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Articles de revues sur le sujet « Nuclei anisotropici »

Auteur : Grafiati
Publié le 9 mars 2023
Mis à jour le 10 mars 2023

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1

Gijón, A., F. J. Gálvez, F. Arias de Saavedra et E. Buendía. « Anisotropic multicluster model in light nuclei ». Journal of Physics G : Nuclear and Particle Physics 43, no 6 (27 avril 2016) : 065103. http://dx.doi.org/10.1088/0954-3899/43/6/065103.

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2

Berggren, Tore. « Anisotropic alpha decay from oriented nuclei ». Hyperfine Interactions 75, no 1-4 (novembre 1992) : 401–8. http://dx.doi.org/10.1007/bf02398996.

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3

Elliott, Stuart J., et Philip W. Kuchel. « What Are the Relative Intensities of the Components of NMR Spectral Multiplets from Quadrupolar Nuclei in Uniformly Anisotropic Media ? » Concepts in Magnetic Resonance Part A 2021 (18 février 2021) : 1–25. http://dx.doi.org/10.1155/2021/8890478.

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Stretched hydrogels make uniformly anisotropic environments for quadrupolar nuclei such as 2H, 23Na, and 133Cs. Such surroundings cause the partial alignment of nuclear spin bearing ions and molecules that is sufficiently pronounced to alter the nuclear magnetic resonance spectra of the guest species. In most cases, resonance splittings are directly related to the spin quantum number I. The relative intensities of the components of the resonance multiplets can be inferred from basic quantum mechanics.
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4

Pogorelov, Ilya V., et Henry E. Kandrup. « Anisotropic distribution functions for relativistic galactic nuclei ». Physical Review E 53, no 2 (1 février 1996) : 1375–81. http://dx.doi.org/10.1103/physreve.53.1375.

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5

Bryce, David L., et Jochen Autschbach. « Relativistic hybrid density functional calculations of indirect nuclear spin–spin coupling tensors — Comparison with experiment for diatomic alkali metal halides »,. Canadian Journal of Chemistry 87, no 7 (juillet 2009) : 927–41. http://dx.doi.org/10.1139/v09-040.

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The accurate calculation of the isotropic (Jiso) and anisotropic (ΔJ) parts of indirect nuclear spin–spin coupling tensors is a stringent test for quantum chemistry, particularly for couplings involving heavy isotopes where relativistic effects and relativity – electron correlation cross terms are expected to play an important role. Experimental measurements on diatomic molecules in the gas phase offer ideal data for testing the success of computational approaches, since the data are essentially free from intermolecular effects, and precise coupling anisotropies may be reliably extracted in favourable cases. On the basis of available experimental molecular-beam coupling-tensor parameters for diatomic alkali metal halides, we tabulate known values of Jiso and, taking rotational–vibrational corrections to the direct dipolar coupling constant into account, precise values of ΔJ are determined for the ground rovibrational state. First-principles calculations of the coupling tensors were performed using a recently developed program based on hybrid density functional theory using the two-component relativistic zeroth-order regular approximation (ZORA). Experimental trends in Jiso and ΔJ are reproduced with correlation coefficients of 0.993 and 0.977, respectively. Periodic trends in the coupling constants and their dependence on the product of the atomic numbers of the coupled nuclei are discussed. Finally, the hybrid functional method is also successfully tested against experimental data for a series of polyatomic xenon fluorides and group-17 fluorides.
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Brandt, William Nielsen. « Multiwavelength surveys for Active Galactic Nuclei ». Proceedings of the International Astronomical Union 15, S356 (octobre 2019) : 11. http://dx.doi.org/10.1017/s1743921320002471.

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AbstractMost of what we know about active galactic nuclei (AGNs) has been driven, or at least strongly shaped, by our methods for finding them, and multiwavelength AGN surveys have achieved remarkable successes in recent decades. I will present a broad, and thus necessarily shallow, review of such multiwavelength AGN surveys. I will first present some brief introductory points on, e.g., general survey approaches, AGN luminosities, host galaxies, and anisotropic emission/obscuration. I will then review many of the key current surveys and their results, separating these into ground-based and space-based surveys. Finally, I will discuss some future prospects including essential remaining questions and “discovery space” considerations.
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7

Vavilov, D. E., S. Eggl, Yu D. Medvedev et P. B. Zatitskiy. « Shape evolution of cometary nuclei via anisotropic mass loss ». Astronomy & ; Astrophysics 622 (29 janvier 2019) : L5. http://dx.doi.org/10.1051/0004-6361/201834806.

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Context. Breathtaking imagery recorded during the European Space Agency Rosetta mission confirmed the bilobate nature of the nucleus of comet 67P/Churyumov-Gerasimenko. The peculiar appearance of the nucleus is not unique among comets. The majority of cometary cores imaged at high resolution exhibit a similar build. Various theories have been brought forward as to how cometary nuclei attain such peculiar shapes. Aims. We illustrate that anisotropic mass loss and local collapse of subsurface structures caused by non-uniform exposure of the nucleus to solar irradiation can transform initially spherical comet cores into bilobed cores. Methods. We derived a mathematical framework to describe the changes in morphology resulting from non-uniform insolation during the spin-orbit evolution of a nucleus. We solved the resulting partial differential equations that govern the change in the shape of a nucleus subject to mass loss and consequent collapse of depleted subsurface structures analytically for simple insolation configurations and numerically for more realistic scenarios. Results. The proposed mechanism is capable of explaining why a large percentage of periodic comets appear to have peanut-shaped cores and why light-curve amplitudes of comet nuclei are on average larger than those of typical main belt asteroids of the same size.
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Baring, Matthew G. « Anisotropic Effects in Thomson Cascade Models of Active Galactic Nuclei ». Symposium - International Astronomical Union 159 (1994) : 343. http://dx.doi.org/10.1017/s0074180900175448.

