Analytic structure of the S-matrix for singular quantum mechanics

The analytic structure of the S-matrix of singular quantum mechanics is examined within a multichannel framework, with primary focus on its dependence with respect to a parameter (Ω) that determines the boundary conditions. Specifically, a characterization is given in terms of salient mathematical and physical properties governing its behavior. These properties involve unitarity and associated current-conserving Wronskian relations, time-reversal invariance, and Blaschke factorization. The approach leads to an interpretation of effective nonunitary solutions in singular quantum mechanics and their determination from the unitary family.Fil: Camblong, Horacio E.. University of San Francisco; Estados UnidosFil: Epele, Luis Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física. Laboratorio de Física Teórica; ArgentinaFil: Fanchiotti, Huner. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física. Laboratorio de Física Teórica; ArgentinaFil: García Canal, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física. Laboratorio de Física Teórica; Argentin

High Carbon in I Zwicky 18: New Results from Hubble Space Telescope Spectroscopy

We present new measurements of the gas-phase C/O abundance ratio in both the NW and SE components of the extremely metal-poor dwarf irregular galaxy I Zw 18, based on ultraviolet spectroscopy of the two H II regions using the Faint Object Spectrograph on the Hubble Space Telescope. We determine values of log C/O = -0.63 +/- 0.10 for the NW component and log C/O = -0.56 +/- 0.09 for the SE component. In comparison, log C/O = -0.37 in the sun, while log C/O = -0.85 +/- 0.07 in the three most metal-poor irregular galaxies measured by Garnett et al. (1995a). Our measurements show that C/O in I Zw 18 is significantly higher than in other comparably metal-poor irregular galaxies, and above predictions for the expected C/O from massive star nucleosynthesis. These results suggest that carbon in I Zw 18 has been enhanced by an earlier population of lower-mass carbon producing stars; this idea is supported by stellar photometry of I Zw 18 and its companion, which demonstrate that the current bursts of massive stars were not the first. Despite its very low metallicity, it is likely that I Zw 18 is not a ``primeval'' galaxy.Comment: 14 pages including 4 figures; uses aaspp4.sty. Accepted for publication in ApJ. Postscript version also available by e-mail request to author at [email protected]

Optical excitations in organic molecules, clusters and defects studied by first-principles Green's function methods

Spectroscopic and optical properties of nanosystems and point defects are discussed within the framework of Green's function methods. We use an approach based on evaluating the self-energy in the so-called GW approximation and solving the Bethe-Salpeter equation in the space of single-particle transitions. Plasmon-pole models or numerical energy integration, which have been used in most of the previous GW calculations, are not used. Fourier transforms of the dielectric function are also avoided. This approach is applied to benzene, naphthalene, passivated silicon clusters (containing more than one hundred atoms), and the F center in LiCl. In the latter, excitonic effects and the $1s \to 2p$ defect line are identified in the energy-resolved dielectric function. We also compare optical spectra obtained by solving the Bethe-Salpeter equation and by using time-dependent density functional theory in the local, adiabatic approximation. From this comparison, we conclude that both methods give similar predictions for optical excitations in benzene and naphthalene, but they differ in the spectra of small silicon clusters. As cluster size increases, both methods predict very low cross section for photoabsorption in the optical and near ultra-violet ranges. For the larger clusters, the computed cross section shows a slow increase as function of photon frequency. Ionization potentials and electron affinities of molecules and clusters are also calculated.Comment: 9 figures, 5 tables, to appear in Phys. Rev. B, 200

Do daily fluctuations in psychological and app-related variables predict engagement with an alcohol reduction app? A series of N-of-1 studies

Background: Previous studies have identified psychological and smartphone app-related predictors of engagement with alcohol reduction apps at a group level. However, strategies to promote engagement need to be effective at the individual level. Evidence as to whether group-level predictors of engagement are also predictive for individuals is lacking. Objective: This study aimed to examine whether daily fluctuations in: i) the receipt of a reminder, ii) motivation to reduce alcohol, iii) perceived usefulness of the app, iv) alcohol consumption, and v) perceived lack of time predicted within-person variability in the frequency and amount of engagement with an alcohol reduction app. Methods: A series of observational N-of-1 studies were conducted. The predictor variables were measured twice daily for 28 days via Ecological Momentary Assessments. The outcome variables were measured through automated recordings of participants’ app screen views. Nine London-based adults who drank alcohol excessively and were willing to set a reduction goal took part. Each participant’s dataset was analysed separately using Generalised Additive Mixed Models to derive incidence rate ratios (IRRs) for the within-person associations of the predictor and outcome variables. Debriefing interviews, analysed using thematic analysis, were used to contextualise the findings. Results: Predictors of the frequency and amount of engagement differed between individuals, and for the variables ‘perceived usefulness of the app’ and ‘perceived lack of time’, the direction of associations also differed between individuals. The most consistent predictors of within-person variability in the frequency of engagement were the receipt of a daily reminder (IRRs = 1.80-3.88, P’s < .05) and perceived usefulness of the app (IRRs = 0.82-1.42, P’s < .05). The most consistent predictors of within-person variability in the amount of engagement were motivation to reduce alcohol (IRRs = 1.67-3.45, P’s < .05) and perceived usefulness of the app (IRRs = 0.52-137.32, P’s < .05). Conclusions: The utility of the selected psychological and app-related variables in predicting the frequency and amount of engagement with an alcohol reduction app differed at the individual level. This highlights that key within-person associations may be masked in group-level designs and suggests that different strategies to promote engagement may be required for different individuals. Clinical Trial: osf.io/zn79

