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1

Angular Resolution of the Pierre Auger Observatory.  

National Technical Information Service (NTIS)

We studied the angular resolution of the Pierre Auger Detector using data collected from January 2004 to May 2005. The detector consists of two independent components, the fluorescence detector and the surface detector. Hybrid events, observed simultaneou...

C. Bonifazi

2005-01-01

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

X-ray astronomy with ultra-high-angular resolution  

Microsoft Academic Search

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

Christoph Braig; Peter Predehl

2004-01-01

4

Angular resolution studies of the CYGNUS array using the shadows of the sun and moon  

SciTech Connect

Using the cosmic ray shadows of the sun and moon, we have estimated the angular resolution of the CYGNUS extensive air shower array. With the event sample now available we estimate the angular resolution of the array to be 0.70{sub {minus}0.06}{sup {plus}0.07} degrees. The resolution depends on the total number of detected shower particles. A new parameterization of the measured shower-front timing structure and the use of counters with small pulse areas lead to a {approximately}25% improvement in the resolution. The systematic pointing error of the array is less than 0.4{degree}.

Shoup, A.L.; The CYGNUS Collaboration

1993-05-01

5

Angular resolution studies of the CYGNUS array using the shadows of the sun and moon  

SciTech Connect

Using the cosmic ray shadows of the sun and moon, we have estimated the angular resolution of the CYGNUS extensive air shower array. With the event sample now available we estimate the angular resolution of the array to be 0.70[sub [minus]0.06][sup [plus]0.07] degrees. The resolution depends on the total number of detected shower particles. A new parameterization of the measured shower-front timing structure and the use of counters with small pulse areas lead to a [approximately]25% improvement in the resolution. The systematic pointing error of the array is less than 0.4[degree].

Shoup, A.L.

1993-01-01

6

Approximate Isometries as an Eigenvalue Problem and Angular Momentum  

NASA Astrophysics Data System (ADS)

In relativistic physics, a precise definition of a black hole's angular momentum is possible only when its horizon possesses an axial symmetry. Unfortunately most black hole horizons have no such symmetry. However, it is possible to pose an eigenvalue problem that has solutions corresponding to any manifold's ``approximate Killing fields.'' This allows one to generalize formulae requiring symmetry to cases where no symmetry is present and thus define, for example, the spin of an arbitrary black hole. This talk will discuss work using perturbation theory of a horizon to quantify the stability of quantities generalized in this way. We will present precise conditions for the stability of solutions to the eigenvalue problem, and discuss potential applications to numerical relativity.

Wilder, Shawn; Beetle, Chris

2013-04-01

7

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

8

Microbeam High Angular Resolution Diffraction Applied to Optoelectronic Devices  

SciTech Connect

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

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

2007-01-19

9

X-ray astronomy with ultra-high-angular resolution  

NASA Astrophysics Data System (ADS)

We present new schemes for a next-generation X-ray telescope for the energy range between approximately 1 and 10 keV providing an angular resolution of at least 1 milli-arcsec. Its technology will be based on diffractive transmission optics, e.g. Fresnel zone plates and their derivatives. Beside near-diffraction limited imaging, these devices hold the potential of a large collecting area well beyond 10 square meters at a simple and lightweight construction, compared to conventional mirror telescopes. However, there are drawbacks. Firstly the intrinsically long focal lengths do require separation and precise formation flight of lens and detector spacecraft. Accordingly, techniques will be discussed for relative stabilization on the one hand and possibilities to reduce focal length and thus lever arm on the other hand. For this purpose, large arrays of small, independent lenses might offer a notable perspective. Secondly, diffractive optics feature severe focal length dispersion which has to be accepted using narrow-band spectral selection or-better-should be corrected over a practicable wide energy range. In the hard X-ray regime, hybrid lens devices made of beryllium, lithium or plastics like polycarbonate will be an appropriate solution for a fixed energy, while tunable systems with variable correction lenses possess-in principle-the capability for dispersion compensation in the soft X-ray region, too. An overview on the science case of milli-arcsec X-ray imaging will conclude the contribution. We show that significant new insights in astrophysical processes are expected just at and beyond this angular scale and give examples from X-ray binaries over AGN's up to gamma-ray bursts.

Braig, Christoph; Predehl, Peter

2004-10-01

10

High angular resolution millimeter observations of circumstellar disks  

NASA Astrophysics Data System (ADS)

In this lecture, we review the properties of protoplanetary disks as derived from high angular resolution observations at millimeter wavelengths. We discuss how the combination of several different high angular resolution techniques allow us to probe different regions of the disk around young stellar objects and to derive the properties of the dust when combined with sophisticated disk models. The picture that emerges is that the dust in circumstellar disks surrounding pre-main sequence stars is in many cases significantly evolved compared to the dust in molecular clouds and the interstellar medium. It is however still difficult to derive a consistent picture and timeline for dust evolution in disks as the observations are still limited to small samples of objects. We also review the evidence for and properties of disks around high-mass young stellar objects and the implications on their formation mechanisms. The study of massive YSOs is complicated by their short lifetimes and larger average distances. In most cases high angular resolution data at millimeter wavelengths are the only method to probe the structure of disks in these objects. We provide a summary of the characteristics of available high angular resolution millimeter and submillimeter observatories. We also describe the characteristics of the ALMA observatory being constructed in the Chilean Andes. ALMA is going to be the world leading observatory at millimeter wavelengths in the coming decades, the project is now in its main construction phase with early science activities envisaged for 2010 and full science operations for 2012.

Testi, Leonard; Leurini, Silvia

2008-06-01

11

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

12

X-ray photoelectron diffraction at high angular resolution  

Microsoft Academic Search

We present x-ray photoelectron diffraction (XPD) measurements at an angular resolution of ~+\\/-1.0° which is much higher than in any prior study. Emission from the Ni 2p3\\/2 core level of Ni(001) under Al Kalpha excitation is considered. The azimuthal XPD patterns are found to exhibit considerable fine structure not observed previously, including peaks whose full widths at half-maximum intensity are

J. Osterwalder; E. A. Stewart; D. Cyr; C. S. Fadley; J. Mustre de Leon; J. J. Rehr

1987-01-01

13

High Angular Resolution Electron Detection in the Inner Heliosphere  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

14

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

15

High-energy resolution, high-angular acceptance crystal monochromator  

SciTech Connect

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

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

1992-06-01

16

High-energy resolution, high-angular acceptance crystal monochromator  

SciTech Connect

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

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

1992-06-01

17

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

SciTech Connect

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

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

1988-08-12

18

High-Angular-Resolution Infrared Observations of Protoplanetary Disks  

NASA Astrophysics Data System (ADS)

Observations of protoplanetary disks are essential to understand planet building process since they provide realistic initial conditions as well as insights into new-born planets through disk-planet dynamical interaction. Scattered-light observations at optical and near-infrared are complementary with longer-wavelength studies as they can provide the information on smaller grains in disks, thus useful to discuss such as grain growth and dust transport that can be either the basic step toward or the consequence of planet-forming activity. As a part of Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS), we have observed more than 60 T Tauri and Herbig Ae/Fe stars. Our targets include transitional systems showing the dips in the mid-infrared SEDs and/or the resolved cavities in submillimeter. The technique of polarization differential imaging (PDI) was employed combined with adaptive optics for most cases in order to achieve high contrast by extracting the scattered light from the disk while suppressing the unpolarized stellar light. The PDI observations indeed enabled us to look at the inner region, as close as about 20 AU in radius typically, with the angular resolution of 0.06 arcsec, corresponding to less than 10 AU in nearby star-forming regions. As a result, the SEEDS imaging has newly uncovered rich structures such as spirals, inner holes, and gaps for transitional systems. The highlight is the discovery of two spiral arms in the submillimeter cavity for SAO 206462, and the subsequent finding of similar spirals for MWC 758, which can be explained by possible presence of giant planets. The comparable angular resolution will be achieved in submillimeter soon with ALMA, and multi-wavelength study will become more important for comprehensive understanding of disks.

Fukagawa, M.; Hashimoto, J.; Tamura, M.; Seeds/Hiciao/Ircs/Ao188

2013-10-01

19

POKER: estimating the power spectrum of diffuse emission with complex masks and at high angular resolution  

NASA Astrophysics Data System (ADS)

We describe the implementation of an angular power spectrum estimator in the flat sky approximation. POKER (P. Of k EstimatoR) is based on the MASTER algorithm developped by Hivon and collaborators in the context of CMB anisotropy. It works entirely in discrete space and can be applied to arbitrary high angular resolution maps. It is therefore particularly suitable for current and future infrared to sub-mm observations of diffuse emission, whether Galactic or cosmological. A copy of the code is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/535/A90

Ponthieu, N.; Grain, J.; Lagache, G.

2011-11-01

20

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

21

High angular resolution observations of CS in the Orion nebula  

SciTech Connect

The core of the Orion molecular cloud has been observed in the emission lines of CS, J=3..-->..2 (146.8 GHz) and J=2..-->..1 (97.98 GHz), using the 14m FCRAO telescope which has angular resolutions of 33'' and 55'' at these frequencies. The morphology indicated by these new data, combined with previous observations, is an extremely narrow (<10'') ridge extending 9' N--S as well as a central condensation at the position of the Kleinmann-Low nebula. Within the central condensation our J=3..-->..2 observations at a spacing of 15'' show no evidence of significant clumping on the scale of our beam despite the high sensitivity of this transition to changes in H/sub 2/ density. From the CS lines, we estimate a mean molecular density of 2 x 10/sup 5/ cm/sup -3/ averaged over the inner 1' corresponding to a source radius of 2 x 10/sup 17/ cm. Combining this with analogous determinations based upon /sup 13/CO, H/sub 2/CO, and NH/sub 3/, we find for displacement along an E-W axis the empirical law n/sub H2/proportionalr/sup -2/ for rapprox. =10/sup 17/ to 2 x 10/sup 18/ cm. This radial distribution is similar to that previously derived from long-wavelength dust emission (lambda=0.3--1 mm) over the more limited range rapprox. =10/sup 17/ to 5 x 10/sup 17/ cm.

Goldsmith, P.F.; Langer, W.D.; Schloerb, F.P.; Scoville, N.Z.

1980-09-01

22

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.

Rathi, Yogesh; Dolui, Sudipto

2013-01-01

23

Diffractive–refractive X-ray optics for very high angular resolution X-ray astronomy  

Microsoft Academic Search

The 0.5arcsec angular resolution of the Chandra X-ray Observatory is possibly the best that a grazing incidence telescope with substantial collecting area will ever attain. We describe a telescope consisting of a diffractive and refractive doublet that transmits rather than reflects X-rays. Therefore, its angular resolution is relatively insensitive to figure errors and surface roughness, the factors that limit grazing

Paul Gorenstein

2007-01-01

24

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

25

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

26

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

27

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

28

Improving the angular resolution for the silicon detectors of the STARS array  

NASA Astrophysics Data System (ADS)

The STARS (Silicon Telescope Array for Reaction Studies) array at LBNL is used to measure the emission angles of light charged particles (protons, deuterons and tritons) following transfer reactions. The array consists of two CD-shaped silicon energy detectors: a thin ``delta E'' detector and a thicker ``E'' detector, each segmented into twenty-four concentric rings. The angle at which a particle hits the delta E detector is typically approximated in the off-line analysis code as the angle from the beam axis to the center of the ring traversed by the particle. To improve angular resolution, a new method of approximating the angle was investigated. It was thought that energy loss in the delta E could be used to derive angle. SRIM was used to create functions of energy loss per unit distance with respect to particle energy. These functions were used in Fortran codes to create matrices of energy loss for a range of angles and final energies. The matrices were then worked into the off-line analysis code. Preliminary results will be shown. This work is partly supported by the DOE under grant numbers DE-FG02-52NA26206 and DE-FG02-05ER41379.

Shaw, John; Pauerstein, Benjamin; Chen, Danyi; Ross, Timothy; Hughes, Richard; Beausang, Con

2010-11-01

29

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

PubMed Central

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

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

2012-01-01

30

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

31

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

32

On the angular distributions in molecular photoionization beyond the dipole approximation  

Microsoft Academic Search

The theory of angular distributions and angular correlations of photoelectrons and recoil ions in molecular photoionization is reformulated in terms of the density matrix and statistical tensor formalism, which incorporates a full multipole expansion of the radiation field. The dynamical parameters of the angular distributions are expressed in terms of the multipole photoionization amplitudes. Photoionization of linear molecules is analysed

A N Grum-Grzhimailo

2003-01-01

33

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

34

High-angular-resolution NIR astronomy with large arrays (SHARP I and SHARP II)  

NASA Astrophysics Data System (ADS)

SHARP I and SHARP II are near infrared cameras for high-angular-resolution imaging. Both cameras are built around a 256 X 256 pixel NICMOS 3 HgCdTe array from Rockwell which is sensitive in the 1 - 2.5 micrometers range. With a 0.05'/pixel scale, they can produce diffraction limited K-band images at 4-m-class telescopes. For a 256 X 256 array, this pixel scale results in a field of view of 12.8' X 12.8' which is well suited for the observation of galactic and extragalactic near-infrared sources. Photometric and low resolution spectroscopic capabilities are added by photometric band filters (J, H, K), narrow band filters ((lambda) /(Delta) (lambda) approximately equals 100) for selected spectral lines, and a CVF ((lambda) /(Delta) (lambda) approximately equals 70). A cold shutter permits short exposure times down to about 10 ms. The data acquisition electronics permanently accepts the maximum frame rate of 8 Hz which is defined by the detector time constants (data rate 1 Mbyte/s). SHARP I has been especially designed for speckle observations at ESO's 3.5 m New Technology Telescope and is in operation since 1991. SHARP II is used at ESO's 3.6 m telescope together with the adaptive optics system COME-ON + since 1993. A new version of SHARP II is presently under test, which incorporates exchangeable camera optics for observations with scales of 0.035, 0.05, and 0.1'/pixel. The first scale extends diffraction limited observations down to the J-band, while the last one provides a larger field of view. To demonstrate the power of the cameras, images of the galactic center obtained with SHARP I, and images of the R136 region in 30 Doradus observed with SHARP II are presented.

Hofmann, Reiner; Brandl, Bernhard; Eckart, Andreas; Eisenhauer, Frank; Tacconi-Garman, Lowell E.

1995-06-01

35

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

SciTech Connect

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

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

2010-04-06

36

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

NASA Astrophysics Data System (ADS)

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

Li, Lianlin; Li, Fang

2013-09-01

37

HST/FGS High Angular Resolution Observations of Binary Asteroids  

NASA Astrophysics Data System (ADS)

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

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

2006-09-01

38

Analytic Expressions for the Angular Resolution of Compton Gamma-ray Detectors.  

National Technical Information Service (NTIS)

This paper describes the derivation of analytic expressions for the angular resolution of reconstructing gamma rays detected via Compton interactions. We consider two types of gamma-ray detectors: Compton-ring and electron-tracking devices. In Compton-rin...

D. M. Wright

2004-01-01

39

Hot spot measurements at high angular resolution using POLDER data over Australia  

Microsoft Academic Search

The hot spot is an enhancement in the optical reflectance of land surfaces at view directions close to the antisolar (exact backscatter) direction. The two-dimensional imaging capability of POLDER on ADEOS has previously been exploited to measure the hot spot on homogeneous land surfaces from space with an angular resolution of 0.3°, by using the variation in view direction with

I. F. Grant; C. Heyraud; F. M. Breon; M. M. Leroy

2001-01-01

40

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

41

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

NASA Astrophysics Data System (ADS)

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

Gorenstein, Paul

2013-04-01

42

Modeling Line Profiles of Protostellar Collapse Observed with High Angular Resolution  

NASA Astrophysics Data System (ADS)

We investigated the line profile of moderately optically thick molecular transitions from collapsing protostellar envelopes. Using the inside-out collapse model, we simulated high angular resolution observations, which can probe the infall motion of the inner region better than low angular resolution observations. The degree of line asymmetry becomes substantially larger as the observing beam size becomes smaller. The self-absorption dip at the central velocity also develops a noticeable asymmetry. Therefore, suitability of collapse tracers depends on the angular resolution of the instrument used. Inclusion of the continuum emission from the central object produces another absorption dip on the redshifted side of the line; i.e., the line shows an inverse P Cygni profile. This effect is larger in the submillimeter band than in longer wavelength bands because of the bright continuum emission from dust grains. This redshifted dip is a good probe of the infall motion at the very inner part of the infalling envelope, and is also sensitive to other physical conditions, such as the depletion of molecules and the distribution of dust grains. We discuss how the line profile is affected by the variation of model parameters, such as molecular abundance, infall radius, and luminosity of the central object. In addition to the inside-out collapse model, we also discuss line profiles generated from Hunter's similarity solutions. Since high angular resolution can be achieved by aperture synthesis, its effect on the line profile was examined by simulating observations of the Sub-millimeter Array (SMA) toward B335, as an example. Only the central absorption dip part of the line profile is affected when the SMA is simulated. The simulated SMA line profile is weaker than the profile generated with a Gaussian beam because of the missing short-spacing flux. If the source is closer, or if the size of the element antenna of the interferometer is larger, even the line peaks can be affected.

Choi, Minho

2002-08-01

43

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

PubMed

Diffusion weighted magnetic resonance imaging (DW-MRI) are now widely used to assess brain integrity in clinical populations. The growing interest in mapping brain connectivity has made it vital to consider what scanning parameters affect the accuracy, stability, and signal-to-noise of diffusion measures. Trade-offs between scan parameters can only be optimized if their effects on various commonly-derived measures are better understood. To explore angular versus spatial resolution trade-offs in standard tensor-derived measures, and in measures that use the full angular information in diffusion signal, we scanned eight subjects twice, 2 weeks apart, using three protocols that took the same amount of time (7 min). Scans with 3.0, 2.7, 2.5 mm isotropic voxels were collected using 48, 41, and 37 diffusion-sensitized gradients to equalize scan times. A specially designed DTI phantom was also scanned with the same protocols, and different b-values. We assessed how several diffusion measures including fractional anisotropy (FA), mean diffusivity (MD), and the full 3D orientation distribution function (ODF) depended on the spatial/angular resolution and the SNR. We also created maps of stability over time in the FA, MD, ODF, skeleton FA of 14 TBSS-derived ROIs, and an information uncertainty index derived from the tensor distribution function, which models the signal using a continuous mixture of tensors. In scans of the same duration, higher angular resolution and larger voxels boosted SNR and improved stability over time. The increased partial voluming in large voxels also led to bias in estimating FA, but this was partially addressed by using "beyond-tensor" models of diffusion. Hum Brain Mapp 34:2688-2706, 2013. © 2012 Wiley Periodicals, Inc. PMID:22522814

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

2012-04-21

44

Improving angular resolution with Scan-MUSIC algorithm for real complex targets using 35GHz millimeter-wave radar  

Microsoft Academic Search

Scan-MUSIC algorithm, developed by the U.S. Army Research Laboratory (ARL), improves angular resolution for target detection with the use of a single rotatable radar scanning the angular region of interest. This algorithm has been adapted and extended from the MUSIC algorithm that has been used for a linear sensor array. Previously, it was shown that the SMUSIC algorithm and a

Canh Ly

2004-01-01

45

[Approximate calculation of L-S coupling of aluminum 3p electronic angular momentums].  

PubMed

Al plasma was obtained by a pulsed laser beam, which was produced from a Nd:YAG laser set with Q-switch, ablating metal target Al in Ar. Based on the plasma, radiation of the plasma was recorded with time- and space-resolved technology, so Al characteristic radiation spectra were obtained. According to the spectra, the coupling of aluminum 3p electronic angular momentums was simplified as quasi-hydrogen particle. At the same time, the main quantum and orbit angular quantum shielding coefficients of aluminum nucleus, signed as alpha and s respectively, were carefully figured out with related theories of quantum mechanics. With our experiment, the resonance double lines of aluminum were scaled up at 396.15 and 394.40 nm respectively. As a result of our calculation, the main quantum shielding coefficient of aluminum nucleus was sigma = 10.850359, and the orbit angular quantum one was s = 7.332875. Their values were reasonable in terms of the order of magnitude. PMID:15759976

Li, Zun-ying; Zhao, Ru-jian

2004-03-01

46

X-ray phase-contrast imaging with nanoradian angular resolution.  

PubMed

We present a new quantitative x-ray phase-contrast imaging method based on the edge illumination principle, which allows achieving unprecedented nanoradian sensitivity. The extremely high angular resolution is demonstrated theoretically and through experimental images obtained at two different synchrotron radiation facilities. The results, achieved at both very high and very low x-ray energies, show that this highly sensitive technique can be efficiently exploited over a very broad range of experimental conditions. This method can open the way to new, previously inaccessible scientific applications in various fields including biology, medicine and materials science. PMID:23581380

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

2013-03-28

47

Simulation of angular and energy distributions for heavy evaporation residues using statistical model approximations and TRIM code  

NASA Astrophysics Data System (ADS)

A Monte Carlo approach has been developed for simulations of the angular and energy distributions for heavy evaporation residues (ER) produced in heavy ion fusion-evaporation reactions. The approach uses statistical model approximations of the HIVAP code for the calculations of initial angular and energy distributions inside a target, which are determined by neutron evaporation from an excited compound nucleus. Further step in the simulation of transmission of ER heavy atoms through a target layer is performed with the TRIM code that gives final angle and energy distributions at the exit from the target. Both the simulations (neutron evaporation and transmission through solid media) have been separately considered and good agreement has been obtained between the results of simulations and available experimental data. Some applications of the approach have been also considered.

Sagaidak, R. N.; Utyonkov, V. K.; Scarlassara, F.

2013-02-01

48

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.

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

2011-01-01

49

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

PubMed

This work investigates the possibilities of applying high-angular-resolution-diffusion-imaging- (HARDI-) based methods in a clinical setting by investigating the performance of non-Gaussian diffusion probability density function (PDF) estimation for a range of b-values and diffusion gradient direction tables. It does so at realistic SNR levels achievable in limited time on a high-performance 3T system for the whole human brain in vivo. We use both computational simulations and in vivo brain scans to quantify the angular resolution of two selected reconstruction methods: Q-ball imaging and the diffusion orientation transform. We propose a new analytical solution to the ODF derived from the DOT. Both techniques are analytical decomposition approaches that require identical acquisition and modest postprocessing times and, given the proposed modifications of the DOT, can be analyzed in a similar fashion. We find that an optimal HARDI protocol given a stringent time constraint (<10?min) combines a moderate b-value (around 2000?s/mm(2)) with a relatively low number of acquired directions (>48). Our findings generalize to other methods and additional improvements in MR acquisition techniques. PMID:23554808

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

2013-03-11

50

High angular resolution imaging of the circumstellar material around intermediate mass (IM) stars  

NASA Astrophysics Data System (ADS)

In this paper we present high angular resolution imaging of 3 intermediate-mass (IM) stars using the Plateau de Bure Interferometer (PdBI). In particular we present the chemical study we have carried out towards the IM hot core NGC 7129 FIRS 2. This is the first chemical study in an IM hot core and provides important hints to understand the dependence of the hot core chemistry on the stellar luminosity. We also present our high angular resolution (0.3?) images of the borderline Class 0-Class I object IC1396 N. These images trace the warm region of this IM protostar with unprecedented detail (0.3?˜200 AU at the distance of IC1396 N) and provide the first detection of a cluster of IM hot cores. Finally, we present our interferometric continuum and spectroscopic images of the disk around the Herbig Be star R Mon. We have determined the kinematics and physical structure of the disk associated with this B0 star. The low spectral index derived from the dust emission as well as the flat geometry of the disk suggest a more rapid evolution of the disks associated with massive stars (see Alonso-Albi et al., arXiv:astro-ph/0702119, 2007). In the Discussion, we dare to propose a possible evolutionary sequence for the warm circumstellar material around IM stars.

Fuente, A.

2008-01-01

51

Contrast and resolution analysis of angular domain imaging for iterative optical projection tomography reconstruction  

NASA Astrophysics Data System (ADS)

Angular domain imaging (ADI) generates a projection image of an attenuating target within a turbid medium by employing a silicon micro-tunnel array to reject photons that have deviated from the initial propagation direction. In this imaging method, image contrast and resolution are position dependent. The objective of this work was to first characterize the contrast and resolution of the ADI system at a multitude of locations within the imaging plane. The second objective was to compare the reconstructions of different targets using filtered back projection and iterative reconstruction algorithms. The ADI system consisted of a diode laser laser (808nm, CW, ThorLabs) with a beam expander for illumination of the sample cuvette. At the opposite side of the cuvette, an Angular Filter Array (AFA) of 80 ?m x 80 ?m square-shaped tunnels 1 cm in length was used to reject the transmitted scattered light. Image-forming light exiting the AFA was detected by a linear CCD (16-bit, Mightex). Our approach was to translate two point attenuators (0.5 mm graphite rod, 0.368 mm drill bit) submerged in a 0.6% IntralipidTM dilution using a SCARA robot (Epson E2S351S) to cover a 37x37 and 45x45 matrix of grid points in the imaging plane within the 1 cm path length sample cuvette. At each grid point, a one-dimensional point-spread distribution was collected and system contrast and resolution were measured. Then, the robot was used to rotate the target to collect projection images at several projection angles of various objects, and reconstructed with a filtered back projection and an iterative reconstruction algorithm.

Ng, Eldon; Vasefi, Fartash; Kaminska, Bozena; Chapman, Glenn H.; Carson, Jeffrey J. L.

2010-02-01

52

ATLAS CONSTRUCTION FROM HIGH ANGULAR RESOLUTION DIFFUSION IMAGING DATA REPRESENTED BY GAUSSIAN MIXTURE FIELDS  

PubMed Central

Groupwise image registration is an essential part of atlas construction which is a very import and challenging task in medical image analysis. In this paper, we present a novel atlas construction technique using a groupwise registration of high angular resolution diffusion (MR) imaging datasets each of which is represented by a Gaussian Mixture field. To solve the registration problem, an L2 distance is used to measure the similarity between two Gaussian Mixtures, which leads to an energy function whose gradient can be computed in closed form. A projection method is developed to construct a “sharp” (not blurred) atlas from the result of this groupwise registration. Synthetic and real data experiments are presented to demonstrate the efficacy of the proposed method.

Cheng, Guang; Hwang, Min-Sig; Howland, Dena; Forder, John R.

2011-01-01

53

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

PubMed Central

Comparison of high angular resolution diffusion imaging (HARDI) measurements between subjects or between time points for the same subject are facilitated by spatial normalization. In this work, an algorithm is 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 is tested using simulated data, and intra-subject and inter-subject normalization of in vivo human data. All cases demonstrate reliable transformation of the FOD. This technique makes it possible to compare the intra-voxel fiber distribution between subjects, between groups, or between time points for a single subject, which will be helpful in HARDI studies of white matter disease.

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

2009-01-01

54

Acceptance and Angular Resolution of an Infill Array for the Pierre Auger Surface Detector  

SciTech Connect

The Pierre Auger Observatory has been designed to study the highest-energy cosmic rays in nature (E {>=} 1019 eV). The determination of their arrival direction, energy and composition is performed by the analysis of the atmospheric showers they produce. The Auger Surface Array will consist of 1600 water Cerenkov detectors placed in an equilateral triangular grid of 1.5 km. In this paper we show how adding a ''small'' area of surface detectors at half the above mentioned spacing would make it possible to lower the detection threshold by one order of magnitude, thus allowing the Observatory to reach lower energies where the cross-over from galactic to extragalactic sources is expected. We also analyze the angular resolution that can be attained with such an infill array.

Medina, C. [Tandar Laboratory (CAC - CNEA), Buenos Aires (Argentina); Gomez Berisso, M.; Allekotte, I. [I. Balseiro and Centro Atomico Bariloche (CNEA), Bariloche (Argentina); Etchegoyen, A.; Supanitsky, D. [Tandar Laboratory (CAC - CNEA), Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Medina-Tanco, G. [I. Astronomico e Geofisico, Univ. de Sao Paulo, Sao Paulo (Brazil)

2007-02-12

55

Coexistence of Near-Field and Far-Field Sources: the Angular Resolution Limit  

NASA Astrophysics Data System (ADS)

Passive source localization is a well known inverse problem in which we convert the observed measurements into information about the direction of arrivals. In this paper we focus on the optimal resolution of such problem. More precisely, we propose in this contribution to derive and analyze the Angular Resolution Limit (ARL) for the scenario of mixed Near-Field (NF) and Far-Field (FF) Sources. This scenario is relevant to some realistic situations. We base our analysis on the Smith's equation which involves the Cramér-Rao Bound (CRB). This equation provides the theoretical ARL which is independent of a specific estimator. Our methodology is the following: first, we derive a closed-form expression of the CRB for the considered problem. Using these expressions, we can rewrite the Smith's equation as a 4-th order polynomial by assuming a small separation of the sources. Finally, we derive in closed-form the analytic ARL under or not the assumption of low noise variance. The obtained expression is compact and can provide useful qualitative informations on the behavior of the ARL.

Boyer, Rémy; El Korso, Mohammed Nabil; Renaux, Alexandre; Marcos, Sylvie

2013-10-01

56

Angular resolution in magnification radiography and the observation of x-ray wave interaction signatures.  

