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Observations of the 57Fe+23 hyperfine transition in clusters of galaxies
No full textWe present a search for the hyperfine transition of the 57Fe+23 ion at 3.071 mm in clusters of galaxies with the ATNF Mopra telescope. The results are compared with a realistic estimate of the peak brightness temperature of the line in a cooling flow cluster A85, using the available X-ray data
High-precision QED calculations of the hyperfine structure in hydrogen and transition rates in multicharged ions
No full textStudies of the hyperfine splitting in hydrogen are strongly motivated by the level of accuracy achieved in recent atomic physics experiments, which yield finally model-independent informations about nuclear structure parameters with utmost precision. Considering the current status of the determination of corrections to the hyperfine splitting of the ground state in hydrogen, this thesis provides further improved calculations by taking into account the most recent value for the proton charge radius. Comparing theoretical and experimental data of the hyperfine splitting in hydrogen the proton-size contribution is extracted and a relativistic formula for this contribution is derived in terms of moments of the nuclear charge and magnetization distributions. An iterative scheme for the determination of the Zemach and magnetic radii of the proton is proposed. As a result, the Zemach and magnetic radii are determined and the values are compared with the corresponding ones deduced from data obtained in electron-proton scattering experiments. The extraction of the Zemach radius from a rescaled difference between the hyperfine splitting in hydrogen and in muonium is considered as well. Investigations of forbidden radiative transitions in few-electron ions within ab initio QED provide a most sensitive tool for probing the influence of relativistic electron-correlation and QED corrections to the transition rates. Accordingly, a major part of this thesis is devoted to detailed studies of radiative and interelectronic-interaction effects to the transition probabilities. The renormalized expressions for the corresponding corrections in one- and two-electron ions as well as for ions with one electron over closed shells are derived employing the two-time Green's function method. Numerical results for the correlation corrections to magnetic transition rates in He-like ions are presented. For the first time also the frequency-dependent contribution is calculated, which has to be accounted for preserving gauge invariance. One-loop QED corrections to the magnetic-dipole transition amplitude between the fine-structure levels 2p_{3/2} and 2p_{1/2} are calculated to all orders in \alpha Z. Taking into account consistently relativistic, interelectronic-interaction, and QED corrections to the magnetic-dipole transition amplitude allows for predictions of the lifetimes of the states (1s^2 2s^2 2p)^2P_{3/2} in B-like ions and (1s^2 2s 2p)^3P_2 in Be-like ions with utmost precision. The results of corresponding calculations are compared with experimental data obtained in recent measurements at the Heidelberg EBIT. Finally, for He-like ions with nonzero-spin nuclei the effect of hyperfine quenching on the lifetimes of the 2^3P_{0,2} states is investigated and again compared available experimental data
Vacuum birefringence and dichroism in a strong plane-wave background
No full textIn the present study, we consider the effects of vacuum birefringence and
dichroism in strong electromagnetic fields. According to quantum
electrodynamics, the vacuum state exhibits different refractive properties
depending on the probe photon polarization and one also obtains different
probabilities of the photon decay via production of electron-positron pairs.
