DNA polymerase enzymes make an error only once per 10(4)-10(5) initial nucleotide insertions during DNA replication. Most currently held models of this high fidelity cite the hydrogen bonds between ...complementary pyrimidines and purines as a critical controlling factor. Testing this has been difficult, however, since standard molecular strategies for blocking or removing polar hydrogen-bonding groups cause changes to size and shape as well as hydrogen bonding ability. One answer to this problem is the use of nonpolar molecules that mimic the shape of natural DNA bases. Here we show that a non-hydrogen-bonding shape mimic for adenine is replicated efficiently and selectively against a nonpolar shape mimic for thymine. The results establish that hydrogen bonds in a base pair are not absolutely required for efficient nucleotide insertion. This adds support to the idea that shape complementarity may play as important a role in replication as base-base hydrogen bonds.
In the Netherlands, a percentage of newly qualified midwives start work in maternity care as a hospital-based midwife, although prepared particularly for working autonomously in the community.
This ...study aimed to explore newly qualified Dutch midwives' perceptions of their job demands and resources during their initiation to hospital-based practice.
We conducted a qualitative study with semi structured interviews using the Job Demands-Resources model as theoretical framework.
Twenty-one newly qualified midwives working as hospital-based midwives in the Netherlands were interviewed individually between January and July 2018. Transcripts were analyzed using thematic content analysis.
High workload, becoming a team member, learning additional medical procedures and job insecurity were perceived demands. Participants experienced the variety of the work, the teamwork, social support, working with women, and employment conditions as job resources. Openness for new experiences, sociability, calmness and accuracy were experienced as personal resources, and perfectionism, self-criticism, and fear of failure as personal demands.
Initiation to hospital-based practice requires from newly qualified midwives adaptation to new tasks: working with women in medium and high-risk care, managing tasks, as well as often receiving training in additional medical skills. Sociability helps newly qualified midwives in becoming a member of a multidisciplinary team; neuroticism and perfectionism hinders them in their work. Clear expectations and a settling-in period may help newly qualified midwives to adapt to practice. The initiation phase could be better supported by preparing student midwives for working in a hospital setting and helping manage expectations about the settling-in period.
Context.
We present our observations and analysis of SN 2020cxd, a low-luminosity (LL), long-lived Type IIP supernova (SN). This object is a clear outlier in the magnitude-limited SN sample recently ...presented by the Zwicky Transient Facility’s (ZTF) Bright Transient Survey.
Aims.
We demonstrate that SN 2020cxd is an additional member of the group of LL SNe and we discuss the rarity of LL SNe in the context of the ZTF survey. We consider how further studies of these faintest members of the core-collapse (CC) SN family might help improve the general understanding of the underlying initial mass function for stars that explode.
Methods.
We used optical light curves (LCs) from the ZTF in the
gri
bands and several epochs of ultraviolet data from the
Neil Gehrels Swift
observatory as well as a sequence of optical spectra. We constructed the colour curves and a bolometric LC. Then we compared the evolution of the ejecta velocity and black-body temperature for LL SNe as well as for typical Type II SNe. Furthermore, we adopted a Monte Carlo code that fits semi-analytic models to the LC of SN 2020cxd, which allows for the estimation of the physical parameters. Using our late-time nebular spectra, we also make a comparison against SN II spectral synthesis models from the literature to constrain the progenitor properties of SN 2020cxd.
Results.
The LCs of SN 2020cxd show a great similarity with those of LL SNe IIP in terms of luminosity, timescale, and colours. Also, the spectral evolution of SN 2020cxd is that of a Type IIP SN. The spectra show prominent and narrow P-Cygni lines, indicating low expansion velocities. This is one of the faintest LL SNe observed, with an absolute plateau magnitude of
M
r
= −14.5 mag and also one with the longest plateau lengths, with a duration of 118 days. Finally, the velocities measured from the nebular emission lines are among the lowest ever seen in a SN, with an intrinsic full width at half maximum value of 478 km s
−1
. The underluminous late-time exponential LC tail indicates that the mass of
56
Ni ejected during the explosion is much smaller than the average of normal SNe IIP, we estimate
M
56
Ni
= 0.003
M
⊙
. The Monte Carlo fitting of the bolometric LC suggests that the progenitor of SN 2020cxd had a radius of
R
0
= 1.3 × 10
13
cm, kinetic energy of
E
kin
= 4.3 × 10
50
erg, and ejecta mass of
M
ej
= 9.5
M
⊙
. From the bolometric LC, we estimated the total radiated energy
E
rad
= 1.52 × 10
48
erg. Using our late-time nebular spectra, we compared these results against SN II spectral synthesis models to constrain the progenitor zero-age main sequence mass and found that it is likely to be ≲15
M
⊙
.
