17,257 research outputs found
Theory and Simulation of the diffusion of kinks on dislocations in bcc metals
Isolated kinks on thermally fluctuating (1/2) screw, edge and
(1/2) edge dislocations in bcc iron are simulated under zero stress
conditions using molecular dynamics (MD). Kinks are seen to perform stochastic
motion in a potential landscape that depends on the dislocation character and
geometry, and their motion provides fresh insight into the coupling of
dislocations to a heat bath. The kink formation energy, migration barrier and
friction parameter are deduced from the simulations. A discrete
Frenkel-Kontorova-Langevin (FKL) model is able to reproduce the coarse grained
data from MD at a fraction of the computational cost, without assuming an a
priori temperature dependence beyond the fluctuation-dissipation theorem.
Analytic results reveal that discreteness effects play an essential r\^ole in
thermally activated dislocation glide, revealing the existence of a crucial
intermediate length scale between molecular and dislocation dynamics. The model
is used to investigate dislocation motion under the vanishingly small stress
levels found in the evolution of dislocation microstructures in irradiated
materials
Scattering and Diffraction in Magnetospheres of Fast Pulsars
We apply a theory of wave propagation through a turbulent medium to the
scattering of radio waves in pulsar magnetospheres. We find that under
conditions of strong density modulation the effects of magnetospheric
scintillations in diffractive and refractive regimes may be observable. The
most distinctive feature of the magnetospheric scintillations is their
independence on frequency.
Results based on diffractive scattering due to small scale inhomogeneities
give a scattering angle that may be as large as 0.1 radians, and a typical
decorrelation time of seconds.
Refractive scattering due to large scale inhomogeneities is also possible,
with a typical angle of radians and a correlation time of the order
of seconds. Temporal variation in the plasma density may also result
in a delay time of the order of seconds. The different scaling of the
above quantities with frequency may allow one to distinguish the effects of
propagation through a pulsar magnetosphere from the interstellar medium. In
particular, we expect that the magnetospheric scintillations are relatively
more important for nearby pulsars when observed at high frequencies.Comment: 19 pages, 1 Figur
How to identify when a performance indicator has run its course
The official published version can be found at the link below.Increasing numbers of countries are using indicators to evaluate the quality of clinical care, with some linking payment to achievement. For performance frameworks to remain effective the indicators need to be regularly reviewed. The frameworks cannot cover all clinical areas, and achievement on chosen indicators will eventually reach a ceiling beyond which further improvement is not feasible. However, there has been little work on how to select indictors for replacement. The Department of Health decided in 2008 that it would regularly replace indicators in the national primary care pay for performance scheme, the Quality and Outcomes Framework, making a rigorous approach to removal a priority. We draw on our previous work on pay for performance and our current work advising the National Institute for Health and Clinical Excellence (NICE) on the Quality and Outcomes Framework to suggest what should be considered when planning to remove indicators from a clinical performance framework
Temperature dependence of surface reconstructions of Au on Pd(110)
Surface reconstructions of Au film on Pd(110) substrate are studied using a
local Einstein approximation to quasiharmonic theory with the Sutton-Chen
interatomic potential. Temperature dependent surface free energies for
different coverages and surface structures are calculated. Experimentally
observed transformations from to and
structures can be explained in the framework of this model. Also conditions for
Stranski-Krastanov growth mode are found to comply with experiments. The domain
of validity of the model neglecting mixing entropy is analyzed.Comment: 7 pages, REVTeX two-column format, 3 postscript figures available on
request from [email protected] To appear in Phys. Rev. Letter
Site categorisation for nitrogen measures
Final report to Natural England on project IPENS-049
SIT4 protein phosphatase is required for the normal accumulation of SWI4, CLN1, CLN2, and HCS26 RNAs during late G1
In Saccharomyces cerevisiae, the RNA levels of the G1 cyclins CLN1, CLN2, and HCS26 increase dramatically during the late G1 phase of the cell cycle. The SIT4 gene, which encodes a serine/threonine protein phosphatase, is required for the normal accumulation of CLN1, CLN2, and HCS26 RNAs during late G1. This requirement for SIT4 in normal G1 cyclin RNA accumulation is at least partly via SWI4. Strains containing mutations in SIT4 are sensitive to the loss of either CLN2 or CLN3 function. At the nonpermissive temperature, temperature-sensitive sit4 strains are blocked for both bud emergence and DNA synthesis. Heterologous expression of CLN2 in the absence of SIT4 function results in DNA synthesis, but most of the cells are still blocked for bud emergence. Therefore, SIT4 is required for at least two late G1 or G1/S functions: the normal accumulation of G1 cyclin RNAs (which is required for DNA synthesis) and some additional function that is required for bud emergence or cell cycle progression through late G1 or G1/S
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