Interference effects in the photorecombination of argonlike Sc3+ ions: Storage-ring experiment and theory

Absolute total electron-ion recombination rate coefficients of argonlike Sc3+(3s2 3p6) ions have been measured for relative energies between electrons and ions ranging from 0 to 45 eV. This energy range comprises all dielectronic recombination resonances attached to 3p -> 3d and 3p -> 4s excitations. A broad resonance with an experimental width of 0.89 +- 0.07 eV due to the 3p5 3d2 2F intermediate state is found at 12.31 +- 0.03 eV with a small experimental evidence for an asymmetric line shape. From R-Matrix and perturbative calculations we infer that the asymmetric line shape may not only be due to quantum mechanical interference between direct and resonant recombination channels as predicted by Gorczyca et al. [Phys. Rev. A 56, 4742 (1997)], but may partly also be due to the interaction with an adjacent overlapping DR resonance of the same symmetry. The overall agreement between theory and experiment is poor. Differences between our experimental and our theoretical resonance positions are as large as 1.4 eV. This illustrates the difficulty to accurately describe the structure of an atomic system with an open 3d-shell with state-of-the-art theoretical methods. Furthermore, we find that a relativistic theoretical treatment of the system under study is mandatory since the existence of experimentally observed strong 3p5 3d2 2D and 3p5 3d 4s 2D resonances can only be explained when calculations beyond LS-coupling are carried out.Comment: 11 pages, 7 figures, 3 tables, Phys. Rev. A (in print), see also: http://www.strz.uni-giessen.de/~k

Dielectronic Recombination of Ground-State and Metastable Li+ Ions

Dielectronic recombination has been investigated for Delta-n = 1 resonances of ground-state Li+(1s^2) and for Delta-n = 0 resonances of metastable Li+(1s2s ^3S). The ground-state spectrum shows three prominent transitions between 53 and 64 eV, while the metastable spectrum exhibits many transitions with energies < 3.2 eV. Reasonably good agreement of R-matrix, LS coupling calculations with the measured recombination rate coefficient is obtained. The time dependence of the recombination rate yields a radiative lifetime of 52.2 +- 5.0 s for the 2 ^3S level of Li+.Comment: Submitted to Phys. Rev. A; REVTeX, 4 pages, 3 figure

Super-Radiant Dynamics, Doorways, and Resonances in Nuclei and Other Open Mesoscopic Systems

The phenomenon of super-radiance (Dicke effect, coherent spontaneous radiation by a gas of atoms coupled through the common radiation field) is well known in quantum optics. The review discusses similar physics that emerges in open and marginally stable quantum many-body systems. In the presence of open decay channels, the intrinsic states are coupled through the continuum. At sufficiently strong continuum coupling, the spectrum of resonances undergoes the restructuring with segregation of very broad super-radiant states and trapping of remaining long-lived compound states. The appropriate formalism describing this phenomenon is based on the Feshbach projection method and effective non-Hermitian Hamiltonian. A broader generalization is related to the idea of doorway states connecting quantum states of different structure. The method is explained in detail and the examples of applications are given to nuclear, atomic and particle physics. The interrelation of the collective dynamics through continuum and possible intrinsic many-body chaos is studied, including universal mesoscopic conductance fluctuations. The theory serves as a natural framework for general description of a quantum signal transmission through an open mesoscopic system.Comment: 85 pages, 10 figure

Self-Consistent R-matrix Approach To Photoionization And Unified Electron-Ion Recombination

A unified scheme using the R-matrix method has been developed for electron-ion recombination subsuming heretofore separate treatments of radiative and dielectronic recombination (RR and DR). The ab initio coupled channel approach unifies resonant and non-resonant phenomena, and enables a general and self-consistent treatment of photoionization and electron-ion recombination employing idential wavefunction expansion. Detailed balance takes account of interference effects due to resonances in cross sections, calculated explicitly for a large number of recombined (e+ion) bound levels over extended energy regions. The theory of DR by Bell and Seaton is adapted for high-n resonances in the region below series limits. The R-matrix method is employed for (A) partial and total photoionization and photorecombination cross sections of (e+ion) bound levels, and (B) DR and (e+ion) scattering cross sections. Relativistic effects and fine structure are considered in the Breit-Pauli approximation. Effects such as radiation damping may be taken into account where necessary. Unfiied recombination cross sections are in excellent agreement with measurements on ion storage rings to about 10-20%. In addition to high accuracy, the strengths of the method are: (I) both total and level-specific cross sections and rate coefficients are obtained, and (II) a single (e+ion) recombination rate coefficient for any given atom or ion is obtained over the entire temperature range of practical importance in laboratory and astrophysical plasmas, (III) self-consistent results are obtained for photoionization and recombination; comprehensive datasets have been computed for over 50 atoms and ions. Selected data are presented for iron ions.Comment: 33 pages, 13 figures, Review in "Radiation Processes In Physics and Chemistry", Elsevier (in press). Postscript file with higher resolution figures at http://www.astronomy.ohio-state.edu/~pradhan/pr.p