Conclusions.
SN 2020cxd is a LL Type IIP SN. The inferred progenitor parameters and the features observed in the nebular spectrum favour a low-energy, Ni-poor, iron CC SN from a low-mass (∼12
M
⊙
) red supergiant.
Oligomeric fluorescent labels for DNA Cuppoletti, Andrea; Cho, Younjin; Park, Jin-Seong ...
Bioconjugate chemistry,
05/2005, Letnik:
16, Številka:
3
Journal Article
Recenzirano
In an effort to find fluorescent labels that have large Stokes shifts and increased emission intensity, a strategy for fluorescence labeling of DNA was explored in which multiple individual ...fluorophores are incorporated at adjacent positions at the end of a DNA probe. To encourage close interactions, hydrocarbon and heterocycle fluorophores were substituted at C-1 of deoxyribose, replacing the DNA base. The C-glycosides studied contained the well-known fluorophores terphenyl, pyrene, and terthiophene. For comparison, a commercial fluorescein-dU nucleotide was examined. Oligomeric labels containing up to five fluorophores were tested. Interestingly, all four dyes behaved differently on multiple substitution. Fluorescein displayed strong self-quenching properties, with the quantum yield dropping severalfold with each additional substitution and with a constant, small Stokes shift. In contrast, pyrene showed increases in quantum yield on addition of more than one fluorophore and yielded efficient long-wavelength emission on multiple substitution, with Stokes shifts of >130 nm. Oligomeric terphenyl labels gave a small progressive red shift in absorption and a marked red shift in emission wavelength and showed a strong increase in brightness with more monomers. Finally, terthiophene oligomers showed self-quenching combined with increasing Stokes shifts. Overall, the results suggest that some oligomeric fluorescent labels exhibit properties not available in common fluorescein class (or other commercial) labels, such as large Stokes shifts and increasing brightness with increasing substitution.
Early life determinants of sleep problems are mostly unknown. The first 1000 days of life (ie, the time between conception and a child's second birthday) is a period where the foundations for optimum ...health, growth and neurodevelopment are established. The aim of this explorative study is to identify potential early life determinants of sleep problems at age 7–8 years.
Data from the Amsterdam Born Children and their Development cohort study (n = 2746) were analyzed. Sleep problems at age 7–8 years were reported by the caregiver in the ‘Child Sleep Habits Questionnaire’. A higher total score indicates more sleep problems. After multiple imputation (n = 20), we studied multivariable associations between all potential determinants and sleep problems using regression analysis.
A higher pre-pregnancy body mass index (BMI) was associated with more sleep problems at age 7–8 years β 0.12 (95% CI 0.05, 0.18). Children of mothers with symptoms of anxiety during pregnancy β 0.06 (95% CI 0.03, 0.09) and infancy period β 0.04 (95% CI 0.00, 0.07) had more sleep problems. Children of mothers drinking ≥1 glass of alcohol a day around 14 weeks of gestation had a 2 points higher sleep problem score β 2.55 (95% CI 0.21, 4.89) and children of mothers smoking ≥1 cigarette per day in that period had a one point higher score β 1.07 (95% CI 0.10, 2.03). Infants with relative weight loss (delta BMI-SD) had a higher sleep problem score during childhood β −0.32 (95%CI -0.60, −0.04).
We identified several potential determinants during pregnancy and infancy associated with childhood sleeping problems. We encourage further research into these and other potential determinants to replicate results and to identify underlying mechanisms.
Display omitted
•Sleep related problems are common among children which may extend into adulthood.•The cause of these problems might have started between pregnancy and the first two years of life.•We explored which early life factors are associated with sleep problems at age 7–8 years.•During pregnancy a healthy weight and abstinence from alcohol and tobacco related to better sleep.•Maternal anxiety and infant relative weight loss are associated with more sleep problems.
