Sturmian bases for two-electron systems in hyperspherical coordinates

We give a detailed account of an $\it{ab}$ $\it{initio}$ spectral approach for the calculation of energy spectra of two active electron atoms in a system of hyperspherical coordinates. In this system of coordinates, the Hamiltonian has the same structure as the one of atomic hydrogen with the Coulomb potential expressed in terms of a hyperradius and the nuclear charge replaced by an angle dependent effective charge. The simplest spectral approach consists in expanding the hyperangular wave function in a basis of hyperspherical harmonics. This expansion however, is known to be very slowly converging. Instead, we introduce new hyperangular sturmian functions. These functions do not have an analytical expression but they treat the first term of the multipole expansion of the electron-electron interaction potential, namely the radial electron correlation, exactly. The properties of these new functions are discussed in detail. For the basis functions of the hyperradius, several choices are possible. In the present case, we use Coulomb sturmian functions of half integer angular momentum. We show that, in the case of H$^-$, the accuracy of the energy and the width of the resonance states obtained through a single diagonalization of the Hamiltonian, is comparable to the values given by state-of-the-art methods while using a much smaller basis set. In addition, we show that precise values of the electric-dipole oscillator strengths for $S\rightarrow P$ transitions in helium are obtained thereby confirming the accuracy of the bound state wave functions generated with the present method.Comment: 28 pages, 4 figure

Treatment trends in allergic rhinitis and asthma: a British ENT survey

<p>Abstract</p> <p>Background</p> <p>Allergic Rhinitis is a common Ear, Nose and Throat disorder. Asthma and Allergic Rhinitis are diseases with similar underlying mechanism and pathogenesis. The aim of this survey was to highlight current treatment trends for Allergic Rhinitis and Asthma.</p> <p>Method</p> <p>A questionnaire was emailed to all registered consultant members of the British Association of Otorhinolaryngologists - Head and Neck Surgeons regarding the management of patients with Allergic Rhinitis and related disorders.</p> <p>Results</p> <p>Survey response rate was 56%. The results indicate a various approach in the investigation and management of Allergic Rhinitis compatible with recommendations from the Allergic Rhinitis and Its Impact on Asthma guidelines in collaboration with the World Health Organisation.</p> <p>Conclusion</p> <p>A combined management approach for patients with Allergic Rhinitis and concomitant Asthma may reduce medical treatment costs for these conditions and improve symptom control and quality of life.</p

Two-photon double ionization of atoms in attosecond x-ray radiation fields

We consider two-photon double ionization of helium with 100, 200, and 400 eV excess energy for the two ejected electrons, corresponding to photon energies of 89.5, 139.5, and 239.5 eV, respectively. We focus on the case of ultrashort pulses (two oscillations of the field) and develop an approach to calculate the two-photon transition matrix elements within the lowest order of the time-dependent perturbation theory. One of the major difficulties in calculating such amplitudes is the infinite summation over a complete set of intermediate states. In the subfemtosecond regime, however, this summation can be performed accurately by means of the closure approximation. This results in a simple expression for the two-photon amplitude that contains a dipole term and a quadrupole term. The dipole term can be clearly associated to a process in which each electron absorbs a photon whereas the quadrupole term is associated to a process in which one electron absorbs two photons and ejects the second one by collision. We analyze in detail how the relative weight of both processes influences the behavior of the electron energy and angular distributions. In particular we study how the shape of these distributions changes with the amount of electron correlations taken into account in both initial and final states. For 100 eV excess energy, our results for the electron energy distribution are compared with those obtained by solving the time-dependent Schrodinger equation. All these results unveil the crucial role of electron correlations in this transient regime of ionization which is neither sequential nor direct