53 research outputs found
Marine Monitoring Program: Annual report for inshore seagrass monitoring 2015-2016
The Marine Monitoring Program (MMP) undertaken in the Great Barrier Reef (GBR) lagoon, assesses the long-term effectiveness of the Australian and Queensland Government’s Reef Water Quality Protection Plan (Reef Plan). The MMP, established in 2005, is a critical component in the paddock to reef monitoring modelling and reporting program (P2R) that tracks changes in regional water quality and its impact on the GBR as land management practices are improved across Reef catchments.
The inshore seagrass component of the MMP assessed seagrass abundance (per cent cover), community structure, relative meadow extent, reproductive health, and nutrient status from inshore seagrass meadows at 29 locations throughout the GBR. Sites were predominately lower littoral (only exposed to air at the lowest of low tides), hereafter referred to as intertidal, although four locations also included shallow subtidal meadows. Each of the Natural Resource Management regions (Cape York, Wet Tropics, Burdekin, Mackay Whitsunday, Fitzroy and Burnett Mary) were represented, including each of the major seagrass habitat types where possible (estuarine, coastal, reef, subtidal).
Environmental pressures are also recorded including within-canopy water temperature, canopy light, sediment composition as well as macroalgae and epiphyte abundance, further data obtained from the Australian Bureau of Meteorology and from the MMP inshore water quality subprogram
Can Inflating Braneworlds be Stabilized?
We investigate scalar perturbations from inflation in braneworld cosmologies
with extra dimensions. For this we calculate scalar metric fluctuations around
five dimensional warped geometry with four dimensional de Sitter slices. The
background metric is determined self-consistently by the (arbitrary) bulk
scalar field potential, supplemented by the boundary conditions at both
orbifold branes. Assuming that the inflating branes are stabilized (by the
brane scalar field potentials), we estimate the lowest eigenvalue of the scalar
fluctuations - the radion mass. In the limit of flat branes, we reproduce well
known estimates of the positive radion mass for stabilized branes.
Surprisingly, however, we found that for de Sitter (inflating) branes the
square of the radion mass is typically negative, which leads to a strong
tachyonic instability. Thus, parameters of stabilized inflating braneworlds
must be constrained to avoid this tachyonic instability. Instability of
"stabilized" de Sitter branes is confirmed by the BraneCode numerical
calculations in the accompanying paper hep-th/0309001. If the model's
parameters are such that the radion mass is smaller than the Hubble parameter,
we encounter a new mechanism of generation of primordial scalar fluctuations,
which have a scale free spectrum and acceptable amplitude.Comment: 7 pages, RevTeX 4.
Marine Monitoring Program: Inshore seagrass, annual report for the sampling period 1st June 2013 - 31st May 2014
A key component of Reef Plan is the implementation of a long-term water quality and ecosystem monitoring program in the Great Barrier Reef lagoon. James Cook University were contracted to conduct the intertidal seagrass monitoring component and produce this report, which examines the status and trend of Reef intertidal seagrass (detect long-term trends in seagrass abundance, community structure, distribution, reproductive health, and nutrient status from representative inshore seagrass meadows) and identifies response of seagrass to environmental drivers of change
Oscillations During Inflation and the Cosmological Density Perturbations
Adiabatic (curvature) perturbations are produced during a period of
cosmological inflation that is driven by a single scalar field, the inflaton.
