4,212 research outputs found
Phylogenetic Analysis of Cell Types using Histone Modifications
In cell differentiation, a cell of a less specialized type becomes one of a
more specialized type, even though all cells have the same genome.
Transcription factors and epigenetic marks like histone modifications can play
a significant role in the differentiation process. In this paper, we present a
simple analysis of cell types and differentiation paths using phylogenetic
inference based on ChIP-Seq histone modification data. We propose new data
representation techniques and new distance measures for ChIP-Seq data and use
these together with standard phylogenetic inference methods to build
biologically meaningful trees that indicate how diverse types of cells are
related. We demonstrate our approach on H3K4me3 and H3K27me3 data for 37 and 13
types of cells respectively, using the dataset to explore various issues
surrounding replicate data, variability between cells of the same type, and
robustness. The promising results we obtain point the way to a new approach to
the study of cell differentiation.Comment: Peer-reviewed and presented as part of the 13th Workshop on
Algorithms in Bioinformatics (WABI2013
Influence of the Coriolis force in atom interferometry
In a light-pulse atom interferometer, we use a tip-tilt mirror to remove the
influence of the Coriolis force from Earth's rotation and to characterize
configuration space wave packets. For interferometers with large momentum
transfer and large pulse separation time, we improve the contrast by up to 350%
and suppress systematic effects. We also reach what is to our knowledge the
largest spacetime area enclosed in any atom interferometer to date. We discuss
implications for future high performance instruments.Comment: 4 pages, 5 figures, 1 tabl
Topological magneto-optical effects and their quantization in noncoplanar antiferromagnets
Reflecting the fundamental interactions of polarized light with magnetic
matter, magneto-optical effects are well known since more than a century. The
emergence of these phenomena is commonly attributed to the interplay between
exchange splitting and spin-orbit coupling in the electronic structure of
magnets. Using theoretical arguments, we demonstrate that topological
magneto-optical effects can arise in noncoplanar antiferromagnets due to the
finite scalar spin chirality, without any reference to exchange splitting or
spin-orbit coupling. We propose spectral integrals of certain magneto-optical
quantities that uncover the unique topological nature of the discovered effect.
We also find that the Kerr and Faraday rotation angles can be quantized in
insulating topological antiferromagnets in the low-frequency limit, owing to
nontrivial global properties that manifest in quantum topological
magneto-optical effects. Although the predicted topological and quantum
topological magneto-optical effects are fundamentally distinct from
conventional light-matter interactions, they can be measured by readily
available experimental techniques.Comment: 10 pages, 5 figure
Epitaxial growth and magnetic properties of Sr2CrReO6 thin films
The double perovskite Sr2CrReO6 is an interesting material for spintronics,
showing ferrimagnetism up to 635 K with a predicted high spin polarization of
about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition
on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum
crystallographic and magnetic properties were obtained by growing at a
substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films
are c-axis oriented, coherently strained, and show less than 20% anti-site
defects. The magnetization curves reveal high saturation magnetization of 0.8
muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic
anisotropy.Comment: accepted for publicatio
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