Representation of a complex Green function on a real basis: I. General Theory

When the Hamiltonian of a system is represented by a finite matrix, constructed from a discrete basis, the matrix representation of the resolvent covers only one branch. We show how all branches can be specified by the phase of a complex unit of time. This permits the Hamiltonian matrix to be constructed on a real basis; the only duty of the basis is to span the dynamical region of space, without regard for the particular asymptotic boundary conditions that pertain to the problem of interest.Comment: about 40 pages with 5 eps-figure

Elastic scattering of protons from hydrogen atoms at energies 15-200keV

Differential and integrated cross sections for the elastic process H^+ + H(1s) → H^+ + H(1s) were calculated with the use of results of coupled-state calculations in the energy range 15-200 keV. Results are presented and, at 60 keV, compared favorably with preliminary experimental data. The asymptotic form of the elastic amplitude for b≫a_0 (where b is the impact parameter) is derived for the two cases λ≪1 and λ≫1, where λ is the ratio of the collision duration to the orbital period. The asymptotic form for λ≫1 provides a useful test on the numerical accuracy of the amplitudes

Application of an extremum principle to the variational determination of the generalized oscillator strengths of helium

Variational principles have been used extensively for estimating some given functional F(φ, φ†) where the functions φ and φ† are well defined by a set of differential equations and boundary conditions but cannot be determined exactly. The variational principle for the estimation of a matrix element of an arbitrary Hermitian operator W involves not only the trial wave functions φt but also trial auxiliary Lagrange functions Lt; the Lt depend on the φt and on W. To determine the parameters in the Lt efficiently, a functional M(Ltt) is constructed which is an extremum for Ltt=Lt. The technique was recently used successfully in the variational estimation of two diagonal matrix elements. We here use this technique for the variational estimation of an off-diagonal matrix element, the generalized oscillator strengths of helium for the transition between the ground state and the excited 21P state. Two Lt\u27s must be determined. Our results on helium indicate that variational estimates are a significant improvement over the first-order estimates. The results are also compared with those obtained nonvariationally using more elaborate ground-and excited-state wave functions; the comparison represents a check on the method. It is not yet clear which of the two approaches is more efficient

Distorted-wave Born approximation for inelastic collisions: Application to electron capture by positrons from hydrogen atoms

We have re-examined the distorted-wave Born approximation for inelastic collisions. We find that the distortion in the relative motion of the collision partners cannot be neglected even for high-energy ion-atom collisions. Furthermore, if the distortion in the relative motion is not treated exactly, post-prior discrepancies will occur. We have applied the distorted-wave Born approximation, with distortion included through first order, to ground-state-to-ground-state electron capture by positrons from hydrogen atoms. The results are presented in this paper. We have also examined the nonrelativistic asymptotic behavior of the cross section for electron capture from hydrogen by positrons incident with a speed v∼∞. We find that, for e2ℏv≪1, capture occurs primarily to states of positronium that have an odd orbital-angular-momentum quantum number. It follows that the cusp signifying charge transfer to the continuum will, for positron impact, be symmetric when e2ℏv≪1

A radio continuum survey of the southern sky at 1420 MHz. Observations and data reduction

We describe the equipment, observational method and reduction procedure of an absolutely calibrated radio continuum survey of the South Celestial Hemisphere at a frequency of 1420 MHz. These observations cover the area 0h < R.A. < 24h for declinations less than -10 degree. The sensitivity is about 50 mK T_B (full beam brightness) and the angular resolution (HPBW) is 35.4', which matches the existing northern sky survey at the same frequency.Comment: 9 pages with 9 figures, A&A, in pres

A Search for Isolated Radio Pulses from the Crab Nebula at 151.5 MHz

A search has been made for large bursts of radio emission at 151.5 MHz from the direction of the Crab Nebula. In 605 hr of observation, no events exceeding a flux of 1.4 × 10^(−22) W m^(−2) Hz^(−1) were detected. This therefore sets an upper limit for the energy in radio pulses from the direction of the Crab Nebula which might be associated with the events recorded in the gravitational wave experiments of Weber. Implications of the results with regard to ‘strong pulses’ and phase fluctuations in the periodic emissions from the pulsar NP 0532 are also examined

Gender and educational leadership in England: a comparison of secondary headteachers' views over time

In the context of gender being a barrier to accessing leadership, this paper presents a comparison of the views of men and women head teacher (principals) of secondary schools in England in the 1990s and in 2004. The same survey instrument was used on both occasions. The perceptions of the head teachers show change in some areas and no change in others. Overall, women are more likely to become head teachers and are now less likely to be categorised into pastoral roles, but in some cases women still meet prejudice from governors and others in the wider community. Women head teachers are more likely to have partners and children than in the 1990s, sharing equally or carrying most of the domestic responsibilities, whereas male colleagues are most likely to have partners who take the majority of responsibility in the home. Essentialist stereotypes about women and men as leaders still prevail, although both the women and men head teachers see themselves as adopting a traditionally ‘feminine’ style of leadership. Women head teachers are likely to see some benefits in being a woman in a role stereotypically associated with men. However, there has been an increase in the proportion of women who feel that they have to prove their worth as a leader, and this may be linked with increased levels of accountability in schools

The effectiveness, safety and cost-effectiveness of cytisine versus varenicline for smoking cessation in an Australian population: a study protocol for a randomized controlled non-inferiority trial

Smoking cessation medications are effective but often underutilised because of costs and side effects. Cytisine is a plant-based smoking cessation medication with over 50 years of use in Central and Eastern Europe. While cytisine has been found to be well-tolerated and more effective than nicotine replacement therapy, direct comparison with varenicline have not been conducted. This study evaluates the effectiveness, safety and cost-effectiveness of cytisine compared with varenicline.Two arm, parallel group, randomised, non-inferiority trial, with allocation concealment and blinded outcome assessment.Australian population-based study.Adult daily smokers (N=1266) interested in quitting will be recruited through advertisements and Quitline telephone-based cessation support services.Eligible participants will be randomised (1:1 ratio) to receive either cytisine capsules (25-day supply) or varenicline tablets (12-week supply), prescribed in accordance with the manufacturer's recommended dosing regimen. The medication will be mailed to each participant's nominated residential address. All participants will also be offered standard Quitline behavioural support (up to six 10-12 minute sessions).Assessments will be undertaken by telephone at baseline, 4- and 7-months post-randomisation. Participants will also be contacted twice (two and four weeks post-randomisation) to ascertain adverse events, treatment adherence and smoking status. The primary outcome will be self-reported 6-month continuous abstinence from smoking, verified by carbon monoxide at 7-month follow-up. We will also evaluate the relative safety and cost-effectiveness of cytisine compared with varenicline. Secondary outcomes will include self-reported continuous and 7-day point prevalence abstinence and cigarette consumption at each follow-up interview.If cytisine is as effective as varenicline, its lower cost and natural plant-based composition may make it an acceptable and affordable smoking cessation medication that could save millions of lives worldwide