A primordial magnetic field may be generated during an inflationary period if conformal invariance is broken. We reexamine and generalize previous results about the magnetic field produced by couplings of the form RFμνF μν . We show that the amplitude of the magnetic field depends strongly on n. For adequate values of n the field produced can serve as seed for galactic magnetic fields. We also ...

‎We consider the oscillator group equipped with‎ ‎a biinvariant Lorentzian metric‎. ‎Some geometrical properties of this space and the harmonicity properties of left-invariant vector fields on this space are determined‎. ‎In some cases‎, ‎all these vector fields are critical points for the energy functional‎ ‎restricted to vector fields‎. ‎Left-invariant vector fields defining harmonic maps are...

In the first part of this paper, some theorems are given for a Riemannian manifold with semi-symmetric metric connection. In the second part of it, some special vector fields, for example, torse-forming vector fields, recurrent vector fields and concurrent vector fields are examined in this manifold. We obtain some properties of this manifold having the vectors mentioned above.

we need sociology theories, for that understand of sociology and politic problems. french sociologist pierre bourdieu's theory practice and symbolic power are our best resource; for understanding social and political fields. this article reviews the language and symbolic power; indicating its function in social and political fields. we need sociology theories, for that understand of sociol...

background: with increased use of computers, exposure to electric and magnetic fields is increasing, the main objective of this study was to evaluate the electric and magnetic field strength in portable computers (laptops) and its relation with eyestrain users. methods: in this cross – sectional study, magnetic and electric fields in 125 laptop computers were measured from 30 cm and 50 cm dista...