Journal articles: 'Angular Densities'

1

Eisenstein, Daniel J. "Deprojecting Densities from Angular Cross‐Correlations." Astrophysical Journal 586, no. 2 (April 2003): 718–22. http://dx.doi.org/10.1086/367851.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Hansen, Klavs, and Piero Ferrari. "Vibrational angular momentum level densities of linear molecules." Chemical Physics Letters 768 (April 2021): 138385. http://dx.doi.org/10.1016/j.cplett.2021.138385.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Le, Huiling. "Random spherical triangles II: Shape densities." Advances in Applied Probability 21, no. 3 (September 1989): 581–94. http://dx.doi.org/10.2307/1427637.

Full text

Abstract:

This paper gives the exact evaluation of the shape density on the shape space Σ(S2, 3) for a labelled random spherical triangle whose vertices are i.i.d.-uniform in a ‘cap' of S2 bounded by a ‘small' circle of angular radius ρ0.

APA, Harvard, Vancouver, ISO, and other styles

4

Le, Huiling. "Random spherical triangles II: Shape densities." Advances in Applied Probability 21, no. 03 (September 1989): 581–94. http://dx.doi.org/10.1017/s0001867800018826.

Full text

Abstract:

This paper gives the exact evaluation of the shape density on the shape space Σ(S 2, 3) for a labelled random spherical triangle whose vertices are i.i.d.-uniform in a ‘cap' of S2 bounded by a ‘small' circle of angular radius ρ 0 .

APA, Harvard, Vancouver, ISO, and other styles

5

Hanson, Timothy E., Miguel de Carvalho, and Yuhui Chen. "Bernstein polynomial angular densities of multivariate extreme value distributions." Statistics & Probability Letters 128 (September 2017): 60–66. http://dx.doi.org/10.1016/j.spl.2017.03.030.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Agrawal, B. K., and A. Ansari. "On the angular-momentum dependence of nuclear-level densities." Nuclear Physics A 576, no. 2 (August 1994): 189–204. http://dx.doi.org/10.1016/0375-9474(94)90256-9.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Hale, Michael, and Norman Fitz-Coy. "Control of an Over-Actuated Single-Degree-of-Freedom Excitation System." Journal of the IEST 53, no. 1 (April 1, 2010): 31–43. http://dx.doi.org/10.17764/jiet.53.1.1tp80t7p057487n2.

Full text

Abstract:

This paper provides results of a laboratory experiment designed to illustrate the theoretical control considerations for an over-actuated excitation system. The experiment is based on control of a beam pinned at one end providing a single rotational degree of freedom and excited by two electrodynamic actuators. Control is achieved through implementation of two different control reference techniques: (1) reference based on linear acceleration autospectral densities (ASD) and cross-spectral densities (CSD) using linear accelerometer feedback and (2) reference based on an angular acceleration ASD using estimates of angular acceleration as feedback. Correlations to the theoretical based predictions were conducted based on common measurements of both linear acceleration and estimates of angular acceleration acquired during each trial.

APA, Harvard, Vancouver, ISO, and other styles

8

Etschmann, B. E., and E. N. Maslen. "Atomic radii from electron densities." Australian Journal of Physics 53, no. 2 (2000): 317. http://dx.doi.org/10.1071/ph99028.

Full text

Abstract:

Bond lengths for diatomic molecules are predicted from atomic radii derived from free atom one-electron densities by postulating shielding factors for their valence electrons that depend on orbital angular momentum and on the bond order. The predicted values are closer to spectroscopically measured bond lengths than those based on earlier atomic radii inferred from a wider range of structural evidence. The bond lengths predicted by the sum of the atomic radii are corrected by a reduction that allows for charge transfer and by an extension associated with exchange repulsion of the overlapping electrons in the inter-nuclear region. Both corrections are related to free atom one-electron densities.

APA, Harvard, Vancouver, ISO, and other styles

9

Kontrym-Sznajd, G., M. Samsel-Czekała, and S. Kaprzyk. "Electronic Structure via 1D Electron Momentum Densities." Materials Science Forum 666 (December 2010): 142–46. http://dx.doi.org/10.4028/www.scientific.net/msf.666.142.

Full text

Abstract:

We demonstrate what kind of information about the electronic structure one can get from plane projections of electron densities. As an example we use one dimensional (1D) angular correlation of annihilation radiation (ACAR) and Compton scattering spectra for Cd “measured” only for two crystal orientations. Spectra are interpreted in terms of reconstructed 2D densities both in the reduced and extended zone schemes.

APA, Harvard, Vancouver, ISO, and other styles

10

Kotlyar, Victor V., Alexey A. Kovalev, and Alexey M. Telegin. "Angular and Orbital Angular Momenta in the Tight Focus of a Circularly Polarized Optical Vortex." Photonics 10, no. 2 (February 2, 2023): 160. http://dx.doi.org/10.3390/photonics10020160.