PubMed

High resolution x-ray imaging studies have demonstrated significant radiographic contrast enhancements that are attributed to wave interactions within the sample. This paper reviews diffraction and refraction in the context of medical radiography, describing signatures produced by each process and the necessary experimental conditions for observing them. The concept of angular resolution is introduced and applied to current x-ray source and detector configurations, testing their ability to record these features. It is difficult to record interference patterns arising from refractive phase shifts because their formation requires a mono-energetic beam. The refraction of x-rays across boundaries, as described by Snell's law, produces strong contrast enhancements when they are struck at close to the glancing incidence. Deflections are proportional to the change in electron density (at energies above the K-edge) and square root of the wavelength, so they can be observed with a poly-energetic beam. Diffraction can also be observed with white radiation, but produce fringes with far narrower separation under the same irradiation conditions. In both cases, the observation of wave interaction signatures requires a propagation distance between the sample and detector, and selection of an appropriate geometric magnification, which can be estimated using a simple model presented here. PMID:17762079

Midgley, S

2007-08-09

57

A balloon-borne coded aperture telescope for ARC-minute angular resolution at hard X-ray energies  

Microsoft Academic Search

We describe the development of a new balloon-borne telescope known as MARGIE (Minute-of-Arc Resolution Gamma ray Imaging Experiment). It is a coded aperture telescope designed to image photons (in various configurations) over the 20–600 keV range with an angular resolution approaching 1?. MARGIE will use one (or both) of two different detection plane technologies. One such technology involves the use

J. Ryan; V. Boykin; R. M. Kippen; K. Larson; J. Macri; M. Mayer; M. McConnell; P. Altice; M. L. Cherry; S. B. Ellison; B. Price; T. G. Guzik; R. Lockwood; M. B. Barakat; K. Johnston; N. Zotov; M. Elaasar

1998-01-01

58

Balloon-borne coded aperture telescope for arc-minute angular resolution at hard x-ray energies  

Microsoft Academic Search

We are working on the development of a new balloon-borne telescope, MARGIE (minute-of-arc resolution gamma ray imaging experiment). It will be a coded aperture telescope designed to image hard x-rays (in various configurations) over the 20 - 600 keV range with an angular resolution approaching one arc minute. MARGIE will use one (or both) of two different detection plane technologies,

Mark L. McConnell; Valerie Boykin; R. N. Kippen; K. Larson; John R. Macri; Michelle Mayer; James M. Ryan; Peter P. Altice; Michael L. Cherry; Steven B. Ellison; B. Price; T. Gregory Guzik; R. Lockwood; M. B. Barakat; K. Johnston; N. Zotov; M. Elaasar

1996-01-01

59

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

60

Instrument for underwater high-angular resolution volume scattering function measurements  

NASA Astrophysics Data System (ADS)

A prototype instrument for in situ measurements of the volume scattering function (VSF) and the beam attenuation of water has been built and tested in the EOO laboratory. The intended application of the instrument is the enhancement of Navy operational optical systems for finding and imaging underwater objects such as mines. A description of the apparatus that was built and preliminary laboratory data will be presented. The instrument measures the VSF, (beta) ((theta) ), near the optical axis in both the forward and back directions from approximately 0.2 degrees off axis to approximately 5 degrees in 0.1 degree steps and at side angles of 45 degrees, 90 degrees, and 135 degrees. A diode- pumped, frequency-doubled, Nd:YAG laser provides the 532 nm light. This is the most used wavelength for underwater optical systems. The forward and back scattered light is collected and focused to a plane where scattering angles in the water are mapped onto concentric rings. At this focal plane, a conical reflector compresses the annular optical data onto a line along the cone axis where it is read by a MOS linear image array providing over 500 separate angular measurements. The beam attenuation coefficient, c, is also measured by means of a unique dual path configuration.

Dueweke, Paul W.; Bolstad, Jay; Leonard, Donald A.; Sweeney, Harold E.; Boyer, Philip A.; Winkler, Erik M.

1997-02-01

61

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

62

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

PubMed

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

Hénault, François

2010-03-01

63

Exploring AGNs in the Local Universe through High Angular Resolution Spectroscopy and Optical Variability Monitoring  

NASA Astrophysics Data System (ADS)

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

Walsh, Jonelle L.

64

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

NASA Astrophysics Data System (ADS)

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

Schödel, Rainer

2009-01-01

65

Measurements of X-ray photoelectron diffraction using high angular resolution and high transmission electron energy analyzer  

Microsoft Academic Search

We have developed an angle-resolving electron energy analyzer with a newly designed input-lens system. In this lens system, angle resolving is accomplished by use of a diffraction-plane aperture. Using this system, both high angular resolution (<0.1°) and high transmission are easily achieved in photoelectron diffraction measurements. In order to evaluate this analyzer, we measured the X-ray photoelectron diffraction (XPED) patterns

S. Shiraki; H Ishii; M Amano; Y Nihei; M Owari; C Oshima; T Koshikawa; R Shimizu

2001-01-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

67

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

68

High angular resolution studies of the structure and evolution of protoplanetary disks  

NASA Astrophysics Data System (ADS)

Young stars are surrounded by massive, rotating disks of dust and gas, which supply a reservoir of material that may be incorporated into planets or accreted onto the central star. In this dissertation, I use high angular resolution observations at a range of wavelengths to understand the structure, ubiquity, and evolutionary timescales of protoplanetary disks. First, I describe a study of Class I protostars, objects believed to be at an evolutionary stage between collapsing spherical clouds and fully-assembled young stars surrounded by protoplanetary disks. I use a Monte Carlo radiative transfer code to model new 0.9 micron scattered light images, 1.3 mm continuum images, and broadband spectral energy distributions. This modeling shows that Class I sources are probably surrounded by massive protoplanetary disks embedded in massive infalling envelopes. For the best-fitting models of the circumstellar dust distributions, I determine several important properties, including envelope and disk masses, mass infall rates, and system inclinations, and I use these results to constrain the evolutionary stage of these objects. Second, I discuss observations of the innermost regions of more evolved disks around T Tauri and Herbig Ae/Be stars, obtained with the Palomar Testbed and Keck Interferometers. I constrain the spatial and temperature structure of the circumstellar material at sub-AU radii, and demonstrate that lower-mass staers are surrounded by inclined disks with puffed-up inner edges 0.1-1 AU from the star. In contrast, the truncated inner disks around more massive stars may not puff-up, indicating that disk structure depends on stellar properties. I discuss the implications of these results for disk accretion, terrestrial planet formation and giant planet migration. Finally, I put these detailed studies of disk structure into a broader context by constraining the mass distribution and evolutionary timescales of circumstellar disks. Using the Owens Valley Millimeter Array, I mapped the millimeter continuum emission toward >300 low-mass stars in the NGC 2024 and Orion Nebula clusters. These observations demonstrate that the average disk mass in each cluster is comparable to the "minimum-mass protosolar nebula", and that there may be disk evolution on one million year timescales.

Eisner, Joshua A.

69

Improving angular resolution with Scan-MUSIC algorithm for real complex targets using 35-GHz millimeter-wave radar  

NASA Astrophysics Data System (ADS)

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

Ly, Canh

2004-08-01

70

Characterization of anisotropy in high angular resolution diffusion-weighted MRI  

Microsoft Academic Search

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

Lawrence R. Frank

2002-01-01

71

A High Angular Resolution Multiplicity Survey of the Open Clusters ? Persei and Praesepe  

NASA Astrophysics Data System (ADS)

Two hundred forty-two members of the Praesepe and ? Persei clusters have been surveyed with high angular resolution 2.2 ?m speckle imaging on the 3 m Infrared Telescope Facility, the 5 m Hale, and the 10 m Keck telescopes, along with direct imaging using the near-infrared camera (NICMOS) aboard the Hubble Space Telescope. The observed stars range in spectral type from B (~5 Msolar) to early M (~0.5 Msolar), with the majority of the targets more massive than ~0.8 Msolar. The one quadruple and 39 binary systems detected encompass separations from 0.053" to 7.28" 28 of the systems are new detections, and there are nine candidate substellar companions. The results of the survey are used to test binary star formation and evolution scenarios and to investigate the effects of companion stars on X-ray emission and stellar rotation. The main results are as follows:1. Over the projected separation range of 26 to 581 AU and magnitude differences of ?K<4.0 (comparable to mass ratios q=Msec/Mprim>0.25), the companion-star fraction (CSF) for ? Per is 0.09+/-0.03, and that for Praesepe is 0.10+/-0.03. This fraction is consistent with the field G dwarf value, implying that there is not a systematic decline in multiplicity with age at these separations on timescales of a few times 107 yr. The combination of previous spectroscopic work and the current cluster survey results in a cluster binary separation distribution that peaks at 4+1-1.5 AU, a significantly smaller value than the peaks of both the field G dwarf and the nearby T Tauri distributions. If the field G dwarf distribution represents a superposition of distributions from the populations that contributed to the field, then the data imply that ~30% of field binaries formed in dark clouds like the nearby T Tauri stars and the remaining ~70% formed in denser regions.2. An exploration of the binary star properties reveals a cluster CSF that increases with decreasing target mass, and a cluster mass ratio distribution that rises more sharply for higher mass stars but is independent of binary separation. These observational trends are consistent with several models of capture in small clusters and simulations of accretion following fragmentation in a cluster environment. Other types of capture and fragmentation are either inconsistent with these data or currently lack testable predictions.3. Among the cluster A stars, there is a higher fraction of binaries in the subset with X-ray detections, consistent with the hypothesis that lower mass companions are the true source of X-ray emission.4. Finally, in the younger cluster ? Per, the rotational velocities for solar-type binaries with separations less than 60 AU are significantly higher than those of wider systems. This suggests that companions may critically affect the rotational evolution of young stars.

Patience, J.; Ghez, A. M.; Reid, I. N.; Matthews, K.

2002-03-01

72

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

73

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): High Angular Resolution in the Far-Infrared  

NASA Astrophysics Data System (ADS)

Astronomical studies at infrared wavelengths have dramatically improved our understanding of the universe, and observations with Spitzer, Herschel, and SOFIA will continue to provide exciting new discoveries. The relatively low angular resolution of these missions, however, is insufficient to resolve the physical scale 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 - a powerful tool for scientific discovery. We are building the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII), an eight-meter baseline Michelson stellar interferometer to fly on a high-altitude balloon. BETTII's spectral-spatial capability, provided by an instrument using double-Fourier techniques, will address key questions about the nature of disks in young star clusters and active galactic nuclei and the envelopes of evolved stars. BETTII will also lay the technological groundwork for future balloon programs, paving the way for interferometric observations of exoplanets.

Rinehart, Stephen

2011-01-01

74

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

75

Approximated electron repulsion integrals: Cholesky decomposition versus resolution of the identity methods.  

PubMed

We compare two procedures to gain efficiency by approximating two-electron integrals in molecular electronic structure calculations. The first one is based on a Cholesky decomposition (CD) of two-electron integrals, the second one on the use of preoptimized auxiliary or fitting basis sets employed in a "resolution of the identity" (RI) technique. We present and test auxiliary bases for approximating the Coulomb term, which further improves accuracy over previously proposed fitting bases. It is shown that RI methods lead to insignificant errors only, which are partly comparable to or even better than that of CD treatments; but RI procedures are superior in speed. CD methods have certain advantages, however, particularly for extended basis sets. PMID:19405560

Weigend, Florian; Kattannek, Marco; Ahlrichs, Reinhart

2009-04-28

76

Approximated electron repulsion integrals: Cholesky decomposition versus resolution of the identity methods  

NASA Astrophysics Data System (ADS)

We compare two procedures to gain efficiency by approximating two-electron integrals in molecular electronic structure calculations. The first one is based on a Cholesky decomposition (CD) of two-electron integrals, the second one on the use of preoptimized auxiliary or fitting basis sets employed in a ``resolution of the identity'' (RI) technique. We present and test auxiliary bases for approximating the Coulomb term, which further improves accuracy over previously proposed fitting bases. It is shown that RI methods lead to insignificant errors only, which are partly comparable to or even better than that of CD treatments; but RI procedures are superior in speed. CD methods have certain advantages, however, particularly for extended basis sets.

Weigend, Florian; Kattannek, Marco; Ahlrichs, Reinhart

2009-04-01

77

The polarized emission from the galactic plane at arcminute angular resolution  

Microsoft Academic Search

As part of the Canadian Galactic Plane Survey (CGPS) we have imaged the polarized emission from the plane of the Milky Way at 1420 MHz, covering 1200 square degrees with arc-minute resolution. Structure on all scales is represented by combining aperture-synthesis data with single-antenna data. The survey depicts the Magneto-Ionic Medium at a resolution that matches images of other components

Tom L. Landecker; W. Reich; R. I. Reid; P. Reich; M. Wolleben; R. Kothes; D. Del Rizzo; B. Uyaniker; A. D. Gray; E. Fürst; A. R. Taylor; R. Wielebinski

2009-01-01

78

Explicit, approximate expressions for the resolution and a posteriori covariance of massive tomographic systems  

NASA Astrophysics Data System (ADS)

We present an approximate method to estimate the resolution, covariance and correlation matrix for linear tomographic systems Ax=b that are too large to be solved by singular value decomposition. An explicit expression for the approximate inverse matrix A^- is found using one-step backprojections on the Penrose condition AA^- ~ I, from which we calculate the statistical properties of the solution. The computation of A^- can easily be parallelized, each column being constructed independently. The method is validated on small systems for which the exact covariance can still be computed with singular value decomposition. Though A^- is not accurate enough to actually compute the solution x, the qualitative agreement obtained for resolution and covariance is sufficient for many purposes, such as rough assessment of model precision or the reparametrization of the model by the grouping of correlating parameters. We present an example for the computation of the complete covariance matrix of a very large (69043 x 9610) system with 5.9 x 10^6 non-zero elements in A. Computation time is proportional to the number of non-zero elements in A. If the correlation matrix is computed for the purpose of reparametrization by combining highly correlating unknowns x_i, a further gain in efficiency can be obtained by neglecting the small elements in A, but a more accurate estimation of the correlation requires a full treatment of even the smaller A_ij. We finally develop a formalism to compute a damped version of A^-.

Nolet, Guust; Montelli, Raffaella; Virieux, Jean

1999-07-01

79

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

NASA Astrophysics Data System (ADS)

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 Mode, a star's interferometric fringes are tracked to determine its angular position relative to other stars in the detector's field of view. Using this method, a star's parallax, proper motion, and reflex motion can be measured with a precision of about 1 mas per observation, while multi-epoch observing programs have yielded astrometry with accuracies approaching 0.2 mas for objects as bright as V=3 or as faint as V=16.5. Transfer Mode observations repeatedly scan an object's interferometric fringes to achieve sub-mas sampling of the fringe morphology with high signal-to-noise (conceptually analogous to imaging with a 1 mas pixel array). Post-observation analysis allows the measurement of angular separation, position angle and relative brightness of binary components, or a determination of the angular size of an extended object. Close binary systems with V < 12 can be detected down to 7 mas, while systems as faint as V=15 can be characterized to 12 mas, provided the magnitude difference between the components is less than about 2. (Wider systems with magnitude differences as large as 3.5 can be resolved.) Both FGS observing modes can be utilized to derive the total and fractional masses of binary systems, and thus the mass-luminosity relationship of the binary components. The FGS have also been used to observe and characterize non-point source objects, including Mira variables, asteroids, and active galactic nuclei, yielding information on the structure of these objects on scales as small as 8 mas. The FGS also function as 40 Hz photometers, offering milli-magnitude precision for relative photometry at 1 second intervals (V=10), a capability which has allowed the FGS to study flare stars and stellar occultations by the Neptunian moon Triton. In this paper we present examples for each of these capabilities and compare FGS results to those of ground-based interferometers, astrometric observing facilities, and to HST's own WFPC2 imager. STScI invites you to consider using the FGS as a science instrument in Cycle 11.

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

2001-05-01

80

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

81

High-resolution energy analyzer with a large angular acceptance for photoelectron spectromicroscopy applications  

Microsoft Academic Search

A new design of an electrostatic electron energy analyzer is presented, that is characterized by a high energy resolution and a high efficiency of collection of photoelectrons originating from submicron areas. The analyzer uses an original low-aberration electrostatic mirror for collecting electrons, followed by a retarding hollow cylindrical lens and a hemispherical energy analyzer. Feasible modifications of the analyzer are

V. D. Belov; M. I. Yavor

2000-01-01

82

Auger-electron angular distributions calculated without the two-step approximation: Calculation of angle-resolved resonant Auger spectra of C2 H2  

NASA Astrophysics Data System (ADS)

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

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

2004-10-01

83

High angular resolution millimetre continuum observations and modelling of S140-IRS1  

NASA Astrophysics Data System (ADS)

We present high-resolution 1.3 mm continuum observations of the massive young stellar object S140-IRS1. S140-IRS1 is a disc wind prototype with elongated radio emission (PA ˜ 45°) perpendicular to the large-scale CO outflow in the region. The observations taken with the CARMA B array and the Submillimetre Array (SMA) compact configuration correspond to a spatial resolution of 0.3 and 3.0 arcsec, respectively. Complementary 2.7 and 3.5 mm data taken with OVRO in a compact configuration are also discussed. The deconvolved position angle for S140-IRS1 of 37° ±15° is compatible with a disc perpendicular to the main CO outflow and near-infrared monopolar reflection nebula. We have utilized two-dimensional axisymmetric radiative transfer modelling to interpret the millimetre wave emission from S140-IRS1. The model required the addition of a disc component, as the observed image, flux and visibilities cannot be represented solely by a dusty envelope with polar cavities. We report that the high-resolution image of S140-IRS1 is consistent with the interpretation of emission from a dust disc in a large-scale envelope with cleared bipolar cavities. Strong continuum emission is also detected in both SMA and OVRO maps from the previously discovered submillimetre source S140-SMM1 and from the infrared source S140-IRS3. Furthermore, S140-SMM1 is identified with maser sources whose proper motions are consistent with being the source of the outflow with position angle ˜20° previously associated by some authors with a second outflow created by S140-IRS1. Our findings are consistent with a disc wind interpretation of the radio emission for S140-IRS1 rather than that of a jet.

Maud, Luke T.; Hoare, Melvin G.; Gibb, Andy G.; Shepherd, Debra; Indebetouw, Rémy

2013-01-01

84

Atmospheric Phase Correction Using CARMA-PACS: High Angular Resolution Observations of the FU Orionis Star PP 13S*  

NASA Astrophysics Data System (ADS)

We present 0farcs15 resolution observations of the 227 GHz continuum emission from the circumstellar disk around the FU Orionis star PP 13S*. The data were obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) Paired Antenna Calibration System (C-PACS), which measures and corrects the atmospheric delay fluctuations on the longest baselines of the array in order to improve the sensitivity and angular resolution of the observations. A description of the C-PACS technique and the data reduction procedures are presented. C-PACS was applied to CARMA observations of PP 13S*, which led to a factor of 1.6 increase in the observed peak flux of the source, a 36% reduction in the noise of the image, and a 52% decrease in the measured size of the source major axis. The calibrated complex visibilities were fitted with a theoretical disk model to constrain the disk surface density. The total disk mass from the best-fit model corresponds to 0.06 M sun, which is larger than the median mass of a disk around a classical T Tauri star. The disk is optically thick at a wavelength of 1.3 mm for orbital radii less than 48 AU. At larger radii, the inferred surface density of the PP 13S* disk is an order of magnitude lower than that needed to develop a gravitational instability.

Pérez, Laura M.; Lamb, James W.; Woody, David P.; Carpenter, John M.; Zauderer, B. Ashley; Isella, Andrea; Bock, Douglas C.; Bolatto, Alberto D.; Carlstrom, John; Culverhouse, Thomas L.; Joy, Marshall; Kwon, Woojin; Leitch, Erik M.; Marrone, Daniel P.; Muchovej, Stephen J.; Plambeck, Richard L.; Scott, Stephen L.; Teuben, Peter J.; Wright, Melvyn C. H.

2010-11-01

85

Using high angular resolution diffusion imaging data to discriminate cortical regions.  

PubMed

Brodmann's 100-year-old summary map has been widely used for cortical localization in neuroscience. There is a pressing need to update this map using non-invasive, high-resolution and reproducible data, in a way that captures individual variability. We demonstrate here that standard HARDI data has sufficiently diverse directional variation among grey matter regions to inform parcellation into distinct functional regions, and that this variation is reproducible across scans. This characterization of the signal variation as non-random and reproducible is the critical condition for successful cortical parcellation using HARDI data. This paper is a first step towards an individual cortex-wide map of grey matter microstructure, The gray/white matter and pial boundaries were identified on the high-resolution structural MRI images. Two HARDI data sets were collected from each individual and aligned with the corresponding structural image. At each vertex point on the surface tessellation, the diffusion-weighted signal was extracted from each image in the HARDI data set at a point, half way between gray/white matter and pial boundaries. We then derived several features of the HARDI profile with respect to the local cortical normal direction, as well as several fully orientationally invariant features. These features were taken as a fingerprint of the underlying grey matter tissue, and used to distinguish separate cortical areas. A support-vector machine classifier, trained on three distinct areas in repeat 1 achieved 80-82% correct classification of the same three areas in the unseen data from repeat 2 in three volunteers. Though gray matter anisotropy has been mostly overlooked hitherto, this approach may eventually form the foundation of a new cortical parcellation method in living humans. Our approach allows for further studies on the consistency of HARDI based parcellation across subjects and comparison with independent microstructural measures such as ex-vivo histology. PMID:23691102

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

2013-05-17

86

MUSTANG HIGH ANGULAR RESOLUTION SUNYAEV-ZEL'DOVICH EFFECT IMAGING OF SUBSTRUCTURE IN FOUR GALAXY CLUSTERS  

SciTech Connect

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

Korngut, P. M.; Dicker, S. R.; Reese, E. D.; Devlin, M. J.; Mroczkowski, T. [Department of Physics and Astronomy, University of Pennsylvania, 209 S. 33rd St., Philadelphia, PA 19104 (United States); Mason, B. S. [National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903 (United States); Sarazin, C. L.; Sun, M. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Sievers, J., E-mail: pkorngut@physics.upenn.edu [Canadian Institute of Theoretical Astrophysics, 60 St. George Street, Toronto, Ontario M5S 3H8 (Canada)

2011-06-10

87

Achieving diffraction-limited angular resolutions in the optical through speckle stabilization  

NASA Astrophysics Data System (ADS)

I present results from a new observational technique for ground-based astronomy called speckle stabilization. This technique is similar to other speckle-based techniques and is capable of producing diffraction-limited images in the optical, but has the added advantage of being able to employ an integral field spectrograph. Performance simulations show that a speckle stabilization system on a 10-meter class telescope should be capable of achieving resolutions as fine as 15 milliarcseconds in the optical. I also show that guide stars can be as faint as 16th magnitude and be located up to 30 arcseconds away. I present the design, fabrication and assembly of a prototype instrument the Stabilized sPeckle Integral Field Spectrograph Proof of Concept (SPIFS-POC) and describe the algorithms and programming necessary to control such a system and discuss optimization efforts. I compare speckle stabilization to other methods, including lucky imaging, and find that in certain circumstances, speckle stabilization is able to match or even outperform lucky imaging by up to a factor of 3 in signal-to-noise. Finally, this dissertation also covers the scientific gains speckle stabilization should be able to achieve. In particular, I address impacts on research in the field of super-massive black holes and demonstrate that the technique will fill an important niche in detecting the kinematic influence of SMBH on their host galaxies, aiding in the detection of the highest and lowest mass SMBH.

Keremedjiev, Mark Stanley

88

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

SciTech Connect

The authors present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3--0.5 resolution from 4.7 {micro}m to 22 {micro}m. The young stellar objects designed infrared source n and radio source I are believed to dominate the BN/KL region. They have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L{sub {center_dot}}. Although source I is believed to be more luminous, they do not detect an infrared counterpart even at the longest wavelengths. However, they resolve the closeby infrared source, IRc2, into an arc of knots {approx} 10{sup 3} AU long at all wavelengths. Although the physical relation of source I to IRc2 remains ambiguous, they suggest these sources mark a high density core (10{sup 7}-10{sup 8} pc{sup -3} over {approx} 10{sup 3} AU) within the larger BN/KL star forming cluster. The high density may be a consequence of the core being young and heavily embedded. The authors suggest the energetics of the BN/KL region may be dominated by this cluster core rather than one or two individual sources.

greenhill, l

2004-06-25

89

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

NASA Astrophysics Data System (ADS)

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

Boyle, Latham; Pen, Ue-Li

2012-12-01

90

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

91

An automated strategy for the delineation and parcellation of commissural pathways suitable for clinical populations utilising high angular resolution diffusion imaging tractography  

Microsoft Academic Search

There is a growing interest in understanding alterations to the interhemispheric transfer of information as a result of brain injury and neurological disease. To facilitate research, we have developed a fully automated method for the accurate extraction of commissural pathways (corpus callosum (CC) and anterior commissure (AC)) and functional parcellation of the CC using a high angular resolution diffusion imaging

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

2010-01-01

92

Fiber Tractography Based on Diffusion Tensor Imaging Compared With High-Angular-Resolution Diffusion Imaging With Compressed Sensing: Initial Experience  

PubMed Central

Background The most frequently used method for fiber tractography based on diffusion tensor imaging (DTI) is associated with restrictions in the resolution of crossing or kissing fibers and in the vicinity of tumor or edema. Tractography based on high-angular-resolution diffusion imaging (HARDI) is capable of overcoming this restriction. With compressed sensing (CS) techniques, HARDI acquisitions with a smaller number of directional measurements can be used, thus enabling the use of HARDI-based fiber tractography in clinical practice. Objective To investigate whether HARDI+CS-based fiber tractography improves the display of neuroanatomically complex pathways and in areas of disturbed diffusion properties. Methods Six patients with gliomas in the vicinity of language-related areas underwent 3-T magnetic resonance imaging including a diffusion-weighted data set with 30 gradient directions. Additionally, functional magnetic resonance imaging for cortical language sites was obtained. Fiber tractography was performed with deterministic streamline algorithms based on DTI using 3 different software platforms. Additionally, tractography based on reconstructed diffusion signals using HARDI+CS was performed. Results HARDI+CS-based tractography displayed more compact fiber bundles compared with the DTI-based results in all cases. In 3 cases, neuroanatomically plausible fiber bundles were displayed in the vicinity of tumor and peritumoral edema, which could not be traced on the basis of DTI. The curvature around the sylvian fissure was displayed properly in 6 cases and in only 2 cases with DTI-based tractography. Conclusion HARDI+CS seems to be a promising approach for fiber tractography in clinical practice for neuroanatomically complex fiber pathways and in areas of disturbed diffusion, overcoming the problem of long acquisition times.

Kuhnt, Daniela; Bauer, Miriam H.A.; Egger, Jan; Richter, Mirco; Kapur, Tina; Sommer, Jens; Merhof, Dorit; Nimsky, Christopher

2013-01-01

93

ESTIMATING SMALL ANGULAR SCALE COSMIC MICROWAVE BACKGROUND ANISOTROPY WITH HIGH-RESOLUTION N-BODY SIMULATIONS: WEAK LENSING  

SciTech Connect

We estimate the impact of weak lensing by strongly nonlinear cosmological structures on the cosmic microwave background. Accurate calculation of large l multipoles requires N-body simulations and ray-tracing schemes with both high spatial and temporal resolution. To this end, we have developed a new code that combines a gravitational Adaptive Particle-Particle, Particle-Mesh solver with a weak-lensing evaluation routine. The lensing deviations are evaluated while structure evolves during the simulation so that all evolution steps-rather than just a few outputs-are used in the lensing computations. The new code also includes a ray-tracing procedure that avoids periodicity effects in a universe that is modeled as a three-dimensional torus in the standard way. Results from our new simulations are compared with previous ones based on Particle-Mesh simulations. We also systematically investigate the impact of box volume, resolution, and ray-tracing directions on the variance of the computed power spectra. We find that a box size of 512 h {sup -1} Mpc is sufficient to provide a robust estimate of the weak-lensing angular power spectrum in the l-interval (2000-7000). For a reaslistic cosmological model, the power [l(l + 1)C{sub l}/2pi]{sup 1/2} takes on values of a few muK in this interval, which suggests that a future detection is feasible and may explain the excess power at high l in the Berkeley-Illinois-Maryland Association and Cosmic Background Imager observations.

Fullana, M. J. [Institut de Matematica Multidisciplinaria, Universitat Politecnica de Valencia, 46022 Valencia (Spain); Arnau, J. V. [Departamento de Matematica Aplicada, Universidad de Valencia, 46100 Burjassot, Valencia (Spain); Thacker, R. J. [Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scotia, B3H 3C3 (Canada); Couchman, H. M. P. [Department of Physics and Astronomy, McMaster University, 1280 Main St. West, Hamilton, Ontario, L8S 4M1 (Canada); Saez, D., E-mail: diego.saez@uv.e [Departamento de AstronomIa y Astrofisica, Universidad de Valencia, 46100 Burjassot, Valencia (Spain)

2010-03-20

94

A Nonparametric Riemannian Framework for Processing High Angular Resolution Diffusion Images and its Applications to ODF-based Morphometry  

PubMed Central

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

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

2011-01-01

95

Contrast and phase closure acquisitions in photon counting regime using a frequency upconversion interferometer for high angular resolution imaging  

NASA Astrophysics Data System (ADS)

In the context of new generation instruments for astronomical interferometer, we have developed in laboratory a new kind of optical interferometer using the frequency conversion of the star light. We investigate the sensitivity limit and reliability of our so-called upconversion interferometer when operating in photon counting mode. For this purpose, we have implemented a laboratory test bench including two three-arm interferometers dedicated to high angular resolution imaging. The first classical one works at the same wavelength as the laboratory star (infrared) and operates with high optical flux levels (used as a reference interferometer). The second one, under test, uses sum frequency generation process in a non-linear optical waveguide placed on each arm to shift the wavelength of the infrared laboratory star to the visible domain. The observables are obtained in photon counting operation, involving signal processing to recover unbiased data. The reference measurement (high flux complex visibilities in infrared) and the upconversion interferometer observables (complex visibilities obtained in photon counting regime) are in good agreement. We notice a degradation on the phase closure terms reliability for low values of the triple product (bispectrum). We estimate from the experimental results the related limiting magnitude for several configurations using an upconversion interferometer.

Ceus, D.; Delage, L.; Grossard, L.; Reynaud, F.; Herrmann, H.; Sohler, W.

2013-04-01

96

A BEA Science Program: A High Angular Resolution Survey of Some of the Galaxy's Most Massive Stars  

NASA Astrophysics Data System (ADS)

We propose to make optimal use of otherwise unused telescope time while HST's pointing is restricted to the BEA cone during the first 12 days of SMOV3B. A launch date of Feb 28 places two of the Galaxy's most active star forming regions, Trumplers 14 & 16 in the Carina Nebula, within the BEA for the entire 12 day period. We propose to use FGS1r to conduct a high angular resolution survey of the most massive and luminous stars in these two magnificent clusters to establish the incidence of binarity at the high mass end of the HR diagram. This survey will close the detection gap between spectroscopic and speckle surveys in which duplicity can be concealed. This will dramatically improve our knowledge of the IMF at the high mass end of the main sequence as well as the luminosity function {LF} of star forming regions which produce such high mass stars. Finally, this survey will identify targets for an approved SIM Key Science project to dynamically determine O-star masses. This proposal also benefits SMOV3B. The data from these observations will sensitively monitor the jitter, if any, induced by the NCS cool down. This might prove valuable for future reference if the NCS ever needs to be recyled.

