693 research outputs found
The strength of the analog and Gamow-Teller giant resonances and hindrance of the 2\nu\beta\beta -decay rate
An approach for describing the hindrance of the nuclear 2\nu\beta\beta-decay
amplitude is proposed. The approach is based on a new formula obtained by a
model-independent transformation of the initial expression for the amplitude.
This formula takes explicitly into account the hindrance of the decay-amplitude
due to the presence of the collective Gamow-Teller state. Calculations are
performed within the simplest version of the approach. Calculated and
experimental 2\nu\beta\beta halve-lives are compared for a wide range of
nuclei.Comment: 11 pages, 1 tabl
A clinical evaluation of the performance of the GP-II contact lens
A clinical evaluation of the GP-II Contact Lens was made. Subjects were fitted with standard availability lenses and were subsequently monitored for a two month period. Of the twenty who started, twelve completed the study, thus 60% were successful. This study showed that corneal physiology was basically uncompromised within this experimental period. Variables considered were subjective symptoms, corneal health, lens centration and movement pachometry, keratometry, and distance refraction
Intensive care doctors and nurses personal preferences for intensive Care, as compared to the general population: a discrete choice experiment
Background
To test the hypothesis that Intensive Care Unit (ICU) doctors and nurses differ in their personal preferences for treatment from the general population, and whether doctors and nurses make different choices when thinking about themselves, as compared to when they are treating a patient.
Methods
Cross sectional, observational study conducted in 13 ICUs in Australia in 2017 using a discrete choice experiment survey. Respondents completed a series of choice sets, based on hypothetical situations which varied in the severity or likelihood of: death, cognitive impairment, need for prolonged treatment, need for assistance with care or requiring residential care.
Results
A total of 980 ICU staff (233 doctors and 747 nurses) participated in the study. ICU staff place the highest value on avoiding ending up in a dependent state. The ICU staff were more likely to choose to discontinue therapy when the prognosis was worse, compared with the general population. There was consensus between ICU staff personal views and the treatment pathway likely to be followed in 69% of the choices considered by nurses and 70% of those faced by doctors. In 27% (1614/5945 responses) of the nurses and 23% of the doctors (435/1870 responses), they felt that aggressive treatment would be continued for the hypothetical patient but they would not want that for themselves.
Conclusion
The likelihood of returning to independence (or not requiring care assistance) was reported as the most important factor for ICU staff (and the general population) in deciding whether to receive ongoing treatments. Goals of care discussions should focus on this, over likelihood of survival
Modeling of complex oxide materials from the first principles: systematic applications to vanadates RVO3 with distorted perovskite structure
"Realistic modeling" is a new direction of electronic structure calculations,
where the main emphasis is made on the construction of some effective
low-energy model entirely within a first-principle framework. Ideally, it is a
model in form, but with all the parameters derived rigorously, on the basis of
first-principles electronic structure calculations. The method is especially
suit for transition-metal oxides and other strongly correlated systems, whose
electronic and magnetic properties are predetermined by the behavior of some
limited number of states located near the Fermi level. After reviewing general
ideas of realistic modeling, we will illustrate abilities of this approach on
the wide series of vanadates RVO3 (R= La, Ce, Pr, Nd, Sm, Gd, Tb, Yb, and Y)
with distorted perovskite structure. Particular attention will be paid to
computational tools, which can be used for microscopic analysis of different
spin and orbital states in the partially filled t2g-band. We will explicitly
show how the lifting of the orbital degeneracy by the monoclinic distortion
stabilizes C-type antiferromagnetic (AFM) state, which can be further
transformed to the G-type AFM state by changing the crystal distortion from
monoclinic to orthorhombic one. Two microscopic mechanisms of such a
stabilization, associated with the one-electron crystal field and electron
correlation interactions, are discussed. The flexibility of the orbital degrees
of freedom is analyzed in terms of the magnetic-state dependence of interatomic
magnetic interactions.Comment: 23 pages, 13 figure
Structural, Electronic, and Magnetic Properties of MnO
We calculate the structural, electronic, and magnetic properties of MnO from
first principles, using the full-potential linearized augmented planewave
method, with both local-density and generalized-gradient approximations to
exchange and correlation. We find the ground state to be of rhombohedrally
distorted B1 structure with compression along the [111] direction,
antiferromagnetic with type-II ordering, and insulating, consistent with
experiment. We show that the distortion can be understood in terms of a
Heisenberg model with distance dependent nearest-neighbor and
