4,298 research outputs found
Calibration update of the COMBO-17 CDFS catalogue
We present an update to the photometric calibration of the COMBO-17 catalogue
on the Extended Chandra Deep Field South, which is now consistent with the
GaBoDS and MUSYC catalogues. As a result, photometric redshifts become slightly
more accurate, with <0.01 rms and little bias in the delta_z/(1+z) of galaxies
with R<21 and of QSOs with R<24. With increasing photon noise the rms of
galaxies reaches 0.02 for R<23 and 0.035 at R~23.5. Consequences for the
rest-frame colours of galaxies at z<1 are discussed.Comment: A&A research note, resubmitted 02 Oct 2008, 4 pages in print forma
Evaluation of two thermal neutron detection units consisting of ZnS/LiF scintillating layers with embedded WLS fibers read out with a SiPM
Two single channel detection units for thermal neutron detection are
investigated in a neutron beam. They consist of two ZnS/LiF scintillating
layers sandwiching an array of WLS fibers. The pattern of this units can be
repeated laterally and vertically in order to build up a one dimensional
position sensitive multi-channel detector with the needed sensitive surface and
with the required neutron absorption probability. The originality of this work
arises from the fact that the WLS fibers are read out with SiPMs instead of the
traditionally used PMTs or MaPMTs. The signal processing system is based on a
photon counting approach. For SiPMs with a dark count rate as high as 0.7 MHz,
a trigger efficiency of 80% is achieved together with a system background rate
lower than Hz and a dead time of 30 s. No change of
performance is observed for neutron count rates of up to 3.6 kHz.Comment: Submitted to Nuclear Instruments and Methods
Modeling and Simulation of Temperature Profiles in a Reactive Distillation System for Esterification of Acetic Anhydride with Methanol
This paper pertains to an experimental and theoretical study of simulation of temperature profiles in a one- stage adiabatic batch distillation/reactor for the production of methyl acetate and acetic acid from the esterification of acetic anhydride with methanol. Basically it deals with the development of a mathematical model for temperature predictions in the reactor. The reaction kinetics of the process was modeled using information obtained from experimental temperature –time data during the esterification processes. The simulation results were then compared with the experimental data. The maximum deviation of the model –predicted temperature form the corresponding experimentally measured temperature was less than 4% which is quite within the acceptable deviation range of experimental results.. Keywords: Modeling, Simulation, Reactive distillation, Temperature, Esterification, Acetic anhydride, Methano
Monte Carlo simulations of fluid vesicles with in plane orientational ordering
We present a method for simulating fluid vesicles with in-plane orientational
ordering. The method involves computation of local curvature tensor and
parallel transport of the orientational field on a randomly triangulated
surface. It is shown that the model reproduces the known equilibrium
conformation of fluid membranes and work well for a large range of bending
rigidities. Introduction of nematic ordering leads to stiffening of the
membrane. Nematic ordering can also result in anisotropic rigidity on the
surface leading to formation of membrane tubes.Comment: 11 Pages, 12 Figures, To appear in Phys. Rev.
A novel transcriptome subtraction method for the detection of differentially expressed genes in highly complex eukaryotes
We have designed a novel transcriptome subtraction method for the genome-scale analysis of differential gene expression in highly complex eukaryotes, in which suppression subtractive hybridization (SSH) is performed first to enrich the target and, after exchange of adapters, negative subtraction chain (NSC) is then used to eliminate the remaining background. NSC evolved from differential subtraction chain (DSC). We designed novel adapters which make the subtraction system more robust. SSH and NSC were then combined to successfully detect differentially expressed genes in Solanum. The combined technique improves qualitatively upon SSH, the only commercially available transcriptome subtraction system, by detecting target genes in the middle abundance class, to which most differentially expressed genes in highly complex eukaryotes are expected to belong. The main advantage of the combined technique with SSH/NSC is its ability to isolate differentially expressed genes quickly and cost-efficiently from non-standard models, for those microarrays are unavailable
Cosmic shear analysis of archival HST/ACS data: I. Comparison of early ACS pure parallel data to the HST/GEMS Survey
This is the first paper of a series describing our measurement of weak
lensing by large-scale structure using archival observations from the Advanced
Camera for Surveys (ACS) on board the Hubble Space Telescope (HST).
In this work we present results from a pilot study testing the capabilities
of the ACS for cosmic shear measurements with early parallel observations and
presenting a re-analysis of HST/ACS data from the GEMS survey and the GOODS
observations of the Chandra Deep Field South (CDFS). We describe our new
correction scheme for the time-dependent ACS PSF based on observations of
stellar fields. This is currently the only technique which takes the full time
variation of the PSF between individual ACS exposures into account. We estimate
that our PSF correction scheme reduces the systematic contribution to the shear
correlation functions due to PSF distortions to < 2*10^{-6} for galaxy fields
containing at least 10 stars. We perform a number of diagnostic tests
indicating that the remaining level of systematics is consistent with zero for
the GEMS and GOODS data confirming the success of our PSF correction scheme.
For the parallel data we detect a low level of remaining systematics which we
interpret to be caused by a lack of sufficient dithering of the data.
Combining the shear estimate of the GEMS and GOODS observations using 96
galaxies arcmin^{-2} with the photometric redshift catalogue of the GOODS-MUSIC
sample, we determine a local single field estimate for the mass power spectrum
normalisation sigma_{8,CDFS}=0.52^{+0.11}_{-0.15} (stat) +/- 0.07 (sys) (68%
confidence assuming Gaussian cosmic variance) at fixed Omega_m=0.3 for a
LambdaCDM cosmology. We interpret this exceptionally low estimate to be due to
a local under-density of the foreground structures in the CDFS.Comment: Version accepted for publication in Astronomy & Astrophysics with 28
pages, 25 figures. A version with full resolution figures can be downloaded
from http://www.astro.uni-bonn.de/~schrabba/papers/cosmic_shear_acs1_v2.pd
Uncovering the (un-)occupied electronic structure of a buried hybrid interface
The energy level alignment at organic/inorganic (o/i) semiconductor
interfaces is crucial for any light-emitting or -harvesting functionality.
Essential is the access to both occupied and unoccupied electronic states
directly at the interface, which is often deeply buried underneath thick
organic films and challenging to characterize. We use several complementary
experimental techniques to determine the electronic structure of
p-quinquephenyl pyridine (5P-Py) adsorbed on ZnO(10-10). The parent anchoring
group, pyridine, significantly lowers the work function by up to 2.9 eV and
causes an occupied in-gap state (IGS) directly below the Fermi level
. Adsorption of upright-standing 5P-Py also leads to a strong work
function reduction of up to 2.1 eV and to a similar IGS. The latter is then
used as an initial state for the transient population of three normally
unoccupied molecular levels through optical excitation and, due to its
localization right at the o/i interface, provides interfacial sensitivity, even
for thick 5P-Py films. We observe two final states above the vacuum level and
one bound state at around 2 eV above , which we attribute to the
5P-Py LUMO. By the separate study of anchoring group and organic dye combined
with the exploitation of the occupied IGS for selective interfacial
photoexcitation this work provides a new pathway for characterizing the
electronic structure at buried o/i interfaces
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