2,547 research outputs found
Two-loop QED corrections with closed fermion loops for the bound-electron g factor
Two-loop QED corrections with closed fermion loops are calculated for the 1s
bound-electron g factor. Calculations are performed to all orders in the
nuclear binding strength parameter Z\alpha (where Z is the nuclear charge and
\alpha is the fine structure constant) except for the closed fermion loop,
which is treated within the free-loop (Uehling) approximation in some cases.
Comparison with previous Z\alpha-expansion calculations is made and the
higher-order remainder of order \alpha^2(Z\alpha)^5 and higher is separated out
from the numerical results
Nuclear-size self-energy and vacuum-polarization corrections to the bound-electron g factor
The finite nuclear-size effect on the leading bound-electron g factor and the
one-loop QED corrections to the bound-electron g factor is investigated for the
ground state of hydrogen-like ions. The calculation is performed to all orders
in the nuclear binding strength parameter Z\alpha\ (where Z is the nuclear
charge and \alpha\ is the fine structure constant) and for the Fermi model of
the nuclear charge distribution. In the result, theoretical predictions for the
isotope shift of the 1s bound-electron g factor are obtained, which can be used
for the determination of the difference of nuclear charge radii from
experimental values of the bound-electron g factors for different isotopes
QED calculation of the nuclear magnetic shielding for hydrogen-like ions
We report an ab initio calculation of the shielding of the nuclear magnetic
moment by the bound electron in hydrogen-like ions. This investigation takes
into account several effects that have not been calculated before (electron
self-energy, vacuum polarization, nuclear magnetization distribution), thus
bringing the theory to the point where further progress is impeded by the
uncertainty due to nuclear-structure effects. The QED corrections are
calculated to all orders in the nuclear binding strength parameter and,
independently, to the leading order in the expansion in this parameter. The
results obtained lay the ground for the high-precision determination of nuclear
magnetic dipole moments from measurements of the g-factor of hydrogen-like
ions
Electron-correlation effects in the -factor of light Li-like ions
We investigate electron-correlation effects in the -factor of the ground
state of Li-like ions. Our calculations are performed within the
nonrelativistic quantum electrodynamics (NRQED) expansion up to two leading
orders in the fine-structure constant , and . The
dependence of the NRQED results on the nuclear charge number is studied and
the individual -expansion contributions are identified. Combining the
obtained data with the results of the all-order (in ) calculations
performed within the expansion, we derive the unified theoretical
predictions for the -factor of light Li-like ions.Comment: 9 pages, 4 table
QED theory of the nuclear magnetic shielding in hydrogen-like ions
The shielding of the nuclear magnetic moment by the bound electron in
hydrogen-like ions is calculated ab initio with inclusion of relativistic,
nuclear, and quantum electrodynamics (QED) effects. The QED correction is
evaluated to all orders in the nuclear binding strength parameter and,
independently, to the first order in the expansion in this parameter. The
results obtained lay the basis for the high-precision determination of nuclear
magnetic dipole moments from measurements of the g-factor of hydrogen-like
ions.Comment: 4 pages, 2 tables, 2 figure
Nuclear-resonant electron scattering
We investigate nuclear-resonant electron scattering as occurring in the
two-step process of nuclear excitation by electron capture (NEEC) followed by
internal conversion. The nuclear excitation and decay are treated by a
phenomenological collective model in which nuclear states and transition
probabilities are described by experimental parameters. We present capture
rates and resonant strengths for a number of heavy ion collision systems
considering various scenarios for the resonant electron scattering process. The
results show that for certain cases resonant electron scattering can have
significantly larger resonance strengths than NEEC followed by the radiative
decay of the nucleus. We discuss the impact of our findings on the possible
experimental observation of NEEC.Comment: 24 pages, 2 plots, 5 table
Family practices and temporality at breakfast: hot spots, convenience and care
Drawing on 34 semi-structured interviews, this study investigates the temporality of family practices taking place in the hot spot (Southerton, 2003). It does so by looking at how breakfast is inserted in the economy of family time in Italy. Our data show that breakfast, contrary to other meals, allows the adoption of more individualised and asynchronous practices, hinged on the consumption of convenience products. These time-saving strategies are normalised as part of doing family. Although the existing literature suggests that convenience and care are in opposition, and consumers of convenience products can experience anxiety and a lack of personal integrity, such features were not a dominant feature of our participants’ accounts. These findings suggest that the dichotomies of hot/cold spots and care/convenience are not always experienced in opposition when embedded within family practices. Hence, this study furthers understandings of family meals, temporality and the distinction between hot and cold spots
Intensive Grandmothering? Exploring the Changing Nature of Grandmothering in the Context of Changes to Parenting Culture
This paper explores the ways in which the intensification of parenting and the notion of children at risk have influenced grandmothers’ narratives and practices. Interviews with grandmothers who regularly look after their grandchildren, reveal that their practices are framed around the notions of children to be protected, educated and entertained. Such notions reveal that aspects of grandmothers’ roles as protectors, educators, playmates and confidants involved negotiations with parents around the ideal of ‘putting the child first’. The paper argues that intensive parenting has influenced grandmothering but the way this is enacted reveals resistance to certain aspects of intensive parenting
Two-photon-exchange corrections to the g factor of Li-like ions
We report calculations of QED corrections to the factor of Li-like ions induced by the exchange of two virtual photons between the electrons. The calculations are performed within QED theory to all orders in the nuclear binding strength parameter , where is the nuclear charge number and is the fine-structure constant. In the region of low nuclear charges we compare results from three different methods: QED, relativistic many-body perturbation theory, and nonrelativistic QED. All three methods are shown to yield consistent results. With our calculations we improve the accuracy of the theoretical predictions of the factor of the ground state of Li-like carbon and oxygen by about an order of magnitude. Our theoretical results agree with those from previous calculations but differ by 3-4 standard deviations from the experimental results available for silicon and calcium
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