2,486 research outputs found
Electron scattering in isotonic chains as a probe of the proton shell structure of unstable nuclei
Electron scattering on unstable nuclei is planned in future facilities of the
GSI and RIKEN upgrades. Motivated by this fact, we study theoretical
predictions for elastic electron scattering in the N=82, N=50, and N=14
isotonic chains from very proton-deficient to very proton-rich isotones. We
compute the scattering observables by performing Dirac partial-wave
calculations. The charge density of the nucleus is obtained with a covariant
nuclear mean-field model that accounts for the low-energy electromagnetic
structure of the nucleon. For the discussion of the dependence of scattering
observables at low-momentum transfer on the gross properties of the charge
density, we fit Helm model distributions to the self-consistent mean-field
densities. We find that the changes shown by the electric charge form factor
along each isotonic chain are strongly correlated with the underlying proton
shell structure of the isotones. We conclude that elastic electron scattering
experiments in isotones can provide valuable information about the filling
order and occupation of the single-particle levels of protons.Comment: 13 pages; 19 figure
Electron-induced proton knockout from neutron rich nuclei
We study the evolution of the \eep cross section on nuclei with increasing
asymmetry between the number of neutrons and protons. The calculations are done
within the framework of the nonrelativistic and relativistic distorted-wave
impulse approximation. In the nonrelativistic model phenomenological
Woods-Saxon and Hartree-Fock wave functions are used for the proton bound-state
wave functions, in the relativistic model the wave functions are solutions of
Dirac-Hartree equations. The models are first tested against experimental data
on Ca and Ca nuclei, and then they are applied to a set of
spherical calcium isotopes.Comment: 5 pages, 2 figures. contribution to the XIX International School on
Nuclear Physics, Neutron Physics and Applications, Varna (Bulgaria) September
19-25, 201
Nucleosynthesis in Supernovae, Hypernovae/Gamma-ray Bursts and Compact Binary Mergers
We present the status and open problems of the astrophysical sites responsible for the nucleosynthesis of Fe-group and heavier elements (with the exception of the s-process). This involves type Ia supernovae with the requirement to have a low Ye-component (for the explanation of 55Mn), the role of the core collapse supenova explosion mechanism in the composition of the Fe-group (and heavier?) ejecta, the transition between neutron star and black hole remnants as the result of the collapse of massive stars, and the relation of the latter with supernova and/or gamma-ray bursts/hypernovae. In addition, the role of compact binary mergers is discussed, especially with respect to forming the heaviest r-process elements in galactic eveolution
Comparison of opioid prescribing by dentists in the United States and England
Importance: The United States consumes most of the opioids worldwide despite representing a small portion of the world\u27s population. Dentists are one of the most frequent US prescribers of opioids despite data suggesting that nonopioid analgesics are similarly effective for oral pain. While oral health and dentist use are generally similar between the United States and England, it is unclear how opioid prescribing by dentists varies between the 2 countries.
Objective: To compare opioid prescribing by dentists in the United States and England.
Design, Setting, and Participants: Cross-sectional study of prescriptions for opioids dispensed from outpatient pharmacies and health care settings between January 1 and December 31, 2016, by dentists in the United States and England. Data were analyzed from October 2018 to January 2019.
Exposures: Opioids prescribed by dentists.
Main Outcomes and Measures: Proportion and prescribing rates of opioid prescriptions.