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CGRO observations of high energy γ-rays from active galactic nuclei (AGN) suggest that beaming may be prevalent in these sources. Anisotropic effects in AGN continuum spectra produced by the inverse Compton scattering mechanism are outlined, in particular the resulting spectral breaks and modification of spectral indices that depend strongly on the electron anisotropy and the observational viewing perspective.
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9

Goyal, Supriya. « How Much Asymmetry of Colliding Pair Affects Nuclear Dynamics at Balance Point ? » Physics Research International 2014 (20 août 2014) : 1–10. http://dx.doi.org/10.1155/2014/619360.

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Using the quantum molecular dynamics model, we study the nuclear dynamics at the balance energy of mass asymmetric colliding nuclei by keeping the total mass of the system fixed and by varying the mass asymmetry (η = (AT-AP)/(AT+AP), where AT and AP are the masses of the target and projectile, resp.) of the reaction. In particular, we study the various quantities like average and maximum density and temperature, collision rate, participant-spectator matter, anisotropic ratio, relative momentum, and their mass asymmetry and mass dependence. Our results indicate sizeable effect of mass asymmetry on these quantities.
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10

Augustine, Cyril. « Two-Pulse Phase Modulation Based Decoupling Schemes for Removing Heteronuclear Spin Interactions in the NMR Spectroscopy of Isotropic Systems : An Analysis Using Experiments and Numerical Simulations ». International Journal of Spectroscopy 2014 (15 mai 2014) : 1–8. http://dx.doi.org/10.1155/2014/641473.

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Heteronuclear spin interactions in solids and anisotropic liquids can be removed by phase modulated decoupling sequences with frequency sweep, such as SWf-TPPM and its variants. The performance of these sequences in isotropic spin systems with regard to the experimental parameters, phase angle, and decoupler offset is presented here. A comparison is made with other commonly used heteronuclear decoupling schemes in liquids, namely, WALTZ-16, GARP, and MLEV. Also, the trajectories of nuclear magnetization vector of abundant nuclei in a simple spin system during TPPM and SWf-TPPM decoupling sequences are traced out using computer simulations.
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11

Bonatsos, Dennis, C. Daskaloyannis, P. Kolokotronis et D. Lenis. « Nonlinear extension of the u(3) algebra as the symmetry algebra of the three-dimensional anisotropic quantum harmonic oscillator with rational ratios of frequencies and the Nilsson model ». HNPS Proceedings 5 (19 février 2020) : 14. http://dx.doi.org/10.12681/hnps.2891.

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The symmetry algebra of the N-dimensional anisotropic quantum har- monic oscillator with rational ratios of frequencies is constructed by a method of general applicability to quantum superintegrable systems. The special case of the 3-dim oscillator is studied in more detail, because of its relevance in the description of superdeformed nuclei and nuclear and atomic clusters. In this case the symmetry algebra turns out to be a nonlinear extension of the u(3) algebra. A generalized angular momentum operator useful for labeling the degenerate states is constructed, clarifying the connection of the present formalism to the Nilsson model.
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12

Vandermeer, R. A., et Dorte Juul Jensen. « Effects of Nuclei Clustering on Recrystallization Kinetics ». Materials Science Forum 467-470 (octobre 2004) : 193–96. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.193.

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In this work, it is shown that the contiquity ratio, Crr, defined as the fraction of the total grain boundary area of recrystallized grains shared by other recrystallized grains, is a useful experimental parameter for describing the clustering of recrystallization nuclei in partially recrystallized microstructures. Two experimental examples are presented where anisotropic impingement behavior, i.e. non random recrystallized grain distributions, is thought to be important. In the experimental examples, the deviation of Crr from Crr = Vv which is a characteristic of a random distribution, is clearly shown. The results justify the need for these cases to be modelled, as had been done, by impingement patterns other than the simple random nucleation behavior so often postulated without proof in recrystallization kinetics studies.
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13

Weller, Andreas, Sven Nordsiek et Wolfgang Debschütz. « Estimating permeability of sandstone samples by nuclear magnetic resonance and spectral-induced polarization ». GEOPHYSICS 75, no 6 (novembre 2010) : E215—E226. http://dx.doi.org/10.1190/1.3507304.

