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1

Angular Resolution Enhanced Spitzer images  

NASA Astrophysics Data System (ADS)

We have developed a 'HiRes' software for deconvolution of Spitzer images that increases the angular resolution by a factor of two to three over that obtainable in a standard mosaiced image. This software is an extension of the Maximum Correlation Method (MCM) described by Aumann et al. (1990 AJ, 99, 1674), incorporating features that are applicable to the Spitzer data and FFT convolutions to speed up. While the Spitzer Space Telescope provides unprecedented sensitivity in the infrared, its spatial resolution is limited by the relatively small aperture (0.85 m) of the primary mirror. In this paper we present resolution enhanced Spitzer images demonstrating the benefits of HiRes imaging: (1) The ability to detect sources below the diffraction-limited confusion level; at 160 micron, the corresponding increase in confusion-limited sensitivity is about a factor of two. (2) The ability to separate blended sources, and thereby provide guidance to point-source extraction procedures. (3) An improved ability to show the spatial morphology of resolved sources. This work was performed by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Velusamy, T.; Beichman, C. A.; Backus, C. R.; Marsh, K. A.; Thompson, T. J.

2004-05-01

2

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

3

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

4

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

NASA Astrophysics Data System (ADS)

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

Ng, Eldon; Carson, Jeffrey J. L.

2013-02-01

5

High resolution angular studies of layered superconductors  

NASA Astrophysics Data System (ADS)

Torque and magnetotransport measurements on single crystals of several high Tc superconductors reveal new effects which appear when a magnetic field is applied very close to the layer direction. In the flux-motion resistance, a local maximum is observed, centered at ?=90°, where ? is the angle between the applied field and the c-axis. This resistance peak has an angular width of about 0.03° in TlBa2Ca2Cu3Ox and 0.30° in Bi2Sr2CaCu2Ox, and is highly nonlinear with applied current. This result is at odds with all previous reports of resistance anisotropy in the mixed state of the high Tc materials, where only an overall resistance minimum at the parallel orientation was observed. We suggest a possible mechanism for the new resistance peak: an instability in the vortex lattice at zero tilt angle resulting in the random flipping of vortex ``pancakes,'' from the ±c to the ?c directions, producing additional flux motion and dissipation. In the torque, a deviation is observed from that expected for an anisotropic, 3D superconductor in the same angular range as the resistance peak. This deviation, seen in TlBa2Ca2Cu3Ox and Tl2Ba2CaCu2Ox crystals, is similar in appearance to a prediction by Feinberg of a torque enhancement near the parallel orientation arising from the locking-in of the vortices along the layer direction.

Chung, O. H.; Chaparala, M.; Naughton, M. J.

1992-02-01

6

Angular resolution obtained with a LaBr3-based rotational modulator  

NASA Astrophysics Data System (ADS)

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

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

2009-08-01

7

Genetic Analysis of High Angular Resolution Diffusion Images (HARDI)  

E-print Network

Diffusion Imaging, tensor distribution function, structural equation model, twins, quantitative geneticsGenetic Analysis of High Angular Resolution Diffusion Images (HARDI) Liang Zhan1 , Alex D. Leow2 of Medical Research, Brisbane, Australia Abstract. Imaging genetics is a new field that extends methods from

Thompson, Paul

8

The AT20G high-angular-resolution catalogue  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

9

Quark Orbital Angular Momentum in the Wandzura-Wilczek Approximation  

E-print Network

We show that quark orbital angular momentum is directly related to off-forward correlation functions which include intrinsic transverse momentum corresponding to a derivative with respect to the transverse coordinates. Its possible contribution to scattering processes is therefore of higher twist and vanishes in the forward limit. The relation of OAM to other twist 2 and 3 distributions known in the literature is derived and formalized by an unintegrated sum rule.

Ph. Hagler; A. Mukherjee; A. Schafer

2003-12-08

10

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

11

A multiple streamline approach to high angular resolution diffusion tractography.  

PubMed

Diffusion-weighted magnetic resonance imaging has the ability to map neuronal architecture by estimating the 3D diffusion displacement within fibrous brain structures. This approach has non-invasively been demonstrated in the human brain with diffusion tensor tractography. Despite its valuable application in neuroscience and clinical studies however, it faces an inherent limit in mapping fiber tracts through areas with intervoxel incoherence. Recent advances in high angular resolution diffusion imaging have surpassed this limit and have the ability to resolve the complex fiber intercrossing within each MR voxel. To connect the fiber tracts from a multi-fiber system, this study proposed a modified fiber assignment using the continuous tracking (MFACT) algorithm and a tracking browser to propagate tracts along complex diffusion profiles. The Q-ball imaging method was adopted to acquire the diffusion displacements. Human motor pathways with seed points from the internal capsule, motor cortex, and pons were studied respectively. The results were consistent with known anatomy and demonstrated the promising potential of the MFACT method in mapping the complex neuronal architecture in the human brain. PMID:18375171

Chao, Yi-Ping; Chen, Jyh-Horng; Cho, Kuan-Hung; Yeh, Chun-Hung; Chou, Kun-Hsien; Lin, Ching-Po

2008-10-01

12

Trade-off between angular resolution and straylight contamination in CMB anisotropy experiments. II. Straylight evaluation  

E-print Network

Satellite CMB anisotropy missions and new generation of balloon-borne and ground experiments, make use of complex multi-frequency instruments at the focus of a meter class telescope. Between 70 GHz and 300 GHz, where foreground contamination is minimum, it is extremely important to reach the best trade-off between the improvement of the angular resolution and the minimization of the straylight contamination mainly due to the Galactic emission. We focus here, as a working case, on the 30 and 100 GHz channels of the Planck Low Frequency Instrument (LFI). We evaluate the GSC introduced by the most relevant Galactic foreground components for a reference set of optical configurations. We show that it is possible to improve the angular resolution of 5-7% by keeping the overall GSC below the level of few microKelvin. A comparison between the level of straylight introduced by the different Galactic components for different beam regions is presented. Simple approximate relations giving the rms and peak-to-peak levels of the GSC are provided. We compare the results obtained at 100 GHz with those at 30 GHz, where GSC is more critical. Finally, we compare the results based on Galactic foreground templates derived from radio and IR surveys with those based on WMAP maps including CMB and extragalactic source fluctuations.

C. Burigana; M. Sandri; F. Villa; D. Maino; R. Paladini; C. Baccigalupi; M. Bersanelli; N. Mandolesi

2003-03-29

13

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

SciTech Connect

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

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

2013-05-10

14

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

E-print Network

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

Chen, Yiling

15

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

16

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

NASA Astrophysics Data System (ADS)

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

2010-04-01

17

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

18

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

19

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

20

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

E-print Network

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

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

2015-01-28

21

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

E-print Network

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

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

2015-01-01

22

Bayesian deconvolution for angular super-resolution in forward-looking scanning radar.  

PubMed

Scanning radar is of notable importance for ground surveillance, terrain mapping and disaster rescue. However, the angular resolution of a scanning radar image is poor compared to the achievable range resolution. This paper presents a deconvolution algorithm for angular super-resolution in scanning radar based on Bayesian theory, which states that the angular super-resolution can be realized by solving the corresponding deconvolution problem with the maximum a posteriori (MAP) criterion. The algorithm considers that the noise is composed of two mutually independent parts, i.e., a Gaussian signal-independent component and a Poisson signal-dependent component. In addition, the Laplace distribution is used to represent the prior information about the targets under the assumption that the radar image of interest can be represented by the dominant scatters in the scene. Experimental results demonstrate that the proposed deconvolution algorithm has higher precision for angular super-resolution compared with the conventional algorithms, such as the Tikhonov regularization algorithm, the Wiener filter and the Richardson-Lucy algorithm. PMID:25806871

Zha, Yuebo; Huang, Yulin; Sun, Zhichao; Wang, Yue; Yang, Jianyu

2015-01-01

23

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

PubMed

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

Li, Lianlin; Li, Fang

2013-09-01

24

Millimetre-wave imaging with reduced number of degrees of freedom in array signal processing: concepts for enhanced angular resolution  

NASA Astrophysics Data System (ADS)

This paper deals with millimetre-wave imaging systems based on linear receiving arrays and is focused on the issue of angular resolution and coverage for arrays where the number M of ports is smaller than the number N of elements due to forming of subarrays. For a wide angular coverage a trade-off between a narrow beam width and a high side-lobe suppression is shown to occur which requires proper synthesis of the subarray pattern. Two concepts for an enhanced angular resolution are presented. The first uses a combination of a frequency dependent distribution network (frequency scanning) with array signal processing to enhance angular resolution by cost of a reduced range resolution. The second approach takes advantage of relative movements to enhance angular resolution via a combined angular and temporal (Doppler) processing.

Kotyrba, G.; Chaloupka, H.

2003-05-01

25

Measurement of the angular resolution of the ARGO-YBJ detector  

E-print Network

The ARGO-YBJ experiment is a full coverage EAS-array installed at the YangBaJing Cosmic Ray Laboratory (4300 m a.s.l., Tibet, P.R. China). We present the results on the angular resolution measured with different methods with the full central carpet. The comparison of experimental results with MC simulations is discussed.

G. Di Sciascio; E. Rossi

2007-10-10

26

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

Microsoft Academic Search

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

Fang-Cheng Yeh; Wen-Yih Isaac Tseng

2011-01-01

27

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

E-print Network

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

Lynne A. Hillenbrand

2003-12-06

28

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

E-print Network

ATLAS-BASED FIBER CLUSTERING FOR MULTI-SUBJECT ANALYSIS OF HIGH ANGULAR RESOLUTION DIFFUSION and a co-registered probabilistic DTI atlas to select key pathways, applied a threshold and median anatomy 3. Make tract analysis robust to differences in the atlas and subject 1. Image Data · 105-gradient

Thompson, Paul

29

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

30

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

SciTech Connect

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

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

2013-07-01

31

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

PubMed

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

Varentsova, Anna; Zhang, Shengwei; Arfanakis, Konstantinos

2014-05-01

32

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

33

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

34

Method for improving the angular resolution of a neutron scatter camera  

DOEpatents

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

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

2012-12-25

35

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. PMID:22522814

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

2013-10-01

36

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

PubMed Central

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, two weeks apart, using three protocols that took the same amount of time (7 minutes). Scans with 3, 2.7, 2.5 mm isotropic voxels were collected using 48, 41, and 37 diffusion-sensitized gradients to equalize scan times. A specially designed DTI phantom was also scanned with the same protocols, and different b-values. We assessed how several diffusion measures including fractional anisotropy (FA), mean diffusivity (MD), and the full 3D orientation distribution function (ODF) depended on the spatial/angular resolution and the SNR. We also created maps of stability over time in the FA, MD, ODF, skeleton FA of 14 TBSS-derived ROIs, and an information uncertainty index derived from the tensor distribution function, which models the signal using a continuous mixture of tensors. In scans of the same duration, higher angular resolution and larger voxels boosted SNR and improved stability over time. The increased partial voluming in large voxels also led to bias in estimating FA, but this was partially addressed by using “beyond-tensor” models of diffusion. PMID:22522814

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

2012-01-01

37

High-angular-resolution stellar imaging with occultations from the Cassini spacecraft - I. Observational technique  

NASA Astrophysics Data System (ADS)

We present novel observations utilizing the Cassini spacecraft to conduct an observing campaign for stellar astronomy from a vantage point in the outer Solar system. By exploiting occultation events in which Mira passed behind the Saturnian ring plane as viewed by Cassini, parametric imaging data were recovered spanning the near-infrared. From this, spatial information at extremely high angular resolution was recovered enabling a study of the stellar atmospheric extension across a spectral bandpass spanning the 1-5 ?m spectral region in the near-infrared. The resulting measurements of the angular diameter of Mira were found to be consistent with existing observations of its variation in size with wavelength. The present study illustrates the validity of the technique; more detailed exploration of the stellar physics obtained by this novel experiment will be the subject of forthcoming papers.

Stewart, Paul N.; Tuthill, Peter G.; Hedman, Matthew M.; Nicholson, Philip D.; Lloyd, James P.

2013-08-01

38

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

39

Trade-off between angular resolution and straylight contamination in CMB anisotropy experiments. I. Pattern simulations  

E-print Network

The study of Cosmic Microwave Background (CMB) anisotropies represents one of the most powerful Cosmological tools. After the great success of the two NASA's satellite missions COBE and WMAP, Planck represents the third generation of mm-wave instruments designed for space observations of CMB anisotropies within the new Cosmic Vision 2020 ESA Science Programme. The Planck survey will cover the whole sky with unprecedented sensitivity, angular resolution and frequency coverage, using two instruments that share the focal region of a 1.5 m off-axis dual reflector telescope: the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI). Within the LFI optical interfaces optimisation activity, two concurrent demands have to be satisfied: the best angular resolution (which impacts the ability to reconstruct the anisotropy power spectrum of the CMB anisotropies at high multipoles) and the lowest level of straylight contamination (that may be one of the most critical sources of systematic effects). We present the results of the optical simulations aimed to establish the trade-off between angular resolution and straylight rejection, carried out for the 100 GHz channel of Planck Low Frequency Instrument. Antenna pattern of different models of dual profiled corrugated conical feed horns have been simulated using advanced simulation techniques, considering the whole spacecraft geometry in order to obtain truthful sidelobe predictions. Optical computation accuracy necessary to provide strong straylight evaluation in reasonable computational time is shown and the inadequacy of a Gaussian feed model in realistic far pattern predictions is demonstrated. This paper is based on LFI activities.

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

2003-05-09

40

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

NASA Astrophysics Data System (ADS)

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

Zhang, William; NGXO

2014-01-01

41

Examining young stellar systems in birth by high angular resolution observations  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

42

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

43

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

PubMed

We present a high angular resolution brain atlas constructed by averaging 90 diffusion spectrum imaging (DSI) datasets in the ICBM-152 space. The spatial normalization of the diffusion information was conducted by a novel q-space diffeomorphic reconstruction method, which reconstructed the spin distribution function (SDF) in the ICBM-152 space from the diffusion MR signals. The performance of this method was examined by a simulation study modeling nonlinear transformation. The result showed that the reconstructed SDFs can resolve crossing fibers and that the accumulated quantitative anisotropy can reveal the relative ratio of the fiber populations. In the in vivo study, the SDF of the constructed atlas was shown to resolve crossing fiber orientations. Further, fiber tracking showed that the atlas can be used to present the pathways of fiber bundles, and the termination locations of the fibers can provide anatomical localization of the connected cortical regions. This high angular resolution brain atlas may facilitate future connectome research on the complex structure of the human brain. PMID:21704171

Yeh, Fang-Cheng; Tseng, Wen-Yih Isaac

2011-09-01

44

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

45

Trade-off between angular resolution and straylight contamination in the PLANCK Low Frequency Instrument. II. Straylight evaluation  

NASA Astrophysics Data System (ADS)

The last generation of CMB anisotropy experiments operating either from space, like the WMAP and PLANCK satellite, from the atmosphere, such as balloons, or from the ground, like interferometers, make use of complex multi-frequency instruments at the focus of meter class telescopes to allow the joint study of CMB and foreground anisotropies, necessary to achieve an accurate component separation. Between ˜ 70 GHz and ˜ 300 GHz, where foreground contamination is minimum, it is extremely important to reach the best trade-off between the improvement of the angular resolution, necessary for measuring the high order acoustic peaks of CMB anisotropy, and the minimization of the straylight contamination mainly due to the Galactic emission. This is one of the most critical systematic effects at large and intermediate angular scales (i.e. at multipoles ? less than ? 100) and consists in unwanted radiation entering the beam at large angles from the direction of the antenna boresight direction. We consider here the 30 and 100 GHz channels of the PLANCK Low Frequency Instrument (LFI). Assuming the nominal PLANCK scanning strategy, we evaluate the straylight contamination introduced by the most relevant Galactic foreground components for a reference set of optical configurations, accurately simulated as described in Sandri et al. (\\cite{Sandri04}, A&A, 428, 299) (hereafter Paper I). Given the overall constraints to the LFI optical design, we show that it is possible to improve the angular resolution by 5-7% by keeping the overall peak-to-peak signal of the Galaxy straylight contamination (GSC) below the level of few ?K (and about 10 times smaller in terms of rms). A comparison between the level of straylight introduced by the different Galactic components for different beam regions (intermediate and far beam) is presented. We provide approximate relations, both for the intermediate and the far beam, for the rms and the peak-to-peak levels of the GSC as functions of the corresponding contributions to the integrated beam or of the spillover. For some reference cases we compare the results based on Galactic foreground maps derived from radio, IR, and H? templates with those based on WMAP maps including CMB and extragalactic source fluctuations. The implications for the GSC in the PLANCK LFI polarization data are discussed. Finally, we compare the results obtained at 100 GHz with those at 30 GHz, where the GSC is more critical. Appendices are only available in electronic form at http://www.edpsciences.org}

Burigana, C.; Sandri, M.; Villa, F.; Maino, D.; Paladini, R.; Baccigalupi, C.; Bersanelli, M.; Mandolesi, N.

2004-12-01

46

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

SciTech Connect

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

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

2010-06-01

47

High Angular Resolution Observations of the Massive Stars in Cyg OB2  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

48

High-resolution asymptotics for the angular bispectrum of spherical random fields  

E-print Network

In this paper we study the asymptotic behavior of the angular bispectrum of spherical random fields. Here, the asymptotic theory is developed in the framework of fixed-radius fields, which are observed with increasing resolution as the sample size grows. The results we present are then exploited in a set of procedures aimed at testing non-Gaussianity; for these statistics, we are able to show convergence to functionals of standard Brownian motion under the null hypothesis. Analytic results are also presented on the behavior of the tests in the presence of a broad class of non-Gaussian alternatives. The issue of testing for non-Gaussianity on spherical random fields has recently gained enormous empirical importance, especially in connection with the statistical analysis of cosmic microwave background radiation.

Domenico Marinucci

2006-05-11

49

Submillimeter Array High-angular Resolution Observations of the Monoceros R2 Star Forming Cluster  

E-print Network

We present the first high-angular resolution study of the MonR2 star-forming complex carried out with the Submillimeter Array at (sub-)millimeter wavelengths. We image the continuum and molecular line emission toward the young stellar objects in MonR2 at 0.85mm and 1.3mm, with resolutions ranging from 0.5" to ~3". While free-free emission dominates the IRS1 and IRS2 continuum, dust thermal emission prevails for IRS3 and IRS5, giving envelope masses of ~0.1-0.3 M_Sun. IRS5 splits into at least two sub-arcsecond scale sources, IRS5B and the more massive IRS5A. Our 12CO(2-1) images reveal 11 previously unknown molecular outflows in the MonR2 clump. Comparing these outflows with known IR sources in the IRS5 and IRS3 subclusters allows for tentative identification of driving stars. Line images of molecular species such as CH3CN or CH3OH show that, besides IRS3 (a well-known hot molecular core), IRS5 is also a chemically active source in the region. The gas excitation temperature derived from CH3CN lines toward IRS...

Dierickx, Marion; Rivilla, Victor; Zhang, Qizhou

2015-01-01

50

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

51

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

52

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

SciTech Connect

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

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

2014-04-15

53

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

54

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

55

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

PubMed

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

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

2014-02-01

56

Segmentation of High Angular Resolution Diffusion MRI using Sparse Riemannian Manifold Clustering  

PubMed Central

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

Wright, Margaret J.; Thompson, Paul M.; Vidal, René

2015-01-01

57

First Results from High Angular Resolution ALMA Observations Toward the HL Tau Region  

E-print Network

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.075 arcseconds (10 AU) to 0.025 arcseconds (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72pm0.05 degrees) and position angle (+138.02pm0.07 degrees). We obtain a high-fidelity image of the 1.0 mm spectral index ($\\alpha$), which ranges from $\\alpha\\sim2.0$ in the optically-thick central peak and two brightest rings, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for ...

Partnership, ALMA; Perez, L M; Hunter, T R; Dent, W R F; Hales, A S; Hills, R; Corder, S; Fomalont, E B; Vlahakis, C; Asaki, Y; Barkats, D; Hirota, A; Hodge, J A; Impellizzeri, C M V; Kneissl, R; Liuzzo, E; Lucas, R; Marcelino, N; Matsushita, S; Nakanishi, K; Phillips, N; Richards, A M S; Toledo, I; Aladro, R; Broguiere, D; Cortes, J R; Cortes, P C; Dhawan, V; Espada, D; Galarza, F; Garcia-Appadoo, D; Guzman-Ramirez, L; Humphreys, E M; Jung, T; Kameno, S; Laing, R A; Leon, S; Marconi, G; Nikolic, B; Nyman, L -A; Radiszcz, M; Remijan, A; Rodon, J A; Sawada, T; Takahashi, S; Tilanus, R P J; Vilaro, B Vila; Watson, L C; Wiklind, T; Akiyama, E; Chapillon, E; de Gregorio, I; Di Francesco, J; Gueth, F; Kawamura, A; Lee, C -F; Luong, Q Nguyen; Mangum, J; Pietu, V; Sanhueza, P; Saigo, K; Takakuwa, S; Ubach, C; van Kempen, T; Wootten, A; Castro-Carrizo, A; Francke, H; Gallardo, J; Garcia, J; Gonzalez, S; Hill, T; Kaminski, T; Kurono, Y; Liu, H -Y; Lopez, C; Morales, F; Plarre, K; Schieven, G; Testi, L; Videla, L; Villard, E; Andreani, P; Hibbard, J E; Tatematsu, K

2015-01-01

58

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

59

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

PubMed Central

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

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

2014-01-01

60

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

61

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

62

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

Microsoft Academic Search

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

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

2011-01-01

63

Two Approximate Analytic Eigensolutions of the Hellmann Potential with any Arbitrary Angular Momentum  

NASA Astrophysics Data System (ADS)

The parametric Nikiforov-Uvarov (pNU) and asymptotic iteration method (AIM) are applied to study the approximate analytic bound state eigensolutions (energy levels and wave functions) of the radial Schr¨odinger equation (SE) for the Hellmann potential which represents the superposition of the attractive Coulomb potential (-a/r) and the Yukawa potential bexp(-?/r)/r of arbitrary strength b and screening parameter d in closed form. The analytical expressions to the energy eigenvalues Enl yield quite accurate results for a wide range of n; l in the limit of very weak screening but the results become gradually worse as the strength b and the screening coefficient d increase. The calculated bound state energies have been compared with available numerical data. Special cases of our solution like pure Coulomb and Yukawa potentials are also investigated.

Ikhdair, Sameer M.; Falaye, Babatunde J.

