434 research outputs found
A note on the large-angle anisotropies in the WMAP cut-sky maps
Recent analyses of the WMAP data seem to indicate the possible presence of
large-angle anisotropy in the Universe. If confirmed, these can have important
consequences for our understanding of the Universe. A number of attempts have
recently been made to establish the reality and nature of such anisotropies in
the CMB data. Among these is a directional indicator recently proposed by the
authors. A distinctive feature of this indicator is that it can be used to
generate a sky map of the large-scale anisotropies of the CMB maps. Applying
this indicator to full-sky temperature maps we found a statistically
significant preferred direction. The full-sky maps used in these analyses are
known to have residual foreground contamination as well as complicated noise
properties. Thus, here we performed the same analysis for a map where regions
with high foreground contamination were removed. We find that the main feature
of the full-sky analysis, namely the presence of a significant axis of
asymmetry, is robust with respect to this masking procedure. Other subtler
anomalies of the full-sky are on the other hand no longer present.Comment: 10 pages, 3 figeres. We performed a similar analysis of
arXiv:astro-ph/0511666 by considering the LILC map with a Kp2 sky cut, and
find that the presence of a significant axis of asymmetry is robust with
respect to this masking procedur
Inflationary Cosmology and Oscillating Universes in Loop Quantum Cosmology
We study oscillatory universes within the context of Loop Quantum Cosmology.
We make a comparative study of flat and positively curved universes sourced by
scalar fields with either positive or negative potentials. We investigate how
oscillating universes can set the initial conditions for successful slow-roll
inflation, while ensuring that the semi-classical bounds are satisfied. We
observe rich oscillatory dynamics with negative potentials, although it is
difficult to respect the semi-classical bounds in models of this type.Comment: 7 pages, In Press Int. Mod. Phys.
Evolution of the density contrast in inhomogeneous dust models
With the help of families of density contrast indicators, we study the
tendency of gravitational systems to become increasingly lumpy with time.
Depending upon their domain of definition, these indicators could be local or
global. We make a comparative study of these indicators in the context of
inhomogeneous cosmological models of Lemaitre--Tolman and Szekeres. In
particular, we look at the temporal asymptotic behaviour of these indicators
and ask under what conditions, and for which class of models, they evolve
monotonically in time. We find that for the case of ever-expanding models,
there is a larger class of indicators that grow monotonically with time,
whereas the corresponding class for the recollapsing models is more restricted.
Nevertheless, in the absence of decaying modes, indicators exist which grow
monotonically with time for both ever-expanding and recollapsing models
simultaneously. On the other hand, no such indicators may found which grow
monotonically if the decaying modes are allowed to exist. We also find the
conditions for these indicators to be non-divergent at the initial singularity
in both models. Our results can be of potential relevance for understanding
structure formation in inhomogeneous settings and in debates regarding
gravitational entropy and arrow of time. In particular, the spatial dependence
of turning points in inhomogeneous cosmologies may result in multiple density
contrast arrows in recollapsing models over certain epochs. We also find that
different notions of asymptotic homogenisation may be deduced, depending upon
the density contrast indicators used.Comment: 22 pages, 1 figure. To be published in Classical and Quantum Gravit
In--out intermittency in PDE and ODE models
We find concrete evidence for a recently discovered form of intermittency,
referred to as in--out intermittency, in both PDE and ODE models of mean field
dynamos. This type of intermittency (introduced in Ashwin et al 1999) occurs in
systems with invariant submanifolds and, as opposed to on--off intermittency
which can also occur in skew product systems, it requires an absence of skew
product structure. By this we mean that the dynamics on the attractor
intermittent to the invariant manifold cannot be expressed simply as the
dynamics on the invariant subspace forcing the transverse dynamics; the
transverse dynamics will alter that tangential to the invariant subspace when
one is far enough away from the invariant manifold.
Since general systems with invariant submanifolds are not likely to have skew
product structure, this type of behaviour may be of physical relevance in a
variety of dynamical settings.
The models employed here to demonstrate in--out intermittency are
axisymmetric mean--field dynamo models which are often used to study the
observed large scale magnetic variability in the Sun and solar-type stars. The
occurrence of this type of intermittency in such models may be of interest in
understanding some aspects of such variabilities.Comment: To be published in Chaos, June 2001, also available at
http://www.eurico.web.co
Psychological Safety and Norm Clarity in Software Engineering Teams
In the software engineering industry today, companies primarily conduct their
work in teams. To increase organizational productivity, it is thus crucial to
know the factors that affect team effectiveness. Two team-related concepts that
have gained prominence lately are psychological safety and team norms. Still,
few studies exist that explore these in a software engineering context.
Therefore, with the aim of extending the knowledge of these concepts, we
examined if psychological safety and team norm clarity associate positively
with software developers' self-assessed team performance and job satisfaction,
two important elements of effectiveness.
We collected industry survey data from practitioners (N = 217) in 38
development teams working for five different organizations. The result of
multiple linear regression analyses indicates that both psychological safety
and team norm clarity predict team members' self-assessed performance and job
satisfaction. The findings also suggest that clarity of norms is a stronger
(30\% and 71\% stronger, respectively) predictor than psychological safety.
This research highlights the need to examine, in more detail, the
relationship between social norms and software development. The findings of
this study could serve as an empirical baseline for such, future work.Comment: Submitted to CHASE'201
Transverse instability for non-normal parameters
We consider the behaviour of attractors near invariant subspaces on varying a
parameter that does not preserve the dynamics in the invariant subspace but is
otherwise generic, in a smooth dynamical system. We refer to such a parameter
as ``non-normal''. If there is chaos in the invariant subspace that is not
structurally stable, this has the effect of ``blurring out'' blowout
bifurcations over a range of parameter values that we show can have positive
measure in parameter space.
Associated with such blowout bifurcations are bifurcations to attractors
displaying a new type of intermittency that is phenomenologically similar to
on-off intermittency, but where the intersection of the attractor by the
invariant subspace is larger than a minimal attractor. The presence of distinct
repelling and attracting invariant sets leads us to refer to this as ``in-out''
intermittency. Such behaviour cannot appear in systems where the transverse
dynamics is a skew product over the system on the invariant subspace.
We characterise in-out intermittency in terms of its structure in phase space
and in terms of invariants of the dynamics obtained from a Markov model of the
attractor. This model predicts a scaling of the length of laminar phases that
is similar to that for on-off intermittency but which has some differences.Comment: 15 figures, submitted to Nonlinearity, the full paper available at
http://www.maths.qmw.ac.uk/~eo
Dynamically generated embeddings of spacetime
We discuss how embeddings in connection with the Campbell-Magaard (CM)
theorem can have a physical interpretation. We show that any embedding whose
local existence is guaranteed by the CM theorem can be viewed as a result of
the dynamical evolution of initial data given in a four-dimensional spacelike
hypersurface. By using the CM theorem, we establish that for any analytic
spacetime, there exist appropriate initial data whose Cauchy development is a
five-dimensional vacuum space into which the spacetime is locally embedded. We
shall see also that the spacetime embedded is Cauchy stable with respect these
the initial data.Comment: (8 pages, 1 figure). A section on Cauchy Stability of the embedding
was added. (To appear in Class. Quant. Grav.
Circles-in-the-sky searches and observable cosmic topology in the inflationary limit
While the topology of the Universe is at present not specified by any known
fundamental theory, it may in principle be determined through observations. In
particular, a non-trivial topology will generate pairs of matching circles of
temperature fluctuations in maps of the cosmic microwave background, the
so-called circles-in-the-sky. A general search for such pairs of circles would
be extremely costly and would therefore need to be confined to restricted
parameter ranges. To draw quantitative conclusions from the negative results of
such partial searches for the existence of circles we need a concrete
theoretical framework. Here we provide such a framework by obtaining
constraints on the angular parameters of these circles as a function of
cosmological density parameters and the observer's position. As an example of
the application of our results, we consider the recent search restricted to
pairs of nearly back-to-back circles with negative results. We show that
assuming the Universe to be very nearly flat, with its total matter-energy
density satisfying the bounds , compatible
with the predictions of typical inflationary models, this search, if confirmed,
could in principle be sufficient to exclude a detectable non-trivial cosmic
topology for most observers. We further relate explicitly the fraction of
observers for which this result holds to the cosmological density parameters.Comment: 8 pages, 4 figures. V2: Version to appear in Phys. Rev. D (2008),
typos corrected, references adde
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