273 research outputs found
Scalar field phase dynamics in preheating
We study the model of a massive inflaton field coupled to another
scalar filed with interaction term for the first stage
of preheating. We obtain the the behavior of the phase in terms of the
iteration of a simple family of circle maps. When expansion of the universe is
taken into account the qualitative behavior of the phase and growth number
evolution is reminiscent of the behavior found in the case without expansion.Comment: 4 pages, 4 figures, LaTeX; submitted to the Proceedings of Eleventh
Marcel Grossmann Meetin
Report on "Scheduling in a factory"
In order to carry out their orders of shoe soles, this company has a number of tasks T_1, ..., T_n of different lengths to be assigned to groups of machines.
Each group is operated by one worker (two in one case), and an operation cycle corresponds to injection, cooling, and removal of the sole. The time taken at each step varies from one order to another, and when starting a new task a machine needs to be tuned, which takes some extra time. Machines are working in parallel. At the moment the assignment is carried out empirically, and the problem proposed is to optimize the procedure
Self-interacting scalar field cosmologies: unified exact solutions and symmetries
We investigate a mechanism that generates the exact solutions of scalar field
cosmologies in a unified way. The procedure investigated here permits to
recover allmost all known solutions, and allows one to derive new solutions as
well. In particular, we derive and discuss one novel solution defined in terms
of the Lambert function. The solutions are organized in a classification which
depends on the choice of a generating function which we have denoted by
that reflects the underlying thermodynamics of the model. We also
analyse and discuss the existence of form invariances and dualities between
solutions. A general way of defining the latter in an appropriate fashion for
scalar fields is put forward.Comment: 6 figures, 30 page
Reheating induced by competing decay modes
We address the problem of studying the decay of the inflaton field to
another scalar field through parametric resonance in the case of a
coupling that involves several decay modes. This amounts to the presence of
extra harmonic terms in the perturbation of the field dynamics. For the
case of two frequencies we compute the geometry of the resonance regions, which
is significantly altered due to the presence of non-cuspidal resonance regions
associated to higher harmonics and to the emergence of instability `pockets'.
We discuss the effect of this change in the efficiency of the energy transfer
process for the simplest case of a coupling given by a combination of the two
interaction terms of homogeneous degree usually considered in the literature.
We find that the presence of higher harmonics has limited cosmological
implications.Comment: 14 pages, 4 figures Added references. Corrected typo
Form invariance symmetry generates a large set of FRW cosmologies
We show that Einstein's field equations for spatially flat
Friedmann-Robertson-Walker (FRW) space times have a form invariance symmetry
(FIS) realized by the form invariance transformations (FIT) which are indeed
generated by an invertible function of the source energy density. These
transformations act on the Hubble expansion rate, the energy density, and
pressure of the cosmic fluid; likewise such transformations are endowed with a
Lie group structure. Each representation of this group is associated with a
particular fluid and consequently a determined cosmology, so that, the FIS
defines a set of equivalent cosmological models. We focus our seek in the FIT
generated by a linear function because it provides a natural framework to
express the duality and also produces a large sets of cosmologies, starting
from a seed one, in several contexts as for instance in the cases of a perfect
fluid source and a scalar field driven by a potential depending linearly on the
scalar field kinetic energy density.Comment: 11 pages, 3 figures. Accepted for publication in Modern Physics
Letters A (2012
Generation Y and sparkling wines: a cross-cultural perspective
The aim of this study was to investigate and compare the engagement of Generation Y consumers with champagne and sparkling wine across five Anglophone countries. A qualitative approach was adopted using focus groups with young consumers, including images and wine tasting as projective stimuli. There were significant trans-cultural similarities between consumption behaviour (sparkling wine is a womenâs drink, and a separate category from still wine, and that they will âgrow intoâ drinking it) but also noticeable differences (responses to images and colours varied substantially, as did attitudes to price and the particular status of champagne). Research into the behaviour of Generation Y as a cohort needs to take account of cultural as much as generational context. However, as a qualitative study the findings need further quantitative validation. Marketers cannot view Generation Y as a single group; even within countries marketing strategies may need to be refined depending on where a product is being sold
Influence of groundwater condition on nutrient dynamics in urban waterways
Excess nutrients in waterways contribute to eutrophication and decrease aquatic ecosystem health, a
problem affecting both rural and urban catchments. In order to address excess nutrient problems in urban
waterways, authorities have been developing strategies to mitigate impacts by using in-channel and landbased stormwater treatment to remove pollutants via settling and other physical, chemical and/or
biological processes. However, little is known about how pollutants are transported and transformed in
urban in-channel systems under the influence of different groundwater conditions. Therefore, this research
aims to understand nutrient dynamics (nitrogen and phosphorus) in waterway channels under the
influence of seepage, neutral, and drainage conditions. It was hypothesized that groundwater and bed
material characteristics affect the concentration and form of surface pollutants, as well as their mobility.
This understanding could help guide stream management decisions
Comparison of engagement and emotional responses of older and younger adults interacting with 3D cultural heritage artefacts on personal devices
The availability of advanced software and less expensive hardware allows museums to preserve and share artefacts digitally. As a result, museums are frequently making their collections accessible online as interactive, 3D models. This could lead to the unique situation of viewing the digital artefact before the physical artefact. Experiencing artefacts digitally outside of the museum on personal devices may affect the user's ability to emotionally connect to the artefacts. This study examines how two target populations of young adults (18â21 years) and the elderly (65 years and older) responded to seeing cultural heritage artefacts in three different modalities: augmented reality on a tablet, 3D models on a laptop, and then physical artefacts. Specifically, the time spent, enjoyment, and emotional responses were analysed. Results revealed that regardless of age, the digital modalities were enjoyable and encouraged emotional responses. Seeing the physical artefacts after the digital ones did not lessen their enjoyment or emotions felt. These findings aim to provide an insight into the effectiveness of 3D artefacts viewed on personal devices and artefacts shown outside of the museum for encouraging emotional responses from older and younger people
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