Nelan, Edmund

2001-07-01

97

Vibrational configuration interaction using a tiered multimode scheme and tests of approximate treatments of vibrational angular momentum coupling: a case study for methane.  

PubMed

We present vibrational configuration interaction calculations employing the Watson Hamiltonian and a multimode expansion. Results for the lowest 36 eigenvalues of the zero total angular momentum rovibrational spectrum of methane agree with the accurate benchmarks of Wang and Carrington to within a mean unsigned deviation of 0.68, 0.033, and 0.014 cm(-1) for 4-mode, 5-mode, and 6-mode representations, respectively. We note that in the case of the 5-mode results, this is a factor of 10 better agreement than for 5-mode calculations reported earlier by Wu, Huang, Carter, and Bowman for the same set of eigenvalues, which indicates that the multimode expansion is even more rapidly convergent than previously demonstrated. Our largest calculations employ a tiered approach with matrix elements treated using a variable-order multimode expansion with orders ranging from 4-mode to 7-mode; strategies for assigning matrix elements to particular multimode tiers are discussed. Improvements of 7-mode coupling over 6-mode coupling are small (averaging 0.002 cm(-1) for the first 36 eigenvalues) suggesting that 7-mode coupling is sufficient to fully converge the results. A number of approximate treatments of the computationally expensive vibrational angular momentum terms are explored. The use of optimized vibrational quadratures allows rapid integration of the matrix elements, especially the vibrational angular momentum terms, which require significantly fewer quadrature points than are required to integrate the potential. We assign the lowest 243 states and compare our results to those of Wang and Carrington, who provided assignments for the same set of states. Excellent agreement is observed for most states, but our results are lower for some of the higher-energy states by as much as 20 cm(-1), with the largest deviations being for the states with six quanta of excitation in the F2 bends, suggesting that the earlier results were not fully converged with respect to the basis set. We also provide corrections to several of the state assignments published previously. PMID:23565728

Mielke, Steven L; Chakraborty, Arindam; Truhlar, Donald G

2013-04-30

98

Angular Acceleration  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2008-02-19

99

An emission-potential multislice approximation to simulate thermal diffuse scattering in high-resolution transmission electron microscopy.  

PubMed

Thermal diffuse scattered electrons significantly contribute to high-resolution transmission electron microscopy images. Their intensity adds to the background and is peaked at positions of atomic columns. In this paper we suggest an approximation to simulate intensity of thermal diffuse scattered electrons in plane-wave illumination transmission electron microscopy using an emission-potential multislice algorithm which is computationally less intensive than the frozen lattice approximation or the mutual intensity approach. Intensity patterns are computed for Au and InSb for different crystal orientations. These results are compared with intensities from the frozen lattice approximation based on uncorrelated vibration of atoms as well as with the frozen phonon approximation for Au. The frozen phonon method uses a detailed phonon model based on force constants we computed by a density functional theory approach. The comparison shows that our suggested emission-potential method is in close agreement with both the frozen lattice and the frozen phonon approximations. PMID:18514420

Rosenauer, Andreas; Schowalter, Marco; Titantah, John T; Lamoen, Dirk

2008-04-20

100

Photoelectron angular distributions from autoionizing 4s¹4p?6p¹ states in atomic krypton probed with femtosecond time resolution.  

PubMed

Photoelectron angular distributions (PADs) are obtained for a pair of 4s(1)4p(6)6p(1) (a singlet and a triplet) autoionizing states in atomic krypton. A high-order harmonic pulse is used to excite the pair of states and a time-delayed 801 nm ionization pulse probes the PADs to the final 4s(1)4p(6) continuum with femtosecond time resolution. The ejected electrons are detected with velocity map imaging to retrieve the time-resolved photoelectron spectrum and PADs. The PAD for the triplet state is inherently separable by virtue of its longer autoionization lifetime. Measuring the total signal over time allows for the PADs to be extracted for both the singlet state and the triplet state. Anisotropy parameters for the triplet state are measured to be ?(2)=0.55 ± 0.17 and ?(4)=-0.01 ± 0.10, while the singlet state yields ?(2)=2.19 ± 0.18 and ?(4)=1.84 ± 0.14. For the singlet state, the ratio of radial transition dipole matrix elements, X, of outgoing S to D partial waves and total phase shift difference between these waves, ?, are determined to be X=0.56 ± 0.08 and ?=2.19 ± 0.11 rad. The continuum quantum defect difference between the S and D electron partial waves is determined to be -0.15 ± 0.03 for the singlet state. Based on previous analyses, the triplet state is expected to have anisotropy parameters independent of electron kinetic energy and equal to ?(2)=5?7 and ?(4)=-12?7. Deviations from the predicted values are thought to be a result of state mixing by spin-orbit and configuration interactions in the intermediate and final states; theoretical calculations are required to quantify these effects. PMID:21384969

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

2011-03-01

101

Thin monolithic glass shells for future high angular resolution and large collecting area x-ray telescope  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

102

MILLIMETER AND SUBMILLIMETER HIGH ANGULAR RESOLUTION INTERFEROMETRIC OBSERVATIONS: DUST IN THE HEART OF IRAS 18162-2048  

SciTech Connect

The GGD27 complex includes the HH 80-81-80N system, which is one of the most powerful molecular outflows associated with a high-mass star-forming region observed to date. This outflow is powered by the star associated with the source IRAS 18162-2048. Here, we report on the detection of continuum emission at subarcsec/arcsec resolution with the Submillimeter Array (SMA) at 1.36 mm and 456 {mu}m, respectively. We detected dust emission arising from two compact cores, MM1 and MM2, separated by about 7'' ({approx}12,000 AU in projected distance). MM1 spatially coincides with the powerful thermal radio continuum jet that powers the very extended molecular outflow, while MM2 is associated with the protostar that drives the compact molecular outflow recently found in this region. High angular resolution observations at 1.36 mm show that MM1 is unresolved and that MM2 splits into two subcomponents separated by {approx}1''. The mass of MM1 is about 4 M{sub sun} and it has a size of {approx}<300 AU. This is consistent with MM1 being associated with a massive and dense (n(H{sub 2}) {approx}> 10{sup 9} cm{sup -3}) circumstellar dusty disk surrounding a high-mass protostar, which has not yet developed a compact H II region. On the other hand, the masses of the two separate components of MM2 are about 2 M{sub sun} each. One of these components is a compact core with an intermediate-mass young protostar inside and the other component is probably a prestellar core. MM1 is the brightest source at 1.36 mm, while MM2 dominates the emission at 456 {mu}m. These are the only (sub)millimeter sources detected in the SMA observations. Hence, it seems that both sources may contribute significantly to the bolometric luminosity of the region. Finally, we argue that the characteristics of these two sources indicate that MM2 is probably in an earlier evolutionary stage than MM1.

Fernandez-Lopez, M.; Curiel, S. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM), Apartado Postal 70-264, 04510 Mexico, DF (Mexico); Girart, J. M. [Institut de Ciencies de l'Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, Torre C5-parell 2, 08193 Bellaterra, Catalunya (Spain); Ho, P. T. P. [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Patel, N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gomez, Y., E-mail: manferna@gmail.com, E-mail: scuriel@astroscu.unam.mx, E-mail: girart@ieec.cat, E-mail: y.gomez@astrosmo.unam.mx [Centro de Radioastronomia y Astrofisica, UNAM, Apartado Postal 3-72, Morelia, Michoacan 58089 (Mexico)

2011-03-15

103

Photoelectron angular distributions from autoionizing 4s14p66p1 states in atomic krypton probed with femtosecond time resolution  

Microsoft Academic Search

Photoelectron angular distributions (PADs) are obtained for a pair of 4s14p66p1 (a singlet and a triplet) autoionizing states in atomic krypton. A high-order harmonic pulse is used to excite the pair of states and a time-delayed 801 nm ionization pulse probes the PADs to the final 4s14p6 continuum with femtosecond time resolution. The ejected electrons are detected with velocity map

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

2011-01-01

104

High Angular Resolution Radio Observations of a Coronal Mass Ejection Source Region at Low Frequencies during a Solar Eclipse  

NASA Astrophysics Data System (ADS)

We carried out radio observations of the solar corona in the frequency range 109-50 MHz during the annular eclipse of 2010 January 15 from the Gauribidanur Observatory, located about 100 km north of Bangalore in India. The radio emission in the above frequency range originates typically in the radial distance range ?1.2-1.5 R ? in the "undisturbed" solar atmosphere. Our analysis indicates that (1) the angular size of the smallest observable radio source (associated with a coronal mass ejection in the present case) is ?1' ± 0farcm3, (2) the source size does not vary with radial distance, (3) the peak brightness temperature of the source corresponding to the above size at a typical frequency like 77 MHz is ?3 × 109 K, and (4) the coronal magnetic field near the source region is ?70 mG.

Ramesh, R.; Kathiravan, C.; Barve, Indrajit V.; Rajalingam, M.

2012-01-01

105

Improving the angular resolution of EGRET and new limits on supersymmetric dark matter near the galactic center  

NASA Astrophysics Data System (ADS)

Using the EGRET data and an improved point source analysis, including an energy-dependent point spread function and an unbinned maximum likelihood technique, we have been able to place considerably lower limits on the ?-ray flux from the galactic center region. We also test this method on known sources, the Crab and Vela pulsars. In both cases, we find that our method improves the angular precision of EGRET data over the 3EG catalog. This new limit on ?-rays from the galactic center can be used to test models of annihilating supersymmetric dark matter and galactic halo profiles. We find that the present EGRET data can limit many supersymmetric models if the density of the galactic dark matter halo is cuspy or spiked toward the galactic center. We also discuss the ability of GLAST to test these models.

Hooper, D.; Dingus, B.

106

Intermediate-resolution spectroscopy of the radio galaxy B2 0902+34 at Z approximately equal 3.4  

NASA Astrophysics Data System (ADS)

We have carried out spectroscopic observations of the high-redshift (z approximately equal 3.4) radio galaxy 0902+34 at intermediate resolution with the William Herschel Telescope. The dynamical spectral ranges covered are 4600-5480 A and 5920-7680 A with resolutions of 5.4 and 9.5 A, respectively. We detect a continuum that is almost flat and also resolve three emission lines: Ly-alpha, C IV lambda(1549) and He II lambda(1640), the last one previously undetected. The line ratios are similar to the typical values found for narrow-line high-redshift radio galaxies. Line ratios observed in different regions of the galaxy seem to indicate the presence of strong ionization and/or dust density gradients. We have not detected any Ly-alpha absorption at z = 3.3968 (red wing of the Ly-alpha emission line) as might be expected from the absorption found at 21 cm by other authors using the Very Large Array (VLA) and Arecibo antennas. We discuss possible models for the H I absorbing cloud.

Martin-Mirones, J. M.; Martinez-Gonzalez, E.; Gonzalez-Serrano, J. I.; Sanz, J. L.

1995-02-01

107

Comparison of the angular resolution limit and SNR of the Space Hubble Telescope and the large ground-based telescopes  

Microsoft Academic Search

This paper compares and discusses the attempts to overcome the 'seeing' resolution limit imposed by spherical aberration for the Hubble Space Telescope and by atmospheric turbulences for the case of ground-based telescopes. From recently reposed experimental data it is shown that wavefront reconstruction algorithms are capable of restoring nearly fully the Hubble's spherical aberration of the primary mirror. Also from

D. Souilhac; D. Billerey

1991-01-01

108

Fast computation of molecular random phase approximation correlation energies using resolution of the identity and imaginary frequency integration.  

PubMed

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

Eshuis, Henk; Yarkony, Julian; Furche, Filipp

2010-06-21

109

Dynamical correlation in double excitations of helium studied by high-resolution and angular-resolved fast-electron energy-loss spectroscopy in absolute measurements.  

PubMed

The momentum transfer dependence of fundamental double excitation processes of helium is studied by absolute measurements using an angular resolved fast-electron energy loss spectrometer with high energy resolution. It elucidates the dynamical correlations, in terms of internal correlation quantum numbers, K, T, and A. The Fano profile parameters q, f(a), rho2, f, and S of doubly excited states (2)(1,0)+2 (1)S(e), (2)(1,0)+2 (1)D(e), and (2)(0,1)+2 (1)P(o) are reported as functions of momentum transfer K2. Qualitative analysis is given for the states of (2)(-1,0)+2 (1)S(e) and (2)(1,0)+2 (1)S(e). PMID:14611580

Liu, Xiao-jing; Zhu, Lin-fan; Yuan, Zhen-sheng; Li, Wen-bin; Cheng, Hua-dong; Huang, Yu-ping; Zhong, Zhi-ping; Xu, Ke-zun; Li, Jia-ming

2003-11-06

110

Ring-shaped cyclotron radiation source on the example of the NOAA 11140 active region according to high angular resolution observations  

NASA Astrophysics Data System (ADS)

Using observations with a high angular resolution of ˜1?, we reveal a cyclotron radiation source with a ring-shaped structure of the image. The source is located in the solar corona above the main spot of the NOAA 11140 active region. Observations were carried out during the solar eclipse of January 4, 2011, using two RT-32 radio telescopes that operated at wavelengths of 3.5, 6.2, and 13 cm and registered Stokes parameters I and V. The features of the structure are interpreted within the known theory of the cyclotron radio radiation of hot coronal plasma (2-4 MK) in the presence of the strong magnetic field of the sunspot (˜3 kG).

Korzhavin, A. N.; Peterova, N. G.; Topchilo, N. A.

2012-12-01

111

IMPLICATIONS OF A HIGH ANGULAR RESOLUTION IMAGE OF THE SUNYAEV-ZEL'DOVICH EFFECT IN RXJ1347-1145  

SciTech Connect

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

Mason, B. S.; Cotton, W. D. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Dicker, S. R.; Korngut, P. M.; Devlin, M. J.; Aguirre, J. E. [University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Koch, P. M.; Molnar, S. M. [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); Sievers, J. [The Canadian Institute of Theoretical Astrophysics, 60 St. George Street, Toronto, Ontario M5S 3H8 (Canada); Benford, D.; Staguhn, J. G.; Moseley, H. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Irwin, K. D. [National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80303 (United States); Ade, P., E-mail: bmason@nrao.ed [School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3AA (United Kingdom)

2010-06-10

112

Adaptive lobster-eye hard x-ray telescope with high-angular resolution and wide field of view  

Microsoft Academic Search

High-resolution, wide-field-of-view hard X-ray telescopes are essential for detecting and studying cosmic sources in the 10-100 keV photon energy band, which are typically inaccessible to conventional Wolter I X-ray telescopes. To focus such high-energy photons, we developed special Lobster-Eye optics consisting of multiple reflective channels with square cross sections, which are formed by intersecting two sets of semiconductor-grade gold-coated flat

Victor Grubsky; Michael Gertsenshteyn; Keith Shoemaker; Tomasz Jannson

2007-01-01

113

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

SciTech Connect

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

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

2012-01-10

114

A high angular resolution hard X-ray imager for the high energy detector on-board the Spectrum X-Gamma satellite  

NASA Astrophysics Data System (ADS)

Consideration is given to a new type of position-sensitive MultiWire Proportional Counter proposed as the high-energy instrument for the Spectrum X-Gamma Satellite. Two of them are based on high-throughput X-ray optics, sensitive up to about 20 keV. The third one, MART-LIME, is the high-energy instrument to cover the band 5-150 keV. This X-ray observatory-class orbiter comprises three major coaligned instruments. The scientific objective of this hard X-ray telescope is to produce sky images with arcmin angular resolution and good spectral resolution and submilliCrab sensitivity, during a typical observation time of 100,000 sec. The MART-LIME experiment is expected to produce a breakthrough in high-energy astrophysics by means of deep observations over a wide field of view. The missions are to produce a complete hard X-ray catalog, which is still nonexistent at the milliCrab sensitivity level.

Ubertini, P.; Bazzano, A.; Boccaccini, L.; Federici, M.; Frutti, M.; Gianni, G.; Manzan, M.; Patriarca, R.; Soggiu, M. E.; Ugazio, S.

1990-11-01

115

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

116

Attosecond angular streaking  

Microsoft Academic Search

Ultrashort measurement-time resolution is traditionally obtained in pump–probe experiments, for which two ultrashort light pulses are required; the time resolution is then determined by the pulse duration. But although pulses of subfemtosecond duration are available, so far the energy of these pulses is too low to fully implement the traditional pump–probe technique. Here, we demonstrate ‘attosecond angular streaking’, an alternative

Mathias Smolarski; Philip Schlup; Jens Biegert; André Staudte; Markus Schöffler; Harm G. Muller; Reinhard Dörner; Ursula Keller; Petrissa Eckle

2008-01-01

117

Spectroscopic studies on AGNs and High angular resolution in the NIR: The construction of an imaging beam combiner for the LBT  

NASA Astrophysics Data System (ADS)

The current thesis is divided into two projects. The first part deals with studies on active galaxies hosting an Active Galactic Nucleus (AGN). Specifically, an optical spectroscopic study of a nearby (z < 0.06) volume - limited sample of Low - Luminosity Quasi - Stellar Objects (LLQSOs) has been carried out. The sample has been drawn from the Hamburg/ESO QSO survey (HES), which has a well-defined flux limit of B_j < 17.3. The aim of the present project is to characterize the excitation degree of the sample, distinguish between possible star forming and Seyfert activity and to investigate the spectral characteristics of the sample. The spectroscopic data were analyzed and emission lines were fitted using a routine, which employs Levenberg - Marquardt least square minimization. The same analysis was also applied for some additional archival data from the 6 Degree Field Galaxy Survey (6dFGS). The objects of the LLQSOs sample are classified according to the classical optical diagnostic diagrams, based on optical emission lines close in wavelength, avoiding almost any impact of reddening. The diagrams provide a diagnosis of the ionizing source within a galaxy, hence activity between Hii, LINERs (Low Ionization Nuclear Emission-line Region), and Seyfert galaxies can be clearly distinguished. The classification of all members of the LLQSOs sample is shown in chapter 3. The broadness of the emission lines, cases with double components and the electron density are also analyzed. The comparison of the diagnostic diagrams between the two data sets (HES and 6DFGS) results in different classifications of most of the sources. This is due to the different spectroscopic techniques applied in the two data sets during the observations, and is sketched in chapter 4. Several galaxies at a variety of cosmological distances, with elliptical and circular morphologies, were simulated. In these simulations, different instruments (different spectroscopic techniques, i.e. slit, fiber) were applied to the galaxies, in order to ! study the instrumental effect (aperture effect). The impact of the aperture effect in local and high redshift universe is discussed in detail. The second project of the thesis focuses on the construction of an image beam combiner for the Large Binocular Telescope (LBT). The LINC - NIRVANA instrument will be operating in the near - infrared (1 - 2.4 ?m) and will provide a high angular resolution (~9 mas at 1.25 ?m) over a wide field of view (~100 arcsec at 1.25 ?m). A fundamental component of the instrument, the Fringe and Flexure Tracking System (FFTS) is responsible to ensure a complete and time-stable wavefront correction at the position of the science detector. This will allow for long integration times at interferometric angular resolutions. A historical overview and our current achievements are also discussed in chapter 5. Laboratory tests of specific parts of the FFTS are presented in chapter 6. Especially, the subparts of the Detector Positioning Unit (DPU), which has to be moved with respect to an altitude - azimuth mounting under vacuum conditions, are characterized. The tilting of the instrument as a function of elevation results in a flexure of the system that has to be corrected by an algorithm.

Tremou, Evangelia

2011-04-01

118

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

SciTech Connect

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

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

2010-07-10

119

Photoelectron angular distributions from autoionizing 4s14p66p1 states in atomic krypton probed with femtosecond time resolution  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

120

The Angular Momentum Distribution within Dark Matter Halos  

NASA Astrophysics Data System (ADS)

We study the angular momentum profile of dark matter halos for a statistical sample drawn from a set of high-resolution cosmological simulations of 2563 particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and the halos are selected to have at least 3× 104 particles in order to reliably measure the angular momentum profile. In contrast with the recent claims of Bullock et al. (2001), we find that the degree of misalignment of angular momentum within a halo is very high. About 50 percent of halos have more than 10 percent of halo mass in the mass of negative angular momentum j. After the mass of negative j is excluded, the cumulative mass function M(approximately the universal function proposed by Bullock et al. (2001), though we still find a significant fraction of halos (˜ 50%) which exhibit systematic deviations from the universal function. Our results, however, are broadly in good agreement with the recent work of van den Bosch et al. (2002). We also study the angular momentum profile of halos in a Warm Dark Matter (WDM) model and a Self-Interacting Dark Matter (SIDM) model. We find that the angular momentum profile of halos in the WDM is statistically indistinguishable from that in the CDM model, but the angular momentum of halos in the SIDM is reduced by the self-interaction of dark matter.

Chen, D.; Jing, Y.

121

An Evaluation of Exact and Approximate 3-D Reconstruction Algorithms for a High-Resolution, Small Animal PET Scanner  

Microsoft Academic Search

MicroPET is a low-cost, high resolution positron emission tomography (PET) scanner designed for imaging small animals. MicroPET operates exclusively without septa, acquiring fully three-dimensional (3-D) data sets. The performance of the projection-reprojection (3DRP), variable axial rebinning (VARB), single slice rebinning (SSRB), and Fourier rebinning (FORE) methods for reconstruction of microPET data were evaluated. The algorithms were compared with respect to

T. H. Farquhar; A. Chatziioannou; S. R. Cherry

1998-01-01

122

Transition moments and excited-state first-order properties in the coupled-cluster model CC2 using the resolution-of-the-identity approximation  

NASA Astrophysics Data System (ADS)

An implementation of transition moments and excited-state first-order properties is reported for the approximate coupled-cluster singles-and-doubles model (CC2) using the resolution of the identity (RI) approximation. In parallel to the previously reported code for the ground- and excited-state amplitude equations, we utilize a partitioned form of the CC2 equations and thus eliminate the need to store any N4 intermediates. This opens the perspective for applications on molecules with 30 and more atoms. The accuracy of the RI approximation is tested for a set of 29 molecules for the aug-cc-pVXZ (X=D,T,Q) basis sets in connection with the recently optimized auxiliary basis sets. These auxiliary basis sets are found to be sufficient even for the description of diffuse states. The RI error is compared to the usual basis set error and is demonstrated to be insignificant.

Hättig, Christof; Köhn, Andreas

2002-10-01

123

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

124

Plasmons with orbital angular momentum  

SciTech Connect

Electron plasma waves carrying orbital angular momentum are investigated in an unmagnetized collisionless plasma composed of inertial electrons and static ions. For this purpose, the usual plasmon dispersion relation is employed to derive an approximate paraxial equation. The latter is analyzed with a Gaussian beam solution. For a finite angular momentum associated with the plasmon, Laguerre-Gaussian (LG) solutions are employed for solving the electrostatic potential problem which gives approximate solution and is valid for plasmon beams in the paraxial approximation. The LG potential determines the electric field components and energy flux of plasmons with finite angular momentum. Numerical illustrations show that the radial and angular mode numbers strongly modify the profiles of the LG potential.

Mendonca, J. T. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Ali, S. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); National Centre for Physics, Shahdra Valley Road, Islamabad 44000 (Pakistan); Thide, B. [Swedish Institute of Space Physics, Angstroem Laboratory, P.O. Box 537, SE-751 21 Uppsala (Sweden)

2009-11-15

125

Inner structure of QED and its gauge invariant angular momenta: A new viewpoint to the final resolution of the nucleon spin crisis  

Microsoft Academic Search

We discover an inner structure of QED while the gauge potential is decomposed into two orthogonal components. Based on this, the Lagrangian of the electron-photon system is expanded to a new form and by the general method of field theory, the gauge invariant spin and orbital angular momentum operators of the electron and photon are naturally obtained from Noether's theorem.

Bao-Hua Zhou; Yong-Chang Huang

2011-01-01

126

Analytic gradients for excited states in the coupled-cluster model CC2 employing the resolution-of-the-identity approximation  

NASA Astrophysics Data System (ADS)

The derivation and implementation of excited state gradients is reported for the approximate coupled-cluster singles and doubles model CC2 employing the resolution-of-the-identity approximation for electron repulsion integrals. The implementation is profiled for a set of examples with up to 1348 basis functions and exhibits no I/O bottlenecks. A test set of sample molecules is used to assess the performance of the CC2 model for adiabatic excitation energies, excited state structure constants and vibrational frequencies. We find very promising results, especially for adiabatic excitation energies, though the need of a single-reference ground state and a single-replacement dominated excited state puts some limits on the applicability of the method. Its reliability, however, can always be tested on grounds of diagnostic measures. As an example application, we present calculations on the ?*<--? excited state of trans-azobenzene.

Köhn, Andreas; Hättig, Christof

2003-09-01

127

Feynman's angular momentum paradox revisited  

NASA Astrophysics Data System (ADS)

We reexamine Feynman's angular momentum paradox, in which a cylinder of charge around a current carrying solenoid is set in rotational motion when the current is turned off (due to the induced electric field caused by the change in magnetic flux), apparently violating conservation of angular momentum. The standard explanation of the resolution of this paradox is that, when the electric current in the solenoid is on, the combination of the magnetic field from the current and the electric field from the charges results in non-zero angular momentum which is stored in the electromagnetic fields in the vicinity of the solenoid. This angular momentum is transferred to the charged cylinder when the current is turned off. However, we show that for certain geometries of the solenoid and position of the charges, the angular momentum in the vicinity of the solenoid is in fact zero even when the solenoid carries electric current and hence magnetic field is present in the vicinity of the solenoid. We show that angular momentum is in fact still conserved, because the electromagnetic fields which radiate outwards from the solenoid after the current is turned off carry angular momentum which is opposite to the direction of the angular momentum imparted to the charge on the cylinder.

Hu, Ben Yu-Kuang; Loeber, Brian

2012-04-01

128

Chiral and Angular Momentum Content of Mesons  

SciTech Connect

First, we overview the present status of the effective chiral restoration in excited hadrons and an alternative explanation of the symmetry observed in the highly excited hadrons. Then we discuss a method how to define and measure in a gauge invariant manner the chiral and angular momentum content of mesons at different resolution scales, including the infrared scale, where mass is generated. We illustrate this method by presenting results on chiral and angular momentum content of {rho} and {rho}' mesons obtained in dynamical lattice simulations. The chiral symmetry is strongly broken in the {rho}(770) and neither the a{sub 1}(1260) nor the h{sub 1}(1170) can be considered as its chiral partners. Its angular momentum content in the infrared is approximately the {sup 3}S{sub 1} partial wave, in agreement with the quark model language. However, in its first excitation, {rho}(1450), the chiral symmetry breaking is much weaker and in the infrared this state belongs predominantly to the (1/2,1/2) chiral representation. This state is dominated in the infrared by the {sup 3}D{sub 1} partial wave and cannot be considered as the first radial excitation of the {rho}(770)-meson, in contrast to the quark model.

Glozman, Leonid Ya. [Institute for Physics, Theoretical Physics Branch, University of Graz, A-8010 Graz (Austria)

2011-05-24

129

The angular momentum distribution within haloes in different dark matter models  

NASA Astrophysics Data System (ADS)

We study the angular momentum profile of dark matter haloes for a statistical sample drawn from a set of high-resolution cosmological simulations of 2563 particles. Two typical cold dark matter (CDM) models have been analysed, and the haloes are selected to have at least 3 × 104 particles in order to measure the angular momentumprofile reliably. In contrast with the recent claims of Bullock et al., we find that the degree of misalignment of angular momentum within a halo is very high. Approximately 50 per cent of haloes have more than 10 per cent of the halo mass in the mass of negative angular momentum j. After the mass of negative j is excluded, the cumulative mass function M(approximately the universal function proposed by Bullock et al., although we still find a significant fraction of haloes (~50 per cent) that exhibit systematic deviations from the universal function. Our results, however, are broadly in good agreement with a recent work of van den Bosch et al. We also study the angular momentum profile of haloes in a warm dark matter (WDM) model and a self-interacting dark matter (SIDM) model. We find that the angular momentum profile of haloes in the WDM is statistically indistinguishable from that in the CDM model, but the angular momentum of haloes in the SIDM is reduced by the self-interaction of dark matter.

Chen, D. N.; Jing, Y. P.

2002-10-01

130

Angular Distance Weighting technique for developing a daily high-resolution gridded precipitation dataset for the South of the Iberian Peninsula  

NASA Astrophysics Data System (ADS)

An assessment of the skill of "Angular Distance Weighting" (ADW) technique used to interpolate daily precipitation records is presented. A dataset of 102 stations in the South of the Iberian Peninsula for the period 1961-2000 was used after overcoming a quality control carried out to ensure the homogeneity of the series. The interpolation method was evaluated for different values of the exponent of the weight function for the distance between stations (parameter m = 2, 4 and 8), the Correlation Decay Distance (CDD) and the amount of stations considered in order to create the interpolated values. Finally, a cross-validation exercise 'leave one out', calculating the Pearson correlation coefficient (R), the root mean squared error (RMSE) and the mean bias error (MBE), has been carried out. The worst correlation values were found in the East part of the region under study. This result may be consequence of convective precipitation nature in this area, due to its orographical characteristics and the different Atlantic influence on this region. The highest RMSE and MBE values were found in the South. The reason of this result is the existence of a specific microclimate displayed by the singular behaviour of a station located in this area (Grazalema), where much higher values of precipitation than in closed stations have been found, so the interpolated values can be affected. In addition, worse results for R, RMSE and MBE were found using m = 8, while there are no significant differences between m = 4 and m = 2. Finally, varying CDD along with the number of stations considered, the results suggest that lower CDD values and larger number of station provide better results. Acknowledgements: The Spanish Ministry of Science and Innovation, with additional support from the European Community Funds (FEDER), project CGL2007-61151/CLI, and the Regional Government of Andalusia project P06-RNM-01622, have financed this study. Key words: interpolation method, gridded daily precipitation, angular distance weighting.

Hidalgo-Muñoz, J. M.; Argüeso, D.; Gámiz-Fortis, S. R.; Esteban-Parra, M. J.; Castro-Díez, Y.

