Classical approach in quantum physics

The application of a classical approach to various quantum problems - the secular perturbation approach to quantization of a hydrogen atom in external fields and a helium atom, the adiabatic switching method for calculation of a semiclassical spectrum of hydrogen atom in crossed electric and magnetic fields, a spontaneous decay of excited states of a hydrogen atom, Gutzwiller's approach to Stark problem, long-lived excited states of a helium atom recently discovered with the help of Poincar$\acute{\mathrm{e}}$ section, inelastic transitions in slow and fast electron-atom and ion-atom collisions - is reviewed. Further, a classical representation in quantum theory is discussed. In this representation the quantum states are treating as an ensemble of classical states. This approach opens the way to an accurate description of the initial and final states in classical trajectory Monte Carlo (CTMC) method and a purely classical explanation of tunneling phenomenon. The general aspects of the structure of the semiclassical series such as renormgroup symmetry, criterion of accuracy and so on are reviewed as well. In conclusion, the relation between quantum theory, classical physics and measurement is discussed.Comment: This review paper was rejected from J.Phys.A with referee's comment "The author has made many worthwhile contributions to semiclassical physics, but this article does not meet the standard for a topical review"

Resonance scattering and singularities of the scattering function

Recent studies of transport phenomena with complex potentials are explained by generic square root singularities of spectrum and eigenfunctions of non-Hermitian Hamiltonians. Using a two channel problem we demonstrate that such singularities produce a significant effect upon the pole behaviour of the scattering matrix, and more significantly upon the associated residues. This mechanism explains why by proper choice of the system parameters the resonance cross section is increased drastically in one channel and suppressed in the other channel.Comment: 4 pages, 3 figure

Transcranial Doppler ultrasound is a diagnostic and predicting tool for movement disorders in children after hypoxic ischemic encephalopathy

K.A. Pugolovkin, E.A. Efimova, E.A. Dombrovskaya, I.Yu. Platonova, A.A. Solov’ev Research Practical Center for Children’s Psychoneurology, Moscow, Russia Aim: to assess brain circulation in the regions supplied by the basilar artery (BA) in children with movement disorders and motor skill delay in the late rehabilitative period after hypoxic ischemic encephalopathy and its importance for the objectivity of clinical data and evaluation of rehabilitative effect. Patients and Methods: 28 children (mean age one year seven months) with movement disorders and motor skill delay (after hypoxic ischemic CNS lesion in the perinatal period) without lower extremity paraparesis or Willis circle abnormalities (by Doppler ultrasound) were examined. Doppler ultrasound was performed using the suboccipital approach at 3–8 months with 3–4-month intervals. The parameters of blood flow in BA, i.e., resistivity index (RI) and mean blood flow velocity (Vm), were measured. Retrospectively, children were divided into three groups based on motor skill delay severity (mild, moderate, or severe) and time for standing unaided to walking. Mean values in the groups and relative deviations (increase/decrease) from reference values in a given age group were compared. Results: motor skill delay severity and predicting time for standing unaided to walking correlated with RI and Vm. RI was a diagnostically valuable parameter whose reference values differed from motor skill delay severity. Isolated increase in Vm and normal RI were reported in children with motor skill dela y 1–3 months before standing unaided to walking. This type of blood circulation is a transitional one during clinical improvement in some children. Conclusions: a set of instrumental data allow for describing motor skill delay severity depending on RI deviations from normal values in the regions supplied by BA. The sequence of brain circulation parameter changes is in line with the clinical course, e.g., RI normalization and further gradual recovery of blood flow velocity. Keywords: movement disorders, motor skill delay, Transcranial Doppler ultrasound, basilar artery, resistivity index RI, mean blood flow velocity Vm. For citation: Pugolovkin K.A., Efimova E.A., Dombrovskaya E.A. et al. Transcranial Doppler ultrasound is a diagnostic and predicting tool for movement disorders in children after hypoxic ischemic encephalopathy. Russian Journal of Woman and Child Health. 2021;4(3):254–259 (in Russ.). DOI: 10.32364/2618-8430-2021-4-3-254-259. </p

Frozen-planet resonances in doubly excited helium atom; adiabatic approach

Abstract: An improved adiabatic method is applied to study the highly excited asymmetric two-electron configurations of helium atom known as frozen-planet resonances. It is shown that our approach provides much better agreement with numerically calculated resonance positions than the previously used Born–Oppenheimer type approximation. Wide range of states were studied, related to N = 7 − 15 first-ionization thresholds. We show that estimates of tunneling widths of these states however are not reliable, because of the breakdown of adiabatic approximation in the underbarrier region of configuration space. We also provide computational evidence that a single-potential approximation in hyperspherical coordinates would be inferior to our approach. Graphical abstract: [Figure not available: see fulltext.]. © 2020, EDP Sciences / Società Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature