High density cluster jet target for storage ring experiments

The design and performance of a newly developed cluster jet target installation for hadron physics experiments are presented which, for the first time, is able to generate a hydrogen cluster jet beam with a target thickness of above $10^{15}\,\mathrm{atoms/cm}^2$ at a distance of two metres behind the cluster jet nozzle. The properties of the cluster beam and of individual clusters themselves are studied at this installation. Special emphasis is placed on measurements of the target beam density as a function of the relevant parameters as well as on the cluster beam profiles. By means of a time-of-flight setup, measurements of the velocity of single clusters and velocity distributions were possible. The complete installation, which meets the requirements of future internal fixed target experiments at storage rings, and the results of the systematic studies on hydrogen cluster jets are presented and discussed.Comment: 10 pages, 18 figure

Fast rotating stars resulting from binary evolution will often appear to be single

Rapidly rotating stars are readily produced in binary systems. An accreting star in a binary system can be spun up by mass accretion and quickly approach the break-up limit. Mergers between two stars in a binary are expected to result in massive, fast rotating stars. These rapid rotators may appear as Be or Oe stars or at low metallicity they may be progenitors of long gamma-ray bursts. Given the high frequency of massive stars in close binaries it seems likely that a large fraction of rapidly rotating stars result from binary interaction. It is not straightforward to distinguish a a fast rotator that was born as a rapidly rotating single star from a fast rotator that resulted from some kind of binary interaction. Rapidly rotating stars resulting from binary interaction will often appear to be single because the companion tends to be a low mass, low luminosity star in a wide orbit. Alternatively, they became single stars after a merger or disruption of the binary system during the supernova explosion of the primary. The absence of evidence for a companion does not guarantee that the system did not experience binary interaction in the past. If binary interaction is one of the main causes of high stellar rotation rates, the binary fraction is expected to be smaller among fast rotators. How this prediction depend on uncertainties in the physics of the binary interactions requires further investigation.Comment: 2 pages, 1 figure, to be published in the proceedings of IAU 272 "Active OB stars: structure, evolution, mass loss and critical limit", Paris 19-23 July 201

Dynkin games with heterogeneous beliefs

Copyright © 2017 Applied Probability Trust. We study zero-sum optimal stopping games (Dynkin games) between two players who disagree about the underlying model. In a Markovian setting, a verification result is established showing that if a pair of functions can be found that satisfies some natural conditions then a Nash equilibrium of stopping times is obtained, with the given functions as the corresponding value functions. In general, however, there is no uniqueness of Nash equilibria, and different equilibria give rise to different value functions. As an example, we provide a thorough study of the game version of the American call option under heterogeneous beliefs. Finally, we also study equilibria in randomized stopping times

Beyond viral suppression: the quality of life of people living with HIV in Sweden

Sweden has one of the best HIV treatment outcomes in the world and an estimated 95% of all diagnosed people living with HIV are virally suppressed, but the quality of life (QoL) is understudied. The aim of this study was to examine the associations between variables within sociodemographic, behavioural, clinical, psychological, sexual life, social support and personal resource component and the QoL of people living with HIV in Sweden. Data were derived from a cross-sectional, nation-wide survey completed by 15% (n = 1096) of all people living with HIV and collected at 15 infectious disease clinics and 2 needle exchange sites during 2014. Ordinal univariate and multivariate logistic regression analyses were used to examine associations between potential contributors and QoL. Respondents reported high QoL: 63% rated their QoL 7 or higher on a scale ranging from 0 to 10. QoL was independent of gender, age, mode of HIV transmission and country of origin. Lower QoL was associated with recent homelessness, hazardous alcohol consumption, comorbidities, treatment side-effects, HIV-related physical symptoms, hopelessness, negative self-image, sexual dissatisfaction, and negative changes in sex life after HIV. The QoL of people living with HIV in Sweden was high overall, but still significantly influenced by HIV

Constraints on the variations of fundamental couplings by stellar models

The effect of variations of the fundamental constants on the thermonuclear rate of the triple alpha reaction, 4He(αα,γ)12C, that bridges the gap between 4He and 12C is investigated. We follow the evolution of 15 and 60 M⊙ zero metallicity star models, up to the end of core helium burning. They are assumed to be representative of the first, Population III stars undergoing a very peculiar evolution due to the absence of initial CNO elements (zero metallicity). The calculated oxygen and carbon abundances resulting from helium burning can then be used to constrain the variations of the fundamental constant

The impact of mass-loss on the evolution and pre-supernova properties of red supergiants