2013-11-01

64

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

65

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

66

Tensor Distribution Function in Multiple Shell High Angular Resolution Diffusion Imaging  

E-print Network

complicated white matter configurations. This issue can be addressed using the model-free diffusion spectrum, Minneapolis, MN, USA Introduction: DTI reveals white matter microstructure and fiber pathways in the living on sampling only on one or multiple spherical shells in q-space has been proposed, referred to as high angular

Thompson, Paul

67

Recent Advances in Multi-Resolution Approximation for Modeling and Control  

E-print Network

Recent Advances in Multi-Resolution Approximation for Modeling and Control John L. Junkins Texas A progress is being made. The ideas presented are applicable to a large family of problems. Dr. Junkins (Ph Center and has consulted with over two dozen laboratories. Dr. Junkins is the author of over 370

Krstic, Miroslav

68

Variational Posterior Distribution Approximation in Bayesian Super Resolution Reconstruction of Multispectral Images  

Microsoft Academic Search

In this paper we present a super resolution Bayesian methodology for pansharpening of multispectral images. By following the hierarchical Bayesian framework, and by applying variational methods to approximate probability distributions this methodology is able to: (a) incorporate prior knowledge on the expected characteristics of the multispectral images, (b) use the sensor charac- teristics to model the observation process of both

Rafael Molina; Miguel Vega; Javier Mateos; Aggelos K. Katsaggelos

2007-01-01

69

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

NASA Technical Reports Server (NTRS)

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

Rinehart, Stephen A.

2008-01-01

70

Angular Scaling In Jets  

SciTech Connect

We introduce a jet shape observable defined for an ensemble of jets in terms of two-particle angular correlations and a resolution parameter R. This quantity is infrared and collinear safe and can be interpreted as a scaling exponent for the angular distribution of mass inside the jet. For small R it is close to the value 2 as a consequence of the approximately scale invariant QCD dynamics. For large R it is sensitive to non-perturbative effects. We describe the use of this correlation function for tests of QCD, for studying underlying event and pile-up effects, and for tuning Monte Carlo event generators.

Jankowiak, Martin; Larkoski, Andrew J.; /SLAC

2012-02-17

71

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

E-print Network

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

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

2006-10-16

72

High Angular Resolution Stellar Imaging with Occultations from the Cassini Spacecraft II: Kronocyclic Tomography  

E-print Network

We present an advance in the use of Cassini observations of stellar occultations by the rings of Saturn for stellar studies. Stewart et al. (2013) demonstrated the potential use of such observations for measuring stellar angular diameters. Here, we use these same observations, and tomographic imaging reconstruction techniques, to produce two dimensional images of complex stellar systems. We detail the determination of the basic observational reference frame. A technique for recovering model-independent brightness profiles for data from each occulting edge is discussed, along with the tomographic combination of these profiles to build an image of the source star. Finally we demonstrate the technique with recovered images of the {\\alpha} Centauri binary system and the circumstellar environment of the evolved late-type giant star, Mira.

Stewart, Paul N; Nicholson, Philip D; Hedman, Matthew M; Lloyd, James P

2015-01-01

73

Angular super-resolution with array antennas: Application to seeker-heads  

NASA Astrophysics Data System (ADS)

Monopulse seeker-heads can give large errors due to closely spaced targets or even completely wrong directions in the case of cross-eye deception. The effective countermeasure against these errors is resolution enhancement. Super-resolution methods offer the possibility to resolve targets closer than the antenna beamwidth. Such methods are favorable for seeker-head applications, because the target separation as well as the signal-to-noise ratio increases as the missile approaches the target. All effective super-resolution methods require an antenna array with access to the single element outputs. Thus mechanical scanning is replaced by electronic scanning. Depending on the type of missile, sometimes antenna pattern restrictions have to be tolerated. Among all super-resolution methods the parametric target model fitting (PTMF) method seems to be most appropriate for this application. This method tries to fit a completely parameterized target model directly to the measured data. It can be rather easily computed, and it is the only method which can resolve completely correlated targets, which arise in the case of multipath and cross-eye deception. For seeker-heads with few antenna elements an implementation with digital signal processor chips is most suited. Computer simulations and experiments with measured data using the DESAS test equipment show that two targets separated at 0.3 beamwidth can be resolved in azimuth and elevation and that the switch from conventional monopulse to two-target estimation (super-resolution), which is crucial for the approaching missile, can be done by a reliable automatic test procedure.

Nickel, U.

1986-07-01

74

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

75

High angular resolution far-infrared and submillimeter mapping survey of the dust cores associated with ultracompact H II regions  

NASA Technical Reports Server (NTRS)

The primary objective of the research funded under this grant has been to perform a high angular resolution mapping survey of the far-infrared and submillimeter continuum emission from the dust cocoons surrounding young, deeply embedded massive stars and the ultracompact H II regions they create. The high infrared, submillimeter, and radio luminosity makes the ultracompact H II regions ideal tracers of current high-mass star formation. Detailed investigations of their structure, evolution, and interaction with their parent molecular clouds are thus important for understanding the early evolutionary phases of massive main sequence stars, the nature of the dense molecular cores in which they form, and the relationship to coeval low-mass star formation.

Phillips, T. G.

1995-01-01

76

High-resolution electron diffraction: accounting for radially and angularly invariant distortions.  

PubMed

The distortions present in an electron diffraction pattern can be classified into two categories: one is radially invariant and the other is angularly invariant. We report a method to compensate these displacements undergone by diffraction features promoted by any kind of artifacts generated in parallel beam electron diffraction conditions. This approach is not aimed at quantifying these distortions but only intends to aid in the measurement of lattice parameters of crystals with a significant increase of accuracy and precision as compared to previous approaches. It is based on statistical estimations of the relative positions between diffraction rings and/or spots after performing a transformation of the digitalized patterns to polar coordinates. The analytical method is based on fitting a Gaussian type profile to intensity distributions. This makes it possible to determine the lattice parameters of a polycrystal or single crystal with relative errors smaller than 0.1% for diffractograms acquired in photographic films and below 0.01% for those collected in imaging plates. PMID:22564419

Carvalho, Daniel; Morales, Francisco M

2012-06-01

77

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

NASA Astrophysics Data System (ADS)

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

Moser, D. E.

2012-12-01

78

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

79

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

PubMed

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

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

2013-02-01

80

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

81

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

82

ATMOSPHERIC PHASE CORRECTION USING CARMA-PACS: HIGH ANGULAR RESOLUTION OBSERVATIONS OF THE FU ORIONIS STAR PP 13S*  

SciTech Connect

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

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

2010-11-20

83

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

SciTech Connect

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

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

2014-09-15

84

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

85

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

86

High resolution laser beam induced current images under trichromatic laser radiation: approximation to the solar irradiation.  

PubMed

A laser beam induced current (LBIC) map of a photoactive surface is a very useful tool when it is necessary to study the spatial variability of properties such as photoconverter efficiency or factors connected with the recombination of carriers. Obtaining high spatial resolution LBIC maps involves irradiating the photoactive surface with a photonic beam with Gaussian power distribution and with a low dispersion coefficient. Laser emission fulfils these characteristics, but against it is the fact that it is highly monochromatic and therefore has a spectral distribution different to solar emissions. This work presents an instrumental system and procedure to obtain high spatial resolution LBIC maps in conditions approximating solar irradiation. The methodology developed consists of a trichromatic irradiation system based on three sources of laser excitation with emission in the red, green, and blue zones of the electromagnetic spectrum. The relative irradiation powers are determined by either solar spectrum distribution or Planck's emission formula which provides information approximate to the behavior of the system if it were under solar irradiation. In turn, an algorithm and a procedure have been developed to be able to form images based on the scans performed by the three lasers, providing information about the photoconverter efficiency of photovoltaic devices under the irradiation conditions used. This system has been checked with three photosensitive devices based on three different technologies: a commercial silicon photodiode, a commercial photoresistor, and a dye-sensitized solar cell. These devices make it possible to check how the superficial quantum efficiency has areas dependent upon the excitation wavelength while it has been possible to measure global incident photon-to-current efficiency values approximating those that would be obtained under irradiation conditions with sunlight. PMID:20370214

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

2010-03-01

87

The Milli-Arc-Second Structure Imager, MASSIM: A New Concept for a High Angular Resolution X-ray Telescope  

NASA Technical Reports Server (NTRS)

MASSIM, the Milli-Arc-Second Structure Imager, is a mission that has been proposed for study within the context of NASA's "Astrophysics Strategic Mission Concept Studies" program. It uses a set of achromatic diffractive-refractive Fresnel lenses on an optics spacecraft to focus 5-11 keV X-rays onto detectors on a second spacecraft flying in formation 1000 km away. It will have a point-source sensitivity comparable with that of the current generation of major X-ray observatories (Chandra, XMM-Newton) but an angular resolution some three orders of magnitude better. MASSIM is optimized for the study of jets and other phenomena that occur in the immediate vicinity of black holes and neutron stars. It can also be used for studying other astrophysical phenomena on the milli-arc-second scale, such as those involving proto-stars, the surfaces and surroundings of nearby active stars and interacting winds. After introducing the principle of diffractive imaging in the x-ray/gamma-ray regime, the MASSIM mission concept and baseline design will be described along with a discussion of the options and trade-offs within the X-ray optics design.

Skinner, Gerry; Arzoumanian, Z.; Cash, W.; Gehrels, N.; Gendreau, K.; Gorenstein, P.; Krizmanic, J.; Leitner, J.; Miller, M.; Reasenberg, R.; Reynolds, C.; Sambruna, R.; Streitmatter, R.; Windt, D.

2008-01-01

88

Detection of Postmortem Human Cerebellar Cortex and White Matter Pathways Using High Angular Resolution Diffusion Tractography: A feasibility study  

PubMed Central

Imaging three-dimensional cerebellar connectivity using diffusion tractography is challenging because of the ubiquitous features of crossing axonal pathways within a folium as well as intersecting pathways from neighboring folia. We applied high-angular resolution diffusion imaging (HARDI) tractography to intact postmortem adult brainstem and cerebellum to examine the 3-dimensional white matter and local gray matter pathways. The middle cerebellar peduncles conveyed fibers from the rostral pons to the lateral and caudal aspects of the cerebellar hemisphere, and from the caudal pons to medial and rostral parts of the cerebellar hemisphere. In the cerebellar cortex, tractography detected tangential coherence superficially in the cerebellar cortex and revealed fibers coursing parallel to the long axis of the folia. These fibers were consistent with the location and direction of parallel fibers in the molecular layer. Crossing with these parallel fibers were tangential fibers running perpendicular to the long axis of the folia, consistent with axons othe cortical interneurons – stellate cells and basket cells. These tangential fibers within the cerebellar cortex were distinct from fibers linking the cerebellar cortex with the deep cerebellar nuclei and the brainstem. Our results show the potential for HARDI tractography to resolve axonal pathways from different neuronal elements within the cerebellar cortex, and improve our understanding of adult cerebellar neural circuitry and connectivity in both white and gray matter. PMID:23238434

Takahashi, Emi; Song, Jae W.; Folkerth, Rebecca D.; Grant, P. Ellen; Schmahmann, Jeremy D.

2015-01-01

89

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. PMID:21292013

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

2011-01-01

90

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

NASA Astrophysics Data System (ADS)

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

Dutt, Ranabir; Mukherji, Uma

1982-08-01

91

A Super-high Angular Resolution Principle for Coded-mask X-ray Imaging Beyond the Diffraction Limit of Single Pinhole  

E-print Network

High angular resolution X-ray imaging is always demanded by astrophysics and solar physics, which can be realized by coded-mask imaging with very long mask-detector distance in principle. Previously the diffraction-interference effect has been thought to degrade coded-mask imaging performance dramatically at low energy end with very long mask-detector distance. In this work the diffraction-interference effect is described with numerical calculations, and the diffraction-interference cross correlation reconstruction method (DICC) is developed in order to overcome the imaging performance degradation. Based on the DICC, a super-high angular resolution principle (SHARP) for coded-mask X-ray imaging is proposed. The feasibility of coded mask imaging beyond the diffraction limit of single pinhole is demonstrated with simulations. With the specification that the mask element size of 50* 50 square micrometers and the mask-detector distance of 50 m, the achieved angular resolution is 0.32 arcsec above about 10 keV, and 0.36 arcsec at 1.24 keV where diffraction can not be neglected. The on-axis source location accuracy is better than 0.02 arcsec. Potential applications for solar observations and wide-field X-ray monitors are also shortly discussed.

Chen Zhang; Shuang Nan Zhang

2008-06-25

92

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

NASA Astrophysics Data System (ADS)

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

Ibach, Harald

2014-12-01

93

Characterization of a submillimeter high-angular-resolution camera with a monolithic silicon bolometer array for the Caltech Submillimeter Observatory  

NASA Astrophysics Data System (ADS)

We constructed a 24-pixel bolometer camera operating in the 350- and 450- mu m atmospheric windows for the Caltech Submillimeter Observatory (CSO). This instrument uses a monolithic silicon bolometer array that is cooled to approximately 300 mK by a single-shot 3He refrigerator. First-stage amplification is provided by field-effect transistors at approximately 130 K. The sky is imaged onto the bolometer array by means of several mirrors outside the Dewar and a cold off-axis elliptical mirror inside the cryostat. The beam is defined by cold aperture and field stops, which eliminates the need for any condensing horns. We describe the instrument, present measurements of the physical properties of the bolometer array, describe the performance of the electronics and the data-acquisition system, and demonstrate the sensitivity of the instrument operating at the observatory. Approximate detector noise at 350 mu m is 5 \\times 10-15 W/\\radicalHz\\end-radical, referenced to the entrance of the Dewar, and the CSO system noise-equivalent flux density is approximately 4 Jy/\\radicalHz\\end-radical. These values are within a factor of 2.5 of the background limit.

Wang, Ning; Hunter, T. R.; Benford, D. J.; Serabyn, E.; Lis, D. C.; Phillips, T. G.; Moseley, S. H.; Boyce, K.; Szymkowiak, A.; Allen, C.; Mott, B.; Gygax, J.

1996-12-01

94

Characterization of a submillimeter high-angular-resolution camera with a monolithic silicon bolometer array for the Caltech Submillimeter Observatory.  

PubMed

We constructed a 24-pixel bolometer camera operating in the 350- and 450-?m atmospheric windows for the Caltech Submillimeter Observatory (CSO). This instrument uses a monolithic silicon bolometer array that is cooled to approximately 300 mK by a single-shot (3)He refrigerator. First-stage amplification is provided by field-effect transistors at approximately 130 K. The sky is imaged onto the bolometer array by means of several mirrors outside the Dewar and a cold off-axis elliptical mirror inside the cryostat. The beam is defined by cold aperture and field stops, which eliminates the need for any condensing horns. We describe the instrument, present measurements of the physical properties of the bolometer array, describe the performance of the electronics and the data-acquisition system, and demonstrate the sensitivity of the instrument operating at the observatory. Approximate detector noise at 350 ?m is 5 × 10(-15) W/?Hz, referenced to the entrance of the Dewar, and the CSO system noise-equivalent flux density is approximately 4 Jy/?Hz. These values are within a factor of 2.5 of the background limit. PMID:21151241

Wang, N; Hunter, T R; Benford, D J; Serabyn, E; Lis, D C; Phillips, T G; Moseley, S H; Boyce, K; Szymkowiak, A; Allen, C; Mott, B; Gygax, J

1996-12-01

95

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

96

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

NASA Technical Reports Server (NTRS)

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 = 33 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 (>20keV) 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.; Dicker, S. R.; Korngut, P. M.; Devlin, M.; Cotton, W. D.; Koch, P. M.; Molnar, S. M.; Sievers, J.; Aguirre, J. E.; Benford, D.; Staguhn, J. G.; Moseley, H.; Irwin, K. D.; Ade, P.

2010-01-01

97

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

98

High-angular resolution HC_3N and CS observations of the dense core in the cirrus cloud MCLD123.5+24.9  

E-print Network

We report on high-angular resolution observations of a dense core in the cirrus cloud MCLD123.5+24.9 obtained with the PdB and the OVRO interferometers. Our maps show substructures down to the scale of the beam (~ 1000 AU). The chosen molecules CS(2-1) and HC_3N(10-9) trace different regions in the core. This can be explained by time-dependent chemical evolution of the cloud and therefore provides constraints on the timescales of the fragmentation and core formation processes. Our data demonstrate that the chemical evolution plays the decisive role in our attempt to interpret observational data of different gas density tracers.

C. Boettner; A. Heithausen; F. Walter

2003-11-11

99

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

NASA Technical Reports Server (NTRS)

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

Young, David T.

1991-01-01

100

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

101

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

102

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

E-print Network

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

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

2014-01-01

103

Beyond the Born-Oppenheimer approximation: High-resolution overtone spectroscopy of H2D+ and D2H+  

NASA Astrophysics Data System (ADS)

Transitions to overtone 2?2 and 2?3, and combination ?2+?3 vibrations in jet-cooled H2D+ and D2H+ molecular ions have been measured for the first time by high-resolution IR spectroscopy. The source of these ions is a pulsed slit jet supersonic discharge, which allows for efficient generation, rotational cooling, and high frequency (100 KHz) concentration modulation for detection via sensitive lock-in detection methods. Isotopic substitution and high-resolution overtone spectroscopy in this fundamental molecular ion permit a systematic, first principles investigation of Born-Oppenheimer "breakdown" effects due to large amplitude vibrational motion as well as provide rigorous tests of approximate theoretical methods beyond the Born-Oppenheimer level. The observed overtone transitions are in remarkably good agreement (<0.1 cm-1) with non-Born-Oppenheimer ab initio theoretical predictions, with small but systematic deviations for 2?2, ?2+?3, and 2?3 excited states indicating directions for further improvement in such treatments. Spectroscopic assignment and analysis of the isotopomeric transitions reveals strong Coriolis mixing between near resonant 2?3 and ?2+?3 vibrations in D2H+. Population-independent line intensity ratios for transitions from common lower states indicate excellent overall agreement with theoretical predictions for D2H+, but with statistically significant discrepancies noted for H2D+. Finally, H2D+ versus D2H+ isotopomer populations are analyzed as a function of D2/H2 mixing ratio and can be well described by steady state kinetics in the slit discharge expansion.

Fárník, Michal; Davis, Scott; Kostin, Maxim A.; Polyansky, Oleg L.; Tennyson, Jonathan; Nesbitt, David J.

2002-04-01

104

Radiofrequency encoded angular-resolved light scattering  

NASA Astrophysics Data System (ADS)

The sensitive, specific, and label-free classification of microscopic cells and organisms is one of the outstanding problems in biology. Today, instruments such as the flow cytometer use a combination of light scatter measurements at two distinct angles to infer the size and internal complexity of cells at rates of more than 10 000/s. However, by examining the entire angular light scattering spectrum, it is possible to classify cells with higher resolution and specificity. Current approaches to performing these angular spectrum measurements all have significant throughput limitations, making them incompatible with other state-of-the-art flow cytometers. Here, we introduce a method for performing complete angular scattering spectrum measurements at high throughput combining techniques from the field of scattering flow-cytometry and radiofrequency communications. Termed Radiofrequency Encoded Angular-resolved Light Scattering, this technique multiplexes angular light scattering in the radiofrequency domain, such that a single photodetector captures the entire scattering spectrum from a particle over approximately 100 discrete incident angles on a single shot basis. As a proof-of-principle experiment, we use this technique to perform scattering measurements over a range of 30° from a tapered optical fiber at a scan rate of 250 kHz.

Buckley, Brandon W.; Akbari, Najva; Diebold, Eric D.; Adam, Jost; Jalali, Bahram

2015-03-01

105

Angular pregnancy.  

PubMed

Angular pregnancy, a type of cornual pregnancy, is a rare obstetric complication that can be life-threatening. In this situation, the embryo is implanted in the lateral angle of the uterine cavity, medial to the uterotubal junction and round ligament. Angular pregnancy must be distinguished from interstitial pregnancy, in which the embryo is implanted lateral to the round ligament. The report presented here describes a case of angular pregnancy that was diagnosed by endovaginal ultrasonography and magnetic resonance imaging. Laparoscopy can be useful for guiding dilatation and curettage in angular pregnancies, and may circumvent the need for invasive surgery or hysterectomy. PMID:15327452

Tarim, Ebru; Ulusan, Serife; Kilicdag, Esra; Yildirim, Tulin; Bagis, Tayfun; Kuscu, Esra

2004-10-01

106

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

107

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

108

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

109

Beyond the relativistic mean-field approximation. II. Configuration mixing of mean-field wave functions projected on angular momentum and particle number  

SciTech Connect

The framework of relativistic self-consistent mean-field models is extended to include correlations related to the restoration of broken symmetries and to fluctuations of collective variables. The generator coordinate method is used to perform configuration mixing of angular-momentum and particle-number projected relativistic wave functions. The geometry is restricted to axially symmetric shapes, and the intrinsic wave functions are generated from the solutions of the relativistic mean-field+Lipkin-Nogami BCS equations, with a constraint on the mass quadrupole moment. The model employs a relativistic point-coupling (contact) nucleon-nucleon effective interaction in the particle-hole channel, and a density-independent {delta}-interaction in the pairing channel. Illustrative calculations are performed for {sup 24}Mg, {sup 32}S, and {sup 36}Ar, and compared with results obtained employing the model developed in the first part of this work, i.e., without particle-number projection, as well as with the corresponding nonrelativistic models based on Skyrme and Gogny effective interactions.

Niksic, T.; Vretenar, D.; Ring, P. [Physics Department, Faculty of Science, University of Zagreb (Croatia) and Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching (Germany); Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching (Germany)

2006-12-15

110

Angular resolution measurements at SPring-8 of a hard x-ray optic for the New Hard X-ray Mission  

NASA Astrophysics Data System (ADS)

The realization of X-ray telescopes with imaging capabilities in the hard (> 10 keV) X-ray band requires the adoption of optics with shallow (< 0.25 deg) grazing angles to enhance the reflectivity of reflective coatings. On the other hand, to obtain large collecting area, large mirror diameters (< 350 mm) are necessary. This implies that mirrors with focal lengths >=10 m shall be produced and tested. Full-illumination tests of such mirrors are usually performed with onground X-ray facilities, aimed at measuring their effective area and the angular resolution; however, they in general suffer from effects of the finite distance of the X-ray source, e.g. a loss of effective area for double reflection. These effects increase with the focal length of the mirror under test; hence a "partial" full-illumination measurement might not be fully representative of the in-flight performances. Indeed, a pencil beam test can be adopted to overcome this shortcoming, because a sector at a time is exposed to the X-ray flux, and the compensation of the beam divergence is achieved by tilting the optic. In this work we present the result of a hard X-ray test campaign performed at the BL20B2 beamline of the SPring-8 synchrotron radiation facility, aimed at characterizing the Point Spread Function (PSF) of a multilayer-coated Wolter-I mirror shell manufactured by Nickel electroforming. The mirror shell is a demonstrator for the NHXM hard X-ray imaging telescope (0.3 - 80 keV), with a predicted HEW (Half Energy Width) close to 20 arcsec. We show some reconstructed PSFs at monochromatic X-ray energies of 15 to 63 keV, and compare them with the PSFs computed from post-campaign metrology data, self-consistently treating profile and roughness data by means of a method based on the Fresnel diffraction theory. The modeling matches the measured PSFs accurately.