Full text

Abstract:

Based on the Richards-Wolf (RW) formalism, we obtain two different exact expressions for the angular momentum (AM) density of light in the focus of an optical vortex with a topological charge n and right circular polarization. One expression for the AM density is derived as the cross product of the position vector and the Poynting vector and has a nonzero value in the focus for an arbitrary integer n. Another expression for the AM density is equal to a sum of the orbital angular momentum (OAM) and the spin angular momentum (SAM) and, in the focus of a considered light field, is equal to zero at n = −1. These expressions are not equal at each point in space, but their 3D integrals are equal. Thus, we derive exact expressions for the AM, SAM and OAM densities in the focus of an optical vortex with right circular polarization and demonstrate that the identity for the densities AM = SAM + OAM is not valid. In addition, we show that the expressions for the strength vectors of the electric and magnetic field near the tight focus, obtained on the basis of the RW formalism, are exact solutions of Maxwell’s equations. Thus, the RW theory exactly describes the behavior of light near the tight focus in free space.

APA, Harvard, Vancouver, ISO, and other styles

11

Pylak, M., Ludwik Dobrzyński, and G. Kontrym-Sznajd. "Reconstruction of Momentum Density Distribution from 2D ACAR Data via Maximum Entropy and Cormack Methods." Materials Science Forum 666 (December 2010): 151–54. http://dx.doi.org/10.4028/www.scientific.net/msf.666.151.

Full text

Abstract:

Novel application of Maximum Entropy method to the reconstruction of electron momentum density distribution from line projections is presented. Our new algorithm is applied to two dimensional angular correlation of annihilation radiation data in Gd. Reconstructed densities are in very good agreement with corresponding densities reconstructed by Cormack’s method.

APA, Harvard, Vancouver, ISO, and other styles

12

Slaný, Petr, and Zdeněk Stuchlík. "Marginally stable thick discs orbiting the Kerr–de Sitter black holes: the mass estimates." Proceedings of the International Astronomical Union 2, S238 (August 2006): 449–50. http://dx.doi.org/10.1017/s1743921307005893.

Full text

Abstract:

AbstractBasic properties of equipotential surfaces in test perfect fluid tori with uniform distribution of the specific angular momentum orbiting KdS black holes are summarized. The central mass-densities of adiabatic non-relativistic tori, for which the approximation of test fluid is adequate, are given and compared with the typical densities of Giant Molecular Clouds.

APA, Harvard, Vancouver, ISO, and other styles

13

Van Houcke, K., and S. M. A. Rombouts. "Nuclear level densities and their dependence on pairing and angular momentum." Nuclear Physics A 788, no. 1-4 (May 2007): 389–92. http://dx.doi.org/10.1016/j.nuclphysa.2007.01.068.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Bell, F., Th Tschentscher, and A. J. Rollason. "Electron Momentum Densities by (y, e y)-Spectroscopy." Zeitschrift für Naturforschung A 48, no. 1-2 (February 1, 1993): 273–78. http://dx.doi.org/10.1515/zna-1993-1-251.

Full text

Abstract:

Abstract We report coincidence measurements of inelastically scattered 148 keV photons and the recoil electrons generated within thin Al and Cu foils. We have analyzed both the Doppler broadening of the scattered photon intensity and the angular correlation of the recoil electron. This corresponds to different scans through the three-dimensional electron momentum density of the target. Estimates of the triple-differential cross-section for Compton scattering are given. The experiment was performed with synchrotron radiation from a bending magnet of the DORIS storage ring at DESY, Hamburg.

APA, Harvard, Vancouver, ISO, and other styles

15

Zatula, N. I., and D. V. Zatula. "Approximation of density of potentials for the flat viscoelastic bodies with inclusions, bounded by a piecewise smooth contours." Bulletin of Taras Shevchenko National University of Kyiv. Series: Physics and Mathematics, no. 1 (2021): 39–42. http://dx.doi.org/10.17721/1812-5409.2021/1.4.

Full text

Abstract:

An approach for approximating unknown densities of potentials in the study of the stressed state of a flat viscoelastic piecewise homogeneous body with inclusions, bounded by piecewise smooth contours, is proposed. The method is based on the construction of a system of boundary-time integral equations to determine the unknown densities of potentials along the contours of the inclusions. The approximation of the unknown densities of potentials was performed taking into account the singularity of the stressed state of a flat viscoelastic body near the angular point of the dividing line of the regions.

APA, Harvard, Vancouver, ISO, and other styles

16

Biasini, M., and G. Kontrym-Sznajd. "What Else for Improvement of Reconstructed Densities?" Materials Science Forum 666 (December 2010): 147–50. http://dx.doi.org/10.4028/www.scientific.net/msf.666.147.

Full text

Abstract:

Reconstruction techniques, belonging to two different categories (series expansion and transform methods), are compared with regard to their applicability to line projections of a model density. It is demonstrated that in the case of this model the algebraic technique gives much better results than the filtered back projection (FBP) algorithm. However, it could not be a case for real data where a region of densities to be considered is very large comparing to the modelled one. In this connection we propose a new way of dealing with two-dimensional (2D) angular correlation of annihilation radiation (ACAR) data. Such a treatment, proposed for all reconstruction techniques, allows to improve reconstructed densities and filters the experimental noise.

APA, Harvard, Vancouver, ISO, and other styles

17

Svendsen, Bob. "Constitutive relations for polar continua based on statistical mechanics and spatial averaging." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, no. 2233 (January 2020): 20190407. http://dx.doi.org/10.1098/rspa.2019.0407.