2009-04-01

131

High Angular Resolution Observation of the Sunyaev-Zel'Dovich Effect in the Massive z ? 0.83 Cluster Cl J0152-1357  

NASA Astrophysics Data System (ADS)

X-ray observations of galaxy clusters at high redshift (z >~ 0.5) indicate that they are more morphologically complex and less virialized than those at low redshift. We present the first subarcminute resolution synthesis observations at 18 GHz of the Sunyaev-Zel'dovich (SZ) effect for Cl J0152-1357 using the Australia Telescope Compact Array. Cl J0152-1357 is a massive cluster at redshift z = 0.83 and has a complex structure including several merging subclumps which have been studied at optical, X-ray, and radio wavelengths. Our high-resolution observations indicate a clear displacement of the maximum SZ effect from the peak of X-ray emission for the most massive subclump. This result shows that the cluster gas within the cluster substructures is not virialized in Cl J0152-1357, and we suggest that it is still recovering from a recent merger event. A similar offset of the SZ effect has recently been seen in the "bullet cluster" and in RX J1347-1145. This non-equilibrium situation implies that high-resolution observations are necessary to investigate galaxy cluster evolution and to extract cosmological constraints from a comparison of the SZ effect and X-ray signals.

Massardi, M.; Ekers, R. D.; Ellis, S. C.; Maughan, B.

2010-07-01

132

HIGH ANGULAR RESOLUTION OBSERVATION OF THE SUNYAEV-ZEL'DOVICH EFFECT IN THE MASSIVE z {approx} 0.83 CLUSTER Cl J0152-1357  

SciTech Connect

X-ray observations of galaxy clusters at high redshift (z {approx_gt} 0.5) indicate that they are more morphologically complex and less virialized than those at low redshift. We present the first subarcminute resolution synthesis observations at 18 GHz of the Sunyaev-Zel'dovich (SZ) effect for Cl J0152-1357 using the Australia Telescope Compact Array. Cl J0152-1357 is a massive cluster at redshift z = 0.83 and has a complex structure including several merging subclumps which have been studied at optical, X-ray, and radio wavelengths. Our high-resolution observations indicate a clear displacement of the maximum SZ effect from the peak of X-ray emission for the most massive subclump. This result shows that the cluster gas within the cluster substructures is not virialized in Cl J0152-1357, and we suggest that it is still recovering from a recent merger event. A similar offset of the SZ effect has recently been seen in the 'bullet cluster' and in RX J1347-1145. This non-equilibrium situation implies that high-resolution observations are necessary to investigate galaxy cluster evolution and to extract cosmological constraints from a comparison of the SZ effect and X-ray signals.

Massardi, M. [INAF-Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, I-35122 (Italy); Ekers, R. D. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, Epping NSW 1710 (Australia); Ellis, S. C. [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Maughan, B., E-mail: marcella.massardi@oapd.inaf.i [HH Wills Physics Laboratory, University of Bristol, Tyndall Ave, Bristol BS81TL (United Kingdom)

2010-07-20

133

Molecular-Frame Angular Distributions of Resonant CO:C(1s) Auger Electrons  

SciTech Connect

The molecular-frame angular distributions of resonantly excited CO:C(1s){yields}{pi}* Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy in combination with a novel transformation procedure. Our new methodology yields full three-dimensional electron angular distributions with high energy resolution from the measurement of electrons at only two angles. The experimentally determined distributions are well reproduced by calculations performed in a simple one-center approximation, allowing an unambiguous identification of several overlapping Auger lines.

Rolles, D.; Pesic, Z. D.; Dumitriu, I. [Physics Department, Western Michigan University, Kalamazoo, Michigan 49008 (United States); Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Pruemper, G.; Fukuzawa, H.; Liu, X.-J.; Ueda, K. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Fink, R. F. [Institute of Physical Chemistry, University of Wuerzburg, 97074 Wuerzburg (Germany); Grum-Grzhimailo, A. N. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Institute of Nuclear Physics, Moscow State University, Moscow 119991 (Russian Federation); Berrah, N. [Physics Department, Western Michigan University, Kalamazoo, Michigan 49008 (United States)

2008-12-31

134

Molecular-frame angular distributions of resonant CO:C(1s) Auger electrons.  

PubMed

The molecular-frame angular distributions of resonantly excited CO:C(1s) --> pi* Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy in combination with a novel transformation procedure. Our new methodology yields full three-dimensional electron angular distributions with high energy resolution from the measurement of electrons at only two angles. The experimentally determined distributions are well reproduced by calculations performed in a simple one-center approximation, allowing an unambiguous identification of several overlapping Auger lines. PMID:19437639

Rolles, D; Prümper, G; Fukuzawa, H; Liu, X J; Pesi?, Z D; Fink, R F; Grum-Grzhimailo, A N; Dumitriu, I; Berrah, N; Ueda, K

2008-12-31

135

Structural characterization of selectively grown multilayers with new high angular resolution and sub-millimeter spot-size x-ray diffractometer  

NASA Astrophysics Data System (ADS)

This paper reports the latest improvements performed on structural characterization by high resolution x-ray diffraction (XRD) on InGaAlAs-based multiple quantum well (MQW) structures on InP substrates, produced by metal organic vapor phase epitaxy in the regime of selective area growth (SAG). A new diffractometer, with a sub-millimeter x-ray spot, was used in the laboratory to study the MQW properties specifically in the SAG area. The results were compared to those obtained with a much smaller beam size using synchrotron radiation-based XRD. We show that a unique diffraction curve measured with the first setup fits the summation of a series of diffraction curves taken with the second setup in the cross section of the SAG area. More interestingly, applying some deconvolution criteria on this curve, a diffraction curve corresponding to the center of the mask area could be calculated and compared to the corresponding one taken among the second series. The excellent agreement between those curves proves that precious information of structural properties (such as strain and thickness) of the MQW in the center of the SAG area can be obtained from laboratory based measurements.

Décobert, J.; Guillamet, R.; Mocuta, C.; Carbone, G.; Guerault, H.

2013-05-01

136

High resolution Dopplerimetry of correlated angular and quantum state-resolved CO(2) scattering dynamics at the gas-liquid interface.  

PubMed

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

Perkins, Bradford G; Nesbitt, David J

2010-10-01

137

Inverting the angular correlation function  

NASA Astrophysics Data System (ADS)

The two point angular correlation function is an excellent measure of structure in the Universe. To extract from it the three-dimensional power spectrum, one must invert Limber's equation. Here we perform this inversion using a Bayesian prior constraining the smoothness of the power spectrum. Among other virtues, this technique allows for the possibility that the estimates of the angular correlation function are correlated from bin to bin. The outputs of this technique are estimators for the binned power spectrum and a full covariance matrix. Angular correlations mix small and large scales but after the inversion, small-scale data can be trivially eliminated, thereby allowing for realistic constraints on theories of large-scale structure. We analyse the automated plate measurement (APM) catalogue as an example, comparing our results with previous results. As a by-product of these tests, we find - in rough agreement with previous work - that APM places stringent constraints on cold dark matter inspired models, with the shape parameter constrained to be 0.25+/-0.04 (using data with wavenumber k<=0.1hMpc-1). This range of allowed values uses the full power spectrum covariance matrix, but assumes negligible covariance in the off-diagonal angular correlation error matrix, which is estimated with a large angular resolution of 0.5 deg (in the range 0.5 deg and 20 deg).

Dodelson, Scott; Gaztañaga, Enrique

2000-03-01

138

Analytic Approximations to the 2-60 micrometer 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. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

Convenient two-parameter analytic expressions approximating the long-wavelength (2-60 micron) infrared continua expected from over a dozen stellar calibration standards are derived. These analytic spectral functions are based on the implicit scaling of a ...

C. W. Engelke

1992-01-01

139

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

140

Angular Momentum Experiment  

NSDL National Science Digital Library

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

Trapp, David

141

Optical Angular Motion Sensor.  

National Technical Information Service (NTIS)

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...

H. T. Braswell J. W. Fontenot L. L. Hartley B. F. Heinrich W. E. Miller

1975-01-01

142

THEORIES FOR ANGULAR DISTRIBUTIONS IN LOW ENERGY NUCLEAR REACTIONS  

Microsoft Academic Search

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

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

1962-01-01

143

Phonons with orbital angular momentum  

NASA Astrophysics Data System (ADS)

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

Ayub, M. K.; Ali, S.; Mendonca, J. T.

2011-10-01

144

Phonons with orbital angular momentum  

SciTech Connect

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

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

2011-10-15

145

Angular Momentum Acquisition in Galaxy Halos  

NASA Astrophysics Data System (ADS)

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 ~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 ? ~ 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.; Brooks, Alyson M.; Bullock, James S.; Maller, Ariyeh H.; Diemand, Jürg; Wadsley, James; Moustakas, Leonidas A.

2013-05-01

146

Photoelectron angular distributions from autoionizing 4s{sup 1}4p{sup 6}6p{sup 1} states in atomic krypton probed with femtosecond time resolution  

SciTech Connect

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

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

2011-03-07

147

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

148

Sonar image segmentation using the angular dependence of backscattering distributions  

Microsoft Academic Search

In high resolution sonar imaging, the K-distribution has shown interesting properties for describing the statistics of backscattered intensity. This distribution is a function of two parameters. The first one is the mean intensity which is classically angular dependent. It has been found that the second one, the shape parameter, is also angular dependent. The K-distribution shape parameter shows two types

G. Le. Chenadec; J. M. Boucher

2005-01-01

149

Angular Momentum of Baryons and Dark Matter Halos Revisited.  

National Technical Information Service (NTIS)

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 hydrodynamic...

A. Slyz C. Pichon J. Devriendt S. A. Kassin T. Kimm Y. Dubois

2011-01-01

150

Angular and interstitial pregnancy.  

PubMed

Two cases of interstitial and one of angular pregnancy have been presented. Angular pregnancy occurs in the angle of the uterine cavity, while interstitial pregnancy is a true ectopic pregnancy. The outcome may therefore be different: the first may develop or abort into the cavity, while the second will almost always rupture. Because of the rich vascularization of this area, hemorrhage is usually profuse and may be catastrophic. Preoperative diagnosis is rare, but the triad of bleeding in pregnancy, no fetal remnants on dialation and curettage and an asymmetric uterus suggest angular or interstitial pregnancy. More liberal use of laparoscopy may increase the number of cases diagnosed before severe bleeding occurs. PMID:844965

Lancet, M; Bin-Nun, I; Kessler, I

1977-02-01

151

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

152

Magnetostrictive Angular Positioning Motor.  

National Technical Information Service (NTIS)

This patent application discloses a device in which a plurality of axially elongated drive modules are interconnected at their opposite ends in a polygonal arrangement to angularly spaced locations on an outer annular ring to establish compressive stress ...

A. E. Clark J. P. Teter

1990-01-01

153

Seismic Angular Motion Sensor.  

National Technical Information Service (NTIS)

The design, fabrication and evaluation of a fused silica, balanced rotor, angular motion sensor which is insensitive to linear accelerations is described. A mathematical model was developed which defines the physical parameters that could be controlled du...

S. Okubo

1973-01-01

154

Optical Angular Motion Sensor.  

National Technical Information Service (NTIS)

The Optical Angular Motion Sensor (OAMS) Program, Phase II, consisted of the fabrication and testing of a prototype model to demonstrate compilance with OAMS performance requirements. The qualification model consisted of a transmitter, a receiver, and an ...

H. T. Braswell S. A. Chin Bing J. W. Fontenot W. E. Miller N. J. Ockman

1977-01-01

155

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

156

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

157

Simultaneous angular multiplexing optical projection tomography at shifted focal planes.  

PubMed

We describe an angular multiplexing technique for optical projection tomography that improves resolution, signal-to-noise ratio, and imaging speed by ameliorating the trade-off between spatial resolution and depth of field and improving the light collection efficiency. Here we demonstrate that imaging at two orthogonal angular projections simultaneously, focused on shifted planes in the sample, improves the average spatial resolution by ~20% and the light collection efficiency by a factor of ~4, thereby enabling increased acquisition speed and reduced light dose. PMID:23503237

Chen, Lingling; Andrews, Natalie; Kumar, Sunil; Frankel, Paul; McGinty, James; French, Paul M W

2013-03-15

158

Ultra high resolution soft x-ray tomography  

SciTech Connect

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

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

1995-07-19

159

Automated and angular time-synchronized directional gamma-ray scintillation sensor  

Microsoft Academic Search

The authors` previous research resulted in directional sensors for gamma rays and X rays that have a 4Ï solid angle of acceptance and, at the same time, a high angular resolution that is limited only by their ability to measure small angles. Angular resolution of â¼1 s of arc was achieved. These sensors are capable of operating and accurately detecting

S. Kronenberg; G. J. Brucker

1998-01-01

160

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

161

Angular Momentum Diagrams  

NASA Astrophysics Data System (ADS)

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

Wormer, Paul E. S.; Paldus, Josef

162

Angular distributions in multifragmentation  

SciTech Connect

Angular distributions are reported for {sup 37}Ar and {sup 127}Xe from 381-GeV {sup 28}Si+Au interactions and for products between {sup 24}Na and {sup 149}Gd from 28-GeV {sup 1}H+Au. Sideward peaking and forward deficits for multifragmentation products are significantly enhanced for heavy ions compared with protons. Projectile kinetic energy does not appear to be a satisfactory scaling variable. The data are discussed in terms of a kinetic-focusing model in which sideward peaking is due to transverse motion of the excited product from the initial projectile-target interaction.

Stoenner, R.W.; Klobuchar, R.L.; Haustein, P.E.; Virtes, G.J.; Cumming, J.B.; Loveland, W. [Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Department of Chemistry, Oregon State University, Corvallis, Oregon 97331 (United States)

2006-04-15

163

Angularly selective mesoscopic tomography.  

PubMed

We report three-dimensional tomographic reconstruction of optical parameters for the mesoscopic light-scattering regime from experimentally obtained datasets by employing angularly selective data acquisition. The approach is based on the assumption that the transport coefficient of a scattering medium differs by an order of magnitude for weakly and highly scattering regions. Datasets were obtained by imaging a weakly scattering phantom, which embeds a highly scattering cylinder of two to three photons' mean path length in diameter containing light-absorbing inclusions. Reconstruction results are presented and discussed. PMID:22181452

Soloviev, Vadim Y; Bassi, Andrea; Fieramonti, Luca; Valentini, Gianluca; D'Andrea, Cosimo; Arridge, Simon R

2011-11-22

164

Estimating energy-momentum and angular momentum near null infinity  

SciTech Connect

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

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

2010-04-15

165

Precompound nucleon angular distributions in the continuum  

SciTech Connect

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

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

1985-08-01

166

Fission-fragment angular distributions  

Microsoft Academic Search

The universally used ''exact'' formula for fission-fragment angular distributions is shown to be valid only under restrictive assumptions. The more general expression, which depends crucially on the final fragment spin distributions, predicts dramatically more anisotropic angular distributions for fission from nuclei at high spin. Recent ''anomalous'' results are analyzed.

P. Bond

1984-01-01

167

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

168

Intrinsic Angular Momentum of Light.  

ERIC Educational Resources Information Center

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

Santarelli, Vincent

1979-01-01

169

Angular momentum of synchrotron radiation  

NASA Astrophysics Data System (ADS)

Exact methods of the theory of relativistic radiation of an arbitrarily moving charge provide the basis for the theory of radiation of the angular momentum of an electromagnetic field stated here. As an application, properties of orbital and spin angular momenta of synchrotron radiation are considered.

Bordovitsyn, V. A.; Konstantinova, O. A.; Nemchenko, E. A.

2012-06-01

170

Exploring Angular Distance in Protein-Protein Docking Algorithms  

PubMed Central

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

Vreven, Thom; Hwang, Howook; Weng, Zhiping

2013-01-01

171

Rational approximations for tomographic reconstructions  

NASA Astrophysics Data System (ADS)

We use optimal rational approximations of projection data collected in x-ray tomography to improve image resolution. Under the assumption that the object of interest is described by functions with jump discontinuities, for each projection we construct its rational approximation with a small (near optimal) number of terms for a given accuracy threshold. This allows us to augment the measured data, i.e., double the number of available samples in each projection or, equivalently, extend (double) the domain of their Fourier transform. We also develop a new, fast, polar coordinate Fourier domain algorithm which uses our nonlinear approximation of projection data in a natural way. Using augmented projections of the Shepp–Logan phantom, we provide a comparison between the new algorithm and the standard filtered back-projection algorithm. We demonstrate that the reconstructed image has improved resolution without additional artifacts near sharp transitions in the image.

Reynolds, Matthew; Beylkin, Gregory; Monzón, Lucas

2013-06-01

172

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

Microsoft Academic Search

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

Rozaimi Che Hasan; Daniel Ierodiaconou; Laurie Laurenson

173

Is angular impulse always equal to the change of angular momentum in collisions between rigid bodies?  

Microsoft Academic Search

The relationships between angular impulse and angular momentum have been derived in the particular case of collisions between rigid bodies. It is shown that the change in absolute angular momentum about an arbitrary reference point is always equal to the angular impulse. However, the change in relative angular momentum is equal to the angular impulse only when it is calculated

M. A. Illarramendi; T. del Río Gaztelurrutia; L. M. Villar

1997-01-01

174

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

NASA Astrophysics Data System (ADS)

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

Richichi, A.; Roccatagliata, V.

2005-04-01

175

Angular Momentum Profiles of Warm Dark Matter Halos  

NASA Astrophysics Data System (ADS)

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 and coworkers, 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 in 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.

Bullock, James S.; Kravtsov, and Andrey V.; Colín, Pedro

2002-01-01

176

Transverse angular momentum of photons  

SciTech Connect

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

Aiello, Andrea [Max Planck Institute for the Science of Light, Guenter-Scharowsky-Strasse 1/Bau 24, D-91058 Erlangen (Germany); Marquardt, Christoph; Leuchs, Gerd [Max Planck Institute for the Science of Light, Guenter-Scharowsky-Strasse 1/Bau 24, D-91058 Erlangen (Germany); Institute for Optics, Information and Photonics, University Erlangen-Nuernberg, Staudtstrasse 7/B2, D-91058 Erlangen (Germany)

2010-05-15

177

Optimal Estimation of Angular Misalignment.  

National Technical Information Service (NTIS)

This work considers the application of optimal estimation theory to the general problem of coordinate frame angular misalignment estimation. Two cases of interest are considered in the theoretical investigations and simulations presented.

J. C. Ryles

1973-01-01

178

Axial-conductances angular filter investigation  

NASA Astrophysics Data System (ADS)

This report describes the concept, analysis, design, construction, and tests of an angular filter using an axial-conductance medium. The filter provides rejection that increases with incidence angle in the E plane. It is essentially invisible at broadside incidence, does not have critical tolerances on dimensions or materials, and operates over a wide frequency band. Analysis of an ideal homogeneous axial-conductance medium shows that the optimum value for the axial loss tangent is unity. With this value, the homogeneous medium provides approximately 8 dB of absorptive rejection per wavelength of filter thickness at a 45 E-plane incidence angle. Analysis of a practical inhomogeneous axial-conductance medium shows that some loss is introduced at broadside incidence, and that two types of waves can exist in the medium when only one wave is incident at an oblique angle. When the practical medium has dimensions that are properly chosen, its broadside loss can be negligible, and its rejection versus incidence angle can approximate that of the ideal medium. Tests of inhomogeneous samples in simulator wave guide confirm these analytical results. A screen printing method for depositing thick-film resistive ink on thin dielectric sheets has been investigated. With this method a 5x5 foot angular filter, designed for operation at 10 GHz, has been constructed containing over 70,000 axial-conductance elements.

Hannan, P. W.; Pedersen, J. F.

1984-04-01

179

Automated angular momentum recoupling algebra  

SciTech Connect

We describe a code, RACAH, for algebraic solution of angular momentum recoupling problems. The general problem is to find an optimal path from one binary tree (representing the angular momentum coupling scheme for the reduced matrix element) to another (representing the sub-integrals and spin sums to be done). RACAH is implemented on a MS-DOS microcomputer, using the SCHEME dialect of LISP. 6 refs.

Williams, H.T. (Washington and Lee Univ., Lexington, VA (USA). Dept. of Physics); Silbar, R.R. (Los Alamos National Lab., NM (USA))

1990-01-01

180

On the perturbed angular correlation attenuation factor for relaxing systems  

NASA Astrophysics Data System (ADS)

The attenuation factor of gamma-gamma perturbed angular correlation in the isotropic random-phase approximation is deduced for an axially symmetric quadrupole interaction and spins 1, 3/2, 2 and 5/2. It is shown that modifications to the usual expression are significant. Useful expressions for fitting procedures are obtained.

Martínez, J. A.; Sanchez, F. H.; Vasquez, A.

1982-05-01

181

Studies of gas phase chemical kinetics angular momentum effects in ion-molecule reactions  

Microsoft Academic Search

The relative contributions of angular momentum arising from rotation of reactants and from the orbital motion associated with a collision process are analyzed for linear and spherical species undergoing ion-molecule or neutral-neutral reactions by deriving distribution functions of angular momenta. A measure for the goodness of the neglect of molecular rotation is developed, and it is shown that the approximation

G. M. L. Verboom

1978-01-01

182

Estimates of mass and angular momentum in the oort cloud.  

PubMed

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

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

1988-10-28

183

Nanoradian angular stabilization of x-ray optical components  

SciTech Connect

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

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

2010-05-15

184

Haze of surface random systems: An approximate analytic approach  

Microsoft Academic Search

Approximate analytic expressions for haze (and gloss) of Gaussian randomly rough surfaces for various types of correlation functions are derived within phase-perturbation theory. The approximations depend on the angle of incidence, polarization of the incident light, the surface roughness, sigma , and the average of the power spectrum taken over a small angular interval about the specular direction. In particular

Ingve Simonsen; Åge Larsen; Erik Andreassen; Espen Ommundsen; Katrin Nord-Varhaug

2009-01-01

185

High Angular Resolution and Position Determinations by Infrared Interferometry.  

National Technical Information Service (NTIS)

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 Interferomet...

1974-01-01

186

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

187

An Acousto-Optical Sensor with High Angular Resolution  

PubMed Central

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

Kaloshin, Gennady; Lukin, Igor

2012-01-01

188

Spectroscopy of {sup 110}Sn via the high-resolution {sup 112}Sn(p,t){sup 110}Sn reaction  

SciTech Connect

The {sup 112}Sn(p,t){sup 110}Sn reaction was studied in a high-resolution experiment at an incident proton energy of 26 MeV. Angular distributions for 27 transitions to levels of {sup 110}Sn up to an excitation energy of {approx}4.3 MeV were measured. A distorted-wave Born approximation (DWBA) analysis of experimental angular distributions using conventional Woods-Saxon potentials were done, allowing either the confirmation of previous spin and parity values or the assignment of new spin and parity to a large number of {sup 110}Sn states. A shell-model study was performed using an effective interaction derived from the CD-Bonn nucleon-nucleon potential. The energy spectra are calculated and compared with experiment, whereas the theoretical two-nucleon spectroscopic amplitudes, evaluated in a truncated seniority space, are used in the microscopic DWBA calculation of some cross-section angular distributions.

Guazzoni, P.; Zetta, L.; Covello, A.; Gargano, A.; Bayman, B. F.; Graw, G.; Hertenberger, R.; Wirth, H.-F.; Jaskola, M. [Dipartimento di Fisica dell'Universita, and Istituto Nazionale di Fisica Nucleare, Via Celoria 16, I-20133 Milan (Italy); Dipartimento di Scienze Fisiche, Universita di Napoli Federico II, and Istituto Nazionale di Fisica Nucleare, Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Naples (Italy); School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota (United States); Sektion Physik der Universitaet Muenchen, D-85748 Garching (Germany); Soltan Institute for Nuclear Studies, Warsaw (Poland)

2006-11-15

189

Angular momentum of a magnetically trapped atomic condensate.  

PubMed

For an atomic condensate in an axially symmetric magnetic trap, the sum of the axial components of the orbital angular momentum and the hyperfine spin is conserved. Inside an Ioffe-Pritchard trap (IPT) whose magnetic field (B field) is not axially symmetric, the difference of the two becomes surprisingly conserved. In this Letter we investigate the relationship between the values of the sum or difference angular momentums for an atomic condensate inside a magnetic trap and the associated gauge potential induced by the adiabatic approximation. Our result provides significant new insight into the vorticity of magnetically trapped atomic quantum gases. PMID:17358664

Zhang, P; Jen, H H; Sun, C P; You, L

2007-01-17

190

The angular momentum of condensations within elephant trunks  

NASA Astrophysics Data System (ADS)

Aims: The radiation from newly born stars photoevaporates their parental neutral cloud, leading to the formation of dense clumps that will eventually form stars. Methods: We present 3D simulations of the interaction of a neutral cloud with an external ionising radiation field, and compute the angular momenta of these collapsing clumps. Results: The angular momenta of these collapsing clumps show that they have preferential orientations mostly perpendicular to the direction of the incident ionising photon field. Therefore, the axes of the jet systems that will be eventually ejected (from the star + accretion disk systems that will form) will be oriented approximately perpendicular to the direction to the photoionising source.

Lora, V.; Raga, A. C.; Esquivel, A.

2009-08-01

191

Angular sensitivity of gated microchannel plate framing cameras  

SciTech Connect

Gated, microchannel-plate-based (MCP) framing cameras have been deployed worldwide for 0.2--9 keV x-ray imaging and spectroscopy of transient plasma phenomena. For a variety of spectroscopic and imaging applications, the angular sensitivity of MCPs must be known for correctly interpreting the data. We present systematic measurements of angular sensitivity at discrete relevant photon energies and arbitrary MCP gain. The results can been accurately predicted by using a simple two-dimensional approximation to the three-dimensional MCP geometry and by averaging over all possible photon ray paths.

Landen, O. L.; Lobban, A.; Tutt, T.; Bell, P. M.; Costa, R.; Hargrove, D. R.; Ze, F.

2001-01-01

192

Automated and angular time-synchronized directional gamma-ray scintillation sensor  

SciTech Connect

The authors` previous research resulted in directional sensors for gamma rays and X rays that have a 4{pi} solid angle of acceptance and, at the same time, a high angular resolution that is limited only by their ability to measure small angles. Angular resolution of {approximately}1 s of arc was achieved. These sensors are capable of operating and accurately detecting high and very low intensity radiation patterns. Such a system can also be used to image broad area sources and their scattering patterns. The principle of operation and design of directional sensors used in this study was described elsewhere; however, for convenience, a part of that text is repeated here. It was shown analytically that the angular distribution of radiation incident on the sensor is proportional to the first derivative of the scan data, that is, of the events` count rate versus orientation of the detector. The previously published results were obtained with a annual operating system. The detector assembly was set at a specific angle, and a pulse rate count was made. This was repeated at numerous other angles of orientation, a time-consuming and labor-intensive process. Recently, the authors automated this system, which is based on the detection of scintillations. The detector, which consists of a stack of plates of Lucite, plastic scintillator, and lead foils, rotates by means of a motor in front of a stationary photomultiplier tube (PMT). One revolution per second was chosen for the motor. At time zero, a trigger indicates that a revolution has started. The angle of orientation of the detector in the laboratory system is proportional to the time during one revolution. The process repeats itself a desired number of times. The trigger signal initiates a scan of a multichannel scalar (MCS). The detector assembly is allowed to rotate in the radiation field, and the MCS scans are repeated in an accumulated mode of operation until enough events are collected for the location of the radiation source to be determined. They describe this sensor design as the angular time synchronized directional sensor (ATSDS).

Kronenberg, S.; Brucker, G.J.

1998-12-31

193

Interferometric measurement of angular motion  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

194

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

195

FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Effects of Turbulent Aberrations on Probability Distribution of Orbital Angular Momentum for Optical Communication  

NASA Astrophysics Data System (ADS)

Effects of atmospheric turbulence tilt, defocus, astigmatism and coma aberrations on the orbital angular momentum measurement probability of photons propagating in weak turbulent regime are modeled with Rytov approximation. By considering the resulting wave as a superposition of angular momentum eigenstates, the orbital angular momentum measurement probabilities of the transmitted digit are presented. Our results show that the effect of turbulent tilt aberration on the orbital angular momentum measurement probabilities of photons is the maximum among these four kinds of aberrations. As the aberration order increases, the effects of turbulence aberrations on the measurement probabilities of orbital angular momentum generally decrease, whereas the effect of turbulence defocus can be ignored. For tilt aberration, as the difference between the measured orbital angular momentum and the original orbital angular momentum increases, the orbital angular momentum measurement probability decreases.

Zhang, Yi-Xin; Cang, Ji

2009-07-01

196

Quantum theory of angular momentum  

SciTech Connect

Containing basic definitions and theorems as well as relations, tables of formulas and numerical tables which are essential for applications to many physical problems, the book is useful for specialists in nuclear and particle physics, atomic and molecular spectroscopy, plasma physics, collision and reaction theory, quantum chemistry, etc. The authors write many formulas in different coordinate systems. Each chapter opens with a list of its contents. New results relating to different aspects of the angular momentum theory are included. This book gathers together many useful formulas besides those related to angular momentum, and compares different notations used by previous authors.

Varshalovich, D.A.; Moskalev, A.N.; Khersonskii, V.K.

1987-01-01

197

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

2011-02-01

198

Improving displayed resolution in convolution reconstruction of digital holograms  

NASA Astrophysics Data System (ADS)

In digital holographic microscopy, when the object is placed near the COD, the Fresnel approximation is no longer valid and the convolution approach has to be applied. With this approach, the sampling spacing of the reconstructed image plane is equal to the pixel size of the CCD. If the lateral resolution of the reconstructed image is higher than that of the CCD, Nyquist sampling criterion is violated and aliasing errors will be introduced. In this Letter, a new method is proposed to solve this problem by investigating convolution reconstruction of holograms. By appending enough zeros to the angular spectrum between the two FFT's in convolution reconstruction of digital holograms, the displayed resolution of the reconstructed image can be improved. Experimental results show a good agreement with theoretical analysis.