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Two techniques to estimate permeability are compared in this paper: nuclear magnetic resonance (NMR) and spectral-induced polarization (SIP). Both methods are based on relaxation processes. NMR records the relaxation of hydrogen nuclei after excitation in an external magnetic field. The phenomenon of induced polarization can be characterized by a relaxation of ions after excitation by an electric field. Hydrogen nuclei are concentrated in the pore water, the current flow is restricted to the pore space for most reservoir rocks, and permeability is related to the pore space geometry. Based on the similarity between fluid movement and current flow in the pore space, different relations have been published linking parameters derived from NMRand SIP data to predict permeability. NMR, SIP and permeability data have been acquired on 53 sandstone samples of the cretaceous Bahariya Formation (Western Desert, Egypt) including 27 samples showing a lamination that causes anisotropy. We compare the applicability of known and generalized relations for permeability prediction including isotropic and anisotropic samples. Because NMR relaxation ignores directionality of pore space geometry, the known relations provide only a weak accuracy in permeability estimation. The integrating parameters derived from a Debye decomposition of SIP data are partly sensitive to anisotropy. A generalized power-law relation using resistivity, chargeability, and mean relaxation time provide a reliable permeability prediction for isotropic and anisotropic samples.
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14

SOHEYLI, S., H. NOSHAD et M. LAMEHI-RACHTI. « MEASUREMENT OF FISSION FRAGMENT ANISOTROPIES FOR PROTON-INDUCED FISSION OF TWO PRE-ACTINIDE NUCLEI AT SEVERAL ENERGIES ». International Journal of Modern Physics A 22, no 05 (20 février 2007) : 1027–37. http://dx.doi.org/10.1142/s0217751x07034428.

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The angular distribution of fission fragments has been measured for proton-induced fission of 197 Au and 209 Bi nuclei at several energies between 25 and 30 MeV using surface-barrier detectors. The measured anisotropies are found to be in agreement with the predictions of the standard saddle-point statistical model. The measured anisotropies for neither of the nuclei show any anomalous behavior as a function of both energy and entrance channel mass asymmetry. The fission cross sections of 197 Au and 209 Bi nuclei were also measured and compared with that of the previous works.
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15

Mattar, Saba M. « Anisotropic hyperfine interactions of xenon nuclei surrounding a copper atom ». Journal of Physical Chemistry 92, no 12 (juin 1988) : 3360–62. http://dx.doi.org/10.1021/j100323a011.

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16

Du, Feng, et Hanchen Huang. « Closed-form theory of nuclei separation on highly anisotropic surfaces ». Applied Surface Science 390 (décembre 2016) : 107–10. http://dx.doi.org/10.1016/j.apsusc.2016.08.070.

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17

Xu, Ya-Di. « Anisotropic radiation from accretion disc coronae in active galactic nuclei ». Monthly Notices of the Royal Astronomical Society 449, no 1 (17 mars 2015) : 191–98. http://dx.doi.org/10.1093/mnras/stv290.

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18

Berggren, Tore. « Interpretation of anisotropic alpha emission from oriented odd-mass nuclei ». Hyperfine Interactions 43, no 1-4 (décembre 1988) : 407–14. http://dx.doi.org/10.1007/bf02398321.

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19

Halle, Bertil. « Spin dynamics of exchanging quadrupolar nuclei in locally anisotropic systems ». Progress in Nuclear Magnetic Resonance Spectroscopy 28, no 2 (janvier 1996) : 137–59. http://dx.doi.org/10.1016/0079-6565(95)01022-x.

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20

Halle, B. « Spin dynamics of exchanging quadrupolar nuclei in locally anisotropic systems ». Progress in Nuclear Magnetic Resonance Spectroscopy 28 (1996) : 137–59. http://dx.doi.org/10.1016/0079-6565(96)90000-x.

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21

Sarwar, Golam, et Jan-e. Alam. « Kinetic evolution and correlation of fluctuations in an expanding quark gluon plasma ». International Journal of Modern Physics A 33, no 08 (20 mars 2018) : 1850040. http://dx.doi.org/10.1142/s0217751x18500409.

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Evolution of spatially anisotropic perturbation created in the system formed after Relativistic Heavy Ion Collisions has been studied. The microscopic evolution of the fluctuations has been examined within the ambit of Boltzmann Transport Equation (BTE) in a hydrodynamically expanding background. The expansion of the background composed of quark gluon plasma (QGP) is treated within the framework of relativistic hydrodynamics. Spatial anisotropic fluctuations with different geometries have been evolved through Boltzmann equation. It is observed that the trace of such fluctuation survives the evolution. Within the relaxation time approximation, analytical results have been obtained for the evolution of these anisotropies. Explicit relations between fluctuations and transport coefficients have been derived. The mixing of various Fourier (or k) modes of the perturbations during the evolution of the system has been explicitly demonstrated. This study is very useful in understanding the presumption that the measured anisotropies in the data from heavy ion collisions at relativistic energies imitate the initial state effects. The evolution of correlation function for the perturbation in pressure has been studied and shows that the initial correlation between two neighbouring points in real space evolves to a constant value at later time which gives rise to Dirac delta function for the correlation function in Fourier space. The power spectrum of the fluctuation in thermodynamic quantities (like temperature estimated in this work) can be connected to the fluctuation in transverse momentum of the thermal hadrons measured experimentally. The bulk viscous coefficient of the QGP has been estimated by using correlations of pressure fluctuation with the help of Green–Kubo relation. Angular power spectrum of the anisotropies has been estimated in the appendix.
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22

Abrosimov, V. I., et O. I. Davydovska. « Nature of Isoscalar Dipole Resonances in Heavy Nuclei ». Ukrainian Journal of Physics 63, no 12 (9 décembre 2018) : 1043. http://dx.doi.org/10.15407/ujpe63.12.1043.