Spiga, D.; Raimondi, L.; Furuzawa, A.; Basso, S.; Binda, R.; Borghi, G.; Cotroneo, V.; Grisoni, G.; Kunieda, H.; Marioni, F.; Matsumoto, H.; Mori, H.; Miyazawa, T.; Negri, B.; Orlandi, A.; Pareschi, G.; Salmaso, B.; Tagliaferri, G.; Uesugi, K.; Valsecchi, G.; Vernani, D.

2011-09-01

111

Please cite this article in press as: C.S. Fadley, Hard X-ray photoemission with angular resolution and standing-wave excitation, J. Electron Spectrosc. Relat. Phenom. (2013), http://dx.doi.org/10.1016/j.elspec.2013.06.008  

E-print Network

and standing-wave excitation, J. Electron Spectrosc. Relat. Phenom. (2013), http://dx.doi.org/10.1016/j with angular resolution and standing-wave excitation Charles S. Fadleya,b, a Department of Physics, University Standing wave a b s t r a c t Several aspects of hard X-ray photoemission that make use of angular

Fadley, Charles

112

Fluidic angular velocity sensor  

NASA Technical Reports Server (NTRS)

A fluidic sensor providing a differential pressure signal proportional to the angular velocity of a rotary input is described. In one embodiment the sensor includes a fluid pump having an impeller coupled to a rotary input. A housing forming a constricting fluid flow chamber is connected to the fluid input of the pump. The housing is provided with a fluid flow restrictive input to the flow chamber and a port communicating with the interior of the flow chamber. The differential pressure signal measured across the flow restrictive input is relatively noise free and proportional to the square of the angular velocity of the impeller. In an alternative embodiment, the flow chamber has a generally cylindrical configuration and plates having flow restrictive apertures are disposed within the chamber downstream from the housing port. In this embodiment, the differential pressure signal is found to be approximately linear with the angular velocity of the impeller.

Berdahl, C. M. (inventor)

1986-01-01

113

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

114

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

115

Angular Measure  

NSDL National Science Digital Library

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

116

Angular momentum  

NASA Astrophysics Data System (ADS)

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

Shakur, Asif; Sinatra, Taylor

2013-12-01

117

Miniaturized photoelectric angular sensor with simplified design  

Microsoft Academic Search

In building the movable elements of robots, peripheral devices and measuring apparata, increasing the resolution of the angular sensor systems, based on incremental rotary encoders, is essential, together with decreasing the complexity, dimensions and weight. Especially when the angular sensor is integrated in a measuring system, belonging to a programmed light airplane for surveillance, the key issue is to reduce

Niculae Dumbravescu; Silviu Schiaua

1999-01-01

118

Multi-Resolution Approximate Inverses  

E-print Network

to Green's functions and reading the drafts; to Rob Zvan for getting me started on irregular meshes; to Justin Wan for some fruitful conversations and sample meshes; to David Pooley for the barrier option.6 Discrete Green's Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.7 Multi

Bridson, Robert

119

High Angular Resolution Observations of Episodic Dust Emission from Long Period Variable Stars Twenty Years of Observations with the Berkeley Infrared Spatial Interferometer  

NASA Technical Reports Server (NTRS)

Over the past twenty years the U. C. Berkeley Infrared Spatial Interferometer has observed a number of Long Period Variable stars in the mid-infrared, obtaining information on the spatial distribution of dust around these stars with resolutions of the order of a few tens of milliarcseconds. The ISI is a heterodyne interferometer operating mostly at 11.15 microns, initially with two telescopes. In the last decade, it has been taking data regularly with three telescopes, thus obtaining visibility data on three baselines and also a closure phase. Over the course of the years, the ISI has been able to measure the physical properties of the dust shells surrounding these stars, in particular the inner radii of the dust shells, as well as the temperature and density distribution. For some stars, the ISI has also made precision measurements of their diameters in the mid-infrared. Closure phase measurements have revealed asymmetries in the dust distributions around many stars. Most surprisingly the ISI data has shown evidence for substantial changes in the amount of dust on time scales of 5-10 years, rather than being directly correlated with the stellar pulsation periods, which are of the order of one year. We discuss past results and new results from the ISI that highlight the dynamic environment around these stars.

Danchi, William

2010-01-01

120

Orbital angular momentum and nonparaxial light beams  

Microsoft Academic Search

The simple relationship between total angular momentum and energy and the seemingly natural separation of the angular momentum into spin and orbital components in the paraxial approximation, are investigated for a general nonparaxial form of monochromatic beam with near cylindrical symmetry.

Stephen M. Barnett; L. Allen

1994-01-01

121

Light's Orbital Angular Momentum  

Microsoft Academic Search

The realization that light beams can have quantized orbital angular momentum in addition to spin angular momentum has led, in recent years, to novel experiments in quantum mechanics and new methods for manipulating microparticles.

Miles Padgett; Johannes Courtial; Les Allen

2004-01-01

122

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.

David Trapp

123

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

124

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

125

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

126

Improving the resolution of chopper spectrometers at pulsed neutron sources  

SciTech Connect

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

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

1990-01-01

127

Fourier relationship between angular position and optical orbital angular momentum  

E-print Network

We demonstrate the Fourier relationship between angular position and angular momentum for a light mode. In particular we measure the distribution of orbital angular momentum states of light that has passed through an aperture and verify that the orbital angular momentum distribution is given by the complex Fourier-transform of the aperture function. We use spatial light modulators, configured as diffractive optical components, to define the initial orbital angular momentum state of the beam, set the defining aperture, and measure the angular momentum spread of the resulting beam. These measurements clearly confirm the Fourier relationship between angular momentum and angular position, even at light intensities corresponding to the single photon level.

Eric Yao; Sonja Franke-Arnold; Johannes Courtial; Stephen Barnett; Miles Padgett

2006-06-15

128

Optical Broadband Angular Selectivity  

E-print Network

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

Shen, Yichen

129

Metamaterial broadband angular selectivity  

E-print Network

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

Shen, Yichen

130

Angular velocity discrimination  

NASA Technical Reports Server (NTRS)

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

Kaiser, Mary K.

1990-01-01

131

Minimum uncertainty states of angular momentum and angular position  

E-print Network

Minimum uncertainty states of angular momentum and angular position David T Pegg1 , Stephen M of linear momentum that satisfy the equality in the Heisenberg uncertainty principle for position for position and momentum. The corresponding uncertainty relation for angular momentum and angular position

Zambrini, Roberta

132

Quantum Entanglement of High Angular Momenta  

E-print Network

Single photons with helical phase structures may carry a quantized amount of orbital angular momentum (OAM) and their entanglement is important for quantum information science and fundamental tests of quantum theory. Because there is no theoretical upper limit on how many quanta of OAM a single photon can carry, it is possible to create entanglement between two particles with an arbitrary high difference in the quantum number. By transferring polarization entanglement to OAM with an interferometric scheme, we generate and verify entanglement up to 600 quanta difference in the orbital angular momentum. The only restrictive factors towards higher numbers are current technical limitations. We also experimentally demonstrate that the entanglement of very high OAM can improve the sensitivity of the angular resolution in remote sensing.

Robert Fickler; Radek Lapkiewicz; William N. Plick; Mario Krenn; Christoph Schaeff; Sven Ramelow; Anton Zeilinger

2014-06-06

133

Creating high-harmonic beams with controlled orbital angular momentum.  

PubMed

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

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

2014-10-10

134

Creating High-Harmonic Beams with Controlled Orbital Angular Momentum  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

135

The Angular Momentum Dichotomy  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

136

Miniaturized photoelectric angular sensor with simplified design  

NASA Astrophysics Data System (ADS)

In building the movable elements of robots, peripheral devices and measuring apparata, increasing the resolution of the angular sensor systems, based on incremental rotary encoders, is essential, together with decreasing the complexity, dimensions and weight. Especially when the angular sensor is integrated in a measuring system, belonging to a programmed light airplane for surveillance, the key issue is to reduce both dimensions and weight. This can be done using a simplified design, which consists in the following solutions: replacement of the fragile Cr on glass substrate, 1.5 mm thick (normally used for the fabrication of incremental disks), with light Cr on polycarbonate substrate, with only 0.15 mm thick; the absence of collimating optics (based on microlenses, used in IR emitter-photocell receiver assembly), as a result of the good coupling efficiency (due to the possible approaching of these elements at minimum 0.45 mm); the shrinkage of the disk's diameters to only 14 mm; the use of surface mounting devices and the related surface mounting technology, enabling to reduce dimensions and weight. The maximum number of slits on a 14 mm diameter dividing disk, usually obtained in a Cr on polycarbonate version, being approx. 1000, no problem occurs in our case, for 360 slits. The requested angular resolution (only 0.5 degrees for the light airplane), using the whole classical '4x digital multiplication' is not necessary, but a lower one of only 2x, resulting in a simplified electronics. The proposed design permitted, that an original arrangement, for building a small size, lightweight, heavy-duty incremental transducer based angular sensor system, to be obtained, useful not only in avionics, but also in robotics, or other special applications. Besides, extending the number of fixed gratings (masks) allows, that many primary signals to be derived, and a further increase in resolution of even 6 angular minutes to be obtained from the initial 360 slits.

Dumbravescu, Niculae; Schiaua, Silviu

1999-09-01

137

Metamaterial broadband angular selectivity  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

138

Angular shear plate  

DOEpatents

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

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

2009-07-14

139

Test of special resolution and trigger efficiency  

E-print Network

The forthcoming luminosity upgrade of LHC to super-LHC (sLHC) will increase the expected background rate in the forward region of the ATLAS Muon Spectrometer by approximately the factor of five. Some of the present Muon Spectrometer components will fail to cope with these high rates and will have to be replaced. The results of a test of a device consisting of Thin Gap Chambers (TGC) and a fast small-diameter Muon Drift Tube Chamber (sMDT) using the 180 GeV/c muons at the SPS-H8 muon beam at CERN are presented. The goal of the test was to study the combined TGC-sMDT system as tracking and triggering device in the ATLAS muon spectrometer after high-luminosity upgrades of the LHC. The analysis of the recorded data shows a very good correlation between the TGC and sMDT track position and inclination. This technology offers the combination of trigger and tracking and has good angular and spatial resolutions. The angular resolution is 0.4 mrad for each system individually. For the spatial resolution, the width of t...

Benhammou, Y

2015-01-01

140

Gears: Determining Angular Velocity  

NSDL National Science Digital Library

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

AMPS GK-12 Program,

141

Induced Angular Momentum  

ERIC Educational Resources Information Center

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

Parker, G. W.

1978-01-01

142

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

143

Uncorrelated scattering approximation revisited  

E-print Network

The formalism to describe the scattering of a weakly bound projectile nucleus by a heavy target is investigated, using the Uncorrelated Scattering Approximation. The main assumption involved is to neglect the correlation between the fragments of the projectile in the region where the interaction with the target is important. It is shown that the angular momentum of each fragment with respect to the target is conserved. Moreover, when suitable approximations are assumed, the kinetic energy of each fragment is also shown to be conserved. The S-matrix for the scattering of the composite system can be written as a combination of terms, each one being proportional to the product of the S-matrices of the fragments.

A. M. Moro; J. A. Caballero; J. Gomez-Camacho

2004-05-24

144

Approximate resolution of hard numbering problems  

SciTech Connect

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

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

1996-12-31

145

Nanofabricated quartz cylinders for angular  

E-print Network

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

Wang, Michelle

146

Mesoscopic reflectance angular domain spectroscopic imaging  

NASA Astrophysics Data System (ADS)

The advancement of angular domain imaging in mesoscopic reflectance multispectral imaging is reported. The key component is an angular filter array that performs the angular filtration of the back-scattered photons and generates image contrast due to the variances in tissue optical properties. The proposed modality enables multispectral imaging of subsurface features for samples too thick for transillumination angular domain spectroscopic imaging (ADSI) approaches. The validation was carried out with tissue-mimicking phantoms with multiple absorptive features embedded below the surface. Multispectral images in the range of 666 to 888 nm clearly revealed the location of the features with the background scattering levels up to 20. The shape of the features was recoverable at depths of up to three to four times the transport mean free path. The spatial resolution was <1 mm and the field-of-view was larger than 2.5 cm×3.0 cm. Furthermore, the attenuation spectra of measured absorptive features were successfully extracted. Target detectability and imaging quality with different background scattering levels, target depths, and illumination focal depths were discussed, as well as the capability of ADSI in reflectance optical mesoscopic imaging and its potential applications.

Zhang, Yan; Vasefi, Fartash; Ng, Eldon; Chamson-Reig, Astrid; Kaminska, Bozena; Carson, Jeffrey J. L.

2014-07-01

147

Structure of an edge-diffraction wave over a wide angular range  

Microsoft Academic Search

Experimental data on the angular dependence of the amplitude function of the edge diffraction wave originating behind a metallic knife edge that is illuminated nonenlarged laser beam are represented. It is shown that the scalar diffraction theory approximation (in particular, so-called `Rubinowicz's representation of the Kirhhoff's diffraction integral) is valid up to the diffraction angle approximately 206. Outside this angular

Galina V. Bogatiryova; Peter V. Polyanskii

1999-01-01

148

Angular Momentum in Dwarf Galaxies  

NASA Astrophysics Data System (ADS)

We study the ``angular momentum catastrophe" in the framework of interaction among baryons and dark matter through dynamical friction. By means of Del Popolo (2009) model we simulate 14 galaxies similar to those investigated by van den Bosch, Burkert and Swaters (2001), and calculate the distribution of their spin parameters and the angular momenta. Our model gives the angular momentum distribution which is in agreement with the van den Bosch et al. observations. Our result shows that the ``angular momentum catastrophe" can be naturally solved in a model that takes into account the baryonic physics and the exchange of energy and angular momentum between the baryonic clumps and dark matter through dynamical friction.

Del Popolo, A.

149

The close environment of high-mass X-ray binaries at high angular resolution. I. VLTI/AMBER and VLTI/PIONIER near-infrared interferometric observations of Vela X-1  

NASA Astrophysics Data System (ADS)

Context. Recent improvements in the sensitivity and spectral resolution of X-ray observations have led to a better understanding of the properties of matter in the near vicinity of high-mass X-ray binaries (HMXB) hosting a supergiant star and a compact object. However, the geometry and physical properties of their environments on larger scales (up to a few stellar radii) are currently only predicted by simulations but have never been directly observed. Aims: We aim to explore the environment of Vela X-1 at a few stellar radii (R?) of the supergiant using spatially resolved observations in the near-infrared, and to study its dynamical evolution along the nine-day orbital period of the system. Methods: We observed Vela X-1 in 2010 and 2012 using near-infrared long baseline interferometry at the Very Large Telescope Interferometer (VLTI), respectively with the AMBER instrument in the K band (medium spectral resolution), and the PIONIER instrument in the H band (low spectral resolution). The PIONIER observations span one orbital period to monitor possible evolutions in the geometry of the system. Results: We resolved a structure of 8 ± 3 R? from the AMBER K-band observations, and 2.0-1.2+0.7R* from the PIONIER H-band data. From the closure phase observable, we found that the circumstellar environment of Vela X-1 is symmetrical in the near-infrared. We observed comparable interferometric measurements between the continuum and the spectral lines in the K band, meaning that both emissions originate from the same forming region. From the monitoring of the system over one period in the H band in 2012, we found the signal to be constant with the orbital phase within the error bars. Conclusions: We propose three possible scenarios for this discrepancy between the two measurements: 1) there is a strong temperature gradient in the supergiant wind, leading to a hot component that is much more compact than the cool part of the wind observed in the K band; 2) we observed a diffuse shell in 2010, possibly triggered by an off-state in the accretion rate of the neutron star that was dissolved in the interstellar medium in 2012 during our second observations; or 3) the structure observed in the H band was the stellar photosphere instead of the supergiant wind. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile. Programs 085.D-0029(A) and 088.D-0185(A).

Choquet, É.; Kervella, P.; Le Bouquin, J.-B.; Mérand, A.; Berger, J.-P.; Haubois, X.; Perrin, G.; Petrucci, P.-O.; Lazareff, B.; Pott, J.-U.

2014-01-01

150

Angular displacement measuring device  

NASA Technical Reports Server (NTRS)

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

Seegmiller, H. Lee B. (inventor)

1992-01-01

151

Uniaxial angular accelerometers  

NASA Astrophysics Data System (ADS)

The basic mechanical components of an angular accelerometer are the sensor, the damper, and the transducer. Penumatic dampers are simplest in construction, but the viscosity of air is very low and, therefore, dampers with special purpose oils having a high temperature stability (synthetic silicon or organosilicon oils) are most widely used. The most common types of viscous dampers are lamellar with meshed opposed arrays of fixed and movable vanes in the dashpot, piston dampers regulated by an adjustable-length capillary tube, and dampers with paddle wheel in closed tank. Another type of damper is an impact-inertial one with large masses absorbing the rotational energy upon collision with the sensor. Conventional measuring elements are resistive, capacitive, electromagnetic, photoelectric, and penumatic or hydraulic. Novel types of angular accelerometers are based on inertia of gas jets, electron beams, and ion beams, the piezoelectric effect in p-n junctions of diode and transistors, the electrokinetic effect in fluids, and cryogenic suspension of the sensor.

Seleznev, A. V.; Shvab, I. A.

1985-05-01

152

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

153

Wissenschaftliches Approximation  

E-print Network

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

Auzinger, Winfried

154

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

E-print Network

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

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

2007-03-29

155

Localizing the angular momentum of linear gravity  

NASA Astrophysics Data System (ADS)

In a previous article [L. M. Butcher, , Phys. Rev. D 82, 104040 (2010).], we derived an energy-momentum tensor for linear gravity that exhibited positive energy density and causal energy flux. Here we extend this framework by localizing the angular momentum of the linearized gravitational field, deriving a gravitational spin tensor which possesses similarly desirable properties. By examining the local exchange of angular momentum (between matter and gravity) we find that gravitational intrinsic spin is localized, separately from “orbital” angular momentum, in terms of a gravitational spin tensor. This spin tensor is then uniquely determined by requiring that it obey two simple physically motivated algebraic conditions. Firstly, the spin of an arbitrary (harmonic-gauge) gravitational plane wave is required to flow in the direction of propagation of the wave. Secondly, the spin tensor of any transverse-traceless gravitational field is required to be traceless. (The second condition ensures that local field redefinitions suffice to cast our gravitational energy-momentum tensor and spin tensor as sources of gravity in a quadratic approximation to general relativity.) Additionally, the following properties arise in the spin tensor spontaneously: all transverse-traceless fields have purely spatial spin, and any field generated by a static distribution of matter will carry no spin at all. Following the structure of our previous paper, we then examine the (spatial) angular momentum exchanged between the gravitational field and an infinitesimal detector, and develop a microaveraging procedure that renders the process gauge-invariant. The exchange of nonspatial angular momentum (i.e., moment of energy) is also analyzed, leading us to conclude that a gravitational wave can displace the center of mass of the detector; this conclusion is also confirmed by a “first principles” treatment of the system. Finally, we discuss the spin carried by a gravitational plane wave.

Butcher, Luke M.; Lasenby, Anthony; Hobson, Michael

2012-10-01

156

Supersensitive measurement of angular displacements using entangled photons  

SciTech Connect

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

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

2011-05-15

157

Quasiclassical Born-Oppenheimer approximations  

E-print Network

We discuss several problems in quasiclassical physics for which approximate solutions were recently obtained by a new method, and which can also be solved by novel versions of the Born-Oppenheimer approximation. These cases include the so-called bouncing ball modes, low angular momentum states in perturbed circular billiards, resonant states in perturbed rectangular billiards, and whispering gallery modes. Some rare, special eigenstates, concentrated close to the edge or along a diagonal of a nearly rectangular billiard are found. This kind of state has apparently previously escaped notice.

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

2000-09-29

158

Angular momentum evolution in dark-matter haloes  

NASA Astrophysics Data System (ADS)

We have analysed high-resolution N-body simulations of dark-matter (DM) haloes, focusing specifically on the evolution of angular momentum. We find that not only is individual particle angular momentum not conserved, but the angular momentum of radial shells also varies over the age of the Universe by up to factors of a few. We find that torques from external structure are the most likely cause for this distribution shift. Since the model of adiabatic contraction that is often applied to model the effects of galaxy evolution on the DM density profile in a halo assumes angular momentum conservation, this variation implies that there is a fundamental limit on the possible accuracy of the adiabatic contraction model in modelling the response of DM haloes to the growth of galaxies.

Book, Laura G.; Brooks, Alyson; Peter, Annika H. G.; Benson, Andrew J.; Governato, Fabio

2011-03-01

159

The angular momentum of baryons and dark matter halos revisited  

Microsoft Academic Search

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

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

2011-01-01

160

Fabricating BRDFs at high spatial resolution using wave optics  

E-print Network

Recent attempts to fabricate surfaces with custom reflectance functions boast impressive angular resolution, yet their spatial resolution is limited. In this paper we present a method to construct spatially varying reflectance ...

Levin, Anat

161

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

Microsoft Academic Search

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

Yi-Xin Zhang; Ji Cang

2009-01-01

162

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

163

Multispectral angular domain optical tomography in scattering media with argon and diode laser sources  

NASA Astrophysics Data System (ADS)

Angular Domain Imaging (ADI) within highly scattering media employs micromachined angular filter tunnels to detect nonscattered photons which pass through the tunnels unattenuated while scattered photons collide with the tunnel walls. Each tunnel is micromachined approximately 51 ?m wide by 10 mm long in silicon, giving a maximum acceptance angle of 0.29 degrees. The ADI technique is inherently independent of wavelength, and thus multispectral laser sources can be incorporated. Previous ADI experiments employed a 488-514 nm Argon ion laser source. This paper describes the construction of a new imaging system utilizing a high-power (up to 0.5 W) laser diode at the 670 nm wavelength, along with an aspheric and cylindrical lens system for shaping the beam into a collimated line of light. ADI results of biological samples (i.e. chicken breast tissue) are also presented. Image resolution is 204 ?m or better in compressed chicken breast tissue approximately 3.8 mm in thickness. Digital image processing techniques are employed to improve image contrast, definition, and detectability of test structures. Because silicon is 40% reflective, scattered light at up to three times the acceptance angle is not sufficiently absorbed by the angular filter tunnels and contributes significant background noise, thus decreasing image contrast and detectability. Roughening of the tunnel surface using a NH4OH etchant solution scatters light hitting the walls, thus allowing it to be absorbed. Images after roughening show dramatic reductions in background scattered light levels between tunnels, suggesting that further experiments will make progress towards improved contrast and detectability of structures.

