931 research outputs found
The Tidal Tails of 47 Tucanae
The Galactic globular cluster 47 Tucanae (47 Tuc) shows a rare increase in
its velocity dispersion profile at large radii, indicative of energetic, yet
bound, stars at large radii dominating the velocity dispersion and,
potentially, of ongoing evaporation. Escaping stars will form tidal tails, as
seen with several Galactic globular clusters, however, the tidal tails of 47
Tuc are yet to be uncovered. We model these tails of 47 Tuc using the most
accurate input data available, with the specific aim of determining their
locations, as well as the densities of the epicyclic overdensities within the
tails. The overdensities from our models show an increase of 3-4% above the
Galactic background and, therefore, should be easily detectable using matched
filtering techniques. We find that the most influential parameter with regard
to both the locations and densities of the epicyclic overdensities is the
Heliocentric distance to the cluster. Hence, uncovering these tidal features
observationally will contribute greatly to the ongoing problem of determining
the distance to 47 Tuc, tightly constraining the distance of the cluster
independent of other methods. Using our streakline method for determining the
locations of the tidal tails and their overdensities, we show how, in
principle, the shape and extent of the tidal tails of any Galactic globular
cluster can be determined without resorting to computationally expensive N-body
simulations.Comment: Original paper has 10 pages, 10 figures and 2 tables. Please note
that this now includes an erratum. Erratum has 6 pages, 8 figures and 2
tables. Ignore the exclamation marks in Section 2 of the erratum, these are
an artifact of the LaTeX class file used to produce the manuscrip
Arbeitsmarkt und Beschäftigung
The Labor Market and Employment (Handbook article).
The labor market differs from typical markets in important ways. We find job competition and collective mechanisms that set wages and working conditions. Changes in employment bring about changes in wages and prices and entail political and monetary responses. The goals of price stability and full employment cannot, usually, be attained simultaneously under the present conditions.Der Arbeitsmarkt unterscheidet sich grundlegend von anderen Märkten. Wir finden hier einen ausgeprägten Qualifikationswettbewerb und kollektive Mechanismen der Festlegung von Entlohnungs- und Arbeitsbedingungen. Beschäftigungsänderungen müssen im Zusammenhang mit Lohn- und Preisbewegungen gesehen werden. Die wirtschaftspolitischen Ziele von Vollbeschäftigung und Preisstabilität stehen bei den gegebenen Lohnsetzungsmechanismen typischerweise im Widerspruch zueinander
Strongly driven quantum pendulum of the OCS molecule
We demonstrate and analyze a strongly driven quantum pendulum in the angular
motion of stateselected and laser aligned OCS molecules. Raman-couplings during
the rising edge of a 50-picosecond laser pulse create a wave packet of pendular
states, which propagates in the confining potential formed by the
polarizability interaction between the molecule and the laser field. This
wave-packet dynamics manifests itself as pronounced oscillations in the degree
of alignment with a laser-intensity dependent period.Comment: 6 pages, 4 figure
Collisionless dynamics in Globular Clusters
Since globular clusters (GCs) are old, low-N systems their dynamics is widely
believed to be fully dominated by collisional two-body processes, and their
surface brightness profiles are fit by King models. However, for many GCs,
especially those with HST-resolved central regions, and `extra-tidal' features,
King models provide poor fits. We suggest that this is partly because
collisionless dynamics is also important and contribute to shaping the cluster
properties. We show using time-scale and length-scale arguments that except for
the very centers of clusters, collisionless dynamics should be more important
than collisional. We then fit 38 GCs analyzed by Noyola and Gebhardt (2006)
with (collisional) King and (collisionless) DARKexp models over the full
available radial range, and find that the latter provide a better fit to 29
GCs; for six of these the fit is at least ~5x better in term of rms. DARKexp
models are theoretically derived maximum entropy equilibrium states of
self-gravitating collisionless systems and have already been shown to fit the
results of dark matter N-body simulations. (We do not attempt fits with ad hoc
fitting functions.)Comment: 27 pages, 18 figures; accepted to MNRA
Emission of volatile halogenated compounds, speciation and localization of bromine and iodine in the brown algal genome model Ectocarpus siliculosus
This study explores key features of bromine and iodine metabolism in the filamentous brown alga and genomics model Ectocarpus siliculosus. Both elements are accumulated in Ectocarpus, albeit at much lower concentration factors (2-3 orders of magnitude for iodine, and < 1 order of magnitude for bromine) than e.g. in the kelp Laminaria digitata. Iodide competitively reduces the accumulation of bromide. Both iodide and bromide are accumulated in the cell wall (apoplast) of Ectocarpus, with minor amounts of bromine also detectable in the cytosol. Ectocarpus emits a range of volatile halogenated compounds, the most prominent of which by far is methyl iodide. Interestingly, biosynthesis of this compound cannot be accounted for by vanadium haloperoxidase since the latter have not been found to catalyze direct halogenation of an unactivated methyl group or hydrocarbon so a methyl halide transferase-type production mechanism is proposed
Improved spatial separation of neutral molecules
We have developed and experimentally demonstrated an improved electrostatic
deflector for the spatial separation of molecules according to their
dipole-moment-to-mass ratio. The device features a very open structure that
allows for significantly stronger electric fields as well as for stronger
deflection without molecules crashing into the device itself. We have
demonstrated its performance using the prototypical OCS molecule and we discuss
opportunities regarding improved quantum-state-selectivity for complex
molecules and the deflection of unpolar molecules.Comment: 6 figure
Dark Matter Sub-Halo Counts via Star Stream Crossings
Dark matter sub-halos create gaps in the stellar streams orbiting in the
halos of galaxies. We evaluate the sub-halo stream crossing integral with the
guidance of simulations to find that the linear rate of gap creation, R_gap, in
a typical Cold Dark Matter (CDM) galactic halo at 100 kpc is R_gap = 0.0066
M_8^-0.35 kpc^-1 Gyr^-1$, where M_8 = M/10^8 M_sun, is the minimum mass halo
that creates a visible gap. The relation can be recast entirely in terms of
observables, as R_gap= 0.059 w^-0.85 kpc^-1 Gyr^-1, for w in kpc, normalized at
100 kpc. Using published data, the density of gaps is estimated for M31's NW
stream and the Milky Way Pal 5 stream, Orphan stream, and Eastern Banded
Structure. The estimated rates of gap creation all have errors of 50% or more
due to uncertain dynamical ages and the relatively noisy stream density
measurements. The gap rate-width data are in good agreement with the CDM
predicted relation. The high density of gaps in the narrow streams require a
total halo population of 10^5 sub-halos above a minimum mass of 10^5 M_sun.Comment: ApJ accepted and copy-edite
Molecular movie of ultrafast coherent rotational dynamics of OCS
Recording molecular movies on ultrafast timescales has been a longstanding goal for unravelling detailed information about molecular dynamics. Here we present the direct experimental recording of very-high-resolution and -fidelity molecular movies over more than one-and-a-half periods of the laser-induced rotational dynamics of carbonylsulfide (OCS) molecules. Utilising the combination of single quantum-state selection and an optimised two-pulse sequence to create a tailored rotational wavepacket, an unprecedented degree of field-free alignment, 〈cos2θ2D〉 = 0.96 (〈cos2θ〉 = 0.94) is achieved, exceeding the theoretical limit for single-pulse alignment. The very rich experimentally observed quantum dynamics is fully recovered by the angular probability distribution obtained from solutions of the time-dependent Schrödinger equation with parameters refined against the experiment. The populations and phases of rotational states in the retrieved time-dependent three-dimensional wavepacket rationalises the observed very high degree of alignment
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