329 research outputs found
Scalar-Tensor theories from Plebanski gravity
We study a modification of the Plebanski action, which generically
corresponds to a bi-metric theory of gravity, and identify a subclass which is
equivalent to the Bergmann-Wagoner-Nordtvedt class of scalar-tensor theories.
In this manner, scalar-tensor theories are displayed as constrained BF
theories. We find that in this subclass, there is no need to impose reality of
the Urbantke metrics, as also the theory with real bivectors is a scalar-tensor
theory with a real Lorentzian metric. Furthermore, while under the former
reality conditions instabilities can arise from a wrong sign of the scalar mode
kinetic term, we show that such problems do not appear if the bivectors are
required to be real. Finally, we discuss how matter can be coupled to these
theories. The phenomenology of scalar field dark matter arises naturally within
this framework.Comment: 21 page
Constructive factorization of LPDO in two variables
We study conditions under which a partial differential operator of arbitrary
order in two variables or ordinary linear differential operator admits a
factorization with a first-order factor on the left. The factorization process
consists of solving, recursively, systems of linear equations, subject to
certain differential compatibility conditions. In the generic case of partial
differential operators one does not have to solve a differential equation. In
special degenerate cases, such as ordinary differential, the problem is finally
reduced to the solution of some Riccati equation(s). The conditions of
factorization are given explicitly for second- and, and an outline is given for
the higher-order case.Comment: 16 pages, to be published in Journal "Theor. Math. Phys." (2005
Laser-induced optical changes in amorphous multilayers
It is shown that the well-known blue-shift of the fundamental absorption edge
in as-deposited compositionally modulated amorphous Si/Ge and As6Se94/Se80Te20
multilayers (with periods of 4-8 nm) is further enhanced due to the thermal or
laser-induced intermixing of adjacent layers. The laser-induced intermixing
process, as supported by experiments and model calculations, can be attributed
to both the local heating and photo-effects in As6Se94/Se80Te20 multilayers,
while only the thermal effects were observed for Si/Ge multilayers. Structural
transformations, based on this enhanced interdiffusion, provides good
capability for spatially patterning optoelectronic devices and digital
information recording
Multi-drug-resistant tuberculosis clusters in Mpumalanga province, South Africa, 2013–2016 : a spatial analysis
OBJECTIVE : To identify spatial clusters with unusually high levels of MDR-TB, which are highly unlikely to have arisen by chance in Mpumalanga Province, South Africa.
METHODS : Home addresses of all MDR-TB patients were collected from four MDR-TB facilities from 2013 to 2016. We mapped all addresses, linking them to the nearest ward with population estimates. A spatial analysis was conducted using kernel density in ArcGIS to estimate and map the distribution of the disease and used Gertis-Ord Gi to test for significant clustering.
RESULTS : A total of 4065 MDR-TB patients were mapped. Ten significant clusters (p-value <0.05) were found across the province in six sub-districts: Mbombela, Nkomazi, Emalahleni, Govan Mbeki, Lekwa and Mkhondo. Mbombela has the highest number of significant clusters. The central region did not have any MDR-TB clusters.
CONCLUSION : There is clear evidence of MDR-TB clustering in Mpumalanga. This calls for concentrated TB prevention efforts and proper allocation of resources. Further investigations are needed to identify MDR-TB predictors.http://www.wileyonlinelibrary.com/journal/tmihj2022School of Health Systems and Public Health (SHSPH
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