88 research outputs found
Characterization and Minimization of Background Processes in the KATRIN Main Spectrometer
This thesis summarizes work performed in the context of the identification, characterization, and minimization of background sources in the large-scale main spectrometer of the Karlsruhe Tritium Neutrino (KATRIN) experiment. These works are of crucial importance to reach the nominal background level of 10 mcps which is an essential prerequisite for KATRIN to assess the absolute mass scale of neutrinos with an unsurpassed sensitivity of 200 meV (90% C.L.)
Large-angle scattered light measurements for quantum-noise filter cavity design studies
Optical loss from scattered light could limit the performance of
quantum-noise filter cavities being considered for an upgrade to the Advanced
LIGO gravitational-wave detectors. This paper describes imaging scatterometer
measurements of the large-angle scattered light from two high-quality sample
optics, a high reflector and a beam splitter. These optics are each
superpolished fused silica substrates with silica:tantala dielectric coatings.
They represent the current state-of-the art optical technology for use in
filter cavities. We present angle-resolved scatter values and integrate these
to estimate the total scatter over the measured angles. We find that the total
integrated light scattered into larger angles can be as small as 4 ppm.Comment: 11 pages, 9 figure
Cold Feedback in Cooling-Flow Galaxy Clusters
We put forward an alternative view to the Bondi-driven feedback between
heating and cooling of the intra-cluster medium (ICM) in cooling flow galaxies
and clusters. We adopt the popular view that the heating is due to an active
galactic nucleus (AGN), i.e. a central black hole accreting mass and launching
jets and/or winds. We propose that the feedback occurs with the entire cool
inner region (5-30 kpc). A moderate cooling flow does exist here, and
non-linear over-dense blobs of gas cool fast and are removed from the ICM
before experiencing the next major AGN heating event. Some of these blobs may
not accrete on the central black hole, but may form stars and cold molecular
clouds. We discuss the conditions under which the dense blobs may cool to low
temperatures and feed the black hole.Comment: 6 pages, no figures, to appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
A diffuse bubble-like radio-halo source MRC 0116+111: imprint of AGN feedback in a low-mass cluster of galaxies
We present detailed observations of MRC 0116+111, revealing a luminous, mini
radio-halo of ~240 kpc diameter located at the centre of a cluster of galaxies
at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA radio
observations reveal a highly unusual radio source: showing a pair of giant
(~100 kpc diameter) bubble-like diffuse structures, that are about three times
larger than the analogous extended radio emission observed in M87 - the
dominant central radio galaxy in the Virgo Cluster. However, in MRC 0116+111 we
do not detect any ongoing Active Galactic Nucleus (AGN) activity, such as a
compact core or active radio jets feeding the plasma bubbles. The radio
emitting relativistic particles and magnetic fields were probably seeded in the
past by a pair of radio-jets originating in the AGN of the central cD galaxy.
The extremely steep high-frequency radio spectrum of the north-western bubble,
located ~100 kpc from cluster centre, indicates radiation losses, possibly
because having detached, it is rising buoyantly and moving away into the
putative hot intra-cluster medium. The other bubble, closer to the cluster
centre, shows signs of ongoing particle re-acceleration. We estimate that the
radio jets which inflated these two bubbles might have also fed enough energy
into the intra-cluster medium to create an enormous system of cavities and
shock fronts, and to drive a massive outflow from the AGN, which could
counter-balance and even quench a cooling flow. Therefore, this source presents
an excellent opportunity to understand the energetics and the dynamical
evolution of radio-jet inflated plasma bubbles in the hot cluster atmosphere.Comment: 15 pages, 8 figures. Accepted for publication in MNRA
Ammonia Inhibition of Anaerobic Volatile Fatty Acid Degrading Microbial Communities
