1,286 research outputs found
Evaluation with Simulation of Lucerne-Based Cropping Systems to Combat Dryland Salinity in Australia
Dryland salinity is one of the most significant forms of land degradation that farmers face in Australia. There are currently 2.5 million ha affected by dryland salinity in Australia, and this may rise to 15 million ha over the next 30 to 100 years if no action is taken. National field experiments suggest that adoption of cropping systems that integrate deep-rooted perennials, such as lucerne, are important to reduce dryland salinity. This paper reports simulation results with APSIM (The Agricultural Production Systems Simulator), that have been used to explore climate, soil and agronomic factors affecting effectiveness of lucerne-based phase and companion cropping systems in sustaining crop yield and reducing deep-water drainage in South Australia
Mobile spin impurity in an optical lattice
We investigate the Fermi polaron problem in a spin-1/2 Fermi gas in an
optical lattice for the limit of both strong repulsive contact interactions and
one dimension. In this limit, a polaronic-like behaviour is not expected, and
the physics is that of a magnon or impurity. While the charge degrees of
freedom of the system are frozen, the resulting tight-binding Hamiltonian for
the impurity's spin exhibits an intriguing structure that strongly depends on
the filling factor of the lattice potential. This filling dependency also
transfers to the nature of the interactions for the case of two magnons and the
important spin balanced case. At low filling, and up until near unit filling,
the single impurity Hamiltonian faithfully reproduces a single-band,
quasi-homogeneous tight-binding problem. As the filling is increased and the
second band of the single particle spectrum of the periodic potential is
progressively filled, the impurity Hamiltonian, at low energies, describes a
single particle trapped in a multi-well potential. Interestingly, once the
first two bands are fully filled, the impurity Hamiltonian is a near-perfect
realisation of the Su-Schrieffer-Heeger model. Our studies, which go well
beyond the single-band approximation, that is, the Hubbard model, pave the way
for the realisation of interacting one-dimensional models of condensed matter
physics.Comment: 13 pages, 12 figures, accepted in New Journal of Physic
Specification and Verification of Media Constraints using UPPAAL
We present the formal specification and verification of a multimedia stream. The stream is described in a timed automata notation. We verify that the stream satisfies certain quality of service properties, in particular, throughput and end-to-end latency. The verification tool used is the real-time model checker UPPAAL
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
Energy Spectra, Altitude Profiles and Charge Ratios of Atmospheric Muons
We present a new measurement of air shower muons made during atmospheric
ascent of the High Energy Antimatter Telescope balloon experiment. The muon
charge ratio mu+ / mu- is presented as a function of atmospheric depth in the
momentum interval 0.3-0.9 GeV/c. The differential mu- momentum spectra are
presented between 0.3 and about 50 GeV/c at atmospheric depths between 13 and
960 g/cm^2. We compare our measurements with other recent data and with Monte
Carlo calculations of the same type as those used in predicting atmospheric
neutrino fluxes. We find that our measured mu- fluxes are smaller than the
predictions by as much as 70% at shallow atmospheric depths, by about 20% at
the depth of shower maximum, and are in good agreement with the predictions at
greater depths. We explore the consequences of this on the question of
atmospheric neutrino production.Comment: 11 pages, 8 figures, to appear in Phys. Rev. D (2000
Measurement of the flux of atmospheric muons with the CAPRICE94 apparatus
A new measurement of the momentum spectra of both positive and negative muons
as function of atmospheric depth was made by the balloon-borne experiment
CAPRICE94. The data were collected during ground runs in Lynn Lake on the
19-20th of July 1994 and during the balloon flight on the 8-9th of August 1994.
We present results that cover the momentum intervals 0.3-40 GeV/c for negative
muons and 0.3-2 GeV/c for positive muons, for atmospheric depths from 3.3 to
1000 g/cm**2, respectively. Good agreement is found with previous measurements
for high momenta, while at momenta below 1 GeV/c we find latitude dependent
geomagnetic effects. These measurements are important cross-checks for the
simulations carried out to calculate the atmospheric neutrino fluxes and to
understand the observed atmospheric neutrino anomaly.Comment: 28 pages, 13 Postscript figures, uses revtex.sty, to appear in Phys.
Rev.
Evolution of Integrated Crop-Livestock Production Systems
Many factors contribute to changes in the crop-livestock systems, but no logical end-point in the evolution process exists. While benefits of integrated crop-livestock systems over specialised crop and livestock systems are well documented, there has been a move to specialised crop and livestock production. Sustainability issues (manure nutrient concentration, soil quality maintenance, salinity, herbicide resistance, economic instability) have created a renewed interest in integrated crop-livestock systems. Farmer adaptability is as an important link in the evolution between ‘states of integration’
Calcium Binds to Transthyretin with Low Affinity
The plasma protein transthyretin (TTR), a transporter for thyroid hormones and retinol in plasma and cerebrospinal fluid, is responsible for the second most common type of systemic (ATTR) amyloidosis either in its wild type form or as a result of destabilizing genetic mutations that increase its aggregation propensity. The association between free calcium ions (Ca2+) and TTR is still debated, although recent work seems to suggest that calcium induces structural destabilization of TTR and promotes its aggregation at non-physiological low pH in vitro. We apply high-resolution NMR spectroscopy to investigate calcium binding to TTR showing the formation of labile interactions, which leave the native structure of TTR substantially unaltered. The effect of calcium binding on TTR-enhanced aggregation is also assessed at physiological pH through the mechano-enzymatic mechanism. Our results indicate that, even if the binding is weak, about 7% of TTR is likely to be Ca2+-bound in vivo and therefore more aggregation prone as we have shown that this interaction is able to increase the protein susceptibility to the proteolytic cleavage that leads to aggregation at physiological pH. These events, even if involving a minority of circulating TTR, may be relevant for ATTR, a pathology that takes several decades to develop
Evolution of Integrated Crop-Livestock Production Systems
Key points
1. Many factors contribute to changes in the crop-livestock systems, but no logical end-point in the evolution process exists.
2. While benefits of integrated crop-livestock systems over specialised crop and livestock systems are well documented, there has been a move to specialised crop and livestock production.
3. Sustainability issues (manure nutrient concentration, soil quality maintenance, salinity, herbicide resistance, economic instability) have created a renewed interest in integrated crop-livestock systems.
4. Farmer adaptability is as an important link in the evolution between ‘states of integration’
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