Bounded and unitary elements in pro-C^*-algebras

A pro-C^*-algebra is a (projective) limit of C^*-algebras in the category of topological *-algebras. From the perspective of non-commutative geometry, pro-C^*-algebras can be seen as non-commutative k-spaces. An element of a pro-C^*-algebra is bounded if there is a uniform bound for the norm of its images under any continuous *-homomorphism into a C^*-algebra. The *-subalgebra consisting of the bounded elements turns out to be a C^*-algebra. In this paper, we investigate pro-C^*-algebras from a categorical point of view. We study the functor (-)_b that assigns to a pro-C^*-algebra the C^*-algebra of its bounded elements, which is the dual of the Stone-\v{C}ech-compactification. We show that (-)_b is a coreflector, and it preserves exact sequences. A generalization of the Gelfand-duality for commutative unital pro-C^*-algebras is also presented.Comment: v2 (accepted

Temporal build-up of electromagnetically induced transparency and absorption resonances in degenerate two-level transitions

The temporal evolution of electromagnetically induced transparency (EIT) and absorption (EIA) coherence resonances in pump-probe spectroscopy of degenerate two-level atomic transition is studied for light intensities below saturation. Analytical expression for the transient absorption spectra are given for simple model systems and a model for the calculation of the time dependent response of realistic atomic transitions, where the Zeeman degeneracy is fully accounted for, is presented. EIT and EIA resonances have a similar (opposite sign) time dependent lineshape, however, the EIA evolution is slower and thus narrower lines are observed for long interaction time. Qualitative agreement with the theoretical predictions is obtained for the transient probe absorption on the $^{85}Rb$ $D_{2}$ line in an atomic beam experiment.Comment: 10 pages, 9 figures. Submitted to Phys. Rev.

Procedure Volume and the Association with Short-term Mortality Following Abdominal Aortic Aneurysm Repair in European Populations: A Systematic Review

Objective: To evaluate the relationship between the volume of abdominal aortic aneurysm (AAA) procedures undertaken and the primary outcome of mortality in Europe. Previous systematic reviews of this relationship are outdated and are overwhelmingly based on US data. Data sources: Comprehensive searching within MEDLINE and other bibliographic databases supplemented by citation searching and hand-searching of journals was undertaken to identify studies that reported the effect of hospital or clinician volume on any reported outcomes in adult, European populations, undergoing AAA repair and published in the last 10 years. Methods: Two reviewers conducted study selection with independent, duplicate data extraction and quality assessment. A planned meta-analysis was not conducted because of the high risk of bias, the likelihood of individual study subjects being included in more than one study and diversity in the clinical populations studied and methods used. Results: Sixteen studies (n = 237,074 participants) from the UK (n = 11 studies), Germany (n = 3 studies), Norway (n = 1 study), and one from the UK and Sweden were included. Data in the included studies came from administrative databases and clinical registries incorporating a variety of clinical and procedural groups; the study quality was limited by the use of observational study designs. Overall, the evidence favoured the existence of an inverse volume outcome relationship between hospital volume and mortality. Insufficient evidence was available to reach conclusions on the relationship between clinician volume and outcome and between hospital or clinician volume and secondary outcomes including complications and length of hospital stay. Conclusions: The evidence from this review suggests a relationship between the hospital volume of AAA procedures conducted and short-term mortality; however, as volume typically represents a complex amalgamation of factors further research will be useful to identify the core characteristics of volume that influence improved outcomes

The effect of a barnacle-shaped excrescence on the hydrodynamic performance of a tidal turbine blade section

Efficient tidal turbine designs rely upon the hydrodynamic performance of the turbine blade sections. A significant consideration for the likely power generation capacity of a tidal turbine is the effect of biofouling on the blade performance. A turbine blade surface is susceptible to large scale macrofouling, mainly from encrusters, such as barnacles and molluscs, colonising the developing surface. This paper considers the case of when a barnacle attaches to the upper (suction) surface of the blade section. Results of experiments to investigate the unsteady flow characteristics of the blade section are presented, and the modification of the hydrodynamic performance coefficients due to the presence of a barnacle is evaluated. The barnacle has no significant effect upon the lift in steady flow and unsteady flow, but there is a very large increase in the drag. Dependent upon the degree of barnacle encrustation, the effect on a turbine blade drag may be significant and lead to a degradation of a turbine predicted performance