Full text

Abstract:

The purpose of the current work is the formulation of macroscopic constitutive relations, and in particular continuum flux densities, for polar continua from the underlying mass point dynamics. To this end, generic microscopic continuum field and balance relations are derived from phase space transport relations for expectation values of point fields related to additive mass point quantities. Given these, microscopic energy, linear momentum and angular momentum, balance relations are obtained in the context of the split of system forces into non-conservative and conservative parts. In addition, divergence–flux relations are formulated for the conservative part of microscopic supply-rate densities. For the case of angular momentum, two such relations are obtained. One of these is force-based, and the other is torque-based. With the help of physical and material theoretic restrictions (e.g. material frame-indifference), reduced forms of the conservative flux densities are obtained. In the last part of the work, formulation of macroscopic constitutive relations from their microscopic counterparts is investigated in the context of different spatial averaging approaches. In particular, these include (weighted) volume-averaging based on a localization function, surface averaging of normal flux densities based on Cauchy flux theory and volume averaging with respect to centre of mass.

APA, Harvard, Vancouver, ISO, and other styles

18

Knöpfle, K., L. M. Sandratskii, and J. Kübler. "Symmetry properties of intra-atomic spin and angular momentum densities: application to." Journal of Physics: Condensed Matter 9, no. 33 (August 18, 1997): 7095–104. http://dx.doi.org/10.1088/0953-8984/9/33/012.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Tschentscher, Thomas, Jochen R. Schneider, and Friedhelm Bell. "Two-dimensional electron-momentum densities from angular-correlation measurements of Compton scattering." Physical Review B 48, no. 23 (December 15, 1993): 16965–73. http://dx.doi.org/10.1103/physrevb.48.16965.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Trouard, Theodore P., Todd M. Alam, Jaroslav Zajicek, and Michael F. Brown. "Angular anisotropy of 2H NMR spectral densities in phospholipid bilayers containing cholesterol." Chemical Physics Letters 189, no. 1 (January 1992): 67–75. http://dx.doi.org/10.1016/0009-2614(92)85154-3.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Holland, Peter. "Trajectory construction of Dirac evolution." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, no. 2236 (April 2020): 20190682. http://dx.doi.org/10.1098/rspa.2019.0682.

Full text

Abstract:

We extend our programme of representing the quantum state through exact stand-alone trajectory models to the Dirac equation. We show that the free Dirac equation in the angular coordinate representation is a continuity equation for which the real and imaginary parts of the wave function, angular versions of Majorana spinors, define conserved densities. We hence deduce an exact formula for the propagation of the Dirac spinor derived from the self-contained first-order dynamics of two sets of trajectories in 3-space together with a mass-dependent evolution operator. The Lorentz covariance of the trajectory equations is established by invoking the ‘relativity of the trajectory label'. We show how these results extend to the inclusion of external potentials. We further show that the angular version of Dirac's equation implies continuity equations for currents with non-negative densities, for which the Dirac current defines the mean flow. This provides an alternative trajectory construction of free evolution. Finally, we examine the polar representation of the Dirac equation, which also implies a non-negative conserved density but does not map into a stand-alone trajectory theory. It reveals how the quantum potential is tacit in the Dirac equation.

APA, Harvard, Vancouver, ISO, and other styles

22

Kingsburgh, Robin L., and M. J. Barlow. "Mean Electron Densities, Distances and Filling Factors for Galactic Planetary Nebulae." Symposium - International Astronomical Union 155 (1993): 185. http://dx.doi.org/10.1017/s0074180900170470.

Full text

Abstract:

Mean electron densities are presented for over 100 planetary nebulae (PN). Distances to the majority of these PN are then derived, based on calibrations from observations of Magellanic Cloud PN. Absolute radii and filling factors have also been determined. A trend is seen in that for larger radii, smaller filling factors are found, however we show that such a trend results from uncertainties in the observed angular diameters.

APA, Harvard, Vancouver, ISO, and other styles

23

Wang, Yi, Honghua Wang, Jingwei Zhang, and Chao Tan. "A piecewise analytical model of bearingless switched reluctance motor for full rotor angular positions." COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 41, no. 1 (November 11, 2021): 22–47. http://dx.doi.org/10.1108/compel-06-2019-0268.

Full text

Abstract:

Purpose This paper aims to establish a piecewise Maxwell stress analytical model of bearingless switched reluctance motor (BSRM) for the full rotor angular positions. The proposed model varies from the existing models, which are only applicable to the partial-overlapping positions of stator and rotor poles. By extending the applicable rotor angular positions, this model provides a basic analytical model for the multi-phase excitation control of BSRM. Design/methodology/approach The full rotor angular positions are classified into the partial-overlapping positions and the non-overlapping positions. At first, two different air gap subdividing methods are proposed, respectively, for the two-position ranges. Then, different integration paths are selected accordingly. Furthermore, two approximate methods are presented to calculate the average flux density of each air gap subdivision. Finally, considering the mutual coupling between the two perpendicular radial suspension forces, a piecewise Maxwell stress analytical model is derived for the full rotor angular positions of BSRM. Findings A piecewise Maxwell stress analytical model of BSRM is built for the full rotor angular positions, and applicable to the multi-phase excitation mode of BSRM. For the partial-overlapping positions and the non-overlapping positions, two sets of air gap subdividing methods, integration paths and approximate calculation methods of air gap flux densities are proposed, respectively. The accuracy and reliability of the proposed model are verified by the finite element method. Originality/value The piecewise Maxwell stress analytical model of BSRM for the full rotor angular positions is proposed for the first time. The novel air gap subdividing methods, integration paths, approximate calculation methods of air gap flux densities and the coupling between the two radial suspension forces are adopted to improve the modeling accuracy. As the applicable range of rotor angular position is extended, this model overcomes the limitation of the existing models only for single-phase excitation mode and contributes to the accurate control of BSRM multi-phase excitation mode.

