1,519 research outputs found
The far-infrared - radio correlation in dwarf galaxies
The far-infrared - radio correlation connects star formation and magnetic
fields in galaxies, and has been confirmed over a large range of far-infrared
luminosities. Recent investigations indicate that it may even hold in the
regime of local dwarf galaxies, and we explore here the expected behavior in
the regime of star formation surface densities below 0.1 M_sun kpc^{-2}
yr^{-1}. We derive two conditions that can be particularly relevant for
inducing a change in the expected correlation: a critical star formation
surface density to maintain the correlation between star formation rate and the
magnetic field, and a critical star formation surface density below which
cosmic ray diffusion losses dominate over their injection via supernova
explosions. For rotation periods shorter than 1.5x10^7 (H/kpc)^2 yrs, with H
the scale height of the disk, the first correlation will break down before
diffusion losses are relevant, as higher star formation rates are required to
maintain the correlation between star formation rate and magnetic field
strength. For high star formation surface densities Sigma_SFR, we derive a
characteristic scaling of the non-thermal radio to the far-infrared / infrared
emission with Sigma_SFR^{1/3}, corresponding to a scaling of the non-thermal
radio luminosity L_s with the infrared luminosity L_{th} as L_{th}^{4/3}. The
latter is expected to change when the above processes are no longer steadily
maintained. In the regime of long rotation periods, we expect a transition
towards a steeper scaling with Sigma_SFR^{2/3}, implying L_s~L_th^{5/3}, while
the regime of fast rotation is expected to show a considerably enhanced
scatter. These scaling relations explain the increasing thermal fraction of the
radio emission observed within local dwarfs, and can be tested with future
observations by the SKA and its precursor radio telescopes.Comment: 16 pages, 11 figures, accepted at A&
A new interpretation of the far-infrared - radio correlation and the expected breakdown at high redshift
(Abrigded) Observations of galaxies up to z 2 show a tight correlation
between far-infrared and radio continuum emission. We explain the far-infrared
- radio continuum correlation by relating star formation and magnetic field
strength in terms of turbulent magnetic field amplification, where turbulence
is injected by supernova explosions from massive stars. We calculate the
expected amount of turbulence in galaxies based on their star formation rates,
and infer the expected magnetic field strength due to turbulent dynamo
amplification. We estimate the timescales for cosmic ray energy losses via
synchrotron emission, inverse Compton scattering, ionization and bremsstrahlung
emission, probing up to which redshift strong synchrotron emission can be
maintained. We find that the correlation between star formation rate and
magnetic field strength in the local Universe can be understood as a result of
turbulent magnetic field amplification. If the typical gas density in the
interstellar medium increases at high z, we expect an increase of the magnetic
field strength and the radio emission, as indicated by current observations.
Such an increase would imply a modification of the far-infrared - radio
correlation. We expect a breakdown when inverse Compton losses start dominating
over synchrotron emission. For a given star formation surface density, we
calculate the redshift where the breakdown occurs, yielding z (Sigma_SFR/0.0045
M_solar kpc^{-2} yr^{-1})^{1/(6-alpha/2)}. In this relation, the parameter
\alpha describes the evolution of the characteristic ISM density in galaxies as
(1+z)^\alpha. Both the possible raise of the radio emission at high redshift
and the final breakdown of the far-infrared -- radio correlation at a critical
redshift will be probed by the Square Kilometre Array (SKA) and its
pathfinders, while the typical ISM density in galaxies will be probed with
ALMA.Comment: 13 pages, 14 figures, 1 table, accepted at A&A (proof corrections
included
Mean distance in polyhedra
Given any polyhedron from which we select two random points uniformly and
independently, we show that all the moments of the distance between those
points can be always written in terms of elementary functions. As an
illustration, the mean distance is found in the exact form for all Platonic
solids
On the fourth moment of a random determinant
In this paper, we generalise the formula for the fourth moment of a random
determinant to account for entries with asymmetric distribution
It was (not) me: Causal Inference of Agency in goal-directed actions
Summary: 
The perception of one’s own actions depends on both sensory information and predictions derived from internal forward models [1]. The integration of these information sources depends critically on whether perceptual consequences are associated with one’s own action (sense of agency) or with changes in the external world that are not related to the action. The perceived effects of actions should thus critically depend on the consistency between the predicted and the actual sensory consequences of actions. To test this idea, we used a virtual-reality setup to manipulate the consistency between pointing movements and their visual consequences and investigated the influence of this manipulation on self-action perception. We then asked whether a Bayesian causal inference model, which assumes a latent agency variable controlling the attributed influence of the own action on perceptual consequences [2,3], would account for the empirical data: if the percept was attributed to the own action, visual and internal information should fuse in a Bayesian optimal manner, while this should not be the case if the visual stimulus was attributed to external influences. The model correctly fits the data, showing that small deviations between predicted and actual sensory information were still attributed to one’s own action, while this was not the case for large deviations when subjects relied more on internal information. We discuss the performance of this causal inference model in comparison to alternative biologically feasible statistical models applying methods for Bayesian model comparison.

