1,984 research outputs found
Environmental challenges to operationalisation of South African rainfall enhancement
Most of the atmospheric moisture in systems moving across South Africa leaves the sub-continent as the weather systems move
out over the ocean, only a tenth of it falls on the landmass as rain. An increase in the efficiency of the atmospheric moisture delivery
system by means of rainfall enhancement is therefore an attractive concept. Rainfall enhancement functions by either providing
additional Cloud Condensation Nuclei or Ice forming Nuclei that will beneficially influence the precipitation formation process,
improving the efficiency of moisture to rainfall conversion.
Systematic South African research into rainfall enhancement started in the 1970s. The South African Rainfall Enhancement
Programme (SAREP), initiated in the late 1990\'s, is the most recent in a series of studies and was the first semi-operational rainfall
enhancement project to occur in South Africa as a response to drought conditions. In a recent study (DWAF, 2004 in prep) to finalise
SAREP and provide guidance on operationalising rainfall enhancement, it was recommended that environmental impact
assessment must be undertaken before this technology is implemented further.
Rainfall enhancement falls specifically within the jurisdiction of the National Water Act (NWA) and the National
Environmental Management Act (NEMA). A licence to undertake rainfall enhancement activities is required from the Minister of Water Affairs and Forestry after an appropriate environmental impact assessment has been undertaken to inform his decision. This paper proposes an approach to fulfil the legal requirements for operationalising future rainfall enhancement. The interaction between the science of rainfall enhancement and the ability of scientific disciplines to determine relevant environmental impacts, to appropriately inform the decision-making process, is specifically highlighted. The data requirements identified by scientists during the study varies in duration and resource needs and does not differentiate between ongoing scientific research and the requisite information required for informed decision making. This paper contemplates an approach which provides for holistic and co-ordinated investigation of South African rainfall enhancement into the future. Water SA Vol. 30 (5) 2005: pp.88-9
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The microbiome in patients with atopic dermatitis.
As an interface with the environment, the skin is a complex ecosystem colonized by many microorganisms that coexist in an established balance. The cutaneous microbiome inhibits colonization with pathogens, such as Staphylococcus aureus, and is a crucial component for function of the epidermal barrier. Moreover, crosstalk between commensals and the immune system is now recognized because microorganisms can modulate both innate and adaptive immune responses. Host-commensal interactions also have an effect on the developing immune system in infants and, subsequently, the occurrence of diseases, such as asthma and atopic dermatitis (AD). Later in life, the cutaneous microbiome contributes to the development and course of skin disease. Accordingly, in patients with AD, a decrease in microbiome diversity correlates with disease severity and increased colonization with pathogenic bacteria, such as S aureus. Early clinical studies suggest that topical application of commensal organisms (eg, Staphylococcus hominis or Roseomonas mucosa) reduces AD severity, which supports an important role for commensals in decreasing S aureus colonization in patients with AD. Advancing knowledge of the cutaneous microbiome and its function in modulating the course of skin disorders, such as AD, might result in novel therapeutic strategies
Identifying Planetary Biosignature Impostors: Spectral Features of CO and O4 Resulting from Abiotic O2/O3 Production
O2 and O3 have been long considered the most robust individual biosignature
gases in a planetary atmosphere, yet multiple mechanisms that may produce them
in the absence of life have been described. However, these abiotic planetary
mechanisms modify the environment in potentially identifiable ways. Here we
briefly discuss two of the most detectable spectral discriminants for abiotic
O2/O3: CO and O4. We produce the first explicit self-consistent simulations of
these spectral discriminants as they may be seen by JWST. If JWST-NIRISS and/or
NIRSpec observe CO (2.35, 4.6 um) in conjunction with CO2 (1.6, 2.0, 4.3 um) in
the transmission spectrum of a terrestrial planet it could indicate robust CO2
photolysis and suggest that a future detection of O2 or O3 might not be
biogenic. Strong O4 bands seen in transmission at 1.06 and 1.27 um could be
diagnostic of a post-runaway O2-dominated atmosphere from massive H-escape. We
find that for these false positive scenarios, CO at 2.35 um, CO2 at 2.0 and 4.3
um, and O4 at 1.27 um are all stronger features in transmission than O2/O3 and
could be detected with SNRs 3 for an Earth-size planet orbiting a
nearby M dwarf star with as few as 10 transits, assuming photon-limited noise.
O4 bands could also be sought in UV/VIS/NIR reflected light (at 0.345, 0.36,
0.38, 0.445, 0.475, 0.53, 0.57, 0.63, 1.06, and 1.27 um) by a next generation
direct-imaging telescope such as LUVOIR/HDST or HabEx and would indicate an
oxygen atmosphere too massive to be biologically produced.Comment: 7 pages, 4 figures, accepted to the Astrophysical Journal Letter
VPLanet: The Virtual Planet Simulator
We describe a software package called VPLanet that simulates fundamental
aspects of planetary system evolution over Gyr timescales, with a focus on
investigating habitable worlds. In this initial release, eleven physics modules
are included that model internal, atmospheric, rotational, orbital, stellar,
and galactic processes. Many of these modules can be coupled simultaneously to
simulate the evolution of terrestrial planets, gaseous planets, and stars. The
code is validated by reproducing a selection of observations and past results.
