Selective Production of Rydberg-Stark States of Positronium

Rydberg positronium (Ps) atoms have been prepared in selected Stark states via two-step (1s→2p→nd/ns) optical excitation. Two methods have been used to achieve Stark-state selection: a field ionization filter that transmits the outermost states with positive Stark shifts, and state-selected photoexcitation in a strong electric field. The former is demonstrated for n=17 and 18 while the latter is performed for n=11 in a homogeneous electric field of 1.9  kV/cm. The observed spectral intensities and their dependence on the polarization of the laser radiation are in agreement with calculations that include the perturbations of the intermediate n=2 manifold. Our results pave the way for the generation of Rydberg Ps atoms with large electric dipole moments that are required for the realization of schemes to control their motion using inhomogeneous electric fields, an essential feature of some proposed Ps free-fall measurements requiring focused beams of long-lived atoms

Production of 2(3) S-1 positronium atoms by single-photon excitation in an electric field

We report experiments in which positronium (Ps) atoms are produced in the 2 3 S1 level by single-photon excitation from the ground state. To accomplish this, Stark-mixed n = 2 states were optically excited in electric fields. By adiabatically switching off the electric field after laser excitation, some of the mixed states evolved into pure 2 3 S1 levels, whose presence was detected via the time dependence of their annihilation γ radiation. The observed ≈4% production efficiency relative to that of Rydberg Ps states is consistent with a Monte Carlo simulation that takes into account the rate at which the electric fields were switched off

Electrostatically Guided Rydberg Positronium

We report experiments in which positronium (Ps) atoms were guided using inhomogeneous electric fields. Ps atoms in Rydberg-Stark states with principal quantum number n=10 and electric dipole moments up to 610 D were prepared via two-color two-photon optical excitation in the presence of a 670  V cm−1 electric field. The Ps atoms were created at the entrance of a 0.4 m long electrostatic quadrupole guide, and were detected at the end of the guide via annihilation gamma radiation. When the lasers were tuned to excite low-field-seeking Stark states, a fivefold increase in the number of atoms reaching the end of the guide was observed, whereas no signal was detected when high-field-seeking states were produced. The data are consistent with the calculated geometrical guide acceptance

Positronium decay from n=2 states in electric and magnetic fields

We report measurements and the results of calculations demonstrating that the annihilation dynamics of positronium (Ps) atoms can be controlled by Stark and Zeeman mixing of optically excited states. In the experiments a trap-based pulsed positron beam was employed to generate a dilute Ps gas with a density of ∼107 cm−3 using a porous silica target. These atoms were excited via 13S1→23PJ transitions in parallel electric and magnetic fields using a nanosecond pulsed dye laser, and Ps annihilation was measured using single-shot lifetime spectroscopy. The composition of the excited n=2 sublevels was controlled by varying the polarization of the excitation laser radiation and the strength of the electric and magnetic fields in the excitation region. The overall decay rates of the excited states can vary by a large amount, owing to the enormous differences between the annihilation and florescence lifetimes of the accessible field-free states. The energy-level structure, spectral intensities, and florescence and annihilation lifetimes in the presence of the fields were determined from the eigenvalues and eigenvectors of the complete n=2 Hamiltonian matrix in an |nSℓJMJ⟩ basis. Using these data as the input to a Monte Carlo model yielded calculated values which could be compared with experimentally measured quantities; qualitative agreement with the measurements was found. Varying the electric field in the presence of a weak parallel magnetic field provides control over the amount of level mixing that occurs, making it possible to increase or decrease the Ps lifetime. Field-controlled Ps decay can be used as an ionization-free detection method. Conversely, increasing the excited-state lifetime can potentially be exploited to optimize multistep excitation processes using mixed intermediate states. This will be useful either in minimizing losses through intermediate-state decay during excitation or by making it possible to separate excitation laser pulses in time. In addition, the adiabatic extraction of appropriate eigenstates from the electric field in which they are excited can, in principle, be used to prepare pure 23S1 atoms. The availability of atoms in these states produced via single-photon excitation will facilitate high-resolution microwave spectroscopy of the Ps n=2 fine structure

Measurement of Rydberg positronium fluorescence lifetimes

We report measurements of the fluorescence lifetimes of positronium (Ps) atoms with principal quantum numbers n=10–19. Ps atoms in Rydberg-Stark states were produced via a two-color two-step 1S3→2P3→nS3/nD3 excitation scheme and subsequently detected after traveling 1.2 m. The measured time-of-flight distributions were used to determine the mean lifetimes of the Rydberg levels, yielding values ranging from 3μs to 26μs. Our data are in accord with the expected radiative lifetimes of Rydberg-Stark states of Ps

"...they should be offering it": a qualitative study to investigate young peoples' attitudes towards chlamydia screening in GP surgeries