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The isoscalar dipole nuclear response reveals low- and high-energy resonances. The nature of isoscalar dipole resonances in heavy spherical nuclei is studied, by using a translation-invariant kinetic model of small oscillations of finite Fermi systems. Calculations of the velocity field at the centroid energy show a pure vortex character of the low-energy isoscalar dipole resonance in spherical nuclei and confirm the anisotropic compression character of the high-energy one. The evolution of the velocity field as a function of the excitation energy of the nucleus within the resonance width is studied. It is found that the low-energy isoscalar dipole resonance retains a vortex character, while with this collective excitation also involves a compression, as the energy increases. The high-energy resonance keeps the compression character with a change in the excitation energy within the resonance width, but the compression-expansion region of the velocity field related to this resonance shifts inside the nucleus.
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23

Smith, J. A. S. « Nuclear Quadrupole Resonance : The Present State and Further Development ». Zeitschrift für Naturforschung A 41, no 1-2 (1 février 1986) : 453–62. http://dx.doi.org/10.1515/zna-1986-1-289.

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The importance of nuclear electric quadrupole interactions in chemistry, both present and future, depends very much on their power to resolve problems in electronic structure and molecular dynamics. Fortunately, the subject, by its very nature, is “multinuclear”; even if the ground state of a given nucleus is non-quadrupolar, there often exist excited nuclear states which are, an example being 19F, for which quadrupole coupling constants are now being published from angular correlation measurements. Other new techniques are constantly extending the range of the experiments, recent examples being the use of SQUID magnetometers to detect acoustic 121Sb and 123Sb quadrupole resonance in antimony metal and Fourier transform quadrupole resonance spectroscopy based on fast field cycling to measure 2H quadrupole interactions in powders. Recently, much work on quadrupole interactions in solids of half-integral spin nuclei such as 17O or 27Al has been pursued in two different ways; by quadrupole double resonance in natural abundance, and nuclear magnetic resonance in very high magnetic fields, for which enrichment of low-abundance nuclei such as 170 is often required. In the liquid phase, measurements are now sufficiently reliable for comparisons of changes in the nuclear electric quadrupole tensor from gas to liquid and solid phases to be made. The new methods of partial alignment of polar molecules in the liquid phase in strong electric fields, or magnetically anisotropic molecules in high magnetic fields, seem certain to contribute to these developments.
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24

Ambrosius, Frank, Elke Klaus, Torsten Schaller et Angelika Sebald. « CP/MAS NMR of Heavy Spin-1/2 Nuclei at B0 = 2.35T ». Zeitschrift für Naturforschung A 50, no 4-5 (1 mai 1995) : 423–28. http://dx.doi.org/10.1515/zna-1995-4-515.

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Perspectives of CP/MAS NMR at low external magnetic field (B0=2.35T) are discussed. Applications are illustrated for the case of heavy spin-1/2 nuclei such as 195Pt and 199Hg: 195Pt and 199Hg CP/MAS spectra of a variety of organometallic compounds are reported. Aspects of shielding anisotropics, of 195Pt-35/37Cl interactions and of 31P-M (M=Cd, Hg, Pt) coupling in transition metal phosphine complexes will be briefly addressed
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HE ZHI-YONG, LI ZU-YU, JIN GEN-MING, DUAN LI-MIN, DAI GUANG-XI, WU HE-YU, ZHANG BAO-GUO, WEN WAN-XIN, QI YU-JIN et LUO QING-ZHEN. « AZIMUTHALLY ANISOTROPIC EMISSION OF UNSTABLE LIGHT NUCLEI IN NUCLEUS-NUCLEUS COLLISIONS ». Acta Physica Sinica 45, no 9 (1996) : 1438. http://dx.doi.org/10.7498/aps.45.1438.

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26

Coppi, P., R. D. Blandford et M. J. Rees. « Anisotropic induced Compton scattering - Constraints on models of active galactic nuclei ». Monthly Notices of the Royal Astronomical Society 262, no 3 (1 juin 1993) : 603–18. http://dx.doi.org/10.1093/mnras/262.3.603.

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27

Furó, István, et Bertil Halle. « Multiple quantum NMR spectroscopy onI> ; 1 nuclei in anisotropic systems ». Molecular Physics 76, no 5 (10 août 1992) : 1169–97. http://dx.doi.org/10.1080/00268979200101961.

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28

Andersen et Gundersen. « Pronounced loss of cell nuclei and anisotropic deformation of thick sections ». Journal of Microscopy 196, no 1 (octobre 1999) : 69–73. http://dx.doi.org/10.1046/j.1365-2818.1999.00555.x.

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29

Tremblay, Dominique, et Andrew E. Pelling. « Complex Substrate Strain Fields Reveal Anisotropic Deformation of C2C12 Cell Nuclei ». Biophysical Journal 102, no 3 (janvier 2012) : 707a. http://dx.doi.org/10.1016/j.bpj.2011.11.3838.

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30

Power, William P., Roderick E. Wasylishen et Ronald D. Curtis. « Phosphorus-31 solid-state nuclear magnetic resonance study of monophosphazenes ». Canadian Journal of Chemistry 67, no 3 (1 mars 1989) : 454–59. http://dx.doi.org/10.1139/v89-072.

