70 research outputs found
The abundances of hydrocarbon functional groups in the interstellar medium inferred from laboratory spectra of hydrogenated and methylated polycyclic aromatic hydrocarbons
Infrared (IR) absorption spectra of individual polycyclic aromatic
hydrocarbons (PAHs) containing methyl (-CH3), methylene (>CH2), or diamond-like
*CH groups and IR spectra of mixtures of methylated and hydrogenated PAHs
prepared by gas phase condensation were measured at room temperature (as grains
in pellets) and at low temperature (isolated in Ne matrices). In addition, the
PAH blends were subjected to an in-depth molecular structure analysis by means
of high-performance liquid chromatography, nuclear magnetic resonance
spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry. Supported by calculations at the density functional theory
level, the laboratory results were applied to analyze in detail the aliphatic
absorption complex of the diffuse interstellar medium at 3.4 mu-m and to
determine the abundances of hydrocarbon functional groups. Assuming that the
PAHs are mainly locked in grains, aliphatic CHx groups (x = 1,2,3) would
contribute approximately in equal quantities to the 3.4 mu-m feature (N_{CHx} /
N_{H} approx 10^{-5} - 2 * 10^{-5}). The abundances, however, may be two to
four times lower if a major contribution to the 3.4 mu-m feature comes from
molecules in the gas phase. Aromatic =CH groups seem to be almost absent from
some lines of sight, but can be nearly as abundant as each of the aliphatic
components in other directions (N_{=CH} / N_{H} < 2 * 10^{-5}; upper value for
grains). Due to comparatively low binding energies, astronomical IR emission
sources do not display such heavy excess hydrogenation. At best, especially in
proto-planetary nebulae, >CH2 groups bound to aromatic molecules, i.e., excess
hydrogens on the molecular periphery only, can survive the presence of a nearby
star.Comment: 34 pages, 19 figures, ApJS, 208, 2
Is general relativity `essentially understood' ?
The content of Einstein's theory of gravitation is encoded in the properties
of the solutions to his field equations. There has been obtained a wealth of
information about these solutions in the ninety years the theory has been
around. It led to the prediction and the observation of physical phenomena
which confirm the important role of general relativity in physics. The
understanding of the domain of highly dynamical, strong field configurations
is, however, still quite limited. The gravitational wave experiments are likely
to provide soon observational data on phenomena which are not accessible by
other means. Further theoretical progress will require, however, new methods
for the analysis and the numerical calculation of the solutions to Einstein's
field equations on large scales and under general assumptions. We discuss some
of the problems involved, describe the status of the field and recent results,
and point out some open problems.Comment: Extended version of a talk which was to be delivered at the DPG
Fruehjahrstagung in Berlin, 5 March 200
On "many black hole" space-times
We analyze the horizon structure of families of space times obtained by
evolving initial data sets containing apparent horizons with several connected
components. We show that under certain smallness conditions the outermost
apparent horizons will also have several connected components. We further show
that, again under a smallness condition, the maximal globally hyperbolic
development of the many black hole initial data constructed by Chrusciel and
Delay, or of hyperboloidal data of Isenberg, Mazzeo and Pollack, will have an
event horizon, the intersection of which with the initial data hypersurface is
not connected. This justifies the "many black hole" character of those
space-times.Comment: several graphic file
Conformal Einstein evolution
We discuss various properties of the conformal field equations and their consequences for the asymptotic structure of space-times
Towards the classification of static vacuum spacetimes with negative cosmological constant
We present a systematic study of static solutions of the vacuum Einstein
equations with negative cosmological constant which asymptotically approach the
generalized Kottler (``Schwarzschild--anti-de Sitter'') solution, within
(mainly) a conformal framework. We show connectedness of conformal infinity for
appropriately regular such space-times. We give an explicit expression for the
Hamiltonian mass of the (not necessarily static) metrics within the class
considered; in the static case we show that they have a finite and well defined
Hawking mass. We prove inequalities relating the mass and the horizon area of
the (static) metrics considered to those of appropriate reference generalized
Kottler metrics. Those inequalities yield an inequality which is opposite to
the conjectured generalized Penrose inequality. They can thus be used to prove
a uniqueness theorem for the generalized Kottler black holes if the generalized
Penrose inequality can be established.Comment: the discussion of our results includes now some solutions of Horowitz
and Myers; typos corrected here and there; a shortened version of this
version will appear in Journal of Mathematical Physic
Helium nanodroplet isolation ro-vibrational spectroscopy: methods and recent results
In this article, recent developments in HElium NanoDroplet Isolation (HENDI)
spectroscopy are reviewed, with an emphasis on the infrared region of the
spectrum. Topics discussed include experimental details, comparison of
radiation sources, symmetry issues of the helium solvation structure, sources
of line broadening, changes in spectroscopic constants upon solvation, and
applications including formation of novel chemical structures.Comment: 24 pages, 8 figures, 3 tables; to be published in the Journal of
Chemical Physic
Getting the whole picture: High content screening using three-dimensional cellular model systems and whole animal assays
Phenotypic or High Content Screening (HCS) is becoming more widely used for primary screening campaigns in drug discovery. Currently the vast majority of HCS campaigns are using cell lines grown in well-established monolayer cultures (2D tissue culture). There is widespread recognition that the more biologically relevant 3D tissue culture technologies such as spheroids and organoids and even whole animal assays will eventually be run as primary HCS. Upgrading the IT infrastructure to cope with the increase in data volumes requires investments in hardware (and software) and this will be manageable. However, the main bottleneck for the effective adoption and use of 3D tissue culture and whole animal assays in HCS is anticipated to be the development of software for the analysis of 3D images. In this review we summarize the current state of the available software and how they may be applied to analyzing 3D images obtained from a HCS campaign
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