248,418 research outputs found
Temperature inversion in long-range interacting systems
Temperature inversions occur in nature, e.g., in the solar corona and in
interstellar molecular clouds: somewhat counterintuitively, denser parts of the
system are colder than dilute ones. We propose a simple and appealing way to
spontaneously generate temperature inversions in systems with long-range
interactions, by preparing them in inhomogeneous thermal equilibrium states and
then applying an impulsive perturbation. In similar situations, short-range
systems would typically relax to another thermal equilibrium, with uniform
temperature profile. By contrast, in long-range systems, the interplay between
wave-particle interaction and spatial inhomogeneity drives the system to
nonequilibrium stationary states that generically exhibit temperature
inversion. We demonstrate this mechanism in a simple mean-field model and in a
two-dimensional self-gravitating system. Our work underlines the crucial role
the range of interparticle interaction plays in determining the nature of
steady states out of thermal equilibrium.Comment: 5 pages + 6 pages of appendix, 5 figures, REVTeX 4-1. To appear in
Physical Review E (Rapid Communications). Appendix will be published
online-only as Supplemental Materia
Unsupervised vector-based classification of single-molecule charge transport data
The stochastic nature of single-molecule charge transport measurements requires collection of large data sets to capture the full complexity of a molecular system. Data analysis is then guided by certain expectations, for example, a plateau feature in the tunnelling current distance trace, and the molecular conductance extracted from suitable histogram analysis. However, differences in molecular conformation or electrode contact geometry, the number of molecules in the junction or dynamic effects may lead to very different molecular signatures. Since their manifestation is a priori unknown, an unsupervised classification algorithm, making no prior assumptions regarding the data is clearly desirable. Here we present such an approach based on multivariate pattern analysis and apply it to simulated and experimental single-molecule charge transport data. We demonstrate how different event shapes are clearly separated using this algorithm and how statistics about different event classes can be extracted, when conventional methods of analysis fail
Hsp70 and Hsp40 inhibit an inter-domain interaction necessary for transcriptional activity in the androgen receptor.
Molecular chaperones such as Hsp40 and Hsp70 hold the androgen receptor (AR) in an inactive conformation. They are released in the presence of androgens, enabling transactivation and causing the receptor to become aggregation-prone. Here we show that these molecular chaperones recognize a region of the AR N-terminal domain (NTD), including a FQNLF motif, that interacts with the AR ligand-binding domain (LBD) upon activation. This suggests that competition between molecular chaperones and the LBD for the FQNLF motif regulates AR activation. We also show that, while the free NTD oligomerizes, binding to Hsp70 increases its solubility. Stabilizing the NTD-Hsp70 interaction with small molecules reduces AR aggregation and promotes its degradation in cellular and mouse models of the neuromuscular disorder spinal bulbar muscular atrophy. These results help resolve the mechanisms by which molecular chaperones regulate the balance between AR aggregation, activation and quality control
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