Chan, Paulman K. Y.; Vasefi, Fartash; Chapman, Glenn H.; Kaminska, Bozena; Pfeiffer, Nick

2007-02-01

164

Sub-micron resolution selected area electron channeling patterns.  

PubMed

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

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

2015-02-01

165

Angular momentum evolution for galaxies  

E-print Network

Using cosmological hydrodynamics simulations we study the angular momentum content of the simulated galaxies in relation with their morphological type. We found that not only the angular momentum of the disk component follow the expected theoretical relation, Mo, Mao & Whiye (1998), but also the spheroidal one, with a gap due to its lost of angular momentum, in agreement with Fall & Romanowsky (2013),. We also found that the galaxy size can plot in one general relation, despite the morphological type, as found by Kravtsov (2013).

Pedrosa, Susana

2015-01-01

166

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

NASA Technical Reports Server (NTRS)

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

Roddier, Francois

1999-01-01

167

An Acousto-Optical Sensor with High Angular Resolution  

PubMed Central

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

Kaloshin, Gennady; Lukin, Igor

2012-01-01

168

High angular resolution and position determinations by infrared interferometry  

NASA Technical Reports Server (NTRS)

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

1974-01-01

169

High angular resolution observations of CS in the Orion nebula  

NASA Astrophysics Data System (ADS)

The core of the Orion molecular cloud has been observed in the emission lines of CS at 146.8 and 97.98 GHz, using the 14 m FCRAO telescope. The morphology indicated by these new data, combined with previous observations, is an extremely narrow ridge extending 9 min N-S as well as a central condensation at the position of the Kleinmann-Low nebula. Within the central condensation the observations show no evidence of significant clumping on the scale of the beam despite the high sensitivity of this transition to changes in H2 density.

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

1980-09-01

170

Scene reconstruction from high spatio-angular resolution light fields  

E-print Network

Figure 1: Our method reconstructs accurate depth from light fields of complex scenes. The images on the left show a 2D slice of a 3D input light field, a so called epipolar-plane image (EPI), and two out of one hundred 21 megapixel images that were used to construct the light field. Our method computes 3D depth information for all visible scene points, illustrated by the depth EPI on the right. From this representation, individual depth maps or segmentation masks for any of the input views can be extracted as well as other representations like 3D point clouds. The horizontal red lines connect corresponding scanlines in the images with their respective position in the EPI. This paper describes a method for scene reconstruction of complex, detailed environments from 3D light fields. Densely sampled light fields in the order of 109 light rays allow us to capture the real world in unparalleled detail, but efficiently processing this amount of data to generate an equally detailed reconstruction represents a significant challenge to existing algorithms. We propose an algorithm that leverages coherence in massive light fields by breaking with a number of established practices in image-based reconstruction. Our algorithm first computes reliable depth estimates specifically

Changil Kim; Henning Zimmer; Yael Pritch Alex; Er Sorkine-hornung Markus Gross

171

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

172

A novel model of the geometric and detector response for limited angular sampling pinhole SPECT  

NASA Astrophysics Data System (ADS)

Reconstruction methodologies for data sets with reduced angular sampling (RAS) are essential for efficient dynamic or static preclinical animal imaging research using single photon emission computed tomography (SPECT). Modern iterative reconstruction methods can obtain 3D radiotracer distributions of the highest possible quality and resolution. Essential to these algorithms is an accurate model of the physical imaging process. We developed a new point-spread function (PSF) model for the pinhole geometry and compared it to a Gaussian model in a RAS setting. The new model incorporates the geometric response of the pinhole and the detector response of the camera by simulating the system PSF using the error function. Reconstruction of simulated data was done with OS-EM and COS-EM: a new convergent OS-EM based algorithm. The reconstruction of projection data of a simulated point source using the novel method showed improved FWHM values compared to a standard Gaussian method. COS-EM delivers improved results for RAS data, although it converges slower than OS-EM. The reconstruction of Monte Carlo simulated projection data from a resolution phantom shows that as few as 40 projections are sufficient to reconstruct an image with a resolution of approximately 4 mm. The new pinhole model applied to iterative reconstruction methods can reduce imaging time in small animal experiments by a factor of three or reduce the number of cameras needed to perform dynamic SPECT.

Wietholt, Christian; Hsiao, Ing-Tsung; Clough, Anne V.; Chen, Chin-Tu

2006-03-01

173

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

174

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

NASA Astrophysics Data System (ADS)

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

Zhang, Yin; Wu, Junjie; Yang, Jianyu

2014-12-01

175

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

SciTech Connect

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

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

2012-05-03

176

A Role for Improved Angular Observations in Geosynchronous Orbit Determination  

NASA Astrophysics Data System (ADS)

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

Sabol, Christopher Andrew

1998-12-01

177

Angular Diameters of O- and B-type Stars  

NASA Astrophysics Data System (ADS)

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

Gordon, Kathryn; Gies, Douglas; Schaefer, Gail

2015-01-01

178

Paraxial Light Beams with Angular Momentum  

Microsoft Academic Search

Fundamental and applied concepts concerning the ability of light beams to carry a certain mechanical angular momentum with respect to the propagation axis are reviewed and discussed. Following issues are included: Historical reference; Angular momentum of a paraxial beam and its constituents; Spin angular momentum and paradoxes associated with it; Orbital angular momentum; Circularly-spiral beams: examples and methods of generation;

A. Bekshaev; M. Soskin; M. Vasnetsov

2008-01-01

179

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

NASA Technical Reports Server (NTRS)

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

Omidvar, K.

1977-01-01

180

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

NASA Technical Reports Server (NTRS)

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

Omidvar, K.

1977-01-01

181

Variations in atmospheric angular momentum  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

182

RIS-M-2426 RESOLUTION IN DIFFRACTION  

E-print Network

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

183

Measuring Angular Size and Distance  

NSDL National Science Digital Library

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

184

Angular Momentum in QGP Holography  

E-print Network

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

Brett McInnes

2014-08-25

185

Solar cell angular position transducer  

NASA Technical Reports Server (NTRS)

An angular position transducer utilizing photocells and a light source is disclosed. The device uses a fully rotatable baffle which is connected via an actuator shaft to the body whose rotational displacement is to be measured. The baffle blocks the light path between the light source and the photocells so that a constant semicircular beam of light reaches the photocells. The current produced by the photocells is fed through a resistor, a differential amplifier measures the voltage drop across the resistor which indicates the angular position of the actuator shaft and hence of the object.

Sandford, M. C.; Gray, D. L. (inventors)

1980-01-01

186

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

SciTech Connect

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

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

2013-07-01

187

The Angular Momentum of Baryons and Dark Matter Halos Revisited  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

188

Near-perfect sorting of orbital angular momentum and angular position states  

E-print Network

Near-perfect sorting of orbital angular momentum and angular position states of light Malcolm N. O for efficient sorting of photons prepared in states of orbital angular momentum (OAM) and angular position (ANG, "Orbital angular momentum of light and the transfor- mation of Laguerre-Gaussian laser modes," Phys. Rev

Boyd, Robert W.

189

The Cosmological Dependence of Galactic Specific Angular Momenta  

E-print Network

Hydrodynamical simulations of galaxy formation in spatially flat Cold Dark Matter (CDM) cosmologies with and without a cosmological constant (Lambda) are described. A simple star formation algorithm is employed and radiative cooling is allowed only after redshift z=1 so that enough hot gas is available to form large, rapidly rotating stellar discs if angular momentum is approximately conserved during collapse. The specific angular momenta of the final galaxies are found to be sensitive to the assumed background cosmology. This dependence arises from the different angular momenta contained in the haloes at the epoch when the gas begins to collapse and the inhomogeneity of the subsequent halo evolution. In the Lambda-dominated cosmology, the ratio of stellar specific angular momentum to that of the dark matter halo (measured at the virial radius) has a median value of ~0.24 at z=0. The corresponding quantity for the Lambda=0 cosmology is over 3 times lower. It is concluded that the observed frequency and angular momenta of disc galaxies pose significant problems for spatially flat CDM models with Lambda=0 but may be consistent with a Lambda-dominated CDM universe.

Vincent Eke; George Efstathiou; Lisa Wright

1999-08-26

190

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

191

Gravitational lenses with angular momentum  

NASA Astrophysics Data System (ADS)

The Einstein (1936), Liebes (1964), Refsdal (1965), and Bourassa et al. (1973, 1975) theories of the effects of gravitational lenses have considered the bending of light as due to the mass distribution of the deflector. The effect of deflector dynamical properties has not been taken into account. The influence of angular momentum in a gravitational lens is presently demonstrated by the bending angle of a photon passing near a rotating body. The expressions used are evaluated for spherical and spheroidal deflectors.

Ibanez, J.

1983-08-01

192

Angular Correlations in ^96Mo  

NASA Astrophysics Data System (ADS)

Gamma-gamma coincidences from ^96Mo were detected by the OSIRIS cube spectrometer at the University of Cologne's FN Tandem Accelerator, to identify low-lying M1 transitions between 2+ states using angular correlations. Preliminary analysis of the low energy 2+ to 2+ cascades will be presented. This work was supported by NSF 0555665, Jeffress Fund J-809, and USDOE DE-FG02-91ER-40609 grants.

Atwater, S.; Aleksandrova, K.; Werner, V.; von Brentano, P.; Fitzler, A.; Fransen, C.; Linnemann, A.; Terry, J. R.; Fetea, M. S.

2007-10-01

193

Achromatic orbital angular momentum generator  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

194

Orbital angular momentum in phase space  

E-print Network

A comprehensive theory of the Weyl-Wigner formalism for the canonical pair angle-angular momentum is presented. Special attention is paid to the problems linked to rotational periodicity and angular-momentum discreteness.

I. Rigas; L. L. Sanchez-Soto; A. B. Klimov; J. Rehacek; Z. Hradil

2010-11-29

195

Observing angular deviations in the specular reflection of a light beam  

NASA Astrophysics Data System (ADS)

The Law of Reflection of a light ray incident upon a mirror (?in = ?out) was first formulated by Euclid around 300 BC in his book Catoptrics; it has been a tenet of geometrical optics ever since. However, more recently, a small angular deviation of the Law of Reflection has been predicted for a physical light beam when this is regarded as the implementation of a ray. The deviation is a diffractive consequence of the angular dependence of the reflectivity and should occur for any mirror with less than 100% reflectivity. We report here experimental proof of this angular deviation by determining the direction of an optical beam after reflection from an air-glass interface, using a position detector with nanometre resolution. Our results are relevant for angular metrology in general and cantilever-based surface microscopies in particular. Analogous angular deviations are expected for reflection of acoustic waves and quantum matter waves.

Merano, M.; Aiello, A.; van Exter, M. P.; Woerdman, J. P.

2009-06-01

196

Asteroid orbit fitting with radar and angular observations  

NASA Astrophysics Data System (ADS)

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

Baturin, A. P.

2013-12-01

197

The Impact of Self-Construal on Aesthetic Preference for Angular Versus Rounded Shapes  

Microsoft Academic Search

In this article, the authors examine the role of self-construal in aesthetic preference for angular versus rounded shapes. Previous research found an independent self-construal is associated with a confrontation approach to conflict resolution, whereas an inter- dependent self-construal is associated with compromise. Further- more, the literature in empirical aesthetics suggests that angular shapes tend to generate confrontational associations, and rounded

Yinlong Zhang

2006-01-01

198

The angular momentum of the Oort cloud  

Microsoft Academic Search

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

P Weissman

1991-01-01

199

Spin Angular Momentum Imparted by Gravitational Waves  

E-print Network

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

M Sharif

2007-01-23

200

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

201

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; Hikmat, BC [Department of Physics, New Mexico State University, Las Cruces, New Mexico 88003-0001 (United States)

2009-04-01

202

Photoionization with Orbital Angular Momentum Beams  

Microsoft Academic Search

Intense laser ionization expands Einstein's photoelectric effect rules giving a wealth of phenomena widely studied over the last decades. In all cases, so far, photons were assumed to carry one unit of angular momentum. However it is now clear that photons can possess extra angular momentum, the orbital angular momentum (OAM), related to their spatial profile. We show a complete

A. Picón; J. Mompart; J. R. Vázquez de Aldana; L. Plaja; G. F. Calvo; L. Roso

2010-01-01

203

What is Orbital Angular Matthias Burkardt  

E-print Network

What is Orbital Angular Momentum? Matthias Burkardt burkardt@nmsu.edu New Mexico State University What is Orbital Angular Momentum? ­ p.1/22 #12;Motivation polarized DIS: only 30% of the proton spin = 1 quest for the remaining 70% quark orbital angular momentum (OAM) gluon spin gluon OAM How

204

Photon Orbital Angular Momentum in Astrophysics  

Microsoft Academic Search

Observations of the orbital angular momentum of photons --- a property of electromagnetic radiation that has come to the fore in recent years --- have apparently never been attempted in astronomy. By now it is known from laboratory studies that, in addition to carrying spin angular momentum, individual photons can carry N >> 100 units of orbital angular momentum h\\/2pi

Martin Harwit

2003-01-01

205

Probes of Orbital Angular Matthias Burkardt  

E-print Network

Probes of Orbital Angular Momentum Matthias Burkardt burkardt@nmsu.edu New Mexico State University Las Cruces, NM, 88003, U.S.A. Probes of Orbital Angular Momentum ­ p.1/40 #12;Motivation Decomposition carry the nucleon spin? Probes of Orbital Angular Momentum ­ p.2/40 #12;Outline The anomalous magnetic

206

Angular dependent study on ferromagnetic resonance and spin excitations by spin rectification  

NASA Astrophysics Data System (ADS)

We report angular dependent spin rectification spectra which are applied to studying spin excitations in single permalloy stripe. Based on planar Hall effect, those spin excitations generate special resonant dc Hall voltages, which have been characterized as functions of the amplitude and direction of applied magnetic field. Through high angular resolution 2D mappings, the evolutions of different spin excitation can be directly presented, and the dynamic magnetic parameters such as the gyromagnetic ratio, effective exchange field, as well as the quantized numbers of standing spin waves can be accurately determined through fitting the angular evolution of each resonance.

Zhang, Yichao; Fan, Xiaolong; Zhao, Xiaobing; Rao, Jinwei; Zhou, Hengan; Guo, Dangwei; Gui, Y. S.; Hu, C.-M.; Xue, Desheng

2015-01-01

207

Angular momentum density of a Gaussian vortex beam  

NASA Astrophysics Data System (ADS)

The Gaussian vortex beam is assumed to be linearly polarized. The analytical expression of the electric field of a linearly polarized Gaussian vortex beam propagating in free space is derived by using the vectorial Rayleigh-Sommerfeld integral formulae. The propagating magnetic field of the linearly polarized Gaussian vortex beam is presented by taking the curl of the electric field. By employing the electromagnetic field of the linearly polarized Gaussian vortex beam beyond the paraxial approximation, the analytical expression of the angular momentum density of the linearly polarized Gaussian vortex beam is derived. The three components of the angular momentum density of a linearly polarized Gaussian vortex beam are demonstrated in the reference plane. The effects of the linearly polarized angle and the topological charge on the three components of the angular momentum density are investigated. To acquire the more longitudinal angular momentum density requires such an optimal choice that the linearly polarized angle is set to be zero and the topological charge increases. This research is useful to the optical trapping, the optical guiding, and the optical manipulation.

Zhou, GuoQuan; Wang, XiaoGang; Dai, ChaoQing; Chu, XiuXiang

2014-04-01

208

Variable Distance Angular Symbology Reader  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

209

Two-axis angular effector  

DOEpatents

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

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

1997-01-21

210

Interpolation and Approximation Theory.  

ERIC Educational Resources Information Center

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

Kaijser, Sten

1991-01-01

211

Fast Approximate Convex Decomposition  

E-print Network

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

Ghosh, Mukulika

2012-10-19

212

Secondary Cosmic Muon Angular Distributions with High Statistics  

E-print Network

Project GRAND preents a map in right ascension and declination for single cosmic secondary tracks which have been identified as muons. These muons are measured in stations of proportional wire chambers (PWCs) which have a mean angular resolution of 0.26 deg. A 50 mm steel plate interspersed with the PWCs is used to distinguish muons from electrons. Two years of data are accumulated in a map of right ascension and declination which covers all of the northern hemisphere and a small portion of the southern hemisphere. The total number of muon tracks in this data sample are 40 billion. Significant large angular structure is found in this map; the deviations from average are small compared to the average, but because of the high statistics, the deviations from average are statistically significant to many standard deviations. Systematic effects in the data are minimized by averaging over this two year period. These results are similar to those obtained in previous data.

J. Poirier; J. Gress; T. F. Lin

2000-04-28

213

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

PubMed

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

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

2015-01-01

214

Resolution Matters  

NSDL National Science Digital Library

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

2013-02-14

215

On demand generation of propagation invariant photons with orbital angular momentum  

E-print Network

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

Y. Jerónimo-Moreno; R. Jáuregui

2014-08-11

216

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

NASA Astrophysics Data System (ADS)

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

Jerónimo-Moreno, Y.; Jáuregui, R.

2014-07-01

217

Small angular scale simulations of the microwave sky  

SciTech Connect

We describe and compare two types of microwave sky simulations that are good for small angular scales. The first type uses expansions in spherical harmonics, and the second one is based on plane waves and the fast Fourier transform. The angular power spectrum is extracted from maps corresponding to both types of simulations, and the resulting spectra are appropriately compared. In this way, the features and usefulness of Fourier simulations are pointed out. For {ital l}{ge}100, all the simulations lead to similar accuracies; however, the CPU cost of Fourier simulations is {approximately}10 times smaller than that for spherical harmonic simulations. For {ital l}{le}100, the simulations based on spherical harmonics seem to be preferable. {copyright} {ital 1996 The American Astronomical Society.}

Saez, D. [Departamento de Astronomia y Astrofisica, Universidad de Valencia, Burjassot, Valencia (Spain)] [Departamento de Astronomia y Astrofisica, Universidad de Valencia, Burjassot, Valencia (Spain); Holtmann, E.; Smoot, G.F. [Lawrence Berkeley Laboratory, Space Science Laboratory, CfPA, Building 50-204, University of California, Berkeley, California 94720 (United States)] [Lawrence Berkeley Laboratory, Space Science Laboratory, CfPA, Building 50-204, University of California, Berkeley, California 94720 (United States)

1996-12-01

218

Angular Momentum Transport in Convectively Unstable Shear Flows  

NASA Astrophysics Data System (ADS)

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

Käpylä, Petri J.; Brandenburg, Axel; Korpi, Maarit J.; Snellman, Jan E.; Narayan, Ramesh

2010-08-01

219

Measurement of polarization with the Degree Angular Scale Interferometer.  

PubMed

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

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

220

Radial and vertical angular momentum transport in protostellar discs  

E-print Network

Angular momentum in protostellar discs can be transported either radially, through turbulence induced by the magnetorotational instability (MRI), or vertically, through the torque exerted by a large-scale magnetic field. We present a model of steady-state discs where these two mechanisms operate at the same radius and derive approximate criteria for their occurrence in an ambipolar diffusion dominated disc. We obtain "weak field'' solutions - which we associate with the MRI channel modes in a stratified disc - and transform them into accretion solutions with predominantly radial angular-momentum transport by implementing a turbulent-stress prescription based on published results of numerical simulations. We also analyze "intermediate field strength'' solutions in which both radial and vertical transport operate at the same radial location. Our results suggest, however, that this overlap is unlikely to occur in real discs.

Raquel Salmeron; Arieh Königl; Mark Wardle

2007-06-28

221

High-Resolution X-Ray Telescopes  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

222

Transverse and longitudinal angular momenta of light  

E-print Network

We review basic physics and novel types of optical angular momentum. We start with a theoretical overview of momentum and angular momentum properties of generic optical fields, and discuss methods for their experimental measurements. In particular, we describe the well-known longitudinal (i.e., aligned with the mean momentum) spin and orbital angular momenta in polarized vortex beams. Then, we focus on the transverse (i.e., orthogonal to the mean momentum) spin and orbital angular momenta, which were recently actively discussed in theory and observed in experiments. First, the recently-discovered transverse spin angular momenta appear in various structured fields: evanescent waves, interference fields, and focused beams. We show that there are several kinds of transverse spin angular momentum, which differ strongly in their origins and physical properties. We describe extraordinary features of the transverse optical spins and overview recent experiments. In particular, the helicity-independent transverse spin...

Bliokh, Konstantin Y

2015-01-01

223

Variations in atmospheric angular momentum and the length of day  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

224

Amplified dispersive delay generator using angular dispersion amplification.  

PubMed

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

Basu, Santanu

2009-10-10

225

Angular dependence of sampling MTF  

NASA Astrophysics Data System (ADS)

Sampling MTF defined in Park, Hock, and de Luca, as an x and y sampling, can be generalized for image data not along x and y directions. For a given sampling lattice (such as in a laser printer, a scene projector, or a focal plane array), we construct a two-dimensional sampling MTF based on the distance between nearest samples in each direction. Because the intersample distance depends on direction, the sampling MTF will be best in the directions of highest spatial sampling, and poorer in the directions of sparse sampling. We compare hexagonal and rectangular lattices in terms of their equivalent spatial frequency bandwidth. We filter images as demonstration of the angular-dependent two-dimensional sampling MTF.

Hadar, Ofer; Dogariu, Aristide C.; Boreman, Glenn D.

1997-09-01

226

Orbital angular momentum in phase space  

SciTech Connect

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

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

2011-02-15

227

Quantum Formulation of Fractional Orbital Angular Momentum  

E-print Network

The quantum theory of rotation angles (S. M. Barnett and D. T. Pegg, Phys. Rev. A, 41, 3427-3425 (1990)) is generalised to non-integer values of the orbital angular momentum. This requires the introduction of an additional parameter, the orientation of a phase discontinuity associated with fractional values of the orbital angular momentum. We apply our formalism to the propagation of light modes with fractional orbital angular momentum in the paraxial and non-paraxial regime.

J. B. Goette; S. Franke-Arnold; R. Zambrini; Stephen M. Barnett

2006-11-15

228

Relativistic Statistical Mechanics with Angular Momentum  

E-print Network

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

Tadas K Nakamura

2011-12-09

229

Angularly inhomogeneous piezoelectric piezomagnetic magnetoelectric anisotropic media  

Microsoft Academic Search

The field around a line defect along the axis of an angularly inhomogeneous, elastically anisotropic medium with piezoelectric, piezomagnetic and magnetoelectric coupling has a surprisingly simple form.

