51 research outputs found
A tabletop Optically Pumped Magnetometer setup for the monitoring of magnetic nanoparticle clustering and immobilization using Thermal Noise Magnetometry
Many characterization techniques for magnetic nanoparticles depend on the
usage of external fields. This is not the case in Thermal Noise Magnetometry
(TNM), where thermal fluctuations in the magnetic signal of magnetic
nanoparticle ensembles are measured without any external excitation. This can
provide valuable information about the fundamental dynamical properties of the
particles, due to the purely observative experiments of this relatively new
technique. Until now, TNM signals have been detected only by a superconducting
quantum interference device (SQUID) sensor. We present a tabletop setup using
Optically Pumped Magnetometers (OPMs) in a small magnetic shield, offering a
flexible and accessible alternative and show the agreement between both
measurement systems for two different commercially available nanoparticle
samples. We argue that the OPM setup with high accessibility complements the
SQUID setup with high sensitivity and bandwidth. Furthermore, because of its
excellent sensitivity in the lower frequencies, the OPM tabletop setup is well
suited to monitor aggregation processes where the magnetization dynamics of the
particles tend to slow down, e.g. in biological processes. As a proof of
concept, we show for three different immobilization and clustering processes
the changes in the noise spectrum measured in the tabletop setup: 1) the
aggregation of particles due to the addition of ethanol, 2) the formation of
polymer structures in the sample due to UV exposure, and 3) the cellular uptake
of the particles by THP-1 cells. From our results we conclude that the tabletop
setup offers a flexible and widely adoptable sensor measurement unit to monitor
the immobilization and clustering of magnetic nanoparticles over time for
different applications
AT 2018cow VLBI: No Long-Lived Relativistic Outflow
Abstract We report on VLBI observations of the fast and blue optical transient (FBOT), AT 2018cow. At ∼62 Mpc, AT 2018cow is the first relatively nearby FBOT. The nature of AT 2018cow is not clear, although various hypotheses from a tidal disruption event to different kinds of supernovae have been suggested. It had a very fast rise time (3.5 d) and an almost featureless blue spectrum although high photospheric velocities (40,000 km s−1) were suggested early on. The X-ray luminosity was very high, ∼1.4 × 1043 erg s−1, larger than those of ordinary SNe, and more consistent with those of SNe associated with gamma-ray bursts. Variable hard X-ray emission hints at a long-lived “central engine.” It was also fairly radio luminous, with a peak 8.4-GHz spectral luminosity of ∼4 × 1028 erg s−1 Hz−1, allowing us to make VLBI observations at ages between 22 and 287 d. We do not resolve AT 2018cow. Assuming a circularly symmetric source, our observations constrain the average apparent expansion velocity to be <0.49 c by t = 98 d (3σ limit). We also constrain the proper motion of AT 2018cow to be <0.51 c. Since the radio emission generally traces the fastest ejecta, our observations make the presence of a long-lived relativistic jet with a lifetime of more than one month very unlikely
Parallel Chemical Genetic and Genome-Wide RNAi Screens Identify Cytokinesis Inhibitors and Targets
Cytokinesis involves temporally and spatially coordinated action of the cell cycle and cytoskeletal and membrane systems to achieve separation of daughter cells. To dissect cytokinesis mechanisms it would be useful to have a complete catalog of the proteins involved, and small molecule tools for specifically inhibiting them with tight temporal control. Finding active small molecules by cell-based screening entails the difficult step of identifying their targets. We performed parallel chemical genetic and genome-wide RNA interference screens in Drosophila cells, identifying 50 small molecule inhibitors of cytokinesis and 214 genes important for cytokinesis, including a new protein in the Aurora B pathway (Borr). By comparing small molecule and RNAi phenotypes, we identified a small molecule that inhibits the Aurora B kinase pathway. Our protein list provides a starting point for systematic dissection of cytokinesis, a direction that will be greatly facilitated by also having diverse small molecule inhibitors, which we have identified. Dissection of the Aurora B pathway, where we found a new gene and a specific small molecule inhibitor, should benefit particularly. Our study shows that parallel RNA interference and small molecule screening is a generally useful approach to identifying active small molecules and their target pathways
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