3,255 research outputs found
The age of data-driven proteomics : how machine learning enables novel workflows
A lot of energy in the field of proteomics is dedicated to the application of challenging experimental workflows, which include metaproteomics, proteogenomics, data independent acquisition (DIA), non-specific proteolysis, immunopeptidomics, and open modification searches. These workflows are all challenging because of ambiguity in the identification stage; they either expand the search space and thus increase the ambiguity of identifications, or, in the case of DIA, they generate data that is inherently more ambiguous. In this context, machine learning-based predictive models are now generating considerable excitement in the field of proteomics because these predictive models hold great potential to drastically reduce the ambiguity in the identification process of the above-mentioned workflows. Indeed, the field has already produced classical machine learning and deep learning models to predict almost every aspect of a liquid chromatography-mass spectrometry (LC-MS) experiment. Yet despite all the excitement, thorough integration of predictive models in these challenging LC-MS workflows is still limited, and further improvements to the modeling and validation procedures can still be made. In this viewpoint we therefore point out highly promising recent machine learning developments in proteomics, alongside some of the remaining challenges
Super-massive binary black holes and emission lines in active galactic nuclei
The broad emission spectral lines emitted from AGNs are our main probe of the
geometry and physics of the broad line region (BLR) close to the SMBH. There is
a group of AGNs that emits very broad and complex line profiles, showing two
displaced peaks, one blueshifted and one redshifted from the systemic velocity
defined by the narrow lines, or a single such peak. It has been proposed that
such line shapes could indicate a supermassive binary black hole (SMB) system.
We discuss here how the presence of an SMB will affect the BLRs of AGNs and
what the observational consequences might be.
We review previous claims of SMBs based on broad line profiles and find that
they may have non-SMB explanations as a consequence of a complex BLR structure.
Because of these effects it is very hard to put limits on the number of SMBs
from broad line profiles. It is still possible, however, that unusual broad
line profiles in combination with other observational effects (line ratios,
quasi-periodical oscillations, spectropolarimetry, etc.) could be used for SMBs
detection.
Some narrow lines (e.g., [O\,III]) in some AGNs show a double-peaked profile.
Such profiles can be caused by streams in the Narrow Line Region (NLR), but may
also indicate the presence of a kilo-parsec scale mergers. A few objects
indicated as double-peaked narrow line emitters are confirmed as kpc-scale
margers, but double-peaked narrow line profiles are mostly caused by the
complex NLR geometry.
We briefly discuss the expected line profile of broad Fe K that
probably originated in the accretion disk(s) around SMBs.
Finally we consider rare configurations where a SMB system might be
gravitationally lensed by a foreground galaxy, and discuss the expected line
profiles in these systems.Comment: The work was presented as an invited talk at special workshop
"Spectral lines and super-massive black holes" held on June 10, 2011 as a
part of activity within the frame of COST action 0905 "Black holes in a
violent universe" and as a part of the 8th Serbian Conference on Spectral
Line Shapes in Astrophysics.Sent to New Astronomy Review as a review pape
The Outer Disks of Early-Type Galaxies. I. Surface-Brightness Profiles of Barred Galaxies
We present a study of 66 barred, early-type (S0-Sb) disk galaxies, focused on
the disk surface brightness profile outside the bar region and the nature of
Freeman Type I and II profiles, their origins, and their possible relation to
disk truncations. This paper discusses the data and their reduction, outlines
our classification system, and presents -band profiles and classifications
for all galaxies in the sample.
The profiles are derived from a variety of different sources, including the
Sloan Digital Sky Survey (Data Release 5). For about half of the galaxies, we
have profiles derived from more than one telescope; this allows us to check the
stability and repeatability of our profile extraction and classification. The
vast majority of the profiles are reliable down to levels of mu_R ~ 27 mag
arcsec^-2; in exceptional cases, we can trace profiles down to mu_R > 28. We
can typically follow disk profiles out to at least 1.5 times the traditional
optical radius R_25; for some galaxies, we find light extending to ~ 3 R_25.
