The Einstein-Friedrich-nonlinear scalar field system and the stability of scalar field Cosmologies

A frame representation is used to derive a first order quasi-linear symmetric hyperbolic system for a scalar field minimally coupled to gravity. This procedure is inspired by similar evolution equations introduced by Friedrich to study the Einstein-Euler system. The resulting evolution system is used to show that small nonlinear perturbations of expanding Friedman-Lema\^itre-Robertson-Walker backgrounds, with scalar field potentials satisfying certain future asymptotic conditions, decay exponentially to zero, in synchronous time.Comment: Version 4: Matches final published versio

On the non-linear stability of scalar field cosmologies

We review recent work on the stability of flat spatially homogeneous and isotropic backgrounds with a self-interacting scalar field. We derive a first order quasi-linear symmetric hyperbolic system for the Einstein-nonlinear-scalar field system. Then, using the linearized system, we show how to obtain necessary and sufficient conditions which ensure the exponential decay to zero of small non-linear perturbations.JAVK was supported by an EPSRC Advanced Research Fellowship and by a project research grant from the Leverhulme Trust (F/07 476/AI). AA and FM are supported by projects FCT/PTDC/MAT/108921/2008 and CERN/FP/116377/2010 and by CMAT, Univ. Minho, through FCT plurianual funding. AA thanks FCT grant SFRH/BD/48658/2008. FM thanks FCT grant SFRH/BSAB/967/2010

Farm Deaths in North Karelia

This study examined the effect of farm size on the mortality and survival of EasternFinnish farms in the late 1990s. Three different dimensions of farm size (i.e. hectaresoperated, number of milk cows, and hectares of forest) were compared. Data wereextracted from administrative records and covered all 4,527 active farms in NorthKarelia from 1995 to 1998. Results did not support the disappearing middle sizehypothesis presented by Weiss (1999). Farm size distributions were not bimodal.No empirical evidence was found of a process of polarisation into two centres ofattraction. As a whole, the analysis provides some support for the conclusion thatthe size of forest holding as measured by hectares of forest owned by farm does nothave an independent effect on the likelihood of survival. Its contribution dependson the other variables in the model

Dynamics of Robertson-Walker spacetimes with diffusion

We study the dynamics of spatially homogeneous and isotropic spacetimes containing a fluid undergoing microscopic velocity diffusion in a cosmological scalar field. After deriving a few exact solutions of the equations, we continue by analyzing the qualitative behavior of general solutions. To this purpose we recast the equations in the form of a two dimensional dynamical system and perform a global analysis of the flow. Among the admissible behaviors, we find solutions that are asymptotically de-Sitter both in the past and future time directions and which undergo accelerated expansion at all times.Fundação para a Ciência e a Tecnologia (FCT

Oxygen Ion Escape From Venus Is Modulated by Ultra‐Low Frequency Waves

We study the solar wind‐driven, nonthermal escape of O+ ions from Venus in a global hybrid simulation. In the model, a well‐developed ion foreshock forms ahead of the Venusian quasi‐parallel bow shock under nominal upstream conditions. Large‐scale magnetosonic ultra‐low frequency (ULF) waves at 20‐ to 30‐s period are excited and convect downstream along the foreshock with the solar wind. We show that the foreshock ULF waves transmit through the bow shock in the downstream region and interact with the planetary ion acceleration, causing 25% peak‐to‐peak fluctuations in the O+ escape rate. These results demonstrate the importance of upstream plasma waves on the energization and escape of heavy ions from the planetary atmospheres.Key PointsA global hybrid simulation predicts fluctuations in the O+ escape from VenusThe fluctuations are associated with the foreshock ULF waves, which modulate the acceleration of heavy pickup ionsUpstream waves need to be taken into account in the interpretation of heavy ion erosion from unmagnetized planetsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155962/1/grl60648_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155962/2/grl60648-sup-0001-Figure_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155962/3/grl60648.pd

a case study from Portugal

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