Results: In 2016, the proportion of prescriptions written by US dentists that were for opioids was 37 times greater than the proportion written by English dentists. In all, 22.3% of US dental prescriptions were opioids (11.4 million prescriptions) compared with 0.6% of English dental prescriptions (28 082 prescriptions) (difference, 21.7%; 95% CI, 13.8%-32.1%; P \u3c .001). Dentists in the United States also had a higher number of opioid prescriptions per 1000 population (35.4 per 1000 US population [95% CI, 25.2-48.7 per 1000 population] vs 0.5 per 1000 England population [95% CI, 0.03-3.7 per 1000 population]) and number of opioid prescriptions per dentist (58.2 prescriptions per dentist [95% CI, 44.9-75.0 prescriptions per dentist] vs 1.2 prescriptions per dentist [95% CI, 0.2-5.6 prescriptions per dentist]). While the codeine derivative dihydrocodeine was the sole opioid prescribed by English dentists, US dentists prescribed a range of opioids containing hydrocodone (62.3%), codeine (23.2%), oxycodone (9.1%), and tramadol (4.8%). Dentists in the United States also prescribed long-acting opioids (0.06% of opioids prescribed by US dentists [6425 prescriptions]). Long-acting opioids were not prescribed by English dentists.
Conclusions and Relevance: This study found that in 2016, dentists in the United States prescribed opioids with significantly greater frequency than their English counterparts. Opioids with a high potential for abuse, such as oxycodone, were frequently prescribed by US dentists but not prescribed in England. These results illustrate how 1 source of opioids differs substantially in the United States vs England. To reduce dental opioid prescribing in the United States, dentists could adopt measures similar to those used in England, including national guidelines for treating dental pain that emphasize prescribing opioids conservatively
Effect of Long-lived Strongly Interacting Relic Particles on Big Bang Nucleosynthesis
It has been suggested that relic long-lived strongly interacting massive
particles (SIMPs, or particles) existed in the early universe. We study
effects of such long-lived unstable SIMPs on big bang nucleosynthesis (BBN)
assuming that such particles existed during the BBN epoch, but then decayed
long before they could be detected. The interaction strength between an
particle and a nucleon is assumed to be similar to that between nucleons. We
then calculate BBN in the presence of the unstable neutral charged
particles taking into account the capture of particles by nuclei to form
-nuclei. We also study the nuclear reactions and beta decays of -nuclei.
We find that SIMPs form bound states with normal nuclei during a relatively
early epoch of BBN. This leads to the production of heavy elements which remain
attached to them. Constraints on the abundance of particles during BBN
are derived from observationally inferred limits on the primordial light
element abundances. Particle models which predict long-lived colored particles
with lifetimes longer than 200 s are rejected based upon these
constraints.Comment: 19 pages, 4 figure
Stiffness Characterization of Cold Recycled Mixtures
AbstractOne of the objectives within the European research project CoRePaSol (supported within the CEDR Transnational Program) was to summarize assessment and research of stiffness modulus of cold recycled mixes determined according to repeated indirect tensile stress test (IT-CY). In most cases the stiffness modulus values were compared to the values of indirect tensile strength (ITS), which is currently the most commonly used characteristic for proving the quality of a cold recycled mix. The first part of experimental measurements was focused on the standard cold recycled mixes, thus mixes whose aggregate skeleton is formed entirely by RAP and which contain either just the bituminous binder (bituminous emulsion or foamed bitumen), or a combination of one of these binders and a hydraulic binder (cement). Later also combinations with other types of recyclable materials were done and tested. Stiffness modulus and in most cases also the indirect tensile strength values were investigated from many points of view, e.g. the effect of different bituminous / hydraulic binder content on these characteristics, time-dependent progress in change of these characteristics, effect of testing temperature or the influence of fines addition on the stiffness modulus value. This paper therefore brings some summarization of the gained experience
Decidability of the Monadic Shallow Linear First-Order Fragment with Straight Dismatching Constraints
The monadic shallow linear Horn fragment is well-known to be decidable and
has many application, e.g., in security protocol analysis, tree automata, or
abstraction refinement. It was a long standing open problem how to extend the
fragment to the non-Horn case, preserving decidability, that would, e.g.,
enable to express non-determinism in protocols. We prove decidability of the
non-Horn monadic shallow linear fragment via ordered resolution further
extended with dismatching constraints and discuss some applications of the new
decidable fragment.Comment: 29 pages, long version of CADE-26 pape
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