2,929 research outputs found
Some thoughts on GAIA and the sulfur cycle
The data hypothesis states that the composition, oxidation reduction state, and temperature of the troposphere are actively regulated by the biota for the biota. One of the early predictions of the Gaia hypothesis was that there should be a sulfur compound made by the biota in the oceans. It would need to be stable enough against oxidation in water to allow its transfer to the air. Either the sulfur compound itself or its atmospheric oxidation product would have to return sulfur from the sea to the land surfaces. The most likely candidate for this role was dimethyl sulfide. Another sulfur compound of interest from a Gaian viewpoint CS2 (carbon disulfide) is discussed. Theories on the production of dimethyl sulfide and carbon disulfide related to the Gaian hypothesis are examined
Martian atmospheric compositional analysis- its biological significance first quarterly progress report, 15 may - 15 aug. 1965
Biological significance of Martian atmospheric compositional analysis, and life detection studies of chemical free energy in surface matte
Chapter 09: Vulnerability of mangroves and tidal wetlands of the Great Barrier Reef to climate change
Climate change will have an enormous influence on the intertidal wetlands of the Great Barrier Reef
(GBR). Increases in atmospheric carbon dioxide (CO2) concentrations and associated increases in air
and sea temperatures, rising sea level, changes in oceanic circulation, rainfall patterns and frequency
and intensity of storms are highly likely to affect the physiology, ecology and ultimately the stability
of wetland habitats. The intertidal position of mangroves, salt marshes and salt flats makes
them particularly vulnerable to changes in sea level, although other climate change factors will also
exert a strong influence on wetland communities. Past rises in sea level have led to increases
in the area of mangroves in northern Australia. However, past climate change has occurred with
limited human modification of the coast compared to current levels of development. Human activities
have resulted in loss of wetlands, disruption to connectivity, enhanced availability of nutrients, changed
sediment dynamics and the creation of structures that will prevent landward migration of wetlands
with sea level rise (eg roads, berms, bunds and sea walls). Many of these human impacts will reduce
the resilience of intertidal wetlands to climate change. To conserve the intertidal wetlands of the GBR
and the ecosystem services they provide, we will need to manage the coastal zone in a way that
enhances the resilience of mangroves, salt marshes and salt flats during climate change.This is Chapter 9 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13
Daisyworld: a review
Daisyworld is a simple planetary model designed to show the long-term effects of coupling between life and its environment. Its original form was introduced by James Lovelock as a defense against criticism that his Gaia theory of the Earth as a self-regulating homeostatic system requires teleological control rather than being an emergent property. The central premise, that living organisms can have major effects on the climate system, is no longer controversial. The Daisyworld model has attracted considerable interest from the scientific community and has now established itself as a model independent of, but still related to, the Gaia theory. Used widely as both a teaching tool and as a basis for more complex studies of feedback systems, it has also become an important paradigm for the understanding of the role of biotic components when modeling the Earth system. This paper collects the accumulated knowledge from the study of Daisyworld and provides the reader with a concise account of its important properties. We emphasize the increasing amount of exact analytic work on Daisyworld and are able to bring together and summarize these results from different systems for the first time. We conclude by suggesting what a more general model of life-environment interaction should be based on
Spectral Evolution of an Earth-Like Planet
We have developed a characterization of the geological evolution of the
Earths atmosphere and surface in order to model the observable spectra of an
Earth-like planet through its geological history. These calculations are
designed to guide the interpretation of an observed spectrum of such a planet
by future instruments that will characterize exoplanets. Our models focus on
spectral features that either imply habitability or are required for
habitability. These features are generated by H2O, CO2, CH4, O2, O3, N2O, and
vegetation-like surface albedos. We chose six geological epochs to
characterize. These epochs exhibit a wide range in abundance for these
molecules, ranging from a CO2 rich early atmosphere, to a CO2/CH4-rich
atmosphere around 2 billion years ago to a present-day atmosphere. We analyzed
the spectra to quantify the strength of each important spectral feature in both
the visible and thermal infrared spectral regions, and the resolutions required
to unambiguously observe the features for each epoch. We find a wide range of
spectral resolutions required for observing the different features. For
example, H2O and O3 can be observed with relatively low resolution, while O2
and N2O require higher resolution. We also find that the inclusion of clouds in
our models significantly affects both the strengths and resolutions required to
observe all spectral features.Comment: 34 pages, 24 fig, pdf, ApJ, TB
Quantized Friction across Ionic Liquid Thin Films
Ionic liquids, salts in the liquid state under ambient conditions, are of
great interest as precision lubricants. Ionic liquids form layered structures
at surfaces, yet it is not clear how this nano-structure relates to their
lubrication properties. We measured the friction force between atomically
smooth solid surfaces across ionic liquid films of controlled thickness in
terms of the number of ion layers. Multiple friction-load regimes emerge, each
corresponding to a different number of ion layers in the film. In contrast to
molecular liquids, the friction coefficients differ for each layer due to their
varying composition
Gauss-Bonnet lagrangian G ln G and cosmological exact solutions
For the lagrangian L = G ln G where G is the Gauss-Bonnet curvature scalar we
deduce the field equation and solve it in closed form for 3-flat Friedman
models using a statefinder parametrization. Further we show, that among all
lagrangians F(G) this L is the only one not having the form G^r with a real
constant r but possessing a scale-invariant field equation. This turns out to
be one of its analogies to f(R)-theories in 2-dimensional space-time. In the
appendix, we systematically list several formulas for the decomposition of the
Riemann tensor in arbitrary dimensions n, which are applied in the main
deduction for n=4.Comment: 18 pages, amended version, accepted by Phys. Rev.
Positioning the Destination Product-Can Regional Tourist Boards Learn from Private Sector Practice?
This article examines the role of positioning in the
marketing of a tourism destination. The study focuses on the current positioning strategies pursued by the Regional Tourist Boards (RTBs) in England. A recent nationwide consumer research study into short holiday destination choice in the UK revealed that consumers were confused by the regional product message. The evidence suggests that current RTB positioning strategies are failing to keep pace with the constantly evolving needs of the consumer. This
article explores the reasons for clearly positioning the destination product and suggests that, although RTBs could learn from marketing strategies employed in other sectors of the tourism industry, there are likely to be organisational and cultural barriers inhibiting this
learning curve
Black Hole Entropy and the Dimensional Continuation of the Gauss-Bonnet Theorem
The Euclidean black hole has topology . It is
shown that -in Einstein's theory- the deficit angle of a cusp at any point in
and the area of the are canonical conjugates. The
black hole entropy emerges as the Euler class of a small disk centered at the
horizon multiplied by the area of the there.These results are
obtained through dimensional continuation of the Gauss-Bonnet theorem. The
extension to the most general action yielding second order field equations for
the metric in any spacetime dimension is given.Comment: 7 pages, RevTe
Environmental Regulation Can Arise Under Minimal Assumptions
Models that demonstrate environmental regulation as a consequence of organism and environment coupling all require a number of core assumptions. Many previous models, such as Daisyworld, require that certain environment-altering traits have a selective advantage when those traits also contribute towards global regulation. We present a model that results in the regulation of a global environmental resource through niche construction without employing this and other common assumptions. There is no predetermined environmental optimum towards which regulation should proceed assumed or coded into the model. Nevertheless, polymorphic stable states that resist perturbation emerge from the simulated co-evolution of organisms and environment. In any single simulation a series of different stable states are realised, punctuated by rapid transitions. Regulation is achieved through two main subpopulations that are adapted to slightly different resource values, which force the environmental resource in opposing directions. This maintains the resource within a comparatively narrow band over a wide range of external perturbations. Population driven oscillations in the resource appear to be instrumental in protecting the regulation against mutations that would otherwise destroy it. Sensitivity analysis shows that the regulation is robust to mutation and to a wide range of parameter settings. Given the minimal assumptions employed, the results could reveal a mechanism capable of environmental regulation through the by-products of organisms
- …