APA, Harvard, Vancouver, ISO, and other styles

24

Alvarez, Jose R., and Peter Rez. "Density of states calculations for Ni-Al Alloys." Proceedings, annual meeting, Electron Microscopy Society of America 54 (August 11, 1996): 524–25. http://dx.doi.org/10.1017/s0424820100165082.

Full text

Abstract:

Impurities at grain boundaries can have dramatic effects on the ductility or embrittlement of metals and metallic alloys. The mechanism for these effects is controversial, but it is believed that charge redistribution induced by the impurity atoms is responsible. Electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) can be used to measure changes in unoccupied densities of states (DOS) when a small nanometer sized probe is moved across a grain boundary. To interpret the energy loss fine structure band theory is needed to relate the observations, which represent an angular momentum resolved density of states at a particular atomic site, to the local electronic structure in the material.We compare the Linearized Augmented Plane Wave (LAPW) and layered Korringa-Kohn-Rostoker (LKKR) methods for calculating densities of states relevant for energy loss in Ni-Al alloys. Both methods can give the angular momentum resolved densities of states at a particular site and both use the Local Density Approximation (LDA). The LAPW method allows ab initio electronic structure calculations of materials by introducing atomic spheres where the basis wave functions are approximated by solutions of a radial potential; for the interstitial region between the atoms the basis wave functions are approximated by plane waves.

APA, Harvard, Vancouver, ISO, and other styles

25

Gillman, S., A. L. Tiley, A. M. Swinbank, C. M. Harrison, Ian Smail, U. Dudzevičiūtė, R. M. Sharples, et al. "From peculiar morphologies to Hubble-type spirals: the relation between galaxy dynamics and morphology in star-forming galaxies at z ∼ 1.5." Monthly Notices of the Royal Astronomical Society 492, no. 1 (December 23, 2019): 1492–512. http://dx.doi.org/10.1093/mnras/stz3576.

Full text

Abstract:

ABSTRACT We present an analysis of the gas dynamics of star-forming galaxies at z ∼ 1.5 using data from the KMOS Galaxy Evolution Survey. We quantify the morphology of the galaxies using HSTcandels imaging parametrically and non-parametrically. We combine the H α dynamics from KMOS with the high-resolution imaging to derive the relation between stellar mass (M*) and stellar specific angular momentum (j*). We show that high-redshift star-forming galaxies at z ∼ 1.5 follow a power-law trend in specific stellar angular momentum with stellar mass similar to that of local late-type galaxies of the form j* ∝ M$_*^{0.53\, \pm \, 0.10}$. The highest specific angular momentum galaxies are mostly disc-like, although generally both peculiar morphologies and disc-like systems are found across the sequence of specific angular momentum at a fixed stellar mass. We explore the scatter within the j* – M* plane and its correlation with both the integrated dynamical properties of a galaxy (e.g. velocity dispersion, Toomre Qg, H α star formation rate surface density ΣSFR) and its parametrized rest-frame UV / optical morphology (e.g. Sérsic index, bulge to total ratio, clumpiness, asymmetry, and concentration). We establish that the position in the j* – M* plane is strongly correlated with the star-formation surface density and the clumpiness of the stellar light distribution. Galaxies with peculiar rest-frame UV / optical morphologies have comparable specific angular momentum to disc- dominated galaxies of the same stellar mass, but are clumpier and have higher star formation rate surface densities. We propose that the peculiar morphologies in high-redshift systems are driven by higher star formation rate surface densities and higher gas fractions leading to a more clumpy interstellar medium.

APA, Harvard, Vancouver, ISO, and other styles

26

Sousa, A. A., R. B. Pereira, and A. C. Silva. "Energy and angular momentum densities in a Gödel-type universe in teleparallel geometry." Gravitation and Cosmology 16, no. 1 (January 2010): 25–33. http://dx.doi.org/10.1134/s0202289310010044.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Chadwick, M. B., and P. Obložinský. "Particle-hole state densities with linear momentum and angular distributions in preequilibrium reactions." Physical Review C 46, no. 5 (November 1, 1992): 2028–41. http://dx.doi.org/10.1103/physrevc.46.2028.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Oya, Gin-ichiro, and Yasuji Sawada. "An anomaly in the angular dependence of critical current densities of niobium films." Physica B: Condensed Matter 165-166 (August 1990): 1425–26. http://dx.doi.org/10.1016/s0921-4526(09)80298-6.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Jalilian-Marian, Jamal. "Azimuthal Angular correlations in high energy processes in QCD." EPJ Web of Conferences 182 (2018): 02058. http://dx.doi.org/10.1051/epjconf/201818202058.

