A repeating fast radio burst associated with a persistent radio source.

The dispersive sweep of fast radio bursts (FRBs) has been used to probe the ionized baryon content of the intergalactic medium1, which is assumed to dominate the total extragalactic dispersion. Although the host-galaxy contributions to the dispersion measure appear to be small for most FRBs2, in at least one case there is evidence for an extreme magneto-ionic local environment3,4 and a compact persistent radio source5. Here we report the detection and localization of the repeating FRB 20190520B, which is co-located with a compact, persistent radio source and associated with a dwarf host galaxy of high specific-star-formation rate at a redshift of 0.241 ± 0.001. The estimated host-galaxy dispersion measure of approximately [Formula: see text] parsecs per cubic centimetre, which is nearly an order of magnitude higher than the average of FRB host galaxies2,6, far exceeds the dispersion-measure contribution of the intergalactic medium. Caution is thus warranted in inferring redshifts for FRBs without accurate host-galaxy identifications.

The host galaxy of a fast radio burst.

In recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts. These signals are dispersed according to a precise physical law and this dispersion is a key observable quantity, which, in tandem with a redshift measurement, can be used for fundamental physical investigations. Every fast radio burst has a dispersion measurement, but none before now have had a redshift measurement, because of the difficulty in pinpointing their celestial coordinates. Here we report the discovery of a fast radio burst and the identification of a fading radio transient lasting ~6 days after the event, which we use to identify the host galaxy; we measure the galaxy's redshift to be z = 0.492 ± 0.008. The dispersion measure and redshift, in combination, provide a direct measurement of the cosmic density of ionized baryons in the intergalactic medium of ΩIGM = 4.9 ± 1.3 per cent, in agreement with the expectation from the Wilkinson Microwave Anisotropy Probe, and including all of the so-called 'missing baryons'. The ~6-day radio transient is largely consistent with the radio afterglow of a short γ-ray burst, and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. This contrasts with the interpretation of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts.

The increasing cesarean rate globally and what we can do about it.

Cesarean sections sometimes save the lives of mothers and babies; however, they are excessively used compared to medical necessity, which is influenced by various factors that are explored in this article. Since, in most cases the risks of cesarean sections are greater than the benefits, particularly in cesareans that are not medically indicated, it is astonishing that cesarean surgery is the most common surgical procedure, taking away resources from medically necessary care. While economic incentive is counted among the reasons for the increasing cesarean trend, the situation is not so simple since many factors interact to cause the trend. Since reversal of the vaginal birth after cesarean (VBAC) trend downward is correlated with revised policy statements by e.g. American College of Obstetricians and Gynecologists (ACOG), which have since been partially moderated, it became much more difficult for medical institutions to provide VBACs due to concerns about liability. Although whether to give birth by cesarean delivery is a matter for informed consent, yet childbearing women are influenced significantly by their health service providers' opinions. Even though the World Health Organization (WHO) recommends the most peripheral level of maternity care for normal pregnancy and childbirth that is safe using midwives, yet the percentage of midwife deliveries is low. Among other things, it has been suggested that more childbirth by midwife delivery and in out-of-hospital settings can reduce medically unnecessary cesareans and the undue risks associated with them, and free up medical resources for those in need.

ATPase sites in two-headed fragment of Tetrahymena 22S ciliary dynein.

Three-headed Tetrahymena 22S ciliary dynein was found to consist of three heavy chains (HCs) and decompose into two-headed and single-headed fragments upon chymotrypsin digestion. The three HCs (A alpha, A beta, and A gamma) were immunologically different, and presumed to be located on each of the head regions. The two-headed fragment contained A beta and A gamma HCs, while the A alpha HC originated in the single-headed fragment. Both fragments were associated with ATPase activity (Toyoshima, Y. (1987a) J. Cell Biol. 105, 887-895 and Toyoshima, Y. (1987b) J. Cell Biol. 105, 897-901). Using the two-headed dynein fragment, we attempted to determine the site of ATP hydrolysis in the fragment. After digestion of the fragment with 100 micrograms/ml thermolysin for 45 min, we noted eight thermolysin-digested polypeptides (TH 1, 2, 3, 4, 5 alpha, 5 beta, 6 alpha, and 6 beta). By precisely analyzing the degradation process and the products using peptide mapping, immunoblotting and high pressure liquid chromatography, it appeared that the two-headed fragment is dissociated as two separate fragments, each of which contained A beta or A gamma HC. Thermolysin digests, TH 1, 2, 5 alpha and 6 beta were found to be derived from A beta HC, while TH 3, 4, 5 beta and 6 alpha originated in the A gamma HC. Based on the measurements of ATPase activity of these polypeptides, we concluded that the ATPase site is located in the A beta and A gamma HCs, which may have their origins in each head of the two-headed fragment of Tetrahymena 22S ciliary dynein.

Cloning of macromomycin apoprotein gene from Streptomyces macromomyceticus by use of 50-mer deoxynucleotide probes.

A mixed probe consisting of two synthetic deoxynucleotides (52 and 54 mers referred to as 50-mer) with arbitrarily chosen C or G for the third letters was prepared based on the amino acid sequences No. 31-48 and No. 72-90 of macromomycin (MCM) apoprotein and successfully used to clone the MCM apoprotein gene. Digestion with Sph I of total DNA of MCM-producing Streptomyces macromomyceticus M480-M1 yielded a 2.6-kb fragment that hybridized strongly to the probes. The hybridized probe was stable to washing with 3 x SSC at 75 degrees C. Radioactivity derived from the hybridized probe was comparable to that expected theoretically from hybridization between the probe and the true target sequence. The 2.6-kb fragment was cloned into Escherichia coli RR1 with pBR322 and subsequently subcloned into Streptomyces lividans TK21 with pIJ702. Nucleotide sequence analysis of the cloned fragment verified the existence of the sequence corresponding to the amino acid sequence of MCM apoprotein and about 90% homologies with the probes. Thus, the use of relatively long deoxynucleotide probes with arbitrarily chosen C or G for the third letters will be advantageous in cloning Streptomyces protein genes where more than 90% of the third letters have been known to be C or G. In addition, theoretical diagnosis of hybridization should be a great help to distinguish true positives from false ones.