V. I. Alshits; H. O. K. Kirchner; T. C. T. Ting

1995-01-01

230

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

231

Anisotropy of the Cosmic Microwave Background Radiation on Large and Medium Angular Scales  

NASA Technical Reports Server (NTRS)

This grant has supported work at Brown University on measurements of the 2.7 K Cosmic Microwave Background Radiation (CMB). The goal has been to characterize the spatial variations in the temperature of the CMB in order to understand the formation of large-scale structure in the universe. We have concurrently pursued two measurements using millimeter-wave telescopes carried aloft by scientific balloons. Both systems operate over a range of wavelengths, chosen to allow spectral removal of foreground sources such as the atmosphere, Galaxy, etc. The angular resolution of approx. 25 arcminutes is near the angular scale at which the most structure is predicted by current models to be visible in the CMB angular power spectrum. The main goal is to determine the angular scale of this structure; in turn we can infer the density parameter, Omega, for the universe as well as other cosmological parameters, such as the Hubble constant.

Houghton, Anthony; Timbie, Peter

1998-01-01

232

Angular momentum distribution of hot gas and implications for disk galaxy formation  

E-print Network

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 ``non-radiative'' 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 non-radiative 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 $\\mu$ 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.

D. N. Chen; Y. P. Jing; Kohji Yoshikawa

2003-07-14

233

APPROXIMATE DYNAMIC PROGRAMMING  

E-print Network

LEARNING AND APPROXIMATE DYNAMIC PROGRAMMING Scaling Up to the Real World #12;#12;LEARNING AND APPROXIMATE DYNAMIC PROGRAMMING Scaling Up to the Real World Edited by Jennie Si, Andy Barto, Warren Powell

Mahadevan, Sridhar

234

Approximating distributions from moments  

Microsoft Academic Search

A method based upon Pearson-type approximations from statistics is developed for approximating a symmetric probability density function from its moments. The extended Fokker-Planck equation for non-Markov processes is shown to be the underlying foundation for the approximations. The approximation is shown to be exact for the beta probability density function. The applicability of the general method is illustrated by numerous

R. F. Pawula

1987-01-01

235

A SIMILARITY THEORY OF APPROXIMATE DECONVOLUTION MODELS OF TURBULENCE  

Microsoft Academic Search

We apply the phenomenology of homogeneous, isotropic turbulence to the family of approximate deconvolution models proposed by Stolz and Adams. In particular, we establish that the models themselves have an energy cascade with two asymptotically dierent inertial ranges. Delineation of these gives insight into the resolution requirements of using approximate deconvolution models. The approximate deconvolution model's energy balance contains both

MONIKA NEDAz

236

Angular-Rate Estimation Using Quaternion Measurements  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

237

Angular Momentum Eigenstates for Equivalent Electrons.  

ERIC Educational Resources Information Center

Simple and efficient methods for adding angular momenta and for finding angular momentum eigenstates for systems of equivalent electrons are developed. Several different common representations are used in specific examples. The material is suitable for a graduate course in quantum mechanics. (SK)

Tuttle, E. R.; Calvert, J. B.

1981-01-01

238

Specific Angular Momentum of Extrasolar Planetary Systems  

E-print Network

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

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

2011-09-02

239

Photon orbital angular momentum: problems and perspectives  

Microsoft Academic Search

The availability of laser beams carrying orbital angular momentum in addition to spin angular momentum paved the way to the observation of novel effects in quantum and classical optics. These effects are reviewed in this paper with emphasis on future perspectives.

E. Santamato

2004-01-01

240

Optical Solitons Carrying Orbital Angular Momentum  

Microsoft Academic Search

We predict a new kind of ring-profile solitary wave in nonlinear optical media, with finite orbital angular momentum. During propagation these fragment into fundamental solitons. Like free Newtonian particles, these fly off tangential to the ring, vividly demonstrating conservation of orbital angular momentum in soliton motion.

W. J. Firth; D. V. Skryabin

1997-01-01

241

SPECIAL NATURE OF ORBITAL ANGULAR MOMENTUM  

Microsoft Academic Search

The properties of orbital angular momentam operators are examined within ; the framework of the formal theory of angular momentum. It is demonstrated that ; the occurrence of only integral quantum numbers in the orbital theory is a ; consequence of the particular form of the orbital operators. Single-valuedness ; of the eigenfunctions need not be postulated. (auth);

James D. Louck

1963-01-01

242

Orbital angular momentum in the nucleon  

SciTech Connect

Analysis of the measured value of the integrated d-bar-u-bar asymmetry (I{sub fas} = 0.147 +- 0.027) in the nucleon show it to arise from nucleon fluctuations into baryon plus pion. Requiring angular momentum conservation in these fluctuations shows the associated orbital angular momentum is equal to the value of the flavor asymmetry.

Garvey, Gerald T. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2010-05-15

243

Orbital Angular Momentum in the Nucleon  

E-print Network

Analysis of the measured value of the integrated \\bar{d}-\\bar{u} asymmetry (Ifas = 0.147+-0.027) in the nucleon show it to arise from nucleon fluctuations into baryon plus pion. Requiring angular momentum conservation in these fluctuations shows the associated orbital angular momentum is equal to the value of the flavor asymmetry.

Gerald T. Garvey

2010-03-12

244

Detecting orbital angular momentum in radio signals  

E-print Network

Electromagnetic waves with an azimuthal phase shift are known to have a well defined orbital angular momentum. Different methods that allow for the detection of the angular momentum are proposed. For some, we discuss the required experimental setup and explore the range of applicability.

H. Then; B. Thidé; J. T. Mendonça; T. D. Carozzi; J. Bergman; W. A. Baan; S. Mohammadi; B. Eliasson

2008-05-18

245

A bulk micromachined silicon angular rate sensor  

Microsoft Academic Search

We describe an angular rate sensor based on bulk micro-machining of silicon. A silicon beam suspended on two sets of torsion springs has two orthogonal degrees of freedom for angular motion. The Coriolis force induced by external rotation modulates the coupling between the two modes which is then converted to a voltage output by an electro mechanical system operating at

Heikki Kuisma; Tapani Ryhanen; Juha Lahdenpera; Eero Punkka; S. Ruotsalainen; T. Sillanpaa; H. Seppa

1997-01-01

246

The Angular Momentum-Energy Space  

E-print Network

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

Dan Comanescu

2007-02-09

247

Angular momentum in the global atmospheric circulation  

Microsoft Academic Search

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

Joseph Egger; Klaus Weickmann; Klaus-Peter Hoinka

2007-01-01

248

Dijet angular distributions at D0  

SciTech Connect

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

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

1996-09-01

249

Approximate solution in gasdynamics  

NASA Technical Reports Server (NTRS)

One-dimensional unsteady gasdynamics is considered. An approximation based mainly on the interaction of simple and entropy waves is adopted. A discussion supporting this approximation, based in part on shock expansion theory, is given. By the use of certain transformations the approximation leads to solution in terms of quadratures. Excellent agreement with exact numerical results is obtained over a wide range of cases.

Sirovich, L.; Chong, T. H.

1980-01-01

250

Integrals and static solutions of general relativistic Liouville's equation in post Newtonian approximation  

E-print Network

The post-Newtonian approximation of general relativistic Liouville's equation is presented. Two integrals of it, generalizations of the classical energy and angular momentum, are obtained. Polytropic models are constructed as an application.

V. Rezania; Y. Sobouti

1998-04-27

251

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

252

The angular momentum of the Oort cloud  

NASA Technical Reports Server (NTRS)

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

Weissman, Paul R.

1991-01-01

253

Angular two-photon interference and angular two-qubit states.  

PubMed

Using angular-position-orbital-angular-momentum entangled photons, we study angular two-photon interference in a scheme in which entangled photons are made to pass through apertures in the form of double angular slits, and using this scheme, we demonstrate an entangled two-qubit state that is based on the angular-position correlations of entangled photons. The entanglement of the two-qubit state is quantified in terms of concurrence. These results provide an additional means for preparing entangled quantum states for use in quantum information protocols. PMID:20366353

Jha, Anand Kumar; Leach, Jonathan; Jack, Barry; Franke-Arnold, Sonja; Barnett, Stephen M; Boyd, Robert W; Padgett, Miles J

2010-01-01

254

Molecular collisions 21: Semiclassical approximation to atom-symmetric top rotational excitation  

NASA Technical Reports Server (NTRS)

A distorted wave approximation to the T matrix for atom-symmetric top scattering was developed. The approximation is correct to first order in the part of the interaction potential responsible for transitions in the component of rotational angular momentum along the symmetry axis of the top. A semiclassical expression for this T matrix is derived by assuming large values of orbital and rotational angular momentum quantum numbers.

Russell, D.; Curtiss, C. F.

1973-01-01

255

Approximate Maximum Principle for Discrete Approximations of ...  

E-print Network

we have the following relationships: either d(uN (??(N)) .... Therefore, in what follows, we prove Theorem 3.1 in the case q = 0, breaking down the proof .... combination of type (4.10) can be approximated up to a small quantity of order o(

2012-03-20

256

Angular distribution of atoms during the magnetron sputtering of polycrystalline targets  

NASA Astrophysics Data System (ADS)

The angular distributions of atoms are measured during the dc magnetron sputtering of Mg, Al, Cu, Ag, Ta, Pt, Au, Ti, Cr, Zn, Zr, and Nb polycrystals by Ar ions with an energy up to 0.5 keV. These angular distributions are phenomenologically approximated, and adjustable parameters are found for each element. Computer simulation of sputtering based on the pair collision approximation is used to determine the coefficient of proportionality between the magnetron discharge voltage and the average sputtering ion energy and to find the interatomic interaction potentials that provide the most accurate description of the experimental data. Both the angular distribution width and the sputtering coefficient are shown to have a periodic dependence on the atomic number of the target Z 2, and materials with the maximum sputtering coefficients have the narrowest distribution of sputtered atoms.

Martynenko, Yu. V.; Rogov, A. V.; Shul'ga, V. I.

2012-04-01

257

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

258

Monitoring Location and Angular Orientation of a Pill  

NASA Technical Reports Server (NTRS)

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

Schipper, John F.

2012-01-01

259

Calculate engine crankshaft angular acceleration based on original flywheel data  

Microsoft Academic Search

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

Longxin Zhen; Zijun An; Qiang Li; Baocheng Wang

2010-01-01

260

Structural Design of Observers For Estimation of Spaceraft's Angular Velocity  

Microsoft Academic Search

It is proposed that measuring information about angular motion of spacecraft can be received form gryrostabilized platform, angular velocity measurers or having no platform system of attitude determination. In this case, angular position of orientation object is determinated by integration of kinematic equations of angular motion according to information received from angular velocity measurers or one-axis gyrostabilizers. Though the output

A. F. Djumin; S. N. Yegorov

1996-01-01

261

Semiparametric Efficiency of GMM under Approximate Constraints  

E-print Network

Generalized empirical likelihood and generalized method of moments are well spread methods of resolution of inverse problems in econometrics. Each method defines a specific semiparametric model for which it is possible to calculate efficiency bounds. By this approach, we provide a new proof of Chamberlain's result on optimal GMM. We also discuss conditions under which GMM estimators remain efficient with approximate moment constraints.

Rochet, Paul

2010-01-01

262

NCAI Resolutions  

ERIC Educational Resources Information Center

Five Major Policy Resolutions were adopted, without objection, at the 33rd Annual Convention of the National Congress of American Indians (NCAI) held in Salt Lake City, Utah, in October 1976. The issues involved were: Treaties and Trust Responsibilities, Tribal Government, Jurisdiction, Federal Administration and Structure of Indian Affairs, and…

American Indian Journal of the Institute for the Development of Indian Law, 1977

1977-01-01

263

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

PubMed Central

Background Angular spectroscopy of light scattering can be used for quantitative analysis of cellular and subcellular properties, and thus promises a noninvasive methodology for in vivo assessment cellular integrity to complement in vitro histological examination. Spatial information is essential for accurate identification of localized abnormalities. However, conventional angular spectroscopy systems only provide single-channel measurement, which suffers from poor spatial resolution or requires time-consuming scanning over extended area. The purpose of this study was to develop a multi-channel angular spectroscopy for light field imaging in biological tissues. Materials and methods A microlens array (MLA) (8×8) based light field imager for 64-channel angular spectroscopy was developed. A pair of crossed polarizers was employed for polarization-sensitive recording to enable quantitative measurement at high signal specificity and sensitivity. The polarization-sensitive light field imager enables rapid measurement of multiple sampling volumes simultaneously at 18 ?m spatial-resolution and 3° angular-resolution. Comparative light field imaging and electrophysiological examination of freshly isolated and physiologically deteriorated lobster leg nerves have been conducted. Results Two-dimensional (2D) polarization-sensitive scattering patterns of the fresh nerves were highly elliptical, while they gradually lost the ellipticity and became rotationally symmetric (i.e., circular) as the nerves physiologically deteriorated due to repeated electrical stimulations. Characterized parameters, i.e., the ellipticity and the scattering intensity, rendered spatially various characteristics such as different values and deteriorating rates. Conclusions The polarization-sensitive light field imager is able to provide multi-channel angular spectroscopy of light scattering with both spatial and angular resolutions. The light scattering properties of nerves are highly dependent on the orientation of nerves and their physiological status. Further development of polarization-sensitive multi-channel angular spectroscopy may promise a methodology for rapid and reliable identification of localized abnormalities in biological tissues. PMID:25694947

Lu, Rongwen; Zhang, Qiuxiang; Zhi, Yanan

2015-01-01

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

Approximation for the Rayleigh Resolution of a Circular Aperture  

ERIC Educational Resources Information Center

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

Mungan, Carl E.

2009-01-01

266

Why Outflows Have Low Angular Momentum  

NASA Astrophysics Data System (ADS)

We outline why galactic outflows preferentially remove low angular momentum material, and show that this is a natural result when structure forms in a cold dark matter cosmology. The driving factors are the fact that the mean angular momentum of accreted material increases with time, the existence of an extended reservoir of low angular momentum gas which is not within star forming regions and hence not subjected to being directly blown out and the tendency for outflows to follow the path of least resistance which is perpendicular to the disk.

Brook, C.; Governato, F.; Roškar, R.; Brooks, A.; Mayer, L.; Quinn, T.; Wadsley, J.

2010-06-01

267

Pretzelosity TMD and Quark Orbital Angular Momentum  

E-print Network

We study the connection between the quark orbital angular momentum and the pretzelosity transverse-momentum dependent parton distribution function. We discuss the origin of this relation in quark models, identifying as key ingredient for its validity the assumption of spherical symmetry for the nucleon in its rest frame. Finally we show that the individual quark contributions to the orbital angular momentum obtained from this relation can not be interpreted as the intrinsic contributions, but include the contribution from the transverse centre of momentum which cancels out only in the total orbital angular momentum.

C. Lorce'; B. Pasquini

2012-03-22

268

Angular momentum decomposition from a QED example  

NASA Astrophysics Data System (ADS)

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

Liu, Tianbo; Ma, Bo-Qiang

2015-01-01

269

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

270

Angular momentum decomposition from a QED example  

E-print Network

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

Tianbo Liu; Bo-Qiang Ma

2014-12-25

271

ALMA Observations of Asteroid 3 Juno at 60 Kilometer Resolution  

E-print Network

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0.042 arcseconds (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of ten consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259pm4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215pm13 K, while the median over the whole surface is 197pm15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies ...

Partnership, ALMA; Kneissl, R; Moullet, A; Brogan, C L; Fomalont, E B; Vlahakis, C; Asaki, Y; Barkats, D; Dent, W R F; Hills, R; Hirota, A; Hodge, J A; Impellizzeri, C M V; Liuzzo, E; Lucas, R; Marcelino, N; Matsushita, S; Nakanishi, K; Perez, L M; Phillips, N; Richards, A M S; Toledo, I; Aladro, R; Broguiere, D; Cortes, J R; Cortes, P C; Dhawan, V; Espada, D; Galarza, F; Garcia-Appadoo, D; Guzman-Ramirez, L; Hales, A S; Humphreys, E M; Jung, T; Kameno, S; Laing, R A; Leon, S; Marconi, G; Nikolic, B; Nyman, L -A; Radiszcz, M; Remijan, A; Rodon, J A; Sawada, T; Takahashi, S; Tilanus, R P J; Vilaro, B Vila; Watson, L C; Wiklind, T; de Gregorio, I; Di Francesco, J; Mangum, J; Francke, H; Gallardo, J; Garcia, J; Gonzalez, S; Hill, T; Kaminski, T; Kurono, Y; Lopez, C; Morales, F; Plarre, K; Randall, S; van kempen, T; Videla, L; Villard, E; Andreani, P; Hibbard, J E; Tatematsu, K

2015-01-01

272

Detection of the Angular Correlation of Faint X-ray Sources  

E-print Network

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

A. Vikhlinin; W. Forman

1995-10-06

273

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

PubMed

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

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

2014-10-01

274

Structural Design of Observers For Estimation of Spaceraft's Angular Velocity  

NASA Astrophysics Data System (ADS)

It is proposed that measuring information about angular motion of spacecraft can be received form gryrostabilized platform, angular velocity measurers or having no platform system of attitude determination. In this case, angular position of orientation object is determinated by integration of kinematic equations of angular motion according to information received from angular velocity measurers or one-axis gyrostabilizers. Though the output of gyrostabilizers are increments of quasicoordinates, this information is equivalent to measuring of angular velocity vector in basis connected with spacecraft.

Djumin, A. F.; Yegorov, S. N.

1996-08-01

275

Entanglement of Polarization and Orbital Angular Momentum  

E-print Network

We investigate two-photon entangled states using two important degrees of freedom of the electromagnetic field, namely orbital angular momentum (OAM) and spin angular momentum. For photons propagating in the same direction we apply the idea of $\\textit{entanglement duality}$ and develop schemes to do $\\textit{entanglement sorting}$ based either on OAM or polarization. In each case the entanglement is tested using appropriate witnesses. We finally present generalizations of these ideas to three- and four-photon entangled states.

Daniel Bhatti; Joachim von Zanthier; Girish S. Agarwal

2015-02-06

276

Angular performance measure for tighter uncertainty relations  

SciTech Connect

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

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

2010-01-15

277

Angular momentum effects in weak gravitational fields  

E-print Network

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

A. Tartaglia

2002-01-02

278

APPROXIMATE DYNAMIC PROGRAMMING  

E-print Network

LEARNING AND APPROXIMATE DYNAMIC PROGRAMMING Scaling Up to the Real World #12;#12;LEARNING AND APPROXIMATE DYNAMIC PROGRAMMING Scaling Up to the Real World Edited by Jennie Si, Andy Barto, Warren Powell-reference adaptive critic designs. Various ADP designs such as Heuristic Dynamic Programming (HDP), Dual HDP (DHP

Ferrari, Silvia

279

Approximation of Hopf bifurcation  

Microsoft Academic Search

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

C. Bernardi; M. Curie

1982-01-01

280

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

281

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

282

Green Ampt approximations  

NASA Astrophysics Data System (ADS)

The solution to the Green and Ampt infiltration equation is expressible in terms of the Lambert W-1 function. Approximations for Green and Ampt infiltration are thus derivable from approximations for the W-1 function and vice versa. An infinite family of asymptotic expansions to W-1 is presented. Although these expansions do not converge near the branch point of the W function (corresponds to Green-Ampt infiltration with immediate ponding), a method is presented for approximating W-1 that is exact at the branch point and asymptotically, with interpolation between these limits. Some existing and several new simple and compact yet robust approximations applicable to Green-Ampt infiltration and flux are presented, the most accurate of which has a maximum relative error of 5 × 10 -5%. This error is orders of magnitude lower than any existing analytical approximations.

Barry, D. A.; Parlange, J.-Y.; Li, L.; Jeng, D.-S.; Crapper, M.

2005-10-01

283

Angular momentum density of a linearly polarized Lorentz-Gauss vortex beam  

NASA Astrophysics Data System (ADS)

Based on the vectorial Rayleigh-Sommerfeld integral formulae, the analytical propagation equation of a linearly polarized Lorentz-Gauss vortex beam is derived in free space. By taking curl of the electric field, the propagating magnetic field of the linearly polarized Lorentz-Gauss vortex beam is also presented. By using the analytical propagation equation of the Lorentz-Gauss vortex beam beyond the paraxial approximation, the analytical expression of the angular momentum density of a Lorentz-Gauss vortex beam is obtained. The effects of the linearly polarized angle and the beam parameters on the three components of the angular momentum density of a Lorentz-Gauss vortex beam are analyzed in detail. The two transversal components of the angular momentum of a Lorentz-Gauss vortex beam beyond the paraxial approximation must be zero in an arbitrary reference plane. The longitudinal component of the angular momentum is determined by the linearly polarized angle and the beam parameters. The distributions of the angular momentum densities of the Lorentz-Gauss vortex beam are also compared with those of the Gaussian vortex beam. This research is very useful to the optical trapping, the optical guiding, and the optical manipulation of microscopic particles using the single mode diode laser beams.

Zhou, Guoquan; Ru, Guoyun

2014-02-01

284

Measures and models for angular correlation and angular-linear correlation. [correlation of random variables  

NASA Technical Reports Server (NTRS)

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

Johnson, R. A.; Wehrly, T.

1976-01-01

285

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

286

Phasing at resolution higher than the experimental resolution.  

PubMed

Limited experimental resolution is a unavoidable feature in macromolecular crystallography: it may hinder or make difficult the determination of the crystal structure. A novel procedure is presented which from an approximate electron-density map extrapolates the moduli and phases of non-measured reflections beyond and behind the experimental resolution limit. Applications to a set of test structures show that the extrapolation can be successfully accomplished. As a consequence, the phase estimates of the observed reflections are subsequently improved and the interpretability of the corresponding electron-density map increases. The use of the extrapolated values for the non-measured reflections provides additional information for the map, which shows a resolution higher than the experimental resolution. PMID:15858265

Caliandro, Rocco; Carrozzini, Benedetta; Cascarano, Giovanni L; De Caro, Liberato; Giacovazzo, Carmelo; Siliqi, Dritan

2005-05-01

287

Magnetic field and angular momentum evolution models  

NASA Astrophysics Data System (ADS)

The magnetic field in young stellar object is clearly the most important component when one dealing with the angular momentum evolution of solar-like stars. It controls this latter one from the pre-main sequence, during the ``disk locking'' phase where the stars magnetically interact with their surrounding disk, to the main-sequence through powerful stellar winds that remove angular momentum from the stellar surface. We present new models for the rotational evolution of solar-like stars between 1 Myr and 10 Gyr with the aim to reproduce the distributions of rotational periods observed for star forming regions and young open clusters within this age range. Our simulations are produced by a recent model dedicated to the study of the angular momentum evolution of solar-type stars. This model include a new wind braking law based on recent numerical simulations of magnetized stellar winds and a specific dynamo and mass-loss prescription are used to link the angular momentum loss-rate to angular velocity evolution. The model additionally allows for a core/envelope decoupling with an angular momentum transfer between these two regions. Since this former model didn't include any physical star/disk interaction description, two star/disk interaction processes are eventually added to it in order to reproduce the apparent small angular velocities to which the stellar surface is subject during the disk accretion phase. We have developed rotational evolution models for slow, median and fast rotators including two star/disk interaction scenarios that are the magnetospheric ejection and the accretion powered stellar winds processes. The models appear to fail at reproducing the rotational behaviour of solar-type stars except when a more intense magnetic field is used during the disk accretion phase.

