Photoionization of helium-like ions in asymptotic nonrelativistic region

The cross section for single K-shell ionization by a high-energy photon is evaluated in the next-to-leading order of the nonrelativistic perturbation theory with respect to the electron-electron interaction. The screening corrections are of particular importance for light helium-like ions. Even in the case of neutral He atom, our analytical predictions turn out to be in good agreement with the numerical calculations performed with the use of the sophisticated wave functions. The universal high-energy behavior is studied for the ratio of double-to-single photoionization cross sections. We also discuss the fast convergence of the perturbation theory over the reversed nuclear charge number 1/Z.Comment: 12 pages, 1 figure. to be published in Physics Letters

About universal scalings in double K-shell photoionization

We discuss the problem of the universal scalings in the double ionization of atomic K-shell electrons caused by absorption of a single photon. In particular, we envisage the following questions: Under which conditions and up to which accuracy the universal scalings are realized? Does it make sense to talk about different physical mechanisms in the double-ionization process? Finally, we present also the theoretical analysis of recent experimental measurements performed on neutral atoms. As a testing ground, QED perturbation theory is employed.Comment: 5 pages, 4 figure

Nuclear-polarization effect to the hyperfine structure in heavy multicharged ions

We have investigated the correction to the hyperfine structure of heavy multicharged ions, which is connected with the nuclear-polarization effect caused by the unpaired bound electron. Numerical calculations are performed for hydrogenlike ions taking into account the dominant collective nuclear excitations. The correction defines the ultimate limit of precision in accurate theoretical predictions of the hyperfine-structure splittings

Excitation of K-shell electrons by electron impact

The universal scaling behavior for the electron-impact excitation cross sections of the $2s$ states of hydrogen- and helium-like multicharged ions is deduced. The study is performed within the framework of non-relativistic perturbation theory, taking into account the one-photon exchange diagrams. Special emphasis is laid on the near-threshold energy domain. The parametrical relationship between the cross sections for excitation of multicharged ions with different number of electrons is established.Comment: to be published in Physics Letters

The hyperfine structure of highly charged 92238^{238}_{92}U ions with rotationally excited nuclei

The hyperfine structure (hfs) of electron levels of $^{238}_{92}$U ions with the nucleus excited in the low-lying rotational $2^+$ state with an energy $E_{2^+} = 44.91$ keV is investigated. In hydrogenlike uranium, the hfs splitting for the $1s_{1/2}$-ground state of the electron constitutes 1.8 eV. The hyperfine-quenched (hfq) lifetime of the $1s2p ^3P_0$ state has been calculated for heliumlike $^{238}_{92}$U and was found to be two orders of magnitude smaller than for the ion with the nucleus in the ground state. The possibility of a precise determination of the nuclear $g_r$ factor for the rotational $2^+$ state by measurements of the hfq lifetime is discussed.Comment: 10 LaTex page

A critical analysis of the assumptions underlying the formulation of maximum potential intensity for tropical cyclones

Emanuel's concept of maximum potential intensity (E-PI) estimates the maximum velocity of tropical cyclones from environmental parameters assuming thermal wind (gradient-wind and hydrostatic balances) and slantwise neutrality in the free troposphere. E-PI's key equation relates proportionally the radial gradients of saturated moist entropy and angular momentum. Here the E-PI derivation is reconsidered to show that the thermal wind and slantwise neutrality imply zero radial gradients of saturation entropy and angular momentum at an altitude where, for a given radius, the tangential wind has a maximum. It is further shown that, while E-PI's key equation requires that, at the point of maximum tangential wind, the air temperature must increase towards the storm center, the thermal wind equation dictates the opposite. From the analysis of the equations of motion at the altitude of maximum tangential wind in the free troposphere, it is concluded that here the air flow must be supergradient. This implies that the supergradiency factor (a measure of the gradient-wind imbalance) must change in the free troposphere as the air flow tends to restore the balance. It is shown that such a change modifies the derivative of saturation entropy over angular momentum, which cannot therefore remain constant in the free troposphere as E-PI requires. The implications of these findings for the internal coherence of E-PI, including its boundary layer closure, are discussed.Comment: Revised for JAS. Reply to three reviewers can be found in appendix C. 25 pages, 1 figur