9,233 research outputs found
Indicator systems - resource use in organic systems
A balanced use of resources within organic farming systems is required to maintain sustainable systems. Hence, it is essential to have tools that can assess the use of resources within the farming system and their impact on the environment. The range of tools that have been developed include those assessing local farm-scale issues together with those that assess impacts at the global scale. At the global scale assessments are usually made on the basis of a unit of product whereas at the local scale assessments can also be made on an area basis. In addition, the tools also assess a variety of issues, e.g. biodiversity, pollution potential, energy and water use. The level of detail required for the different assessment tools differs substantially; nevertheless it is essential that the indicator systems developed are based on sound knowledge, are acceptable to the farmers and can guide their future actions
The Minimum Description Length Principle and Model Selection in Spectropolarimetry
It is shown that the two-part Minimum Description Length Principle can be
used to discriminate among different models that can explain a given observed
dataset. The description length is chosen to be the sum of the lengths of the
message needed to encode the model plus the message needed to encode the data
when the model is applied to the dataset. It is verified that the proposed
principle can efficiently distinguish the model that correctly fits the
observations while avoiding over-fitting. The capabilities of this criterion
are shown in two simple problems for the analysis of observed
spectropolarimetric signals. The first is the de-noising of observations with
the aid of the PCA technique. The second is the selection of the optimal number
of parameters in LTE inversions. We propose this criterion as a quantitative
approach for distinguising the most plausible model among a set of proposed
models. This quantity is very easy to implement as an additional output on the
existing inversion codes.Comment: Accepted for publication in the Astrophysical Journa
Improving supply and phosphorous use efficiency in organic farming systems
Phosphorus (P) is an essential plant nutrient that needs to be managed carefully in organic systems so that crop yield and quality remain sustainable without contributing to environmental damage, particularly that associated with eutrophication. Under organic regulations, minimally processed rock phosphate (PR) can be used to amend low P fertility soils, although the solubility is extremely low at optimum soil pH for most crop growth (pH 6.5). This paper describes a project (PLINK) which aims to develop methods of improving P efficiency on organic farms, although the same approaches may also be applicable on conventional and low-input farms. The methodologies that the project is developing include the fermentation and composting of crop waste material with PR in order to solubilise P and make it more available to the crop. Some initial results are described here. In addition, the project will investigate the alteration of the rotation to include crops or varieties with high P uptake efficiency, or roots that possess acidifying properties which improve P availability for following crops
Recommended from our members
HAGE, a cancer/testis antigen expressed at the protein level in a variety of cancers
The search for novel tumour antigens that are either uniquely expressed or over-expressed in a wide variety of tumours is still ongoing. Because of their expression in a broad spectrum of cancers and limited expression in normal tissues, cancer/testis antigens are considered to be potentially reliable targets for immunotherapy of cancer in general. The helicase antigen HAGE has been identified as a cancer/testis antigen. However, little is known about its expression in normal and cancer tissues. Using a newly developed antibody against HAGE, specific staining of its expression by immunohistochemistry was validated and optimised on murine tumours transfected to express the HAGE protein. The antibody was subsequently used to determine HAGE expression in normal human and cancer tissue microarrays. HAGE protein expression was confirmed in 75% (12/16) of carcinomas as compared to normal tissues, which either did not express HAGE at all or expressed HAGE at very low levels with the exception of testis. Interestingly, discrepancies were also found between mRNA analysis by real time quantitative PCR (RT-qPCR) and protein analysis by immunohistochemistry, emphasising the need to validate the expression of cancer/testis antigens at the protein level prior to the development of new vaccine strategies. HAGE is therefore proposed to be a valid candidate for designing a broad spectrum vaccine against cancer
Rings and Jets around PSR J2021+3651: the `Dragonfly Nebula'
We describe recent Chandra ACIS observations of the Vela-like pulsar PSR
J2021+3651 and its pulsar wind nebula (PWN). This `Dragonfly Nebula' displays
an axisymmetric morphology, with bright inner jets, a double-ridged inner
nebula, and a ~30" polar jet. The PWN is embedded in faint diffuse emission: a
bow shock-like structure with standoff ~1' brackets the pulsar to the east and
emission trails off westward for 3-4'. Thermal (kT=0.16 +/-0.02 keV) and power
law emission are detected from the pulsar. The nebular X-rays show spectral
steepening from Gamma=1.5 in the equatorial torus to Gamma=1.9 in the outer
nebula, suggesting synchrotron burn-off. A fit to the `Dragonfly' structure
suggests a large (86 +/-1 degree) inclination with a double equatorial torus.
Vela is currently the only other PWN showing such double structure. The >12 kpc
distance implied by the pulsar dispersion measure is not supported by the X-ray
data; spectral, scale and efficiency arguments suggest a more modest 3-4 kpc.Comment: 22 pages, 5 figures, 3 tables, Accepted to Ap
Can Virialization Shocks be Detected Around Galaxy Clusters Through the Sunyaev-Zel'dovich Effect?