<p>Abstract</p> <p>Background</p> <p>Despite the known health and healthcare costs of untreated chlamydia infection and the efforts of the National Chlamydia Screening Programme (NCSP) to control chlamydia through early detection and treatment of asymptomatic infection, the rates of screening are well below the 2010-2011 target rate of 35%. General Practitioner (GP) surgeries are a key venue within the NCSP however; previous studies indicate that GP surgery staff are concerned that they may offend their patients by offering a screen. This study aimed to identify the attitudes to, and preferences for, chlamydia screening in 15-24 year old men and women attending GP surgeries (the target group).</p> <p>Methods</p> <p>We undertook 36 interviews in six surgeries of differing screening rates. Our participants were 15-24 year olds attending a consultation with a staff member. Data were analysed thematically.</p> <p>Results</p> <p>GP surgeries are acceptable to young people as a venue for opportunistic chlamydia screening and furthermore they think it is the duty of GP surgery staff to offer it. They felt strongly that it is important for surgery staff to have a non-judgemental attitude and they did not want to be singled out as 'needing' a chlamydia screen. Furthermore, our sample reported a strong preference for being offered a screen by staff and providing the sample immediately at the surgery rather than taking home a testing kit. The positive attitude and subjective norms demonstrated by interviewees suggest that young peoples' behaviour would be to accept a screen if it was offered to them.</p> <p>Conclusion</p> <p>Young people attending GP surgeries have a positive attitude towards chlamydia screening and given the right environment are likely to take up the offer in this setting. The right environment involves normalising screening by offering a chlamydia screen to all 15-24 year olds at every interaction with staff, offering screening with a non-judgemental attitude and minimising barriers to screening such as embarrassment. The GP surgery is the ideal place to screen young people for chlamydia as it is not a threatening place for them and our study has shown that they think it is the normal place to go to discuss health matters.</p

Valuing Governance

Book Summary: As has been abundantly documented in the popular and academic press, the humanities are facing challenging times marked by national debate regarding the importance of the humanities in higher education, program and budget cuts, and an ever-decreasing number of tenure-track jobs. In addition, the humanities face quite literally a quantification of their value as the Academy adopts a more corporate mindset. This volume provides advice to professionals in the humanities on how to forge a useful, compelling, and productive career. The book’s 13 chapters address professional approaches to developing and maintaining an active research agenda, fomenting the ideals of the teacher-scholar model, managing the service demands within and outside the college or university, and navigating institutional politics. The collection offers practical and theoretical approaches to higher education, personal anecdotes, intelligent advice, and interviews with colleagues in the humanities. Specific themes addressed include the transition from graduate student to humanities professional, diverging from prescribed paths, the humanities professor as creative writer, moving from secondary to post-secondary education, humanities in an international, market-based context, and participation in governance structures. [From the publisher] Chapter Summary: This essay focuses on providing insight and practical advice on how committed participation in the governance process offers many positives at any stage of the academic ladder. Drawing upon a practical, theoretical, and anecdotal approach, this article reflects on four areas that are enhanced by participation in governance: 1) visibility; 2) knowledge of the institution and its culture; 3) establishing meaningful friendships campus-wide; and 4) governance as a resource of invaluable advice

Incubation with sodium nitrite attenuates fatigue development in intact single mouse fibres at physiological PO2

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordDietary nitrate (NO3−) supplementation, which increases plasma nitrite (NO2−) concentration, has been reported to attenuate skeletal muscle fatigue development. Sarcoplasmic reticulum (SR) calcium (Ca2+) release is enhanced in isolated single skeletal muscle fibres following NO3− supplementation or NO2− incubation at a supra‐physiological PO2 but it is unclear whether NO2− incubation can alter Ca2+ handling and fatigue development at a near‐physiological PO2. We hypothesised that NO2− treatment would improve Ca2+ handling and delay fatigue at a physiological PO2 in intact single mouse skeletal muscle fibres. Each muscle fibre was perfused with Tyrode's solution pre‐equilibrated with either 20% (PO2∼150 Torr) or 2% O2 (PO2 = 15.6 Torr) in the absence and presence of 100 µM NaNO2. At supra‐physiological PO2 (i.e. 20% O2), time to fatigue was lowered by 34% with NaNO2 (control: 257 ± 94 vs. NaNO2: 159 ± 46 s, d = 1.63, P0.05) but [Ca2+]c accumulation between contractions was lower, concomitant with a greater SR Ca2+ pumping rate (P<0.05) compared to the control condition. These results demonstrate that increased exposure to NO2− blunts fatigue development at near‐physiological, but not at supra‐physiological, PO2 through enhancing SR Ca2+ pumping rate in single skeletal muscle fibres. These findings extend our understanding of the mechanisms by which increased NO2− exposure can mitigate skeletal muscle fatigue development.Ministry of Science, Technology and InnovationConselho Nacional de Desenvolvimento Científico e Tecnológico (National Council for Scientific and Technological Development)US Department of Health and Human Services (HHS)National Institutes of Health (NIH)National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS

State-selective electric-field ionization of Rydberg positronium

We report experiments in which positronium (Ps) atoms, optically excited to Rydberg states with principal quantum numbers n in the range 18–25, were selectively ionized by both static and pulsed electric fields. The experiments were modeled using Monte Carlo simulations that include tunnel ionization rates calculated for hydrogen and scaled by the Ps reduced mass. Our measurements exhibit a small disagreement with the calculated tunnel ionization rates. Despite this we show that the electric fields in which different Ps states are ionized are sufficiently separated to allow selective field-ionization methods to be used in typical experimental conditions

Velocity selection of Rydberg positronium using a curved electrostatic guide

We report experiments in which a slow Rydberg positronium (Ps) beam was produced by velocity selection using a curved electrostatic quadrupole guide. Ps atoms in Rydberg-Stark states with principal quantum number n = 14 were prepared by a two-color optical excitation process in a uniform electric field. Low-field-seeking Stark states were produced at the entrance of a 0.6-m-long quadrupole guide that includes a 45◦ bend, and were detected at the end of the guide via their annihilation γ radiation. The mean speed (kinetic energy) of atoms entering the guide was estimated to be ≈180 km s−1 (185 meV), whereas the mean longitudinal speed of guided atoms was measured via time of flight and found to be ≈90 km s−1, equivalent to a kinetic energy of 45 meV. The measured transport data are in broad agreement with Monte Carlo simulations, which are also used to establish the efficacy with which the arrangement we describe could be used to perform Ps-atom scattering measurements