On particle physics grounds -- though -- it is natural to expect that this
scalar field is coupled to other scalar degrees of freedom. This gives rise to
oscillations between the perturbation of the inflaton field and the
perturbations of the other scalar degrees of freedom, similar to the phenomenon
of neutrino oscillations. Since the degree of the mixing is governed by the
squared mass matrix of the scalar fields, the oscillations can occur even if
the energy density of the extra scalar fields is much smaller than the energy
density of the inflaton field. The probability of oscillation is resonantly
amplified when perturbations cross the horizon and the perturbations in the
inflaton field may disappear at horizon crossing giving rise to perturbations
in scalar fields other than the inflaton. Adiabatic and isocurvature
perturbations are inevitably correlated at the end of inflation and we provide
a simple expression for the cross-correlation in terms of the slow-roll
parameters.Comment: 23 pages, uses LaTeX, added few reference
Inflationary models inducing non-Gaussian metric fluctuations
We construct explicit models of multi-field inflation in which the primordial
metric fluctuations do not necessarily obey Gaussian statistics. These models
are realizations of mechanisms in which non-Gaussianity is first generated by a
light scalar field and then transferred into curvature fluctuations. The
probability distribution functions of the metric perturbation at the end of
inflation are computed. This provides a guideline for designing strategies to
search for non-Gaussian signals in future CMB and large scale structure
surveys.Comment: 4 pages, 7 figure
Correlated Hybrid Fluctuations from Inflation with Thermal Dissipation
We investigate the primordial scalar perturbations in the thermal dissipative
inflation where the radiation component (thermal bath) persists and the density
fluctuations are thermally originated. The perturbation generated in this model
is hybrid, i.e. it consists of both adiabatic and isocurvature components. We
calculate the fractional power ratio () and the correlation coefficient
() between the adiabatic and the isocurvature perturbations at the
commencing of the radiation regime. Since the adiabatic/isocurvature
decomposition of hybrid perturbations generally is gauge-dependent at
super-horizon scales when there is substantial energy exchange between the
inflaton and the thermal bath, we carefully perform a proper decomposition of
the perturbations. We find that the adiabatic and the isocurvature
perturbations are correlated, even though the fluctuations of the radiation
component is considered uncorrelated with that of the inflaton. We also show
that both and depend mainly on the ratio between the
dissipation coefficient and the Hubble parameter during inflation.
The correlation is positive () for strong dissipation cases
where , and is negative for weak dissipation instances where
. Moreover, and in this model are not
independent of each other. The predicted relation between and
is consistent with the WMAP observation. Other testable predictions are also
discussed.Comment: 18 pages using revtex4, accepted for publication in PR
Has the Universe always expanded ?
We consider a cosmological setting for which the currently expanding era is
preceded by a contracting phase, that is, we assume the Universe experienced at
least one bounce. We show that scalar hydrodynamic perturbations lead to a
singular behavior of the Bardeen potential and/or its derivatives (i.e. the
curvature) for whatever Universe model for which the last bounce epoch can be
smoothly and causally joined to the radiation dominated era. Such a Universe
would be filled with non-linear perturbations long before nucleosynthesis, and
would thus be incompatible with observations. We therefore conclude that no
observable bounce could possibly have taken place in the early universe if
Einstein gravity together with hydrodynamical fluids is to describe its
evolution, and hence, under these conditions, that the Universe has always
expanded.Comment: 11 pages, LaTeX-ReVTeX, no figures, submitted to PR
Observational constraints on the curvaton model of inflation
Simple curvaton models can generate a mixture of of correlated primordial
adiabatic and isocurvature perturbations. The baryon and cold dark matter
isocurvature modes differ only by an observationally null mode in which the two
perturbations almost exactly compensate, and therefore have proportional
effects at linear order. We discuss the CMB anisotropy in general mixed models,
and give a simple approximate analytic result for the large scale CMB
anisotropy. Working numerically we use the latest WMAP observations and a
variety of other data to constrain the curvaton model. We find that models with
an isocurvature contribution are not favored relative to simple purely
adiabatic models. However a significant primordial totally correlated baryon
isocurvature perturbation is not ruled out. Certain classes of curvaton model
are thereby ruled out, other classes predict enough non-Gaussianity to be
detectable by the Planck satellite. In the appendices we review the relevant
equations in the covariant formulation and give series solutions for the
radiation dominated era.Comment: Minor changes and corrections to match version accepted by PR
A solution of the coincidence problem based on the recent galactic core black hole mass density increase
A mechanism capable to provide a natural solution to two major cosmological
problems, i.e. the cosmic acceleration and the coincidence problem, is
proposed. A specific brane-bulk energy exchange mechanism produces a total dark
pressure, arising when adding all normal to the brane negative pressures in the
interior of galactic core black holes. This astrophysically produced negative
dark pressure explains cosmic acceleration and why the dark energy today is of
the same order to the matter density for a wide range of the involved
parameters. An exciting result of the analysis is that the recent rise of the
galactic core black hole mass density causes the recent passage from cosmic
deceleration to acceleration. Finally, it is worth mentioning that this work
corrects a wide spread fallacy among brane cosmologists, i.e. that escaping
gravitons result to positive dark pressure.Comment: 14 pages, 3 figure
- …