The ^4He trimer as an Efimov system

We review the results obtained in the last four decades which demonstrate the Efimov nature of the $^4$He three-atomic system.Comment: Review article for a special issue of the Few-Body Systems journal devoted to Efimov physic

Preferences for e-Mental Health Interventions in Germany

_Objectives:_ Recent evidence suggests that e-mental health interventions can be effective at improving mental health but that there is still a notable hesitation among patients to use them. Previous research has revealed that they are perceived by patients as being less helpful than face-to-face psychotherapy. The reasons for this unfavorable perception are, however, not yet well understood. The aim of our study was to address this question by eliciting preferences for individual components of e-mental health interventions in a discrete choice experiment. _Methods:_ Using a stepwise qualitative approach, we developed the following 5 attributes of eMHIs: introductory training,human contact, peer support, proven effectiveness, content delivery, and price. Additionally, we asked questions about re-spondents’ demographics, attitudes, and previous experience of traditional psychotherapy, as well as their distress level. _Results:_ A total of 1984 respondents completed the survey. Using mixed logit models, we found that personal contact with a psychotherapist in blended care, proven effectiveness, and low price were highly valued by participants. Participants were indifferent toward the mode of content delivery but showed a slight preference for introductory training via phone, as well as for peer support via online forum alongside coach-led group meetings on site. _Discussion:_ Our results suggest a clear preference for blended care that includes face-to-face contact with a psychotherapist. This preference remained stable irrespective of sociodemographics, previous experience of psychotherapy, distress level, and the 2 context scenarios used in our discrete choice experiment. Further investigations looking at the potential benefits and risks of blended care are needed

An ansatz for the nonlinear Demkov-Kunike problem for cold molecule formation

We study nonlinear mean-field dynamics of ultracold molecule formation in the case when the external field configuration is defined by the level-crossing Demkov-Kunike model, characterized by a bell-shaped coupling and finite variation of the detuning. Analyzing the fast sweep rate regime of the strong interaction limit, which models a situation when the peak value of the coupling is large enough and the resonance crossing is sufficiently fast, we construct a highly accurate ansatz to describe the temporal dynamics of the molecule formation in the mentioned interaction regime. The absolute error of the constructed approximation is less than 3*10^-6 for the final transition probability while at certain time points it might increase up to 10^-3. Examining the role of the different terms in the constructed approximation, we prove that in the fast sweep rate regime of the strong interaction limit the temporal dynamics of the atom-molecule conversion effectively consists of the process of resonance crossing, which is governed by a nonlinear equation, followed by atom-molecular coherent oscillations which are basically described by a solution of the linear problem, associated with the considered nonlinear one.Comment: Accepted for publication in J. Contemp. Phys. (Armenian National Academy of Sciences) 8 pages, 4 figure

Scaling limit of virtual states of triatomic systems

For a system with three identical atoms, the dependence of the $s-$wave virtual state energy on the weakly bound dimer and trimer binding energies is calculated in a form of a universal scaling function. The scaling function is obtained from a renormalizable three-body model with a pairwise Dirac-delta interaction. It was also discussed the threshold condition for the appearance of the trimer virtual state.Comment: 9 pages, 3 figure

Radiation-induced oscillatory magnetoresistance as a sensitive probe of the zero-field spin splitting in high mobility GaAs/AlGaAs devices

We suggest an approach for characterizing the zero-field spin splitting of high mobility two-dimensional electron systems, when beats are not readily observable in the Shubnikov-de Haas effect. The zero-field spin splitting and the effective magnetic field seen in the reference frame of the electron is evaluated from a quantitative study of beats observed in radiation-induced magnetoresistance oscillations.Comment: 4 pages, 4 color figure