11,037 research outputs found
Anisotropic multi-gap superfluid states in nuclear matter
It is shown that under changing density or temperature a nucleon Fermi
superfluid can undergo a phase transition to an anisotropic superfluid state,
characterized by nonvanishing gaps in pairing channels with singlet-singlet
(SS) and triplet-singlet (TS) pairing of nucleons (in spin and isospin spaces).
In the SS pairing channel nucleons are paired with nonzero orbital angular
momentum. Such two-gap states can arise as a result of branching from the
one-gap solution of the self-consistent equations, describing SS or TS pairing
of nucleons, that depends on the relationship between SS and TS coupling
constants at the branching point. The density/temperature dependence of the
order parameters and the critical temperature for transition to the anisotropic
two-gap state are determined in a model with the SkP effective interaction. It
is shown that the anisotropic SS-TS superfluid phase corresponds to a
metastable state in nuclear matter.Comment: Prepared with RevTeX4, 7p., 5 fi
Radio-wave propagation in the non-Gaussian interstellar medium
Radio waves propagating from distant pulsars in the interstellar medium
(ISM), are refracted by electron density inhomogeneities, so that the intensity
of observed pulses fluctuates with time. The theory relating the observed pulse
time-shapes to the electron-density correlation function has developed for 30
years, however, two puzzles have remained. First, observational scaling of
pulse broadening with the pulsar distance is anomalously strong; it is
consistent with the standard model only when non-uniform statistics of electron
fluctuations along the line of sight are assumed. Second, the observed pulse
shapes are consistent with the standard model only when the scattering material
is concentrated in a narrow slab between the pulsar and the Earth.
We propose that both paradoxes are resolved at once if one assumes stationary
and uniform, but non-Gaussian statistics of the electron-density distribution.
Such statistics must be of Levy type, and the propagating ray should exhibit a
Levy flight. We propose that a natural realization of such statistics may be
provided by the interstellar medium with random electron-density
discontinuities. We develop a theory of wave propagation in such a non-Gaussian
random medium, and demonstrate its good agreement with observations. The
qualitative introduction of the approach and the resolution of the
anomalous-scaling paradox was presented earlier in [PRL 91, 131101 (2003); ApJ
584, 791 (2003)].Comment: 27 pages, changes to match published versio
Using non-participant observation to uncover mechanisms: insights from a realist evaluation
This article outlines how a realist evaluation of dementia care in hospitals used non-participant observation to support the refinement and testing of mechanisms likely to lead to the use of person-centred care. We found that comments and explanations of their actions from hospital staff during observation periods provided insights into the reasoning that generated their actions for care in real time. This informed subsequent data collection and analysis. Two worked examples of mechanisms first identified during non-participant observation demonstrate (1) how they were uncovered, and (2) how this informed research activities for theory refinement. Early, iterative engagement with the analytic process, primarily involving reflection and debate with the research team, maximised the potential of observation data to support surfacing underlying mechanisms, linking them to specific contexts and outcomes.Peer reviewedFinal Accepted Versio
Non-substitutional single-atom defects in the Ge_(1-x)Sn_x alloy
Ge_(1-x)Sn_x alloys have proved difficult to form at large x, contrary to
what happens with other group IV semiconductor combinations. However, at low x
they are typical examples of well-behaved substitutional compounds, which is
desirable for harnessing the electronic properties of narrow band
semiconductors. In this paper, we propose the appearance of another kind of
single-site defect (), consisting of a single Sn atom in the center
of a Ge divacancy, that may account for these facts. Accordingly, we examine
the electronic and structural properties of these alloys by performing
extensive numerical ab-initio calculations around local defects. The results
show that the environment of the defect relaxes towards a cubic
octahedral configuration, facilitating the nucleation of metallic white tin and
its segregation, as found in amorphous samples. Using the information stemming
from these local defect calculations, we built a simple statistical model to
investigate at which concentration these defects can be formed in
thermal equilibrium. These results agree remarkably well with experimental
findings, concerning the critical concentration above which the homogeneous
alloys cannot be formed at room temperature. Our model also predicts the
observed fact that at lower temperature the critical concentration increases.
We also performed single site effective-field calculations of the electronic
structure, which further support our hypothesis.Comment: 12 pages, 1 table, 16 figure
Material studies related to lunar surface exploration, volume 3 Final report, 6 Mar. 1967 - 30 Jun. 1968
Mechanical properties of lunar soils related to lunar exploratio
Material studies related to lunar surface exploration. Volume 4 - Preliminary studies for the design of engineering probes Final report, 6 Mar. 1967 - 30 Jun. 1968
Preliminary design of engineering probes for studying lunar surface material propertie
Material studies related to lunar surface exploration Technical summary report, 6 Mar. 1967 - 30 Jun. 1968
Summary of research studies on lunar surface material propertie
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