In cosmological structure formation models, massive non-linear objects in the
process of formation, such as galaxy clusters, are surrounded by large-scale
shocks at or around the expected virial radius. Direct observational evidence
for such virial shocks is currently lacking, but we show here that their
presence can be inferred from future, high resolution, high-sensitivity
observations of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. We study
the detectability of virial shocks in mock SZ maps, using simple models of
cluster structure (gas density and temperature distributions) and noise
(background and foreground galaxy clusters projected along the line of sight,
as well as the cosmic microwave background anisotropies). We find that at an
angular resolution of 2'' and sensitivity of 10 micro K, expected to be reached
at ~ 100 GHz frequencies in a ~ 20 hr integration with the forthcoming ALMA
instrument, virial shocks associated with massive M ~ 10^15 M_Sun clusters will
stand out from the noise, and can be detected at high significance. More
generally, our results imply that the projected SZ surface brightness profile
in future, high-resolution experiments will provide sensitive constraints on
the density profile of cluster gas.Comment: 15 pages, submitted to Ap
Methods for differentiating prion types in food-producing animals
Prions are an enigma amongst infectious disease agents as they lack a genome yet confer specific pathologies thought to be dictated mainly, if not solely, by the conformation of the disease form of the prion protein (PrPSc). Prion diseases affect humans and animals, the latter including the food-producing ruminant species cattle, sheep, goats and deer. Importantly, it has been shown that the disease agent of bovine spongiform encephalopathy (BSE) is zoonotic, causing variant Creutzfeldt Jakob disease (vCJD) in humans. Current diagnostic tests can distinguish different prion types and in food- producing animals these focus on the differentiation of BSE from the non-zoonotic agents. Whilst BSE cases are now rare, atypical forms of both scrapie and BSE have been reported, as well as two types of chronic wasting disease (CWD) in cervids. Typing of animal prion isolates remains an important aspect of prion diagnosis and is now becoming more focused on identifying the range of prion types that are present in food-producing animals and also developing tests that can screen for emerging, novel prion diseases. Here, we review prion typing methodologies in light of current and emerging prion types in food-producing animals
The observable effects of a photospheric component on GRB's and XRF's prompt emission spectrum
A thermal radiative component is likely to accompany the first stages of the
prompt emission of Gamma-ray bursts (GRB's) and X-ray flashes (XRF's). We
analyze the effect of such a component on the observable spectrum, assuming
that the observable effects are due to a dissipation process occurring below or
near the thermal photosphere. We consider both the internal shock model and a
'slow heating' model as possible dissipation mechanisms. For comparable energy
densities in the thermal and the leptonic component, the dominant emission
mechanism is Compton scattering. This leads to a nearly flat energy spectrum
(\nu F_\nu \propto \nu^0) above the thermal peak at ~10-100 keV and below
10-100 MeV, for a wide range of optical depths 0.03 <~ \tau_{\gamma e} <~ 100,
regardless of the details of the dissipation mechanism or the strength of the
magnetic field. At lower energies steep slopes are expected, while above 100
MeV the spectrum depends on the details of the dissipation process. For higher
values of the optical depth, a Wien peak is formed at 100 keV - 1 MeV, and no
higher energy component exists. For any value of \tau_{\gamma e}, the number of
pairs produced does not exceed the baryon related electrons by a factor larger
than a few. We conclude that dissipation near the thermal photosphere can
naturally explain both the steep slopes observed at low energies and a flat
spectrum above 10 keV, thus providing an alternative scenario to the optically
thin synchrotron - SSC model.Comment: Discussion added on the results of Baring & Braby (2004); Accepted
for publication in Ap.
Temporal Variability of the X-ray Emission of the Crab Nebula Torus
We have analyzed five ROSAT HRI images of the Crab Nebula spanning the years
1991 to 1997 and have found significant changes in the emission structure of
the X-ray torus surrounding the pulsar. Certain regions increase in brightness
by about 20% over the six years, while others show decreases in surface
brightness. The origin of these changes is unclear, but a possible explanation
is that the bulk velocity of the synchrotron radiating electrons has decreased
on the order of 20% as well.Comment: 15 pages plus 6 figures, figure 1 and figure 6 are in color, to
appear in The Astrophysical Journal, Jan 1, 1999, Vol. 510, #
Asymmetric Supernovae, Pulsars, Magnetars, and Gamma-Ray Bursts
We outline the possible physical processes, associated timescales, and
energetics that could lead to the production of pulsars, jets, asymmetric
supernovae, and weak gamma-ray bursts in routine circumstances and to a
magnetar and perhaps stronger gamma-ray burst in more extreme circumstances in
the collapse of the bare core of a massive star. The production of a
LeBlanc-Wilson MHD jet could provide an asymmetric supernova and result in a
weak gamma-ray burst when the jet accelerates down the stellar density gradient
of a hydrogen-poor photosphere. The matter-dominated jet would be formed
promptly, but requires 5 to 10 s to reach the surface of the progenitor of a
Type Ib/c supernova. During this time, the newly-born neutron star could
contract, spin up, and wind up field lines or turn on an alpha-Omega dynamo. In
addition, the light cylinder will contract from a radius large compared to the
Alfven radius to a size comparable to that of the neutron star. This will
disrupt the structure of any organized dipole field and promote the generation
of ultrarelativistic MHD waves (UMHDW) at high density and Large Amplitude
Electromagnetic Waves (LAEMW) at low density. The generation of the these waves
would be delayed by the cooling time of the neutron star about 5 to 10 seconds,
but the propagation time is short so the UMHDW could arrive at the surface at
about the same time as the matter jet. In the density gradient of the star and
the matter jet, the intense flux of UMHDW and LAEMW could drive shocks,
generate pions by proton-proton collision, or create electron/positron pairs
depending on the circumstances. The UMHDW and LAEMW could influence the
dynamics of the explosion and might also tend to flow out the rotation axis to
produce a collimated gamma-ray burst.Comment: 31 pages, LaTeX, revised for referee comments, accepted for ApJ, July
10 issu
- âŠ