Ammonia inhibition is an important reason for reactor failures and economic losses in anaerobic digestion. Its impact on acetic acid degradation is well-studied, while its effect on propionic and butyric acid degradation has received little attention and is consequently not considered in the Anaerobic Digestion Model No. 1 (ADM1). To compare ammonia inhibition of the degradation of these three volatile fatty acids (VFAs), we fed a mixture of them as sole carbon source to three continuous stirred tank reactors (CSTRs) and increased ammonium bicarbonate concentrations in the influent from 52 to 277 mM. The use of this synthetic substrate allowed for the determination of degradation efficiencies for the individual acids. While butyric acid degradation was hardly affected by the increase of ammonia concentration, propionic acid degradation turned out to be even more inhibited than acetic acid degradation with degradation efficiencies dropping to 31 and 65% for propionic and acetic acid, respectively. The inhibited reactors acclimatized and approximated pre-disturbance degradation efficiencies toward the end of the experiment, which was accompanied by strong microbial community shifts, as observed by amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism (T-RFLP) of mcrA genes. The acetoclastic methanogen Methanosaeta was completely replaced by Methanosarcina. The propionic acid degrading genus Syntrophobacter was replaced by yet unknown propionic acid degraders. The butyric acid degrading genus Syntrophomonas and hydrogenotrophic Methanomicrobiaceae were hardly affected. We hypothesized that the ammonia sensitivity of the initially dominating taxa Methanosaeta and Syntrophobacter led to a stronger inhibition of the acetic and propionic acid degradation compared to butyric acid degradation and hydrogenotrophic methanogenesis, which were facilitated by the ammonia tolerant taxa Syntrophomonas and Methanomicrobiaceae. We implemented this hypothesis into a multi-taxa extension of ADM1, which was able to simulate the dynamics of both microbial community composition and VFA concentration in the experiment. It is thus plausible that the effect of ammonia on VFA degradation strongly depends on the ammonia sensitivity of the dominating taxa, for syntrophic propionate degraders as much as for acetoclastic methanogens
Kassiopeia: A Modern, Extensible C++ Particle Tracking Package
The Kassiopeia particle tracking framework is an object-oriented software
package using modern C++ techniques, written originally to meet the needs of
the KATRIN collaboration. Kassiopeia features a new algorithmic paradigm for
particle tracking simulations which targets experiments containing complex
geometries and electromagnetic fields, with high priority put on calculation
efficiency, customizability, extensibility, and ease of use for novice
programmers. To solve Kassiopeia's target physics problem the software is
capable of simulating particle trajectories governed by arbitrarily complex
differential equations of motion, continuous physics processes that may in part
be modeled as terms perturbing that equation of motion, stochastic processes
that occur in flight such as bulk scattering and decay, and stochastic surface
processes occuring at interfaces, including transmission and reflection
effects. This entire set of computations takes place against the backdrop of a
rich geometry package which serves a variety of roles, including initialization
of electromagnetic field simulations and the support of state-dependent
algorithm-swapping and behavioral changes as a particle's state evolves. Thanks
to the very general approach taken by Kassiopeia it can be used by other
experiments facing similar challenges when calculating particle trajectories in
electromagnetic fields. It is publicly available at
https://github.com/KATRIN-Experiment/Kassiopei
Determination of Microbial Maintenance in Acetogenesis and Methanogenesis by Experimental and Modeling Techniques
For biogas-producing continuous stirred tank reactors, an increase in dilution rate increases the methane production rate as long as substrate input can be converted fully. However, higher dilution rates necessitate higher specific microbial growth rates, which are assumed to have a strong impact on the apparent microbial biomass yield due to cellular maintenance. To test this, we operated two reactors at 37°C in parallel at dilution rates of 0.18 and 0.07 days-1 (hydraulic retention times of 5.5 and 14 days, doubling times of 3.9 and 9.9 days in steady state) with identical inoculum and a mixture of volatile fatty acids as sole carbon sources. We evaluated the performance of the Anaerobic Digestion Model No. 1 (ADM1), a thermodynamic black box approach (TBA), and dynamic flux balance analysis (dFBA), to describe the experimental observations. All models overestimated the impact of dilution rate on the apparent microbial biomass yield when using default parameter values. Based on our analysis, a maintenance coefficient value below 0.2 kJ per carbon mole of microbial biomass per hour should be used for the TBA, corresponding to 0.12 mmol ATP per gram dry weight per hour for dFBA, which strongly deviates from the value of 9.8 kJ Cmol h-1 that has been suggested to apply to all anaerobic microorganisms at 37°C. We hypothesized that a decrease in dilution rate might select taxa with minimized maintenance expenditure. However, no major differences in the dominating taxa between the reactors were observed based on amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism analysis of mcrA genes. Surprisingly, Methanosaeta dominated over Methanosarcina even at a dilution rate of 0.18 days-1, which contradicts previous model expectations. Furthermore, only 23–49% of the bacterial reads could be assigned to known syntrophic fatty acid oxidizers, indicating that unknown members of this functional group remain to be discovered. In conclusion, microbial maintenance was found to be much lower for acetogenesis and methanogenesis than previously assumed, likely due to the exceptionally low growth rates in anaerobic digestion. This finding might also be relevant for other microbial systems operating at similarly low growth rates
