Моделювання динамічних силових характеристик плунжерних токарних патронів з компенсаторами відцентрових сил

Efficient energy transfer was demonstrated in the SrF2:Eu2+, Pr3+ phosphor synthesized by the co-precipitation method. Results obtained with X-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray spectroscopy (XPS), photoluminescence (PL) and decay curves proposed the UV-Vis energy transfer process. The energy transfer process between the Eu2+ and Pr3+ ions in SrF2 was investigated to evaluate the potential of the Eu2+ ion as a sensitizer for the Pr3+ ion. The results proposed that Eu2+ could be a good sensitizer for absorbing the UV photons and efficiently enhancing the Pr3+ emission intensity. The energy transfer process was effective until concentration quenching for the Pr3+ ions occurred. The concentration quenching was attributed to cross-relaxation between the Pr3+ ions. (C) 2016 Author(s).Funding Agencies|South African Research Chairs Initiative of the Department of Science and Technology; National Research Foundation of South Africa; National Research Foundation (NRF); Cluster program of the University of the Free State</p

Genome-wide analysis of genetic and epigenetic control of programmed DNA deletion

During the development of the somatic genome from the Paramecium germline genome the bulk of the copies of ∼45 000 unique, internal eliminated sequences (IESs) are deleted. IES targeting is facilitated by two small RNA (sRNA) classes: scnRNAs, which relay epigenetic information from the parental nucleus to the developing nucleus, and iesRNAs, which are produced and used in the developing nucleus. Why only certain IESs require sRNAs for their removal has been enigmatic. By analyzing the silencing effects of three genes: PGM (responsible for DNA excision), DCL2/3 (scnRNA production) and DCL5 (iesRNA production), we identify key properties required for IES elimination. Based on these results, we propose that, depending on the exact combination of their lengths and end bases, some IESs are less efficiently recognized or excised and have a greater requirement for targeting by scnRNAs and iesRNAs. We suggest that the variation in IES retention following silencing of DCL2/3 is not primarily due to scnRNA density, which is comparatively uniform relative to IES retention, but rather the genetic properties of IESs. Taken together, our analyses demonstrate that in Paramecium the underlying genetic properties of developmentally deleted DNA sequences are essential in determining the sensitivity of these sequences to epigenetic contro

Chiral effective theory predictions for deuteron form factor ratios at low Q^2

We use chiral effective theory to predict the deuteron form factor ratio G_C/G_Q as well as ratios of deuteron to nucleon form factors. These ratios are calculated to next-to-next-to-leading order. At this order the chiral expansion for the NN isoscalar charge operator (including consistently calculated 1/M corrections) is a parameter-free prediction of the effective theory. Use of this operator in conjunction with NLO and NNLO chiral effective theory wave functions produces results that are consistent with extant experimental data for Q^2 < 0.35 GeV^2. These wave functions predict a deuteron quadrupole moment G_Q(Q^2=0)=0.278-0.282 fm^2-with the variation arising from short-distance contributions to this quantity. The variation is of the same size as the discrepancy between the theoretical result and the experimental value. This motivates the renormalization of G_Q via a two-nucleon operator that couples to quadrupole photons. After that renormalization we obtain a robust prediction for the shape of G_C/G_Q at Q^2 < 0.3 GeV^2. This allows us to make precise, model-independent predictions for the values of this ratio that will be measured at the lower end of the kinematic range explored at BLAST. We also present results for the ratio G_C/G_M.Comment: 31 pages, 7 figure

On the pion-nucleon coupling constant

In view of persisting misunderstanding about the determination of the pion-nucleon coupling constants in the Nijmegen multienergy partial-wave analyses of pp, np, and pbar-p scattering data, we present additional information which may clarify several points of discussion. We comment on several recent papers addressing the issue of the pion-nucleon coupling constant and criticizing the Nijmegen analyses.Comment: 19 pages, Nijmegen preprint THEF-NYM-92-0

The hyperon-nucleon interaction: conventional versus effective field theory approach

Hyperon-nucleon interactions are presented that are derived either in the conventional meson-exchange picture or within leading order chiral effective field theory. The chiral potential consists of one-pseudoscalar-meson exchanges and non-derivative four-baryon contact terms. With regard to meson-exchange hyperon-nucleon models we focus on the new potential of the Juelich group, whose most salient feature is that the contributions in the scalar--isoscalar (\sigma) and vector--isovector (\rho) exchange channels are constrained by a microscopic model of correlated \pi\pi and KKbar exchange.Comment: 28 pages, 8 figures, submitted to Lecture Notes in Physic

Hyperon-nucleon scattering and hyperon masses in the nuclear medium

We analyze low-energy hyperon-nucleon scattering using an effective field theory in next-to-leading order. By fitting experimental cross sections for laboratory hyperon momenta below 200 MeV/c and using information from the hypertriton we determine twelve contact-interaction coefficients. Based on these we discuss the low-density expansion of hyperon mass shifts in the nuclear medium.Comment: 10 pages, 2 figure

Soft-core hyperon-nucleon potentials

A new Nijmegen soft-core OBE potential model is presented for the low-energy YN interactions. Besides the results for the fit to the scattering data, which largely defines the model, we also present some applications to hypernuclear systems using the G-matrix method. An important innovation with respect to the original soft-core potential is the assignment of the cut-off masses for the baryon-baryon-meson (BBM) vertices in accordance with broken SU(3)$_F$, which serves to connect the NN and the YN channels. As a novel feature, we allow for medium strong breaking of the coupling constants, using the $^3P_0$ model with a Gell-Mann--Okubo hypercharge breaking for the BBM coupling. We present six hyperon-nucleon potentials which describe the available YN cross section data equally well, but which exhibit some differences on a more detailed level. The differences are constructed such that the models encompass a range of scattering lengths in the $\Sigma N$ and $\Lambda N$ channels. For the scalar-meson mixing angle we obtained values $\theta_S=37$ to 40 degrees, which points to almost ideal mixing angles for the scalar $q\bar{q}$ states. The G-matrix results indicate that the remarkably different spin-spin terms of the six potentials appear specifically in the energy spectra of $\Lambda$ hypernuclei.Comment: 37 pages, 4 figure