Gallet, F.

2013-11-01

288

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

289

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

NASA Astrophysics Data System (ADS)

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

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

1989-12-01

290

Linear Approximation SAR Azimuth Processing Study  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

291

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 ...

Eric Grosfils

292

Approximate Decentralized Bayesian Inference  

E-print Network

This paper presents an approximate method for performing Bayesian inference in models with conditional independence over a decentralized network of learning agents. The method first employs variational inference on each ...

Campbell, Trevor David

293

Calculator Function Approximation.  

ERIC Educational Resources Information Center

The general algorithm used in most hand calculators to approximate elementary functions is discussed. Comments on tabular function values and on computer function evaluation are given first; then the CORDIC (Coordinate Rotation Digital Computer) scheme is described. (MNS)

Schelin, Charles W.

1983-01-01

294

Approximate kernel competitive learning.  

PubMed

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

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

2015-03-01

295

Establishing an IERS Sub-Center for Ocean Angular Momentum  

NASA Technical Reports Server (NTRS)

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

Ponte, Rui M.

2001-01-01

296

Ultrafast angular momentum transfer in multisublattice ferrimagnets.  

PubMed

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

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

2014-01-01

297

Angular momentum conservation for dynamical black holes  

E-print Network

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.

Sean A. Hayward

2006-11-04

298

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

299

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

E-print Network

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

Chapman, Glenn H.

300

Angular Two-Photon Interference and Angular Two-Qubit States Anand Kumar Jha,1  

E-print Network

an entangled two-qubit state that is based on the angular-position correlations of entangled photons. The entanglement of the two-qubit state is quantified in terms of concurrence. These results provide an additional in the form of double angular slits and, using this scheme, we demonstrate an entangled two-qubit state

Boyd, Robert W.

301

Degree Angular Scale Interferometer First Results: A Measurement of the Cosmic Microwave Background Angular Power Spectrum  

Microsoft Academic Search

We present measurements of anisotropy in the cosmic microwave background (CMB) from the first season of observations with the Degree Angular Scale Interferometer (DASI). The instrument was deployed at the South Pole in the austral summer 1999-2000, and we made observations throughout the following austral winter. We present a measurement of the CMB angular power spectrum in the range 100

N. W. Halverson; E. M. Leitch; C. Pryke; J. Kovac; J. E. Carlstrom; W. L. Holzapfel; M. Dragovan; J. K. Cartwright; B. S. Mason; S. Padin; T. J. Pearson; A. C. S. Readhead; M. C. Shepherd

2002-01-01

302

Angular momentum of a strongly focused Gaussian beam  

Microsoft Academic Search

A circularly polarized paraxial Gaussian laser beam carries angular momentum per photon as spin, with zero orbital angular momentum. Focusing the beam with a rotationally symmetric lens cannot change this angular momentum flux, yet the focused beam must have spin per photon. The remainder of the original spin is converted to orbital angular momentum, manifesting itself as a longitudinal optical

Timo A. Nieminen; Alexander B Stilgoe; Norman R Heckenberg; Halina Rubinsztein-Dunlop

2008-01-01

303

Analysis of orbital angular momentum of a misaligned optical beam  

Microsoft Academic Search

We report an analysis of the orbital angular momentum of an optical beam misaligned with respect to a reference axis. Both laterally displaced and angularly deflected Laguerre–Gaussian beams are represented in terms of the superposition of azimuthal harmonics with well-defined orbital angular momentum. Simultaneous parallel displacement and angular tilt cause the coupling between azimuthal harmonics and therefore change the projection

M V Vasnetsov; V A Pas'ko; M S Soskin

2005-01-01

304

ARCSECOND RESOLUTION MAPPING OF SULFUR DIOXIDE EMISSION IN THE CIRCUMSTELLAR ENVELOPE OF VY CANIS MAJORIS  

E-print Network

We report Submillimeter Array observations of SO[subscript 2] emission in the circumstellar envelope (CSE) of the red supergiant VY Canis Majoris, with an angular resolution of ?1''. SO[subscript 2] emission appears in ...

Moullet, Arielle

305

Physics from Angular Projection of Rectangular Grids  

E-print Network

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

Singh, Ashmeet

2015-01-01

306

Pumping angular momentum by driven chaotic scattering  

E-print Network

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

T. Dittrich; F. L. Dubeibe

2008-04-29

307

Quark Orbital Angular Momentum from Lattice QCD  

E-print Network

We calculate the quark orbital angular momentum of the nucleon from the quark energy-momentum tensor form factors on the lattice. The disconnected insertion is estimated stochastically which employs the $Z_2$ noise with an unbiased subtraction. This reduced the error by a factor of 4 with negligible overhead. The total quark contribution to the proton spin is found to be $0.30 \\pm 0.07$. From this and the quark spin content we deduce the quark orbital angular momentum to be $0.17 \\pm 0.06$ which is $\\sim 34$% of the proton spin. We further predict that the gluon angular momentum to be $0.20 \\pm 0.07$, i. e. $\\sim$ 40% of the proton spin is due to the glue.

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

1999-12-10

308

Energy angular momentum closed-loop guidance  

NASA Astrophysics Data System (ADS)

A novel guidance algorithm for launch vehicle ascent to the desired mission orbit is proposed. The algorithm uses total specific energy and orbital angular momentum as new state vector parameters. These parameters are ideally suited for the ascent guidance task, since the guidance algorithm steers the launch vehicle along a pre-flight optimal trajectory in energy angular momentum space. The guidance algorithm targets apogee, perigee, inclination and right ascension of ascending node. Computational complexities are avoided by eliminating time in the guidance computation and replacing it with angular momentum magnitude. As a result, vehicle acceleration, mass, thrust, length of motor burns, and staging times are also eliminated from the pitch plane guidance calculations. The algorithm does not involve launch vehicle or target state propagation, which results in minimal computational effort. Proof of concept of the new algorithm is presented using several numerical examples that illustrate performance results.

Patera, Russell P.

2015-03-01

309

Angular analysis of the decay ? b ? ?(? N?) ? + ? -  

NASA Astrophysics Data System (ADS)

We study the differential decay rate for the rare ? b ? ?(? N?) ? + ? - transition, including a determination of the complete angular distribution, assuming unpolarized ? b baryons. On the basis of a properly chosen parametrization of the various helicity amplitudes, we provide expressions for the angular observables within the Standard Model and a subset of new physics models with chirality-flipped operators. Hadronic effects at low recoil are estimated by combining information from lattice QCD with (improved) form-factor relations in Heavy Quark Effective Theory. Our estimates for large hadronic recoil — at this stage — are still rather uncertain because the baryonic input functions are not so well known, and non-factorizable spectator effects have not been worked out systematically so far. Still, our phenomenological analysis of decay asymmetries and angular observables for ? b ? ?(? N?) ? + ? - reveals that this decay mode can provide new and complementary constraints on the Wilson coefficients in radiative and semileptonic b ? s transitions compared to the corresponding mesonic modes.

Böer, Philipp; Feldmann, Thorsten; van Dyk, Danny

2015-01-01

310

Angular momentum transport by internal waves in the solar interior  

E-print Network

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 (1981) and Garcia Lopez & Spruit (1991). 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 1989). 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.

Jean-Paul Zahn; Suzanne Talon; Jose Matias

1996-11-22

311

BAYESIAN ANGULAR POWER SPECTRUM ANALYSIS OF INTERFEROMETRIC DATA  

SciTech Connect

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

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

2012-09-15

312

Optimization of Angular-Momentum Biases of Reaction Wheels  

NASA Technical Reports Server (NTRS)

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

Lee, Clifford; Lee, Allan

2008-01-01

313

Photoelectron angular distributions along Ar and Ca isonuclear sequences  

NASA Astrophysics Data System (ADS)

The dipole angular distribution asymmetry parameter, ?, for photoelectrons resulting from 2p photoionization of members of the Ar and Ca isonuclear sequences (Ar, Ar^6+, Ar^8+, Ca, Ca^2+, Ca^8+) has been studied using the relativistic random phase approximation (RRPA) [1] over a broad range of photon energy. In the absence of relaxation, it known that inner shell cross sections are essentially unchanged, as a function of photon energy, on the removal of outer shell electrons [2]. The situation is found to be different for angular distributions; the ? parameter is not constant, as a function of photon energy, when outer electrons are removed. However, with increasing photon energy, the ?'s arising from the varying stages of ionization become essentially constant. The reason for this behavior is traced to the dependence of ? upon the Coulomb phase shifts which are not constant as a function of photon energy. At the higher energies, the Coulomb phase becomes less important, resulting in the ?'s coalescing. [1] W. R. Johnson and C. D. Lin, Phys. Rev. A 20, 964(1979). [2] G. Nasreen, S. T. Manson and P. C. Deshmukh, Phys. Rev. A 40, 6091(1989).

Pradhan, Gagan B.; Jose, Jobin; Radojevic', Vojislav; Deshmukh, Pranawa C.; Manson, Steven T.

2010-03-01

314

ANGULAR MOMENTUM TRANSPORT IN CONVECTIVELY UNSTABLE SHEAR FLOWS  

SciTech Connect

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

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

2010-08-10

315

Evaluation of the table Mountain Ronchi telescope for angular tracking  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

316

Angular distribution of emission from hyperbolic metamaterials  

PubMed Central

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

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

2014-01-01

317

Angular distribution of emission from hyperbolic metamaterials  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

318

Wilson lines and orbital angular momentum  

E-print Network

We present an explicit realization of the Chen et al. approach to the proton spin decomposition in terms of Wilson lines, generalizing the light-front gauge-invariant extensions discussed recently by Hatta. Particular attention is drawn to the residual gauge freedom by further separating the pure-gauge term into contour and residual terms. We show that the kinetic orbital angular momentum operator can be expressed in terms of the Wigner operator only when the momentum variable is integrated over. Finally, we confirm from twist-2 arguments that the advanced, retarded and antisymmetric light-front canonical orbital angular momenta are the same.

Cédric Lorcé

2013-01-07

319

Angular distribution of emission from hyperbolic metamaterials.  

PubMed

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

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

2014-01-01

320

Orbital angular momentum in the nucleons  

E-print Network

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

Cédric Lorcé

2014-06-26

321

HOCl Ro-vibrational bound-state calculations for nonzero total angular momentum.  

PubMed

The Lanczos homogeneous filter diagonalization method has been employed to compute the HOCl ro-vibrational states for a range of total angular momenta (J = 0, 1, 5, 10, 11, 20, 30) on a newly developed ab initio potential energy surface by Nanbu et al. (J. Theor. Comput. Chem. 2002, 1, 263). For such computationally challenging calculations, a parallel computing strategy has been incorporated into our method to perform the matrix-vector multiplications. For the computed low bound states, a spectroscopic assignment has been made and the widely used approximate adiabatic rotation method has been tested for the broad range of total angular momenta for this deep-well system. Comparison of experimental results with exact quantum mechanical calculations for the selected far-infrared transitions involving the range of total angular momenta has been made possible for the first time. PMID:16623477

Zhang, Hong; Smith, Sean C; Nanbu, Shinkoh; Nakamura, Hiroki

2006-04-27

322

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

323

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

E-print Network

PHYSICAL REVIEW A 86, 063806 (2012) Measurement of the orbital-angular-momentum spectrum of fields method using two angular slits to measure the orbital-angular-momentum (OAM) mode spectrum of a field, orbital angular momentum (OAM), form Fourier transform pairs [3]. This is convincingly demonstrated

Boyd, Robert W.

2012-01-01

324

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

325

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

326

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

327

Approximate Degradable Quantum Channels  

E-print Network

Degradable quantum channels are an important class of completely positive trace-preserving maps. Among other properties, they offer a single-letter formula for the quantum and the private classical capacity and are characterized by the fact that the complementary channel can be obtained from the channel by applying a degrading map. In this work we introduce the concept of approximate degradable channels, which satisfy this condition up to some finite $\\varepsilon\\geq0$. That is, there exists a degrading map which upon composition with the channel is $\\varepsilon$-close in the diamond norm to the complementary channel. We show that for any fixed channel the smallest such $\\varepsilon$ can be efficiently determined via a semidefinite program. Moreover, these approximate degradable channels also approximately inherit all other properties of degradable channels. As an application, we derive improved upper bounds to the quantum and private classical capacity for certain channels of interest in quantum communication.

David Sutter; Volkher B. Scholz; Renato Renner

2014-12-02

328

Angular aspects of electron correlation and the Coulomb hole  

NASA Astrophysics Data System (ADS)

The simple physical picture of the Coulomb hole due to Coulson and Neilson has been extended to reveal the shape of the Coulomb hole in the ground state of helium. The approach is based on a pair distribution function h(r12,r1,?) which depends on the position of a reference electron and the angle between the nucleus, the reference electron, and a second electron. Following a discussion of the properties of this new function, the angular features of the Coulomb hole are studied in terms of the difference between the values of the pair distribution function obtained from good approximations to the exact and to the Hartree-Fock wave functions. The Coulomb hole is essentially spherically symmetric when the reference electron is close to the nucleus. As the reference electron is removed to larger radial distances, substantial polarization appears. The polarization is greater away from the nucleus than toward the nucleus.

Boyd, Russell J.; Yee, Main C.

1982-10-01

329

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

330

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

331

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

2010-01-01

332

ON ANGULAR DISTRIBUTION OF NEUTRONS IN C¹³(d,n)N¹⁴ REACTION  

Microsoft Academic Search

Calculations were made of the angular distribution of neutrons in the C\\/; sup 13\\/(d,n)N¹⁴ reaction, experimentally studied by L. L. Green et al. ; (Proc. Phys. Soc. A68, 386, 1955). with incident deuterons of 0.B6 Mev and ; four-group neutron resolution (gâ, gâ, gâ, and gâ), where ; first group corresponds to the finite nucleus N¹⁴ groundstate and the rest

T. L. Abelishvili; T. G. Gachechiladze; O. M. Mdivani

1960-01-01

333

Angular distributions of photoneutrons in 206 Pb and 208 Pb using monochromatic photons  

Microsoft Academic Search

The angular distributions of neutrons produced in the (?, n) reaction are reported for the separated isotopes206Pb and208Pb. The experiment made use of highly chromatic photons generated by neutron capture on nickel and chromium in the core of the McMaster Nuclear Reactor, and a high resolution3He detector. Photoneutron spectra were recorded at 7 angles between 20° and 160°. The results

J. N. Barkman; T. J. Kennett; W. V. Prestwich

1983-01-01

334

Momentum measurement by the angular method in the Emulsion Cloud Chamber  

Microsoft Academic Search

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

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

2003-01-01

335

An experimental investigation of angular resolved energy distributions of atoms sputtered from evaporated aluminum films  

Microsoft Academic Search

A study of angular resolved velocity (energy) distributions of atoms sputtered from in situ prepared metal films is described in this contribution. The velocity resolution of the set-up is based on the pulsed laser-induced fluorescence technique, i.e., scanning the narrow bandwidth dye laser radiation over the Doppler broadened absorption profile of the sputtered particles. The arrangement of the vacuum vessel

A. Goehlich; D. Gillmann; H. F. Döbele

2001-01-01

336

Angular spectrum of quantized light beams  

E-print Network

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

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

2006-02-20

337

Spacecraft Angular State Estimation After Sensor Failure  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

338

Orbital angular momentum in triatomic molecules  

Microsoft Academic Search

A general method is described for calculating the vibronic energy levels associated with two Born-Oppenheimer states of a triatomic molecule that become degenerate in the linear limit. The method combines Renner's matrix treatment of orbital angular momentum in linear molecules with Hougen, Bunker and Johns' formalism for large amplitude bending motions, and allows for the effects of electron spins; it

Ch. Jungen; A. J. Merer

1980-01-01

339

Wigner Functions and Quark Orbital Angular Momentum  

E-print Network

Wigner distributions contain combined position and momentum space information of the quark distributions and are related to both generalized parton distributions (GPDs) and transverse momentum dependent parton distributions (TMDs). We report on a recent model calculation of the Wigner distributions for the quark and their relation to the orbital angular momentum.

Asmita Mukherjee; Sreeraj Nair; Vikash Kumar Ojha

2014-09-25

340

Uniqueness of the orbital angular momentum operators  

Microsoft Academic Search

Summary  In a separable Hilbert space in which the three Cartesian coordinates form a complete set of commuting variables, it is proved\\u000a that Hermitian operators which satisfy the commutation relations for the angular momentum operators are unique within a unitary\\u000a transformation.

J. S. Lomont; H. E. Moses

1960-01-01

341

Photon Orbital Angular Momentum in Astrophysics  

E-print Network

Astronomical observations of the orbital angular momentum of photons, a property of electromagnetic radiation that has come to the fore in recent years, have apparently never been attempted. Here, I show that measurements of this property of photons have a number of astrophysical applications.

Martin Harwit

2003-07-24

342

Optical angular momentum: Multipole transitions and photonics  

SciTech Connect

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

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

2010-03-15

343

An angular momentum bound at null infinity  

E-print Network

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

Piotr T. Chru?ciel; Paul Tod

2007-06-27

344

Strain uniformity through equal channel angular extrusion  

E-print Network

The objective of this work is to characterize the processing effects of equal channel angular extrusion (ECAE) on aluminum 6063, copper I 10, and filamentary Cu/NbTi composite superconductor. The major objective of this study is to measure strain...

Bier, Derek Werner

1997-01-01

345

Gene Microarray Analysis using Angular Distribution Decomposition  

E-print Network

Gene Microarray Analysis using Angular Distribution Decomposition Karen Lees1 , Stephen Roberts1 of microarray data to group genes with similar expression profiles. The similarity of expres- sion profiles to define the similarity of gene expression patterns. The pairwise comparisons of exper- imental conditions

Roberts, Stephen

346

Extended Abstract Approximating Visibility  

E-print Network

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

Franklin, W. Randolph

347

Hypergeometric approximations to polylogarithms  

E-print Network

values and, in particular, of zeta values. Part 1 is joint work with Khodabakhsh and Tatiana Hessami and Tatiana Hessami 1 A talk at the conference "Diophantine approximation and transcendental numbers" (CIRM values of the di- and trilogarithm The irrationality result proved jointly with Khodabakhsh and Tatiana

Zudilin, Wadim

348

Approximating Integrals Using Probability  

ERIC Educational Resources Information Center

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

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

2005-01-01

349

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

350

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

351

Optimal approximate doubles  

NASA Astrophysics Data System (ADS)

The nonlocality of quantum states on a bipartite system \\mathcal {A+B} is tested by comparing probabilistic outcomes of two local observables of different subsystems. For a fixed observable A of the subsystem \\mathcal {A,} its optimal approximate double A' of the other system \\mathcal {B} is defined such that the probabilistic outcomes of A' are almost similar to those of the fixed observable A. The case of ?-finite standard von Neumann algebras is considered and the optimal approximate double A' of an observable A is explicitly determined. The connection between optimal approximate doubles and quantum correlations is explained. Inspired by quantum states with perfect correlation, like Einstein-Podolsky-Rosen states and Bohm states, the nonlocality power of an observable A for general quantum states is defined as the similarity that the outcomes of A look like the properties of the subsystem \\mathcal {B} corresponding to A'. As an application of optimal approximate doubles, maximal Bell correlation of a pure entangled state on \\mathcal {B}(\\mathbb {C}^{2})\\otimes \\mathcal {B}(\\mathbb {C}^{2}) is found explicitly.

Huang, Siendong

2009-11-01

352

Saddlepoint Approximations in Statistics  

Microsoft Academic Search

It is often required to approximate to the distribution of some statistic whose exact distribution cannot be conveniently obtained. When the first few moments are known, a common procedure is to fit a law of the Pearson or Edgeworth type having the same moments as far as they are given. Both these methods are often satisfactory in practice, but have

H. E. Daniels

1954-01-01

353

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

SciTech Connect

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

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

2013-07-20

354

Determination of Optimum Viewing Angles for the Angular Normalization of Land Surface Temperature over Vegetated Surface.  

PubMed

Multi-angular observation of land surface thermal radiation is considered to be a promising method of performing the angular normalization of land surface temperature (LST) retrieved from remote sensing data. This paper focuses on an investigation of the minimum requirements of viewing angles to perform such normalizations on LST. The normally kernel-driven bi-directional reflectance distribution function (BRDF) is first extended to the thermal infrared (TIR) domain as TIR-BRDF model, and its uncertainty is shown to be less than 0.3 K when used to fit the hemispheric directional thermal radiation. A local optimum three-angle combination is found and verified using the TIR-BRDF model based on two patterns: the single-point pattern and the linear-array pattern. The TIR-BRDF is applied to an airborne multi-angular dataset to retrieve LST at nadir (Te-nadir) from different viewing directions, and the results show that this model can obtain reliable Te-nadir from 3 to 4 directional observations with large angle intervals, thus corresponding to large temperature angular variations. The Te-nadir is generally larger than temperature of the slant direction, with a difference of approximately 0.5~2.0 K for vegetated pixels and up to several Kelvins for non-vegetated pixels. The findings of this paper will facilitate the future development of multi-angular thermal infrared sensors. PMID:25825975

Ren, Huazhong; Yan, Guangjian; Liu, Rongyuan; Li, Zhao-Liang; Qin, Qiming; Nerry, Françoise; Liu, Qiang

2015-01-01

355

Angular vibration measurement using grating and laser interferometer  

NASA Astrophysics Data System (ADS)

Primary angular acceleration calibration standard is developed by CIMM to generate standard rotational angle, angular velocity and angular acceleration, which are traceable to the International System of Units (SI). It can be used to calibrate angular transducers, i.e. angular accelerometer, angular velocity transducer, and rotational angle transducer to obtain amplitude sensitivity and phase shift by sinusoidal vibration. The measurement systems based on grating and laser interferometers are introduced in this paper. The measurement system based on PXI bus instrument is used to control the angular exciter, measure the output signal of the laser interferometers and the transducer to be calibrated synchronously. The methods for calculating the amplitude and phase of sinusoidal angular movement are investigated and high performance has been achieved. It shows the standard can be used in angular movement calibration in the frequency range from 0.1Hz to 200Hz.