Small Stem Total Hip Arthroplasty in Hypoplasia of the Femur

Total hip arthroplasty in hypoplastic femurs is technically difficult and the incidence of complications and aseptic loosening is relatively high. Cemented, uncemented, off-the-shelf, and custom-made stems all have been advocated in these cases. From 1978 to 1997, we performed 86 total hip arthroplasties in 77 patients with a hypoplastic femur using a cemented, off-the-shelf, small, curved, cobalt-chromium stem. We hypothesized results equaled those of the identical but larger-sized stems in normal-sized femora which were used as comparisons. Clinical and radiographic evaluations were performed. Minimum followup was 4.2 years (mean, 12 years; range, 4.2–20.3 years); mean Harris hip score was 88, and mean hip flexion was 104°. Six stems were revised: four because of aseptic loosening, one after a femoral fracture, and one because of malpositioning. Complications included one perforation and one fracture of the femur, one fracture, one nonunion of the greater trochanter, and one deep infection. Implant survivorship for all hips at 15 years with aseptic revision of the stem as the end point was 90% (confidence interval, 82–99) which equaled results of the larger stems. The small off-the-shelf cemented Weber stem has a high long-term survival and a low complication rate. Survival compares favorably with other small-sized total hip systems

Polyethylene thickness is a risk factor for wear necessitating insert exchange

PURPOSE: The aim of this observational study was to investigate the optimal minimal polyethylene (PE) thickness in total knee arthroplasty (TKA) and identify other risk factors associated with revision of the insert due to wear. METHODS: A total of 84 TKA were followed for 11-16 years. All patients received the same prosthesis design (Interax; Howmedica/ Stryker) with halfbearings: separate PE-inserts medially and laterally. Statistical analysis comprised Cox-regression to correct for confounding. RESULTS: Eight knees (9.5%) had been revised due to thinning inserts and an additional patient is scheduled for revision. PE thickness, diagnosis, BMI and weight are risk factors for insert exchange. For each millimetre decrease in PE thickness, the risk of insert exchange increases 3.0 times, which remains after correction for age, gender, weight, diagnosis and femoral-tibial angle. Insert exchange was 4.73 times more likely in OA-patients compared to RA-patients. For every unit increase in BMI and weight the risk for insert exchange increases 1.40 times and 1.14 times, respectively. CONCLUSIONS: In conclusion we therefore advise against the use of thin PE inserts in modular TKA and recommend PE inserts with a minimal 8-mm thickness.Optimising joint reconstruction management in arthritis and bone tumour patient

Metal on metal hip resurfacing versus uncemented custom total hip replacement - early results

<p>Abstract</p> <p>Introduction</p> <p>There is no current consensus on the most appropriate prosthesis for treating symptomatic osteoarthritis (OA) of the hip in young, active patients. Modern metal on metal hip resurfacing arthroplasty (HR) has gained popularity as it is theoretically more stable, bone conserving and easier to revise than total hip arthroplasty. Early results of metal on metal resurfacing have been encouraging. We have compared two well matched cohorts of patients with regard to function, pain relief and patient satisfaction.</p> <p>Methods</p> <p>This prospective study compares 2 cohorts of young, active patients treated with hip resurfacing (137 patients, 141 hips) and custom uncemented (CADCAM) stems (134 patients, 141 hips). All procedures were performed by a single surgeon. Outcome measures included Oxford, WOMAC and Harris hip scores as well as an activity score. Statistical analysis was performed using the unpaired student's t-test.</p> <p>Results</p> <p>One hundred and thirty four and 137 patients were included in the hip replacement and resurfacing groups respectively. The mean age of these patients was 54.6 years. The mean duration of follow up for the hip resurfacing group was 19.2 months compared to 13.4 months for the total hip replacement group.</p> <p>Pre operative oxford, Harris and WOMAC scores in the THA group were 41.1, 46.4 and 50.9 respectively while the post operative scores were 14.8, 95.8 and 5.0. In the HR group, pre- operative scores were 37.0, 54.1 and 45.9 respectively compared to 15.0, 96.8 and 6.1 post operatively. The degree of improvement was similar in both groups.</p> <p>Conclusion</p> <p>There was no significant clinical difference between the patients treated with hip resurfacing and total hip arthroplasty in the short term.</p

Bone and joint infections in adults: a comprehensive classification proposal

Ten currently available classifications were tested for their ability to describe a continuous cohort of 300 adult patients affected by bone and joint infections. Each classification only focused, on the average, on 1.3\u2009\ub1\u20090.4 features of a single clinical condition (osteomyelitis, implant-related infections, or septic arthritis), being able to classify 34.8\u2009\ub1\u200924.7% of the patients, while a comprehensive classification system could describe all the patients considered in the study. RESULT AND CONCLUSION: A comprehensive classification system permits more accurate classification of bone and joint infections in adults than any single classification available and may serve for didactic, scientific, and clinical purposes

Pulse shape analysis in Gerda Phase II

The GERmanium Detector Array (Gerda) collaboration searched for neutrinoless double-β decay in 76Ge using isotopically enriched high purity germanium detectors at the Laboratori Nazionali del Gran Sasso of INFN. After Phase I (2011–2013), the experiment benefited from several upgrades, including an additional active veto based on LAr instrumentation and a significant increase of mass by point-contact germanium detectors that improved the half-life sensitivity of Phase II (2015–2019) by an order of magnitude. At the core of the background mitigation strategy, the analysis of the time profile of individual pulses provides a powerful topological discrimination of signal-like and background-like events. Data from regular 228Th calibrations and physics data were both considered in the evaluation of the pulse shape discrimination performance. In this work, we describe the various methods applied to the data collected in Gerda Phase II corresponding to an exposure of 103.7 kg year. These methods suppress the background by a factor of about 5 in the region of interest around Qββ=2039 keV, while preserving (81±3)% of the signal. In addition, an exhaustive list of parameters is provided which were used in the final data analysis