VPLanet is written in C and designed so that the user can choose the physics
modules to apply to an individual object at runtime without recompiling, i.e.,
a single executable can simulate the diverse phenomena that are relevant to a
wide range of planetary and stellar systems. This feature is enabled by
matrices and vectors of function pointers that are dynamically allocated and
populated based on user input. The speed and modularity of VPLanet enables
large parameter sweeps and the versatility to add/remove physical phenomena to
assess their importance. VPLanet is publicly available from a repository that
contains extensive documentation, numerous examples, Python scripts for
plotting and data management, and infrastructure for community input and future
development.Comment: 75 pages, 34 figures, 10 tables, accepted to the Proceedings of the
Astronomical Society of the Pacific. Source code, documentation, and examples
available at https://github.com/VirtualPlanetaryLaboratory/vplane
eleanor: An open-source tool for extracting light curves from the TESS Full-Frame Images
During its two year prime mission the Transiting Exoplanet Survey Satellite
(TESS) will perform a time-series photometric survey covering over 80% of the
sky. This survey comprises observations of 26 24 x 96 degree sectors that are
each monitored continuously for approximately 27 days. The main goal of TESS is
to find transiting planets around 200,000 pre-selected stars for which fixed
aperture photometry is recorded every two minutes. However, TESS is also
recording and delivering Full-Frame Images (FFIs) of each detector at a 30
minute cadence. We have created an open-source tool, eleanor, to produce light
curves for objects in the TESS FFIs. Here, we describe the methods used in
eleanor to produce light curves that are optimized for planet searches. The
tool performs background subtraction, aperture and PSF photometry,
decorrelation of instrument systematics, and cotrending using principal
component analysis. We recover known transiting exoplanets in the FFIs to
validate the pipeline and perform a limited search for new planet candidates in
Sector 1. Our tests indicate that eleanor produces light curves with
significantly less scatter than other tools that have been used in the
literature. Cadence-stacked images, and raw and detrended eleanor light curves
for each analyzed star will be hosted on MAST, with planet candidates on
ExoFOP-TESS as Community TESS Objects of Interest (CTOIs). This work confirms
the promise that the TESS FFIs will enable the detection of thousands of new
exoplanets and a broad range of time domain astrophysics.Comment: 21 pages, 13 figures, 2 tables, Accepted to PAS
Sequence Effects on DNA Entropic Elasticity
DNA stretching experiments are usually interpreted using the worm-like chain
model; the persistence length A appearing in the model is then interpreted as
the elastic stiffness of the double helix. In fact the persistence length
obtained by this method is a combination of bend stiffness and intrinsic bend
effects reflecting sequence information, just as at zero stretching force. This
observation resolves the discrepancy between the value of A measured in these
experiments and the larger ``dynamic persistence length'' measured by other
means. On the other hand, the twist persistence length deduced from
torsionally-constrained stretching experiments suffers no such correction. Our
calculation is very simple and analytic; it applies to DNA and other polymers
with weak intrinsic disorder.Comment: LaTeX; postscript available at
http://dept.physics.upenn.edu/~nelson/index.shtm
Polymer reptation and nucleosome repositioning
We consider how beads can diffuse along a chain that wraps them, without
becoming displaced from the chain; our proposed mechanism is analogous to the
reptation of "stored length" in more familiar situations of polymer dynamics.
The problem arises in the case of globular aggregates of proteins (histones)
that are wound by DNA in the chromosomes of plants and animals; these beads
(nucleosomes) are multiply wrapped and yet are able to reposition themselves
over long distances, while remaining bound by the DNA chain.Comment: 9 pages, including 2 figures, to be published in Phys. Rev. Let
Refraction in exoplanet atmospheres: Photometric signatures, implications for transmission spectroscopy, and search in Kepler data
Refraction deflects photons that pass through atmospheres, which affects
transit light curves. Refraction thus provides an avenue to probe physical
properties of exoplanet atmospheres and to constrain the presence of clouds and
hazes. In addition, an effective surface can be imposed by refraction, thereby
limiting the pressure levels probed by transmission spectroscopy. The main
objective of the paper is to model the effects of refraction on photometric
light curves for realistic planets and to explore the dependencies on
atmospheric physical parameters. We also explore under which circumstances
transmission spectra are significantly affected by refraction. Finally, we
search for refraction signatures in photometric residuals in Kepler data. We
use the model of Hui & Seager (2002) to compute deflection angles and
refraction transit light curves, allowing us to explore the parameter space of
atmospheric properties. The observational search is performed by stacking large
samples of transit light curves from Kepler. We find that out-of-transit
refraction shoulders are the most easily observable features, which can reach
peak amplitudes of ~10 parts per million (ppm) for planets around Sun-like
stars. More typical amplitudes are a few ppm or less for Jovians and at the
sub-ppm level for super-Earths. Interestingly, the signal-to-noise ratio of any
refraction residuals for planets orbiting Sun-like hosts are expected to be
similar for planets orbiting red dwarfs. We also find that the maximum depth
probed by transmission spectroscopy is not limited by refraction for weakly
lensing planets, but that the incidence of refraction can vary significantly
for strongly lensing planets. We find no signs of refraction features in the
stacked Kepler light curves, which is in agreement with our model predictions.Comment: Accepted for publication in A&
Methyl (Z)-2-chloro-3-(2-methoxyÂcarbonylÂphenÂyl)prop-2-enoate
In the title compound, C12H11ClO4, the propenoate C=C bond is in the Z configuration. The propenoate C=O and C=C groups are essentially coplanar [C=C—C=O torsion angle = 172.4 (3)°] with the O atom synperiplanar to the Cl atom. However, the Ï€ systems of the aromatic ring and chloroÂpropenoate substituent are not coplanar; the corresponding dihedral angle is 51.5 (1)°. The noncoplanarity is likely due to steric interÂactions between the propenoate H atom and the ortho-methoxyÂcarbonyl group on the aromatic ring. Even in the observed noncoplanar conformation, the ortho C=O to H distance (2.40 Å) is less than the sum of the van der Waals radii of O and H (2.65 Å)
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