Fan, Qi; Zhao, Jian-Lin; Zhang, Yan-Cao; Wang, Jun; di, Jiang-Lei

2006-07-01

199

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

200

Angular correlation in ^134Pr  

NASA Astrophysics Data System (ADS)

A background subtraction method for ?-ray spectroscopic measurements with large multidetector HpGe arrays has been applied to data from the GS2K009 experiment in which the ^116Cd(^23Na,5n) reaction was employed to study ^134Pr. The method takes advantage of recently developed BLUE data storage which allows for event retrieval in their native fold. The background spectrum is constructed based on the parameters evaluated from one-dimensional spectra only; the method, therefore, is complementary to other methods applied so far which are optimized for multidimensional, symmetrized histograms. When the background subtracted spectra projected on the Gammasphere rings are summed together, the applied algorithm compare well to that in the RADWARE data analysis package. Double gated spectra projected on Gammasphere rings were analyzed for angular correlations and Doppler Shift Attenuation studies. The method allows investigation of triple-? correlations which can be used to enhance angular asymmetry. It can also be apply to DCO or angular distributions studies from doubly gated spectra if appropriate angular conditions are set for the gating ?-rays. The resulting spin/parity assignments in ^134Pr will be presented.

Starosta, Krzysztof

2004-10-01

201

Olympic Wrestling and Angular Momentum.  

ERIC Educational Resources Information Center

Reported is the use of a wrestling photograph in a noncalculus introductory physics course. The photograph presents a maneuver that could serve as an example for a discussion on equilibrium, forces, torque, and angular motion. Provided are some qualitative thoughts as well as quantitative calculations. (YP)

Carle, Mark

1988-01-01

202

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

203

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

204

Improving the resolution of ground-based telescopes  

Microsoft Academic Search

Atmospheric turbulence profoundly limits the angular resolution of astronomical telescopes working at visible and near-infrared wavelengths. In fact, the angular resolution for conventional imaging through turbulence is on the order of 5â20% of the diffraction-limited resolution at the best observatories in the world. The origin of these performance degradations is random turbulence-induced fluctuations in the index of refraction of the

Michael C. Roggemann; Byron M. Welsh; Robert Q. Fugate

1997-01-01

205

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

NASA Astrophysics Data System (ADS)

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 ?CDM universe. We find that although the disc mass fractions are significantly smaller than the universal baryon fraction, the total specific angular momenta of the discs are in good agreement with those of dark matter haloes. This suggests that discs form out of only a small fraction of the available baryons, but yet manage to draw most of the available angular momentum. In addition we find that the angular momentum distributions of discs are clearly distinct from those of the dark matter; discs lack predominantly both low and high specific angular momenta. Understanding these findings in terms of a coherent picture for disc formation is challenging. Cooling, feedback and stripping, which are the main mechanisms to explain the small disc mass fractions found, seem unable to simultaneously explain the angular momentum distributions of the discs. In fact, it seems that the baryons that make up the discs must have been born out of angular momentum distributions that are clearly distinct from those of ?CDM haloes. However, the dark and baryonic mass components experience the same tidal forces, and it is therefore expected that they should have similar angular momentum distributions. Therefore, understanding the angular momentum content of disc galaxies remains an important challenge for our picture of galaxy formation.

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

2001-09-01

206

Approximate flavor symmetries  

SciTech Connect

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

Rasin, A.

1994-04-01

207

Improved Toeplitz Approximation Method.  

National Technical Information Service (NTIS)

This reprint suggests a modification of the Toeplitz approximation method for estimating frequencies of multiple sinusoids from covariance measurements. The method constructs a state-feedback matrix following a low-rank approximation of the Toeplitz covar...

B. D. Rao K. S. Arun

1988-01-01

208

Plate tectonics conserves angular momentum  

NASA Astrophysics Data System (ADS)

A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4 E+27 kgm2s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Bowin, C.

2009-03-01

209

Neoclassical Angular Momentum Flux Revisited  

NASA Astrophysics Data System (ADS)

The toroidal angular momentum flux in neoclassical transport theory of small rotations depends on the second order (in ion poloidal gyroradius over plasma scale length) ion distribution function. Owing to the complexity of the calculation, the result obtained a long time ago for circular cross-section tokamak plasmas in the banana regime [M.N. Rosenbluth, et al., Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1971), Vol. 1, p. 495] has never been reproduced. Using a representation of the angular momentum flux based on the solution of an adjoint equation to the usual linearized drift kinetic equation, and performing systematically a large-aspect-ratio expansion, we have obtained the flux for flux surfaces of arbitrary shape. We have found the same analytic form for the temperature gradient driven part of the flux, but the overall numerical multiplier is different and has the opposite sign. Implications for rotations in discharges with no apparent momentum input will be discussed.

Wong, S. K.; Chan, V. S.

2004-11-01

210

Angular correlations in breakup of three-body halo nuclei  

Microsoft Academic Search

We use the three-body model and the sudden approximation to compute angular correlations in high-energy fragmentation reactions of two-neutron halos on light targets. The contribution from one-neutron absorption by far dominates over that of neutron scattering. We use 6He (n+n+alpha) and 11Li (n+n+9Li) as examples and study the dependence of the predictions of this model on different physical assumptions and

E. Garrido; D. V. Fedorov; A. S. Jensen

1998-01-01

211

The angular momentum of the Oort cloud  

Microsoft Academic Search

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

P Weissman

1991-01-01

212

Angular Momentum Decomposition for an Electron  

SciTech Connect

We calculate the orbital angular momentum of the `quark' in the scalar diquark model as well as that of the electron in QED (to order $\\alpha$). We compare the orbital angular momentum obtained from the Jaffe-Manohar decomposition to that obtained from the Ji relation and estimate the importance of the vector potential in the definition of orbital angular momentum.

Burkardt, Matthias; BC, Hikmat

2009-01-01

213

Molecular-Frame Angular Distributions of Resonant CO:C(1s) Auger Electrons  

Microsoft Academic Search

The molecular-frame angular distributions of resonantly excited CO:C(1s)* Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy in combination with a novel transformation procedure. Our new methodology yields full three-dimensional electron angular distributions with high energy resolution from the measurement of electrons at only two angles. The experimentally determined distributions are well reproduced by calculations performed in a simple one-center

D. Rolles; Z. D. Pesic; I. Dumitriu; G. Pruemper; H. Fukuzawa; X.-J. Liu; K. Ueda; R. F. Fink; A. N. Grum-Grzhimailo; N. Berrah

2008-01-01

214

Molecular-Frame Angular Distributions of Resonant CO:C(1s) Auger Electrons  

Microsoft Academic Search

The molecular-frame angular distributions of resonantly excited CO:C(1s)-->pi* Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy in combination with a novel transformation procedure. Our new methodology yields full three-dimensional electron angular distributions with high energy resolution from the measurement of electrons at only two angles. The experimentally determined distributions are well reproduced by calculations performed in a simple one-center

D. Rolles; G. Prümper; H. Fukuzawa; X.-J. Liu; Z. D. Pesic; R. F. Fink; A. N. Grum-Grzhimailo; I. Dumitriu; N. Berrah; K. Ueda

2008-01-01

215

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

NASA Astrophysics Data System (ADS)

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

Nagashima, Masahiro; Gouda, Naoteru

1998-12-01

216

On the quantum and quasiclassical angular distributions of photofragments  

SciTech Connect

Quantum and quasiclassical expressions for the angular distribution of photofragments from an initially polarized precursor molecule are compared under the conditions of a one-photon electric dipole transition to a repulsive state followed by prompt axial recoil into two separating fragments. The treatment is most readily applicable to diatomic molecules, but it is more general than that. It is shown that when the rotational and electronic angular momentum J{sub i} and its projection along the body-fixed z axis {omega}{sub i} are well defined in the initial state, the quantum and quasiclassical expressions are identical for any initial polarization of the molecule prior to photolysis and for all values of J{sub i} and {omega}{sub i}. For the particular case of an |J{sub i}{omega}{sub i}M{sub i}> selected state this is in agreement with a previous result [T. Seideman, Chem. Phys. Lett. 253, 279 (1996)]. Moreover, the quasiclassical expression is still a good approximation even when the initial state is a coherent superposition of |J{sub i},{omega}{sub i},M{sub i}> levels for the same {omega}{sub i}. This near identity still pertains even when {omega}{sub i} is not well defined for a parallel transition ({delta}{omega}=0) but fails for a perpendicular transition ({delta}{omega}={+-}1) if the initial state is in a coherent superposition of {omega}{sub i} states differing by {+-}2. These conclusions apply to preparation schemes employing optical excitation, static inhomogeneous and/or homogeneous electric and/or magnetic fields, as well as to molecules physisorbed on solids or clusters. We discuss the importance of these results in the interpretation of photofragment distributions when some other angular momenta are involved, such as electronic angular momentum, with and without nuclear spin, coupled to molecular rotation, asymmetric top rotational angular momentum, or internal vibrational angular momentum in polyatomics.

Beswick, J. Alberto [Laboratoire Collisions, Agregats, Reactivite, UMR 5589 du CNRS IRSAMC, Universite Paul Sabatier, 31062 Toulouse (France); Zare, Richard N. [Department of Chemistry, Stanford University, Stanford, California 94305-5080 (United States)

2008-10-28

217

Two-dimensional angular filter array for angular domain imaging with 3D printed angular filters  

NASA Astrophysics Data System (ADS)

Angular Domain Imaging (ADI) is a technique that is capable of generating two dimensional shadowgrams of attenuating targets embedded in a scattering medium. In ADI, an angular filter array (AFA) is positioned between the sample and the detector to distinguish between quasi-ballistic photons and scattered photons. An AFA is a series of micro-channels with a high aspect ratio. Previous AFAs from our group were constructed by micro-machining the micro-channels into a silicon wafer, limiting the imaging area to a one dimensional line. Two dimensional images were acquired via scanning. The objective of this work was to extend the AFA design to two dimensions to allow for two dimensional imaging with minimal scanning. The second objective of this work was to perform an initial characterization of the imaging capabilities of the 2D AFA. Our approach was to use rapid 3D prototyping techniques to generate an array of micro-channels. The imaging capabilities were then evaluated by imaging a 0.9 mm graphite rod submerged in a scattering media. Contrast was observed to improve when a second angular filter array was placed in front of the sample to mask the incoming light.

Ng, Eldon; Carson, Jeffrey J. L.

2013-02-01

218

High resolution spectroscopy of 112Sn through the 114Sn(p,t)112Sn reaction  

NASA Astrophysics Data System (ADS)

The 114Sn(p,t)112Sn reaction has been investigated in a high resolution experiment at incident proton energy of 22 MeV. Angular distributions for 28 transitions to levels of 112Sn up to the excitation energy of 3.624 MeV have been measured. The spin and parity identification has been carried out by means of a distorted-wave Born approximation (DWBA) analysis, performed by using conventional Woods-Saxon potentials. A shell-model study of 112Sn nucleus has been performed using a realistic two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential. The energy spectra have been calculated and compared with the experimental ones, while the theoretical two-nucleon spectroscopic amplitudes, evaluated in a truncated seniority space, have been used in the microscopic DWBA calculation of the cross-section angular distributions.

Guazzoni, P.; Zetta, L.; Covello, A.; Gargano, A.; Bayman, B. F.; Graw, G.; Hertenberger, R.; Wirth, H.-F.; Faestermann, T.; Jaskóla, M.

2012-05-01

219

Plate tectonics conserves angular momentum  

NASA Astrophysics Data System (ADS)

A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4+27 kg m2 s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies revealed by geoid anomalies of the degree 4-10 packet of the Earth's spherical harmonic coefficients. These linear positive geoid anomalies underlie plate subduction zones and are presumed due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. The magnitude of these sinking mass anomalies is inferred also to be sufficient to overcome basal plate and transform fault frictions. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Bowin, C.

2010-03-01

220

Approximating Labeled Markov Processes  

Microsoft Academic Search

We study approximate reasoning about continuous-state labeled Markov processes. We show how to approximate a labeled Markov process by a family offinite-state labeled Markov chains. We show that the collection of labeled Markov processes carries a Polish space structure with a countable basis given by finite state Markov chains with ra- tional probabilities. The primary technical tools that we develop

Josee Desharnais; Vineet Gupta; Radha Jagadeesan; Prakash Panangaden

2000-01-01

221

Angular Momentum Transport in Double White Dwarf Binaries  

NASA Astrophysics Data System (ADS)

We present numerical simulations of dynamically unstable mass transfer in a double white dwarf binary with initial mass ratio, q = 0.4. The binary components are approximated as polytropes of index n = 3/2 and the synchronously rotating, semi-detached equilibrium binary is evolved hydrodynamically with the gravitational potential being computed through the solution of Poisson's equation. Upon initiating deep contact, the mass transfer rate grows by more than an order of magnitude over approximately ten orbits, as would be expected for dynamically unstable mass transfer. However, the mass transfer rate then reaches a peak value, the binary expands and the mass transfer event subsides. The binary must therefore have crossed the critical mass ratio for stability against dynamical mass transfer. Despite the initial loss of orbital angular momentum into the spin of the accreting star, we find that the accretor's spin saturates and angular momentum is returned to the orbit more efficiently than has been previously suspected for binaries in the direct impact accretion mode. To explore this surprising result, we directly measure the critical mass ratio for stability by imposing artificial angular momentum loss at various rates to drive the binary to an equilibrium mass transfer rate. For one of these driven evolutions, we attain equilibrium mass transfer and deduce that the mass ratio for stability is approximately 2/3. This is consistent with the result for mass transferring binaries that effectively return angular momentum to the orbit through an accretion disk. This work has been supported in part by NSF grants AST 04-07070 and PHY 03-26311 and in part through NASA's ATP program grant NAG5-13430. The computations were performed primarily at NCSA through grant MCA98N043 and at LSU's Center for Computation & Technology.

Motl, Patrick M.; Tohline, J. E.; Frank, J.

2006-12-01

222

Angular anisotropy of autoionization electrons from sodium atoms simultaneously excited by laser and electron beams  

Microsoft Academic Search

First measurements of the angular distributions of autoionization electrons from 2p53s3p 2D5\\/2 state of Na atom excited by electron impact from the ground and laser excited 3p 2P3\\/2 state are reported. Strong anisotropy of the angular distribution is revealed, which has different signs for the excitation from the ground and excited states. Theoretical analysis based on the Born approximation is

A. Dorn; J. Nienhaus; M. Wetzstein; C. Winnewissert; W. Mehlhorn; V. V. Balashov; A. N. Grum-Grzhimailo; N. M. Kabachnik; O. I. Zatsarinny

1994-01-01

223

Relativistic Eikonal Approximation.  

National Technical Information Service (NTIS)

The authors earlier claims in support of the eikonal approximation to generalized ladder graph amplitudes are withdrawn -- for the case of scalar-scalar interactions. Justification of the eikonal formula is provided, however, for the more interesting situ...

G. Tiktopoulos S. B. Treiman

1970-01-01

224

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

225

Optimizing the Zeldovich Approximation.  

National Technical Information Service (NTIS)

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 1...

A. L. Melott T. F. Pellman S. F. Shandarin

1994-01-01

226

Anomalous diffraction approximation limits  

NASA Astrophysics Data System (ADS)

It has been reported in a recent article [Liu, C., Jonas, P.R., Saunders, C.P.R., 1996. Accuracy of the anomalous diffraction approximation to light scattering by column-like ice crystals. Atmos. Res., 41, pp. 63-69] that the anomalous diffraction approximation (ADA) accuracy does not depend on particle refractive index, but instead is dependent on the particle size parameter. Since this is at odds with previous research, we thought these results warranted further discussion.

Videen, Gorden; Chýlek, Petr

227

Approximately intertwining mappings  

NASA Astrophysics Data System (ADS)

Let be a Banach algebra, and let E be a weak Banach -bimodule. An approximately intertwining mapping corresponding to a functional equation is a mapping with f(0)=0 such that and for each the mappingsfa(x)=f(ax)-af(x), are continuous at a point. In this paper, we show that every approximately intertwining mapping corresponding to Cauchy, generalized Jensen or Trif functional equation can be estimated by an intertwining mapping.

Moslehian, Mohammad Sal

2007-08-01

228

Pose Calibration using Approximately Planar Urban Structure  

Microsoft Academic Search

We introduce an algorithm that automatically aligns images with partial wireframe models to compute extrinsic camera parameters with respect to the model reference frame. Aligned imagery is fused with the model to incorporate high-resolution textures and to facilitate context sensitive image processing. The technique is designed to exploit the approximately planar structure commonly found in human-made environments such as building

Christopher Jaynes; Mike Partington

229

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

230

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

NASA Astrophysics Data System (ADS)

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

Fields, Brian D.; Hochmuth, Kathrin A.

2006-12-01

231

Adaptive estimation of angular velocity and acceleration of a single-axis MEMS coriolis sensor  

NASA Astrophysics Data System (ADS)

MEMS fabrication technology has facilitated the implementation of a broad variety of low-cost miniature sensors, including those for measuring linear and angular rates of objects-of-interest. Earlier work has focused on component-level sensor fabrication issues and proof-of- concept verification of their sensing ability. This prior work has provided the foundation for design and performance assessment of the next generation of multi-axis embedded MEMS sensors at a subsystem level. Subsequently, this will lead to the fabrication of an integrated self-calibrating 6 degree-of-freedom (DOF) strapdown intertial sensor assembled in a low-cost miniature package. This in turn will lead to a variety of applications that are currently unrealistic because of cost-weight-power considerations. This particular effort is directed toward establishing the feasibility of extracting additional information from a MEMS sensor by appropriately exciting a single-axis Coriolis sensor, for example, to generate optimum angular velocity and angular acceleration estimates, whereas prior studies have shown only the ability to generate approximate angular acceleration estimates, whereas prior studies have shown only the ability to generate approximate angular rotational velocity measurements. This work entailed the dynamic modeling of a representative MEMS sensor and several different angular velocity and angular acceleration driving functions in a MATLAB-based simulation. The corresponding raw sensor outputs were then optimally processed to concurrently generate estimates of both angular velocity and angular acceleration. The graphical results form these simulation studies are included to show the benefit of physically co-locating a digital computing element with the MEMS sensor, thereby facilitating the creation of a new generation of digital smart sensors, that will be capable of self-calibration based performance deterioration assessment, fault detection and recovery.

Karmarkar, Jay; Singh, Sahjendra N.

2002-07-01

232

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…

Mungan, Carl E.

2009-01-01

233

Imaging with extended focal depth by means of lenses with radial and angular modulation  

NASA Astrophysics Data System (ADS)

The paper presents imaging properties of modified lenses with the radial and the angular modulation. We analyze three following optical elements with moderate numerical apertures: the forward logarithmic axicon and the axilens representing the radial modulation as well as the light sword optical element being a counterpart of the axilens with the angular modulation. The abilities of the elements for imaging with extended depth of focus are discussed in detail with the help of structures of output images and modulation transfer functions corresponding to them. According to the obtained results only the angular modulation of the lens makes possible to maintain the acceptable resolution, contrast and brightness of the output images for a wide range of defocusing. Therefore optical elements with angular modulations and moderate numerical apertures seem to be especially suitable for imaging with extended focal depth.

Mikula, G.; Jaroszewicz, Z.; Kolodziejczyk, A.; Petelczyc, K.; Sypek, M.

2007-07-01

234

Quantifiers and approximation  

Microsoft Academic Search

We investigate tile relationship between logical expressibility of NP optimization problems and their approximation properties. First sucll attempt was made by Papadimitriou and Yannakakis, who defined the class of NPO problems MAX NP. We show that many importaut optimization problems do not belong to MAX NP and that in fact there are problems in P which are not ill lk'IAX

Alessandro Panconesi; Desh Ranjan

1990-01-01

235

Approximating Latin Square Extensions  

Microsoft Academic Search

In this paper, we consider the following question: what is the maximum number of entriesthat can be added to a partially filled latin square? The decision version of this question isknown to be NP-complete. We present two approximation algorithms for the optimizationversion of this question. We first prove that the greedy algorithm achieves a factor of 1\\/3. Wethen use insights

Ravi Kumar; Alexander Russell; Ravi Sundaram

1996-01-01

236

Multidimensional Stochastic Approximation Methods  

Microsoft Academic Search

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

Julius R. Blum

1954-01-01

237

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

238

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

239

Approximate Inclusion-Exclusion  

Microsoft Academic Search

The Inclusion-Exclusion formula expresses the size of a union of a family of sets in terms of the sizes of intersections of all subfamilies. This paper considers approximating the size of the union when intersection sizes are known for only some of the subfamilies, or when these quantities are given to within some error, or both.

Nathan Linial; Noam Nisan

1990-01-01

240

Approximate portfolio analysis  

Microsoft Academic Search

This paper presents a portfolio selection model based on the idea of approximation. The model describes a portfolio by its decumulative distribution curve and a preference structure by a family of convex indifference curves. It prescribes the optimal portfolio as the one whose decumulative curve has the highest tangent indifference curve. The model extends the mean–variance model in the sense

Liping Liu

1999-01-01

241

Mean Angular Momenta of Primary Photofission Products  

NASA Astrophysics Data System (ADS)

Isomer ratios and mean angular momenta for photofission products of 237Np and 238U are obtained. The technique of gamma-ray spectrometry for isomeric ratio determination was used. Fissionable nuclei were irradiated by bremsstrahlung spectrum of microtron M-30 with electron energy 16 MeV. Calculations of mean angular momenta were performed by modified version of the EMPIRE II code.

Bezshyyko, O. A.; Kadenko, I. M.; Mazur, V. M.; Plujko, V. A.; Strilchuk, N. V.; Vishnevsky, I. M.; Yermolenko, R. V.; Zheltonozhsky, V. A.

2005-05-01

242

Angular velocity expansions of nuclear rotational energies  

Microsoft Academic Search

A phenomenological expansion of nuclear rotational energies terms of the angular velocity is discussed and applied to the doubly even nucleaides in the massregon between Ce and Pt. The results of fits with two, three and four parameters are presented. The two-parameter angular velocity expansion is equivalent to the VMI (variable moment of inertia) model and gives a remarkably improved

Ø. Saethre; S. A. Hjorth; A. Johnson; S. Jägare; H. Ryde; Z. Szymanski

1973-01-01

243

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

244

Single particle sizing approach using angular optical scattering distributions  

NASA Astrophysics Data System (ADS)

Sizing a small particle from its scattered field has been a long-standing problem. Popular established methods require a priori knowledge of either the refractive index of the particle, or the approximate particle size range. In this paper, the diffraction tomography (DT) theory is studied and a single particle sizing approach using angular optical scattering field is proposed. There is a Fourier relationship between the scattering amplitude in the far zone and the scattering potential of the scatterer, under the 1st-order Born approximation for weakly scattering. Based on this relationship, the distribution of scattering potential can be retrieved from angular resolved scattered field by the use of a fast Fourier transform. Single particle size is estimated from the scattering potential. Numerical simulations for spherical particles are presented and discussed. Simulation results show that in the case of low contrast, the size of the particles can be estimated accurately in the presence of moderate noise. A further variant of this algorithm based on Rytov approximation is also discussed.

Ding, Chizhu; Yang, Kecheng; Li, Wei; Xia, Min

2013-09-01

245

The angular momentum of the Oort cloud  

SciTech Connect

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

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

1991-01-01

246

Shortwave aerosol radiative forcing over cloud-free oceans from Terra: 1. Angular models for aerosols  

Microsoft Academic Search

Using multiple satellite instruments, we demonstrate a new empirical method for obtaining shortwave (SW) aerosol angular distribution models (ADMs) over cloud-free oceans. We use nearly a year's worth of multispectral Moderate Resolution Imaging Spectroradiometer (MODIS) data to obtain aerosol properties within a Clouds and Earth Radiant Energy System (CERES) footprint and Special Sensor Microwave Imager (SSM\\/I) data to obtain near

Jianglong Zhang; Sundar A. Christopher

2005-01-01

247

Angular Momentum Distribution of Hot Gas and Implications for Disk Galaxy Formation  

NASA Astrophysics Data System (ADS)

We study the angular momentum profiles both for dark matter and for gas within virialized halos using a statistical sample of halos drawn from cosmological hydrodynamics simulations. Three simulations have been analyzed: one is the nonradiative simulation and the other two have radiative cooling. We find that the gas component, on average, has a larger spin and contains a smaller fraction of mass with negative angular momentum than its dark matter counterpart in the nonradiative model. As to the cooling models, the gas component shares approximately the same spin parameter as its dark matter counterpart, but the hot gas has a higher spin and is more aligned in angular momentum than dark matter, while the opposite holds for the cold gas. After the mass of negative angular momentum is excluded, the angular momentum profile of the hot gas component approximately follows the universal function originally proposed by Bullock et al. for dark matter, though the shape parameter ? is much larger for hot gas and is comfortably in the range required by observations of disk galaxies. Since disk formation is related to the distribution of hot gas that will cool, our study may explain the fact that the disk component of observed galaxies contains a smaller fraction of low angular momentum material than dark matter in halos.

Chen, D. N.; Jing, Y. P.; Yoshikaw, Kohji

2003-11-01

248

Optimizing the Zeldovich approximation  

NASA Astrophysics Data System (ADS)

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.

249

Novel method to evaluate angular stiffness of prosthetic feet from linear compression tests.  

PubMed

Lower limb amputee gait during stance phase is related to the angular stiffness of the prosthetic foot, which describes the dependence of ankle torque on angular progression of the shank. However, there is little data on angular stiffness of prosthetic feet, and no method to directly measure it has been described. The objective of this study was to derive and evaluate a method to estimate the angular stiffness of prosthetic feet using a simple linear compression test. Linear vertical compression tests were performed on nine configurations of an experimental multicomponent foot (with known component stiffness properties and geometry), which allowed for parametric adjustment of hindfoot and forefoot stiffness properties and geometries. Each configuration was loaded under displacement control at distinct pylon test angles. Angular stiffness was calculated as a function of the pylon angle, normal force, and center of pressure (COP) rate of change with respect to linear displacement. Population root mean square error (RMSE) between the measured and predicted angular stiffness values for each configuration of the multicomponent foot was calculated to be 4.1?N-m/deg, dominated by a bias of the estimated values above the predicted values of 3.8?±?1.6?N-m/deg. The best-fit line to estimated values was approximately parallel to the prediction, with R2?=?0.95. This method should be accessible for a variety of laboratories to estimate angular stiffness of experimental and commercially available prosthetic feet with minimal equipment. PMID:23897236

Adamczyk, Peter G; Roland, Michelle; Hahn, Michael E

2013-10-01

250

Optimal simulations of ultrasonic fields produced by large thermal therapy arrays using the angular spectrum approach  

PubMed Central

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

Zeng, Xiaozheng; McGough, Robert J.

2009-01-01

251

Hybridization of angular-momentum eigenstates in nonspherical sodium clusters  

NASA Astrophysics Data System (ADS)

Angle-resolved photoelectron spectra of low-temperature sodium clusters Na33? and Na34? have been measured as a function of photon energy. The experiments in combination with density functional theory calculations demonstrate that despite the strongly oblate shape of the clusters, most of the occupied valence orbitals are close to angular-momentum eigenstates. Some states, however, exhibit a strongly mixed character. This mixing follows the selection rules ?l=±2 and ?m=0, which result from the approximate symmetry of the cluster deformation.

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

2013-10-01

252

An improved saddlepoint approximation.  

PubMed

Given a set of third- or higher-order moments, not only is the saddlepoint approximation the only realistic 'family-free' technique available for constructing an associated probability distribution, but it is 'optimal' in the sense that it is based on the highly efficient numerical method of steepest descents. However, it suffers from the problem of not always yielding full support, and whilst [S. Wang, General saddlepoint approximations in the bootstrap, Prob. Stat. Lett. 27 (1992) 61.] neat scaling approach provides a solution to this hurdle, it leads to potentially inaccurate and aberrant results. We therefore propose several new ways of surmounting such difficulties, including: extending the inversion of the cumulant generating function to second-order; selecting an appropriate probability structure for higher-order cumulants (the standard moment closure procedure takes them to be zero); and, making subtle changes to the target cumulants and then optimising via the simplex algorithm. PMID:17306841

Gillespie, Colin S; Renshaw, Eric

2006-09-09

253

Approximating Latin Square Extensions  

Microsoft Academic Search

.    In this paper we investigate the problem of computing the maximum number of entries which can be added to a partially filled\\u000a latin square. The decision version of this question is known to be NP-complete. We present two approximation algorithms for the optimization version of this question. We first prove that the\\u000a greedy algorithm achieves a factor of

Ravi Kumar; Alexander Russell; Ravi Sundaram

1999-01-01

254

Approximating labelled Markov processes  

Microsoft Academic Search

Labelled Markov processes are probabilistic versions of labelled transition systems. In general, the state space of a labelled Markov process may be a continuum. In this paper, we study approximation techniques for continuous-state labelled Markov processes.We show that the collection of labelled Markov processes carries a Polish-space structure with a countable basis given by finite-state Markov chains with rational probabilities;

Josee Desharnais; Vineet Gupta; Radha Jagadeesan; Prakash Panangaden

2003-01-01

255

Approximate Probabilistic Model Checking  

Microsoft Academic Search

\\u000a Symbolic model checking methods have been extended recently to the verification of probabilistic systems. However, the representation\\u000a of the transition matrix may be expensive for very large systems and may induce a prohibitive cost for the model checking\\u000a algorithm. In this paper, we propose an approximation method to verify quantitative properties on discrete Markov chains.\\u000a We give a randomized algorithm

Thomas Hérault; Richard Lassaigne; Frédéric Magniette; Sylvain Peyronnet

2004-01-01

256

Interference in the angular distribution of photoelectrons in superimposed XUV and optical laser fields  

NASA Astrophysics Data System (ADS)

The angular distribution of photoelectrons ejected during the ionization of Ne atoms by extreme ultraviolet (XUV) free-electron laser radiation in the presence of an intense near infrared (NIR) dressing field was investigated experimentally and theoretically. A highly nonlinear process with absorption and emission of more than ten NIR photons results in the formation of numerous sidebands. The amplitude of the sidebands varies strongly with the emission angle and the angular distribution pattern reveals clear signatures of interferences between the different angular momenta for the outgoing electron in the multi-photon process. As a specific feature, the central photoelectron line is characterized at the highest NIR fields by an angular distribution, which is peaked perpendicularly to both the XUV and NIR polarization directions. Experimental results are reproduced by a theoretical model based on the strong field approximation.

Düsterer, S.; Rading, L.; Johnsson, P.; Rouzée, A.; Hundertmark, A.; Vrakking, M. J. J.; Radcliffe, P.; Meyer, M.; Kazansky, A. K.; Kabachnik, N. M.