Here we investigate these two phenomena by means of several different
approaches to computing the polarization operator. The external field is
assumed to be a linearly polarized plane electromagnetic wave of arbitrary
amplitude and frequency. Varying the probe-photon energy and the field
parameters, we thoroughly examine the validity of the locally-constant field
approximation (LCFA) and techniques involving perturbative expansions in terms
of the external-field amplitude. Within the latter approach, we develop a
numerical method based on a direct evaluation of the weak-field Feynman
diagrams, which can be employed for investigating more complex external
backgrounds. It is demonstrated that the polarization operator depends on two
parameters: classical nonlinearity parameter and the product of the laser field frequency and the photon energy
( is the electron mass). The domains of validity of the approximate
techniques in the plane are explicitly identified.Comment: 11 pages, 6 figure
Predictors of adverse events in the mid-term postoperative period in patients who underwent carotid endarterectomy
No full text<p><strong>Aim.</strong> Emphasis in the study was placed on the identification of unfavorable prognosis factors associated with carotid endarterectomy (CEE) during mid-term follow-up.<br /><strong>Methods.</strong> Over a period from 2015 to 2016, 222 CEE operations were performed. Most patients (n = 190; 85.5%) underwent CEE using a patch of xenopericardium, 14.4% (n = 32) received eversion CEE, and a temporary shunt was used in 14.4% (n = 32). Hybrid revascularization in the volume of percutaneous coronary intervention (PCI) + CEE was performed in 9.9% (n = 22) patients. The groups under study were compared by using a chi-square test followed by subsequent analysis of the shares, or if ordinal characters or quantitative traits with a distribution different from the normal one occurred—by using a Mann – Whitney U-test. Correction of multiple comparisons was done by calculating an average fraction of false discoveries of the hypotheses (false discovery rate). The analysis of prognostic factors was done using the odds ratio (OR) by means of the 2 × 2 tables.<br /><strong>Results.</strong> Among the complications detected in the mid-term follow-up, the most common adverse event was the development of MI in 3.6% (n = 8) of patients. According to color duplex scanning of brachiocephalic arteries, restenosis of the operated ICA was observed in 4.5% of patients. The following risk factors significantly increased the risk of adverse events: angina pectoris II–III functional class (OR = 3.84%, CI = 1.24–11.9), SYNTAX Score &gt;22 (OR = 2.83, CI = 1.137–7.086).<br /><strong>Conclusion.</strong> Based on the results of a single-center prospective retrospective study, significant risk factors for adverse outcome in the mid-term postoperative period were identified.</p><p>Received 10 May 2017. Revised 27 September 2017. Accepted 5 October 2017.</p><p><strong>Funding:</strong> The research was done with support of the grant (No. 12090ГУ/2017) awarded by the Fund for Facilitation of Innovations within the framework of the “Umnik-2016” project (Kemerovo).</p><p><strong>Conflict of interest:</strong> The authors declare no conflict of interest.</p><p><strong>Author contributions</strong><br />Conception and study design: R.S. Tarasov, A.I. Anufriyev <br />Data collection and analysis: A.R. Shabaev<br />Drafting the article: A.N. Kazantsev, N.N. Burkov <br />Critical revision of the article: A.V. Mironov<br />Final approval of the version to be published: L.S. Barbarash</p></jats:p
Breit and QED effects on the 3d9 D3/2 2 →2D5/2 transition energy in Co-like ions
No full textThe multiconfiguration Dirac-Hartree-Fock theory is used to calculate the 3d9D3/22→2D5/2 transition energy for Co-like ions with Z=28-100. We investigate how electron correlation, frequency-independent and -dependent Breit interactions, as well as QED corrections vary along the sequence. The well-understood frequency-independent Breit contribution has the largest contribution for all ions. Among the corrections to this, correlation decreases rapidly with Z, the frequency-dependent Breit contribution is important especially for high-Z ions, and the self-energy contribution to the QED becomes the largest correction already for Z>50. We evaluate and compare results for the Self-energy in three different approximations, (i) the approach implemented in the grasp2k package, (ii) the method based on Welton's concept and (iii) a model operator approach recently developed by Shabaev and coworkers. Through comparison with experimental values, it seems that the third set of results have the best agreement with experiments, but the difference from experiments for high-Z ions, is around 0.03%-0.04%, and therefore our results are outside the error bars of the experiments
Calculation of the Interelectronic-Interaction Correction to Radiative Recombination of an Electron with a Heavy He-Like Ion
No full textTemperature Histories of Ti-6Al-4V Pulsed-Mode Laser Welds Calculated Using Multiple Constraints
No full textThermodynamics of droplet formation around a soluble condensation nucleus in the atmosphere of a solvent vapor
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