9,376 research outputs found
Neutron Star Mergers Are the Dominant Source of the r-process in the Early Evolution of Dwarf Galaxies
There are many candidate sites of the r-process: core-collapse supernovae
(including rare magnetorotational core-collapse supernovae), neutron star
mergers, and neutron star/black hole mergers. The chemical enrichment of
galaxies---specifically dwarf galaxies---helps distinguish between these
sources based on the continual build-up of r-process elements. This technique
can distinguish between the r-process candidate sites by the clearest
observational difference---how quickly these events occur after the stars are
created. The existence of several nearby dwarf galaxies allows us to measure
robust chemical abundances for galaxies with different star formation
histories. Dwarf galaxies are especially useful because simple chemical
evolution models can be used to determine the sources of r-process material. We
have measured the r-process element barium with Keck/DEIMOS medium-resolution
spectroscopy. We present the largest sample of barium abundances (almost 250
stars) in dwarf galaxies ever assembled. We measure [Ba/Fe] as a function of
[Fe/H] in this sample and compare with existing [alpha/Fe] measurements. We
have found that a large contribution of barium needs to occur at more delayed
timescales than core-collapse supernovae in order to explain our observed
abundances, namely the significantly more positive trend of the r-process
component of [Ba/Fe] vs. [Fe/H] seen for [Fe/H] <~ -1.6 when compared to the
[Mg/Fe] vs. [Fe/H] trend. We conclude that neutron star mergers are the most
likely source of r-process enrichment in dwarf galaxies at early times.Comment: Accepted to ApJ on 2018 October 2
Anion receptor chemistry: highlights from 2011 and 2012
This review covers advances in anion complexation in the years 2011 and 2012. The review covers both organic and inorganic systems and also highlights the applications to which anion receptors can be applied such as self-assembly and molecular architecture, sensing, catalysis and anion transport
Atomic Hydrogen Cleaning of Polarized GaAs Photocathodes
Atomic hydrogen cleaning followed by heat cleaning at 450C was used
to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions
were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs
cathodes, higher than the results obtained using conventional 600C heat
cleaning. The low-temperature cleaning technique was successfully applied to
thin, strained GaAs cathodes used for producing highly polarized electrons. No
depolarization was observed even when the optimum cleaning time of about 30
seconds was extended by a factor of 100
Numerical modeling of quasiplanar giant water waves
In this work we present a further analytical development and a numerical
implementation of the recently suggested theoretical model for highly nonlinear
potential long-crested water waves, where weak three-dimensional effects are
included as small corrections to exact two-dimensional equations written in the
conformal variables [V.P. Ruban, Phys. Rev. E 71, 055303(R) (2005)]. Numerical
experiments based on this theory describe the spontaneous formation of a single
weakly three-dimensional large-amplitude wave (alternatively called freak,
killer, rogue or giant wave) on the deep water.Comment: revtex4, 8 pages, 7 figure
Estimating HIV Medication Adherence and Persistence: Two Instruments for Clinical and Research Use
Antiretroviral therapy (ART) requires lifelong daily oral therapy. While patient characteristics associated with suboptimal ART adherence and persistence have been described in cohorts of HIV-infected persons, these factors are poor predictors of individual medication taking behaviors. We aimed to create and test instruments for the estimation of future ART adherence and persistence for clinical and research applications. Following formative work, a battery of 148 items broadly related to HIV infection and treatment was developed and administered to 181 HIV-infected patients. ART adherence and persistence were assessed using electronic monitoring for 3 months. Perceived confidence in medication taking and self-reported barriers to adherence were strongest in predicting non-adherence over time. Barriers to adherence (e.g., affordability, scheduling) were the strongest predictors of non-adherence, as well as 3- and 7-day non-persistence. A ten-item battery for prediction of these outcomes (www.med.unc.edu/ncaidstraining/adherence/for-providers) and a 30-item battery reflective of underlying psychological constructs can help identify and study individuals at risk for suboptimal ART adherence and persistence
Highly effective yet simple transmembrane anion transporters based upon ortho-phenylenediamine bis-ureas
Simple, highly fluorinated receptors are shown to function as highly effective transmembrane anion antiporters with the most active transporters rivalling the transport efficacy of natural anion transporter prodigiosin for bicarbonate
Some Abnormal Reactions of Organomagnesium Halides
Nitro and nitroso groups react with methylmagnesium halides (and other RMgX compounds) to give methane and some ethane. The gases so evolved make it necessary to correct for the ordinary determination of active hydrogen by means of the Zerewitinoff method. Accordingly, the new hydroxy structure proposed for o-nitrobenzaladehyde finds no support on the basis of gas evolved when treated with alkylmagnesium halides
A qualitative study of hospital pharmacists and antibiotic governance: Negotiating interprofessional responsibilities, expertise and resource constraints Organization, structure and delivery of healthcare
© 2016 Broom et al. Background: Antibiotic treatment options for common infections are diminishing due to the proliferation of antimicrobial resistance (AMR). The impact of Antimicrobial Stewardship (AMS) programs seeking to preserve viable antibiotic drugs by governing their use in hospitals has hitherto been limited. Pharmacists have been delegated a critical role in antibiotic governance in AMS teams within hospitals but the experience of pharmacists in influencing antibiotic use has received limited attention. In this study we explore the experiences of pharmacists in antibiotic decision-making in two Australian hospitals. Methods: We conducted 19 semi-structured interviews to explore hospital-based pharmacists' perceptions and experiences of antibiotic use and governance. The analysis was conducted with NVivo10 software, utilising the framework approach. Results: Three major themes emerged in the pharmacist interviews including (1) the responsibilities of pharmacy in optimising antibiotic use and the interprofessional challenges therein; (2) the importance of antibiotic streamlining and the constraints placed on pharmacists in achieving this; and (3) the potential, but often under-utilised expertise, pharmacists bring to antibiotic optimisation. Conclusions: Pharmacists have a critical role in AMS teams but their capacity to enact change is limited by entrenched interprofessional dynamics. Identifying how hospital pharmacy's antibiotic gatekeeping is embedded in the interprofessional nature of clinical decision-making and limited by organisational environment has important implications for the implementation of hospital policies seeking to streamline antibiotic use. Resource constraints (i.e. time limitation and task prioritisation) in particular limit the capacity of pharmacists to overcome the interprofessional barriers through development of stronger collaborative relationships. The results of this study suggest that to enact change in antibiotic use in hospitals, pharmacists must be supported in their negotiations with doctors, have increased presence on hospital wards, and must be given opportunities to pass on specialist knowledge within multidisciplinary clinical teams
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