Zhang, Li; Peng, Jun

2006-06-01

356

Molecular collisions. 11: Semiclassical approximation to atom-symmetric top rotational excitation  

NASA Technical Reports Server (NTRS)

In a paper of this series a distorted wave approximation to the T matrix for atom-symmetric top scattering was developed which is correct to first order in the part of the interaction potential responsible for transitions in the component of rotational angular momentum along the symmetry axis of the top. A semiclassical expression for this T matrix is derived by assuming large values of orbital and rotational angular momentum quantum numbers.

Russell, D.; Curtiss, C. F.

1973-01-01

357

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

SciTech Connect

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

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

2012-07-01

358

Accelerated Stochastic Approximation  

Microsoft Academic Search

Using a stochastic approximation procedure $\\\\{X_n\\\\}, n = 1, 2, \\\\cdots$, for a value $\\\\theta$, it seems likely that frequent fluctuations in the sign of $(X_n - \\\\theta) - (X_{n - 1} - \\\\theta) = X_n - X_{n - 1}$ indicate that $|X_n - \\\\theta|$ is small, whereas few fluctuations in the sign of $X_n - X_{n - 1}$ indicate

Harry Kesten

1958-01-01

359

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

PubMed Central

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

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

2011-01-01

360

Strong Angular Clustering of Very Blue Galaxies: Evidence of a Low Redshift Population  

Microsoft Academic Search

We have studied galaxy two-point angular correlations as a function of color\\u000ausing 4-m plate photometry in two independent fields. Each field consists of\\u000aover 2900 galaxies with magnitudes 20approximately 750\\u000aarcmin^2 . We find that the autocorrelation amplitude of the bluest 15% of\\u000agalaxies is surprisingly strong, with a relative increase in clustering

Stephen D. Landy; Alexander S. Szalay; David C. Koo

1995-01-01

361

Mode density of orbital angular momentum modes in a cylindrical cavity and in free space  

E-print Network

In this short note we derive an approximate expression for the mode density of modes carrying orbital angular momentum (OAM) in a cylindrical cavity which is large compared to the inverse wavevector in any direction. We argue that in the large cavity limit the modes asymptotically converges to the corresponding OAM modes in free space. We compare the result to Weyl's law. It is found, as expected, that the mode density does not depend on whether or not the modes carry OAM.

Andersson, Mauritz; Björk, Gunnar

2015-01-01

362

High spatial resolution Galactic 3D extinction mapping with IPHAS  

Microsoft Academic Search

An algorithm, MEAD, is presented, which can map extinction in three dimensions, with fine distance and angular resolutions. MEAD is then employed when studying the structure of the outer Galaxy. We show that the Galaxy's radial density profile takes the form of a broken exponential, with density dropping off more steeply beyond a Galacto-centric radius of ~13 kpc.

S. E. Sale; J. E. Drew

2010-01-01

363

Galactic Microwave Emission at Degree Angular Scales  

NASA Astrophysics Data System (ADS)

We cross-correlate the Saskatoon Ka- and Q-band cosmic microwave background (CMB) data with different maps to quantify possible foreground contamination. We detect a marginal correlation (>~2 ?) with the Diffuse Infrared Background Experiment (DIRBE) 240, 140, and 100 ?m maps, but we find no significant correlation with point sources, with the Haslam 408 MHz map, or with the Reich and Reich 1420 MHz map. The rms amplitude of the component correlated with DIRBE is about 20% of the CMB signal. Interpreting this component as free-free emission, this normalization agrees with that of the 1996 works of Kogut et al. and supports the hypothesis that the spatial correlation between dust and warm ionized gas observed on large angular scales persists to smaller angular scales. Subtracting this contribution from the CMB data reduces the normalization of the Saskatoon power spectrum by only a few percent.

de Oliveira-Costa, Angélica; Kogut, A.; Devlin, Mark J.; Netterfield, C. Barth; Page, Lyman A.; Wollack, Edward J.

1997-06-01

364

The quantum angular Calogero-Moser model  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

365

Angular Momentum Loss Via Stellar Winds  

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

366

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

367

Approximation of Time-Dependent Viscoelastic Fluid Flow: SUPG Approximation  

Microsoft Academic Search

In this article we consider the numerical approximation to the time dependent vis- coelasticity equations with an Oldroyd B constitutive equation. The approximation is stabilized by using a SUPG approximation for the constitutive equation. We analyse both the semi-discrete and fully discrete numerical approximations. For both discretizations we prove the existence of, and derive a priori error estimates for, the

Vincent J. Ervin; William W. Miles

2003-01-01

368

Behavior of nuclei at high angular momentum  

SciTech Connect

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

Stephens, F.S.

1982-07-01

369

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.

Wolfgang Christian

370

Wigner distributions and quark orbital angular momentum  

E-print Network

We discuss the quark phase-space or Wigner distributions of the nucleon which combine in a single picture all the information contained in the generalized parton distributions and the transverse-momentum dependent parton distributions. In particular, we present results for the distribution of unpolarized quarks in a longitudinally polarized nucleon obtained in a light-front constituent quark model. We show how the quark orbital angular momentum can be extracted from the Wigner distributions and compare it with alternative definitions.

Cedric Lorce; Barbara Pasquini

2012-08-15

371

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

372

Angular Momentum Transport in Circumplanetary Disks  

NASA Astrophysics Data System (ADS)

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

Mitchell, Tyler R.

2014-11-01

373

Physics from Angular Projection of Rectangular Grids  

E-print Network

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

Ashmeet Singh

2014-12-08

374

Physics from angular projection of rectangular grids  

NASA Astrophysics Data System (ADS)

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

Singh, Ashmeet

2015-03-01

375

Quark Wigner Distributions and Orbital Angular Momentum  

E-print Network

We study the Wigner functions of the nucleon which provide multidimensional images of the quark distributions in phase space. These functions can be obtained through a Fourier transform in the transverse space of the generalized transverse-momentum dependent parton distributions. They depend on both the transverse position and the three-momentum of the quark relative to the nucleon, and therefore combine in a single picture all the information contained in the generalized parton distributions and the transverse-momentum dependent parton distributions. We focus the discussion on the distributions of unpolarized/longitudinally polarized quark in an unpolarized/longitudinally polarized nucleon. In this way, we can study the role of the orbital angular momentum of the quark in shaping the nucleon and its correlations with the quark and nucleon polarizations. The quark orbital angular momentum is also calculated from its phase-space average weighted with the Wigner distribution of unpolarized quarks in a longitudinally polarized nucleon. The corresponding results obtained within different light-cone quark models are compared with alternative definitions of the quark orbital angular momentum, as given in terms of generalized parton distributions and transverse-momentum dependent parton distributions.

Cedric Lorce; Barbara Pasquini

2011-06-01

376

Schmidt decomposition for non-collinear biphoton angular wave functions  

E-print Network

Schmidt modes of non-collinear biphoton angular wave functions are found analytically. The experimentally realizable procedure is described for their separation. Parameters of the Schmidt decomposition are used for evaluation of the degree of biphoton's angular entanglement.

Mikhail Fedorov

2014-11-08

377

Localization of angular momentum in optical waves propagating through turbulence.  

PubMed

This is the first in a series of papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. The scope of this first paper is much narrower. Here, we demonstrate that atmospheric turbulence can impart non-trivial angular momentum to beams and that this non-trivial angular momentum is highly localized. Furthermore, creation of this angular momentum is a normal part of propagation through atmospheric turbulence. PMID:22273930

Sanchez, Darryl J; Oesch, Denis W

2011-12-01

378

Approximate Bayesian Computation  

PubMed Central

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

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

2013-01-01

379

Orbital angular momentum transfer in helical Mathieu beams  

Microsoft Academic Search

We observe the transfer of orbital angular momentum to trapped particles in the azimuthally asymmetric transverse intensity distribution of a helical Mathieu beam. The average rotation rate, instantaneous angular displacement and terminal velocity of the trapped particles are measured experimentally. The angular dependence of these parameters is found to be in good agreement with the variation of the optical gradient

Carlos López-Mariscal; Julio C. Gutiérrez-Vega; Graham Milne; Kishan Dholakia

2006-01-01

380

Polarization control of single photon quantum orbital angular momentum  

E-print Network

Polarization control of single photon quantum orbital angular momentum states E. Nagali1, F, Italy Abstract: The orbital angular momentum of photons, being defined in an infinite device, the so-called "q-plate", which enables the manipulation of the photon orbital angular momentum

Roma "La Sapienza", Università di

381

Bragg-induced orbital angular-momentum mixing in paraxial  

E-print Network

Bragg-induced orbital angular-momentum mixing in paraxial high-finesse cavities David H. Foster in [4, 5]. 1 #12;Beams carrying orbital angular momentum require an axially symmetric environment). Standard paraxial wave solutions with definite orbital angular momentum are the Laguerre-Gauss beams (LG

Nöckelm, Jens

382

Free-space coherent optical communication with orbital angular, momentum  

E-print Network

Free-space coherent optical communication with orbital angular, momentum multiplexing demonstrate free-space space-division-multiplexing (SDM) with 15 orbital angular momentum (OAM) states using, "Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes," Phys. Rev

Yoo, S. J. Ben

383

Application of the angular correlation formalism to nuclear fission  

Microsoft Academic Search

The angular correlation formalism is applied to calculate angular distributions of fission fragments following light particle induced reactions. The distributions are described by sums over Legendre polynomials, and standard theory is used to calculate statistical tensors to describe the alignment of the compound nucleus, particle parameters and angular correlation coefficients. Comparison with experimental data shows that the importance of higher

Herbert Faust

1998-01-01

384

Super Resolution Imaging Translation  

E-print Network

exploits new methods to restore high resolution super resolution images from low resolution data files represent three different stained structures; Red: Actin, Green: Microtubules and Blue: DNA (DAPI microscopy data files etc. · Complementary to existing microscopy techniques · "wavelength Independent

Painter, Kevin

385

Angularly-resolved elastic light scattering of micro-particles  

NASA Astrophysics Data System (ADS)

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

Aptowicz, Kevin B.

386

Angular distributions of total LMM Auger electron yields produced by energetic He+ ions in Ar, Cl, and S  

NASA Astrophysics Data System (ADS)

Angular distributions from 45° to 135° in 15° intervals of LMM Auger electrons produced by 1.2-MeV and 1.8-MeV He+-ion bombardment of argon, methyl chloride (CH3Cl), and hydrogen sulfide (H2S) have been measured. The LMM total Auger yields were measured at 1.8-eV resolution with an experimental probable error not exceeding 9%. The results revealed that the angular distributions of the LMM total Auger yields of Ar, Cl, and S were isotropic at these bombarding energies.

Guo, P.; Ghebremedhin, A.; Ariyasinghe, W. M.; Powers, D.

1995-03-01

387

The distinguishable cluster approximation  

E-print Network

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

Kats, Daniel

2013-01-01

388

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

389

Angular-momentum loss in evaporating black holes  

NASA Astrophysics Data System (ADS)

Consideration is given to the evolution of the angular momentum of an evaporating black hole. The conclusions of Carter (1974), that the mass and angular momentum losses of a black hole in the initial stages of evaporation are comparable, and of Page (1976), that the angular momentum loss is sufficiently great to reduce the residual angular momentum to zero, are examined. It is pointed out that the limitation of Page that the axial quantum number of particles emitted be greater than zero is too restrictive. With this restriction relaxed, there would then be a nonnegligible residual angular momentum, and the possibility of the formation of Kerr naked singularity as a final state arises.

Balbinot, R.; Bergamini, R.

1981-01-01

390

Angular momentum transfer in optically induced photonic lattices  

SciTech Connect

The transfer of orbital angular momentum from vortex beams to optically induced photonic lattices is demonstrated. It is found that the sum of the angular momenta of interacting incoherent counterpropagating (CP) beams is not conserved, whereas their difference is. The sum of angular momenta of copropagating (CO) interacting beams is strictly conserved. It is also found that the transfer of angular momentum in CP interacting beams is minimal, amounting to a few percent, whereas the transfer in CO interacting beams is substantial, amounting to tens of percent. In fixed lattices, for both CP and CO beams, angular momentum is never conserved.

Petrovic, Milan S.; Jovic, Dragana M.; Prvanovic, Slobodan [Institute of Physics, P.O. Box 57, 11001 Belgrade (Serbia); Belic, Milivoj R. [Institute of Physics, P.O. Box 57, 11001 Belgrade (Serbia); Texas A and M University at Qatar, P.O. Box 5825, Doha (Qatar)

2007-08-15

391

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

NASA Astrophysics Data System (ADS)

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

Brancati, Renato; Rocca, Ernesto; Savino, Sergio

2015-01-01

392

ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED  

SciTech Connect

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

Romanowsky, Aaron J. [University of California Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States); Fall, S. Michael [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2012-12-15

393

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

394

Lunar influence on equatorial atmospheric angular momentum  

NASA Astrophysics Data System (ADS)

This study investigates the relationship between the equatorial atmospheric angular momentum oscillation in the nonrotating frame and the quasi-diurnal lunar tidal potential. Between 2 and 30 days, the corresponding equatorial component, called Celestial Atmospheric Angular Momentum (CEAM), is mostly constituted of prograde circular motions, especially of a harmonic at 13.66 days, a sidelobe at 13.63 days, and of a weekly broadband variation. A simple equilibrium tide model explains the 13.66 day pressure term as a result of the O1 lunar tide. The powerful episodic fluctuations between 5 and 8 days possibly reflect an atmospheric normal mode excited by the tidal waves Q1 (6.86 days) and ?1 (7.095 days). The lunar tidal influence on the spectral band from 2 to 30 days is confirmed by two specific features, not occurring for seasonal band dominated by the solar thermal effect. First, Northern and Southern Hemispheres contribute equally and synchronously to the CEAM wind term. Second, the pressure and wind terms are proportional, which follows from angular momentum budget considerations where the topographic and friction torques on the solid Earth are much smaller than the one resulting from the equatorial bulge. Such a configuration is expected for the case of tidally induced circulation, where the surface pressure variation is tesseral and cannot contribute to the topographic torque, and tidal winds blow only at high altitudes. The likely effects of the lunar-driven atmospheric circulation on Earth's nutation are estimated and discussed in light of the present-day capabilities of space geodetic techniques.

Bizouard, Christian; Zotov, Leonid; Sidorenkov, Nikolay

2014-11-01

395

Whole-body angular momentum during stair ascent and descent.  

PubMed

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

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

2014-04-01

396

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

E-print Network

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

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

2014-10-15

397

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

SciTech Connect

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

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

2006-12-04

398

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

SciTech Connect

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

Dufaux, J. F. [Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); CITA, University of Toronto, 60 St. George st., Toronto, ON M5S 3H8 (Canada); Kofman, L. [CITA, University of Toronto, 60 St. George st., Toronto, ON M5S 3H8 (Canada); Peloso, M. [School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

2008-07-15

399

Linear and angular retroreflecting interferometric alignment target  

DOEpatents

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

Maxey, L. Curtis (Powell, TN)

2001-01-01

400

Angular correlation studies in noble gases  

NASA Technical Reports Server (NTRS)

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

Coleman, P. G.

1990-01-01

401

Angular dependence of coercivity in magnetic nanotubes  

E-print Network

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.

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

2007-10-30

402

Quark Orbital Angular Momentum in the Baryon  

E-print Network

Analytical and numerical results, for the orbital and spin content carried by different quark flavors in the baryons, are given in the chiral quark model with symmetry breaking. The reduction of the quark spin, due to the spin dilution in the chiral splitting processes, is transferred into the orbital motion of quarks and antiquarks. The orbital angular momentum for each quark flavor in the proton as a function of the partition factor $\\kappa$ and the chiral splitting probability $a$ is shown. The cancellation between the spin and orbital contributions in the spin sum rule and in the baryon magnetic moments is discussed.

Xiaotong Song

2001-06-25

403

Angular size-redshift: Experiment and calculation  

NASA Astrophysics Data System (ADS)

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

Amirkhanyan, V. R.

2014-10-01

404

Angular Momentum Distribution of Fission Fragments  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

405

Angular distributions of neutron-nucleus collisions  

SciTech Connect

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

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

2011-06-15

406

Time-dependent angularly averaged inverse transport  

E-print Network

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

Guillaume Bal; Alexandre Jollivet

2009-05-07

407

How did venus lose its angular momentum?  

PubMed

Venus now has a retrograde and negligible spin, but it very likely started with a typical planetary spin: prograde and with a 10- to 20-hour period. The usually assumed mechanism of solar tidal friction is quite insufficient to remove this angular momentum. Instead, we postulate capture of a moonlike object from an initially retrograde orbit: it would despin Venus and suddenly transform the planet's rotational kinetic energy into internal heat, which would lead to volcanism and the liberation of large amounts of volatiles. The moon would disappear by crashing into the surface of Venus. PMID:17744051

Singer, S F

1970-12-11

408

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

NASA Astrophysics Data System (ADS)

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

Yan, Bo; Jiao, Sihai; Zhang, Dianhua

2014-08-01

409

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

410

Dynamic diffusion as approximation of quantum behavior  

E-print Network

The approximation of quantum unitary dynamics of a particle by a swarm of point wise classical samples of this particle is proposed. Quantum mechanism of speedup rests on the creation and annihilation of absolutely rigid bons, which join samples in dot wise symplexes so that the density of swarm approximate the quantum probability. This mechanism does not require differentiation of a density that is adventage of this method over Bohm's quantum hydrodynamics: our method is applicable to many particles in entangled states. In multi particle case the limitation of total number of samples gives the natural model of decoherence, e.g. the divergency from the exact solution of Shredinger equation. Intensity of creation - annihilation of bonds between samples substantially depends on the grain of spatial resolution, which makes impossible to pass to the limits as in a classical substance; this is the price for the scalability of a model to many particles.

Yuri Ozhigov

2010-11-08

411

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

E-print Network

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

Knaust, Helmut

412

Approximation of Time-Dependent, Viscoelastic Fluid Flow: SUPG Approximation  

E-print Network

equations with an Oldroyd B constitutive equation. The approximation is stabilized by using a SUPG the modeling equations, giving the Navier­Stokes equations. In viscoelasticity, assuming an Oldroyd B typeApproximation of Time-Dependent, Viscoelastic Fluid Flow: SUPG Approximation Vincent J. Ervin

Ervin, Vincent J.

413

The coupled states approximation for scattering of two diatoms  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

414

Axions and the galactic angular momentum distribution  

NASA Astrophysics Data System (ADS)

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

Banik, N.; Sikivie, P.

2013-12-01

415

Angular power spectra with finite counts  

NASA Astrophysics Data System (ADS)

Angular anisotropy techniques for cosmic diffuse radiation maps are powerful probes, even for quite small data sets. A popular observable is the angular power spectrum; we present a detailed study applicable to any unbinned source skymap S(n) from which N random, independent events are observed. Its exact variance, which is due to the finite statistics, depends only on S(n) and N; we also derive an unbiased estimator of the variance from the data. First-order effects agree with previous analytic estimates. Importantly, heretofore unidentified higher order effects are found to contribute to the variance and may cause the uncertainty to be significantly larger than previous analytic estimates - potentially orders of magnitude larger. Neglect of these higher order terms, when significant, may result in a spurious detection of the power spectrum. On the other hand, this would indicate the presence of higher order spatial correlations, such as a large bispectrum, providing new clues about the sources. Numerical simulations are shown to support these conclusions. Applying the formalism to an ensemble of Gaussian-distributed skymaps, the noise-dominated part of the power-spectrum uncertainty is significantly increased at high multipoles by the new, higher order effects. This work is important for harmonic analyses of the distributions of diffuse high-energy ?-rays, neutrinos, and charged cosmic rays, as well as for populations of sparse point sources such as active galactic nuclei.

Campbell, Sheldon S.

2015-04-01

416

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

417

Three Approximate Entropies  

NASA Astrophysics Data System (ADS)

In 1993,(E. & T. Lubkin, Int.J.Theor.Phys. 32), 993 (1993) we gave exact mean trace of squared density matrix P for 3 models of an n-dimensional part of an nK-dimensional pure state. Models named: random nK ket (Haar); pure-pure driven by random Hamiltonian (Gauss); Gauss with n,K coupling reset small (weak). Neglecting higher powers of P gives the approximation: ln(n)- defines deficit = (n - 1)/2 which yields deficits, Haar: n((n+K)/(nK+1) - 1)/2 = ( n - 1/n - 1/K + 1/nnK )/2K + Order(f[n] / KKK); Gauss: (n/2)( (n+K)/(nK+1) + 2(nK+1-n-K)/nK(nK+1)(nK+3)) - 1/2 = ( n - 1/n - 1/K + 2/nK - 1/nnK )/2K + Order( f[n]/KKK ); weak: (n/2)(2(K+n)/((K+1)(n+1))) - 1/2 = (n/(n+1))(1 + (n-1)/K - (n-1)/KK + Order(f[n]/KKK)) - 1/2 [unreliable]. These would stay poor even as Karrow? unless deficit << 1 bit. Haar and Gauss come out good, but weak has too large a deficit. Though many authors (beginning with Don Page(D.N.Page, PRL 71), 1291 (1993)) have found the exact for Haar, I haven't yet seen exact for Gauss or for weak.

Lubkin, Elihu

2002-04-01

418

Transient approximations in queueing networks  

E-print Network

Jackson network. The approximations were tested on networks ranging in size from 4 to 61 nodes, with various initial conditions and loading. Both stationary and nonstationary systems were tested. The closure approximations performed well for the Jackson... approximation simulations. The closure simulation and Monte Carlo simulations were compared for networks of up to 32 nodes, containing up to 80 queues. The network simulations were also tested with various parameters. The results of the closure approximation...

Andrewartha, John Michael

1989-01-01

419

Using C++ and SRIM to improve energy resolution using the STARS/LiBerACE arrays  

NASA Astrophysics Data System (ADS)

An experiment was conducted at LBNL using the STARS/LiBerACE arrays in which a 25 MeV proton beam was incident on 154, 156, and 158Gd targets to study nuclei around the N=90 shape-change region. STARS uses a delta-E and E silicon detector telescope to identify the type and direction of emitted light, charged particles. Each CD shaped detector is segmented into 24 rings. The data sorting program approximates the angle at which a charged particle was scattered by choosing the angle required to hit the middle of the ring struck in the delta-E detector. This angle is then used to calculate energy losses in the dead layers, and hence the particle's total energy. This method is non-optimal as not all of the particles hit the detector at these angles, and improving the angular resolution should improve the energy resolution. SRIM was used to calculate particle energy loss per unit distance travelled in various materials; a C++ program was then written to obtain detailed energy loss calculations for particles as a function of angle and particle energy measured in the E detector. Preliminary results will be presented. This work is supported by the DOE under grants DE-FG02-52NA26206 and DE-FG02-05ER41379.