Full text

Abstract:

Angular (azimuthal or polar) correlations between produced particles in high energy hadronic/nuclear collisions carry a wealth of information on the dynamics of the strong interactions in the novel regime where parton densities of the target hadron or nucleus are high. As such they probe a relatively unexplored region of QCD kinematic phase space. Here we consider azimuthal angular correlations between three jets produced in Deep Inelastic Scattering in the kinematics region corresponding to low xBjorken of the target and show that high gluon density effects in the target lead to a disappearance of the away-side peaks.

APA, Harvard, Vancouver, ISO, and other styles

30

HJELM, ANDERS, JOAKIM TRYGG, OLLE ERIKSSON, BÖRJE JOHANSSON, and JOHN M. WILLS. "ORBITAL PARAMAGNETISM IN METALLIC SYSTEMS WITH LARGE ANGULAR MOMENTA." International Journal of Modern Physics B 09, no. 21 (September 30, 1995): 2735–51. http://dx.doi.org/10.1142/s0217979295001026.

Full text

Abstract:

We demonstrate that the field induced spin and orbital moments in paramagnetic metals in general are parallel, since the Zeeman energy overcomes the spin-orbit energy that is in favor of an antiparallel arrangement when the electronic shell is less than half-filled. In the early actinides, however, the spin-orbit energy becomes sufficiently strong to approach the border where the moments can couple antiparallel. This results in peculiar magnetic states for α-Pu and some uranium compounds, where the spin moments are antiparallel to the applied field and the magnetic response dominated by the orbital character, and consequently these systems display unusual spin densities and magnetic form factors.

APA, Harvard, Vancouver, ISO, and other styles

31

Liu, Chang, Yan-Gang Miao, Yu-Mei Wu, and Yu-Hao Zhang. "Self-Regular Black Holes Quantized by means of an Analogue to Hydrogen Atoms." Advances in High Energy Physics 2016 (2016): 1–7. http://dx.doi.org/10.1155/2016/5982482.

Full text

Abstract:

We suggest a quantum black hole model that is based on an analogue to hydrogen atoms. A self-regular Schwarzschild-AdS black hole is investigated, where the mass density of the extreme black hole is given by the probability density of the ground state of hydrogen atoms and the mass densities of nonextreme black holes are given by the probability densities of excited states with no angular momenta. Such an analogue is inclined to adopt quantization of black hole horizons. In this way, the total mass of black holes is quantized. Furthermore, the quantum hoop conjecture and the Correspondence Principle are discussed.

APA, Harvard, Vancouver, ISO, and other styles

32

Nienhuis, Gerard. "Analogies between optical and quantum mechanical angular momentum." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2087 (February 28, 2017): 20150443. http://dx.doi.org/10.1098/rsta.2015.0443.

Full text

Abstract:

The insight that a beam of light can carry orbital angular momentum (AM) in its propagation direction came up in 1992 as a surprise. Nevertheless, the existence of momentum and AM of an electromagnetic field has been well known since the days of Maxwell. We compare the expressions for densities of AM in general three-dimensional modes and in paraxial modes. Despite their classical nature, these expressions have a suggestive quantum mechanical appearance, in terms of linear operators acting on mode functions. In addition, paraxial wave optics has several analogies with real quantum mechanics, both with the wave function of a free quantum particle and with a quantum harmonic oscillator. We discuss how these analogies can be applied. This article is part of the themed issue ‘Optical orbital angular momentum’.

APA, Harvard, Vancouver, ISO, and other styles

33

Amrane, N., M. Benkraouda, N. Qamhieh, and Saleh T. Mahmoud. "Study on anisotropies and momentum densities in AlN, GaN and InN by positron annihilation." JOURNAL OF ADVANCES IN PHYSICS 12, no. 3 (October 30, 2016): 4356–67. http://dx.doi.org/10.24297/jap.v12i3.6161.

Full text

Abstract:

The independent particle model (IPM) coupled with empirical pseudopotential method (EPM) was used to compute the thermalized positron charge densities in specific family of binary tetrahedrally coordinated crystals of formula ANB8-N. Initial results show a clear asymmetrical positron charge distribution relative to the bond center. It is observed that the positron density is maximum in the open interstices and is excluded not only, from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for the (001,110) planes. The results are used to analyze the positron effects in AlN, GaN and InN compounds. Our computational technique provides the theoretical means of interpreting the k-space densities obtained experimentally using the twodimensional angular correlation of annihilation radiation (2D-ACAR).

APA, Harvard, Vancouver, ISO, and other styles

34

AMRANE, N. "STUDY ON MOMENTUM DENSITY IN SEMICONDUCTOR ALLOYS GeC and SnC BY POSITRON ANNIHILATION." International Journal of Modern Physics B 24, no. 18 (July 20, 2010): 3607–18. http://dx.doi.org/10.1142/s0217979210054440.

Full text

Abstract:

The independent particle model (IPM) coupled with empirical pseudopotential method (EPM) was used to compute the thermalized positron charge densities in specific family of binary tetrahedrally coordinated crystals of formula ANB8-N . Initial results show a clear asymmetrical positron charge distribution relative to the bond center. It is observed that the positron density is maximum in the open interstices and is excluded not only from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for the (001, 110) planes. The results are used to analyze the positron effects in GeC and SnC . Our computational technique provides the theoretical means of interpreting the k-space densities obtained experimentally using the two-dimensional angular correlation of annihilation radiation (2D-ACAR).