The gaseous atmosphere of M87 seen with XMM-Newton
M87 is a key object whose study can reveal the complex phenomena in cooling
cores. We use a deep XMM-Newton observation of M87 to produce detailed
temperature, pressure and entropy maps in order to analyze the physical
processes of cooling cores and of their heating mechanisms. We employed both
broad-band fitting and full spectroscopical one-temperature model analysis to
derive temperature and surface brightness maps, from which the
pseudo-deprojected entropy and pressure were calculated. We discuss possible
physical interpretations of small deviations from radial and elliptical
symmetry in these maps. The most prominent features observed are the E and SW
X-ray arms that coincide with powerful radio lobes, a weak shock at a radius of
3', an overall ellipticity in the pressure map and a NW/SE asymmetry in the
entropy map which we associate with the motion of the galaxy towards the NW.
For the first time we find evidence that cold, metal-rich gas is being
transported out of the center, possibly through bubble-induced mixing. Several
edges in the abundance map indicate an oscillation of the galaxy along the
NW/SE direction. Furthermore, the radio lobes appear to rise along the short
axis of the elliptical pressure distribution, following the steepest gradient
of the gravitational potential, and seem to contain a nonthermal pressure
component.Comment: 12 pages, 13 figures, A&A in press; minor modifications of text and
layout, added one reference to RGS data analysis result
On the deep minimum state in the Seyfert galaxy MCG-6-30-15
(abridged) We present a detailed spectral analysis of the first observation
of the Seyfert 1 galaxy MCG-6-30-15 by the European Photon Imaging Camera on
board the XMM-Newton observatory, together with contemporaneous data from the
Proportional Counter Array on the Rossi X-ray Timing Explorer. Confirming our
previously published result, we find that the presence of extremely broadened
reflection features from an ionized relativistic accretion disk is required
even when one employs the latest X-ray reflection models and includes the
effect of complex absorption. The extremely broadened reflection features are
also present if the primary continuum is modeled with a thermal Comptonisation
spectrum rather than a simple power-law continuum. With this fact established,
we examine these data using a relativistic smearing function corresponding to a
``generalized thin accretion disk'' model. We find strong evidence for torquing
of the central parts of the accretion disk (presumably through magnetic
interactions with the plunging region of the disk and/or the rotating black
hole itself). We also perform a study of spectral variability within our
observation. We find that the disk reflection features maintain roughly a
constant equivalent width with respect to the observed continuum, as predicted
by simple reflection models. Taken together with other studies of MCG-6-30-15
that find disk features to possess constant intensity at higher flux states, we
suggest that the flux of disk features undergoes a saturation once the source
emerges from a Deep Minimum state.Comment: 16 pages, accepted for publication in MNRA
The Fueling and Evolution of AGN: Internal and External Triggers
In this chapter, I review the fueling and evolution of active galactic nuclei
(AGN) under the influence of internal and external triggers, namely intrinsic
properties of host galaxies (morphological or Hubble type, color, presence of
bars and other non-axisymmetric features, etc) and external factors such as
environment and interactions. The most daunting challenge in fueling AGN is
arguably the angular momentum problem as even matter located at a radius of a
few hundred pc must lose more than 99.99 % of its specific angular momentum
before it is fit for consumption by a BH. I review mass accretion rates,
angular momentum requirements, the effectiveness of different fueling
mechanisms, and the growth and mass density of black BHs at different epochs. I
discuss connections between the nuclear and larger-scale properties of AGN,
both locally and at intermediate redshifts, outlining some recent results from
the GEMS and GOODS HST surveys.Comment: Invited Review Chapter to appear in LNP Volume on "AGN Physics on All
Scales", Chapter 6, in press. 40 pages, 12 figures. Typo in Eq 5 correcte
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