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
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
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
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
. 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-(DimethylÂamino)benzylÂidene]-2,6-dimethylÂcycloÂhexa-2,5-dienone
The title compound, C17H19NO, crystallized with two molÂecules 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
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
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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