We present the discovery and extensive follow-up observations of SN 2020jfo, a Type IIP supernova (SN) in the nearby (14.5 Mpc) galaxy M 61. Optical light curves (LCs) and spectra from the Zwicky ...Transient Facility (ZTF), complemented with data from
Swift
/UVOT and near-infrared photometry is presented. These were used to model the 350-day duration bolometric light curve, which exhibits a relatively short (∼65 days) plateau. This implies a moderate ejecta mass (∼5
M
⊙
) at the time of explosion, whereas the deduced amount of ejected radioactive nickel is ∼0.025
M
⊙
. An extensive series of spectroscopy is presented, including spectropolarimetric observations. The nebular spectra are dominated by H
α
, but also reveal emission lines from oxygen and calcium. Comparisons to synthetic nebular spectra indicate an initial progenitor mass of ∼12
M
⊙
. We also note the presence of stable nickel in the nebular spectrum, and SN 2020jfo joins a small group of SNe that have inferred super-solar Ni/Fe ratios. Several years of prediscovery data were examined, but no signs of precursor activity were found. Pre-explosion
Hubble
Space Telescope imaging reveals a probable progenitor star, detected only in the reddest band (
M
F
814
W
≈ −5.8) and it is fainter than expected for stars in the 10−15
M
⊙
range. There is thus some tension between the LC analysis, the nebular spectral modeling, and the pre-explosion imaging. To compare and contrast, we present two additional core-collapse SNe monitored by the ZTF, which also have nebular H
α
-dominated spectra. This illustrates how the absence or presence of an interaction with circumstellar material (CSM) affect both the LCs and in particular the nebular spectra. Type II SN 2020amv has a LC powered by CSM interaction, in particular after ∼40 days when the LC is bumpy and slowly evolving. The late-time spectra show strong H
α
emission with a structure suggesting emission from a thin, dense shell. The evolution of the complex three-horn line profile is reminiscent of that observed for SN 1998S. Finally, SN 2020jfv has a poorly constrained early-time LC, but it is of interest because of the transition from a hydrogen-poor Type IIb to a Type IIn, where the nebular spectrum after the light-curve rebrightening is dominated by H
α
, although with an intermediate line width.
Energetic nuclear outbursts have been discovered in luminous and ultraluminous infrared galaxies (U/LIRGs) at unexpectedly high rates. To investigate this population of transients, we performed a ...search in mid-IR data from the Wide-field Infrared Survey Explorer (WISE) satellite and its NEOWISE survey to detect and characterise luminous and smoothly evolving transients in a sample of 215 U/LIRGs. We report three new transients, all with Δ
L
> 10
43
erg s
−1
, in addition to two previously known cases. Their host galaxies are all part of major galaxy mergers, and through radiative transfer model fitting we find that all have a significant contribution from an active galactic nucleus (AGN). We characterised the transients through measurements of their luminosities and resulting energetics, all of which are between 10
50.9
erg and 10
52.2
erg. The IR emission of the five transients was found to be consistent with re-radiation by the hot dust of emission at shorter wavelengths, presumably originating from an accretion event, onto the supermassive black hole. The corresponding transient rate of (1.6–4.6) × 10
−3
yr
−1
galaxy
−1
is over an order of magnitude higher than the rate of large amplitude flares shown by AGN in the optical. We suggest that the observed transients are part of a dust-obscured population of tidal disruption events (TDEs) that have remained out of the reach of optical surveys due to the obscuring dust. In one case, this is supported by our radio observations. We also discuss other plausible explanations. The observed rate of events is significantly higher than optical TDE rates, which can be expected in U/LIRG hosts undergoing a major galaxy merger with increased stellar densities in the nuclear regions. Continued searches for such transients and their multi-wavelength follow-up is required to constrain their rate and nature.
INTRODUCTIONWorking with acute situations is usually part of midwifery practice. In the Netherlands the community midwives work in a context where they are mostly the sole decision-makers and ...policymakers and often do not have the support of a multidisciplinary team during a birth. How Dutch community midwives maintain their emotional hygiene is not known. This study aims to explore how Dutch midwives perceive fear and its influence on their performance.METHODSThis is a qualitative study with semi-structured interviews of 19 Dutch community midwives between October 2018 and January 2019.RESULTSFour themes were identified: 1) midwives' perceptions of fear and anxiety, 2) how years of experience affect fear and anxiety, 3) influence of the work content; and 4) implications for performance. Midwives perceived fear in acute situations where maternal and/or fetal complications were imminent. Participants perceived anxiety either as helpful or a hindrance. Awareness of these feelings helps them to regulate whether or not to give in to these feelings.CONCLUSIONSOur findings suggest similar perspectives on fear in Dutch community midwives compared to previous outcomes. In the Netherlands, midwives seem reluctant to talk about fear and anxiety in the profession. The awareness of these emotions occurring while working is essential for the wellbeing of midwives, as well as the importance of knowing how to act on fear and anxiety.
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