TY  - JOUR
A1  - Kappel, David
A1  - Sachse, Manuel
A1  - Haack, David
A1  - Otto, Katharina A.
T1  - Discrete element modeling of boulder and cliff morphologies on comet 67P/Churyumov-Gerasimenko
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context:
Even after the Rosetta mission, some of the mechanical parameters of comet 67P/Churyumov-Gerasimenko's surface material are not yet well constrained. These parameters are needed to improve our understanding of cometary activity or for planning sample return missions.

Aims:
We study some of the physical processes involved in the formation of selected surface features and investigate the mechanical and geometrical parameters involved.

Methods:
Applying the discrete element method (DEM) in a low-gravity environment, we numerically simulated the surface layer particle dynamics involved in the formation of selected morphological features. The material considered is a mixture of polydisperse ice and dust spheres with inter-particle forces given by the Hertz contact model, translational friction, rolling friction, cohesion from unsintered contacts, and optionally due to bonds from ice sintering. We determined a working set of parameters that enables the simulations to be reasonably realistic and investigated morphological changes due to modifications thereof.

Results:
The selected morphological features are reasonably well reproduced using model materials with a tensile strength on the order of 1-10 Pa. Increasing the diameters of the spherical particles decreases the material strength, and increasing the friction leads to a more brittle but somewhat stronger material. High friction is required to make the material sufficiently brittle to match observations, which points to the presence of very rough, even angular particles. Reasonable seismic activity does not suffice to trigger the collapses of cliffs without material heterogeneities or structural defects.

Conclusions:
DEM modeling can be a powerful tool to investigate mechanical parameters of cometary surface material. However, many uncertainties arise from our limited understanding of particle shapes, spatial configurations, and size distributions, all on multiple length scales. Further numerical work, in situ measurements, and sample return missions are needed to better understand the mechanics of cometary material and cometary activity.
KW  - comets: general
KW  - comets: individual: 67P
KW  - Churyumov-Gerasimenko
KW  - methods: numerical
Y1  - 2020
U6  - https://doi.org/10.1051/0004-6361/201937152
SN  - 0004-6361
SN  - 1432-0746
VL  - 641
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Cui, Huanhuan
A1  - Schlesinger, Jenny
A1  - Schoenhals, Sophia
A1  - Toenjes, Martje
A1  - Dunkel, Ilona
A1  - Meierhofer, David
A1  - Cano, Elena
A1  - Schulz, Kerstin
A1  - Berger, Michael F.
A1  - Haack, Timm
A1  - Abdelilah-Seyfried, Salim
A1  - Bulyk, Martha L.
A1  - Sauer, Sascha
A1  - Sperling, Silke R.
T1  - Phosphorylation of the chromatin remodeling factor DPF3a induces cardiac hypertrophy through releasing HEY repressors from DNA
JF  - Nucleic acids research
N2  - DPF3 (BAF45c) is a member of the BAF chromatin remodeling complex. Two isoforms have been described, namely DPF3a and DPF3b. The latter binds to acetylated and methylated lysine residues of histones. Here, we elaborate on the role of DPF3a and describe a novel pathway of cardiac gene transcription leading to pathological cardiac hypertrophy. Upon hypertrophic stimuli, casein kinase 2 phosphorylates DPF3a at serine 348. This initiates the interaction of DPF3a with the transcriptional repressors HEY, followed by the release of HEY from the DNA. Moreover, BRG1 is bound by DPF3a, and is thus recruited to HEY genomic targets upon interaction of the two components. Consequently, the transcription of downstream targets such as NPPA and GATA4 is initiated and pathological cardiac hypertrophy is established. In human, DPF3a is significantly up-regulated in hypertrophic hearts of patients with hypertrophic cardiomyopathy or aortic stenosis. Taken together, we show that activation of DPF3a upon hypertrophic stimuli switches cardiac fetal gene expression from being silenced by HEY to being activated by BRG1. Thus, we present a novel pathway for pathological cardiac hypertrophy, whose inhibition is a long-term therapeutic goal for the treatment of the course of heart failure.
Y1  - 2016
U6  - https://doi.org/10.1093/nar/gkv1244
SN  - 0305-1048
SN  - 1362-4962
VL  - 44
SP  - 2538
EP  - 2553
PB  - Oxford Univ. Press
CY  - Oxford
ER  -