next-nearest-neighbor couplings determined from first principles. Finally, we
show that magnetic ordering can induce significant charge anisotropy, and give
predictions for electric field gradients in the ground-state rhombohedrally
distorted structure.Comment: Submitted to Physical Review B. Replaced: regenerated figures to
resolve font problems in automatically generated pd
Structural, Magnetic and Electronic Properties of the Iron-Chalcogenide AFeSe (A=K, Cs, Rb, Tl and etc.) Superconductors
The latest discovery of a new iron-chalcogenide superconductor
AFeSe(A=K, Cs, Rb, Tl and etc.) has attracted much attention
due to a number of its unique characteristics, such as the possible insulating
state of the parent compound, the existence of Fe-vacancy and its ordering, a
new form of magnetic structure and its interplay with superconductivity, and
the peculiar electronic structures that are distinct from other Fe-based
superconductors. In this paper, we present a brief review on the structural,
magnetic and electronic properties of this new superconductor, with an emphasis
on the electronic structure and superconducting gap. Issues and future
perspectives are discussed at the end of the paper.Comment: 45 pages, 19 figure
Interstellar MHD Turbulence and Star Formation
This chapter reviews the nature of turbulence in the Galactic interstellar
medium (ISM) and its connections to the star formation (SF) process. The ISM is
turbulent, magnetized, self-gravitating, and is subject to heating and cooling
processes that control its thermodynamic behavior. The turbulence in the warm
and hot ionized components of the ISM appears to be trans- or subsonic, and
thus to behave nearly incompressibly. However, the neutral warm and cold
components are highly compressible, as a consequence of both thermal
instability in the atomic gas and of moderately-to-strongly supersonic motions
in the roughly isothermal cold atomic and molecular components. Within this
context, we discuss: i) the production and statistical distribution of
turbulent density fluctuations in both isothermal and polytropic media; ii) the
nature of the clumps produced by thermal instability, noting that, contrary to
classical ideas, they in general accrete mass from their environment; iii) the
density-magnetic field correlation (or lack thereof) in turbulent density
fluctuations, as a consequence of the superposition of the different wave modes
in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio
(MFR) in density fluctuations as they are built up by dynamic compressions; v)
the formation of cold, dense clouds aided by thermal instability; vi) the
expectation that star-forming molecular clouds are likely to be undergoing
global gravitational contraction, rather than being near equilibrium, and vii)
the regulation of the star formation rate (SFR) in such gravitationally
contracting clouds by stellar feedback which, rather than keeping the clouds
from collapsing, evaporates and diperses them while they collapse.Comment: 43 pages. Invited chapter for the book "Magnetic Fields in Diffuse
Media", edited by Elisabete de Gouveia dal Pino and Alex Lazarian. Revised as
per referee's recommendation
Observation of hard scattering in photoproduction events with a large rapidity gap at HERA
Events with a large rapidity gap and total transverse energy greater than 5
GeV have been observed in quasi-real photoproduction at HERA with the ZEUS
detector. The distribution of these events as a function of the
centre of mass energy is consistent with diffractive scattering. For total
transverse energies above 12 GeV, the hadronic final states show predominantly
a two-jet structure with each jet having a transverse energy greater than 4
GeV. For the two-jet events, little energy flow is found outside the jets. This
observation is consistent with the hard scattering of a quasi-real photon with
a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil
Modelling the COVID-19 pandemic in context : An international participatory approach
Funding RA is funded by the Bill and Melinda Gates Foundation (OPP1193472). LW is funded by the Li Ka Shing Foundation. CF is funded by grant #2017/26770-8, São Paulo Research Foundation (FAPESP). The CoMo Consortium has support from the Oxford University COVID-19 Research Response Fund (ref: 0009280). Scientific writing assistance and editorial support was provided by Adam Bodley, according to Good Publication Practice guidelines.Peer reviewedPublisher PD
The Sudbury Neutrino Observatory
The Sudbury Neutrino Observatory is a second generation water Cherenkov
detector designed to determine whether the currently observed solar neutrino
deficit is a result of neutrino oscillations. The detector is unique in its use
of D2O as a detection medium, permitting it to make a solar model-independent
test of the neutrino oscillation hypothesis by comparison of the charged- and
neutral-current interaction rates. In this paper the physical properties,
construction, and preliminary operation of the Sudbury Neutrino Observatory are
described. Data and predicted operating parameters are provided whenever
possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and
epsf style files. For additional information about SNO see
http://www.sno.phy.queensu.ca . This version has some new reference
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