2013-08-01

257

Approximate IBM-2 calculations  

NASA Astrophysics Data System (ADS)

An approximate method for calculations in the neutron-proton interacting boson model (IBM-2) is investigated. An additional quadrupole q-boson, identified with the antisymmetric neutron-proton state, is added to the IBM-1 space of s- and d-bosons. The states in the (s, d, q)-space with nq = 0, l,... are related to the IBM-2 states with the value of F-spin F = Fmax, Fmax-1,... Equating the matrix elements between corresponding states in the IBM-2 space and the (s, d, q)-space we map the IBM-2 operators onto the operators in the (s, d, q)-space. Comparison of exact IBM-2 calculations and approximate calculations in the (s, d, q)-space shows that the latter reproduces quite well the IBM-2 results for low-lying states. Application of mean field techniques to the approximate (s, d, q)-space method allows a transparent interpretation of the mixed symmetry states and provides simple formulas for their characteristics.

Dobeš, J.

1987-08-01

258

SPIDER: a new balloon-borne experiment to measure CMB polarization on large angular scales  

NASA Astrophysics Data System (ADS)

We describe SPIDER, a novel balloon-borne experiment designed to measure the polarization of the Cosmic Microwave Background (CMB) on large angular scales. The primary goal of SPIDER is to detect the faint signature of inflationary gravitational waves in the CMB polarization. The payload consists of six telescopes, each operating in a single frequency band and cooled to 4 K by a common LN/LHe cryostat. The primary optic for each telescope is a 25 cm diameter lens cooled to 4 K. Each telescope feeds an array of antenna coupled, polarization sensitive sub-Kelvin bolometers that covers a 20 degree diameter FOV with diffraction limited resolution. The six focal planes span 70 to 300 GHz in a manner optimized to separate polarized galactic emission from CMB polarization, and together contain over 2300 detectors. Polarization modulation is achieved by rotating a cryogenic half-wave plate in front of the primary optic of each telescope. The cryogenic system is designed for 30 days of operation. Observations will be conducted during the night portions of a mid-latitude, long duration balloon flight which will circumnavigate the globe from Australia. By spinning the payload at 1 rpm with the six telescopes fixed in elevation, SPIDER will map approximately half of the sky at each frequency on each night of the flight.

Montroy, T. E.; Ade, P. A. R.; Bihary, R.; Bock, J. J.; Bond, J. R.; Brevick, J.; Contaldi, C. R.; Crill, B. P.; Crites, A.; Doré, O.; Duband, L.; Golwala, S. R.; Halpern, M.; Hilton, G.; Holmes, W.; Hristov, V. V.; Irwin, K.; Jones, W. C.; Kuo, C. L.; Lange, A. E.; MacTavish, C. J.; Mason, P.; Mulder, J.; Netterfield, C. B.; Pascale, E.; Ruhl, J. E.; Trangsrud, A.; Tucker, C.; Turner, A.; Viero, M.

2006-07-01

259

Optimizing the Zeldovich Approximation  

NASA Astrophysics Data System (ADS)

We have recently learned that the Zel'dovich 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 by Coles, Melott & Shandarin (hereafter CMS) the accuracy of several analytic approximations to gravitational clustering was studied in the mildly non-linear regime. We found that what was called the `truncated Zel'dovich approximation' (TZA) was better than any other (except, in one case, the ordinary Zel'dovich approximation) over a wide range from linear to mildly non-linear (? ~ 3) regimes. TZA was specified by setting Fourier amplitudes equal to zero for all wavenumbers greater than k_nl_, where k_nl_ marks the transition to the non-linear 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 top-hat in coordinate space, and a Gaussian. We also study the variation in the cross-correlation 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 exp (-k^2^/2k_G_^2^) applied to the initial Fourier amplitudes is the best choice. It produces a greatly improved cross- correlation in those cases that most needed improvement, e.g. those with more small-scale power in the initial conditions. The optimum choice of k_G_ for the Gaussian window is (somewhat spectrum-dependent) 1 to 1.5 times k_nl_, where k_nl_ is defined by equation (3). Although all three windows produce similar power spectra and density distribution functions after application of the Zel'dovich 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 non-linear regime. We also report on the accuracy of particle positions and velocities

Melott, A. L.; Pellman, T. F.; Shandarin, S. F.

1994-08-01

260

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

261

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

262

The photoelectron angular distribution of water clusters  

NASA Astrophysics Data System (ADS)

The angular distribution of photoelectrons emitted from water clusters has been measured by linearly polarized synchrotron radiation of 40 and 60 eV photon energy. Results are given for the three outermost valence orbitals. The emission patterns are found more isotropic than for isolated molecules. While a simple scattering model is able to explain most of the deviation from molecular behavior, some of our data also suggest an intrinsic change of the angular distribution parameter. The angular distribution function was mapped by rotating the axis of linear polarization of the synchrotron radiation.

Zhang, Chaofan; Andersson, Tomas; Förstel, Marko; Mucke, Melanie; Arion, Tiberiu; Tchaplyguine, Maxim; Björneholm, Olle; Hergenhahn, Uwe

2013-06-01

263

Wave function for spontaneous parametric down-conversion with orbital angular momentum  

SciTech Connect

Several wave-function approximations describing spontaneous parametric down-conversion can be found in the literature. Basically all cases are derived from the standard Hamiltonian for parametric down-conversion. Most frequently, particular cases describing collinear or paraxial approximations are described. This work presents a wave function in compact form, valid for all cases of single photon-pair conversion (Type I or Type II), for all angles allowed by the phase-matching conditions and for all orbital angular momentum values l. Examples are given of coincidence structures to be expected for signal and idler photons. Partial transfer of orbital angular momentum from the pump laser to the photon pair is discussed. Some hypothesis for the decay channels of the nontransferred part of the orbital angular momentum is made.

Barbosa, Geraldo A. [Department of Electrical Engineering and Computer Science, Northwestern University, 2145 N. Sheridan Road, Evanston, Illinois 60208-3118 (United States)

2009-12-15

264

THE ANGULAR DIAMETER AND EFFECTIVE TEMPERATURE OF THE LITHIUM-RICH K GIANT HD 148293 FROM THE CHARA ARRAY  

SciTech Connect

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

Baines, Ellyn K. [Remote Sensing Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375 (United States); McAlister, Harold A.; Ten Brummelaar, Theo A.; Turner, Nils H.; Sturmann, Judit; Sturmann, Laszlo; Goldfinger, P. J.; Farrington, Christopher D. [Center for High Angular Resolution Astronomy, Georgia State University, P.O. Box 3969, Atlanta, GA 30302-3969 (United States); Ridgway, Stephen T., E-mail: ellyn.baines@nrl.navy.mil [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States)

2011-04-20

265

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

Microsoft Academic Search

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

M. Tajmar; F. Plesescu; B. Seifert

2009-01-01

266

Sublinear approximation of signals  

NASA Astrophysics Data System (ADS)

It has recently been observed that sparse and compressible signals can be sketched using very few nonadaptive linear measurements in comparison with the length of the signal. This sketch can be viewed as an embedding of an entire class of compressible signals into a low-dimensional space. In particular, d-dimensional signals with m nonzero entries (m-sparse signals) can be embedded in O(m log d) dimensions. To date, most algorithms for approximating or reconstructing the signal from the sketch, such as the linear programming approach proposed by Candes-Tao and Donoho, require time polynomial in the signal length. This paper develops a new method, called Chaining Pursuit, for sketching both m-sparse and compressible signals with O(m polylog d) nonadaptive linear measurements. The algorithm can reconstruct the original signal in time O(m polylog d) with an error proportional to the optimal m-term approximation error. In particular, m-sparse signals are recovered perfectly and compressible signals are recovered with polylogarithmic distortion. Moreover, the algorithm can operate in small space O(m polylog d), so it is appropriate for streaming data.

Gilbert, Anna C.; Strauss, Martin J.; Tropp, Joel A.; Vershynin, Roman

2006-06-01

267

Approximate Bayesian Computation  

PubMed Central

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

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

2013-01-01

268

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

269

Quantum mechanical close coupling approach to molecular collisions: Averaged definite parity jz approximation with Clebsch-Gordan weights  

Microsoft Academic Search

The new averaged definite parity jz(ADPjz) approximation is considered in detail from the standpoint of the exact body frame CC cross section equations. These cross section equations are decomposed into contributions from the various possible orbital angular momenta and projections of the total angular momentum J onto the scattering vector. This decomposition then permits a clearer examination of the quantities

Yair Shimoni; Donald J. Kouri

1977-01-01

270

Anisotropic angular distribution of sputtered atoms  

NASA Astrophysics Data System (ADS)

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

Zhang, Z. L.; Zhang, L.

2004-05-01

271

Angular Relation of Axes in Perceptual Space.  

National Technical Information Service (NTIS)

The geometry of perceptual space needs to be known to model spatial orientation constancy or to create virtual environments. To examine one main aspect of this geometry, the angular relation between the three spatial axes was measured. Experiments were pe...

U. Bucher

1992-01-01

272

Approximate theory for radiation from mesh reflectors  

NASA Astrophysics Data System (ADS)

Reconfigurable shaped reflector antennas have potential applications in satellite communications and satellite broadcasting. When a metallic mesh is employed pillowing occurs between the points at which the reflector is constrained. This paper describes an approximate theory to explain this behavior, and results are obtained which are in good agreement with exact analysis. The effect of pillowing is found to produce a periodic phase modulation across the antenna aperture. This is superimposed on the primary phase variation which controls the beam shape. For a given pillowing amplitude, it produces a gain loss which is independent of the shape of the antenna pattern, provided that the angular position of the first grating lobe of the periodic array is much larger than the intrinsic beamwidth of the antenna. For a regular distribution of points of attachment, the shape of an isotropically elastic mesh surface depends only on the ratio of the area of the attachment region to that of the unit cell.

Poulton, G. T.; Zhou, H.; Clarricoats, P. J. B.

1988-11-01

273

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

274

Design of a high-resolution angle-resolving electron energy analyzer  

Microsoft Academic Search

An angle-resolving electron energy analyzer capable of operating at an energy resolution of ≲20 meV and an angular resoltuion of ≲1\\/4° has been designed, constructed, and tested. A novel input lens allows independent control over both the energy and angular resolution. A series of tests has been performed which indicates that the analyzer operates at the theoretical resolution limit for

S. D. Kevan

1983-01-01

275

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

SciTech Connect

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

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

2011-12-15

276

Approximation by Hill Functions: II.  

National Technical Information Service (NTIS)

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

I. Babuska

1971-01-01

277

The fuzzy rough approximation decomposability  

Microsoft Academic Search

In this paper, we propose the definition of fuzzy rough approximation decomposability, discuss the properties of several fuzzy rough approximations and give several decision theorems for fuzzy rough approximation decomposability.

Xiong Fenglan; Ding Xiangqian; Yuhai Liu

2003-01-01

278

Trapezoidal approximations of fuzzy numbers  

Microsoft Academic Search

The problem of the trapezoidal approximation of fuzzy numbers is discussed. A set of criteria for approximation operators is formulated. These constraints can be used for direct operator derivation. A new nearest trapezoidal approximation operator preserving expected interval is suggested.

Przemyslaw Grzegorzewski; Edyta Mrówka

2005-01-01

279

Beam Angular Divergence Effects in Ion Implantation  

NASA Astrophysics Data System (ADS)

An important difference between monomer ion beams and heavy molecular beams is a significant reduction in beam angular divergence and increased on-wafer angular accuracy for molecular beams. This advantage in beam quality stems from a reduction in space-charge effects within the beam. Such improved angular accuracy has been shown to have a significant impact on the quality and yield of transistor devices [1,12]. In this study, B18Hx+ beam current and angular divergence data collected on a hybrid scanned beam line that magnetically scans the beam across the wafer is presented. Angular divergence is kept below 0.5 deg from an effective boron energy of 200 eV to 3000 eV. Under these conditions, the beam current is shown analytically to be limited by space charge below about 1 keV, but by the matching of the beam emittance to the acceptance of the beam line above 1 keV. In addition, results of a beam transport model which includes variable space charge compensation are presented, in which a drift mode B18Hx+ beam is compared to an otherwise identical boron beam after deceleration. Deceleration is shown to introduce significant space-charge blow up resulting in a large on-wafer angular divergence. The divergence effects introduced by wafer charging are also discussed.

Horsky, T. N.; Current, M. I.; Hahto, S. K.; Bilbrough, D. G.; Jacobson, D. C.; Krull, W. A.; Goldberg, R. D.; Hamamoto, N.; Umisedo, S.

2008-11-01

280

Angular momentum of walking at different speeds.  

PubMed

Recently, researchers in robotics have used regulation of the angular momentum of body segments about the total body center of mass (CoM) to develop control strategies for bipedal gait. This work was spurred by reports finding that for a "large class" of human movement tasks, including standing, walking, and running the angular momentum is conserved about the CoM. However, there is little data presented to justify this position. This paper describes an analysis of 11 male adults walking overground at 0.7, 1.0, and 1.3 times their comfortable walking speed (CWS). The normalized angular momenta about the body CoM of 12 body segments were computed about all three coordinate axes. The normalized angular momenta were both small (<0.03) and highly regulated for all subjects and walking speed with extrema that negatively correlated with walking speeds. It was found that the angular momentum of the body about its CoM during walking could be described by a small number of principal components. For the adult walkers the first three principal components accounted for more than 97% of the variability of the angular momentum about each of the three principal axes at all walking speeds. In addition, it was found that the orthogonal principal components at each speed and for each subject were similar, i.e., the vectors of the principal components at each speed and for each subject were co-linear. PMID:19889468

Bennett, Bradford C; Russell, Shawn D; Sheth, Pradip; Abel, Mark F

2009-11-03

281

Angular Momentum Transfer in a Protolunar Disk  

NASA Astrophysics Data System (ADS)

We numerically calculated angular momentum transfer processes in a dense particulate disk within the Roche limit by global N-body simulations, up to N=105, for parameters corresponding to a protolunar disk generated by a giant impact on a proto-Earth. In the simulations, both self-gravity and inelastic physical collisions are included. We first formalized expressions for angular momentum transfer rate including self-gravity and calculated the transfer rate with the results of our N-body simulations. Spiral structure is formed within the Roche limit by self-gravity and energy dissipation of inelastic collisions, and angular momentum is effectively transferred outward. Angular momentum transfer is dominated by both gravitational torque due to the spiral structure and particles' collective motion associated with the structure. Since formation and evolution of the spiral structure is regulated by the disk surface density, the angular momentum transfer rate depends on surface density, but not on particle size or number, so that the timescale of evolution of a particulate disk is independent of the number of particles (N) that is used to represent the disk, if N is large enough to represent the spiral structure. With N=105, the detailed spiral structure is resolved, while it is only poorly resolved with N=103; however, we found that calculated angular momentum transfer does not change as long as N>~103.

Takeda, Takaaki; Ida, Shigeru

2001-10-01

282

Beam Angular Divergence Effects in Ion Implantation  

SciTech Connect

An important difference between monomer ion beams and heavy molecular beams is a significant reduction in beam angular divergence and increased on-wafer angular accuracy for molecular beams. This advantage in beam quality stems from a reduction in space-charge effects within the beam. Such improved angular accuracy has been shown to have a significant impact on the quality and yield of transistor devices [1,12]. In this study, B{sub 18}H{sub x}{sup +} beam current and angular divergence data collected on a hybrid scanned beam line that magnetically scans the beam across the wafer is presented. Angular divergence is kept below 0.5 deg from an effective boron energy of 200 eV to 3000 eV. Under these conditions, the beam current is shown analytically to be limited by space charge below about 1 keV, but by the matching of the beam emittance to the acceptance of the beam line above 1 keV. In addition, results of a beam transport model which includes variable space charge compensation are presented, in which a drift mode B{sub 18}H{sub x}{sup +} beam is compared to an otherwise identical boron beam after deceleration. Deceleration is shown to introduce significant space-charge blow up resulting in a large on-wafer angular divergence. The divergence effects introduced by wafer charging are also discussed.

Horsky, T. N.; Hahto, S. K.; Bilbrough, D. G.; Jacobson, D. C.; Krull, W. A.; Goldberg, R. D. [SemEquip Inc., 34 Sullivan Road, Suite 18, Billerica, MA 01862 (United States); Current, M. I. [Current Scientific, 1729 Comstock Way, San Jose, CA, 95124 (United States); Hamamoto, N.; Umisedo, S. [Nissin Ion Equipment Co., 575 Kuze Tonoshiro-cho, Minami-ku, Kyoto, Japan, 601-8205 (Japan)

2008-11-03

283

Equipment for Static Characterization of Angular Transmission and Misalignments of CPV  

NASA Astrophysics Data System (ADS)

An equipment aims to perform a static angular transmission measurement based on the electroluminescence inverse method is presented. With this machine it is possible to fully characterize the two-dimensional angular transmittance of a concentration photovoltaic (CPV) module at high resolution, without the need for mechanical module rotation or flashes. Also the misalignment angles between the individual optical units in a CPV module are obtained, a useful metric for manufacturers in improving their assembly processes. A first prototype based on liquid crystal (LC) shutters has been designed to be used in parallel with the Helios 3198 CPV solar simulator.

Herrero, R.; Askins, S.; Domínguez, C.; Antón, I.; Sala, G.

2011-12-01

284

Angular distributions and angular correlations in sequential two-photon double ionization of atoms  

Microsoft Academic Search

A general expression for the angular correlation function of the two emitted photoelectrons in sequential two-photon double ionization of atoms is derived and discussed. The expression can be used in the analysis of angle-resolved coincidence experiments. The angular distributions of the emitted electrons as measured in non-coincidence experiments are also discussed. As an example, the cross sections, angular distributions of

S Fritzsche; A N Grum-Grzhimailo; E V Gryzlova; N M Kabachnik

2008-01-01

285

A system for high resolution 3D mapping using laser radar and requiring no beam scanning mechanisms  

Microsoft Academic Search

The inherently high angular and range resolution capabilities associated with radar systems operating at optical frequencies are at once a blessing and a curse. Standard implementations consist of very narrow field of view optical receivers operating in conjunction with laser transmitters or even narrower illumination beamwidth. While high angular resolution is thus achieved, mechanical scanning is required to gather data

Paul Rademacher

1988-01-01

286

Resolution characteritazion of 3D cameras  

NASA Astrophysics Data System (ADS)

Resolution analysis represents a 2D imaging topic for the use of particular targets for equipment characterization. These concepts can be extended in 3D imaging through the use of specific tridimensional target object. The core of this paper is focused on experimental characterization of seven different 3D laser scanner through the extraction of resolution, accuracy and uncertainly parameters from 3D target object. The process of every single range map defined by the same resolution leads to different results as z-resolution, optical resolution, linear and angular accuracy. The aim of this research is to suggest a characterization process mainly based on resolution and accuracy parameters that allow a reliable comparison between 3D scanner performances.

Guidi, G.; Russo, M.; Magrassi, G.; Bordegoni, M.

2009-01-01

287

The angular spread and directionality of general partially coherent beams in atmospheric turbulence  

NASA Astrophysics Data System (ADS)

Based on the extended Huygens-Fresnel principle and Rytov's approximation of the phase structure function, the analytical expressions for the beam width and angular spread of general partially coherent beams with Schell-model correlator in atmospheric turbulence are derived, and used to study the angular spread and directionality of general partially coherent beams. The relative angular spread, i.e., the ratio of the angular spread of a general partially coherent beam in turbulence to the angular spread of the same general partially coherent beam in free space, is introduced to study the sensitivity of general partially coherent beams to the effect of turbulence. It is shown that the angular spread of general partially coherent beams, including partially coherent Hermite-sin-Gaussian (H-SiG), Hermite-cos-Gaussian (H-CoG), Hermite-sinh-Gaussian (H-ShG), and Hermite-cosh-Gaussian (H-ChG) beams, with smaller spatial correlation length ?0, smaller waist width w0, and larger beam orders m, n, is less affected by turbulence than that of general partially coherent beams with larger ?0, w0, and smaller m, n. The larger the parameter ?0 is, the less the angular spread of partially coherent H-SiG and H-CoG beams is affected by turbulence, whereas the angular spread of partially coherent H-ShG and H-ChG beams with smaller ?0 is less affected by turbulence. There exist equivalent partially coherent and fully coherent H-SiG, H-CoG, H-ShG, and H-ChG beams, which have the same directionality as a fully coherent Gaussian laser beam. The results are illustrated by numerical examples and their validity is interpreted physically.

Li, Jinhong; Yang, Ailin; Lü, Baida

2008-09-01

288

Sequences, Series, and Function Approximation  

Microsoft Academic Search

Sequences are important in approximation: the usual representation of real numbers using decimals is in fact the process of giving a sequence of rational numbers approximation the real number in question successively better as more decimal places are given. These decimal approximation sequences are actually rather special: successive decimal approximations never get smaller (so the sequence is monotone nondecreasing) and

Lawrence N. Stout

2006-01-01

289

Approximation by hinge functions  

SciTech Connect

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

Faber, V.

1997-05-01

290

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

291

Multispectral angular domain imaging with a tunable pulsed laser  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

292

Temperature-controlled autocollimator with ultrahigh angular measuring precision  

SciTech Connect

A temperature-controlled autocollimator with ultrahigh angular measuring precision is proposed in this article, which is different from our previous publication [J. Yuan and X. W. Long, Rev. Sci. Instrum. 74, 1362 (2003)]. The autocollimator consists of a zoom lens illuminating a charge-coupled device (CCD). This design provides a compact size and increased stability without compromising precision. Moreover, this design makes it possible to detect a target mirror with either plane reflectors or spherical reflectors. Devices for shock absorption and heat insulation were implemented to diminish external interferences. A special temperature-control system for the autocollimator is designed to control the temperature of the autocollimator. The temperature of the autocollimator fluctuates less than {+-}0.01 deg. C. The CCD camera's noise is a fatal obstacle that prevents us from achieving an ultrahigh angular measuring precision. In this article, the influence of the CCD camera's noise on the measuring resolution is analyzed theoretically in detail. Based on the analysis, some special noise-suppressing methods to eliminate the influence of the CCD camera's noise are proposed. Both the influence of the CCD camera's noise and the noise-suppressing methods have not been discussed in our previous publication [J. Yuan and X. W. Long, Rev. Sci. Instrum. 74, 1362 (2003)]. By using the methods mentioned above, the measuring precision of the autocollimator has been greatly improved and the requirements on the external condition have been greatly reduced. The method is proved to be reliable by a prototype experiment. Two-axis angular displacement can be measured simultaneously and a measuring precision of 0.005 arcsec has been achieved, which is currently the highest measuring precision in the world.

Yuan Jie; Long Xingwu; Yang Kaiyong [Department of Optoelectronic Engineering, College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2005-12-15

293

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

NASA Astrophysics Data System (ADS)

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

Ansari, R.; Magneville, C.

2010-07-01

294

ANGULAR DIAMETERS AND EFFECTIVE TEMPERATURES OF 25 K GIANT STARS FROM THE CHARA ARRAY  

SciTech Connect

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

Baines, Ellyn K. [Remote Sensing Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375 (United States); Doellinger, Michaela P. [ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Cusano, Felice, E-mail: ellyn.baines.ctr@nrl.navy.mi, E-mail: mdoellin@eso.or, E-mail: cusano@tls-tautenburg.d [Thueringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg (Germany)

2010-02-20

295

Angular-planar CMB power spectrum  

SciTech Connect

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

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

2009-09-15

296

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

297

Angular correlation between proton and neutron rotors  

NASA Astrophysics Data System (ADS)

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

Tajima, N.

2013-07-01

298

Angular Strobe and Tracking of Jammers for Passive Monopulse Seeker  

Microsoft Academic Search

Method of angular strobe and tracking to jammers for passive monopulse seeker is presented. In the case of two wideband noise frequency modulation (FM) jammers within main beam, firstly, the angular extent parameter is used to detect the presence of two jammers. Secondly, angular resolving of the two jammers is realized by using the clustering analysis. Thirdly, angular strobe of

Songtao Xu; Shengda Wang; Chongzhao Han; Jian Ma

2006-01-01

299

Efficient broadband third harmonic frequency conversion via angular dispersion  

SciTech Connect

In this paper we present experimental measurements and theoretical modeling of third harmonic (3{omega}) conversion efficiency with optical bandwidth. Third harmonic conversion efficiency drops precipitously as the input bandwidth significantly exceeds the phase matching limitations of the conversion crystals. For Type I/Type II frequency tripling, conversion efficiency be-gins to decrease for bandwidths greater than {approximately}60 GHz. However, conversion efficiency corresponding to monochromatic phase-matched beams can be recovered provided that the instantaneous Propagation vectors are phase matched at all times. This is achieved by imposing angular spectral dispersion (ASD) on the input beam via a diffraction grating, with a dispersion such that the phase mismatch for each frequency is zero. Experiments were performed on the Optical Sciences Laser (OSL), a 1--100 J class laser at LLNL. These experiments used a 200 GHz bandwidth source produced by a multipassed electro-optic phase modulator. The spectrum produced was composed of discrete frequency components spaced at 3 GHz intervals. Angular dispersion was incorporated by the addition of a 1200 gr/mm diffraction grating oriented at the Littrow angle, and capable of rotation about the beam direction. Experiments were performed with a pulse length of 1-ns and a 1{omega} input intensity of {approximately} 4 GW/cm{sup 2} for near optimal dispersion for phase matching, 5.2 {mu}rad/GHz, with 0.1, 60, and 155 GHz bandwidth, as well as for partial dispersion compensation, 1.66 {mu}rad/GHz, with 155 GHz and 0.1 GHz bandwidth. The direction of dispersion was varied incrementally 360{degrees} about the beam diameter. The addition of the grating to the beamline reduced the narrowband conversion efficiency by approximately 10%.

Pennington, D.M.; Henesian, M.A.; Milam, D.; Eimerl, D.

1995-07-18

300

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

301

Imaging the Cosmic Microwave Background: the Degree Angular Scale Interferometer  

NASA Astrophysics Data System (ADS)

The development of low-noise, broadband millimeter-wave amplifiers has made interferometry the technique of choice for precision ground-based measurement of the cosmic microwave background (CMB). The Degree Angular Scale Interferometer (DASI) is an instrument designed to image the CMB over large regions of the sky. Its 13 element array is configured to optimize sensitivity to the CMB angular power spectrum from l = 160 to l = 710, with single-field resolution of Delta l ~ 30. Each array element consists of a 20-cm diameter lensed corrugated horn and a cryogenic HEMT amplifier-based 26 - 36 GHz receiver. All 13 elements, along with the 10 x 1 GHz bandwidth complex correlator, are mounted to a single 1.6m diameter aperture plate, which is steerable by the telescope about three axes: azimuth, elevation, and the boresight axis. This compact design eliminates the need for delay lines, provides flexibility in sky and u,v coverage, and increases control over instrument systematics. It also will permit efficient installation of the instrument at its observing site, the South Pole, where excellent atmospheric transparency and stability offer ideal conditions for large-field interferometry. Construction of the telescope will be completed in Summer 1998, and DASI will be deployed at the South Pole for year-round operation starting in November 1999.

Kovac, J.; Carlstrom, J. E.; Dragovan, M.; Holzapfel, W. L.; Halverson, N. W.

1998-05-01

302

Resolution performance of the extra ultraviolet telescopes  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

303

Connection between the bremsstrahlung tip and direct radiative recombination: Angular distributions and polarization correlations  

NASA Astrophysics Data System (ADS)

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

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

1983-08-01

304

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

305

Interstellar scattering and resolution limitations  

NASA Astrophysics Data System (ADS)

Density irregularities in both the interplanetary medium and the ionized component of the interstellar medium scatter radio waves, resulting in limitations on the achievable resolution. Interplanetary scattering (IPS) is weak for most observational situations, and in principle the resulting phase corruption can be corrected for when observing with sufficiently many array elements. Interstellar scattering (ISS), on the other hand, is usually strong at frequencies below about 8 GHz, in which case intrinsic structure information over a range of angular scales is irretrievably lost. With the earth-space baselines now planned, it will be possible to search directly for interstellar refraction, which is suspected of modulating the fluxes of background sources.

Dennison, Brian

306

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)

1997-12-01

307

Interpolation function for approximating knee joint behavior in human gait  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

308

Conflict resolution.  

PubMed

The sooner conflict is identified and confronted, the more quickly it can be resolved (and the sooner, the better). When this is accomplished calmly and objectively, many areas of conflict will be eliminated. Addressing conflict as it arises also sends a clear message to the team that the practice seeks resolution, not punishment or negative consequences. In addition, the dentist and the office manager need to lead by example by avoiding gossip and encouraging open communication. The goal is to go from a parent-child relationship with the dental team to an adult-adult relationship using this series of managerial conflict resolution steps. PMID:16570474

Levin, Roger

2006-03-01

309

Angular distribution of electrons from powerful accelerators  

NASA Astrophysics Data System (ADS)

A technique for measuring the angular distribution of electrons escaping from the center of the window of the IGUR-3 and ÉMIR-M powerful accelerators (designed at the All-Russia Institute of Technical Physics, Russian Federal Nuclear Center) into ambient air is presented, and measurement data are reported. The number of electrons is measured with cable detectors (the solid angle of the collimator of the detector is ?0.01 sr). The measurements are made in three azimuthal directions in 120° intervals in the polar angle range 0 22°. The angular distributions of the electrons coming out of the accelerators are represented in the form of B splines.

Stepovik, A. P.; Lartsev, V. D.; Blinov, V. S.

2007-07-01

310

Angular momentum dependence of incomplete fusion reactions  

NASA Astrophysics Data System (ADS)

?-ray multiplicities associated with various reaction channels have been measured for the 14N + 197Au system at Elab = 115 and 168 MeV. Channel selection accomplished via charged ejectile-KX-ray coincidence measurements permitted distinction between reactions with two or more charged fragments in the final state. For the former type of reactions the angular momentum dependence expected for (binary) incomplete fusion reactions is obserbed. For the latter, the same angular momentum dependence is found if sequential decay of the primary light fragment is assumed. On leave from the Institute of Nuclear Research, 05-400 Swierk, Poland.

Wilschut, H. W.; Balster, G. J.; Goldhoorn, P. B.; Siemssen, R. H.; Sujkowski, Z.

1984-04-01

311

Angular and linear momentum of excited ferromagnets  

NASA Astrophysics Data System (ADS)

The angular momentum vector of a Heisenberg ferromagnet with isotropic exchange interaction is conserved, while under uniaxial crystalline anisotropy the projection of the total spin along the easy axis is a constant of motion. Using Noether's theorem, we prove that these conservation laws persist in the presence of dipole-dipole interactions. However, spin and orbital angular momentum are no longer conserved separately. We also define the linear momentum of ferromagnetic textures. We illustrate the general principles with special reference to spin transfer torques and identify the emergence of a nonadiabatic effective field acting on domain walls in ferromagnetic insulators.