The post main-sequence evolution of massive stars is very sensitive to many parameters of the stellar models. Key parameters are the mixing processes, the metallicity, the mass-loss rate and the effect of a close companion. We study how the red supergiant lifetimes, the tracks in the Hertzsprung-Russel diagram (HRD), the positions in this diagram of the pre-supernova progenitor as well as the structure of the stars at that time change for various mass-loss rates during the red supergiant phase (RSG), and for two different initial rotation velocities. The surface abundances of RSGs are much more sensitive to rotation than to the mass-loss rates during that phase. A change of the RSG mass-loss rate has a strong impact on the RSG lifetimes and therefore on the luminosity function of RSGs. At solar metallicity, the enhanced mass-loss rate models do produce significant changes on the populations of blue, yellow and red supergiants. When extended blue loops or blue ward excursions are produced by enhanced mass-loss, the models predict that a majority of blue (yellow) supergiants are post RSG objects. These post RSG stars are predicted to show much smaller surface rotational velocities than similar blue supergiants on their first crossing of the HR gap. The position in the HRD of the end point of the evolution depends on the mass of the hydrogen envelope. More precisely, whenever, at the pre-supernova stage, the H-rich envelope contains more than about 5\% of the initial mass, the star is a red supergiant, and whenever the H-rich envelope contains less than 1\% of the total mass the star is a blue supergiant. For intermediate situations, intermediate colors/effective temperatures are obtained. Yellow progenitors for core collapse supernovae can be explained by the enhanced mass-loss rate models, while the red progenitors are better fitted by the standard mass-loss rate models.Comment: 19 pages, 11 figures, 6 tables, accepted for publication in Astronomy and Astrophysic

A nova origin of the gas cloud at the Galactic Center ?

The recent discovery by Gillessen and collaborators of a cloud of gas falling towards the Galactic Center on a highly eccentric orbit, diving nearly straight into the immediate neighborhood of the central supermassive black hole, raises the important question of its origin. Several models have already been proposed. Here we suggest that a recent nova outburst has ejected a ring-like shell of gas. Viewed at high inclination, that could account for the mass, head and tail structure, and the unusually high eccentricity of the observed cloud in a natural way, even as the nova moves on an orbit quite normal for the young stars in the close neighborhood of the Galactic Center. We illustrate this by calculating orbits for the head and tail parts of the ejecta and the nova that has produced it. We briefly discuss some of the questions that this model, if true, raises about the stellar environment close to the Galactic Center.Comment: 4 pages, 1 figure, Journal reference, correction of a minor erro

Severe breastfeeding difficulties: Existential lostness as a mother—Women's lived experiences of initiating breastfeeding under severe difficulties

A majority of women in Sweden initiate breastfeeding but almost a quarter stop or wean the infant in the first few weeks after birth because of difficulties. In order to develop care that facilitates initiation of breastfeeding and enables mothers to realize their expectations concerning breastfeeding, it is necessary to understand what having severe breastfeeding difficulties means for women who experience them. The aim of this study is to describe the lived experiences of initiating breastfeeding under severe difficulties. A reflective lifeworld research design was used. Eight women, seven primiparous and one multipara, were interviewed within 2 months of giving birth. The essential meaning of the phenomenon is described as “Existential lostness as a mother forcing oneself into a constant fight”. This pattern is further explicated through its constituents; shattered expectations, a lost time for closeness, being of no use to the infant, being forced to expose oneself, and gaining strength through sharing. The results show that mothers with severe breastfeeding difficulties feel alone and exposed because of their suffering and are lost in motherhood. Thus, adequate care for mothers should enhance the forming of a caring relationship through sharing rather than exposing

Seismic moment tensors of the April 2009, L'Aquila (Central Italy), earthquake sequence

On 2009 April 6, the Central Apennines were hit by an Mw = 6.3 earthquake. The region had been shaken since 2008 October by seismic activity that culminated in two foreshocks with Mw > 4, 1 week and a few hours before the main shock. We computed seismic moment tensors for 26 events with Mw between 3.9 and 6.3, using the Regional Centroid Moment Tensor (RCMT) scheme. Most of these source parameters have been computed within 1 hr after the earthquake and rapidly revised successively. The focal mechanisms are all extensional, with a variable and sometimes significant strike-slip component. This geometry agrees with the NE-SW extensional deformation of the Apennines, known from previous seismic and geodetic observations. Events group into three clusters. Those located in the southern area have larger centroid depths and a wider distribution of T-axis directions. These differences suggest that towards south a different fault system was activated with respect to the SW-dipping normal faults beneath L'Aquila and more to the nort