APA, Harvard, Vancouver, ISO, and other styles

35

Aye, Moe M., Elmeri Rivasto, Mukarram Z. Khan, H. Rijckaert, H. Palonen, H. Huhtinen, Isabel Van Driessche, and P. Paturi. "Multilayering BZO nanocolumns with different defect densities for YBCO high field applications." New Journal of Physics 23, no. 11 (November 1, 2021): 113031. http://dx.doi.org/10.1088/1367-2630/ac3682.

Full text

Abstract:

Abstract The multilayer structures of alternating superconducting YBCO films doped with different BZO nanocolumn densities were utilized. We show that using 50 nm thick layers increases J c in the whole angular range by maximum 40% as compared with 200 nm single layer BZO-doped or multilayers with smaller thickness. Multilayering is found to be most effective at high magnetic fields and temperatures. These results indicate that demonstrated multilayer structures are extremely attractive for various electrical power applications in the foreseeable future. The experimental outcomes are thoroughly discussed with the mechanisms of crystalline quality and flux pinning in YBCO with different BZO nanorod densities multilayers of varying thicknesses.

APA, Harvard, Vancouver, ISO, and other styles

36

Randrup, Jørgen, Daniel Ward, Gillis Carlsson, Thomas Døssing, Peter Möller, and Sven Åberg. "Fission dynamics with microscopic level densities." EPJ Web of Conferences 169 (2018): 00019. http://dx.doi.org/10.1051/epjconf/201816900019.

Full text

Abstract:

Working within the Langevin framework of nuclear shape dynamics, we study the dependence of the evolution on the degree of excitation. As the excitation energy of the fissioning system is increased, the pairing correlations and the shell effects diminish and the effective potential-energy surface becomes ever more liquid-drop like. This feature can be included in the treatment in a formally well-founded manner by using the local level densities as a basis for the shape evolution. This is particularly easy to understand and implement in the Metropolis treatment where the evolution is simulated by means of a random walk on the five-dimensional lattice of shapes for which the potential energy has been tabulated. Because the individual steps between two neighboring lattice sites are decided on the basis of the ratio of the statistical weights, what is needed is the ratio of the local level densities for those shapes, evaluated at the associated local excitation energies. For this purpose, we adapt a recently developed combinatorial method for calculating level densities which employs the same single-particle levels as those that were used for the calculation of the pairing and shell contributions to the macroscopic-microscopic deformation-energy surface. For each nucleus under consideration, the level density (for a fixed total angular momentum) is calculated microscopically for each of the over five million shapes given in the three-quadratic-surface parametrization. This novel treatment, which introduces no new parameters, is illustrated for the fission fragment mass distributions for selected uranium and plutonium cases.

APA, Harvard, Vancouver, ISO, and other styles

37

Xiaochuan Pan. "Quasi-bandlimited properties of Radon transforms and their implications for increasing angular sampling densities." IEEE Transactions on Medical Imaging 17, no. 3 (June 1998): 395–406. http://dx.doi.org/10.1109/42.712129.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Wallis, David, Lars N. Hansen, T. Ben Britton, and Angus J. Wilkinson. "Geometrically necessary dislocation densities in olivine obtained using high-angular resolution electron backscatter diffraction." Ultramicroscopy 168 (September 2016): 34–45. http://dx.doi.org/10.1016/j.ultramic.2016.06.002.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Lagoyannis, A., A. Spyrou, S. Harissopulos, S. Galanopoulos, R. Kunz, M. Fey, J. W. Hammer, R. Julin, and P. Demetriou. "(p,γ) Reaction Cross Sections Relevant to the p process: First Results for the Se Isotopes." HNPS Proceedings 13 (February 20, 2020): 161. http://dx.doi.org/10.12681/hnps.2966.

Full text

Abstract:

Proton-capture reaction cross sections of Se isotopes were determined in the 1-6 MeV energy range by means of γ-angular distribution measurements as well as via the activation technique. In this report we compare our first cross-section results with statistical model calculations performed using various microscopic and phenomenological approaches of Optical Model Potentials and Nuclear Level Densities.

APA, Harvard, Vancouver, ISO, and other styles

40

Krygowski, Tadeusz Marek, Günter Häfelinger, and Josef Schüle. "Interpretation of Substituent Angular Parameters of Monosubstituted Benzenes by Means of ab initio STO-3G Fully Optimized Molecular Structures and Charges Densities. Part VI of the Series: “Crystallographic Studies and Physicochemical Properties of π-Electron Systems”." Zeitschrift für Naturforschung B 41, no. 7 (July 1, 1986): 895–903. http://dx.doi.org/10.1515/znb-1986-0717.