Yan, Peng; Kamra, Akashdeep; Cao, Yunshan; Bauer, Gerrit E. W.

2013-10-01

312

Small angular displacement measurement based on an autocollimator and a common-path compensation principle  

NASA Astrophysics Data System (ADS)

A novel method for small angular displacement measurement based on an autocollimator and a common-path compensation principle by using single CCD detector was proposed. The principles of the angular displacement measurement and the common-path compensation were analyzed. The feasibility of measurement method was verified and the experimental results revealed that the linear correlativity between the relative displacement of the measuring beam spot and the angular displacement is 0.99996. And the measurement resolution is about 0.03 arcsec. To test the compensation's effect, a series of experiments introducing three different interferences from system and external environment were performed. The experimental results indicated that the standard deviations of the measuring beam spot's angular drift were improved by at least 25.0% to at most 80.0% in x direction while by at least 28.2% to at most 95.6% in y direction. Thus, the stability of the system and the measurement resolution were improved.

Li, Ke; Kuang, Cuifang; Liu, Xu

2013-01-01

313

Small angular displacement measurement based on an autocollimator and a common-path compensation principle.  

PubMed

A novel method for small angular displacement measurement based on an autocollimator and a common-path compensation principle by using single CCD detector was proposed. The principles of the angular displacement measurement and the common-path compensation were analyzed. The feasibility of measurement method was verified and the experimental results revealed that the linear correlativity between the relative displacement of the measuring beam spot and the angular displacement is 0.99996. And the measurement resolution is about 0.03 arcsec. To test the compensation's effect, a series of experiments introducing three different interferences from system and external environment were performed. The experimental results indicated that the standard deviations of the measuring beam spot's angular drift were improved by at least 25.0% to at most 80.0% in x direction while by at least 28.2% to at most 95.6% in y direction. Thus, the stability of the system and the measurement resolution were improved. PMID:23387696

Li, Ke; Kuang, Cuifang; Liu, Xu

2013-01-01

314

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

315

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

316

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

317

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

PubMed

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

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

2013-08-09

318

Three-dimensional angular domain optical projection tomography  

NASA Astrophysics Data System (ADS)

Angular Domain Imaging (ADI) has been previously demonstrated to generate projection images of attenuating targets embedded within a turbid medium. The imaging system employs a silicon micro-tunnel array positioned between the sample and the detection system to reject scattered photons that have deviated from the initial propagation direction and to select for ballistic and quasi-ballistic photons that have retained their forward trajectory. Two dimensional tomographic images can be reconstructed from ADI projections collected at a multitude of angles. The objective of this work was to extend the system to three dimensions by collecting several tomographic images and stacking the reconstructed slices to generate a three dimensional volume representative of the imaging target. A diode laser (808nm, CW) with a beam expander was used to illuminate the sample cuvette. An Angular Filter Array (AFA) of 80 ?m × 80 ?m square-shaped tunnels 2 cm in length was used to select for image forming quasi-ballistic photons. Images were detected with a linear CCD. Our approach was to use a SCARA robot to rotate and translate the sample to collect sufficient projections to reconstruct a three dimensional volume. A custom designed 3D target consisting of 4 truncated cones was imaged and reconstructed with filtered backprojection and iterative methods. A 0.5 mm graphite rod was used to collect the forward model, while a truncated pseudoinverse was used to approximate the backward model for the iterative algorithm.

Ng, Eldon; Vasefi, Fartash; Roumeliotis, Michael; Kaminska, Bozena; Carson, Jeffrey J. L.

2011-02-01

319

Angular-Momentum-Dependent Orbital-Free Density Functional Theory  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

320

Bayesian Angular Power Spectrum Analysis of Interferometric Data  

NASA Astrophysics Data System (ADS)

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

Sutter, P. M.; Wandelt, Benjamin D.; Malu, Siddarth S.

2012-09-01

321

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

322

Weak Copositive and Intertwining Approximation  

Microsoft Academic Search

It is known that shape preserving approximation has lower rates than unconstrained approximation. This is especially true for copositive and intertwining approximations. Forf?Lp, 1?papproximations and conclude that the most sensible way is the

Y. K. Hu; K. A. Kopotun; X. M. Yu

1999-01-01

323

Photoelectron angular distributions of low-order above-threshold ionization of Xe in the multiphoton regime  

NASA Astrophysics Data System (ADS)

We present high-resolution two-dimensional momentum distributions and energy-angular distributions of photoelectrons from xenon atoms, ionized by an 800-nm, 25-fs linearly polarized laser at intensities of (1.8-4.4) × 1013 W/cm2. The angular distributions of low-energy photoelectrons exhibit pronounced intensity-dependent features. The photoelectron angular distributions (PADs) of nonresonant ionization, Freeman resonance, and main order above-threshold ionization at different laser intensities are analyzed. We have characterized the PADs of above-threshold ionization up to the fourth order and have confirmed the angular momentum selection rule of ?l=1 for above-threshold ionization at all laser intensities. We observe that the channel of nine-photon resonant ionization has switched to a ten-photon process but nine-photon nonresonance still remains for xenon.

Li, Min; Liu, Yunquan; Liu, Hong; Yang, Yudong; Yuan, Jialei; Liu, Xianrong; Deng, Yongkai; Wu, Chengyin; Gong, Qihuang

2012-01-01

324

Approximate convex decomposition of polygons  

Microsoft Academic Search

We propose a strategy to decompose a polygon, containing zero or more holes, into ``approximately convex'' pieces. For many applications, the approximately convex components of this decomposition provide similar benefits as convex components, while the resulting decomposition is significantly smaller and can be computed more efficiently. Moreover, our approximate convex decomposition (ACD) provides a mechanism to focus on key structural

Jyh-Ming Lien; Nancy M. Amato

2004-01-01

325

Flexible lognormal sum approximation method  

Microsoft Academic Search

A simple and novel method is presented to approximate the distribution of the sum of independent, but not necessarily identical, lognormal random variables, by the lognormal distribution. It is shown that matching a short Gauss-Hermite approximation of the moment generating function of the lognormal sum with that of the lognormal distribution leads to an accurate lognormal sum approximation. The advantage

Jingxian Wu; Neelesh B. Mehta; Jin Zhang

2005-01-01

326

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

327

Angular Motion of Spinning Almost Symmetric Missiles.  

National Technical Information Service (NTIS)

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

C. H. Murphy

1978-01-01

328

Thermally Activated Seizure of Angular Contact Bearings  

Microsoft Academic Search

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

R. A. Burton; H. E. Staph

1967-01-01

329

Metal grid angular filters for sidelobe suppression  

Microsoft Academic Search

This report presents an analysis, design data and preliminary experimental results that demonstrate the use of metal grid angular filters for sidelobe suppression. These results indicate that sidelobe suppression in excess of 30 dB is achievable within 20 deg of the transmission pass band.

R. J. Mailloux; P. R. Franchi

1979-01-01

330

An introduction to the angular Fourier transform  

Microsoft Academic Search

The author introduces the angular Fourier transform (AFT), a generalization of the classical Fourier transform. The AFT can be interpreted as a rotation on the time-frequency plane. An AFT with an angle of alpha = pi \\/2 corresponds to the classical Fourier transform, and an AFT with alpha =0 corresponds to the identity operator. The angles of successively performed AFTs

Luis B. Almeida; R. Alves Redol

1993-01-01

331

Heteromodal conceptual processing in the angular gyrus.  

PubMed

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

2013-01-17

332

Nanoplasmonic electron acceleration in silver clusters studied by angular-resolved electron spectroscopy  

Microsoft Academic Search

The nanoplasmonic field enhancement effects in the energetic electron emission from few-nm-sized silver clusters exposed to intense femtosecond dual pulses are investigated by high-resolution double differential electron spectroscopy. For moderate laser intensities of 1014 W cm?2, the delay-dependent and angular-resolved electron spectra show laser-aligned emission of electrons up to keV kinetic energies, exceeding the ponderomotive potential by two orders of

J Passig; R Irsig; N X Truong; Th Fennel; J Tiggesbäumker; K H Meiwes-Broer

2012-01-01

333

A new automatic system for angular measurement and calibration in radiometric instruments.  

PubMed

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

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

2010-04-13

334

High resolution study of isovector negative parity states in the {sup 16}O({sup 3}He,t){sup 16}F reaction at 140 MeV/nucleon  

SciTech Connect

The isovector transitions from the ground state (g.s.) of {sup 16}O to the negative parity states in {sup 16}F, i.e., the J{sup {pi}}=0{sup -} g.s., the 0.193 MeV, 1{sup -} state, the 0.424 MeV, 2{sup -} state, the 0.721 MeV, 3{sup -} state, and the 4{sup -}''stretched'' state at 6.372 MeV, were studied by using a high resolution {sup 16}O({sup 3}He,t){sup 16}F reaction at 140 MeV/nucleon. With the help of high energy resolution, these states were, for the first time, clearly resolved in a charge exchange reaction at an intermediate energy, which favorably excites spin-flip states. Angular distributions of the reaction cross sections were measured in the laboratory frame from 0 deg. to 14 deg. Parameters of phenomenological effective interactions were derived so as to reproduce these angular distributions in distorted wave Born approximation (DWBA) calculations. The angular distribution of the 0{sup -} state could be reproduced well at {theta}{sub c.m.}<10 deg. The empirical values, however, are larger by a factor of 2-2.5 in the larger angle region, where the contribution of the so-called 'condensed pion field' is expected. The high resolution also enabled the decay widths of these states to be measured.

Fujita, H. [School of Physics, University of the Witwatersrand, Johannesburg 2050 (South Africa); iThemba LABS, Somerset West 7129 (South Africa); Berg, G. P. A.; Fujimura, H.; Fujita, K.; Hara, K.; Hatanaka, K.; Kamiya, J.; Nakanishi, K.; Sakamoto, N.; Sakemi, Y.; Shimizu, Y.; Wakasa, T. [Research Center for Nuclear Physics (RCNP), Ibaraki, Osaka 567-0047 (Japan); Fujita, Y.; Adachi, T.; Shimbara, Y.; Yoshifuku, M. [Department of Physics, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Rapaport, J. [Department of Physics, Ohio University, Athens, Ohio 45701 (United States); Botha, N. T. [Department of Physics, University of Cape Town, Rondebosch 7701 (South Africa); Kawabata, T. [Center for Nuclear Study (CNS), University of Tokyo, Bunkyo, Tokyo 113-0033 (Japan); Neveling, R. [iThemba LABS, Somerset West 7129 (South Africa)] (and others)

2009-02-15

335

Temporal resolution enhancement from motion  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

336

Studying oxygen vacancies in ceramics by perturbed angular correlation spectroscopy  

SciTech Connect

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 in tetragonal zirconia and by In in ceria. For Cd in tetragonal zirconia, the vacancy trap energy is found to be 0.44 eV, and the energy barrier between adjacent trap sites is approximately 0.8 eV. The activation energy of an oxygen vacancy hopping between trap sites around {sup 111}Cd in ceria is found to be 0.55 eV. The activation energy for oxygen vacancy hopping in cubic zirconia, as detected by {sup 181}Ta PAC, is about 1.0 eV and independent of the Y concentration. 12 refs., 4 figs.

Su, Han-Tzong; Wang, Ruiping; Fuchs, H.; Gardner, J.A. (Oregon State Univ., Corvallis, OR (USA). Dept. of Physics); Evenson, W.E. (Brigham Young Univ., Provo, UT (USA). Dept. of Physics); Sommers, J.A. (Teledyne-Wah Chang, Albany, OR (USA))

1990-01-01

337

Three-body hyperspherical method with infinite angular expansions  

SciTech Connect

The hyperspherical method based on infinite angular expansions is introduced. We approximate the cusp behavior of a wave function using B-spline techniques. Calculations for the ground-state energies of the atomic helium and the e{sup +}Li system are presented as two examples for testing this method. The computed ground-state energy of He is -2.903 724 a.u. with single particle orbitals l{sub max}=8. For the e{sup +}Li system, with l{sub max}=9, the ground-state energy is -0.250 83 a.u., which is better than the configuration interaction result of -0.250 107 82 a.u. with l{sub max}=30.

Han Huili; Tang Liyan; Shi Tingyun [State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China)

2011-12-15

338

Angles in fuzzy disc and angular noncommutative solitons  

NASA Astrophysics Data System (ADS)

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

Kobayashi, Shinpei; Asakawa, Tsuguhiko

2013-04-01

339

Angular momentum evolution of Algol binaries  

NASA Astrophysics Data System (ADS)

We have compiled the well-determined absolute parameters of Algol-type binaries. The lists contain the parameters of 74 detached and 61 semidetached close binaries. The double-lined eclipsing binaries provide not only the most accurate determinations of stellar mass, radius and temperatures but also distance-independent luminosity for each of their individual components. The distributions of the primary and secondary masses of detached binaries (DBs) are similar, whilst the secondary masses of the semidetached binaries (SDBs) are mostly smaller than 2 Msolar with a peak in the M2-bin (0.21-1.0). The components of the DBs are almost all located in the main-sequence band. On the contrary, the secondary components of the SDBs have larger radii and luminosity with respect to the same mass and the same effective temperature of main-sequence counterparts. They occupy a region of the Hertzsprung-Russell diagram between terminal-age main sequence and giants. Moreover, the total angular momenta and specific angular momenta are larger for the SDBs of orbital periods with P > 5 d than those of the shorter period ones. The specific angular momenta of SDBs with periods longer than 5 d are 65 per cent greater than that of the short period group with the same mass. The DBs and the SDBs with orbital periods longer and shorter than 5 d are separated into three groups in the J/M5/3 - q diagram. The SDBs with mass ratios greater than 0.3 and P > 5 d have almost the same angular momentum to those of DBs. However, the SDBs with short periods have the smallest angular momentum even though they have the same mass ratios. This result reveals that angular momentum loss (AML) considerably affects the evolution of close binary systems. Recently, Chen, Li & Qian suggested that, in addition to magnetic braking, a circumbinary disc may play an important role in AML from Algol-type binaries. Their calculations indicated that the evolution of Algol-type binaries can be significantly affected by the circumbinary disc. Our results show that the evolution of close binaries begins as a DB and losing angular momentum, first via stellar wind and then magnetic braking plus circumbinary disc the period is shortened and orbit shrinks. Thereafter, the evolution of the system is accelerated and mass transfer rates are enhanced which result in a smaller mass ratios.

Ibano?lu, C.; Soydugan, F.; Soydugan, E.; Dervi?o?lu, A.

2006-11-01

340

High Resolution Imaging with AEOS  

SciTech Connect

The U. S. Air Force Advanced Electro-Optical System (AEOS) which includes a 941 actuator adaptive optics system on a 3.7m telescope has recently been made available for astronomical programs. Operating at a wavelength of 750 nm, the diffraction-limited angular resolution of the system is 0.04 inches; currently, the magnitude limit is V {approx} 7 mag. At the distances of nearby open clusters, diffraction-limited images should resolve companions with separations as small as 4-6 AU--comparable to the Sun-Jupiter distance. The ability to study such close separations is critical, since most companions are expected to have separations in the few AU to tens of AU range. With the exceptional angular resolution of the current AEOS setup, but restricted target magnitude range, we are conducting a companion search of a large, well-defined sample of bright early-type stars in nearby open clusters and in the field. Our data set will both characterize this relatively new adaptive optics system and answer questions in binary star formation and stellar X-ray activity. We will discuss our experience using AEOS, the data analysis involved, and our initial results.

Patience, J; Macintosh, B A; Max, C E

2001-08-27

341

Observations and modeling of angular compression and vertical spatial coherence in sea surface forward scattering.  

PubMed

Measurements and modeling of spatial coherence and related angular spreading associated with forward scattering from the sea surface are presented. The measurements were taken in waters 80 m deep off the New Jersey coast in August 2006. Acoustic signals from a source at depth 40 m were recorded on a vertical line array of length 1.4 m, centered at depth 25 m, and at range 200 m. Measurements in the 14-20-kHz frequency range are reported; the rms waveheight H was 0.16 m, setting kH as approximately 10 where k is acoustic wavenumber. A systematic study of measurements taken over four source-receiver bearing angles separated by 90 degrees suggests a null influence of changing bearing angle or equivalently directional wave effects. Sound speed was characterized by a downward-refracting profile. Refraction modifies the vertical angular spread due to rough sea surface scattering, which can be understood from Snell's law. The Snell mapping is smooth, so an approximation based on the mean grazing angle provides a functional relation between the angular variance near the surface and that at the receiver. The latter is measurably reduced owing to refraction, the effect called angular compression, and a parameter that quantifies this effect is defined. PMID:20058954

Dahl, Peter H

2010-01-01

342

Limitations to resolution in superposition eyes  

Microsoft Academic Search

1.Limitations to spatial resolution in the ventral refracting superposition eye of the crepuscular dung beetle, Onitis alexis, were investigated using intracellular electrophysiological recordings and optical modelling.2.The measured angular-sensitivity functions for Onitis are narrow compared to many superposition eyes, but display considerable off-axis flanks, or flare. These flanks are reduced as the eye becomes light adapted, but the acceptance angle remains

Eric J. Warrant; Peter D. McIntyre

1990-01-01

343

Space-angle approximations in the variational nodal method.  

SciTech Connect

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

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

1999-03-12

344

ANGULAR MOMENTUM MISALIGNMENT IN DEEP INELASTIC PROCESSES AND ANGULAR DISTRIBUTION OF SEQUENTIALLY EMITTED PARTICLES AND GAMMA RAYS  

SciTech Connect

The angular momentum misalignment for fragments produced in deep inelastic scattering is discussed in terms of the thermal excitation of angular-momentum-bearing modes in the intermediate complex. Analytical expressions for the in- and out-of-plane angular distributions are obtained for sequentially emitted particles and fission fragments. The angular momentum dependence of the ratio between particle and neutron decay width is explicitly treated and found to be quite important. Similarly angular distributions are obtained both for dipole and quadrupole gamma decay. The theoretical results are compared with experimental angular distributions of sequential fission fragments, sequential alphas and gamma rays and a good agreement is found.

Moretto, L.G.; Blau, S.; Pacheco, A.

1980-12-01

345

Analytic determination of the pinhole collimator's point-spread function and RMS resolution with penetration.  

PubMed

Pinhole collimators are widely used to image small organs and animals. The pinhole response function (PRF) of knife-edge pinhole collimators has been estimated previously using geometric constructions without considering penetration and using "roll-off" models that employ an exponential model for the flux. An analytic expression for the PRF on the imaging plane that includes the effect of aperture penetration is derived in this paper by calculating the flux for photons passing through the aperture and those passing through the attenuating material. The PRF is then used to approximate the angular-dependent root-mean-square resolution in the directions parallel and perpendicular to the tilt of the point source. The corresponding aspect ratio is then obtained. The formulas are then compared with experimental data. PMID:12472261

Metzler, S D; Bowsher, J E; Greer, K L; Jaszczak, R J

2002-08-01

346

Angular momentum in cluster Spherical Collapse Model  

NASA Astrophysics Data System (ADS)

Our new formulation of the Spherical Collapse Model (SCM-L) takes into account the presence of angular momentum associated with the motion of galaxy groups infalling towards the centre of galaxy clusters. The angular momentum is responsible for an additional term in the dynamical equation which is useful to describe the evolution of the clusters in the non-equilibrium region which is investigated in the present paper. Our SCM-L can be used to predict the profiles of several strategic dynamical quantities as the radial and tangential velocities of member galaxies, and the total cluster mass. A good understanding of the non-equilibrium region is important since it is the natural scenario where the infall in galaxy clusters and the accretion phenomena present in these objects can be studied. Our results corroborate previous estimates and are in very good agreement with the analysis of recent observations and of simulated clusters.

Cupani, Guido; Mezzetti, Marino; Mardirossian, Fabio

2011-11-01

347

Angular momentum dependence of incomplete fusion reactions  

Microsoft Academic Search

gamma-ray multiplicities associated with various reaction channels have been measured for the 14N + 197Au system at Elab = 115 and 168 MeV. Channel selection accomplished via charged ejectile-KX-ray coincidence measurements permitted distinction between reactions with two or more charged fragments in the final state. For the former type of reactions the angular momentum dependence expected for (binary) incomplete fusion

H. W. Wilschut; G. J. Balster; P. B. Goldhoorn; R. H. Siemssen; Z. Sujkowski

1984-01-01

348

Enhanced Angular Momentum Transport in Accretion Disks  

Microsoft Academic Search

The status of our current understanding of angular momentum transport in\\u000aaccretion disks is reviewed. The last decade has seen a dramatic increase both\\u000ain the recognition of key physical processes and in our ability to carry\\u000athrough direct numerical simulations of turbulent flow. Magnetic fields have at\\u000aonce powerful and subtle influences on the behavior of (sufficiently) ionized\\u000agas,

Steven A. Balbus

2003-01-01

349

Measurement of angular distributions and  

Microsoft Academic Search

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

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

2000-01-01

350

Chirality and angular momentum in optical radiation  

NASA Astrophysics Data System (ADS)

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

Coles, Matt M.; Andrews, David L.

2012-06-01

351

Modern Physics Problem: Angular Wave Functions  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

352

Angular Propagation Descriptions Relevant for Base Station Adaptive Antenna Operations  

Microsoft Academic Search

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

Patrick C. F. Eggers

1999-01-01

353

Angular Propagation Descriptions Relevant for Base Station Adaptive Antenna Operations  

Microsoft Academic Search

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

PATRICK C. F. EGGERS

1999-01-01

354

Time-dependent photoelectron angular distributions  

NASA Astrophysics Data System (ADS)

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

Wang, Xiangyang

1999-09-01

355

Angular craniometry in craniocervical junction malformation.  

PubMed

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

Botelho, Ricardo Vieira; Ferreira, Edson Dener Zandonadi

2013-05-03

356

Nuclear structure at high angular momentum  

SciTech Connect

This review paper begins by discussing the limits faced in the attempts to get nuclei to hold very high angular momentum. The method presently used to produce nuclei with the maximum angular momentum is described. Then the physics of high-spin states is taken up; some properties of a purely collective, classical rotor are described, and the effects of coupling single-particle motion to this are considered. Next, backbending, its causes, and a new spectroscopy of bands and backbends at high spin values are discussed. Noncollective states occur when the nuclear angular momentum is carried by a few high-j particles and is aligned along a symmetry axis. There results an irregular yrast line, along which there are no collective transitions. Noncollective behavior in the lead region, the hafnium region, and the N = 82 region is examined. Then the discussion moves on to collective behavior and recent studies on continuum spectra. Evidence for rotation is given, and effective moments of inertia for this rotation are evaluated. Finally, current ..gamma..-ray energy correlation studies are described. 68 references, 36 figures. (RWR)

Stephens, F.S.

1980-06-01

357

Threshold photoneutron angular distribution and polarization studies of nuclei  

SciTech Connect

The photoneutron method was applied to the study of: (1) deuteron photodisintegration; (2) giant magnetic dipole resonances in heavy nuclei; (3) mechanism of radiative capture in light nuclei; and (4) isospin splitting of the giant dipole resonance in /sup 60/Ni. These studies were performed with the pulsed bremsstrahlung beam and high-resolution spectrometer available at the Argonne high-current electron linac. A threshold photoneutron polarization method was developed in order to search for the giant M1 resonance in heavy nuclei. A surprisingly small amount of M1 strength was found in /sup 208/Pb. Furthermore, the M1 strength for the 5.08-MeV excitation in /sup 17/O, the best example of a single-particle M1 resonance in nuclei, was found to be strongly quenched. In addition, the /sup 17/O(..gamma..,n/sub 0/)/sup 16/O reaction was found to provide an ideal example of the Lane-Lynn theory of radiative capture. The interplay among the three components of the theory, internal, channel and potential capture, were evident from the data. An electron beam transport system was developed which allows the bremsstrahlung to impinge on the photoneutron target on an axis perpendicular to the usual reaction plane. This system provides an accurate method for the measurement of relative angular distributions in (..gamma..,n) reactions. This system was applied to a high-accuracy measurement of the relative angular distribution for the D(..gamma..,n)H reaction. The question of isospin-splitting of the giant dipole resonance in /sup 60/Ni was studied by using the unique pico-pulse from the accelerator and the newly installed 25-m, neutron flight paths. The results provide clear evidence for the effect of isospin splitting.

Holt, R.J.

1980-01-01

358

Spin angular momentum transfer from TEM(00) focused Gaussian beams to negative refractive index spherical particles.  

PubMed

We investigate optical torques over absorbent negative refractive index spherical scatterers under the influence of linear and circularly polarized TEM(00) focused Gaussian beams, in the framework of the generalized Lorenz-Mie theory with the integral localized approximation. The fundamental differences between optical torques due to spin angular momentum transfer in positive and negative refractive index optical trapping are outlined, revealing the effect of the Mie scattering coefficients in one of the most fundamental properties in optical trapping systems. PMID:21833372

Ambrosio, Leonardo A; Hernández-Figueroa, Hugo E

2011-07-22

359

Structural optimization using Kriging approximation  

Microsoft Academic Search

An optimization method using Kriging approximation is applied to a structural optimization problem. The method involves two main processes. The first is a space estimation process that uses the Kriging method, and the second is an optimization process. The use of the Kriging method makes it easier to perform the approximation optimization. As an example of the estimation performed as

S. Sakata; F. Ashida; M. Zako

2003-01-01

360

Validity of the Rytov Approximation.  

National Technical Information Service (NTIS)

The limitations on the applicability of the Rytov approximation are examined in this paper. It is shown that (1) the singular behavior of the perturbation series of which the Rytov approximation is the first term cannot be removed by adding a 'constant' a...

W. P. Brown

1967-01-01

361

IS HEAD INJURY CAUSED BY LINEAR OR ANGULAR ACCELERATION?  

Microsoft Academic Search

Currently, angular acceleration is believed to be more damaging to the brain than linear acceleration, even though both are present in any head impact. In a recent experiment, it was found that a helmeted head sustained the same degree of angular acceleration as the unhelmeted head for the same impact, but its linear acceleration was decreased significantly. So, if angular

Albert I. King; King H. Yang; Liying Zhang; Warren Hardy

362

Tutorial on the Angular Positions and Velocities of Ground Objects.  

National Technical Information Service (NTIS)

This report is a primer or tutorial on the angular motion of ground objects relative to level-flying aircraft. Both qualitative and quantitative description is used. Equations are derived in detail for angular relationships and for angular velocities in a...

H. C. Self

1989-01-01

363

Angular momentum: Insights into walking and its control  

Microsoft Academic Search

The importance of the organization of angular momenta during walking has been suggested by the efforts of researchers to use it to control and stabilize walking robots. However, there has been little attention to the use of angular momenta as a metric of human walking or to gain insights into the control of walking. This paper analyzes the angular momemta

Bradford C. Bennett; Thomas Robert; Shawn D. Russell

2011-01-01

364

Hartree-Bose mean-field approximation for the interacting boson model (IBM-3)  

NASA Astrophysics Data System (ADS)

A Hartree-Bose mean-field approximation for the IBM-3 is presented. A Hartree-Bose transformation from spherical to deformed bosons with charge-dependent parameters is proposed which allows bosonic pair correlations and includes higher angular momentum bosons. The formalism contains previously proposed IBM-2 and IBM-3 intrinsic states as particular limits.

García-Ramos, J. E.; Arias, J. M.; Dukelsky, J.; Moya de Guerra, E.; Isacker, P. Van

1998-02-01

365

A Hartree-Bose mean-field approximation for IBM-3  

NASA Astrophysics Data System (ADS)

A Hartree-Bose mean-field approximation for the IBM-3 is presented. A Hartree-Bose transformation from the spherical to the deformed bosons with charge-dependent parameters is proposed which allows bosonic pair correlations and includes higher angular momentum bosons. The formalism contains previously proposed IBM-2 and IBM-3 intrinsic states as particular limits.

García-Ramos, J. E.; Arias, J. M.; Dukelsky, J.; de Guerra, E. Moya; van Isacker, P.

1998-06-01

366

Quantum mechanical close coupling approach to molecular collisions. jz -conserving coupled states approximation  

Microsoft Academic Search

New coupled equations describing collisions of an atom and a diatomic molecule are derived in this paper. By utilizing a description of the collision in terms of rotating coordinates, all coupling in the z component of angular momentum is isolated into purely kinematic effects. By neglecting these couplings, one is led to approximate equations for which the jz component of

Paul McGuire; Donald J. Kouri

1974-01-01

367

Approximate Genealogies Under Genetic Hitchhiking  

PubMed Central

The rapid fixation of an advantageous allele leads to a reduction in linked neutral variation around the target of selection. The genealogy at a neutral locus in such a selective sweep can be simulated by first generating a random path of the advantageous allele's frequency and then a structured coalescent in this background. Usually the frequency path is approximated by a logistic growth curve. We discuss an alternative method that approximates the genealogy by a random binary splitting tree, a so-called Yule tree that does not require first constructing a frequency path. Compared to the coalescent in a logistic background, this method gives a slightly better approximation for identity by descent during the selective phase and a much better approximation for the number of lineages that stem from the founder of the selective sweep. In applications such as the approximation of the distribution of Tajima's D, the two approximation methods perform equally well. For relevant parameter ranges, the Yule approximation is faster.

Pfaffelhuber, P.; Haubold, B.; Wakolbinger, A.

2006-01-01

368

Exchange of Spin and Orbital Angular Momentum Between an Ultracold Bose Gas and Optical Angular Momentum Beams  

Microsoft Academic Search

Atoms and photons possess both spin and orbital angular momentum degrees of freedom, which can be coupled under appropriate experimental conditions. Using Laguerre Gaussian laser beams of differing intrinsic angular momentum and polarization, we have investigated various aspects of how the spin and orbital angular momentum of the photons couple to either a nondegenerate or degenerate (BEC) bose gas. In

Kevin C. Wright; Andrew B. Kowalik; L. Suzanne Leslie; Michael V. Pack; Nicholas P. Bigelow

2007-01-01

369

General-relativistic equations of two extended bodies in the post-Newtonian approximation  

NASA Astrophysics Data System (ADS)

Within the framework of Einstein Theory of Gravitation we study the two - body problem and derive the equations of motion in the weak - field, slow - motion approximation. Relativistic definitions of momentum, angular momentum and center of mass in terms of multipole moments, are applied to obtain the laws of motion and the post - Newtonian approximation method is widely used in order to establish the metric to compute the equations and analyze its main characteristics.

