Accretion Disc Wind Variability in the States of the Microquasar GRS 1915+105

Continuing our study of the role and evolution of accretion disc winds in the microquasar GRS 1915+105, we present high-resolution spectral variability analysis of the beta and gamma states with the Chandra High Energy Transmission Grating Spectrometer. By tracking changes in the absorption lines from the accretion disc wind, we find new evidence that radiation links the inner and outer accretion discs on a range of time-scales. As the central X-ray flux rises during the high-luminosity gamma state, we observe the progressive over-ionization of the wind. In the beta state, we argue that changes in the inner disc leading to the ejection of a transient 'baby jet' also quench the highly-ionized wind from the outer disc. Our analysis reveals how the state, structure, and X-ray luminosity of the inner accretion disc all conspire to drive the formation and variability of highly-ionized accretion disc winds.Comment: Accepted for publication in MNRAS. 11 pages, 7 figures, uses mn2e.cls. Comments welcom

No Correlation Between Disc Scale-Height and Jet Power in GRMHD Simulations

It is now well established that changes in the X-ray spectral state of black hole low-mass X-ray binaries are correlated with changes in the radio properties of those systems. Assuming radio power is a proxy for jet power, we can say that the jet is continuously present in the hard state and undetectable (and therefore weaker) in the soft state. Since the different accretion states are also generally assumed to be associated with different disc geometries -- the hard state with a hot, thick flow, and the soft state with a cold, thin disc -- we investigate the possibility that these two phenomena are linked; i.e., that the difference in disc geometry is the cause of the difference in observed jet power. We do this by comparing various measures of jet power in numerical simulations of accretion discs of differing temperatures and thicknesses. We perform these simulations using the general relativistic magnetohydrodynamic code Cosmos++ and a newly added cooling function, which allows us to regulate the disc scale height H/r at different radii. We find no apparent correlation between the disc scale height and jet power whenever we normalize the latter by the mass accretion history of each simulation. We attribute this result to the role that the "corona" plays in confining and accelerating the jet (our corona may also be considered a failed MHD "wind"). The properties of the corona do not vary significantly from one simulation to another, even though the scale heights of the discs vary by up to a factor of four. If this holds true in nature, then it suggests that the correlation between spectral state and jet power must be attributable to some other property, possibly the topology of the magnetic field. Alternatively, it could be that the corona disappears altogether in the soft state, which would be consistent with observations, but has so far not been seen in simulations.Comment: 9 pages, 7 figures, accepted for publication in MNRA

Visible-Light Photoswitchable Benzimidazole Azo-Arenes as beta-Arrestin2-Biased Selective Cannabinoid 2 Receptor Agonists

Acknowledgements The authors would like to acknowledge Dr. Andrea Holme for excellent technical support and the Iain Fraser Cytometry Centre (University of Aberdeen) for providing access to their equipment. The authors would like to thank Dr. Matthias Scheiner for his contributions towards the development of the calcium mobilization assay and Dr. Valérie Jahns for her efforts towards faster automated analysis of the obtained results. Nick Verhavert is acknowledged for his assistance with the NanoBiT® assay. Diego Rodriguez-Soacha is acknowledged for establishing the rCB1R radioligand binding assay in our laboratory. Special thanks to Dr. Rangan Maitra and RTI International for providing the G16 coupled hCB1 and hCB2 CHO-K1 cell lines. The authors thank Nadine Yurdagül-Hemmrich and Annette Hannawacker for excellent technical support. This project was funded by the German Research Foundation (Deutsche Forschungsgemeinschaft under DFG DE1546/10-1). J. N. Hislop’s financing support was given by NHS Grampian. The research visit of S. A. M. Steinmüller in Dr. Hislop’s laboratory was funded by the Elite Network of Bavaria (grant N° K-BM-2013-247). J. Fender and A. Tutov were supported by the International Doctoral Program “Receptor Dynamics” funded within the framework of the Elite Network of Bavaria (grant N° K-BM-2013- 247). M. H. Deventer was funded by the Research FoundationFlanders (FWO; grant 1S54521N).Peer reviewe

Rapid binding and release of Hfq from ternary complexes during RNA annealing

The Sm protein Hfq binds small non-coding RNA (sRNAs) in bacteria and facilitates their base pairing with mRNA targets. Molecular beacons and a 16 nt RNA derived from the Hfq binding site in DsrA sRNA were used to investigate how Hfq accelerates base pairing between complementary strands of RNA. Stopped-flow fluorescence experiments showed that annealing became faster with Hfq concentration but was impaired by mutations in RNA binding sites on either face of the Hfq ring or by competition with excess RNA substrate. A fast bimolecular Hfq binding step (∼108 M−1s−1) observed with Cy3-Hfq was followed by a slow transition (0.5 s−1) to a stable Hfq–RNA complex that exchanges RNA ligands more slowly. Release of Hfq upon addition of complementary RNA was faster than duplex formation, suggesting that the nucleic acid strands dissociate from Hfq before base pairing is complete. A working model is presented in which rapid co-binding and release of two RNA strands from the Hfq ternary complex accelerates helix initiation 10 000 times above the Hfq-independent rate. Thus, Hfq acts to overcome barriers to helix initiation, but the net reaction flux depends on how tightly Hfq binds the reactants and products and the potential for unproductive binding interactions