235 research outputs found
On the Formation of Boxy and Disky Elliptical Galaxies
The origin of boxy and disky elliptical galaxies is investigated. The results
of two collisionless N-body simulations of spiral-spiral mergers with mass
ratios of 1:1 and 3:1 are discussed and the projected properties of the merger
remnants are investigated. It is shown that the equal-mass merger leads to an
anisotropic, slowly rotating system with preferentially boxy isophotes and
significant minor axis rotation. The unequal-mass merger results in the
formation of a rotationally supported elliptical with disky isophotes and small
minor axis rotation. The observed scatter in the kinematical and isophotal
properties of both classes of elliptical galaxies can be explained by
projection effects.Comment: 12 pages, incl. 5 figures, accepted by ApJ Letter
E-Mail Tracking in Online Marketing - Methods, Detection, and Usage
E-Mail tracking uses personalized links and pictures for gathering information on user behavior, for example, where, when, on what kind of device, and how often an e-mail has been read. This information can be very useful for marketing purposes. On the other hand, privacy and security requirements of customers could be violated by tracking. This paper examines how e-mail tracking works, how it can be detected automatically, and to what extent it is used in German e-commerce. We develop a detection model and software tool in order to collect and analyze more than 600 newsletter e-mails from companies of several different industries. The results show that the usage of e-mail tracking in Germany is prevalent but also varies depending on the industry
Kinematic Structure of Merger Remnants
We use numerical simulations to study the kinematic structure of remnants
formed from mergers of equal-mass disk galaxies. In particular, we show that
remnants of dissipational mergers, which include the radiative cooling of gas,
star formation, feedback from supernovae, and the growth of supermassive black
holes, are smaller, rounder, have, on average, a larger central velocity
dispersion, and show significant rotation compared to remnants of
dissipationless mergers. The increased rotation speed of dissipational remnants
owes its origin to star formation that occurs in the central regions during the
galaxy merger. We have further quantified the anisotropy, three-dimensional
shape, minor axis rotation, and isophotal shape of each merger remnant, finding
that dissipational remnants are more isotropic, closer to oblate, have the
majority of their rotation along their major axis, and are more disky than
dissipationless remnants. Individual remnants display a wide variety of
kinematic properties. A large fraction of the dissipational remnants are oblate
isotropic rotators. Many dissipational, and all of the dissipationless, are
slowly rotating and anisotropic. The remnants of gas-rich major mergers can
well-reproduce the observed distribution of projected ellipticities, rotation
parameter (V/\sigma)*, kinematic misalignments, Psi, and isophotal shapes. The
dissipationless remnants are a poor match to this data. Our results support the
merger hypothesis for the origin of low-luminosity elliptical galaxies provided
that the progenitor disks are sufficiently gas-rich, however our remnants are a
poor match to the bright ellipticals that are slowly rotating and uniformly
boxy.Comment: 22 pages, 17 figures, accepted to Ap
04301 Abstracts Collection -- Cache-Oblivious and Cache-Aware Algorithms
The Dagstuhl Seminar 04301 ``Cache-Oblivious and Cache-Aware Algorithms\u27\u27 was held
in the International Conference and Research Center (IBFI), Schloss Dagstuhl, from 18.07.2004 to 23.07.2004.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Extending in Silico Protein Target Prediction Models to Include Functional Effects.
In silico protein target deconvolution is frequently used for mechanism-of-action investigations; however existing protocols usually do not predict compound functional effects, such as activation or inhibition, upon binding to their protein counterparts. This study is hence concerned with including functional effects in target prediction. To this end, we assimilated a bioactivity training set for 332 targets, comprising 817,239 active data points with unknown functional effect (binding data) and 20,761,260 inactive compounds, along with 226,045 activating and 1,032,439 inhibiting data points from functional screens. Chemical space analysis of the data first showed some separation between compound sets (binding and inhibiting compounds were more similar to each other than both binding and activating or activating and inhibiting compounds), providing a rationale for implementing functional prediction models. We employed three different architectures to predict functional response, ranging from simplistic random forest models ('Arch1') to cascaded models which use separate binding and functional effect classification steps ('Arch2' and 'Arch3'), differing in the way training sets were generated. Fivefold stratified cross-validation outlined cascading predictions provides superior precision and recall based on an internal test set. We next prospectively validated the architectures using a temporal set of 153,467 of in-house data points (after a 4-month interim from initial data extraction). Results outlined Arch3 performed with the highest target class averaged precision and recall scores of 71% and 53%, which we attribute to the use of inactive background sets. Distance-based applicability domain (AD) analysis outlined that Arch3 provides superior extrapolation into novel areas of chemical space, and thus based on the results presented here, propose as the most suitable architecture for the functional effect prediction of small molecules. We finally conclude including functional effects could provide vital insight in future studies, to annotate cases of unanticipated functional changeover, as outlined by our CHRM1 case study.LM thanks the Biotechnology and Biological Sciences Research Council (BBSRC) (BB/K011804/1); and AstraZeneca, grant number RG75821
Quasi-Resonant Theory of Tidal Interactions
When a spinning system experiences a transient gravitational encounter with
an external perturber, a quasi-resonance occurs if the spin frequency of the
victim matches the peak orbital frequency of the perturber. Such encounters are
responsible for the formation of long tails and bridges of stars during galaxy
collisions. For high-speed encounters, the resulting velocity perturbations can
be described within the impulse approximation. The traditional impulse
approximation, however, does not distinguish between prograde and retrograde
encounters, and therefore completely misses the resonant response. Here, using
perturbation theory, we compute the effects of quasi-resonant phenomena on
stars orbiting within a disk. Explicit expressions are derived for the velocity
and energy change to the stars induced by tidal forces from an external
gravitational perturber passing either on a straight line or parabolic orbit.
