute relative atomic photoionization cross sections is presented. The code applies the output of the multiconfiguration Dirac-Fock method for atoms in the single active electron scheme, by computing the overlap of the bound electron states in the initial and final states. The contribution from the single-particle ionization matrix elements is assumed to be the same for each final state. This method gives rather accurate relative ionization probabilities provided the single-electron ionization matrix elements do not depend strongly on energy in the region considered. The method is especially suited for open shell atoms where electronic correlation in the ionic states is large. Program summaryProgram title: IONIS Catalogue identifier: AEKK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKK_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1149 No. of bytes in distributed program, including test data, etc.: 12 877 Distribution format: tar.gz Programming language: Fortran 95 Computer: Workstations Operating system: GNU/Linux, Unix Classification: 2.2, 2.5 Nature of problem: Photoionization intensities for atoms. Solution method: The code applies the output of the multiconfiguration Dirac-Fock codes Grasp92 [1] or Grasp2K [2], to compute approximate photoionization intensities. The intensity is computed within the one-electron transition approximation and by assuming that the sum of the single-particle ionization probabilities is the same for all final ionic states. Restrictions: The program gives nonzero intensities for those transitions where only one electron is removed from the initial configuration(s). Shake-type many-electron transitions are not computed. The ionized shell must be closed in the initial state. Running time: Few seconds for a large problem with a few thousand configurations.

Heinäsmäki, Sami

2012-02-01

434

Irrotational and Incompressible Ellipsoids in the First Post-Newtonian Approximation of General Relativity  

E-print Network

First post-Newtonian (1PN) hydrostatic equations for an irrotational fluid which have been recently derived are solved for an incompressible star. The 1PN configurations are expressed as a deformation of the Newtonian irrotational Riemann ellipsoid using Lagrangian displacement vectors introduced by Chandrasekhar. For the 1PN solutions, we also calculate the luminosity of gravitational waves in the 1PN approximation using the Blanchet-Damour formalism. It is found that the solutions of the 1PN equations exhibit singularities at points where the axial ratios of semi-axes are 1:0.5244:0.6579 and 1:0.2374:0.2963, and the singularities seem to show that at the points, the irrotational Riemann ellipsoid is unstable to the deformation induced by the effect of general relativity. For stable cases (a_2/a_1 > 0.5244, where a_1 and a_2 are the semi-major and minor axes, respectively) we find that when increasing the 1PN correction, the angular velocity and total angular momentum increase, while the total energy and luminosity of gravitational waves decrease. These 1PN solutions will be useful when examining the accuracy of numerical code for obtaining relativistic irrotational stars. We also investigate the validity of an ellipsoidal approximation, in which a 1PN solution is obtained assuming an ellipsoidal figure and neglecting the deformation. It is found that for $a_2/a_1 > 0.7$, the ellipsoidal approximation gives a fairly accurate result for the energy, angular momentum, and angular velocity, although in the approximation we cannot find the singularities.

Keisuke Taniguchi; Hideki Asada; Masaru Shibata

1998-09-10

435

Approximate analytic solutions to the NPDD: Short exposure approximations  

NASA Astrophysics Data System (ADS)

There have been many attempts to accurately describe the photochemical processes that take places in photopolymer materials. As the models have become more accurate, solving them has become more numerically intensive and more 'opaque'. Recent models incorporate the major photochemical reactions taking place as well as the diffusion effects resulting from the photo-polymerisation process, and have accurately described these processes in a number of different materials. It is our aim to develop accessible mathematical expressions which provide physical insights and simple quantitative predictions of practical value to material designers and users. In this paper, starting with the Non-Local Photo-Polymerisation Driven Diffusion (NPDD) model coupled integro-differential equations, we first simplify these equations and validate the accuracy of the resulting approximate model. This new set of governing equations are then used to produce accurate analytic solutions (polynomials) describing the evolution of the monomer and polymer concentrations, and the grating refractive index modulation, in the case of short low intensity sinusoidal exposures. The physical significance of the results and their consequences for holographic data storage (HDS) are then discussed.

Close, Ciara E.; Sheridan, John T.