Guerrero, William Alexander Almonacid; Colorado, Leonardo Castañeda; Cubillos, Joseacute; Fandiño, Fernando

2012-08-01

370

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

2013-09-24

371

Angular-Momentum Evolution in Laser-Plasma Accelerators  

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

372

Angular smoothing and radial regularization of ODF fields: application on deterministic crossing fiber tractography.  

PubMed

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

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

2011-11-02

373

Spectro-Angular Optical Biosensor Based On Surface Plasmon Resonance Operating In The Visible Spectrum  

NASA Astrophysics Data System (ADS)

Surface plasmon resonance (SPR) is one of the most widely used methods to implement biosensors because of its label-free and sensitive detection. Surface plasmon resonance allows the change in the refractive index of a sample to be measured accurately by the analysis of the light reflecting at a metal-dielectric interface. A way to increase the sensitivity of SPR biosensors was found in fabricating a spectro-angular SPR biosensor and using of a newly developed data processing method called the Double Projection Method. The objective of the work presented in this thesis is to improve further the detection limit of the spectro-angular biosensor by upgrading the cameras used for the data acquisition. Simulations have shown that the spatial resolution and the data precision have a significant impact on the accuracy of the refractive index change measurement. In this thesis, simulation results are presented to justify the modifications of the experimental system and to estimate the expected improvement in the detection limit of the spectro-angular biosensor by the use of higher spatial resolution and higher data precision cameras. The new design as well as the components purchased for the experimental set-up are detailed.

Filion Cote, Sandrine

374

(6Li, d) Reaction on fp-Shell Nuclei and Alpha-Transfer Distorted-Wave Born-Approximation Analysis  

Microsoft Academic Search

Strongly structured (6Li, d) angular distributions exhibiting systematic variations with A for A=40 to A=90 target nuclei are well reproduced by alpha-stripping calculations using a single set of potential parameters. Zero-range and finite-range distorted-wave Born-approximation results are found very similar both in the shapes of the angular distributions and in the relative magnitudes. The question of nuclear-structure dependence in the

U. Strohbusch; G. Bauer; W. W. Fulbright

1975-01-01

375

A novel high resolution ion wide angle spectrometer  

SciTech Connect

A novel ion wide angle spectrometer (iWASP) has been developed, which is capable of measuring angularly resolved energy distributions of protons and a second ion species, such as carbon C{sup 6+}, simultaneously. The energy resolution for protons and carbon ions is better than 10% at {approx}50 MeV/nucleon and thus suitable for the study of novel laser-ion acceleration schemes aiming for ultrahigh particle energies. A wedged magnet design enables an acceptance angle of 30 deg. ({approx}524 mrad) and high angular accuracy in the {mu}rad range. First, results obtained at the LANL Trident laser facility are presented demonstrating high energy and angular resolution of this novel iWASP.

Jung, D. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany); Hoerlein, R. [Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany); Gautier, D. C.; Letzring, S.; Albright, B. J.; Shah, R.; Palaniyappan, S.; Yin, L.; Fernandez, J. C. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Kiefer, D.; Habs, D. [Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany); Allinger, K. [Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany); Hegelich, B. M. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany)

2011-04-15

376

Reduced Left Angular Gyrus Volume in First-Episode Schizophrenia  

PubMed Central

Objective Research suggests that the normal left-greater-than-right angular gyrus volume asymmetry is reversed in chronic schizophrenia. The authors examined whether angular gyrus volume and asymmetry were abnormal in patients with first-episode schizophrenia. Method Magnetic resonance imaging scans were obtained from 14 inpatients at their first hospitalization for psychosis and 14 normal comparison subjects. Manual editing was undertaken to delineate postcentral, supramarginal, and angular gyri gray matter volumes. Results Group comparisons revealed that the left angular gyrus gray matter volume in patients was 14.8% less than that of the normal subjects. None of the other regions measured showed significant group volume or asymmetry differences. Conclusions Patients with new-onset schizophrenia showed smaller left angular gyrus volumes than normal subjects, consistent with other studies showing parietal lobe volume abnormalities in schizophrenia. Angular gyrus pathology in first-episode patients suggests that the angular gyrus may be a neuroanatomical substrate for the expression of schizophrenia.

Nierenberg, Jay; Salisbury, Dean F.; Levitt, James J.; David, Elizabeth A.; McCarley, Robert W.; Shenton, Martha E.

2009-01-01

377

Approximate Controllability and Weak Stabilizability.  

National Technical Information Service (NTIS)

A necessary and sufficient condition for the stabilizability of semigroups which are similar to contractions is given in terms of the approximate controllability of the infinite dimensional system dx/dt = Ax + Bu. (Author)

C. D. Benchimol

1977-01-01

378

Computer Experiments for Function Approximations.  

National Technical Information Service (NTIS)

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 engineeri...

A. Chang C. Tong I. Izmailov O. Alexandrov S. Rizzo S. Wynter

2007-01-01

379

Approximate invariant using Lie algebra.  

National Technical Information Service (NTIS)

An approximate invariant is found for sextupole transverse dynamics. It is represented in terms of the elements of a Lie algebra associated with a sextupole contribution to the time-dependent Hamiltonian for transverse dynamics.

T. Garavaglia

1992-01-01

380

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

381

Normed likelihood as saddlepoint approximation  

Microsoft Academic Search

Barndorff-Nielsen's formula (normed likelihood with constant-information metric) has been proffered as an approximate conditional distribution for the maximum-likelihood estimate, based on likelihood functions. Asymptotic justifications are available and the formula coincides with the saddlepoint approximation in full exponential models. It is shown that the formula has wider application than is presently indicated, that in local analysis it corresponds to Laplace's

D. A. S. Fraser

1988-01-01

382

Approximate coloring of uniform hypergraphs  

Microsoft Academic Search

Abstract We consider an algorithmic problem,of coloring r-uniform hypergraphs. The problem,of finding the exact value of the chromatic number of a hypergraph is known to be NP-hard, so we discuss approximate,solutions to it. Using a simple construction and known,results on hardness of graph coloring, we show that for any r 3 it is impossible to approximate in polynomial time the

Michael Krivelevich; Benny Sudakov

2003-01-01

383

The complexity of approximating entropy  

Microsoft Academic Search

(MATH) We consider the problem of approximating the entropy of a discrete distribution under several models. If the distribution is given explicitly as an array where the i-th location is the probability of the i-th element, then linear time is both necessary and sufficient for approximating the entropy.We consider a model in which the algorithm is given access only to

Tu?kan Batu; Sanjoy Dasgupta; Ravi Kumar; Ronitt Rubinfeld

2002-01-01

384

Particle angular distributions and gamma-ray multiplicities as experimental probes for angular-momentum fluctuations  

SciTech Connect

The sequential emission of /sup 4/He is demonstrated in the reaction Ho + Ta and the /sup 4/He angular distribution is used to test the rigid rotation limit in the reaction Ho + Ag. A more refined analysis of the dependence of continuum ..gamma..-ray multiplicities upon Q-value and gamma ray energy shows that reasonable agreement with the statistical model is obtained if one assumes the presence of low energy aligned dipole transitions in the reactions Ho, Yb, Sm, Ag + Ho. Sequential fission angular distributions from very asymmetric reactions U, Au + Ne provide a severe test for the statistical model.

Moretto, L.G.

1982-03-01

385

Managing resolution in multi-resolution databases  

Microsoft Academic Search

Resolution is an integral part of all forms of data. This pa- per presents a framework for quantifying, reasoning with and managing multi-resolution object-based data. The framework diers from other approaches in that it handles resolution at the object level explicitly. It defines a basic set of operations for changing an object's resolution that can be utilized for generalization, consistency

David Skogan

2001-01-01

386

Angular dependence of coercivity in magnetic nanotubes  

NASA Astrophysics Data System (ADS)

The nucleation field for infinite magnetic nanotubes, in the case of a magnetic field applied parallel to the long axis of the tubes, is calculated as a function of their geometric parameters and compared with those produced inside the pores of anodic alumina membranes by atomic layer deposition. We also extended this result to the case of an angular dependence. We observed a transition from curling-mode rotation to coherent-mode rotation as a function of the angle in which the external magnetic field is applied. Finally, we observed that the internal radii of the tubes favors the magnetization curling reversal.

Escrig, J.; Daub, M.; Landeros, P.; Nielsch, K.; Altbir, D.

2007-11-01

387

Matter & Interactions Practice Problems: Angular Momentum  

NSDL National Science Digital Library

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

Titus, Aaron

2010-01-11

388

Angular distributions of high-order ATI  

SciTech Connect

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

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

1993-08-01

389

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

390

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

SciTech Connect

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

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

2006-01-12

391

Local measurements of turbulent angular momentum transport in circular Couette flow  

NASA Astrophysics Data System (ADS)

We report on velocity fluctuations and the fluctuation-driven radial transport of angular momentum in turbulent circular Couette flow. Our apparatus is short (cylinder height to gap width ratio ? ~ 2) and of relatively high wall curvature (ratio of cylinder radii ? ~ 0.35). Fluctuation levels and the mean specific angular momentum are found to be roughly constant over radius, in accordance with previous studies featuring narrower gaps. Synchronized dual beam Laser Doppler Velocimetry (2D LDV) is used to directly measure the r - ? Reynolds stress component as a function of Reynolds number ( Re), revealing approximate scalings in the non-dimensional angular momentum transport that confirm previous measurements of torque in similar flows. 2D LDV further allows for a decomposition of the turbulent transport to assess the relative roles of fluctuation intensity and r - ? cross-correlation. We find that the increasing angular momentum transport with Re is due to intensifying absolute fluctuation levels accompanied by a slightly weakening cross-correlation.

Burin, M. J.; Schartman, E.; Ji, H.

2010-05-01

392

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

NASA Astrophysics Data System (ADS)

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

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

1998-04-01

393

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

NASA Astrophysics Data System (ADS)

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

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

2009-08-01

394

Reflectances from a supercontinuum laser-based instrument: hyperspectral, polarimetric and angular measurements.  

PubMed

Recent developments of active hyperspectral systems require optical characterization of man-made materials for instrument calibration. This work presents an original supercontinuum laser-based instrument designed by Onera, The French Aerospace Lab, for fast hyperspectral polarimetric and angular reflectances measurements. The spectral range is from 480 nm to 1000 nm with a 1 nm spectral resolution. Different polarization configurations are made possible in whole spectrum. This paper reviews the design and the calibration of the instrument. Hyper-spectral polarimetric and angular reflectances are measured for reference and man-made materials such as paint coatings. Physical properties of reflectances as positivity, energy conservation and Helmholtz reciprocity are retrieved from measurements. PMID:23388769

Ceolato, Romain; Riviere, Nicolas; Hespel, Laurent

2012-12-31

395

Angular momentum transport in complex fluids  

NASA Astrophysics Data System (ADS)

When dyes are dissolved in nematic liquid crystals, the light intensity required for the optical Freedericksz transition can be dramatically decreased. This is due to the torque exerted by the dye on the liquid crystal. The dye molecules absorb light energy and rotate; torque balance is mediated by angular momentum transport from the cell walls via shear flow generated by the rotation [1]. We present a model which accounts for the transport of angular momentum caused by singular vortices present in these complex fluids. The singular vortices generate flow, and are transported by the flow which they generate. For simple fluids, the distribution of vorticity satisfies the biharmonic equation in the Stokes limit, which can be solved analytically. In the case of the non-Newtonian fluids, such as liquid crystals, Leslie-Ericksen continuum theory is used to describe the interactions between the rod-like molecules. [1] P. Palffy-Muhoray, T. Kosa and Weinan E, ``Brownian Motors in the Photoalignment of Liquid Crystals'', Appl. Phys. A 75, 293-300 (2002).

Zheng, Xiaoyu; Palffy-Muhoray, Peter; Shelley, Michael

2008-03-01

396

Nonlocal Potentials and Complex Angular Momentum Theory  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to establish meromorphy properties of the partial scattering amplitude T(lambda,k) associated with physically relevant classes N_{w,alpha}^gamma of nonlocal potentials in corresponding domains D_{gamma,alpha}^delta of the space C^2 of the complex angular momentum lambda and of the complex momentum k (namely, the square root of the energy). The general expression of T as a quotient Theta(lambda,k)/sigma(lambda,k) of two holomorphic functions in D_{gamma,alpha}^delta is obtained by using the Fredholm-Smithies theory for complex k, at first for lambda=l integer, and in a second step for lambda complex (Real(lambda)>-1/2). Finally, we justify the "Watson resummation" of the partial wave amplitudes in an angular sector of the lambda-plane in terms of the various components of the polar manifold of T with equation sigma(lambda,k)=0. While integrating the basic Regge notion of interpolation of resonances in the upper half-plane of lambda, this unified representation of the singularities of T also provides an attractive possible description of antiresonances in the lower half-plane of lambda. Such a possibility, which is forbidden in the usual theory of local potentials, represents an enriching alternative to the standard Breit-Wigner hard-sphere picture of antiresonances.

Bros, Jacques; de Micheli, Enrico; Viano, Giovanni Alberto

2010-07-01

397

Approximate entropy of network parameters.  

PubMed

We study the notion of approximate entropy within the framework of network theory. Approximate entropy is an uncertainty measure originally proposed in the context of dynamical systems and time series. We first define a purely structural entropy obtained by computing the approximate entropy of the so-called slide sequence. This is a surrogate of the degree sequence and it is suggested by the frequency partition of a graph. We examine this quantity for standard scale-free and Erdös-Rényi networks. By using classical results of Pincus, we show that our entropy measure often converges with network size to a certain binary Shannon entropy. As a second step, with specific attention to networks generated by dynamical processes, we investigate approximate entropy of horizontal visibility graphs. Visibility graphs allow us to naturally associate with a network the notion of temporal correlations, therefore providing the measure a dynamical garment. We show that approximate entropy distinguishes visibility graphs generated by processes with different complexity. The result probes to a greater extent these networks for the study of dynamical systems. Applications to certain biological data arising in cancer genomics are finally considered in the light of both approaches. PMID:22680542

West, James; Lacasa, Lucas; Severini, Simone; Teschendorff, Andrew

2012-04-19

398

Alignment of the angular momentum vectors of planetary nebulae in the Galactic Bulge  

NASA Astrophysics Data System (ADS)

We use high-resolution H? images of 130 planetary nebulae (PNe) to investigate whether there is a preferred orientation for PNe within the Galactic Bulge. The orientations of the full sample have a uniform distribution. However, at a significance level of 0.01, there is evidence for a non-uniform distribution for those PNe with evident bipolar morphology. If we assume that the bipolar PNe have a unimodal distribution of the polar axis in Galactic coordinates, the mean Galactic position angle is consistent with 90°, i.e. along the Galactic Plane, and the significance level is better than 0.001 (the equivalent of a 3.7? significance level for a Gaussian distribution). The shapes of PNe are related to angular momentum of the original star or stellar system, where the long axis of the nebula measures the angular momentum vector. In old, low-mass stars, the angular momentum is largely in binary orbital motion. Consequently, the alignment of bipolar nebulae that we have found indicates that the orbital planes of the binary systems are oriented perpendicular to the Galactic Plane. We propose that strong magnetic fields aligned along the Galactic Plane acted during the original star formation process to slow the contraction of the star-forming cloud in the direction perpendicular to the Plane. This would have produced a propensity for wider binaries with higher angular momentum with orbital axes parallel to the Galactic Plane. Our findings provide the first indication of a strong, organized magnetic field along the Galactic Plane that impacted on the angular momentum vectors of the resulting stellar population.

Rees, B.; Zijlstra, A. A.

2013-10-01

399

Mass and angular-momentum inequalities for axi-symmetric initial data sets. II. Angular momentum  

SciTech Connect

We extend the validity of Dain's angular-momentum inequality to maximal, asymptotically flat, initial data sets on a simply connected manifold with several asymptotically flat ends which are invariant under a U(1) action and which admit a twist potential.

Chrusciel, Piotr T. [LMPT, Tours and Mathematical Institute, 24-29 St. Giles', Oxford OX1 3LB (United Kingdom)], E-mail: chrusciel@maths.ox.ac.uk; Li, Yanyan [Rutgers University (United States); Weinstein, Gilbert [University of Alabama at Birmingham (United States)

2008-10-15

400

Approximations to camera sensor noise  

NASA Astrophysics Data System (ADS)

Noise is present in all image sensor data. Poisson distribution is said to model the stochastic nature of the photon arrival process, while it is common to approximate readout/thermal noise by additive white Gaussian noise (AWGN). Other sources of signal-dependent noise such as Fano and quantization also contribute to the overall noise profile. Question remains, however, about how best to model the combined sensor noise. Though additive Gaussian noise with signal-dependent noise variance (SD-AWGN) and Poisson corruption are two widely used models to approximate the actual sensor noise distribution, the justification given to these types of models are based on limited evidence. The goal of this paper is to provide a more comprehensive characterization of random noise. We concluded by presenting concrete evidence that Poisson model is a better approximation to real camera model than SD-AWGN. We suggest further modification to Poisson that may improve the noise model.

Jin, Xiaodan; Hirakawa, Keigo

2013-02-01

401

Adaptive approximation models in optimization  

SciTech Connect

The paper proposes a method for optimization of functions of several variables that substantially reduces the number of objective function evaluations compared to traditional methods. The method is based on the property of iterative refinement of approximation models of the optimand function in approximation domains that contract to the extremum point. It does not require subjective specification of the starting point, step length, or other parameters of the search procedure. The method is designed for efficient optimization of unimodal functions of several (not more than 10-15) variables and can be applied to find the global extremum of polymodal functions and also for optimization of scalarized forms of vector objective functions.

Voronin, A.N.

1995-05-01

402

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

SciTech Connect

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

Sun, Yin-e; /Chicago U.

2005-06-01

403

Comparative study of two approaches in improving cross range resolution for an imaging antenna  

Microsoft Academic Search

The high resolution bearing of an antenna is of great importance in many practical applications, especially in microwave imaging. The angular resolution is related to the size of the antenna, but the increase of antenna size is often limited. For a real aperture antenna, the deconvolution technique was used to equivalently enlarge the size of the aperture resulting in the

D. G. Fang; W. X. Sheng; C. Zhangand; Z. Li

1997-01-01

404

The effects of positron binding and annihilation mechanisms in biomolecules on PET resolution  

Microsoft Academic Search

The angular correlation distribution of electron-positron annihilation photons is presented for polar biological molecules, and the associated noncollinearity effect on resolution in positron emission tomography (PET) is discussed. The image resolution in PET is known to be limited by a number of factors such as radioactive decay statistics, attenuation, scatter, or random coincidence of annihilation photons. This paper deals with

L. Pichl; M. Tachikawa; R. J. Buenker; M. Kimura; J.-M. Rost

2005-01-01

405

Quantum tunneling beyond semiclassical approximation  

Microsoft Academic Search

Hawking radiation as tunneling by Hamilton-Jacobi method beyond semiclassical approximation is analysed. We compute all quantum corrections in the single particle action revealing that these are proportional to the usual semiclassical contribution. We show that a simple choice of the proportionality constants reproduces the one loop back reaction effect in the spacetime, found by conformal field theory methods, which modifies

Rabin Banerjee; Bibhas Ranjan Majhi

2008-01-01

406

Approximate Spatial Reasoning (Abstract Only).  

National Technical Information Service (NTIS)

Much of human reasoning is approximate in nature. Formal models of reasoning traditionally try to be precise and reject the fuzziness of concepts in natural use and replace them with non-fuzzy scientific explicata by a process of precisiation. As an alter...

S. Dutta

1988-01-01

407

Approximate factorization for incompressible flow  

Microsoft Academic Search

For computational solution of the incompressible Navier-Stokes equations, the approximate factorization (AF) algorithm is used to solve the vectorized momentum equation in delta form based on the pressure calculated in the previous time step. The newly calculated velocities are substituted into the pressure equation (obtained from a linear combination of the continuity and momentum equation), which is then solved by

R. S. Bernard

1981-01-01

408

Approximations to wire grid inductance.  

SciTech Connect

By using a multipole-conformal mapping expansion for the wire currents we examine the accuracy of approximations for the transfer inductance of a one dimensional array of wires (wire grid). A simple uniform fit is constructed by introduction of the decay factor from bipolar coordinates into existing formulas for this inductance.

Warne, Larry Kevin; Johnson, William Arthur; Merewether, Kimball O.

2004-06-01

409

Best Approximation with Walsh Atoms.  

National Technical Information Service (NTIS)

The authors consider the approximation of L2(R) of a given function using finite linear combinations of Walsh atoms, which are Walsh functions localized to dyadic intervals, also called Haar-Walsh wavelet packets. It is shown that up to a constant factor,...

L. F. Villemoes

1995-01-01

410

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

411

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

412

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

413

Approximation properties of haplotype tagging  

PubMed Central

Background Single nucleotide polymorphisms (SNPs) are locations at which the genomic sequences of population members differ. Since these differences are known to follow patterns, disease association studies are facilitated by identifying SNPs that allow the unique identification of such patterns. This process, known as haplotype tagging, is formulated as a combinatorial optimization problem and analyzed in terms of complexity and approximation properties. Results It is shown that the tagging problem is NP-hard but approximable within 1 + ln((n2 - n)/2) for n haplotypes but not approximable within (1 - ?) ln(n/2) for any ? > 0 unless NP ? DTIME(nlog log n). A simple, very easily implementable algorithm that exhibits the above upper bound on solution quality is presented. This algorithm has running time O((2m - p + 1)) ? O(m(n2 - n)/2) where p ? min(n, m) for n haplotypes of size m. As we show that the approximation bound is asymptotically tight, the algorithm presented is optimal with respect to this asymptotic bound. Conclusion The haplotype tagging problem is hard, but approachable with a fast, practical, and surprisingly simple algorithm that cannot be significantly improved upon on a single processor machine. Hence, significant improvement in computatational efforts expended can only be expected if the computational effort is distributed and done in parallel.

Vinterbo, Staal A; Dreiseitl, Stephan; Ohno-Machado, Lucila

2006-01-01

414

Approximations to optimal nonlinear filters  

Microsoft Academic Search

Let the signal and noise processes be given as solutions to nonlinear stochastic differential equations. The optimal filter for the problem, derived elsewhere, is usually infinite dimensional. Several methods of obtaining possibly useful finite dimensional approximations are considered here, and some of the special problems of simulation are discussed. The numerical results indicate a number of useful features of the

H. Kushner

1967-01-01

415

Weak Approximations for Wiener functionals  

Microsoft Academic Search

In this paper we introduce a simple space-filtration discretization scheme on Wiener space which allows us to study weak decompositions and smooth explicit approximations for a large class of Wiener functionals. We show that any Wiener functional has an underlying robust semimartingale skeleton which under mild conditions converges to it. The discretization is given in terms of discrete-jumping filtrations which

Dorival Leao; Alberto Ohashi

2009-01-01

416

Exact and approximate membership testers  

Microsoft Academic Search

In this paper we consider the question of how much space is needed to represent a set. Given a finite universe U and some subset V (called the vocabulary), an exact membership tester is a procedure that for each element s in U determines if s is in V. An approximate membership tester is allowed to make mistakes: we require

Larry Carter; Robert W. Floyd; John Gill; George Markowsky; Mark N. Wegman

1978-01-01

417

Approximation theory of output statistics  

Microsoft Academic Search

Given a channel and an input process we study the minimum randomness of those input processes whose output statistics approximate the original out- put statistics with arbitrary accuracy. We introduce the notion of resolva- bility of a channel, defined as the number of random bits required per channel use in order to generate an input that achieves arbitrarily accu- rate

Te Sun Han; Sergio Verdii

1993-01-01

418

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

419

Quantitative measurement of variational approximations  

Microsoft Academic Search

Variational problems have long been used to mathematically model physical systems. Their advantage has been the simplicity of the model as well as the ability to deduce information concerning the functional dependence of the system on various parameters embedded in the variational trial functions. However, the only method in use for estimating the error in a variational approximation has been

D. J. Kaup; T. K. Vogel

2007-01-01

420

Incremental Approximation of Optimal Allocations.  

National Technical Information Service (NTIS)

The paper concerns the approximation of optimal allocations by delta allocations. Delta allocations are obtained by fixing an increment delta of effort and deciding at each step upon a single cell in which to allocate the entire increment. It is shown tha...

L. D. Stone

1972-01-01

421

Analytic Approximations for Spread Options  

Microsoft Academic Search

This paper expresses the price of a spread option as the sum of the prices of two compound options. One compound option is to exchange vanilla call options on the two underlying assets and the other is to exchange the corresponding put options. This way we derive a new analytic approximation for the price of a European spread option, and

Carol Alexander; Aanand Venkatramanan

2007-01-01

422

Chemical Laws, Idealization and Approximation  

NASA Astrophysics Data System (ADS)

This paper examines the notion of laws in chemistry. Vihalemm ( Found Chem 5(1):7-22, 2003) argues that the laws of chemistry are fundamentally the same as the laws of physics they are all ceteris paribus laws which are true "in ideal conditions". In contrast, Scerri (2000) contends that the laws of chemistry are fundamentally different to the laws of physics, because they involve approximations. Christie ( Stud Hist Philos Sci 25:613-629, 1994) and Christie and Christie ( Of minds and molecules. Oxford University Press, New York, pp. 34-50, 2000) agree that the laws of chemistry are operationally different to the laws of physics, but claim that the distinction between exact and approximate laws is too simplistic to taxonomise them. Approximations in chemistry involve diverse kinds of activity and often what counts as a scientific law in chemistry is dictated by the context of its use in scientific practice. This paper addresses the question of what makes chemical laws distinctive independently of the separate question as to how they are related to the laws of physics. From an analysis of some candidate ceteris paribus laws in chemistry, this paper argues that there are two distinct kinds of ceteris paribus laws in chemistry; idealized and approximate chemical laws. Thus, while Christie ( Stud Hist Philos Sci 25:613-629, 1994) and Christie and Christie ( Of minds and molecules. Oxford University Press, New York, pp. 34--50, 2000) are correct to point out that the candidate generalisations in chemistry are diverse and heterogeneous, a distinction between idealizations and approximations can nevertheless be used to successfully taxonomise them.

Tobin, Emma

2013-07-01

423

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

424

Calculation of angular distribution of multiply scattered ions  

NASA Astrophysics Data System (ADS)

A SCAT program is developed for calculation of the angular distribution of multiply scattered ions in the case of various interaction potentials. The accuracy attained is higher than that obtained with the well-known Meyer and Sigmund programs. The influence of the interaction potential on the angular distribution of multiply scattered ions is analyzed. A good agreement between the angular distribution calculated by the SCAT program and the experimental data and the results of simulation by the Monte Carlo method is observed.

Abdrashitov, V. G.; Ryzhov, V. V.; Starodumov, V. V.

1993-08-01

425

A representation of angular momentum (SU(2)) algebra  

NASA Astrophysics Data System (ADS)

This paper seeks to construct a representation of the algebra of angular momentum (SU(2) algebra) in terms of the operator relations corresponding to Gentile statistics in which one quantum state can be occupied by n particles. First, we present an operator realization of Gentile statistics. Then, we propose a representation of angular momenta. The result shows that there exist certain underlying connections between the operator realization of the Gentile statistics and the angular momentum (SU(2)) algebra.

Dai, Wu-Sheng; Xie, Mi

2004-01-01

426

Angular momenta creation in relativistic electron-positron plasma.  

PubMed

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

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

2003-07-23

427

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

428

Angular Distribution of Argon Ions and X-Ray Emissions in the Apf Plasma Focus Device  

NASA Astrophysics Data System (ADS)

Angular distribution of ion beam emission from an argon gas-filled plasma focus devices has been investigated using an array of five Faraday cups. The argon ion beam emission is found to be highly pressure-dependent and reaches its maximum at the pressure of 1 torr. The ions flux decreased as the working pressure increased; the maximum ion density at 1 torr was estimated to be around 9.24 × 1024 ions/steradian. Also, the study on the angular distribution of X-rays has been carried out using TLD-100 dosimeters. The intensity of ions reduced significantly at angles higher than ±11° but the X-ray distribution was bimodal, peaked approximately at ±15°.

Etaati, G. R.; Amrollahi, R.; Habibi, M.; Baghdadi, R.

2011-04-01

429

High angular and spectral selectivity of purple emperor (Lepidoptera: Apatura iris and A. ilia) butterfly wings.  

PubMed

The iridescent features of the butterfly species Apatura iris (Linnaeus, 1758) and A. ilia (Denis & Schiffermüller, 1775) were studied. We recognized the structural color of scales only on the dorsal side of both the fore and hind wings of males of both of the aforementioned butterfly species. The scale dimensions and microstructure were analyzed by a scanning electron microscope (SEM) and transmission electron microscope (TEM). The optical properties were measured and it was found that the peak reflectivity is around 380 nm, with a spectral width (full width at half maximum) of approximately 50 nm in both species. The angular selectivity is high and a purple iridescent color is observed within the angular range of only 18 degrees in both species. PMID:21451606

Panteli?, Dejan; Cur?i?, Sre?ko; Savi?-Ševi?, Svetlana; Kora?, Aleksandra; Kova?evi?, Aleksander; Cur?i?, Božidar; Boki?, Bojana

2011-03-28

430

Smooth-particle applied mechanics: Conservation of angular momentum with tensile stability and velocity averaging  

NASA Astrophysics Data System (ADS)

Smooth-particle applied mechanics (SPAM) provides several approaches to approximate solutions of the continuum equations for both fluids and solids. Though many of the usual formulations conserve mass, (linear) momentum, and energy, the angular momentum is typically not conserved by SPAM. A second difficulty with the usual formulations is that tensile stress states often exhibit an exponentially fast high-frequency short-wavelength instability, “tensile instability.” We discuss these twin defects of SPAM and illustrate them for a rotating elastic body. We formulate ways to conserve angular momentum while at the same time delaying the symptoms of tensile instability for many sound-traversal times. These ideas should prove useful in more general situations.

Hoover, Wm. G.; Hoover, Carol G.; Merritt, Elizabeth C.

2004-01-01