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Simultaneous observation of anisotropic chemical shielding and dipolar coupling in polycrystalline monophosphazenes has been used to obtain information on the 31P–14N spin pair. Phosphorus-31 chemical shielding tensor components have been determined; the most shielded component was found to lie along the P=N bond. The 31P–14N dipolar coupling constants have provided P=N bond lengths from powder samples, equivalent for all compounds within experimental error; the value obtained for N–(triphenylphosphoranylidene)-aniline is in excellent agreement with that obtained in a recent X-ray diffraction study. Features of crystallographic significance have been determined from the solid-state nuclear magnetic resonance spectra for two of the compounds without resorting to diffraction techniques. Information on the magnitude and orientation of the 14N electric field gradient tensor has been inferred from 31P MAS spectra and abinitio calculations. Keywords: monophosphazenes, dipolar nmr, 31P chemical shielding anisotropies, solid-state nmr.
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31

Bu, De-Fu, Pei-Yao Xu et Bo-Cheng Zhu. « Self-Similar Solution of Hot Accretion Flow with Anisotropic Pressure ». Universe 5, no 4 (8 avril 2019) : 89. http://dx.doi.org/10.3390/universe5040089.

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For the accretion flow in extremely low-luminosity active galactic nuclei, such as ourGalactic center (Sgr A*) and M 87, the collisional mean-free path of ions may be much larger than itsgyroradius. In this case, the pressure parallel to the magnetic field is different from that perpendicularto the field; therefore, the pressure is anisotropic. We study the effects of anisotropic pressure onthe dynamics of accretion flow by assuming the flow is radially self-similar. We find that in the casewhere the outflow is present, the radial and rotational velocities, the sound speed, and the Bernoulliparameter of the accretion flow are all increased when the anisotropic pressure is taken into account.This result suggests that it becomes easier for the accretion flow to generate outflow in the presenceof anisotropic pressure.
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32

Peckham, Heather E., et Wilma K. Olson. « Nucleic-acid structural deformability deduced from anisotropic displacement parameters ». Biopolymers 95, no 4 (29 novembre 2010) : 254–69. http://dx.doi.org/10.1002/bip.21570.

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33

Lesot, Philippe, Philippe Berdagué et Patrick Giraudeau. « Detection of quadrupolar nuclei by ultrafast 2D NMR : exploring the case of deuterated analytes aligned in chiral oriented solvents ». Chemical Communications 52, no 10 (2016) : 2122–25. http://dx.doi.org/10.1039/c5cc09409g.

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34

Nakano, T., T. Fukushige et J. Makino. « 11.16. On the origin of density cusp in galactic nuclei by central black hole ». Symposium - International Astronomical Union 184 (1998) : 487–88. http://dx.doi.org/10.1017/s0074180900085703.

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We investigated the dynamical reaction of the central region of galaxies to a falling massive black hole by N-body simulations. As the initial galaxy model, we used an isothermal King model and placed a massive black hole at around the half-mass radius of the galaxy. We found that the central core of the galaxy is destroyed by the heating due to the black hole and a very weak density cusp (ρ ∝ r−α, with α ∼ 0.5) is formed around the center. This result is consistent with recent observations of large elliptical galaxies by Hubble Space Telescope (Lauer et al. 1995; Byun et al. 1996; Gebhardt et al. 1996; Faber et al. 1996; Kormendy et al. 1996). The radius of the weak cusp region is large for large black hole mass. The velocity of the stars become tangentially anisotropic in the inner region, while in the outer region the stars have radially anisotropic velocity dispersion. Our result naturally explains the mechanism of the formation of the weak cusp found in the previous simulations of galaxy merging, and implies that the weak cusp observed in large elliptical galaxies may be formed by the heating process by sinking black holes during merging events.
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35

CUOCO, A., F. IOCCO, G. MANGANO, G. MIELE, O. PISANTI et P. D. SERPICO. « PRESENT STATUS OF PRIMORDIAL NUCLEOSYNTHESIS AFTER WMAP : RESULTS FROM A NEW BBN CODE ». International Journal of Modern Physics A 19, no 26 (20 octobre 2004) : 4431–53. http://dx.doi.org/10.1142/s0217751x04019548.

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We report on the status of primordial nucleosynthesis in light of recent results on CMB anisotropies from WMAP experiment. Theoretical estimates for nuclei abundances, along with the corresponding uncertainties, are evaluated using a new numerical code, where all nuclear rates usually considered have been updated using the most recent available data. Moreover, additional processes neglected in previous calculations have been included. The combined analysis of CMB and primordial nucleosynthesis prediction for Deuterium gives an effective number of relativistic degrees of freedom in good agreement with the simplest scenario of three nondegenerate neutrinos. Our findings seem to point out possible systematics affecting 4 He mass fraction measurements, or the effect of exotic physics, like a slightly degenerate relic neutrino background.
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GHOSH, DIPAK, ARGHA DEB, PRABIR KUMAR HALDAR, SIMA GUPTAROY et APARNA DHAR (MITRA). « LÉVY INDEX AND MULTIFRACTAL CHARACTERISTICS OF RING-LIKE AND JET-LIKE EVENTS IN HIGH ENERGY NUCLEAR COLLISIONS ». Fractals 18, no 01 (mars 2010) : 75–86. http://dx.doi.org/10.1142/s0218348x10004695.