Experiment: 
Participants were seated in front of a horizontal board on which their right hand was placed with the index finger on a haptic marker, representing the starting point for each trial. Participants were instructed to execute straight, fast (quasi-ballistic) pointing movements of fixed amplitude, but without an explicit visual target. The hand was obstructed from the view of the participants, and visual feedback about the peripheral part of the movement was provided by a cursor. Feedback was either veridical or rotated against the true direction of the hand movement by predefined angles. After each trial participants were asked to report the subjectively experienced direction of the executed hand movement by placing a mouse-cursor into that direction.

Model: 
We compared two probabilistic models: Both include a binary random gating variable (agency) that models the sense of ‘agency’; that is the belief that the visual feedback is influenced by the subject’s motor action. The first model assumes that both the visual feedback xv and the internal motor state estimate xe are directly caused by the (unobserved) real motor state xt (Fig. 1). The second model assumes instead that the expected visual feedback depends on the perceived direction of the own motor action xe (Fig. 2). 
Results: Both models are in good agreement with the data. Fig. A shows the model fit for Model 1 superpositioned to the data from a single subject. Fig. B shows the belief that the visual stimulus was influenced by the own action, which decreases for large deviations between predicted and real visual feedback. Bayesian model comparison shows a better fit for model 1.
Citations
[1] Wolpert D.M, Ghahramani, Z, Jordan, M. (1995) Science, 269, 1880-1882.
[2] Körding KP, Beierholm E, Ma WJ, Quartz S, Tenenbaum JB, et al (2007) PLoS ONE 2(9): e943.
[3] Shams, L., Beierholm, U. (2010) TiCS, 14: 425-432.
Acknowledgements
This work was supported by the BCCN Tübingen (FKZ: 01GQ1002), the CIN Tübingen, the European Union (FP7-ICT-215866 project SEARISE), the DFG and the Hermann and Lilly Schilling Foundation
Analysis of transcriptional networks and chromatin states in normal and abnormal blood cells
Altered myeloid differentiation can lead to a variety of haematological malignancies including the Myelodysplastic Syndrome (MDS), chronic myelomonocytic leukaemia (CMML) and acute myeloid leukaemia (AML). We have studied transcriptome regulation in haematopoietic stem and progenitor cells (HSPC) using different high-throughput technologies. In this thesis, I introduce bioinformatics pipelines and an algorithm for the analysis of next-generation sequencing (NGS) data and highlight methods to integrate different genome-wide datasets to derive chromatin states, transcriptional and post-transcriptional networks in normal and abnormal blood cells.
Following an introduction to key concepts relevant to this thesis, in the second chapter, I detail the first genome-wide characterisation of small non-coding RNAs in HSPC in MDS patients. By profiling mRNA expression in the same patients, I developed a novel statistical model that integrated miRNA, transcription factors (TF) and gene expression to identify novel regulatory pathways in MDS.
MDS and CMML patients often die following transformation into AML. In the third chapter, I present an analysis of a heptad of HSPC TFs that regulate their own expression by binding enhancers of these genes. The enhancer and the heptad are active in a subset of AMLs, normal HSPC and leukemic stem cells. The heptad and a gene signature derived from enhancer activity, predict clinical outcome in AML, while the expression of four heptad genes further correlated with the underlying genetic mutations in cytogenetically normal AML patients.
In the fourth chapter, I describe a novel algorithm (LPCHP) to define histone states from NGS data. LPCHP makes use of signal characteristics such as peak shape, location and frequencies in contrast to other algorithms, which only evaluate read intensities. LPCHP was evaluated and performed well in terms of correlation with gene expression, prediction of histone states, parameter variations and signal-to-noise ratios.