Qualitative Evaluation of Web-Based Digital Intervention to Prevent and Reduce Excessive Alcohol Use and Harm Among Young People Aged 14-15 Years: A "Think-Aloud" Study

BACKGROUND: In the United Kingdom, despite some downward trends in alcohol use among young people, over one-fifth of young people reported excessive alcohol use in the past month, which is associated with short- and long-term harm to health. Digital interventions to reduce alcohol use, such as websites, among young people present an appealing and cost-effective mode of intervention that can be integrated into the education system. However, relatively few school-based digital alcohol-focused interventions have been developed and evaluated for young people in the United Kingdom. OBJECTIVE: This study aims to develop a novel web-based intervention, Rethink Alcohol, to prevent and reduce excessive alcohol use and related harm among young people aged between 14 and 15 years, and explore the views of young people, teachers, and youth workers in relation to the content, design, and usability of the intervention. METHODS: Intervention development followed the person-based approach, using theories of social norms and social influence. Qualitative "Think-Aloud" interviews, either one-to-one or paired, were conducted while participants perused and worked through the web-based intervention, talking aloud. Participants included 20 young people (12 female, 8 male), 5 youth workers (4 female, 1 male), 3 teachers (2 male, 1 female), and 1 (male) clinical professional, recruited via youth groups and professional networks. Interviews were audio recorded, transcribed verbatim, and analyzed thematically. RESULTS: The prototype web-based intervention included normative feedback, information, a quiz, interactive activities, and scenarios. On a rating scale of impressions from poor (1) to excellent (5), participants gave an average score of 3.6/5. A total of 5 themes were identified: content, credibility of the website, making the website easy to understand, design and navigation, and suitability for the audience. These themes reflected views that the content was interesting, credible, informative, and embodied a neutral and nonjudgmental tone, but stronger messaging was needed regarding social pressures and short-term risks regarding safety and risk behavior alongside clarity around pathways of risk; credibility and trustworthiness of information were critical features, determined in part, by the professionalism of design and referencing of sources of information provided; and messages should be succinct and come to life through design and interactive features. CONCLUSIONS: Together, the data illustrated the importance and challenge of communicating nuanced alcohol-focused public health messages to young people in concise, clear, nonjudgmental, and appealing ways. Young people report interest in clear, credible, neutral, and interactive messages regarding social pressures and short-term risks of alcohol use via a web-based intervention. There is scope for optimization and feasibility testing of the Rethink Alcohol intervention

Fructose transport-deficient Staphylococcus aureus reveals important role of epithelial glucose transporters in limiting sugar-driven bacterial growth in airway surface liquid.

Hyperglycaemia as a result of diabetes mellitus or acute illness is associated with increased susceptibility to respiratory infection with Staphylococcus aureus. Hyperglycaemia increases the concentration of glucose in airway surface liquid (ASL) and promotes the growth of S. aureus in vitro and in vivo. Whether elevation of other sugars in the blood, such as fructose, also results in increased concentrations in ASL is unknown and whether sugars in ASL are directly utilised by S. aureus for growth has not been investigated. We obtained mutant S. aureus JE2 strains with transposon disrupted sugar transport genes. NE768(fruA) exhibited restricted growth in 10 mM fructose. In H441 airway epithelial-bacterial co-culture, elevation of basolateral sugar concentration (5-20 mM) increased the apical growth of JE2. However, sugar-induced growth of NE768(fruA) was significantly less when basolateral fructose rather than glucose was elevated. This is the first experimental evidence to show that S. aureus directly utilises sugars present in the ASL for growth. Interestingly, JE2 growth was promoted less by glucose than fructose. Net transepithelial flux of D-glucose was lower than D-fructose. However, uptake of D-glucose was higher than D-fructose across both apical and basolateral membranes consistent with the presence of GLUT1/10 in the airway epithelium. Therefore, we propose that the preferential uptake of glucose (compared to fructose) limits its accumulation in ASL. Pre-treatment with metformin increased transepithelial resistance and reduced the sugar-dependent growth of S. aureus. Thus, epithelial paracellular permeability and glucose transport mechanisms are vital to maintain low glucose concentration in ASL and limit bacterial nutrient sources as a defence against infection

Carbon in Spiral Galaxies from Hubble Space Telescope Spectroscopy

We present measurements of the gas-phase C/O abundance ratio in six H II regions in the spiral galaxies M101 and NGC 2403, based on ultraviolet spectroscopy using the Faint Object Spectrograph on the Hubble Space Telescope. The C/O ratios increase systematically with O/H in both galaxies, from log C/O approximately -0.8 at log O/H = -4.0 to log C/O approx. -0.1 at log O/H = -3.4. C/N shows no correlation with O/H. The rate of increase of C/O is somewhat uncertain because of uncertainty as to the appropriate UV reddening law, and uncertainty in the metallicity dependence on grain depletions. However, the trend of increasing C/O with O/H is clear, confirming and extending the trend in C/O indicated previously from observations of irregular galaxies. Our data indicate that the radial gradients in C/H across spiral galaxies are steeper than the gradients in O/H. Comparing the data to chemical evolution models for spiral galaxies shows that models in which the massive star yields do not vary with metallicity predict radial C/O gradients that are much flatter than the observed gradients. The most likely hypothesis at present is that stellar winds in massive stars have an important effect on the yields and thus on the evolution of carbon and oxygen abundances. C/O and N/O abundance ratios in the outer disks of spirals determined to date are very similar to those in dwarf irregular galaxies. This implies that the outer disks of spirals have average stellar population ages much younger than the inner disks.Comment: 38 pages, 9 postscript figures, uses aaspp4.sty. Accepted for publication in The Astrophysical Journa