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We perform a Lévy index analysis of relativistic shower particles produced in the interactions of 32 S nuclei at 200A GeV with nuclear emulsion using the results of factorial moment Fq in two-dimensional anisotropic (η - ϕ) space. We carry out the same investigation for target fragments produced in 32 S - AgBr interactions at 200A GeV energy for both events in emission angle space and azimuthal angle space. The analysis reveals that for pions the value of Lévy index μ is 1.491 ± 0.025 for ring-like events and μ ~ 2.004 ± 0.054 for jet-like events which indicates different degree of multifractality. In case of target fragments jet-like events show a value of μ ~ 1.871 ± 0.010 whereas ring-like events yields an unphysical value (μ > 2) the implication of which need to be explored.
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37

Liu, Yuan, et Shuang Nan Zhang. « DUSTY TORUS FORMATION BY ANISOTROPIC RADIATIVE PRESSURE FEEDBACK OF ACTIVE GALACTIC NUCLEI ». Astrophysical Journal 728, no 2 (2 février 2011) : L44. http://dx.doi.org/10.1088/2041-8205/728/2/l44.

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38

Kroeker, Scott, et Roderick E. Wasylishen. « Article ». Canadian Journal of Chemistry 77, no 11 (1 novembre 1999) : 1962–72. http://dx.doi.org/10.1139/v99-181.

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Direct NMR observation of copper-63/65 nuclei in solid K3Cu(CN)4 provides the first experimental example of anisotropic copper chemical shielding. Axially symmetric by virtue of the space group symmetry, the shielding tensor spans 42 ppm, with the greatest shielding when the unique axis is perpendicular to the applied magnetic field. The nuclear quadrupole coupling constant is also appreciable, CQ(63Cu) = -1.125 MHz, reflecting a deviation of the Cu(CN)43- anion from pure tetrahedral symmetry. Spin-spin coupling to 13C nuclei in an isotopically enriched sample is quantified by line-shape simulations of both 13C and 63/65Cu magic-angle spinning (MAS) NMR spectra to be 300 Hz. It is shown that this information is also directly available by 63/65Cu triple-quantum (3Q) MAS NMR. The relative merits of these three approaches to characterizing spin-spin couplings involving half-integer quadrupolar nuclei are discussed. Chemical shielding tensors for nitrogen-15 and carbon-13 are obtained from NMR spectra of non-spinning samples, and are compared to those of tetrahedral group 12 tetracyanometallates. Finally, 2J(63/65Cu,15N) detected in 15N MAS experiments are found to be 19 and 20 Hz for the two crystallographically distinct cyanide ligands.Key words: NMR, quadrupolar nucleus, chemical shielding tensor, multiple-quantum magic-angle spinning, metal cyanide, spin-spin coupling.
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39

Madsen, Anders Østergaard, Sax Mason et Sine Larsen. « A neutron diffraction study of xylitol : derivation of mean square internal vibrations for H atoms from a rigid-body description ». Acta Crystallographica Section B Structural Science 59, no 5 (25 septembre 2003) : 653–63. http://dx.doi.org/10.1107/s010876810301557x.

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A neutron diffraction study of xylitol (C5O5H12) is presented. The nuclear anisotropic displacement parameters have been analysed showing that the carbon–oxygen skeleton conforms to a rigid-body (TLS) description. Applying this TLS model to the xylitol H atoms allows characterization of the internal molecular displacements of the H nuclei, assuming that the observed H nuclear mean-square displacements are a sum of the internal displacements and rigid-body displacements. These internal molecular displacements are very similar for chemically equivalent H atoms and in good agreement with the values obtained by other methods. In all cases the smallest eigenvector of the residual mean-square displacement tensor is almost parallel to the X—H bond. The use of ab initio calculations to obtain the internal vibrations in xylitol is discouraging. Another 12 structures extracted from the literature which have been investigated by neutron diffraction were subjected to a similar analysis. The results for the nine compounds investigated at low temperature conform to the results from xylitol and provide estimates of the internal vibrations of H atoms in a range of chemical environments.
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40

Eitelmann, Sara, Laura Petersilie, Christine R. Rose et Jonathan Stephan. « Altered Gap Junction Network Topography in Mouse Models for Human Hereditary Deafness ». International Journal of Molecular Sciences 21, no 19 (6 octobre 2020) : 7376. http://dx.doi.org/10.3390/ijms21197376.

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Anisotropic gap junctional coupling is a distinct feature of astrocytes in many brain regions. In the lateral superior olive (LSO), astrocytic networks are anisotropic and oriented orthogonally to the tonotopic axis. In CaV1.3 knock-out (KO) and otoferlin KO mice, where auditory brainstem nuclei are deprived from spontaneous cochlea-driven neuronal activity, neuronal circuitry is disturbed. So far it was unknown if this disturbance is also accompanied by an impaired topography of LSO astrocyte networks. To answer this question, we immunohistochemically analyzed the expression of astrocytic connexin (Cx) 43 and Cx30 in auditory brainstem nuclei. Furthermore, we loaded LSO astrocytes with the gap junction-permeable tracer neurobiotin and assessed the network shape and orientation. We found a strong elevation of Cx30 immunoreactivity in the LSO of CaV1.3 KO mice, while Cx43 levels were only slightly increased. In otoferlin KO mice, LSO showed a slight increase in Cx43 as well, whereas Cx30 levels were unchanged. The total number of tracer-coupled cells was unaltered and most networks were anisotropic in both KO strains. In contrast to the WTs, however, LSO networks were predominantly oriented parallel to the tonotopic axis and not orthogonal to it. Taken together, our data demonstrate that spontaneous cochlea-driven neuronal activity is not required per se for the formation of anisotropic LSO astrocyte networks. However, neuronal activity is required to establish the proper orientation of networks. Proper formation of LSO astrocyte networks thus necessitates neuronal input from the periphery, indicating a critical role of neuron-glia interaction during early postnatal development in the auditory brainstem.
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41