Pauerstein, Benjamin; Shaw, Jack; Chen, Danyi; Ross, Tim; Hughes, Richard; Beausang, Con

2010-11-01

420

INTRODUCTION TO APPROXIMATE DYNAMIC PROGRAMMING  

E-print Network

CHAPTER 4 INTRODUCTION TO APPROXIMATE DYNAMIC PROGRAMMING In chapter 3, we saw that we could solve cannot solve Bellman's equation exactly. Approximate dynamic programming offers a powerful set the expectation. Alternatively, consider Approximate Dynamic Programming. By Warren B. Powell Copyright c 2010

Powell, Warren B.

421

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

422

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

423

Analysis of energy-angular spectra of {sup 9}Be(N,2N) reaction  

SciTech Connect

The energy-angular spectra for secondary neutron of {sup 9}Be(n,2n) reaction are of interests in the nuclear data need. This paper treats the reaction as nuclear processes with different mechanisms: two-step cascade decay and few body breakup process the approximate formulae of double differential energy angular spectra corresponding to both mechanisms are derived by using kinematics, statistical mechanisms are derived by using kinematics, statistical model and quasi-free scattering approach. With suitablely chosen decay branch ratios and structure data (level energies and widths) of {sup 9}Be and {sup 8}Be, the calculation of double differential neutron production cross section at some angles for 14.2, 10.1; and 5.9 MeV incident neutron have been performed and shown in qualitative with experiment.

Weili, Sun; Benai, Zhang [Institute of Applied Physics and Computational Mathematics, Beijing (China)

1994-12-31

424

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

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

425

Variation of photoelectron angular distributions along the Ar and Ca isonuclear sequences  

SciTech Connect

The dipole angular distribution asymmetry parameter, {beta}, for photoelectrons resulting from 2p photoionization of Ar, Ar{sup 6+}, and Ar{sup 8+} and Ca, Ca{sup 2+}, and Ca{sup 8+} of the Ar (Z=18) and Ca (Z=20) isonuclear sequences, respectively, have been studied using the relativistic random-phase approximation over a broad range of photon energy. In the absence of relaxation, it is known that inner-shell cross sections are essentially unchanged, as a function of photon energy, upon the removal of outer-shell electrons. The present results show that this is not true for the photoelectron angular distribution asymmetry parameters, particularly near the ionization thresholds.

Pradhan, G. B.; Jose, J.; Deshmukh, P. C. [Department of Physics, Indian Institute of Technology, Madras, Chennai 600 036 (India); Radojevic, V. [Department of Physics, Indian Institute of Technology, Madras, Chennai 600 036 (India); Institute of Physics, Pregrevica 118, Post Office Box 68, 11080 Beograd, Zemun (Serbia); Manson, S. T. [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States)

2010-06-15

426

Angular momentum transport and turbulence in laboratory models of Keplerian flows  

NASA Astrophysics Data System (ADS)

We present angular momentum transport (torque) measurements in two recent experimental studies of the turbulent flow between independently rotating cylinders. In addition to these studies, we reanalyze prior torque measurements to expand the range of control parameters for the experimental Taylor-Couette flows. We find that the torque may be described as a product of functions that depend only on the Reynolds number, which describes the turbulent driving intensity, and the rotation number, which characterizes the effects of global rotation. For a given Reynolds number, the global angular momentum transport for Keplerian-like flow profiles is approximately 14% of the maximum achievable transport rate. We estimate that this level of transport would produce an accretion rate of ?/?0~10-3 in astrophysical disks. We argue that this level of transport from hydrodynamics alone could be significant. We also discuss the possible role of finite-size effects in triggering or sustaining turbulence in our laboratory experiments.

Paoletti, M. S.; van Gils, D. P. M.; Dubrulle, B.; Sun, Chao; Lohse, Detlef; Lathrop, D. P.

2012-11-01

427

The angular momentum transport by unstable toroidal magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

428

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

PubMed Central

Some people may believe that the filtered backprojection (FBP) algorithm does not work if the projection data are measured non-uniformly. Some may also believe that iterative algorithms can automatically handle the non-uniformly sampled data in the projector/backprojector. This paper claims that the FBP algorithm can effectively handle the situation where the angular sampling is not uniform. This paper compares the images that are reconstructed by both the FBP and the iterative Landweber algorithms when the angular sampling is nonuniform. When the iteration number is low, the iterative algorithms do not handle the non-uniform sampling properly. A weighting strategy is then suggested and it makes the image resolution more isotropic. In few-view tomography, the FBP and iterative algorithms both perform poorly if no other prior information is used. We have made the following observations: 1) When using an iterative algorithm, one must use early solutions due to noise amplification. 2) An early solution can have anisotropic spatial resolution if the angular sampling is not uniform. 3) The anisotropic resolution problem can be solved by introducing angle dependent weighting, which is not noise dependent. 4) The weighting is not effective when the iteration number is large. The weighting only affects the early solutions, and does not affect the converged solution. 5) When the iteration number is large, the model-mismatch errors are amplified and cause artifacts in the image. 6) The FBP algorithm is not sensitive to the model-mismatch errors, and does not have the “early solution” problems. 7) In few-view tomography, both FBP and iterative algorithms perform poorly, while the FBP algorithm gives a sharper image than the iterative algorithm does. PMID:25678716

Zeng, Gengsheng L.

2014-01-01

429

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

430

Head kinematics in mini-sled tests of foam padding: relevance of linear responses from free motion headform (FMH) testing to head angular responses.  

PubMed

The revised Federal Motor Vehicle Safety Standard (FMVSS) No. 201 specifies that the safety performance of vehicle upper interiors is determined from the resultant linear acceleration response of a free motion headform (FMH) impacting the interior at 6.7 m/s. This study addresses whether linear output data from the FMH test can be used to select an upper interior padding that decreases the likelihood of rotationally induced brain injuries. Using an experimental setup consisting of a Hybrid III head-neck structure mounted on a mini-sled platform, sagittal plane linear and angular head accelerations were measured in frontal head impacts into foam samples of various stiffness and density with a constant thickness (51 mm) at low (approximately 5.0 m/s), intermediate (approximately 7.0 m/s), and high (approximately 9.6 m/s) impact speeds. Provided that the foam samples did not bottom out, recorded peak values of angular acceleration and change in angular velocity increased approximately linearly with increasing peak resultant linear acceleration and value of the Head Injury Criterion (HIC36). The results indicate that the padding that produces the lowest possible peak angular acceleration and peak change in angular velocity without causing high peak forces is the one that produces the lowest possible HIC36 without bottoming out in the FMH test. PMID:12968577

Ivarsson, J; Viano, D C; Lövsund, P; Parnaik, Y

2003-08-01

431

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

E-print Network

-definite (SPSD) tensor field D : R3 SPSD(3) R3×3 that measures the extent of diffusion in a direction v R3 parameterization, such as a mixture of von Mises-Fisher distributions or a spherical harmonic expansion. Instead

432

Study of the angular resolution of the ARGO-YBJ detector  

E-print Network

The determination of the arrival direction of gamma-induced air showers in the ARGO-YBJ experiment has been investigated using different algorithms in the reconstruction procedure. The calculation has been performed, as a function of pad multiplicity, for different primary energies. The performance of a conical correction to the shower front with a suitable fixed cone slope is discussed.

Giuseppe Di Sciascio; Elvira Rossi

2003-09-03

433

A High Angular Resolution View of Hot Gas in Clusters, Groups, and Galaxies  

E-print Network

We discuss two themes from Chandra and XMM-Newton observations of galaxies, groups, and clusters. First, we review observational aspects of cluster formation and evolution as matter accretes along filaments in A85 and A1367. We describe Chandra observations that probe the later evolutionary phases where the effects of mergers -- both subsonic and supersonic -- are observed in cluster cores as ``cold fronts'' and shocks. Second, we review the interactions between the hot, intracluster gas with relativistic plasma originating in active nuclei within the dominant galaxy at the cluster center. As examples of this interaction, we describe the radio and X-ray observations of M87 where buoyantly rising bubbles transfer energy and matter within the cluster core. We describe the Chandra observations of ZW3146 which exhibits both multiple cold fronts and relativistic plasma interactions. Finally, we describe the X-ray observations of NGC4636 where energy produced by the central AGN imprints a unique signature on the surrounding hot corona of the galaxy.

W. Forman; E. Churazov; L. David; F. Durret; C. Jones; M. Markevitch; S. Murray; M. Sun; A. Vikhlinin

2003-01-23

434

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

435

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

436

High Angular Resolution Diffusion Imaging (HARDI) Probabilistic Tractography of the Auditory Radiation  

PubMed Central

Background and Purpose The auditory radiation crosses other white matter tracks and cannot reliably be delineated or quantitatively assessed with DTI fiber tracking. This study investigates whether HARDI fiber tracking can be used to robustly delineate the full extent of the tract. Materials and Methods HARDI (64-direction, b=3000 s/mm2) and DTI (30-direction, b=1000 s/mm2) were acquired from 25 control subjects between the ages of 8 and 26 years. Probabilistic HARDI and DTI fiber tracking of the auditory radiation was performed with starting and filter regions automatically generated from the freesurfer white matter parcellation. DTI fiber tracking was performed with both the 64 and 30-direction data sets. Fiber tracking trials demonstrating connectivity from Heschl's gyrus to the medial geniculate nucleus were considered successful. Results HARDI fiber tracking success rate was 98% and significantly higher than the 64-direction DTI rate of 50% or the 30-direction DTI rate of 42% (p<0.001). The success rates of HARDI fiber tracking for the left and right auditory radiations were not significantly different. In contrast, the left auditory radiation was successfully delineated with DTI fiber tracking at a higher rate than the right auditory radiation. Conclusions HARDI can discriminate the complex white matter pathways at the junction of the auditory radiation and the inferior longitudinal fasciculus. HARDI fiber tracking can reliably delineate the auditory radiation. PMID:23493892

Berman, Jeffrey I.; Lanza, Matthew R.; Blaskey, Lisa; Edgar, J. Christopher; Roberts, Timothy P. L.

2014-01-01

437

M dwarfs binaries: Results from accurate radial velocities and high angular resolution observations  

NASA Astrophysics Data System (ADS)

We present the results and perspectives of a large program on the stellar physics and the formation of very low mass stars. Using adaptive optics images (from ADONIS and NAOS at ESO and PUE'O at CFHT), infrared interferometric data (from VINCI at ESO) and accurate radial velocity (from ELODIE at OHP, FEROS and HARPS at ESO) for the M dwarfs of the solar neigbhourhood, we have obtained very accurate mass-luminosity and mass-radius relation, and compare them to the prediction of recent stellar structure models. We also present multiplicity statistics of M dwarfs (binary fraction, period and mass ration distribution), which are crucial constraints for stellar formation scenarii. Finally we discuss our results and perspectives on extrasolar planets around M dwarfs.

Delfosse, X.; Beuzit, J.-L.; Marchal, L.; Bonfils, X.; Perrier, C.; Ségransan, D.; Udry, S.; Mayor, M.; Forveille, T.

2004-12-01

438

High angular resolution diffusion imaging reveals intravoxel white matter fiber heterogeneity  

Microsoft Academic Search

Magnetic resonance (MR) diffusion tensor imaging (DTI) can resolve the white matter fiber orientation within a voxel pro- vided that the fibers are strongly aligned. However, a given voxel may contain a distribution of fiber orientations due to, for example, intravoxel fiber crossing. The present study sought to test whether a geodesic, high b-value diffusion gradient sam- pling scheme could

David S. Tuch; Timothy G. Reese; Mette R. Wiegell; Nikos Makris; John W. Belliveau; Van J. Wedeen

2002-01-01

439

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

440

CMB Lensing Power Spectrum Biases from Galaxies and Clusters Using High-angular Resolution Temperature Maps  

NASA Astrophysics Data System (ADS)

The lensing power spectrum from cosmic microwave background (CMB) temperature maps will be measured with unprecedented precision with upcoming experiments, including upgrades to the Atacama Cosmology Telescope and the South Pole Telescope. Achieving significant improvements in cosmological parameter constraints, such as percent level errors on ?8 and an uncertainty on the total neutrino mass of ~50 meV, requires percent level measurements of the CMB lensing power. This necessitates tight control of systematic biases. We study several types of biases to the temperature-based lensing reconstruction signal from foreground sources such as radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from galaxy clusters. These foregrounds bias the CMB lensing signal due to their non-Gaussian nature. Using simulations as well as some analytical models we find that these sources can substantially impact the measured signal if left untreated. However, these biases can be brought to the percent level if one masks galaxies with fluxes at 150 GHz above 1 mJy and galaxy clusters with masses above M vir = 1014 M ?. To achieve such percent level bias, we find that only modes up to a maximum multipole of l max ~ 2500 should be included in the lensing reconstruction. We also discuss ways to minimize additional bias induced by such aggressive foreground masking by, for example, exploring a two-step masking and in-painting algorithm.

van Engelen, A.; Bhattacharya, S.; Sehgal, N.; Holder, G. P.; Zahn, O.; Nagai, D.

2014-05-01

441

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

Microsoft Academic Search

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

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

1998-01-01

442

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

443

Two-photon polymerization of a three dimensional structure using beams with orbital angular momentum  

SciTech Connect

The focus of a beam with orbital angular momentum exhibits internal structure instead of an elliptical intensity distribution of a Gaussian beam, and the superposition of Gauss-Laguerre beams realized by two-dimensional phase modulation can generate a complex three-dimensional (3D) focus. By taking advantage of the flexibility of this 3D focus tailoring, we have fabricated a 3D microstructure with high resolution by two-photon polymerization with a single exposure. Furthermore, we have polymerized an array of double-helix structures that demonstrates optical chirality.

Zhang, Shi-Jie; Li, Yan, E-mail: li@pku.edu.cn; Liu, Zhao-Pei; Ren, Jin-Li; Xiao, Yun-Feng; Yang, Hong; Gong, Qihuang [State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, People's Republic of China and Collaborative Innovation Center of Quantum Matter, Beijing 100871 (China)

2014-08-11

444

High-efficiency piezoelectric motor combining continuous rotation with precise control over angular positioning  

NASA Astrophysics Data System (ADS)

The letter describes a piezoelectric motor that combines the merits of piezoelectric materials, such as high power density generated at electromechanical resonance, and a precise control of displacement. The motor utilizes a direct coupling mechanism between the stator and rotor, where a clutch drives the rotor via locking it. The direct coupling makes it possible to transmit the whole power generated in the piezoelectric element to the rotor, and thus achieve the high efficiency of the motor. It also allows the combining of two regimes of operation: continuous rotation and a stepwise motion within a 360° interval with a high resolution of angular displacement.

Glazounov, A. E.; Wang, S.; Zhang, Q. M.; Kim, C.

1999-08-01

445

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

446

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

447

Angular Flow in Toroid Cavity Probes  

NASA Astrophysics Data System (ADS)

NMR signals from samples that rotate uniformly about the central conductor of a TCD ( toroid cavity detector) exhibit frequency shifts that are directly proportional to the sample's angular velocity. This newly observed effect is based on the unique radiofrequency field inside TCDs, which is variable in direction. If a liquid sample is pumped through a capillary tube wound about the central conductor, the frequency shift is proportional to the flow rate. A mathematical relationship between a volumetric flow rate and the frequency shift is established and experimentally verified to high precision. Additionally, two-dimensional flow-resolved NMR spectroscopy for discrimination between components with different flow velocities yet retaining chemical shift information for structural analysis is presented. The application of the two-dimensional method in chromatographic NMR is suggested. Furthermore, utilization of the frequency-shift effect for rheologic studies if combined with toroid-cavity rotating-frame imaging is proposed.

Trautner, Peter; Woelk, Klaus; Bargon, Joachim; Gerald, Rex E.

2001-08-01

448

Angular flow in toroid cavity probes.  

SciTech Connect

NMR signals from samples that rotate uniformly about the central conductor of a TCD (toroid cavity detector) exhibit frequency shifts that are directly proportional to the sample's angular velocity. This newly observed effect is based on the unique radiofrequency field inside TCDs, which is variable in direction. If a liquid sample is pumped through a capillary tube wound about the central conductor, the frequency shift is proportional to the flow rate. A mathematical relationship between a volumetric flow rate and the frequency shift is established and experimentally verified to high precision. Additionally, two-dimensional flow-resolved NMR spectroscopy for discrimination between components with different flow velocities yet retaining chemical shift information for structural analysis is presented. The application of the two-dimensional method in chromatographic NMR is suggested. Furthermore, utilization of the frequency-shift effect for rheologic studies if combined with toroid-cavity rotating-frame imaging is proposed.

Trautner, P.; Woelk, K.; Bargon, J.; Gerald, R. E.; Chemical Engineering; Univ. of Bonn

2001-08-01

449

Angular momentum effects in subbarrier fusion  

SciTech Connect

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

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

1988-01-01

450

Colliding particles carrying nonzero orbital angular momentum  

SciTech Connect

Photons carrying nonzero orbital angular momentum (twisted photons) are well-known in optics. Recently, using Compton backscattering to boost optical twisted photons to high energies was suggested. Twisted electrons in the intermediate energy range have also been produced recently. Thus, collisions involving energetic twisted particles seem to be feasible and represent a new tool in high-energy physics. Here we discuss some generic features of scattering processes involving twisted particles in the initial and/or final state. In order to avoid additional complications arising from nontrivial polarization states, we focus here on scalar fields only. We show that processes involving twisted particles allow one to perform a Fourier analysis of the plane-wave cross section with respect to the azimuthal angles of the initial particles. In addition, using twisted states, one can probe the autocorrelation function of the amplitude, which is inaccessible in the plane-wave collisions. Finally, we discuss prospects for experimental study of these effects.

Ivanov, Igor P. [IFPA, Universite de Liege, Allee du 6 Aout 17, batiment B5a, 4000 Liege, Belgium and Sobolev Institute of Mathematics, Koptyug avenue 4, 630090, Novosibirsk (Russian Federation)

2011-05-01

451

The Angular Momentum of the Accreting Gas  

NASA Astrophysics Data System (ADS)

Every galaxy is embedded in a multiphase and extended circumgalactic medium that comprises cold high-column density gas, warm ionised filaments and a hot rarefied atmosphere (corona). This circumgalactic medium is vital for maintaining blue star-forming galaxies as it provides new fresh gas for star formation to proceed. At the interface between a galaxy disc and the surrounding corona the mixing between the two media is very efficient and produces exchanges of both matter and angular momentum. After describing the various phases of the circumgalactic medium and its kinematics, I will discuss how the interplay between the host galaxy and its environment can drive a steady flow of material (gas accretion) towards the disc and the spinning up of the inner corona.

Fraternali, F.

2014-05-01

452

Angular relation of axes in perceptual space  

NASA Technical Reports Server (NTRS)

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 performed consisting of a perceptual task in which subjects were asked to set independently their apparent vertical and horizontal plane. The visual background provided no other stimuli to serve as optical direction cues. The task was performed in a number of different body tilt positions with pitches and rolls varied in steps of 30 degs. The results clearly show the distortion of orthogonality of the perceptual space for nonupright body positions. Large interindividual differences were found. Deviations from orthogonality up to 25 deg were detected in the pitch as well as in the roll direction. Implications of this nonorthogonality on further studies of spatial perception and on the construction of virtual environments for human interaction is also discussed.

Bucher, Urs

1992-01-01

453

Angular Size-Redshift: Experiment and Calculation  

E-print Network

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

Amirkhanyan, V R

2015-01-01

454

Quadrupole Approximation for Para-Positronium in Relativistic Schrödinger Theory  

E-print Network

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

M. Mattes; M. Sorg

2011-09-11

455

THE ANGULAR MOMENTUM OF MAGNETIZED MOLECULAR CLOUD CORES: A TWO-DIMENSIONAL-THREE-DIMENSIONAL COMPARISON  

SciTech Connect

In this work, we present a detailed study of the rotational properties of magnetized and self-gravitating dense molecular cloud (MC) cores formed in a set of two very high resolution three-dimensional (3D) MC simulations with decaying turbulence. The simulations have been performed using the adaptative mesh refinement code RAMSES with an effective resolution of 4096{sup 3} grid cells. One simulation represents a mildly magnetically supercritical cloud and the other a strongly magnetically supercritical cloud. We identify dense cores at a number of selected epochs in the simulations at two density thresholds which roughly mimic the excitation densities of the NH{sub 3} (J - K) = (1,1) transition and the N{sub 2}H{sup +} (1-0) emission line. A noticeable global difference between the two simulations is the core formation efficiency (CFE) of the high-density cores. In the strongly supercritical simulations, the CFE is 33% per unit free-fall time of the cloud (t{sub ff,cl}), whereas in the mildly supercritical simulations this value goes down to {approx}6 per unit t{sub ff,cl}. A comparison of the intrinsic specific angular momentum (j{sub 3D}) distributions of the cores with the specific angular momentum derived using synthetic two-dimensional (2D) velocity maps of the cores (j{sub 2D}) shows that the synthetic observations tend to overestimate the true value of the specific angular momentum by a factor of {approx}8-10. We find that the distribution of the ratio j{sub 3D}/j{sub 2D} of the cores peaks at around {approx}0.1. The origin of this discrepancy lies in the fact that contrary to the intrinsic determination of j which sums up the individual gas parcels' contributions to the angular momentum, the determination of the specific angular momentum using the standard observational procedure which is based on a measurement on the global velocity gradient under the hypothesis of uniform rotation smoothes out the complex fluctuations present in the 3D velocity field. Our results may well provide a natural explanation for the discrepancy by a factor of {approx}10 observed between the intrinsic 3D distributions of the specific angular momentum and the corresponding distributions derived in real observations. We suggest that previous and future measurements of the specific angular momentum of dense cores which are based on the measurement of the observed global velocity gradients may need to be reduced by a factor of {approx}10 in order to derive a more accurate estimate of the true specific angular momentum in the cores. We also show that the exponent of the size-specific angular momentum relation is smaller ({approx}1.4) in the synthetic observations than their values derived in the 3D space ({approx}1.8).

Dib, Sami; Csengeri, Timea; Audit, Edouard [Service d'Astrophysique, DSM/Irfu, CEA/Saclay, F-91191,