Full text

Abstract:

AbstractThe angular variations of molecular structures calculated for 17 monosubstituted derivatives of benzene by use of ab initio analytical gradient optimization at the STO -3G level have been correlated by multiple linear regression analysis with Mulliken σ- and π-electron charge densities at corresponding ring carbon atoms. Variations of angles γ at meta positions are solely due to π-electron effects (R = 0.961). Changes in angles β at ortho positions are independent of σ- or π-electron effects but may be related to steric effects (R = 0.719) alone or additionally to charge densities on ortho protons (for dual regression R = 0.846). Angles a at ipso atom s depend significantly on both, σ- and π-electron charge densities in the ratio of 70% to 21% with R = 0.974 for dual regression. Variations of angles δ para-positions depend on all three effects considered (with correlation coefficient for a triple regression R = 0.951) in the ratio 37.6% :2 8 .3% : 34.1% for steric effects, σ- and π-electron charge densities, respectively.

APA, Harvard, Vancouver, ISO, and other styles

41

Haase, Christian, Hoi Pang Ng, Rimma Lapovok, and Yuri Estrin. "Ti-6Al-4V Billet Produced by Compaction of BE Powders Using Equal-Channel Angular Pressing." Key Engineering Materials 520 (August 2012): 301–8. http://dx.doi.org/10.4028/www.scientific.net/kem.520.301.

Full text

Abstract:

In the present study, ECAP compaction was used to produce Ti-6Al-4V billet from CP Ti powder mixed with two different Al-V master alloys. It was demonstrated that ECAP at 400 °C with applied back-pressure of about 210 MPa permits consolidation of the powder mixtures to relative green densities as high as 99.3 %. A combination of temperature, high hydrostatic pressure and plastic shear deformation gave rise to excellent green densities and good compositional homogeneity due to enhanced self-diffusion. It was shown that the temperature of sintering required after direct compaction of BE powders can be reduced by 150-250°C if compaction is conducted by ECAP with back-pressure. This becomes possible due to high green density and the presence of a large number of fast diffusion paths associated with dislocations and grain boundaries. It is suggested that the ECAP-based processing route may offer a significant saving of production cost.

APA, Harvard, Vancouver, ISO, and other styles

42

Siegel, Benjamin M., and John Mioduszewski. "High-Brightness Gaseous Field ION Source for Light ION Species." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 1 (August 12, 1990): 200–201. http://dx.doi.org/10.1017/s0424820100179750.

Full text

Abstract:

We have reported on the very high brightness gaseous field ion source that has been developed at Cornell to produce high angular current density H2+ ion beams with low energy widths. Axially oriented H2+ ion beams from single emission sites with angular currents dl/dΩ= 10-20 μa/sr are obtained routinely. The energy width (FWHM) has been measured to be Δe=1.0 ev. H2+ beams with angular currents as high as 70 μa/sr. have been observed, but these higher current beams have a tail spread on their energy distribution curve.We have now extented this source to produce ion species of He+ with angular current densities, dl/dΩ, in the 10-15 μa/sr range and ions beams of Ne+, A+, N2+ and O+ ions with angular currents dl/dΩ of 3-7 μa/sr.Ion beams with these characteristics have have been achieved by operating the gaseous field ion source under the following conditions:1. In an ultrahigh vacuum system at cryogenic temperatures cooled with LHe and heated to obtain an optimum balance of gas concentration at the emitter tip with physisorption on the tip at temperatures that allow good surface transport from a large area near the apex of the tip to the emission site.

APA, Harvard, Vancouver, ISO, and other styles

43

Locatelli, Nicola, Gabriele Ponti, and Stefano Bianchi. "disnht: Modeling X-ray absorption from distributed column densities." Astronomy & Astrophysics 659 (March 2022): A118. http://dx.doi.org/10.1051/0004-6361/202142655.

Full text

Abstract:

Collecting and analyzing X-ray photons over either spatial or temporal scales encompassing varying optical depth values requires knowledge about the optical depth distribution. For a sufficiently broad optical depth distribution, assuming a single column density value leads to a misleading interpretation of the source emission properties, nominally its spectral model. We present a model description for the interstellar medium absorption in X-ray spectra at moderate energy resolution, extracted over spatial or temporal regions encompassing a set of independent column densities. The absorption model (called disnht) approximates the distribution with a lognormal distribution and is presented in table format. The solution table and source code are made available and can be further generalized or tailored for arbitrary optical depth distributions encompassed by the extraction region. The disnht absorption model and its generalized solution are expected to be relevant for current and upcoming large angular scale analyses of diffuse X-ray emission, such as those from the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) and the future Athena missions.

APA, Harvard, Vancouver, ISO, and other styles

44

Artyukh, V. S. "Physical Conditions in Active Galactic Nuclei." Symposium - International Astronomical Union 134 (1989): 535–36. http://dx.doi.org/10.1017/s0074180900141919.

Full text

Abstract:

Self-absorption of synchrotron radiation in compact radio sources gives rise to a low-frequency cutoff in their spectra. To study this effect it is necessary to observe the radio sources at meter wavelengths with angular resolution < 1″. Such observations of compact radio sources located in active galactic nuclei lead to estimates of magnetic field strengths and relativistic electron number densities in the AGNs.

APA, Harvard, Vancouver, ISO, and other styles

45

Alon, Ofir E. "Morphology of an Interacting Three-Dimensional Trapped Bose–Einstein Condensate from Many-Particle Variance Anisotropy." Symmetry 13, no. 7 (July 9, 2021): 1237. http://dx.doi.org/10.3390/sym13071237.