Chaudhury, M. L., et S. K. Agrawal. « α spectra of deformed even–even nuclei and equivalence of optical model potentials ». Canadian Journal of Physics 69, no 6 (1 juin 1991) : 692–98. http://dx.doi.org/10.1139/p91-116.

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The reduced transition probabilities of the α spectra of some deformed heavy even–even nuclei are calculated, taking the barrier to be the anisotropic electrostatic potential superposed by the deformed nonlocal α-nucleus potential. The latter is described by a deformation parameter, εl, as in our previous treatments and, for its static part, different optical model potentials are now used. Results show that the calculated values of the reduced transition probabilities are in good agreement with the observed values, taking the best-fit values of εl. It is also found, as in the case of spherical nuclei, that the different optical potentials are equivalent for the cases considered, and that the nonlocal effect is predominant.
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42

Ferland, Gary J., Chen Hu, Jian-Min Wang, Jack A. Baldwin, Ryan L. Porter, Peter A. M. van Hoof et R. J. R. Williams. « IMPLICATIONS OF INFALLING Fe II-EMITTING CLOUDS IN ACTIVE GALACTIC NUCLEI : ANISOTROPIC PROPERTIES ». Astrophysical Journal 707, no 1 (30 novembre 2009) : L82—L86. http://dx.doi.org/10.1088/0004-637x/707/1/l82.

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43

Kirkpatrick, C. C., B. R. McNamara et K. W. Cavagnolo. « ANISOTROPIC METAL-ENRICHED OUTFLOWS DRIVEN BY ACTIVE GALACTIC NUCLEI IN CLUSTERS OF GALAXIES ». Astrophysical Journal 731, no 2 (24 mars 2011) : L23. http://dx.doi.org/10.1088/2041-8205/731/2/l23.

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44

Luo, J., J. R. Ruble, B. M. Craven et R. K. McMullan. « Effects of H/D substitution on thermal vibrations in piperazinium hexanoate-h11,d11 ». Acta Crystallographica Section B Structural Science 52, no 2 (1 avril 1996) : 357–68. http://dx.doi.org/10.1107/s0108768195011025.

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The crystal structures of piperazinium hexanoate-h11, {{1}\over{2}}C4H12N2+ 2.C6H11O− 2, and piperazinium hexanoate-d11, {{1}\over{2}}C4H12N2+ 2.C6D11O− 2, have been determined from neutron diffraction data collected at 15 K. Nuclear anisotropic displacement parameters have been analyzed to obtain the internal molecular displacements of the H and D nuclei, given by 〈 u 2 obs〉 − 〈 u 2 ext〉 where 〈 u 2 ext〉 is the contribution assuming all H/D to be carried rigidly on the vibrating molecular framework consisting of the heavier nuclei. In both crystal structures the cation ring is well fitted by the rigid-body model and the anion chain by a model with two rigid segments. In the piperazinium cations the corresponding protons in the two structures have about the same internal vibrational directions and magnitudes except for the two N—H protons, perhaps owing to differences in N—H...O hydrogen bonding. The internal vibrations of corresponding H/D in the h11 and d11 anions have approximately the same vibrational directions. The internal mean-square displacements of the H nuclei are systematically greater than the values of the corresponding D nuclei by an average factor 1.7 (3). For both anions, normal-mode analyses have been carried out using the force fields derived from ab initio quantum-mechanical calculations with HF/3-21 G and HF/6-31G** basis sets. The values of the resultant H/D internal displacements for C—H(D) bond stretching and methylene out-of-plane vibrations are in good agreement with experiment. However, with either basis set, theory predicts methylene in-plane mean-square displacements significantly greater than the experimental values.
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45

Otsuka, Takaharu. « Emerging Concepts in Nuclear Structure Based on the Shell Model ». Physics 4, no 1 (22 février 2022) : 258–85. http://dx.doi.org/10.3390/physics4010018.