We classify the profiles into three main groups: Type I (single-exponential),
Type II (down-bending), and Type III (up-bending). The frequencies of these
types are approximately 27%, 42%, and 24%, respectively, plus another 6% which
are combinations of Types II and III. We further classify Type II profiles by
where the break falls in relation to the bar length, and in terms of the
postulated mechanisms for breaks at large radii ("classical trunction" of star
formation versus the influence of the Outer Lindblad Resonance of the bar). We
also classify the Type III profiles by the probable morphology of the outer
light (disk or spheroid). Illustrations are given for all cases. (Abridged)Comment: 41 pages, 26 PDF figures. To appear in the Astronomical Journal.
Version with full-resolution figures available at
http://www.mpe.mpg.de/~erwin/research
Triangulation of gravitational wave sources with a network of detectors
There is significant benefit to be gained by pursuing multi-messenger
astronomy with gravitational wave and electromagnetic observations. In order to
undertake electromagnetic follow-ups of gravitational wave signals, it will be
necessary to accurately localize them in the sky. Since gravitational wave
detectors are not inherently pointing instruments, localization will occur
primarily through triangulation with a network of detectors. We investigate the
expected timing accuracy for observed signals and the consequences for
localization. In addition, we discuss the effect of systematic uncertainties in
the waveform and calibration of the instruments on the localization of sources.
We provide illustrative results of timing and localization accuracy as well as
systematic effects for coalescing binary waveforms.Comment: 20 pages, 5 figure
Pragmatism, moral responsibility or policy change: the Syrian refugee crisis and selective humanitarianism in the Turkish refugee regime
Field Blue Stragglers and Related Mass Transfer Issues
This chapter contains my impressions and perspectives about the current state
of knowledge about field blue stragglers (FBS) stars, drawn from an extensive
literature that I searched. I conclude my review of issues that attend FBS and
mass transfer, by a brief enumeration of a few mildly disquieting observational
facts.Comment: Chapter 4, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Knowledge, science and death: the theory of brain-sign
In today’s paradigmatic climate, the possibility of knowledge, and therefore science, still depends upon
our being conscious. However, no scientifically accepted account of consciousness exists. In recent years
I have developed the theory of brain-sign which replaces consciousness as a wholly physical neural
condition. The first tenet is that the brain is a causal organ, not a knowledge organ. The second is that
brain-sign, used in inter-neural communication for uncertain or imprecise collective action, derives at
each moment from the causal orientation of the brain. Signs are ubiquitous bio-physical entities. Thus
there is no problematic dualism, consciousness and world. We now have two accounts of the brain
phenomenon. The first (consciousness) is an inexplicable physical anomaly. The second (brain-sign)
belongs in the physical universe, and fulfils a crucial neurobiological function. With brain-sign theory we
even ‘discover’ that we do not know we are alive or will die
Theories of Reference: What Was the Question?
The new theory of reference has won popularity. However, a number of noted philosophers have also attempted to reply to the critical arguments of Kripke and others, and aimed to vindicate the description theory of reference. Such responses are often based on ingenious novel kinds of descriptions, such as rigidified descriptions, causal descriptions, and metalinguistic descriptions. This prolonged debate raises the doubt whether different parties really have any shared understanding of what the central question of the philosophical theory of reference is: what is the main question to which descriptivism and the causal-historical theory have presented competing answers. One aim of the paper is to clarify this issue. The most influential objections to the new theory of reference are critically reviewed. Special attention is also paid to certain important later advances in the new theory of reference, due to Devitt and others
Anisotropic Colossal Magnetoresistance Effects in Fe_{1-x}Cu_xCr_2S_4
A detailed study of the electronic transport and magnetic properties of
FeCuCrS () on single crystals is presented. The
resistivity is investigated for K in magnetic fields up to
14 Tesla and under hydrostatic pressure up to 16 kbar. In addition
magnetization and ferromagnetic resonance (FMR) measurements were performed.
FMR and magnetization data reveal a pronounced magnetic anisotropy, which
develops below the Curie temperature, , and increases strongly
towards lower temperatures. Increasing the Cu concentration reduces this
effect. At temperatures below 35 K the magnetoresistance, , exhibits a strong dependence on the direction of the
magnetic field, probably due to an enhanced anisotropy. Applying the field
along the hard axis leads to a change of sign and a strong increase of the
absolute value of the magnetoresistance. On the other hand the
magnetoresistance remains positive down to lower temperatures, exhibiting a
smeared out maximum with the magnetic field applied along the easy axis. The
results are discussed in the ionic picture using a triple-exchange model for
electron hopping as well as a half-metal utilizing a band picture.Comment: some typos correcte
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