Comparisons with numerical restricted three-body calculations illustrate the
applicability of our analysis.Comment: 22 pages, 13 figures, ApJ submitted, numerical routines for
evaluation of special functions and analytical results are provided upon
reques
The imprint of dissipation on the shapes of merger remnant LOSVDs
The properties of elliptical galaxies are broadly consistent with simulated
remnants of gas-rich mergers between spirals, motivating more detailed studies
of the imprint of this formation mechanism on the remnant distribution
function. Gas has a strong impact on the non-Gaussian shapes of the
line-of-sight velocity distributions (LOSVDs) of the merger remnant, owing to
the embedded disk that forms out of the gas that retains its angular momentum
during the merger, and the strong central mass concentration from the gas that
falls to the center. The deviations from Gaussianity are parametrized by the
Gauss-Hermite moments h_3 and h_4, which are related to the skewness and
kurtosis of the LOSVDs. We quantify the dependence of the (h_3,h_4)-v/sigma
relations on the initial gas fraction of the progenitor disks in 1:1 mergers,
using Gadget-2 simulations including star formation, radiative cooling, and
feedback from supernovae and AGN. For gas fractions f_gas < ~15% the overall
correlation between h_3 and v/sigma is weak, consisting of a flat negatively
correlated component arising from edge-on viewing angles plus a steep
positively correlated part from face-on projections. The spread in v/sigma
values decreases toward high positive h_4, and there is a trend toward lower
h_4 as the gas fraction increases from 0 to 15%. For f_gas > ~20% the (h_3,4)-
v/sigma distributions look quite different - there is a tight negative h_3-
v/sigma correlation, and a wide spread in v/sigma values at all h_4, in better
agreement with observations. Re-mergers of the high-f_gas remnants (dry
mergers) produce slowly rotating systems with nearly Gaussian LOSVDs. We
explain all of these trends in terms of the underlying orbit structure of the
remnants, as molded by their dissipative formation histories.Comment: ApJ accepted - added some references and background on previous
studies. 9 pages, 4 figure
Ropiness in Bread—A Re-Emerging Spoilage Phenomenon
As bread is a very important staple food, its spoilage threatens global food security. Ropy bread spoilage manifests in sticky and stringy degradation of the crumb, slime formation, discoloration, and an odor reminiscent of rotting fruit. Increasing consumer demand for preservative-free products and global warming may increase the occurrence of ropy spoilage. Bacillus amyloliquefaciens, B. subtilis, B. licheniformis, the B. cereus group, B. pumilus, B. sonorensis, Cytobacillus firmus, Niallia circulans, Paenibacillus polymyxa, and Priestia megaterium were reported to cause ropiness in bread. Process hygiene does not prevent ropy spoilage, as contamination of flour with these Bacillus species is unavoidable due to their occurrence as a part of the endophytic commensal microbiota of wheat and the formation of heat-stable endospores that are not inactivated during processing, baking, or storage. To date, the underlying mechanisms behind ropy bread spoilage remain unclear, high-throughput screening tools to identify rope-forming bacteria are missing, and only a limited number of strategies to reduce rope spoilage were described. This review provides a current overview on (i) routes of entry of Bacillus endospores into bread, (ii) bacterial species implicated in rope spoilage, (iii) factors influencing rope development, and (iv) methods used to assess bacterial rope-forming potential. Finally, we pinpoint key gaps in knowledge and related challenges, as well as future research questions
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