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Some emerging concepts of nuclear structure are overviewed. (i) Background: the many-body quantum structure of atomic nucleus, a complex system comprising protons and neutrons (called nucleons collectively), has been studied largely based on the idea of the quantum liquid (à la Landau), where nucleons are quasiparticles moving in a (mean) potential well, with weak “residual” interactions between nucleons. The potential is rigid in general, although it can be anisotropic. While this view was a good starting point, it is time to look into kaleidoscopic aspects of the nuclear structure brought in by underlying dynamics and nuclear forces. (ii) Methods: exotic features as well as classical issues are investigated from fresh viewpoints based on the shell model and nucleon–nucleon interactions. The 70-year progress of the shell–model approach, including effective nucleon–nucleon interactions, enables us to do this. (iii) Results: we go beyond the picture of the solid potential well by activating the monopole interactions of the nuclear forces. This produces notable consequences in key features such as the shell/magic structure, the shape deformation, the dripline, etc. These consequences are understood with emerging concepts such as shell evolution (including type-II), T-plot, self-organization (for collective bands), triaxial-shape dominance, new dripline mechanism, etc. The resulting predictions and analyses agree with experiment. (iv) Conclusion: atomic nuclei are surprisingly richer objects than initially thought.
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46

Tarasov, V. P., V. I. Privalov, Yu A. Buslaev et U. Eichhoff. « 79,81Br and 133Cs Nuclei Quadrupole Interactions and Phase Transitions in Crystalline Caesium Perbromate ». Zeitschrift für Naturforschung B 45, no 7 (1 juillet 1990) : 1005–9. http://dx.doi.org/10.1515/znb-1990-0716.

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NMR experiments in solid caesium perbromate have recently been performed at magnetic fields of 1.88 T and 7.04 T together with spectral simulations for 79Br, 81Br and 133Cs in solid caesium perbromate. The line shapes are dominated by quadrupole effects. For bromine the quadrupole asymmetry parameter [η] is observed to be zero at all temperatures while the quadrupole coupling constant (CQ) as a function of temperature shows two approximately linear regions on either side of a non-linear region between 200 K and 260 K where an extended orientational phase transition occurs. 133Cs shows an increase of CQ and a decrease of η with increasing temperature. This behaviour may be associated with an anisotropic change of the “a” lattice parameter.
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47

Minamisono, T., K. Matsuta, K. Minamisono, S. Kudo, M. Ogura, S. Fukuda, K. Sato et al. « Quadrupole Moments of the 40Ca Core Plus One Nucleon Nuclei 41Sc and 41Ca ». Zeitschrift für Naturforschung A 57, no 6-7 (1 juillet 2002) : 595–98. http://dx.doi.org/10.1515/zna-2002-6-755.

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The electric-field-gradient (EFG) and anisotropic chemical shift of 45Sc(Iπ = 7/2- , stable) in TiO2 crystal were determined by detecting the FT-NMR of 45Sc(0.5 atm% of Ti in TiO2) doped in TiO2 crystal at a high field of 7.0 T and 9.4 T. Using the EFG, an old β-NQR spectrum of 41Sc was reanalyzed to obtain (41Sc)/ which was combined with the renewed (45Sc) = -(23.6 0.2) fm2 to obtain (41Sc; Iπ= 7/2- , T1/2 = 0.596 s) = (15.6±0.3) fm2. Also the atomic EFG in Ca was recalculated, using a finite-element multi configuration Hartree-Fock method to renew Q(43Ca). Finally using the known hyperfine constants of 41Ca, the (41Ca) value has been renewed
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48

Park, Sang Yeup, Jun Ho Song et Young Jin Cho. « Effect of Grain Orientation on the Abnormal Grain Growth with Magetoplumbite Crystal Structure ». Materials Science Forum 558-559 (octobre 2007) : 1265–70. http://dx.doi.org/10.4028/www.scientific.net/msf.558-559.1265.

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The nucleation and growth behavior of magentoplombite has been observed during the abnormal grain growth in the presence of liquid phase. Abnormal grain growth was explained in terms of grain orientation due to liquid phase. It has been observed that the nuclei formation for abnormal grain growth was driven by the capillary force due to the liquid phase. Because magnetoplumbite crystal structure has an anisotropic crystal nature, abnormal grain growth with faceted grain shape was observed depending on its chemical composition. The formation of nuclei and particle orientation was important for the occurrence of abnormal grain growth.
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49

Kuhn, H., D. I. Cherny, V. V. Demidov et M. D. Frank-Kamenetskii. « Inducing and modulating anisotropic DNA bends by pseudocomplementary peptide nucleic acids ». Proceedings of the National Academy of Sciences 101, no 20 (10 mai 2004) : 7548–53. http://dx.doi.org/10.1073/pnas.0308756101.

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50

L’vov, Pavel E., et Renat T. Sibatov. « Phase-field model of grain boundary diffusion in nanocrystalline solids : Anisotropic fluctuations, anomalous diffusion, and precipitation ». Journal of Applied Physics 132, no 12 (28 septembre 2022) : 124304. http://dx.doi.org/10.1063/5.0101489.

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The anisotropic phase-filed model of grain boundary diffusion and precipitation of solute in nanocrystalline solids has been developed. In this model, the Cahn–Hilliard equation is generalized for the anisotropic phase-field diffusion of solute and anisotropic compositional fluctuations. It is found that dynamics of solute concentration profile demonstrates the anomalous diffusion behavior with scaling parameters depending on the mobility ratio and microstructure of a solid solution. It is noteworthy that the increase in source concentration can slow down the concentration front propagation due to uphill diffusion or formation of a new phase. Parameters of grain boundary diffusion control the precipitation dynamics. In particular, a decrease in transverse diffusion coefficient is responsible for longer incubation time, and lower rates of nucleation and nuclei growth in comparison with the case of isotropic solute transport near grain boundaries. Transport properties of boundary and bulk are responsible for the formation of the bimodal size distribution function of second phase particles and specific kinetics of average radius and number density.
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