Full text

Abstract:

The variance of the position operator is associated with how wide or narrow a wave-packet is, the momentum variance is similarly correlated with the size of a wave-packet in momentum space, and the angular-momentum variance quantifies to what extent a wave-packet is non-spherically symmetric. We examine an interacting three-dimensional trapped Bose–Einstein condensate at the limit of an infinite number of particles, and investigate its position, momentum, and angular-momentum anisotropies. Computing the variances of the three Cartesian components of the position, momentum, and angular-momentum operators we present simple scenarios where the anisotropy of a Bose–Einstein condensate is different at the many-body and mean-field levels of theory, despite having the same many-body and mean-field densities per particle. This suggests a way to classify correlations via the morphology of 100% condensed bosons in a three-dimensional trap at the limit of an infinite number of particles. Implications are briefly discussed.

APA, Harvard, Vancouver, ISO, and other styles

46

AVRIGEANU, M., G. S. ANAGNOSTATOS, A. N. ANTONOV, and V. AVRIGEANU. "ELASTIC SCATTERING AS A TEST OF DENSITY DISTRIBUTIONS IN 6He AND 8He." International Journal of Modern Physics E 11, no. 03 (June 2002): 249–64. http://dx.doi.org/10.1142/s021830130200082x.

Full text

Abstract:

Taking elastic scattering of 6,8 He on protons as an example, it is shown that the differences between density distributions coming from different models can be evaluated when scattering data of the nuclei involved are available for comparison. Microscopic elastic-scattering angular distributions have been calculated for incident energies <100A MeV by using the Tanihata and COSMA models for the density distributions of He nuclei, the M3Y-Paris effective NN interaction, and the Bray et al. imaginary part of the optical potential. The present microscopic angular distributions based on the Tanihata densities are in good agreement with the available experimental data and also similar to results of other theoretical calculations, showing the sensitivity of scattering to the density distributions of these helium isotopes.

APA, Harvard, Vancouver, ISO, and other styles

47

Jha, A. K., J. S. Gill, and V. M. Puri. "Percolation Segregation in Binary Size Mixtures of Spherical and Angular-Shaped Particles of Different Densities." Particulate Science and Technology 26, no. 5 (September 29, 2008): 482–93. http://dx.doi.org/10.1080/02726350802367902.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Sakano, Masaaki, Mamiko Nishiuchi, Yoshitomo Maeda, Katsuji Koyama, and Jun Yokogawa. "10.7. Absorption columns with bright X-ray sources near the galactic center: — mass estimation in the Galactic center region." Symposium - International Astronomical Union 184 (1998): 443–44. http://dx.doi.org/10.1017/s0074180900085521.

Full text

Abstract:

We report the column density distribution to the Galactic Center region using the X-ray binary observations with the X-ray satellite ASCA, and demonstrate a new method of the total mass determination near the Galactic Center. The column densities are given by a simple form as a function of the angular distance from the Galactic Plane. Assuming a disklike mass distribution of 500 pc radius, we estimate the total mass to be ~ 6 × 107M⊙.

APA, Harvard, Vancouver, ISO, and other styles

49

Aygun, M. "A comprehensive theoretical analysis of 22Ne nucleus by using different density distributions, different nuclear potentials and different cluster approach." International Journal of Modern Physics E 29, no. 01 (January 2020): 1950112. http://dx.doi.org/10.1142/s021830131950112x.

Full text

Abstract:

In this study, a systematic analysis is made on the [Formula: see text]Ne nucleus. First, using different theoretical approaches, we show eight density distributions for the [Formula: see text]Ne nucleus. For there densities, we obtain the elastic scattering angular distributions of [Formula: see text]Ne by [Formula: see text]C and [Formula: see text]C targets. Then, to offer alternative nuclear potentials in explaining nuclear interactions related to [Formula: see text]Ne projectile, we calculate the elastic scattering cross-sections of [Formula: see text]C and [Formula: see text]C reactions by using six different nuclear potentials. Finally, we investigate cluster structures of the [Formula: see text]Ne nucleus via a simple cluster approach. We compare the calculated elastic scattering angular distributions with the experimental data.

APA, Harvard, Vancouver, ISO, and other styles

50

Berlu, Lilian, and Philip Hoggan. "Useful Integrals for Ab-Initio Molecular Quantum Similarity Measurements Using Slater Type Atomic Orbitals." Journal of Theoretical and Computational Chemistry 02, no. 02 (June 2003): 147–61. http://dx.doi.org/10.1142/s0219633603000513.

Full text

Abstract:

Molecular quantum similarity measurements are based on a quantitative comparison of the one-electron densities of two molecules superposed and aligned to optimize a well-defined similarity function. In most previous work the densities have been related using a Dirac delta leading to the overlap-like quantum similarity function. The densities for the two molecules compared have generally been approximated often with a simple LCAO of s-gaussian functions. In this work, we present a one center two range expansion method for the evaluation of the overlap integrals involved in the overlap-like quantum similarity function over Slater type orbitals (STO). The single center and three types of two-center overlap integrals (involving four atomic orbitals; two in each molecule) have led to finite sums using a single center approach combined with selection rules obtained by analysis of orbital angular momentum (conservation). The three- and four-center integrals are also obtained analytically but involve infinite sums which require further study before leading to a complete set of integral codes for ab-initio quantum similarity.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Angular Densities'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles