A positron lifetime component of ~170 ps has been reported for irradiated tungsten (W) in some studies. This value is considerably shorter than that calculated for isolated monovacancies (~200 ps). ...In this study, positron annihilation lifetime spectroscopy was used to investigate the recovery behavior of the defects with a short positron lifetime of ~170 ps in electron-irradiated W. The binding energies and positron lifetimes of vacancy-impurity complexes decorated with impurity atoms were calculated. A positron lifetime of 169 ps, which was similar to the experimentally observed lifetime of 171 ± 1 ps, was calculated for defect complexes comprising a monovacancy decorated with two hydrogen atoms (V-2H complexes). In addition, a value of 1.42 eV was calculated for the dissociation energy of a hydrogen atom from the V-H and V-2H complexes, and the defects with a positron lifetime of ~170 ps were experimentally observed to migrate at 623 K. These were consistent with previously reported dissociation energy and desorption temperature of deuterium from vacancies in W studied by thermal desorption spectroscopy. These results suggested that the vacancies observed in the electron-irradiated W were hydrogen-decorated V-nH complexes.
Somatic cell nuclear transfer and transcription-factor-based reprogramming revert adult cells to an embryonic state, and yield pluripotent stem cells that can generate all tissues. Through different ...mechanisms and kinetics, these two reprogramming methods reset genomic methylation, an epigenetic modification of DNA that influences gene expression, leading us to hypothesize that the resulting pluripotent stem cells might have different properties. Here we observe that low-passage induced pluripotent stem cells (iPSCs) derived by factor-based reprogramming of adult murine tissues harbour residual DNA methylation signatures characteristic of their somatic tissue of origin, which favours their differentiation along lineages related to the donor cell, while restricting alternative cell fates. Such an 'epigenetic memory' of the donor tissue could be reset by differentiation and serial reprogramming, or by treatment of iPSCs with chromatin-modifying drugs. In contrast, the differentiation and methylation of nuclear-transfer-derived pluripotent stem cells were more similar to classical embryonic stem cells than were iPSCs. Our data indicate that nuclear transfer is more effective at establishing the ground state of pluripotency than factor-based reprogramming, which can leave an epigenetic memory of the tissue of origin that may influence efforts at directed differentiation for applications in disease modelling or treatment.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Irradiation damage and its evolution in noble gas ion-irradiated tungsten have not been investigated in detail other than in the case of helium ion irradiation. In this study, irradiation-induced ...vacancy-type defects in helium ion- and neon ion-irradiated tungsten were investigated by using a slow positron beam, and their annealing behavior in the temperature range of 20∘C-900∘C was compared by characterizing the Doppler broadening of positron annihilation radiation spectra. In helium ion-irradiated tungsten, slight aggregation of irradiation-induced vacancy-type defects was observed upon annealing, but eventually, a large portion of the vacancy clusters was eliminated after annealing at 900∘C. In contrast, in neon ion-irradiated tungsten, irradiation-induced vacancy-type defects were observed to aggregate significantly at 300∘C and 600∘C. In addition, the large vacancy clusters formed by the aggregation survived even after annealing at 900∘C.
To reveal the influence of oversized elements on the thermal stability of vacancies in type 316L stainless steels, vacancy recovery processes were investigated by means of positron annihilation ...spectroscopy. Although vacancies in additive-free 316L stainless steels were mobile at 300°C, which is a typical nuclear reactor operating temperature, vacancies in oversized elements doped 316L were stable up to 300–350°C. This result indicates that oversized elements stabilize vacancies in stainless steels. Stability of vacancies inhibits the radiation-induced grain boundary segregation and may also lead to suppression of high-temperature water stress corrosion cracking that is observed in nuclear materials.
Ovarian stimulation induced by follicle-stimulating hormone and human chorionic gonadotrophin (hCG) is commonly used in assisted reproductive technology to increase embryo production. However, recent ...clinical and animal studies have shown that ovarian stimulation disrupts endometrial function and embryo development and adversely affects pregnancy outcomes. How ovarian stimulation impairs pregnancy establishment and the precise mechanisms by which this stimulation reduces the chances of conception remain unclear. In this study, we first demonstrated that ovarian stimulation using hCG alone impairs implantation, decidualization and fetal development of mice by generating abnormal ovarian hormone levels. We also showed that ovarian hormone levels were altered because of changes in the levels of the enzymes involved in their synthesis in the follicles and corpora lutea. Furthermore, we determined that anomalous ovarian hormone secretion induced by ovarian stimulation alters the spatiotemporal expression of progesterone receptors and their downstream genes, especially in the uterine epithelium. Epithelial estrogenic signaling and cell proliferation were promoted on the day of implantation in stimulated mice and these changes led to the failure of uterine transition from the prereceptive to the receptive state. Collectively, our findings indicate that ovarian stimulation using hCG induces an imbalance in steroid hormone secretion, which causes a failure of the development of uterine receptivity and subsequent implantation and decidualization by altering the expression of steroid receptors and their downstream signaling associated with embryo implantation.
► Major sources of vacancies are the plastic deformation and the Kirkendall effect. ► Monovacancies in Type 304 stainless steels are annealed at 200–400
°C. ► The recovery temperature corresponds to ...the LWR operating temperature.
To reveal vacancy formation during the stress corrosion cracking (SCC), three factors influencing SCC in Type 304 stainless steels—sensitization heat treatment, corrosion treatment and tensile plastic deformation—were investigated by means of positron annihilation spectroscopy. Vacancy defects induced by the sensitization heat treatment and by tensile deformation were identified as monovacancies. These monovacancies were annealed within the same temperature range in which light water reactors are operated (280–320
°C). The above results allow us to conclude that such vacancy defects play an important role in high-temperature-water SCC crack propagation.
Are there any differences in live birth rates (LBR) following fresh blastocyst transfer in natural or clomiphene-stimulated cycles, or after elective blastocyst freezing in clomiphene-stimulated ...cycles followed by thawing and transfer at different time-points?
Clomiphene citrate (CC) administration adversely affected the LBR after single fresh blastocyst transfer (SBT) in CC cycles compared with that in natural cycles, while this adverse effect of CC is not present when a single vitrified-warmed blastocyst transfer (SVBT) is performed in subsequent natural ovulatory cycles, regardless of the duration between CC administration and the day of SVBT.
CC affects uterine receptivity associated with a thinning of the uterine endometrium through an antioestrogenic effect. However, the duration that this adverse effect of CC on uterine endometrium persists after initial use is still unknown.
A retrospective cohort study of 157 natural cycle IVFs followed by SBT and 1496 minimal ovarian stimulation with CC IVF cycles followed by SBT (
= 24) or SVBT (
= 1472) from January 2010 to December 2014 was conducted. SVBT cycles were classified into two groups according to the period between the last day of CC administration and the day of SVBT (A: ≤60 d and B: ≥61 d). All groups were then compared based on pregnancy outcomes (natural-SBT group:
= 157, CC-SBT group:
= 24, SVBT-A:
= 1143, SVBT-B:
= 329).
Women were aged 30-39 years at oocyte retrieval. In SVBT cycles, blastocysts were vitrified and warmed using a Cryotop safety kit. SVBT was performed in subsequent natural ovulatory cycles. The main outcomes were LBR and neonatal outcome, and both were compared among the groups.
The LBR in the CC-SBT group (29.2%, 7/24) was significantly lower compared with the natural-SBT (56.1%, 88/157) (
= 0.01) and SVBT-A (50.0%, 572/1143) (
= 0.04), but not SVBT-B (47.4%, 156/329), groups. Furthermore, multivariate logistic regression analysis revealed that the LBR was comparable among the natural-SBT and SVBT groups, but was significantly lower in the CC-SBT group (adjusted odds ratio: 0.324, 95% CI: 0.119-0.800,
= 0.01). No significant differences among all groups were observed for gestational age (
= 0.19), birthweight (
= 0.41) and incidence of malformation (
= 0.53).
In this study we analysed a biased sample, based on clinical judgement regarding endometrial thickness, and the study was limited by its retrospective nature. The low statistical power caused by the group size disparity was also a limitation, especially in the CC-SBT group. Although the outcome showing inferiority of CC-SBT compared to natural-SBT is consistent with general findings in the literature, further large-scale clinical studies, ideally RCTs, are necessary to validate our results and clarify the prolonged effect of CC in SVBT cycles on pregnancy and neonatal outcomes.
Our observation suggests that CC administered in minimal ovarian stimulation cycles affects adversely the pregnancy outcomes when SBT is performed. Therefore, for a CC-based minimal stimulation IVF cycle, we suggest that frozen embryo transfer should be performed in a subsequent natural ovulatory cycle to avoid the possibility of implantation failure associated with CC administration.
The authors have no conflicts of interest to declare. No external funding was either sought or obtained.
We measured the Doppler broadening of annihilation radiation (DBAR) spectra of 3d (Fe, Co, and Ni) and 4f (Gd, Tb, and Dy) ferromagnets under a magnetic field by using spin-polarized positrons from a ...super(68)Ge- super(68)Ga source. The results showed that the DBAR spectra of these metals have notably different magnetic-field dependences. The differences among Fe, Co, and Ni reflect that the upper minority spin bands of Fe and Co are nearly empty while those of Ni are still mostly occupied. For the rare-earth metals instead of the inner 4f electrons, 5d electrons that mediate the exchange interaction of the 4f electrons are primarily responsible for the magnetic-field effects on the DBAR spectra. Furthermore, the magnetic-field effects on the DBAR spectra of Gd, Tb, and Dy vanished above the Curie temperatures of the magnetic-phase transition for these metals.
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