In the final chapter, I present preliminary data and outline plans for future work. I propose a systems biology approach to study networks of miRNAs and TFs in MDS and CMML. Sequencing of miRNA and mRNA facilitates network reconstruction where interactions between miRNA and mRNA are predicted at single nucleotide resolution, providing avenues for patient stratification and drug response prediction
Effects of Silica Surfaces on the Structure and Dynamics of Room Temperature Ionic Liquids: A Molecular Dynamics Simulation Study
Room temperature ionic liquids (ILs) at solid surfaces have been recognized
for their significant interfacial properties in electrochemical and electronic
devices. To ascertain the interface effects, we investigate dynamical and
structural properties of two ILs in nanoscale confinement at various
temperatures. Specifically, we perform all-atom molecular dynamics simulations
for ILs composed of 1-butyl-3-methylimidazolium cations and hexafluorophosphate
([Bmim][PF6]) or tetrafluoroborate ([Bmim][BF4]) anions sandwiched between
amorphous silica slabs. Density profiles of the ionic species across the slit
reveal that [PF6] and [BF4] anions tend to stay closer to the slab wall than
[Bmim] cations resulting in a bi-layered arrangement in the interfacial region.
For the cations, we observe a preferred orientation at the surface with the
methyl groups pointing towards the wall and the butyl tails projected inwards.
Mean square displacements and incoherent scattering function reveal slowed and
heterogeneous dynamics of all ionic species in the slit pore. In particular,
spatially resolved analyses show that the structural relaxation times increase
by about two orders of magnitude when approaching the silica surfaces, an
effect to be considered when designing applications. The altered structural and
dynamical features of the confined ILs can be related to an existence of
preferred sites for the anions on the amorphous silica surfaces. Detailed
analyses of relations between the broadly distributed site and surface
properties show that particularly stable anion sites result when triangular
arrangements of silanol groups enable multiple hydrogen bonds with the various
fluorine atoms of a given anion, elucidating an important trapping mechanism at
the silica surface
BloodChIP: A database of comparative genome-wide transcription factor binding profiles in human blood cells
The BloodChIP database (http://www.med.unsw.edu.au/CRCWeb.nsf/page/ BloodChIP) supports exploration and visualization of combinatorial transcription factor (TF) binding at a particular locus in human CD34-positive and other normal and leukaemic cells or retrieval of target gene sets for user-defined combinations of TFs across one or more cell types. Increasing numbers of genome-wide TF binding profiles are being added to public repositories, and this trend is likely to continue. For the power of these data sets to be fully harnessed by experimental scientists, there is a need for these data to be placed in context and easily accessible for downstream applications. To this end, we have built a user-friendly database that has at its core the genome-wide binding profiles of seven key haematopoietic TFs in human stem/progenitor cells. These binding profiles are compared with binding profiles in normal differentiated and leukaemic cells. We have integrated these TF binding profiles with chromatin marks and expression data in normal and leukaemic cell fractions. All queries can be exported into external sites to construct TF-gene and protein-protein networks and to evaluate the association of genes with cellular processes and tissue expression. © 2013 The Author(s). Published by Oxford University Press.Link_to_subscribed_fulltex
SKA Deep Polarization and Cosmic Magnetism
Deep surveys with the SKA1-MID array offer for the first time the opportunity
to systematically explore the polarization properties of the microJy source
population. Our knowledge of the polarized sky approaching these levels is
still very limited. In total intensity the population will be dominated by
star-forming and normal galaxies to intermediate redshifts (), and
low-luminosity AGN to high redshift. The polarized emission from these objects
is a powerful probe of their intrinsic magnetic fields and of their magnetic
environments. For redshift of order 1 and above the broad bandwidth of the
mid-bands span the Faraday thick and thin regimes allowing study of the
intrinsic polarization properties of these objects as well as depolarization
from embedded and foreground plasmas. The deep field polarization images will
provide Rotation Measures data with very high solid angle density allowing a
sensitive statistical analysis of the angular variation of RM on critical
arc-minute scales from a magnetic component of Large Scale Structure of the
Universe.Comment: 9 pages, 3 figures; to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)11
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