309 research outputs found
Quiescent X-ray variability in the neutron star Be/X-ray transient GRO J1750-27
The Be/X-ray transient GRO J1750-27 exhibited a type-II (giant) outburst in
2015. After the source transited to quiescence, we triggered our multi-year
Chandra monitoring programme to study its quiescent behaviour. The programme
was designed to follow the cooling of a potentially heated neutron-star crust
due to accretion of matter during the preceding outburst, similar to what we
potentially have observed before in two other Be/X-ray transients, namely 4U
0115+63 and V 0332+53. However, unlike for these other two systems, we do not
find any strong evidence that the neutron-star crust in GRO J1750-27 was indeed
heated during the accretion phase. We detected the source at a rather low X-ray
luminosity (~10^33 erg/s) during only three of our five observations. When the
source was not detected it had very low-luminosity upper limits (<10^32 erg/s;
depending on assumed spectral model). We interpret these detections and the
variability observed as emission likely due to very low-level accretion onto
the neutron star. We also discuss why the neutron-star crust in GRO J1750-27
might not have been heated while the ones in 4U 0115+63 and V 0332+53 possibly
were.Comment: 13 pages, 6 figures, 5 tables. Accepted for A&
Simultaneous multi-frequency limits on radio emission at the time of a bright X-ray burst from SGR 1935+2154
Two bright bursts from FRB 20201124A with the Onsala 25-m telescope at 1.4 GHz, with no simultaneous emission detected at 330 MHz with Westerbork 25-m
The human fungal pathogen Aspergillus fumigatus can produce the highest known number of meiotic crossovers
Sexual reproduction involving meiosis is essential in most eukaryotes. This produces offspring with novel genotypes, both by segregation of parental chromosomes as well as crossovers between homologous chromosomes. A sexual cycle for the opportunistic human pathogenic fungus Aspergillus fumigatus is known, but the genetic consequences of meiosis have remained unknown. Among other Aspergilli, it is known that A. flavus has a moderately high recombination rate with an average of 4.2 crossovers per chromosome pair, whereas A. nidulans has in contrast a higher rate with 9.3 crossovers per chromosome pair. Here, we show in a cross between A. fumigatus strains that they produce an average of 29.9 crossovers per chromosome pair and large variation in total map length across additional strain crosses. This rate of crossovers per chromosome is more than twice that seen for any known organism, which we discuss in relation to other genetic model systems. We validate this high rate of crossovers through mapping of resistance to the laboratory antifungal acriflavine by using standing variation in an undescribed ABC efflux transporter. We then demonstrate that this rate of crossovers is sufficient to produce one of the common multidrug resistant haplotypes found in the cyp51A gene (TR34/L98H) in crosses among parents harboring either of 2 nearby genetic variants, possibly explaining the early spread of such haplotypes. Our results suggest that genomic studies in this species should reassess common assumptions about linkage between genetic regions. The finding of an unparalleled crossover rate in A. fumigatus provides opportunities to understand why these rates are not generally higher in other eukaryotes
Triazole Fungicides Can Induce Cross-Resistance to Medical Triazoles in Aspergillus fumigatus
Contains fulltext :
103858.pdf (publisher's version ) (Open Access)BACKGROUND: Azoles play an important role in the management of Aspergillus diseases. Azole resistance is an emerging global problem in Aspergillus fumigatus, and may develop through patient therapy. In addition, an environmental route of resistance development has been suggested through exposure to 14alpha-demethylase inhibitors (DMIs). The main resistance mechanism associated with this putative fungicide-driven route is a combination of alterations in the Cyp51A-gene (TR(34)/L98H). We investigated if TR(34)/L98H could have developed through exposure to DMIs. METHODS AND FINDINGS: Thirty-one compounds that have been authorized for use as fungicides, herbicides, herbicide safeners and plant growth regulators in The Netherlands between 1970 and 2005, were investigated for cross-resistance to medical triazoles. Furthermore, CYP51-protein homology modeling and molecule alignment studies were performed to identify similarity in molecule structure and docking modes. Five triazole DMIs, propiconazole, bromuconazole, tebuconazole, epoxiconazole and difenoconazole, showed very similar molecule structures to the medical triazoles and adopted similar poses while docking the protein. These DMIs also showed the greatest cross-resistance and, importantly, were authorized for use between 1990 and 1996, directly preceding the recovery of the first clinical TR(34)/L98H isolate in 1998. Through microsatellite genotyping of TR(34)/L98H isolates we were able to calculate that the first isolate would have arisen in 1997, confirming the results of the abovementioned experiments. Finally, we performed induction experiments to investigate if TR(34)/L98H could be induced under laboratory conditions. One isolate evolved from two copies of the tandem repeat to three, indicating that fungicide pressure can indeed result in these genomic changes. CONCLUSIONS: Our findings support a fungicide-driven route of TR(34)/L98H development in A. fumigatus. Similar molecule structure characteristics of five triazole DMIs and the three medical triazoles appear the underlying mechanism of cross resistance development. Our findings have major implications for the assessment of health risks associated with the use of triazole DMIs
Connecting repeating and non-repeating fast radio bursts via their energy distributions
Fast radio bursts (FRBs) are extremely energetic, millisecond-duration radio
flashes that reach Earth from extragalactic distances. Broadly speaking, FRBs
can be classified as repeating or (apparently) non-repeating. It is still
unclear, however, whether the two types share a common physical origin,
differing only in their activity rate. Here we report on an unprecedented
observing campaign that targeted one hyperactive repeating source, FRB
20201124A, for more than using four class
radio telescopes. In total, we detect high-energy bursts, many more than
one would expect given previous observations of lower-energy bursts using
larger radio telescopes. We find a high-energy burst distribution that
resembles that of the non-repeating FRB population, suggesting that apparently
non-repeating FRB sources may simply be the rarest bursts from repeating
sources. We also discuss how FRB 20201124A contributes strongly to the all-sky
FRB rate and how similar sources would be observable even at very high
redshift.Comment: 25 pages, 9 figures. Submitted, comments welcom
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