1,810 research outputs found

    The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds

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    We use archival UV absorption-line data from HST/STIS to statistically analyse the absorption characteristics of the high-velocity clouds (HVCs) in the Galactic halo towards more than 40 extragalactic background sources. We determine absorption covering fractions of low- and intermediate ions (OI, CII, SiIII, MgII, FeII, SiIII, CIV, and SiIV) in the range fc = 0.20 - 0.70. For detailed analysis we concentrate on SiII absorption components in HVCs, for which we investigate the distribution of column densities, b-values, and radial velocities. Combining information for SiII and MgII, and using a geometrical HVC model we investigate the contribution of HVCs to the absorption cross section of strong MgII absorbers in the local Universe. We estimate that the Galactic HVCs would contribute on average ~52 % to the total strong MgII cross section of the Milky Way, if our Galaxy were to be observed from an exterior vantage point. We further estimate that the mean projected covering fraction of strong MgII absorption in the Milky Way halo and disc from an exterior vantage point is fc(sMgII) = 0.31 for a halo radius of R = 61 kpc. These numbers, together with the observed number density of strong MgII absorbers at low redshift, indicate that the contribution of infalling gas clouds (i.e., HVC analogues) in the halos of Milky Way-type galaxies to the cross section of strong MgII absorbers is <34 %. These findings are in line with the idea that outflowing gas (e.g., produced by galactic winds) in the halos of more actively star-forming galaxies dominate the absorption-cross section of strong MgII absorbers in the local Universe

    A Poincar\'e section for the general heavy rigid body

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    A general recipe is developed for the study of rigid body dynamics in terms of Poincar\'e surfaces of section. A section condition is chosen which captures every trajectory on a given energy surface. The possible topological types of the corresponding surfaces of section are determined, and their 1:1 projection to a conveniently defined torus is proposed for graphical rendering.Comment: 25 pages, 10 figure

    Magnetic-field dependence of transport in normal and Andreev billiards: a classical interpretation to the averaged quantum behavior

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    We perform a comparative study of the quantum and classical transport probabilities of low-energy quasiparticles ballistically traversing normal and Andreev two-dimensional open cavities with a Sinai-billiard shape. We focus on the dependence of the transport on the strength of an applied magnetic field BB. With increasing field strength the classical dynamics changes from mixed to regular phase space. Averaging out the quantum fluctuations, we find an excellent agreement between the quantum and classical transport coefficients in the complete range of field strengths. This allows an overall description of the non-monotonic behavior of the average magnetoconductance in terms of the corresponding classical trajectories, thus, establishing a basic tool useful in the design and analysis of experiments.Comment: 11 pages, 12 figures; minor revisions including updated inset of Fig. 4(b) and references; version as accepted for publication to Phys. Rev.

    4-[4-(Dimethyl­amino)benzyl­idene]-2,6-dimethyl­cyclo­hexa-2,5-dienone

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    The title compound, C17H19NO, crystallized with two mol­ecules per asymmetric unit. C—H⋯O hydrogen bonds lead to infinite chains along [100]. According to graph-set theory, the descriptor C 1 1(13)C 1 1(13) can be assigned

    The problem of two fixed centres: bifurcations, actions, monodromy

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    A comprehensive analysis of the Euler-Jacobi problem of motion in the field of two fixed attracting centers is given, first classically and then quantum mechanically in semiclassical approximation. The system was originally studied in the context of celestial mechanics but, starting with Pauli’s dissertation, became a model for one-electron molecules such as H+ 2 (symmetric case of equal centers) or HHe2+ (asymmetric case of different centers). The present paper deals with arbitrary relative strength of the two centers and considers separately the planar and the three-dimensional problems. All versions represent nontrivial examples of integrable dynamics and are studied here from the unifying point of view of the energy momentum mapping from phase space to the space of integration constants. The interesting objects are the critical values of this mapping, i. e., its bifurcation diagram, and their pre-images which organize the foliation of phase space into Liouville-Arnold tori. The classical analysis culminates in the explicit derivation of the action variable representation of iso-energetic surfaces. The attempt to identify a system of global actions, smoothly dependent on the integration constants wherever these are non-critical, leads to the detection of monodromy of a special kind which is here described for the first time. The classical monodromy has its counterpart in the quantum version of the two-center problem where it prevents the assignments of unique quantum numbers even though the system is separable

    Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy

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    We investigated the valence electronic structure of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both the bond type and the combination of bonding partners are shown to affect the overall electronic structure. For singly bonded particles, we observe a small impact of the bond on the electronic structure, whereas for doubly bonded particles, the connecting bond determines the electronic structure of the highest occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The experimental findings are supported by density functional theory computations at the M06-2X/cc-pVDZ level of theory.Comment: 7 pages, 7 figure
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