2014-04-01

436

H + CD4 abstraction reaction dynamics: excitation function and angular distributions.  

PubMed

We compare experimental photoloc measurements and quasi-classical trajectory calculations of the integral cross sections, lab-frame speed distributions, and angular distributions associated with the CD3 products of the H + CD4(nu = 0) --> CD3 + HD reaction at collision energies ranging from 0.5 to 3.0 eV. Of the potential energy surfaces (PES) we explored, the direct dynamics calculations using the B3LYP/6-31G** density functional theory PES provide the best agreement with the experimental measurements. This agreement is likely due to the better overall description that B3LYP provides for geometries well removed from the minimum energy path, even though its barrier height is low by approximately 0.2 eV. In contrast to previous theoretical calculations, the angular distributions on this surface show behavior associated with a stripping mechanism, even at collision energies only approximately 0.1 eV above the reaction barrier. Other potential energy surfaces, which include an analytical potential energy surface from Espinosa-García and a direct dynamics calculation based on the MSINDO semiempirical Hamiltonian, are less accurate and predict more rebound dynamics at these energies than is observed. Reparametrization of the MSINDO surface, though yielding better agreement with the experiment, is not sufficient to capture the observed dynamics. The differences between these surfaces are interpreted using an analysis of the opacity functions, where we find that the wider cone of acceptance on the B3LYP surface plays a crucial role in determining the integral cross sections and angular distributions. PMID:16405340

Camden, Jon P; Hu, Wenfang; Bechtel, Hans A; Brown, Davida J Ankeny; Martin, Marion R; Zare, Richard N; Lendvay, György; Troya, Diego; Schatz, George C

2006-01-19

437

Measurement of polarization with the Degree Angular Scale Interferometer  

E-print Network

........................................................................................................................................................................................................................... Measurements of the cosmic microwave background (CMB) radiation can reveal with remarkable precision designed to measure anisotropy in the CMB radiation on angular scales of 1.3­0.28, corresponding

Cai, Long

438

Design and implementation of a digital angular rate sensor.  

PubMed

With the aim of detecting the attitude of a rotating carrier, the paper presents a novel, digital angular rate sensor. The sensor consists of micro-sensing elements (gyroscope and accelerometer), signal processing circuit and micro-processor (DSP2812). The sensor has the feature of detecting three angular rates of a rotating carrier at the same time. The key techniques of the sensor, including sensing construction, sensing principles, and signal processing circuit design are presented. The test results show that the sensor can sense rolling, pitch and yaw angular rate at the same time and the measurement error of yaw (or pitch) angular rate and rolling rate of the rotating carrier is less than 0.5%. PMID:22163427

Wu, Li-Feng; Peng, Zhen; Zhang, Fu-Xue

2010-01-01

439

Studying oxygen vacancies in ceramics by perturbed angular correlation spectroscopy.  

National Technical Information Service (NTIS)

Perturbed angular correlation measurements in tetragonal and cubic zirconia and in ceria are described. A physically reasonable and self-consistent interpretation of these data implies that oxygen vacancies are trapped at a second neighbor position by Cd ...

H. T. Su R. Wang, H. Fuchs, J. A. Gardner, W. E. Evenson

1990-01-01

440

Two-color ghost imaging with enhanced angular resolving power  

SciTech Connect

This article reports an experimental demonstration on nondegenerate, two-color, biphoton ghost imaging which reproduced a ghost image with enhanced angular resolving power by means of a greater field of view compared with that of classical imaging. With the same imaging magnification, the enhanced angular resolving power and field of view compared with those of classical imaging are 1.25:1 and 1.16:1, respectively. The enhancement of angular resolving power depends on the ratio between the idler and the signal photon frequencies, and the enhancement of the field of view depends mainly on the same ratio and also on the distances of the object plane and the imaging lens from the two-photon source. This article also reports the possibility of reproducing a ghost image with the enhancement of the angular resolving power by means of a greater imaging amplification compared with that of classical imaging.

Karmakar, Sanjit; Shih, Yanhua [Department of Physics, University of Maryland, Baltimore County, Baltimore, Maryland 21250 (United States)

2010-03-15